Showing papers in "Plant and Soil in 2007"

Long term effects of manure, charcoal and mineral fertilization on crop production and fertility on a highly weathered Central Amazonian upland soil

Abstract: Application of organic fertilizers and charcoal increase nutrient stocks in the rooting zone of crops, reduce nutrient leaching and thus improve crop production on acid and highly weathered tropical soils. In a field trial near Manaus (Brazil) 15 different amendment combinations based on equal amounts of carbon (C) applied through chicken manure (CM), compost, charcoal, and forest litter were tested during four cropping cycles with rice (Oryza sativa L.) and sorghum (Sorghum bicolor L.) in five replicates. CM amendments resulted in the highest (P < 0.05) cumulative crop yield (12.4 Mg ha−1) over four seasons. Most importantly, surface soil pH, phosphorus (P), calcium (Ca), and magnesium (Mg) were significantly enhanced by CM. A single compost application produced fourfold more grain yield (P < 0.05) than plots mineral fertilized in split applications. Charcoal significantly improved plant growth and doubled grain production if fertilized with NPK in comparison to the NPK-fertilizer without charcoal (P < 0.05). The higher yields caused a significantly greater nutrient export in charcoal-amended fields, but available nutrients did not decrease to the same extent as on just mineral fertilized plots. Exchangeable soil aluminum (Al) was further reduced if mineral fertilizer was applied with charcoal (from 4.7 to 0 mg kg−1). The resilience of soil organic matter (SOM) in charcoal amended plots (8 and 4% soil C loss, mineral fertilized or not fertilized, respectively) indicates the refractory nature of charcoal in comparison to SOM losses over 20 months in CM (27%), compost amended (27%), and control plots (25% loss).

Mycorrhizal responses to biochar in soil – concepts and mechanisms

Abstract: Experiments suggest that biomass-derived black carbon (biochar) affects microbial populations and soil biogeochemistry. Both biochar and mycor- rhizal associations, ubiquitous symbioses in terrestrial ecosystems, are potentially important in various ecosystem services provided by soils, contributing to sustainable plant production, ecosystem restoration, and soil carbon sequestration and hence mitigation of global climate change. As both biochar and mycor- rhizal associations are subject to management, under- standing and exploiting interactions between them could be advantageous. Here we focus on biochar effects on mycorrhizal associations. After reviewing the experimental evidence for such effects, we critically examine hypotheses pertaining to four mechanisms by which biochar could influence mycorrhizal abundance and/or functioning. These mechanisms are (in decreas- ing order of currently available evidence supporting them): (a) alteration of soil physico-chemical proper- ties; (b) indirect effects on mycorrhizae through effects on other soil microbes; (c) plant-fungus signaling interference and detoxification of allelochemicals on biochar; and (d) provision of refugia from fungal grazers. We provide a roadmap for research aimed at testing these mechanistic hypotheses.

Hydrogen isotope fractionation during water uptake by woody xerophytes

Abstract: Stable isotope measurements are employed extensively in plant–water relations research to investigate physiological and hydrological processes from whole plant to ecosystem scales. Stable isotopes of hydrogen and oxygen are routinely measured to identify plant source water. This application relies on the assumption that no fractionation of oxygen and hydrogen isotopes in water occurs during uptake by roots. However, a large fraction of the water taken up through roots in halophytic and xerophytic plants transverses cell membranes in the endodermis before entering the root xylem. Passage of water through this symplastic pathway has been hypothesized to cause fractionation leading to a decrease in 2H of root xylem water relative to that in the surrounding soil medium. We examined 16 woody halophytic and xerophytic plant species in controlled conditions for evidence of hydrogen isotope fractionation during uptake at the root–soil interface. Isotopic separation (Δ2H = δ2Hsoil water − δ2Hxylem water) ranging from 3‰ to 9‰ was observed in 12 species. A significant positive correlation between salinity tolerance and the magnitude of Δ2H was observed. Water in whole stem segments, sapwood, and roots had significantly lower δ2H values relative to soil water in Prosopis velutina Woot., the species expressing the greatest Δ2H values among the 16 species examined. Pressurized water flow through intact root systems of Artemisia tridentata Nutt. and Atriplex canescens (Pursh) Nutt. caused the δ2H values to decrease as flow rate increased. This relationship was not observed in P. velutina. Destroying the plasma membranes of root cells by excessive heat from boiling did not significantly alter the relationship between δ2H of expressed water and flow rate. In light of these results, care should be taken when using the stable isotope method to examine source-water use in halophytic and xerophytic species.

Osmotic adjustment and ion balance traits of an alkali resistant halophyte Kochia sieversiana during adaptation to salt and alkali conditions

Abstract: Kochia sieversiana (Pall.) C. A. M., a naturally alkali-resistant halophyte, was chosen as the test organism for our research. The seedlings of K. sieversiana were treated with varying (0–400 mM) salt stress (1:1 molar ratio of NaCl to Na2SO4) and alkali stress (1:1 molar ratio of NaHCO3 to Na2CO3). The concentrations of various solutes in fresh shoots, including Na+, K+, Ca2+, Mg2+, Cl−, SO 4 2− , NO 3 − , H2PO 3 − , betaine, proline, soluble sugar (SS), and organic acid (OA), were determined. The water content (WC) of the shoots was calculated and the OA components were analyzed. Finally, the osmotic adjustment and ion balance traits in the shoots of K. sieversiana were explored. The results showed that the WC of K. sieversiana remained higher than 6 [g g−1 Dry weight (DW)] even under the highest salt or alkali stress. At salinity levels >240 mM, proline concentrations increased dramatically, with rising salinity. We proposed that this was not a simple response to osmotic stress. The concentrations of Na+ and K+ all increased with increasing salinity, which implies that there was no competitive inhibition for absorption of either in K. sieversiana. Based on our results, the osmotic adjustment feature of salt stress was similar to that of alkali stress in the shoots of K. sieversiana. The shared essential features were that the shoots maintained a state of high WC, OA, Na+, K+ and other inorganic ions, accumulated largely in the vacuoles, and betaine, accumulated in cytoplasm. On the other hand, the ionic balance mechanisms under both stresses were different. Under salt stress, K. sieversiana accumulated OA and inorganic ions to maintain the intracellular ionic equilibrium, with close to equal contributions of OA and inorganic ions to anion. However, under alkali stress, OA was the dominant factor in maintaining ionic equilibrium. The contribution of OA to anion was as high as 84.2%, and the contribution of inorganic anions to anion was only 15.8%. We found that the physiological responses of K. sieversiana to salt and alkali stresses were unique, and that mechanisms existed in it that were different from other naturally alkali-resistant gramineous plants, such as Aneurolepidium chinense, Puccinellia tenuiflora.

Cytokinin producing bacteria enhance plant growth in drying soil

Abstract: Cytokinins can promote stomatal opening, stimulate shoot growth and decrease root growth. When soil is drying, natural cytokinin concentrations decrease in association with stomatal closure and a redirection of growth away from the shoots to the roots. We asked if decreased cytokinin concentrations mediate these adaptive responses by lessening water loss and promoting root growth thereby favouring exploration for soil water. Our approach was to follow the consequences for 12-d-old lettuce seedlings of inoculating the growing medium with cytokinin-producing bacteria under conditions of water sufficiency and deficit. Inoculation increased shoot cytokinins as assessed by immunoassay and mass spectrometry. Inoculation also promoted the accumulation of shoot mass and shortened roots while having a smaller effect on root mass. Inoculation did not raise stomatal conductance. The possible promoting effect of these cytokinins on stomatal conductance was seemingly hampered by increases in shoot ABA that inoculation also induced. Inoculation lowered root/shoot ratios by stimulating shoot growth. The effect was greater in non-droughted plants but remained sufficiently strong for shoot mass of inoculated droughted plants to exceed that of well-watered non-inoculated plants. We conclude that compensating for the loss of natural cytokinins in droughted plants interferes with the suppression of shoot growth and the enhancement of root elongation normally seen in droughted plants.

The defense hypothesis of elemental hyperaccumulation: status, challenges and new directions

Abstract: Elemental hyperaccumulation may have several functions, including plant defense against natural enemies. A total of 34 studies, including 72 experimental tests, have been conducted to date. At least some tests have demonstrated defense by hyperaccumulated As, Cd, Ni, Se and Zn, but relatively few plant taxa and natural enemies have been investigated. Defense by hyperaccumulated Ni has been shown for most leaf/root chewing herbivores and pathogens tested (20 of 26 tests) but not for herbivores of other feeding modes (1 of 8 tests). Most tests (5 of 6) using Ni concentrations below accumulator levels found no defensive effect, and the single test using plants in the accumulator range also found no effect. For Zn, mixed results have been reported for both hyperaccumulator (3 of 6 tests showed defense) and accumulator levels (3 of 4 tests showed defense). These tests have focused exclusively on leaf chewing/scraping herbivores: no herbivores of other feeding modes, or pathogens, have been tested. Both hyperaccumulator and accumulator concentrations of Se generally have shown defensive effects (12 of 14 tests). Most (75%) of these positive results used plants with accumulator Se concentrations. The three tests of Cd showed defensive effects in two cases, one for hyperaccumulator and one for sub-accumulator Cd concentrations. Arsenic has been tested only once, and was found effective against a leaf-chewing herbivore at a concentration much less than the hyperaccumulator level. Defense studies have used a variety of experimental approaches, including choice and no-choice experiments as well as experiments that use artificial diet or growth media. Investigations of hyperaccumulation as a defense against natural enemies have led to two emerging questions. First, what is the minimum concentration of an element sufficient for defense? Evidence suggests that plants other than hyperaccumulators (such as accumulators) may be defended by elements against some natural enemies. Second, do the effects of an element combine with the effects of organic defensive compounds in plants to produce enhanced joint defensive effects? Recent investigation of this “joint effects hypothesis,” using Ni and secondary plant compounds in artificial insect diet, has demonstrated joint effects. Initial answers to both these questions suggest that defensive effects of elements in plants are more widespread than previously believed. These results also suggest an evolutionary pathway by which elemental hyperaccumulation may have evolved from accumulation. In this “defensive enhancement” scenario, defensive benefits of elevated levels of elements may have led to stepwise increases in element concentrations that further magnified these benefits. This series of steps could have led to increased accumulation, and ultimately hyperaccumulation, of elements by plants.

Water relations and stomatal characteristics of Mediterranean plants with different growth forms and leaf habits: responses to water stress and recovery

Abstract: The aim of this study was to extent the range of knowledge about water relations and stomatal responses to water stress to ten Mediterranean plants with different growth forms and leaf habits. Plants were subjected to different levels of water stress and a treatment of recovery. Stomatal attributes (stomatal density, StoD), stomatal conductance (g s), stomatal responsiveness to water stress (SR), leaf water relations (pre-dawn and midday leaf water potential and relative water content), soil to leaf apparent hydraulic conductance (K L) and bulk modulus of elasticity (e) were determined. The observed wide range of water relations and stomatal characteristics was found to be partially depended on the growth form. Maximum g s was related to StoD and the stomatal area index (SAI), while g s evolution after water stress and recovery was highly correlated with K L. Relationships between SR to water deficit and other morphological leaf traits, such as StoD, LMA or e, provided no general correlations when including all species. It is concluded that a high variability is present among Mediterranean plants reflecting a continuum of leaf water relations and stomatal behaviour in response to water stress.

Biological nitrification inhibition (BNI)—is it a widespread phenomenon?

Abstract: Regulating nitrification could be a key strategy in improving nitrogen (N) recovery and agronomic N-use efficiency in situations where the loss of N following nitrification is significant. A highly sensitive bioassay using recombinant luminescent Nitrosomonas europaea, has been developed that can detect and quantify the amount of nitrification inhibitors produced by plants (hereafter referred to as BNI activity). A number of species including tropical and temperate pastures, cereals and legumes were tested for BNI in their root exudate. There was a wide range in BNI capacity among the 18 species tested; specific BNI (AT units activity g−1 root dry wt) ranged from 0 (i.e. no detectable activity) to 18.3 AT units. Among the tested cereal and legume crops, sorghum [Sorghum bicolor (L.)], pearl millet [Pennisetum glaucum (L.) R. Br.], and groundnut [Arachis hypogaea (L.)] showed detectable BNI in root exudate. Among pasture grasses, Brachiaria humidicola (Rendle) Schweick, B. decumbens Stapf showed the highest BNI capacity. Several high- and low-BNI genotypes were identified within the B. humidicola species. Soil collected from field plots of 10 year-old high-BNI genotypes of B. humidicola, showed a near total suppression (>90%) of nitrification; most of the soil inorganic N remained in the NH 4 + form after 30 days of incubation. In contrast, soils collected from low-BNI genotypes did not show any inhibitory effect; most of the soil inorganic N was converted to NO 3 – after 30 days of incubation. In both the high- and low-BNI genotypes, BNI was detected in root exudate only when plants were grown with NH 4 + , but not when grown with NO 3 – as the sole source of N. BNI compounds when added to the soil inhibited nitrification and the relationship was linear (r 2 = 0.92**; n = 12). The BNI from high- and low-BNI types when added to N. europaea in pure culture, blocked both the ammonia monooxygenase (AMO) and the hydroxylamine oxidoreductase (HAO) pathways. Our results indicated that BNI capacity varies widely among and within species; and that some degree of BNI capacity is likely a widespread phenomenon in tropical pasture grasses. We suggest that the BNI capacity could either be managed and/or introduced into pastures/crops with an expression of this phenomenon, via genetic improvement approaches that combine high productivity along with some capacity to regulate soil nitrification process.

Influence of permanent raised bed planting and residue management on physical and chemical soil quality in rain fed maize/wheat systems

Abstract: Densely populated, intensively cropped highland areas in the tropics and subtropics are prone to erosion and declining soil fertility, making agriculture unsustainable. Conservation agriculture in its version of permanent raised bed planting with crop residue retention has been proposed as an alternative wheat production system for this agro-ecological zone. A five years field experiment comparing permanent and tilled raised beds with different residue management under rainfed conditions was started at El Batan (Mexico) (2,240 m asl; 19.31°N, 98.50°W; Cumulic Phaeozem) in 1999. The objective of this study was to determine the soil quality status after five years of different management practices. The K concentration was 1.65 times and 1.43 times larger in the 0–5 cm and 5–20 cm profiles, respectively, for permanent raised beds compared to conventionally tilled raised beds. The Na concentration showed the opposite trend. Sodicity was highest for conventionally tilled raised beds and for permanent raised beds it increased with decreasing amounts of residue retained on the surface. Permanent raised beds with full residue retention increased soil organic matter content 1.4 times in the 0–5 cm layer compared to conventionally tilled raised beds with straw incorporated and it increased significantly with increasing amounts of residue retained on the soil surface for permanent raised beds. Soil from permanent raised beds with full residue retention had significantly higher mean weight diameter for wet and dry sieving compared to conventionally tilled raised beds. Permanent raised beds with full residue retention had significantly higher aggregate stability compared to those with residue removal. A lower aggregation resulted in a reduction of infiltration. Principal component analysis (PCA) was performed using these soil physicochemical variables that were significantly influenced by tillage or residue management. The PC1 and PC2 separated the conventionally tilled raised beds from the permanent raised beds and PC3 separated permanent raised beds with at least partial residue retention from permanent raised beds with no residue retention. These clear separations suggest that tillage and residue management have an effect on soil processes. The research indicates that permanent raised bed planting increases the soil quality and can be a sustainable production alternative for the (sub)tropical highlands. Extensive tillage with its associated high costs can be reduced by the use of permanent raised beds while at least partial surface residue retention is needed to insure production sustainability.

Root characteristics of representative Mediterranean plant species and their erosion-reducing potential during concentrated runoff

Abstract: Gully erosion is an important soil degradation process in Mediterranean environments. Revegetation strategies for erosion control rely in most cases on the effects of the above-ground biomass on reducing water erosion rates, whereas the role of the below-ground biomass is often neglected. In a Mediterranean context, the above-ground biomass can temporally disappear because of fire or overgrazing and when concentrated flow erosion occurs, roots can play an important role in controlling soil erosion rates. Unfortunately, information on root characteristics of Mediterranean plants, growing on semi-natural lands, and their effects on the topsoil resistance to concentrated flow erosion is lacking. Therefore, typical Mediterranean grass, herb, reed, shrub and tree root systems of plants growing in habitats that are prone to concentrated flow erosion (i.e. in ephemeral channels, abandoned fields and steep badland slopes) are examined and their erosion-reducing potential was evaluated. Root density (RD), root length density (RLD) and root diameters are measured for 26 typical Mediterranean plant species. RD values and root diameter distribution within the upper 0.10–0.90 m of the soil profile are then transformed into relative soil detachment rates using an empirical relationship in order to predict the erosion-reducing effect of root systems during concentrated runoff. Comparing the erosion-reducing potential of different plant species allows ranking them according to their effectiveness in preventing or reducing soil erosion rates by concentrated flow. RD in the 0.10 m thick topsoil ranges between 0.13 kg m−3 for Bromus rubens (L.) and 19.77 kg m−3 for Lygeum spartum (L.), whereas RLD ranges between 0.01 km m−3 for Nerium oleander (L.) and 120.43 km m−3 for Avenula bromoides ((Gouan) H. Scholz.) Relative soil detachment rates, compared to bare soils, range between 0.3 × 10-12 and 0.7 for the 0.10 m thick topsoil. The results show that grasses such as Helictotrichon filifolium ((Lag.) Henrard), Piptatherum miliaceum ((L.) Coss.), Juncus acutus (L.), Avenula bromoides ((Gouan) H. Scholz), Lygeum spartum (L.) and Brachypodium retusum ((Pers.) Beauv.) have the highest potential to reduce soil erosion rates by concentrated flow in the 0–0.1 m topsoil. But also shrubs such as Anthyllis cytisoides (L.) and Tamarix canariensis (Willd.), having high root densities in the topsoil, can reduce erosion rates drastically. Among the species growing in channels, Juncus acutus (L.) has the highest erosion reducing potential, whereas Phragmites australis (Cav.) is the least effective. On abandoned fields, Avenula bromoides ((Gouan) H. Scholz) and Plantago albicans (L.) are the most effective species in reducing concentrated flow erosion rates, while Thymelaea hirsuta (L. (Endl.)) and Bromus rubens (L.) perform the worst. On steep badland slopes, Helictotrichon filifolium ((Lag.) Henrard) and Anthyllis cytisoides (L.) perform the best in the analysis of erosion reducing potential, while Ononis tridentata (L.) is the least effective species. These findings have implications for ecological restoration and management of erosion-prone slopes.

Root exudate components change litter decomposition in a simulated rhizosphere depending on temperature.

Abstract: The release of root exudates into the rhizosphere is known to enhance soil biological activity and alter microbial community structure. To assess whether root exudates also stimulated litter decomposition, in a rhizosphere model system we continuously injected solutions of glucose, malate or glutamate through porous Rhizon® soil solution samplers into the soil at rhizosphere concentrations. The effect of these substances on the decomposition of 14C-labelled Lolium perenne shoot residues present in the soil was evaluated by monitoring 14CO2 evolution at either 15°C or 25°C. The incorporation of the 14C into the microbial biomass and appearance in the dissolved organic matter (DOM) pool was estimated after 32 d incubation. The presence of malate and glutamate increased the mineralization of L. perenne residues by approximately 20% relative to the soil without their addition at 15°C, however, no significant effects on residue decomposition were observed at 25°C. The incorporation of the 14C-label into the microbial biomass and DOM pool was not affected by the addition of either glucose, malate or glutamate. Although nearly the same amount of L. perenne residues were mineralized at either temperature after 32 d, less 14C was recovered in the microbial biomass and DOM pools at 25°C compared to 15°C. Alongside other results, this suggests that the rate of microbial turnover is greater at 25°C compared to 15°C. We conclude that the addition of labile root exudate components to the rhizosphere induced a small but significant increase on litter decomposition but that the magnitude of this effect was regulated by temperature.

Silicon-mediated changes of some physiological and enzymatic parameters symptomatic for oxidative stress in spinach and tomato grown in sodic-B toxic soil

Abstract: We investigated effect of silicon (Si) on the growth, uptake of sodium (Na), chloride (Cl), boron (B), stomatal resistance (SR), lipid peroxidation (MDA), membrane permeability (MP), lipoxygenase (LOX) activity, proline (PRO) accumulation, H2O2 accumulation, non-enzymatic antioxidant activity (AA) and the activities of major antioxidant enzymes (superoxide dismutase, SOD; catalase, CAT and ascorbate peroxidase, APX) of spinach and tomato grown in sodic-B toxic soil. Si applied to the sodic-B toxic soil at 2.5 and 5.0 mM concentrations significantly increased the Si concentration in the plant species and counteracted the deleterious effects of high concentrations of Na, Cl and B on root and shoot growth by lowering the accumulation of these elements in the plants. Stomatal resistance, MP, MDA and the concentrations of H2O2 and PRO were higher in the plants grown in sodic-B toxic soil without Si: LOX activity of excised leaves of both species was increased by Si. Antioxidant activities of both species were significantly affected by Si, with the activities of SOD, CAT and APX decreased and AA increased by applied Si. For most of the parameters measured, it was found that 5 mM Si was more effective than the 2.5 mM Si. Based on the present work, it can be concluded that Si alleviates sodicity and B toxicity of the plants grown in sodic-B toxic soil by preventing both oxidative membrane damage and also translocation of Na, Cl and B from root to shoots and/or soil to plant, and lowering the phytotoxic effects of Na, Cl and B within plant tissues. It was concluded that tomato was more responsive to Si than spinach since it was more salt sensitive than spinach. To our knowledge, this is the first report that Si improves the combined salt and B tolerance of spinach and tomato grown in naturally sodic-B toxic soil, and which describes membrane-related parameters and antioxidant responses.

An invasive aster ( Ageratina adenophora ) invades and dominates forest understories in China: altered soil microbial communities facilitate the invader and inhibit natives

Abstract: Exotic plant invasion may alter underground microbial communities, and invasion-induced changes of soil biota may also affect the interaction between invasive plants and resident native species. Increasing evidence suggests that feedback of soil biota to invasive and native plants leads to successful exotic plant invasion. To examine this possible underlying invasion mechanism, soil microbial communities were studied where Ageratina adenophora was invading a native forest community. The plant–soil biota feedback experiments were designed to assess the effect of invasion-induced changes of soil biota on plant growth, and interactions between A. adenophora and three native plant species. Soil analysis showed that nitrate nitrogen (NO3−-N), ammonium nitrogen (NH4+-N), and available P and K content were significantly higher in a heavily invaded site than in a newly invaded site. The structure of the soil microbial community was clearly different in all four sites. Ageratina adenophora invasion strongly increased the abundance of soil VAM (vesicular-arbuscular mycorrhizal fungi) and the fungi/bacteria ratio. A greenhouse experiment indicated that the soil biota in the heavily invaded site had a greater inhibitory effect on native plant species than on A. adenophora and that soil biota in the native plant site inhibited the growth of native plant species, but not of A. adenophora. Soil biota in all four sites increased A. adenophora relative dominance compared with each of the three native plant species and soil biota in the heavily invaded site had greater beneficial effects on A. adenophora relative dominance index (20% higher on average) than soil biota in the non-invaded site. Our results suggest that A. adenophora is more positively affected by the soil community associated with native communities than are resident natives, and once the invader becomes established it further alters the soil community in a way that favors itself and inhibits natives, helping to promote the invasion. Soil biota alteration after A. adenophora establishment may be an important part of its invasion process to facilitate itself and inhibit native plants.

Soil organic carbon pools and productivity relationships for a 34 year old rice–wheat–jute agroecosystem under different fertilizer treatments

Abstract: Soil organic carbon (SOC) pools are important in maintaining soil productivity and influencing the CO2 loading into the atmosphere. An attempt is made here to investigate into the dynamics of pools of SOC viz., total organic carbon (C tot), oxidisable organic carbon (C oc) and its four different fractions such as very labile (C frac 1), labile (C frac 2), less labile (C frac 3) and non-labile (C frac 4), microbial biomass carbon (C mic), mineralizable carbon (C min), and particulate organic carbon (C p) in relation to crop productivity using a 34 year old rice (Oryza sativa L)–wheat (Triticum aestivum L)–jute (Corchorus olitorius L) cropping system with different management strategies (no fertilization, only N, NP, NPK and NPK + FYM) in the hot humid, subtropics of India. A fallow treatment was also included to compare the impact of cultivation vis-a-vis no cultivation. Cultivation over the years caused a net decrease, while balanced fertilization with NPK maintained the SOC pools at par with the fallow. Only 22% of the C applied as FYM was stabilized into SOC, while the rest got lost. Of the analysed pools, C frac 1, C mic, C p and C min were influenced most by the treatments imposed. Most of the labile pools were significantly correlated with each other and with the yield and sustainable yield index (SYI) of the studied system. Of them, C frac1, C min, C mic and C p explained higher per cent variability in the SYI and yield of the crops. Results suggest that because of low cost and ease of estimation and also for upkeeping environmental conditions, C frac1 may be used as a good indicator for assessment of soil as to its crop productivity.

Changes in soil and vegetation following stabilisation of dunes in the southeastern fringe of the Tengger Desert, China

Abstract: Properties of the soil and sand-binding vegetation were measured at five sites plus a control on dunes of the Tengger Desert stabilized for periods of up to 50 years. In the topsoil, fine particles, total N, P, K and organic matter increased significantly with increasing site age. However, there were no significant changes in deeper soil profiles (>0.4 m depth). Soil pH, calcium carbonate content, and total salt content tended to increase with age. Soil water in the topsoil changed little with increasing age, but was closely related to rainfall during the 50-year period. For deeper soil layers (0.4–3.0 m) soil water decreased significantly with age. After revegetation, the number of herbaceous species increased up to 30 years and then levelled off to 12–14 species, whereas the number of shrub species decreased from the 10 initial sand-binding species to only 3 species. Shrub cover decreased from a highest average of about 33% to the current 9%, whereas cover and biomass of herbaceous species increased throughout succession from 1956 to 2006. The development of soil and cryptogamic crusts on the surface of stabilized dunes enhanced the colonization and establishment of herbaceous plants due to increasing water availability, clay and silt content and soil nutrients. We propose that changes in properties of the surface soil led to increased interception of water, favoring shallow rooted grasses and forbs over perennial shrubs.

In-situ phytoextraction of Ni by a native population of Alyssum murale on an ultramafic site (Albania)

Abstract: Ultramafic outcrops are widespread in Albania and host several Ni hyperaccumulators (e.g., Alyssum murale Waldst. & Kit.). A field experiment was conducted in Pojske (Eastern Albania), a large ultramafic area in which native A. murale was cultivated. The experiment consisted in testing the phytoextraction potential of already installed natural vegetation (including A. murale) on crop fields with or without suitable fertilisation. The area was divided into six 36-m2 plots, three of which were fertilised in April 2005 with (NPK + S). The soil (Magnesic Hypereutric Vertisol) was fully described as well as the mineralogy of horizons and the localisation of Ni bearing phases (TEM-EDX and XRD). Ni availability was also characterised by Isotopic Exchange Kinetics (IEK). The flora was fully described on both fertilised and unfertilised plots and the plant composition (major and trace elements) and biomass (shoots) harvested individually were recorded. The soil had mainly two Ni-bearing phases: high-Mg smectite (1.3% Ni) and serpentine (0.7% Ni), the first one being the source of available Ni. Ni availability was extremely high according to IEK and confirmed by Ni contents in Trifolium nigriscens Viv. reaching 1,442 mg kg−1 (A new hyperaccumulator?). Total biomass yields were 6.3 t ha−1 in fertilised plots and 3.2 t ha−1 in unfertilised plots with a highly significant effect: fertilisation increased dramatically the proportion of A. murale in the plots (2.6 t ha−1 vs. 0.2 t ha−1). Ni content in the shoots of A. murale reached 9,129 mg kg−1 but metal concentration was not significantly affected by fertilisation. Phytoextracted Ni in total harvest reached 25 kg Ni ha−1 on the fertilised plots. It was significantly lower in unfertilised plots (3 kg Ni ha−1). Extensive phytomining on such sites could be promising in the Albanian context by domesticating already installed natural populations with fertilisation.

Fine root diameters can change in response to changes in nutrient concentrations

Abstract: Plant roots function in the critical role of water and nutrient uptake. Although extensive data exist on functioning of seedling roots, little is known of the actual functionality of the fine roots of mature plants. Although this class of root represents 90% or more of the total root length of a given mature plant, their small size has inhibited detailed studies. Commonly, the critical metrics for studies of root function are root length and total weight, expressed as Specific Root Length. The metric that classifies “fine roots,” root diameter, is rarely a focus except as average diameter, even though this is the primary characteristic from which accurate estimates of surface area and volume can be calculated. Using data from several preliminary experiments, this study shows consistent changes in measured fine root diameter with changes in concentration of some nutrients. Twelve different species demonstrated concentration dependent diameter increases, or decreases, in response to increasing concentrations of nitrate, phosphorus, aluminum or tannic acid. On the other hand, Cacao (Theobroma cacao L) fine roots changed diameter in response to changes in nitrate concentration, but not ammonium. Clearly pattern of diameter change in response to nutrient concentration is dependent on nutrient, species and their interaction. It is suggested that the routine assessment of fine root diameter will be essential to understanding nutrient uptake dynamics.

Biological nitrogen fixation and nitrogen and phosphorus budgets in farmer-managed intercrops of maize–pigeonpea in semi-arid southern and eastern Africa

Abstract: Biological nitrogen fixation (BNF), nitrogen (N), and phosphorus (P) imports-exports budgets were estimated at four locations, each with 20 farmer-managed fields for two years in a semi-arid Tanzania and Malawi. The 15N isotope dilution method was used to quantify BNF by three pigeonpea (Cajanus cajan L. Millspp.) varieties intercropped with maize (Zea mays L.). The N and P accumulation in plant components of sole maize and intercrops of maize-pigeonpea systems were used to estimate the mean exports and imports of N and P. The proportion of N derived from air (%Ndfa) by the pigeonpea varieties ranged from 93.8% to 99.9% in Malawi and 65.6% to 99.3% in Tanzania. The amount of fixed N (BNF; kg N ha−1 yr−1) varied from 37.5 to 117.2 in Malawi and 6.3 to 71.5 in Tanzania. The mean values for BNF during the two cropping seasons were 64.3 for Nyambi, 85.3 for Ntonda, 34.1 for Gairo and −54.3 for Babati sites. The mean N budget (kg ha−1) was −26.1 in the sole maize plots and −40.3 for the intercrops at the two locations in Malawi, and −50.1 in the sole crop plots and −51.1 in the intercrops at the locations in Tanzania. In a scenario where all the aboveground material except the edible parts was returned to the soil, a positive value of 30.5 kg N for the intercrops was recorded compared with −8.9 kg N for the sole maize in Malawi. For the same scenario in Tanzania, the budget was more negative (−35.4 kg N) for sole maize compared with intercrops (−5.9 kg N). Including the roots in the calculations, did not change the differences between mono and intercrops. The P budget was negative irrespective of whether the aboveground biomass of maize and pigeonpea was incorporated or exported out of the fields, and the values were similar for intercrops and sole maize. The most negative N and P budgets were recorded in the two study areas where the extractable soil P status of the soils and the maize yields were high. These findings indicate that pigeonpea incorporated into maize-based cropping systems will maintain a very high %Ndfa ( > 90%) in all plant parts and thereby contribute to improved N budgets but not increase the proportion of P mined of the soil.

Evaluation of physiological traits for improving drought tolerance in faba bean (Vicia faba L.)

Abstract: Among grain legumes, faba bean is becoming increasingly popular in European agriculture due to recent economic and environmental interests. Faba bean can be a highly productive crop, but it is sensitive to drought stress and yields can vary considerably from season to season. Understanding the physiological basis of drought tolerance would indicate traits that can be used as indirect selection criteria for the development of cultivars adapted to drought conditions. To assess genotypic variation in physiological traits associated with drought tolerance in faba bean and to determine relationships among these attributes, two pot experiments were established in a growth chamber using genetic materials that had previously been screened for drought response in the field. Nine inbred lines of diverse genetic backgrounds were tested under adequate water supply and limited water conditions. The genotypes showed substantial variation in shoot dry matter, water use, stomatal conductance, leaf temperature, transpiration efficiency, carbon isotope discrimination (Δ13C), relative water content (RWC) and osmotic potential, determined at pre-flowering vegetative stage. Moisture deficits decreased water usage and consequently shoot dry matter production. RWC, osmotic potential, stomatal conductance and Δ13C were lower, whereas leaf temperature and transpiration efficiency were higher in stressed plants, probably due to restricted transpirational cooling induced by stomatal closure. Furthermore, differences in stomatal conductance, leaf temperature, Δ13C and transpiration efficiency characterized genotypes that were physiologically more adapted to water deficit conditions. Correlation analysis also showed relatively strong relationships among these variables under well watered conditions. The drought tolerant genotypes, ILB-938/2 and Melodie showed lower stomatal conductance associated with warmer leaves, whereas higher stomatal conductance and cooler leaves were observed in sensitive lines (332/2/91/015/1 and Aurora/1). The lower value of Δ13C coupled with higher transpiration efficiency in ILB-938/2, relative to sensitive lines (Aurora/1 and Condor/3), is indeed a desirable characteristic for water-limited environments. Finally, the results showed that stomatal conductance, leaf temperature and Δ13C are promising physiological indicators for drought tolerance in faba bean. These variables could be measured in pot-grown plants at adequate water supply and may serve as indirect selection criteria to pre-screen genotypes.

Dependence of the Q10 values on the depth of the soil temperature measuring point

Abstract: The parameter Q10 is commonly used to express the relationship between soil CO2 efflux and soil temperature. One advantage of this parameter is its application in a model expression of respiration losses of different ecosystems. Correct specification of Q10 in these models is indispensable. Soil surface CO2 efflux and soil temperature at different depths were measured in a 21-year-old Norway spruce stand and a mountain grassland site located at the Experimental Ecological Study Site Bily Kriz, Beskydy Mts. (NE Czech Republic), using automated gasometric systems. A time-delay and goodness-of-fit between soil CO2 efflux and soil temperature at different measuring depths were determined. Wide ranges of values for the time-delay of CO2 efflux in response to temperature, Q10 and the determination coefficient (R2) between CO2 efflux and temperature were obtained at the both sites. The values of Q10 and the CO2 time-delay increased with depth, while the R2 of the CO2-temperature relationship significantly decreased. Soil temperature records obtained close to the soil surface showed the highest values of R2 and the lowest value of the time-delay at both sites. Measurement of soil temperature at very shallow soil layer, preferably at the soil surface, is highly recommended to determine useable values of Q10. We present a new procedure to normalize Q10 values for soil temperatures measured at different depths that would facilitate comparison of different sites.

Physiological behaviour, oxidative damage and antioxidative protection of olive trees grown under different irrigation regimes

Abstract: Irrigation effects were investigated on an 8-year-old olive (Olea europaea L., cv. Cobrancosa) commercial orchard located in northeast Portugal. Trees were subjected to a rainfed control (T0) and three treatments (T1, T2, T3) that received a seasonal water amount equivalent to 30%, 60% and 100% of the estimated local evaporative demand by a drip irrigation system. Irrigation increases the photosynthetic activity of olive trees, in association with increases in water status, and reduces the midday and afternoon depression in gas exchange. The closely association between photosynthetic rate (A) and stomatal conductance (gs) revealed that the decline in net photosynthesis over the course of the day was largely a consequence of stomatal limitation. However, the ratio of intercellular to atmospheric CO2 concentration increased markedly from morning to midday in non-irrigated plants, in spite of lower gs, suggesting that non-stomatal limitations of photosynthesis also occur when environmental conditions become more stressful. The occurrence of perturbations at chloroplastic level in rainfed plants was demonstrated by a lower maximum photochemical efficiency of photosystem II during the afternoon. Chlorophyll fluorescence measurements also revealed the occurrence of a dynamic photoinhibition in irrigated trees, mainly in T2 and T3, which seemed to be effective in protecting the photosynthetic apparatus from photodamage. Irrigation enhances antioxidant protection and decreases the oxidative damage at leaf level. Leaves grown under rainfed conditions revealed symptoms of oxidative stress, like the reduction (14%) in chlorophyll concentration and the increased levels (57%) of lipid peroxidation. We also found that the scavenging function of superoxide dismutase was impaired in rainfed plants. In contrast, the low thiobarbituric acid reactive substances concentration in T3 indicates that irrigation enhances the repairing mechanisms and decreases the oxidative damage by lipid peroxidation. Accordingly, leaves in T3 treatment had high levels of –SH compounds and the highest antioxidant potential. Meanwhile, the finding that guaiacol peroxidase activity increased in rainfed plants, associated with the appearance of oxidative damage, suggests that this enzyme has no major antioxidative function in olive.

Copper uptake and phytotoxicity as assessed in situ for durum wheat (Triticum turgidum durum L.) cultivated in Cu-contaminated, former vineyard soils

Abstract: This work assessed in situ, copper (Cu) uptake and phytotoxicity for durum wheat (Triticum turgidum durum L.) cropped in a range of Cu-contaminated, former vineyard soils (pH 4.2–7.8 and total Cu concentration 32–1,030 mg Cu kg−1) and identified the underlying soil chemical properties and related root-induced chemical changes in the rhizosphere. Copper concentrations in plants were significantly and positively correlated to soil Cu concentration (total and EDTA). In addition, Cu concentration in roots which was positively correlated to soil pH tended to be larger in calcareous soils than in non-calcareous soils. Symptoms of Cu phytotoxicity (interveinal chlorosis) were observed in some calcareous soils. Iron (Fe)–Cu antagonism was found in calcareous soils. Rhizosphere alkalisation in the most acidic soils was related to decreased CaCl2-extractable Cu. Conversely, water-extractable Cu increased in the rhizosphere of both non-calcareous and calcareous soils. This work suggests that plant Cu uptake and risks of Cu phytotoxicity in situ might be greater in calcareous soils due to interaction with Fe nutrition. Larger water extractability of Cu in the rhizosphere might relate to greater Cu uptake in plants exhibiting Cu phytotoxic symptoms.

Phytoextraction of Cd and Zn from agricultural soils by Salix ssp. and intercropping of Salix caprea and Arabidopsis halleri

Abstract: Contamination of agricultural topsoils with Cd above guideline values is of concern in many countries throughout the world. Extraction of metals from contaminated soils using high-biomass, metal-accumulating Salix sp. has been proposed as a low-cost, gentle remediation strategy, but reasonable phytoextraction rates remain to be demonstrated. In an outdoor pot experiment we assessed the phytoextraction potential for Cd and Zn of four willow species (Salix caprea, S. fragilis, S. × smithiana, S. × dasyclados) and intercropping of S. caprea with the hyperaccumulator Arabidopsis halleri on three moderately contaminated, agricultural soils. Large concentrations of Cd (250 mg kg−1) and Zn (3,300 mg kg−1) were determined in leaves of Salix × smithiana grown on a soil containing 13.4 mg kg−1 Cd and 955 mg kg−1 Zn, resulting in bioaccumulation factors of 27 (Cd) and 3 (Zn). Total removal of up to 20% Cd and 5% Zn after three vegetation periods were shown for Salix × smithiana closely followed by S. caprea, S. fragilis and S. × dasyclados. While total Cd concentrations in soils were reduced by up to 20%, 1 M NH4NO3-extractable metal concentrations did not significantly decrease within 3 years. Intercropping of S. caprea and A. halleri partly increased total removal of Zn, but did not enhance total Cd extraction compared to single plantings of S. caprea after two vegetation periods.

Long-term nitrogen fertilizer replacement value of cattle manures applied to cut grassland

Abstract: Manures supply nitrogen (N) to crops beyond the year of application. This N must be taken into account for agronomic and environmental reasons. From 2002 to 2006 we conducted a field experiment on a sandy soil in The Netherlands (52°03″N, 6°18″E) to better quantify this residual N effect. Treatments comprised different time series of mineral fertilizer N or cattle manures of different compositions, all applied at a rate of 300 kg total N ha−1 year−1, whilst compensating for differences in available potassium and phosphorus. Dry matter and N yields of cut grassland responded positively (P < 0.05) to both current manure applications and applications in previous years, whereas mineral fertilizer N affected yields in the year of application only. N yields could be reasonably well predicted with a simple N model, adopting an annual relative decomposition rate of the organic N in manure of 0.10–0.33 year−1 during the year of application and 0.10 year−1 in the following years. Subsequent model calculations indicated that the N fertilizer value (NFRV) of injected undigested cattle slurry rises from an observed 51–53% when slurry is applied for the first time, to approximately 70% after 7–10 yearly applications, whereas it took two to four decades of yearly applications to raise the NFRV of surface applied farm yard manure to a similar level from an initial value of 31%. Manures with a relatively high first year NFRV (e.g. anaerobically digested slurry) had a relatively small residual N effect, whereas manures with a low first year NFRV (e.g. farm yard manure) partly compensated for this by showing larger residual effects. Given the long manuring history of most agricultural systems, rethinking the fertilizer value of manure seems justified. The results also imply that the long term consequences of reduced N application rates may be underestimated if manuring histories are insufficiently taken into account.

Revisiting copper and cobalt concentrations in supposed hyperaccumulators from SC Africa: influence of washing and metal concentrations in soil

Abstract: Metal concentrations have been determined in shoots of 12 species considered as Cu and/or Co hyperaccumulators, collected from five subpopulations in a Cu/Co mine in Katanga. Samples have been subjected to three cleansing protocols (water, alconox, alconox + EDTA). Cu/Co concentrations were significantly higher when demineralised water was used to wash samples compared to more aggressive solutions. Washing effect was largest for species with velvety (Acalypha cupricola) or sticky (Haumaniastrum katangense) indumentum. Element concentrations in shoots varied by two orders of magnitude, i.e. 45–2,891 mg kg−1 Cu (median: 329 mg kg−1) and 21–1,971 mg kg−1 Co (median: 426 mg kg−1) and were generally lower than previously published values. Only 9.3% of data exceeded the hyperaccumulation threshold (1,000 mg kg−1) for Cu and 13% for Co. Shoot concentrations varied by up to two orders of magnitude among subpopulations within species which was partly explained by variation of metal concentrations in the soil. Although the species considered in this paper undisputedly accumulate Co and Cu up to very high concentrations that require specific shoot tolerance mechanisms, the concept of hyperaccumulation, as defined for other metals like Zn and Ni, needs to be critically re-examined for Cu and Co. Our results suggest that many species so far regarded as Co/Cu hyperaccumulators might eventually turn out to be indicators.

Niche-based assessment of contributions of legumes to the nitrogen economy of Western Kenya smallholder farms

Abstract: Nitrogen (N) deficiency is a major constraint to the productivity of the African smallholder farming systems. Grain, green manure and forage legumes have the potential to improve the soil N fertility of smallholder farming systems through biological N2-fixation. The N2-fixation of bean (Phaseolus vulgaris), soyabean (Glycine max), groundnut (Arachis hypogaea), Lima bean (Phaseolus lunatus), lablab (Lablab purpureus), velvet bean (Mucuna pruriens), crotalaria (Crotalaria ochroleuca), jackbean (Canavalia ensiformis), desmodium (Desmodium uncinatum), stylo (Stylosanthes guianensis) and siratro (Macroptilium atropurpureum) was assessed using the 15N natural abundance method. The experiments were conducted at three sites in western Kenya, selected on an agro-ecological zone (AEZ) gradient defined by rainfall. On a relative scale, Museno represents high potential AEZ 1, Majengo medium potential AEZ 2 and Ndori low potential AEZ 3. Rainfall in the year of experimentation was highest in AEZ 2, followed by AEZ 1 and AEZ 3. Experimental fields were classified into high, medium and low fertility classes, to assess the influence of soil fertility on N2-fixation performance. The legumes were planted with triple super phosphate (TSP) at 30 kg P ha−1, with an extra soyabean plot planted without TSP (soyabean-P), to assess response to P, and no artificial inoculation was done. Legume grain yield, shoot N accumulation, %N derived from N2-fixation, N2-fixation and net N inputs differed significantly (P<0.01) with rainfall and soil fertility. Mean grain yield ranged from 0.86 Mg ha−1, in AEZ 2, to 0.30 Mg ha−1, in AEZ 3, and from 0.78 Mg ha−1, in the high fertility field, to 0.48 Mg ha−1, in the low fertility field. Shoot N accumulation ranged from a maximum of 486 kg N ha−1 in AEZ 2, to a minimum of 10 kg N ha−1 in AEZ 3. Based on shoot biomass estimates, the species fixed 25–90% of their N requirements in AEZ 2, 23–90% in AEZ 1, and 7–77% in AEZ 3. Mean N2-fixation by green manure legumes ranged from 319 kg ha−1 (velvet bean) in AEZ 2 to 29 kg ha−1 (jackbean) in AEZ 3. For the forage legumes, mean N2-fixation ranged from 97 kg N ha−1 for desmodium in AEZ 2 to 39 kg N ha−1 for siratro in AEZ 3, while for the grain legumes, the range was from 172 kg N ha−1 for lablab in AEZ 1 to 3 kg N ha−1 for soyabean-P in AEZ 3. Lablab and groundnut showed consistently greater N2-fixation and net N inputs across agro-ecological and soil fertility gradients. The use of maize as reference crop resulted in lower N2-fixation values than when broad-leaved weed plants were used. The results demonstrate differential contributions of the green manure, forage and grain legume species to soil fertility improvement in different biophysical niches in smallholder farming systems and suggest that appropriate selection is needed to match species with the niches and farmers’ needs.

Seed germination of agricultural weeds is promoted by the butenolide 3-methyl-2H-furo[2,3-c]pyran-2-one under laboratory and field conditions

Abstract: Here we report that a synthesised form of a naturally occurring chemical (a butenolide, 3-methyl-2H-furo[2,3-c]pyran-2-one) found in smoke can stimulate seedling emergence of the economically important weed species Avena fatua L. (Poaceae), Arctotheca calendula (L.) Levyns (Asteraceae), Brassica tournefortii Gouan (Brassicaceae), and Raphanus raphanistrum L. (Brassicaceae) under field conditions at rates equivalent to 2–20 g/ha a.i. The butenolide also stimulates germination of freshly collected seeds from wild populations of these species, as well as those of Sisymbrium orientale L. (Brassicaceae), Hordeumleporinum Link (Poaceae) and Echium plantagineum L. (Boraginaceae) under laboratory conditions, consistently greater than that of smoke water. Experiments using B. tournefortii seeds collected from several locations across Western Australia and in different growing seasons found that these factors significantly influence the butenolide response, implying a role of the maternal environment in seed germination/dormancy characteristics. This research highlights the potential of butenolide as an agent for broad acre weed control and land restoration.

Root amino acid exudation: measurement of high efflux rates of glycine and serine from six different plant species

Abstract: Amino acid concentration in the rhizosphere results from fluxes between plant roots, soil and microorganisms. In this context, root amino acid exudation process, composed of both efflux and influx, remains unclear. One main issue is to understand the selectivity of amino acid exudation resulting mainly in high proportions of glycine and serine in exudates compared to low proportions inside the root. To reach this point, a quantitative analysis of exudation with dissociated measurements of efflux from influx is needed. We measured efflux and influx by supplying 15N-labelled glycine or serine for a short time of exposure at ecologically relevant concentrations to plants of white clover (Trifolium repens L.), perennial ryegrass (Lolium perenne L.), maize (Zea mays L.), oilseed rape (Brassica napus L.), tomato (Lycopersicon esculentum Mill.) and alfalfa (Medicago sativa L.). Efflux was estimated by the increase of 14N content of amino acids in root exudates and influx was estimated by the increase of 15N content in plant tissue. Glycine efflux exceeded influx for all six species and was much higher in Fabaceae than in Poaceae. Serine efflux exceeded influx in alfalfa, white clover and rape. We conclude that presence of glycine and serine in root bathing solutions results from high glycine and serine efflux rates, observed in all six species studied here. The physiological and ecological significances of these high efflux rates are discussed in the context of N metabolism and plant–soil–microorganisms interactions.

Effects of fertigation scheme on N uptake and N use efficiency in cotton

Abstract: While fertigation can increase fertilizer use efficiency, there is an uncertainly as to whether the fertilizer should be introduced at the beginning of the irrigation or at the end, or introduced during irrigation. Our objective was to determine the effect of different fertigation schemes on nitrogen (N) uptake and N use efficiency (NUE) in cotton plants. A pot experiment was conducted under greenhouse conditions in year 2004 and 2005. According to the application timing of nitrogen (N) fertilizer solution and water (W) involved in an irrigation cycle, four nitrogen fertigation schemes [nitrogen applied at the beginning of the irrigation cycle (N–W), nitrogen applied at the end of the irrigation cycle (W–N), nitrogen applied in the middle of the irrigation cycle (W–N–W) and nitrogen applied throughout the irrigation cycle (N&W)] were employed in a completely randomized design with four replications. Cotton was grown in plastic containers with a volume of 84 l, which were filled with a clay loam soil and fertilized with 6.4 g of N per pot as unlabeled and 15N-labeled urea for 2004 and 2005, respectively. Plant total dry matter (DM) and N content in N–W was significantly higher than in N&W in both seasons, but these were not consistent for W–N and W–N–W treatments. In year 2005, a significantly higher nitrogen derived from fertilizer (NDFF) for the whole plant was found in W–N and N–W than that in W–N–W and N&W. Fertigation scheme had a consistent effect on total NUE: N–W had the highest NUE for the whole plant, but this was not significantly different from W–N. Treatments W–N and W–N–W had similar total NUE, and N&W had the lowest total NUE. After harvesting, the total residual fertilizer N in the soil was highest in W–N, lowest in N–W, but this was not significantly different from N&W and W–N–W treatments. Total residual NO3–N in the soil in N&W and W–N treatments was 20.7 and 21.2% higher than that in N–W, respectively. The total 15N recovery was not statistically significant between the four fertigation schemes. In this study, the fertigation scheme N–W (nitrogen applied at the beginning of an irrigation cycle) increased DM accumulation, N uptake and NUE of cotton. This study indicates that Nitrogen application at the beginning of an irrigation cycle has an advantage on N uptake and NUE of cotton. Therefore, NUE could be enhanced by optimizing fertilization schemes with drip irrigation.

Changes of phenolic metabolism and oxidative status in nitrogen-deficient Matricaria chamomilla plants

Abstract: The effects of nitrogen deficiency on selected physiological attributes, phenylalanine ammonia-lyase (PAL, EC. 4.3.1.5) activity, phenolic contents, peroxidase (EC. 1.11.1.7) and catalase (EC. 1.11.1.6) activities, lipid peroxidation status and H2O2 accumulation were studied in N-deficient Matricaria chamomilla (L.) over 12 days. N deficiency enhanced root growth and inhibited shoot growth. Chlorophyll composition and F v/F m were not affected by N stress, but nitrogen and soluble proteins decreased in both the rosettes and the roots. PAL activity, expressed per mg protein, was enhanced in N-deficient rosettes and tended to decrease by the end of the experiment, while in the roots PAL activity was maintained. Total phenolic contents increased in both rosettes and roots. Peroxidase and catalase activities in N-deficient rosettes tended to decrease by the end of the experiment, while in the roots they increased on the 12th day of deficiency. Furthermore, lipid peroxidation status increased in N-deficient roots on the 12th day, indicating that antioxidative protection was insufficient to scavenge reactive oxygen species being generated. Surprisingly, H2O2 content was even lower in N-deficient roots by the end of the experiment, while in the leaves increased. This observation in correlation to lipid peroxidation and H2O2 degradation is discussed. The importance of PAL activity and phenolic metabolites in combination with antioxidative enzymes for plant protection against oxidative stress and the significance of PAL activity for the mobilization of N availability in N-deficient tissue are also discussed in view of existing information.