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Showing papers on "Growing season published in 1996"


Journal ArticleDOI
TL;DR: Groundwater discharge from sugar maple trees and forest stands of different sizes (ages) differs significantly, and large trees and older forest stands have a greater impact on the hydrologic balance of groundwater than small trees and younger forest stands.
Abstract: Use of soil water and groundwater by open-grown Acer saccharum Marsh. (sugar maple) tree canopies and forests was estimated by measuring transpiration (E) rates using porometry, sap flow methods, and the Bowen ratio method. The Bowen ratio and sap flow methods showed the best agreement; porometer measurements scaled to whole canopies always underestimated E by 15-50%. Trees of different sizes showed very different rates of E. I hypothesized that these differences were due to the differential access of large and small trees to groundwater and soil water, respectively. Transpirational flux was partitioned between soil water and groundwater by tracing the water sources based on their hydrogen stable isotopic composition (deltaD). Soil water deltaD varied between -41 and -16 per thousand seasonally (May to September), whereas groundwater deltaD was -79 +/- 5 per thousand during the entire growing season. Daily transpiration rates of large (9-14 m tall) trees were significantly higher than those of small (3-5 m tall) trees (2.46-6.99 +/- 1.02-2.50 versus 0.69-1.80 +/- 0.39-0.67 mm day(-1)). Small trees also showed greater variation in E during the growing season than large trees. In addition, compared to the large trees, small trees demonstrated greater sensitivity to environmental factors that influence E, such as soil water deficits and increased evaporative demand. Over the entire growing season, large trees and forest stands composed of trees > 10 m tall transpired only groundwater. The high rates of water loss from large trees and older forests were likely a result of the influence of an enhanced "pool" of transpirational water in the upper soil layers caused by hydraulic lift (see Dawson 1993b). The hydraulically lifted water reservoir enabled large trees to use more potential transpirational water during daylight hours than small trees, leading to a greater total water flux. In contrast, small trees and forest stands composed of younger trees almost exclusively used soil water, except during two dry periods when their transpirational water was composed of between 7 and 17% groundwater. Thus groundwater discharge from sugar maple trees and forest stands of different sizes (ages) differs significantly, and large trees and older forest stands have a greater impact on the hydrologic balance of groundwater than small trees and younger forest stands. However, mixed stands (small and large trees) may have a greater overall impact on the regional hydrologic balance than old stands, because trees in mixed stands draw on both soil water and groundwater reservoirs and thus can substantially increase total water discharge on scales from tens to hundreds of hectares.

399 citations


Journal ArticleDOI
TL;DR: It is concluded that tissue structure is an inherent constraint that prevents simultaneous maximization of both nutrient acquisition and nutrient conservation and explains the long-term disadvantage of a high growth rate for plants in low nutrient conditions.
Abstract: Under nutrient-poor conditions initially fast-growing species will in the long term be competitively inferior to slow-growing species. Here, we ask whether this phenomenon can be explained by constraints caused by tissue density. The hypothesis is that low tissue density is necessary for fast growth but has as a consequence short organ life span. This leads to a rapid loss of nutrients that cannot be sustained under nutrient-poor conditions. Biomass accumulation, turnover rate of leaves and roots, and tissue density were studied for five ecologically contrasting grass species. Plants were grown in a garden experiment over two growing seasons on sand with a low nutrient supply level. Species that were characteristic of nutrient-rich sites had a low leaf and root tissue density and were larger after one growing season than species of nutrient-poor sites. However, after two growing seasons the species of nutrient-poor sites were larger. These species had a high tissue density. Life span of both leaves and roots was also correlated with tissue density. Species with low tissue density had a faster turnover of leaves and roots. It is concluded that tissue structure is an inherent constraint that prevents simultaneous maximization of both nutrient acquisition and nutrient conservation. The short life span of fast-growing organs explains the long-term disadvantage of a high growth rate for plants in low nutrient conditions.

354 citations


Journal ArticleDOI
01 Jun 1996-Oikos
TL;DR: Productivity as a function of biotic diversity was examined and showed that species-poor assemblages had wider ranges of possible productivities than more diverse assemblage.
Abstract: We examined productivity as a function of biotic diversity. We manipulated plant species richness as an experimental factor to determine if productivity (net above ground primary productivity or NPP) is affected by changes in plant diversity (species richness). We constructed 164 assemblages that varied in species richness and measured their biomass at the end of one growing season. The plants were drawn from a pool of 16 species of self-pollinating annual herbs common to English weedy fields. On average, species-poor assemblages were less productive. Results also showed, however, that species-poor assemblages had wider ranges of possible productivities than more diverse assemblages.

283 citations


Journal ArticleDOI
TL;DR: In this article, a field study was conducted from 1988 to 1994 to determine the effects of tillage (TILL), crop rotation (ROT) and N fertilizer on wheat yield in a rainfed Mediterranean region.
Abstract: The combined long-term effects of tillage method and crop rotation on crop yield have not been studied in rainfed systems under Mediterranean climates. A field study was conducted from 1988 to 1994 to determine the effects of tillage (TILL), crop rotation (ROT) and N fertilizer on wheat (triticum aestivum L.) yield in a rainfed Mediterranean region. Tillage treatments include no tillage (NT) and conventional tillage (CT). Crop rotations were wheat-sunflower (Helianthus annuus L.) (WS), wheat-chickpea (Cicer arietinum L.) (WCP), wheat-fababean (Vicia faba L.) (WFB), wheat-fallow (WF), and continuous wheat (CW), with N fertilizer rates of 50, 100, and 150 kg N ha -1 . A split-split plot design with four replications was used. Differences in rainfall during the growing season had a marked effect on wheat yield. Amount of rainfall during the vegetative period for wheat (November-February) was highly correlated with yield because of the high water-retention capacity of Vertisols (Typic Haploxerert). In dry years, wheat yield was greater under NT than under CT ; the opposite was true in wet years. The TILL x ROT interaction was also significant in the drought years ; the wheat yield under NT was greater for CW and the WFB and WF rotations than under CT. Wheat yields ranked by crop rotation were : WFB > WF >> WCP > WS >> CW. Wheat did not respond to N fertilizer when rainfall was below 450 mm during the growing season. Using these results strategies can be developed for establishing the N fertilizer rate applied to wheat as a function of rainfall, the preceding crop, and residual N in soil in order to optimize wheat yield and reduce nitrate pollution to groundwater.

185 citations


Journal ArticleDOI
TL;DR: The success of the plant in invading woodlands appears to be related to its autogamous breeding system that allows a single individual, or a few individuals, to establish populations of genetically similar but interfertile individuals; high seed production, permitting establishment of large numbers of individuals; and rapid growth during the second growing season, which increases its competitive ability.
Abstract: Alliaria petiolata (garlic mustard), an exotic plant species, has invaded woodlands in several areas in mid-western and northeastern United States and adjacent Canada, and it is displacing the indigenous under-story flora. This study was conducted to provide information about the species' biology that might be useful in controlling its spread in native woodlands. The plant is a strict biennial in North America, spending the first year of growth as a basal rosette. This period of relatively slow growth is followed by a period of rapid shoot elongation (1.9 cm/day) during early spring of the second growing season. The plant is capable of cross- and self-pollination, although pollination and stigma receptivity occur before the flower is open, so autogamy is the most likely breeding system. Garlic mustard invests 20.4% of its biomass in reproductive effort, with an annual seed rain of 15,000 seeds/m2. Seed dispersal from fruits begins in early July and continues into October. Most seeds germinate in the spring following the year in which they were produced. Seedling recruitment is high (8.3–18.0 seedlings/cm2), but only about 7.5% of the plants survive to maturity. The success of the plant in invading woodlands appears to be related to (1) its autogamous breeding system that allows a single individual, or a few individuals, to establish populations of genetically similar but interfertile individuals; (2) high seed production, permitting establishment of large numbers of individuals; and (3) rapid growth during the second growing season, which increases its competitive ability. Because of garlic mustard's ability to occupy understory habitats successfully, it may be unrealistic to expect to eliminate the plant from many habitats it has already invaded.

173 citations


Journal ArticleDOI
TL;DR: It is hypothesize that increasing abundance, biomass and activity of these nematodes in the spring by organic matter incorporation at the end of the previous crop would reduce the observed nitrogen stress.

169 citations


Journal ArticleDOI
TL;DR: In this article, the sensitivity of the seasonal cycle of heterotrophic respiration to model estimates of litterfall seasonality, herbivory, plant allocation, tissue chemistry, and land use was examined.
Abstract: We examine the sensitivity of the seasonal cycle of heterotrophic respiration to model estimates of litterfall seasonality, herbivory, plant allocation, tissue chemistry, and land use. As a part of this analysis, we compare heterotrophic respiration models based solely on temperature and soil moisture controls (zero-order models) with models that depend on available substrate as well (first-order models). As indicators of regional and global CO2 exchange, we use maps of monthly global net ecosystem production, growing season net flux (GSNF), and simulated atmospheric CO2 concentrations from an atmospheric tracer transport model. In one first-order model, CASA, variations on the representation of the seasonal flow of organic matter from plants to heterotrophs can increase global GSNF as much as 60% (5.7 Pg C yr−1) above estimates obtained from a zero-order model. Under a new first-order scheme that includes separate seasonal dynamics for leaf litterfall, fine root mortality, coarse woody debris, and herbivory, we observe an increase in GSNF of 8% (0.7 Pg C yr−1) over that predicted by the zero-order model. The increase in seasonality of CO2 exchange in first-order models reflects the dynamics of labile litter fractions; specifically, the rapid decomposition of a pulse of labile leaf and fine root litter that enters the heterotrophic community primarily from the middle to the end of the growing season shifts respiration outside the growing season. From the perspective of a first-order model, we then explore the consequences of land use change and winter temperature anomalies on the amplitude of the seasonal cycle of atmospheric CO2. Agricultural practices that accelerate decomposition may drive a long-term increase in the amplitude, independent of human impacts on plant production. Consideration of first-order litter decomposition dynamics may also help explain year-to-year variation in the amplitude.

150 citations


Journal ArticleDOI
TL;DR: In this article, treated effluent from an aerated lagoon and facultative pond system in southern Portugal, was used to irrigate fields planted to maize (Zea mays L.).

146 citations


Journal ArticleDOI
TL;DR: The study shows that under the cool temperate conditions of southern England, M. x giganteus, unlike all C 4 species previously examined, is able to realize the photosynthetic potential of the C 4 process without suffering any apparent low temperature impairment, except possibly at the very end of the growing season.
Abstract: Previous studies have shown that both photoinhibition and low temperature impairment of leaf development occur in C 4 species growing in temperate climates. These result in reductions in the maximum quantum efficiency ( ?) and the light-saturated rate of CO 2 uptake (A sat ). The perennial C 4 -grass Miscanthus x giganteus has been shown to attain high productivity in northern Europe. This study examines and analyses the seasonal variation in photosynthetic gas exchange of M. x giganteus grown in southern England. Although the crop was exposed to chilling temperatures at the start of the season neither A sat nor ? were impaired, when assessed at a measurement temperature of 24°C. Between May and July the mean values of A sat and ? were 34 μmol m -2 s -1 and 0.067, respectively, declining to 20 μmol m -2 s -1 and 0.045 in October. In the field, on clear days between May and July, the typical midday rates of CO 2 uptake ranged between 20-27 μmol m -2 s -1 , although in late-June a peak mean value of 35 μmol m -2 s -1 was attained. The study shows that under the cool temperate conditions of southern England, M. x giganteus, unlike all C 4 species previously examined, is able to realize the photosynthetic potential of the C 4 process without suffering any apparent low temperature impairment, except possibly at the very end of the growing season.

136 citations


Journal ArticleDOI
TL;DR: In this article, the authors quantified variability in five soil resources essential for plant growth (NH4, NO3+, P, K and soil moisture) using univariate, multivariate and geostatistical techniques in a sagebrush-grass steppe ecosystem at three times during the 1994 growing season.
Abstract: Variability in five soil resources essential for plant growth (NH4 +, NO3 -, P, K and soil moisture) was quantified using univariate, multivariate and geostatistical techniques in a sagebrush-grass steppe ecosystem at three times (early April, June and August) during the 1994 growing season. Samples were collected every meter in a 10 × 10-m ‘macrogrid’, every 20 cm within nested 1 × 1-m ‘minigrids’, and every 3 cm within additionally nested 15 × 15-cm ‘microgrids’. Strong autocorrelation for all variables in the three sample periods was only found over distances less than 2 m, indicating that patches of high internal uniformity in this soil were smaller than 2 m during the growing season. Differences in semivariograms between sample periods were most pronounced for NO3 -, NH4 + and soil moisture, variables that we consider to primarily limit plant growth in this system. The distance over which sample points were autocorrelated for NO3 -, NH4 + and soil moisture increased from April to June. In contrast P and K, which are relatively more abundant at the study site, exhibited relatively constant semivariance patterns over the three sample periods. Weak correlation was found between samples collected in the three sample periods for N and soil moisture indicating that the spatial pattern of these limiting resources changed between sample periods. However, P and K had highly significant correlations (p<0.00001) among sample periods, indicating that the distributional patterns of these relatively more abundant resources remained rather constant. There were strong negative correlations between P and K and distance from the base of shrubs for all sample times (p<0.001), indicating an increase in P and K close to shrubs. Similar strong negative correlations were not found between distance from the shrubs and levels of NH4 +, NO3 -, or soil moisture, nor for any soil variable and distance from perennial tussock grasses. Changes in patterns of nutrient and soil moisture variability within a growing season suggest that not only must plants acquire soil resources that vary in time and space, but that they may also have to adjust to different scales of resource patchiness during the season.

120 citations


Journal ArticleDOI
TL;DR: The root systems of these two poplar genotypes apparently contain sufficient carbon and nitrogen reserves to fuel a spring flush of fine-root growth, even though the tops have been severed during the dormant season.

Journal ArticleDOI
TL;DR: The results indicate that carbon/nutrient balance hypothesis fails to predict directly the effects of nitrogen availability on concentrations of carbon-based defensive compounds in mature foliage.
Abstract: Effects of nitrogen availability on secondary compounds, mycorrhizal infection, and aphid growth of 1-year-old Scots pine (Pinus sylvestris L.) seedlings were studied during one growing season. Seedlings were fertilized with nutrient solutions containing low, optimum, and two elevated (2 × and 4 × optimum) levels of NH4NO3. At the end of growing season foliar nitrogen concentration, needle biomass, needle length, water contents of needles, root collar diameter, and number of buds increased with enhanced nitrogen availability. Addition of nitrogen did not have effect on concentrations of monoterpenes in growing needles, but in mature needles significantly decreased concentrations of some individual and total monoterpenes were detected. In growing needles the concentrations of some individual resin acids decreased, and in mature needles concentrations of some individual and total resin acids increased with increased nitrogen fertilization. Higher numbers of resin ducts were found in mature needles with nitrogen fertilization. Nitrogen fertilization decreased total phenolic concentrations in growing and mature needles of the current year, but in needles of the previous year no significant differences occurred. Mycorrhizal infection was highest at medium (optimum and 2 × optimum) nitrogen fertilization levels. The relative growth rate (RGR) of grey pine aphid [Schizolachnus pineti (F.)] responded positively to the increase in foliar nitrogen content. However, the increase in aphid performance between optimum and the highest fertilization level was slight. This may indicate a deterring effect of resin acids on aphids. The results indicate that carbon/nutrient balance hypothesis fails to predict directly the effects of nitrogen availability on concentrations of carbon-based defensive compounds in mature foliage. Altered nitrogen supply affects allocation to secondary metabolites differently, depending on the developmental state of the plant and the biosynthesis pathway, cost of synthesis, and storage of compounds.

Journal ArticleDOI
TL;DR: It is hypothesized that E. terebrans requires a source of sugar and a moderate microclimate available in the woodlot, but not in the cornfield, and field experiments indicate that it needs habitats adjacent to cornfields for sources of sugar & moderate micro climate unavailable in early season corn.
Abstract: Eriborus terebrans (Gravenhorst) is the primary parasitoid of the European corn borer, Ostrinia nubilalis (Hubner) (Lepidoptera: Pyralidae), in Michigan. Previous studies demonstrated that early in the growing season, E. terebrans adults are more abundant, and parasitize a greater proportion of O. nubilalis larvae, near wooded edges of cornfields. We hypothesized that E. terebrans requires a source of sugar and a moderate microclimate available in the woodlot, but not in the cornfield. Growth chamber and greenhouse experiments demonstrated that longevity of E. terebrans that are provided sugar was greater than those provided only water, or neither; and wasp longevity was greater at 25 than 35°c. In field experiments, wasps were caged in cornfields, woodlots, wooded fencerows, and herbaceous vegetation, early and late in the season. Longevity of E. terebrans adults was greater in woodlots than early season cornfields. Wasps lived longer in all habitats late in the season than early in the season. In all habitats, wasp longevity was enhanced by sugar. These and previous studies indicate that E. terebrans needs habitats adjacent to cornfields for sources of sugar and a moderate microclimate unavailable in early season corn. In annual agriculture, perennial habitats adjacent to crop fields may be necessary to provide the structure, stability, and resources needed for the successful conservation of natural enemies and effective biological control.

Journal ArticleDOI
TL;DR: This is the first demonstration that depriving a plant growing in its natural environment of mycorrhiza on a long-term basis can reduce P acquisition, and it confirms that H. non-scripta is an obligately myCorrhizal species.
Abstract: summary We controlled arbuscular mycorrhizal (AM) fungi in the routs of bluebell (Hyacinthoides non-scripta L. Chouard ex Rothm.) in the field by immersina otherwise undisturbed colonies in a fungicide suspension. Monthly application of benomyl successfully reduced root colonization by AM fungi throughout a 2 yr experimental period. Benonlyl had lit) effect on the availability of soil phosphorus (P), but reduced the P concentration of all parts of the plant (bulb, roots, leaves and inflorescences). Unlike the vegetative parts, flowers and seed of benomyl-treated plants had the same P concentration as untreated plants at the end of the first season. However, at the final harvest after two growing seasons flower P concentration had been reduced by treatment. H. non-scripta appears to protect reproductive structures from P deficiency when the plant is deprived of P, suggesting that A.M plays an important role in fitness determination. This is the first demonstration that depriving a plant growing in its natural environment of mycorrhiza on a long-term basis can reduce P acquisition. Taken with data from experiments in controlled conditions, it confirms that H. non-scripta is an obligately mycorrhizal species.

Journal ArticleDOI
TL;DR: Reproductive patterns are analysed in annual legumes of west Asia, and their relationships to increasing aridity determined by multivariate analysis are shown to be partially substitutable in terms of their effect on survival and population growth.
Abstract: Reproductive patterns are analysed in annual legumes of west Asia, and their relationships to increasing aridity determined by multivariate analysis. Dormancy, seed size, dispersal and fecundity are shown to be partially substitutable in terms of their effect on survival and population growth. The range of patterns show greatest diversity under mesic conditions in coastal, mediterranean areas with high winter rainfall, low incidence of frost and long growing season. Increasing aridity leads to increasing reproductive homogeneity, in which a subset of patterns-those composed of high levels of seed dormancy, high seed to pod ratios, restricted dispersal capabilities and early flowering-become predominant. These findings corroborate earlier theoretical and empirical evidence concerning desert annuals. The majority of widespread species are shown to possess “arid-type” patterns. This exerts considerable influence on both the type and degree of ecotypic differentiation within species. The only feature that responds consistently to climatic change is flowering time, particularly among species characterized by high seed dormancy. In the few widespread species that do not display “arid-type” characteristics, ecotypic differentiation appears more frequently in a larger suite of traits. The unequal environmental demands made on species showing different levels of dormancy (e.g. variation in length of growing season from year to year and place to place) leads to strong asymmetries governing the relationships between reproduction and ecological amplitude. In this respect “arid-type” strategists with high seed dormancy appear to have greater chances of expansion than others. This has implications when choosing pasture legumes to improve mediterranean grasslands.

Journal ArticleDOI
TL;DR: In this paper, soil nitrogen transformations were measured the year following nitrogen fertilization of alpine Kobresia myosuroides meadows to determine the influence of greater plant production and N content on net N mineralization and the microbial N pool.
Abstract: Soil nitrogen transformations were measured the year following nitrogen fertilization of alpine Kobresia myosuroides meadows to determine the influence of greater plant production and N content on net N mineralization and the microbial N pool. Previously fertilized soils contained substantially greater amounts of organic N than control soils. The average increase in soil organic N accounted for 75% of total added N and, although variable, this quantity suggests a large capacity for retention of added N in these soils. Nitrogen transformations and more active pools also responded to fertilization. Net N mineralization, nitrification and soil inorganic N concentrations clearly were higher in fertilized than in control plots throughout the snow-free season. The most pronounced increase in mineralization in fertilized relative to control soils occurred during the second half of the snow-free period (mid-July-October), primarily after the short alpine growing season (June-mid-August). Although the soil microbial N pool was not affected by fertilization during the growing season, microbial N did increase in the fall in fertilized compared to control soils, coinciding with the time of greatest N mineralization. The late season net uptake of N into the microbial pool exceeded by several times present rates of anthropogenic N inputs to these soils, and the microbial biomass may act as an increasingly important short-term sink for available N if N deposition to these areas continues to increase.

Journal ArticleDOI
TL;DR: In this paper, the authors examined seasonal fine-root growth in a short-rotation forest plantation of Salix viminalis L, standing crop, growth and decay dynamics and depth distribution of fine roots were investigated with the minirhizotron technique.
Abstract: With the objective of examining seasonal fine-root growth in a short-rotation forest plantation of Salix viminalis L., standing crop, growth and decay dynamics and depth distribution of fine roots were investigated with the minirhizotron technique. Fine-root number was counted during two growing seasons, 1988 and 1989. Soil cores were sampled during the same period for estimation of standing crop and depth distribution of fine-root mass and fine-root length. The experimental site is situated at Uppsala, central Sweden, on former agricultural land, where the soil consists of a heavy clay. The plantation was irrigated and fertilized daily, through a computer controlled system, from late May until mid-August. The intention was to create near-optimum conditions for growth with respect to water and nutrients. Fine-root growth started in May and fine-root number increased throughout summer and early autumn. A decrease followed from September and continued during autumn, although root growth was still occurring in October. Growth and decay of fine roots, measured as positive and negative net changes in fine-root number between observations, occurred simultaneously throughout the growing seasons. Most of the fine roots were found in the upper 40–45 cm of the soil profile. A dry period in the summer of 1989 resulted in a lower fine-root number in the upper soil layers and in a deeper mean root depth, as compared to 1988. A comparison of relative depth distribution of fine-root number, obtained from minirhizotrons, and fine-root mass, achieved from soil coring, revealed a close agreement between methods. The relative depth distribution remained fairly constant during the growing seasons. The seasonal variation of fine-root number, observed in minirhizotrons, and fine-root mass and live fine-root length, measured by soil coring, showed no significant differences between the methods or between mass and length.

Journal ArticleDOI
TL;DR: In this article, the authors measured runoff and interrill erosion in semi-arid rangelands of northern Mexico using simulated rainfall within a shortgrass community in five grass cover classes during the growing and dormant seasons.

Journal ArticleDOI
01 Jun 1996
TL;DR: In this paper, the authors compared 14 land surface parameterization schemes involved in the PILPS-RICE Workshop for a soya crop growing season (from June to September) and observed data from HAPEX-MOBILHY are available for comparison.
Abstract: Results from the 14 land surface parameterization schemes involved in the PILPS-RICE Workshop are compared for a soya crop growing season (from June to September). During this period, the transpiration flux dominates the total surface evapotranspiration and observed data from HAPEX-MOBILHY are available for comparison. Results indicate that during the month of June half of the models fall within the uncertainty range of the observations. The scatter between models behaviour is explained by three major reasons: • The functional dependency between soil moisture and transpiration; • the initial moisture content at the beginning of the period; • the vertical discretization within the soil and the extension of the root system that defines the soil water holding capacity for plants Examination of diurnal cycles of evaporation reveals that formulations based on the supply-demand concept are very sensitive to the specification of the root zone. This analysis underlines the need for more sensitivity experiments to be done with the current forcing data set and more detailed datasets to be collected in future field experiments (e.g. latent heat flux during all the growing season, root zone distribution).

Journal ArticleDOI
Abstract: Rye and grass cover crops can potentially intercept residual soil mineral nitrogen (SMN), reduce overwinter leaching, transfer SMN to next growing seasons and reduce the fertilizer need of subsequent crops. These aspects were studied for 6 years in continuous silage maize cv. LG 2080 production systems receiving 20-304 kg N/ha, on a sandy soil in the Netherlands. Rye cv. Admiraal and grass (Lolium multiflorum cv. Combita) cover crops were able to absorb on average 40 kg N/ha into the shoots. The actual N uptake was largely determined by winter temperatures and hardly affected by residual SMN. At low N input levels cover crops reduced N leaching in accordance with their N uptake. At high N input levels, however, the reduction of leaching losses exceeded the storage capacity of the cover crop, suggesting that cover cropping stimulated the loss of N via denitrification or immobilization. Cover crops had no positive effect on maize yields at larger N rates and under these conditions cover crops did not improve the conversion of SMN into crop N. This was only partly reflected by an increase of residual SMN on plots where cover crops had been incorporated, as a large part of the excess N applied to maize was already lost during the growing season. In N-deficient maize production systems, however, cover crops increased the dry matter yield of maize. Their effect was equivalent to the effect of fertilizer N rates amounting to 105 and 44% of the shoot N in rye and L. multiflorum, respectively. In the first few years cover crops decomposed incompletely during the growing season following their incorporation. In the course of the years, however, effects on subsequent maize crops increased. This supports the hypothesis that the effects of cover crops are cumulative when grown repeatedly. Averaged over the 6 years, 115% and 73% of the shoot rye N and L. multiflorum N, respectively, were recovered in the crop-soil system.

Journal ArticleDOI
TL;DR: In this paper, six distinct plant communities were studied along a single riverside toposequence in northern Alaska, including a riparian shrub community, a wet sedge tundra, a footslope Equisetum community and a hilltop birch-heath community.
Abstract: In the arctic landscape, vegetation composition and structure are strongly affected by topographic position and associated variation in microclimate. Along a single riverside toposequence in northern Alaska, six distinct plant communities were studied including a riparian shrub community, a wet sedge tundra, a footslope Equisetum community, a hillslope shrub/lupine community, a hilltop birch-heath community, and a moist tussock tundra. Total live plant biomass varied threefold along the toposequence (450-1400 g m-2) while live vascular plant biomass (including belowground stems and rhizomes but not roots) varied sevenfold (160970 g m-2). Aboveground vascular plant production varied less than fourfold (80265 g m-2). Although all six communities showed some signs of nutrient limitation, measures of soil nutrient availability were highly variable among communities. Contrary to expectations, the most productive community along the toposequence was the hillslope shrub/lupine community, where a late-lying snowbank delayed the start of the growing season by 2 wk. The second most productive community was the hilltop birch-heath, which was exposed to winter winds and where snow melted earliest; most of the production in this community occurred in relatively protected depressions where there were dense accumulations of plant mass. A conclusion is that soil fertility, soil thaw, and protection from wind are more important than length of the snow-free season in regulating productivity along the toposequence. Also contrary to expectations, overall production:live biomass ratios of the six communities varied little despite large differences in growth form composition among communities and in biomass turnover among growth forms. High-biomass, highly productive communities had the lowest production:live biomass ratios, and thus the lowest biomass turnover. Because production and live biomass were linearly correlated over the entire range sampled, it may be possible to use live biomass and/or leaf area as a reasonably accurate predictor of productivity at the landscape or regional level in the Arctic.

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TL;DR: In this paper, the authors studied the impact of climate changes on arable crop production in Scotland using simulation models for three crops of contrasting developmental type: faba or field bean, potato, spring and winter wheat.

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TL;DR: Three species of the genus Quercus section Erythrobalanus occur together as canopy trees in forests of southern New England and clear differences in patterns of germination and growth among species and among gap/canopy conditions of the sites are demonstrated.

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TL;DR: Ozone exposure reduced foliar nitrogen concentrations and increased woody tissue nutrient concentrations in seedlings and mature trees at the end of the third growing season, suggesting an influence of ozone on retranslocation processes in seedling and mature Trees.

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TL;DR: Variation in length of the growing season among sites was related to daylength and temperature, in that shorter days at emergence and higher temperatures throughout the season resulted in a shorter growth cycle.

Journal ArticleDOI
TL;DR: Despite severe demographic consequences of drought, the study provided no evidence that intraspecific competition, interference by shrub, or facilitation by shrubs increases under limited soil water.
Abstract: The demographic consequences of a severe drought year were examined for two experimental plantings of the herbaceous desert perennial Cryptantha flava(Boraginaceae) in northeastern Utah, United States. A total of 6680 nutlets were planted individually or in clusters of four both under shrubs and in open microhabitats within two natural populations. Survival, growth, and flowering as a function of density and microhabitat were followed for 7 years, including 1 year when precipitation just before and during the growing season was 74.5% below normal. The design permitted assessment of how intraspecific density and shrub cover affect demographic response to drought. Mortality increased and flowering decreased dramatically during drought but neither varied with density or between shrub and open microhabitats. For plants growing under shrubs, survival (at Site 1) and growth (at Site 2) varied with shrub species. Average aboveground plant size also decreased during drought. Population size hierarchies were rearranged because larger plants lost leaf rosettes while many smaller plants grew. Density and microhabitat affected plant performance in non-drought years but more often at Site 1 than at Site 2. Individuals growing alone often were more likely to flower and/or produced more inflorescences when they did flower than did individuals growing with at least one other plant. However, for 2 years, survival rates at Site 1 were higher for plants growing in clumps than for single individuals. Shrubs also had mixed effects on plant performance. In some years, survival was higher under shrubs, but at Site 1 plants in the open often were more likely to flower and/or produced more inflorescences. Thus despite severe demographic consequences of drought, the study provided no evidence that intraspecific competition, interference by shrubs, or facilitation by shrubs increases under limited soil water.

Journal ArticleDOI
TL;DR: Differences in herbicide tolerance existed between market classes and cultivars, although the level of herbicides tolerance varied between years.
Abstract: Dry edible bean tolerance to PPI-applied EPTC, alachlor and POST-applied imazethapyr was evaluated over two years at Scottsbluff, NE. Eight market classes of dry edible beans comprising 12 cultivars were studied. Crop tolerance was assessed by measuring crop injury, stand, leaf area index, leaf chlorosis, plant canopy volume, projected canopy cover, crop maturity, and seed yield. Leaf area index measured late in the growing season provided the best correlation with seed yield in both years. In 1993 and 1994, imazethapyr treatment caused crop injury, which resulted in a decrease of leaf area and in 1994 decreased seed yield. Differences in herbicide tolerance existed between market classes and cultivars, although the level of herbicide tolerance varied between years.

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TL;DR: The capacity of adaptation for living together may explain why the expected differences in the parameters between species and dates are not always significant, and the data highlight the higher xerophytic condition of melojo oak and the more mesophytic character of beech despite the relict condition of the stand.

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TL;DR: In this article, atmospheric sampling of nitric acid vapor, particulate nitrate and ammonium has been ongoing at a 3540 m a.s.l. alpine tundra site on Niwot Ridge, Colorado, since January, 1993.

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TL;DR: It was found that the maximum relative tuber growth rate can influence crop earliness more than the other two factors, but when conditions for tuber growth are optimal, the leaf longevity is most important.