Showing papers by "Swedish University of Agricultural Sciences published in 2001"

Biodiversity and Ecosystem Functioning: Current Knowledge and Future Challenges

Abstract: The ecological consequences of biodiversity loss have aroused considerable interest and controversy during the past decade. Major advances have been made in describing the relationship between species diversity and ecosystem processes, in identifying functionally important species, and in revealing underlying mechanisms. There is, however, uncertainty as to how results obtained in recent experiments scale up to landscape and regional levels and generalize across ecosystem types and processes. Larger numbers of species are probably needed to reduce temporal variability in ecosystem processes in changing environments. A major future challenge is to determine how biodiversity dynamics, ecosystem processes, and abiotic factors interact.

Auxin Transport Promotes Arabidopsis Lateral Root Initiation

Abstract: Lateral root development in Arabidopsis provides a model for the study of hormonal signals that regulate postembryonic organogenesis in higher plants. Lateral roots originate from pairs of pericycle cells, in several cell files positioned opposite the xylem pole, that initiate a series of asymmetric, transverse divisions. The auxin transport inhibitor N-1-naphthylphthalamic acid (NPA) arrests lateral root development by blocking the first transverse division(s). We investigated the basis of NPA action by using a cell-specific reporter to demonstrate that xylem pole pericycle cells retain their identity in the presence of the auxin transport inhibitor. However, NPA causes indoleacetic acid (IAA) to accumulate in the root apex while reducing levels in basal tissues critical for lateral root initiation. This pattern of IAA redistribution is consistent with NPA blocking basipetal IAA movement from the root tip. Characterization of lateral root development in the shoot meristemless1 mutant demonstrates that root basipetal and leaf acropetal auxin transport activities are required during the initiation and emergence phases, respectively, of lateral root development.

Microbial Population Structures in Soil Particle Size Fractions of a Long-Term Fertilizer Field Experiment

Abstract: Soil structure depends on the association between mineral soil particles (sand, silt, and clay) and organic matter, in which aggregates of different size and stability are formed. Although the chemistry of organic materials, total microbial biomass, and different enzyme activities in different soil particle size fractions have been well studied, little information is available on the structure of microbial populations in microhabitats. In this study, topsoil samples of different fertilizer treatments of a long-term field experiment were analyzed. Size fractions of 200 to 63 μm (fine sand fraction), 63 to 2 μm (silt fraction), and 2 to 0.1 μm (clay fraction) were obtained by a combination of low-energy sonication, wet sieving, and repeated centrifugation. Terminal restriction fragment length polymorphism analysis and cloning and sequencing of 16S rRNA genes were used to compare bacterial community structures in different particle size fractions. The microbial community structure was significantly affected by particle size, yielding higher diversity of microbes in small size fractions than in coarse size fractions. The higher biomass previously found in silt and clay fractions could be attributed to higher diversity rather than to better colonization of particular species. Low nutrient availability, protozoan grazing, and competition with fungal organisms may have been responsible for reduced diversities in larger size fractions. Furthermore, larger particle sizes were dominated by α-Proteobacteria, whereas high abundance and diversity of bacteria belonging to the Holophaga/Acidobacterium division were found in smaller size fractions. Although very contrasting organic amendments (green manure, animal manure, sewage sludge, and peat) were examined, our results demonstrated that the bacterial community structure was affected to a greater extent by the particle size fraction than by the kind of fertilizer applied. Therefore, our results demonstrate specific microbe-particle associations that are affected to only a small extent by external factors.

Linking plants to rocks: ectomycorrhizal fungi mobilize nutrients from minerals.

Abstract: Plant nutrients, with the exception of nitrogen, are ultimately derived from weathering of primary minerals. Traditional theories about the role of ectomycorrhizal fungi in plant nutrition have emphasized quantitative effects on uptake and transport of dissolved nutrients. Qualitative effects of the symbiosis on the ability of plants to access organic nitrogen and phosphorus sources have also become increasingly apparent. Recent research suggests that ectomycorrhizal fungi mobilize other essential plant nutrients directly from minerals through excretion of organic acids. This enables ectomycorrhizal plants to utilize essential nutrients from insoluble mineral sources and affects nutrient cycling in forest systems.

Stomatal conductance of forest species after long‐term exposure to elevated CO2 concentration: a synthesis

Abstract: • Data from 13 long-term (> 1 yr), field-based studies of the effects of elevated CO2 concentration ([CO2]) on European forest tree species were analysed using meta-analysis and modelling. Meta-analysis was used to determine mean responses across the data sets, and data were fitted to two commonly used models of stomatal conductance in order to explore response to environmental conditions and the relationship with assimilation. • Meta-analysis indicated a significant decrease (21%) in stomatal conductance in response to growth in elevated [CO2] across all studies. The response to [CO2] was significantly stronger in young trees than old trees, in deciduous compared to coniferous trees, and in water stressed compared to nutrient stressed trees. No evidence of acclimation of stomatal conductance to elevated [CO2] was found. • Fits of data to the first model showed that growth in elevated [CO2] did not alter the response of stomatal conductance to vapour pressure deficit, soil water content or atmospheric [CO2]. Fits of data to the second model indicated that conductance and assimilation responded in parallel to elevated [CO2] except when water was limiting. • Data were compared to a previous meta-analysis and it was found that the response of gs to elevated [CO2] was much more consistent in long-term (> 1 yr) studies, emphasising the need for long-term elevated [CO2] studies. By interpreting data in terms of models, the synthesis will aid future modelling studies of responses of forest trees to elevated [CO2].

Mutant mitochondrial thymidine kinase in mitochondrial DNA depletion myopathy

Abstract: The mitochondrial deoxyribonucleotide (dNTP) pool is separated from the cytosolic pool because the mitochondria inner membrane is impermeable to charged molecules The mitochondrial pool is maintained by either import of cytosolic dNTPs through dedicated transporters1,2 or by salvaging deoxynucleosides within the mitochondria; apparently, enzymes of the de novo dNTP synthesis pathway are not present in the mitochondria In non-replicating cells, where cytosolic dNTP synthesis is down-regulated, mtDNA synthesis depends solely on the mitochondrial salvage pathway enzymes, the deoxyribonucleosides kinases Two of the four human deoxyribonucleoside kinases, deoxyguanosine kinase (dGK) and thymidine kinase-2 (TK2), are expressed in mitochondria3,4,5,6 Human dGK efficiently phosphorylates deoxyguanosine and deoxyadenosine, whereas TK2 phosphorylates deoxythymidine, deoxycytidine and deoxyuridine Here we identify two mutations in TK2, histidine 90 to asparagine and isoleucine 181 to asparagine, in four individuals who developed devastating myopathy and depletion of muscular mitochondrial DNA in infancy In these individuals, the activity of TK2 in muscle mitochondria is reduced to 14–45% of the mean value in healthy control individuals Mutations in TK2 represent a new etiology for mitochondrial DNA depletion, underscoring the importance of the mitochondrial dNTP pool in the pathogenesis of mitochondrial depletion

The deoxyguanosine kinase gene is mutated in individuals with depleted hepatocerebral mitochondrial DNA.

Abstract: Mitochondrial DNA (mtDNA)-depletion syndromes (MDS; OMIM 251880) are phenotypically heterogeneous, autosomal-recessive disorders characterized by tissue-specific reduction in mtDNA copy number. Affected individuals with the hepatocerebral form of MDS have early progressive liver failure and neurological abnormalities, hypoglycemia and increased lactate in body fluids. Affected tissues show both decreased activity of the mtDNA-encoded respiratory chain complexes (I, III, IV, V) and mtDNA depletion. We used homozygosity mapping in three kindreds of Druze origin to map the gene causing hepatocerebral MDS to a region of 6.1 cM on chromosome 2p13, between markers D2S291 and D2S2116. This interval encompasses the gene (DGUOK) encoding the mitochondrial deoxyguanosine kinase (dGK). We identified a single-nucleotide deletion (204delA) within the coding region of DGUOK that segregates with the disease in the three kindreds studied. Western-blot analysis did not detect dGK protein in the liver of affected individuals. The main supply of deoxyribonucleotides (dNTPs) for mtDNA synthesis comes from the salvage pathway initiated by dGK and thymidine kinase-2 (TK2). The association of mtDNA depletion with mutated DGUOK suggests that the salvage-pathway enzymes are involved in the maintenance of balanced mitochondrial dNTP pools.

A transcriptional roadmap to wood formation

Abstract: The large vascular meristem of poplar trees with its highly organized secondary xylem enables the boundaries between different developmental zones to be easily distinguished. This property of wood-forming tissues allowed us to determine a unique tissue-specific transcript profile for a well defined developmental gradient. RNA was prepared from different developmental stages of xylogenesis for DNA microarray analysis by using a hybrid aspen unigene set consisting of 2,995 expressed sequence tags. The analysis revealed that the genes encoding lignin and cellulose biosynthetic enzymes, as well as a number of transcription factors and other potential regulators of xylogenesis, are under strict developmental stage-specific transcriptional regulation.

Lactobacillus coryniformis subsp. coryniformis strain Si3 produces a broad-spectrum proteinaceous antifungal compound.

Abstract: The antifungal activity spectrum of Lactobacillus coryniformis subsp. coryniformis strain Si3 was investigated. The strain had strong inhibitory activity in dual-culture agar plate assays against the molds Aspergillus fumigatus, A. nidulans, Penicillium roqueforti, Mucor hiemalis, Talaromyces flavus, Fusarium poae, F. graminearum, F. culmorum, and F. sporotrichoides. A weaker activity was observed against the yeasts Debaryomyces hansenii, Kluyveromyces marxianus, and Saccharomyces cerevisiae. The yeasts Rhodotorula glutinis, Sporobolomyces roseus, and Pichia anomala were not inhibited. In liquid culture the antifungal activity paralleled growth, with maximum mold inhibition early in the stationary growth phase, but with a rapid decline in antifungal activity after 48 h. The addition of ethanol to the growth medium prevented the decline and gave an increased antifungal activity. The activity was stable during heat treatment and was retained even after autoclaving at 121°C for 15 min. Maximum activity was observed at pH values of between 3.0 and 4.5, but it decreased rapidly when pH was adjusted to a level between 4.5 and 6.0 and was lost at higher pH values. The antifungal activity was fully regained after readjustment of the pH to the initial value (pH 3.6). The activity was irreversibly lost after treatment with proteolytic enzymes (proteinase K, trypsin, and pepsin). The antifungal activity was partially purified using ion-exchange chromatography and (NH4)2SO4 precipitation, followed by gel filtration chromatography. The active compound(s) was estimated to have a molecular mass of approximately 3 kDa. This is the first report of the production of a proteinaceous antifungal compound(s) from L. coryniformis subsp. coryniformis.

Unravelling cell wall formation in the woody dicot stem.

Abstract: Populus is presented as a model system for the study of wood formation (xylogenesis). The formation of wood (secondary xylem) is an ordered developmental process involving cell division, cell expansion, secondary wall deposition, lignification and programmed cell death. Because wood is formed in a variable environment and subject to developmental control, xylem cells are produced that differ in size, shape, cell wall structure, texture and composition. Hormones mediate some of the variability observed and control the process of xylogenesis. High-resolution analysis of auxin distribution across cambial region tissues, combined with the analysis of transgenic plants with modified auxin distribution, suggests that auxin provides positional information for the exit of cells from the meristem and probably also for the duration of cell expansion. Poplar sequencing projects have provided access to genes involved in cell wall formation. Genes involved in the biosynthesis of the carbohydrate skeleton of the cell wall are briefly reviewed. Most progress has been made in characterizing pectin methyl esterases that modify pectins in the cambial region. Specific expression patterns have also been found for expansins, xyloglucan endotransglycosylases and cellulose synthases, pointing to their role in wood cell wall formation and modification. Finally, by studying transgenic plants modified in various steps of the monolignol biosynthetic pathway and by localizing the expression of various enzymes, new insight into the lignin biosynthesis in planta has been gained.

Net primary production and carbon allocation patterns of boreal forest ecosystems

Abstract: The three objectives of this paper were: to summarize net primary production (NPP) and carbon allocation patterns for boreal forests, to examine relationships between climatic and biological variables and NPP, and to examine carbon allocation coefficients for all boreal forests or types of boreal forests that can be used to estimate NPP from easily measured components of NPP. Twenty-four Class I stands (complete NPP budgets) and 45 Class II boreal forest stands (aboveground NPP [NPPA] and budget only) were identified. The geographic distribution of the Class I stands was not uniform; 46% of the stands were from two studies in North America, and only one stand was from the important larch forests of Eurasia. Total (above- and belowground) net primary production (NPPT) ranged from 52 to 868 g C·m−2·yr−1 and averaged 424 g C·m−2·yr−1. NPPA was consistently larger for deciduous than for evergreen boreal forests in each of the major boreal regions, especially for boreal forests in Alaska. Belowground net prima...

Widespread Origins of Domestic Horse Lineages

Abstract: Domestication entails control of wild species and is generally regarded as a complex process confined to a restricted area and culture. Previous DNA sequence analyses of several domestic species have suggested only a limited number of origination events. We analyzed mitochondrial DNA (mtDNA) control region sequences of 191 domestic horses and found a high diversity of matrilines. Sequence analysis of equids from archaeological sites and late Pleistocene deposits showed that this diversity was not due to an accelerated mutation rate or an ancient domestication event. Consequently, high mtDNA sequence diversity of horses implies an unprecedented and widespread integration of matrilines and an extensive utilization and taming of wild horses. However, genetic variation at nuclear markers is partitioned among horse breeds and may reflect sex-biased dispersal and breeding.

Local adaptation enhances performance of common plant species

Abstract: Geographic variation can lead to the evolution of different local varieties, even in widespread forage plants. We investigated the performance of common forage plants in relation to their genetic diversity and local adaptation at a continental scale using reciprocal transplants at eight field sites across Europe over a 2-year period. The overall performance of the three test species, Trifolium pratense, Dactylis glomerata, Plantago lanceolata, was generally highest for plants replanted at their home site and declined with increasing transplanting distance. The three species differed in the fitness components responsible for the increased overall performance and selection advantage at home sites. In addition to the effects of local adaptation, the majority of measured traits in all three species also showed ecotypic variation. However, no single ecotype of any species was able to outperform the locally adapted strains and do best at all sites, highlighting the importance of maintaining these plant genetic resources.

The unexpected versatility of plants: organic nitrogen use and availability in terrestrial ecosystems.

Abstract: The recently recognized importance of organic nitrogen (ON), particularly amino acids, to plant nutrition in many types of agricultural and natural ecosystems has raised questions about plant-microbe interactions, N availability in soils, and the ecological implications of ON use by plants in the light of climate change and N pollution. In this review we synthesize the recent work on availability and plant uptake of amino acids with classic work on ON in soils. We also discuss recent work on the use of natural abundance levels of 15N to infer N sources for plants. Reliance on ON is widespread among plants from many ecosystems. Authors have reached this conclusion based on laboratory studies of amino acid uptake by plants in pure culture, amino acid concentrations in soils, plant uptake of isotopically labeled amino acids in the field and in plant-soil microcosms, and from plant natural abundance values of 15N. The supply of amino acids to plants is determined mainly by the action of soil proteolytic enzymes, interactions between amino acids and the soil matrix, and competition between plants and microbes. Plants generally compete for a minor fraction of the total amino acid flux, but in some cases this forms a significant N resource, especially in ecosystems where microbial biomass undergoes large seasonal fluctuations and contributes labile ON to the soil. A quantitative understanding of ON use by plants is confounded by incomplete data on partitioning of ON between plants, mycorrhizal fungi, and competing soil microbes. Further research is needed to predict the ecological implications of ON use by plants given the influence of climatic change and N pollution.

Genetic dissection of phenotypic diversity in farm animals

Abstract: Farm animal populations harbour rich collections of mutations with phenotypic effects that have been purposefully enriched by breeding. Most of these mutations do not have pathological phenotypic consequences, in contrast to the collections of deleterious mutations in model organisms or those causing inherited disorders in humans. Farm animals are of particular interest for identifying genes that control growth, energy metabolism, development, appetite, reproduction and behaviour, as well as other traits that have been manipulated by breeding. Genome research in farm animals will add to our basic understanding of the genetic control of these traits and the results will be applied in breeding programmes to reduce the incidence of disease and to improve product quality and production efficiency.

Quality properties of pelletised sawdust, logging residues and bark

Abstract: The dominant raw material for wood pellet production in Sweden is sawdust, planer shavings and dry chips. However, other types of biomass, such as bark and logging residues, are also interesting raw materials due to the large volumes available. These alternative raw materials differ from stemwood with regard to physical characteristics and chemical composition. In order to produce high-quality pellets of such materials, it is necessary to understand the role of these variations. Nine pellet assortments, made of fresh and stored sawdust, bark and logging residues (a mixture of Norway spruce and Scots pine) were tested for moisture content, heating value and contents of ash, sulphur, chlorine and Klason lignin. Dimensions, bulk density, density of individual pellets, durability and sintering risk were also determined. The heating value was highest in logging residue pellets. The ash content was highest in the bark and logging residue pellets, implying higher sintering risk compared with sawdust pellets. The results showed that bark pellets had the highest durability, whereas sawdust pellets had the lowest. Pellet density had no effect on durability, unlike lignin content which was positively correlated. It is concluded that bark and logging residues are suitable raw materials for pellets production, especially if the ash content is controlled.

Stress-induced accumulation and tissue-specific localization of dehydrins in Arabidopsis thaliana

Abstract: Stress-induced accumulation of five (COR47, LTI29, ERD14, LTI30 and RAB18) and tissue localization of four (LTI29, ERD14, LTI30 and RAB18) dehydrins in Arabidopsis were characterized immunologically with protein-specific antibodies. The five dehydrins exhibited clear differences in their accumulation patterns in response to low temperature, ABA and salinity. ERD14 accumulated in unstressed plants, although the protein level was up-regulated by ABA, salinity and low temperature. LTI29 mainly accumulated in response to low temperature, but was also found in ABA- and salt-treated plants. LTI30 and COR47 accumulated primarily in response to low temperature, whereas RAB18 was only found in ABA-treated plants and was the only dehydrin in this study that accumulated in dry seeds. Immunohistochemical localization of LTI29, ERD14 and RAB18 demonstrated tissue and cell type specificity in unstressed plants. ERD14 was present in the vascular tissue and bordering parenchymal cells, LTI29 and ERD14 accumulated in the root tip, and RAB18 was localized to stomatal guard cells. LTI30 was not detected in unstressed plants. The localization of LTI29, ERD14 and RAB18 in stress-treated plants was not restricted to certain tissues or cell types. Instead these proteins accumulated in most cells, although cells within and surrounding the vascular tissue showed more intense staining. LTI30 accumulated primarily in vascular tissue and anthers of cold-treated plants. This study supports a physiological function for dehydrins in certain plant cells during optimal growth conditions and in most cell types during ABA or cold treatment. The differences in stress specificity and spatial distribution of dehydrins in Arabidopsis suggest a functional specialization for the members of this protein family.

Hydration of the calcium ion. An EXAFS, large-angle x-ray scattering, and molecular dynamics simulation study.

Abstract: The structure of the hydrated calcium(II) ion in aqueous solution has been studied by means of extended X-ray absorption fine structure spectroscopy (EXAFS), large-angle X-ray scattering (LAXS), and molecular dynamics (MD) methods. The EXAFS data displayed a broad and asymmetric distribution of the Ca−O bond distances with the centroid at 2.46(2) A. LAXS studies on four aqueous calcium halide solutions (1.5−2 mol dm-3) gave a mean Ca−O bond distance of 2.46(1) A. This is consistent with a hydration number of 8 determined from correlations between mean distances and coordination numbers from crystal structures. The LAXS studies showed a second coordination sphere with a mean Ca···OII distance of 4.58(5) A, and for the hydrated halide ions the distances Cl···O 3.25(1) A, Br···O 3.36(1) A, and I···O 3.61(1) A were obtained. Molecular dynamics simulations of CaCl2(aq) were performed using three different Ca2+−OH2 pair potentials. The potential from the GROMOS program gave results in agreement with experiments...

GAMYB-like genes, flowering, and gibberellin signaling in Arabidopsis.

Abstract: We have identified three Arabidopsis genes with GAMYB-like activity, AtMYB33, AtMYB65, and AtMYB101, which can substitute for barley (Hordeum vulgare) GAMYB in transactivating the barley alpha-amylase promoter. We have investigated the relationships between gibberellins (GAs), these GAMYB-like genes, and petiole elongation and flowering of Arabidopsis. Within 1 to 2 d of transferring plants from short- to long-day photoperiods, growth rate and erectness of petioles increased, and there were morphological changes at the shoot apex associated with the transition to flowering. These responses were accompanied by accumulation of GAs in the petioles (GA(1) by 11-fold and GA(4) by 3-fold), and an increase in expression of AtMYB33 at the shoot apex. Inhibition of GA biosynthesis using paclobutrazol blocked the petiole elongation induced by long days. Causality was suggested by the finding that, with GA treatment, plants flowered in short days, AtMYB33 expression increased at the shoot apex, and the petioles elongated and grew erect. That AtMYB33 may mediate a GA signaling role in flowering was supported by its ability to bind to a specific 8-bp sequence in the promoter of the floral meristem-identity gene, LEAFY, this same sequence being important in the GA response of the LEAFY promoter. One or more of these AtMYB genes may also play a role in the root tip during germination and, later, in stem tissue. These findings extend our earlier studies of GA signaling in the Gramineae to include a dicot species, Arabidopsis, and indicate that GAMYB-like genes may mediate GA signaling in growth and flowering responses.

Structure and function of the radical enzyme ribonucleotide reductase.

Abstract: Ribonucleotide reductases (RNRs) catalyze all new production in nature of deoxyribonucleotides for DNA synthesis by reducing the corresponding ribonucleotides. The reaction involves the action of a radical that is produced differently for different classes of the enzyme. Class I enzymes, which are present in eukaryotes and microorganisms, use an iron center to produce a stable tyrosyl radical that is stored in one of the subunits of the enzyme. The other classes are only present in microorganisms. Class II enzymes use cobalamin for radical generation and class III enzymes, which are found only in anaerobic organisms, use a glycyl radical. The reductase activity is in all three classes contained in enzyme subunits that have similar structures containing active site cysteines. The initiation of the reaction by removal of the 3'-hydrogen of the ribose by a transient cysteinyl radical is a common feature of the different classes of RNR. This cysteine is in all RNRs located on the tip of a finger loop inserted into the center of a special barrel structure. A wealth of structural and functional information on the class I and class III enzymes can now give detailed views on how these enzymes perform their task. The class I enzymes demonstrate a sophisticated pattern as to how the free radical is used in the reaction, in that it is only delivered to the active site at exactly the right moment. RNRs are also allosterically regulated, for which the structural molecular background is now starting to be revealed.

Village poultry production systems in the central highlands of Ethiopia.

Abstract: Participatory rural appraisal (PRA), supported by checklists and intensive case studies on individual households, was carried out in three villages at three different altitudes in the central highlands of Ethiopia. The chicken production system in each village is described and the problems are discussed. More than 60% of the families kept chickens, and in most cases the women owned and managed the birds and controlled the cash from the sales. The production systems followed were mainly low-input and small-scale, with 7-10 mature birds per household, reared in the back yards with inadequate housing, feeding and health care. The average egg production per clutch was 15-20, with 3-4 clutches per year. The mean number of eggs set per bird was 12.9 +/- 2.2 (n = 160), depending on the size of the bird and season, and the hatching rate was 80.9% +/- 11.1%, range 44%-100% (n = 160). Poultry meat and eggs were generally accepted and appreciated in all three villages. In addition to the small amount of cash income they provide, scavenging chickens have nutritional, cultural and social functions. The flock composition, price of poultry and poultry products, disease outbreaks and hatching of chicks were strongly affected by season. Disease was cited as the most important problem by most of the members of the community, followed by predation, lack of feed, poor housing, insufficient water and parasites. Disease periodically decimated the flocks, and consequently, about 50% of the eggs produced were incubated in order to replace the birds that had died. The major source of loss in the system was the high mortality of chicks (61%) that occurred between hatching and the end of brooding at 8 weeks of age. The system was characterized by no or few inputs and a low output level. The major input was the cost of foundation stock, but after that virtually no cost was involved. The major source of feed for the birds was from the scavenging feed resource base, which comprised table leftovers, small grain supplements and anything edible from the immediate environment.

Community ecology of ectomycorrhizal fungi: an advancing interdisciplinary field

Abstract: Summary A long-term goal of community ecology is to identify spatial and temporal factors that underlie observed community structures. Ultimately, ecologists seek to relate community patterns to ecosystem processes and functions. Since the mid 1990s, ectomycorrhizal (ECM) research has been equipped with tools to identify and fully quantify the taxonomic diversity in below-ground ECM fungal communities in detail and address such questions. Many of the most important functions of terrestrial ecosystems, as well as interactions, between plants take place below ground and mycorrhizal fungi are among the key players in soil ecology. Here the rapidly increasing knowledge of ECM fungal community ecology is reviewed and the prospects discussed for elucidating processes that structure ECM fungal communities and the way in which such knowledge might be integrated with, and advance, the understanding of plant ecology and ecosystem processes.

Gibberellins are not required for normal stem growth in Arabidopsis thaliana in the absence of GAI and RGA

Abstract: The growth of Arabidopsis thaliana is quantitatively regulated by the phytohormone gibberellin (GA) via two closely related nuclear GA-signaling components, GAI and RGA. Here we test the hypothesis that GAI and RGA function as "GA-derepressible repressors" of plant growth. One prediction of this hypothesis is that plants lacking GAI and RGA do not require GA for normal stem growth. Analysis of GA-deficient mutants lacking GAI and RGA confirms this prediction and suggests that in the absence of GAI and RGA, "growth" rather than "no growth" is the default state of plant stems. The function of the GA-signaling system is thus to act as a control system regulating the amount of this growth. We also demonstrate that the GA dose dependency of hypocotyl elongation is altered in mutants lacking GAI and RGA and propose that increments in GAI/RGA repressor function can explain the quantitative nature of GA responses.

Soil nitrogen form and plant nitrogen uptake along a boreal forest productivity gradient

Abstract: We present results from a study of soil solution concentrations of ammonium (NH4 +), nitrate (NO3 –), and amino acid N over one growing season along a local 90-m-long plant productivity gradient in a boreal forest. Three forest types are found along the gradient: an ericaceous dwarf-shrub type between 0 and 40 m, a low-herb type between 40 and 80 m, and a tall-herb type at 90 m. Soil sampling of the mor layer was performed in June, July, August and October in the three forest types. In addition, plant uptake of NH4 +, NO3 – and the amino acid glycine was investigated. A mixture of the three N forms was injected into the soil; one N form at a time was labeled with 15N, and in the case of glycine also with 13C. In the dwarf-shrub forest, where plant productivity was low, the soil N pool was strongly dominated by amino acid N. There, plants took up more NH4 + than NO3 –. Glycine uptake did not differ significantly from either NH4 + or NO3 – uptake. Along the gradient, soil concentrations of NH4 + and NO3 – increased, as did plant productivity. In the low-herb forest NH4 + comprised a major portion of the soil N pool, and plants took up more NH4 + than NO3 – or glycine. In the tall-herb forest, NO3 – was as abundant as NH4 +, and together these two N forms dominated the soil N pool. Here, plants took up nearly equal amounts of NO3 – and NH4 +, and this uptake exceeded that of glycine severalfold. Apart from the overall preference for NH4 + that plants exhibited throughout the gradient, the results show a correlation between soil concentrations of amino acids and NO3 – and plant preferences for these N forms.

Woodpeckers as Indicators of Forest Bird Diversity

Abstract: We analyzed the usefulness of woodpecker species ( family Picidae) in predicting the diversity of other forest bird species using the Polish Ornithological Atlas data on species distribution in Poland. We used the database (n = 2317) to examine the patterns of woodpecker occurrence in atlas plots and to test how well the occurrence of woodpecker species is related to the occurrence of other forest birds. The occupancy of atlas plots by particular species varied from 98.5% in the Great Spotted Woodpecker ( Dendrocopos major) to only 2.4% in the Three-toed Woodpecker ( Picoides tridactylus). Woodpecker species richness in plots varied between 0 and 10 species, with a mean value of 4.3 species per plot. The occurrence of particular woodpecker species in plots with different woodpecker species richness was associated with the degree of specialization in particular species. Examining the entire data set, we found a positive relationship between woodpecker species richness and the number of species of other forest birds. These relationships were confirmed in three smaller regional data subsets with at least eight woodpecker species present (northeast Poland, r 2 = 0.78, p = 0.0001; east Poland, r 2 = 0.53, p = 0.0001; Carpathians, r 2 = 0.53, p = 0.0001). The mean number of forest specialists increased from 6 to over 30 species in plots with 0 and 9 woodpecker species, respectively. Also, the mean number of woodland generalists increased steadily with woodpecker species richness. Our results confirm the suitability of the woodpecker group as part of an indicator system for assessing avian diversity at the landscape scale. We suggest that in countries or regions in Europe where data on bird diversity are not readily available, woodpecker surveys could serve as a good tool for assessing the diversity of forest birds at the landscape scale. Resumen: Analizamos la utilidad de las especies de pajaros carpinteros ( Familia Picidae) en la prediccion de la diversidad de otras aves forestales usando datos de cooperacion del Atlas Ornitologico Europeo sobre la distribucion de especies de Polonia. Usamos la base de datos (n = 2317) para examinar los patrones de presencia en parcelas del atlas y para evaluar que tan bien se relaciona la presencia de los pajaros carpinteros con la presencia de otras especies de aves del bosque. La ocupacion de parcelas del atlas por especies en particular vario desde un 98.5% para el gran pajaro carpintero manchado ( Dendrocopos major) hasta un 2.4% para el carpintero de tres dedos ( Picoides tridactylus). La riqueza de especies de pajaros carpinteros en parcelas vario entre 0 y 10 especies, con un valor promedio de 4.3 especies por parcela. La aparicion de especies especificas de pajaros carpinteros en parcelas con diferente riqueza de especies de pajaros carpinteros estuvo asociada con el grado de especializacion de ciertas especies en particular. Al examinar el juego de datos completo, encontramos una relacion positiva entre la riqueza de especies de pajaros carpinteros y el numero de especies de otras aves del bosque. Estas relaciones fueron confirmadas en tres subgrupos de datos regionales con al menos 8 especies de pajaros carpinteros presentes (Polonia nororiental r 2 = 0.78, p = 0.0001; Polonia oriental r 2 = 0.53, p = 0.0001; Carpatos, r 2 = 0.53, p = 0.0001). El numero promedio de especialistas del bosque se incremento respectivamente de seis a mas de 30 especies en parcelas con cero y nueve especies de pajaros carpinteros. Asimismo, el numero promedio de generalistas del bosque incremento aceleradamente con la riqueza de especies de pajaros carpinteros. Nuestros resultados confirman la viabilidad del grupo de los pajaros carpinteros como parte de un sistema indicador para evaluar la diversidad de aves a escala de paisaje. Sugerimos que en paises o regiones de Europa donde los datos sobre diversidad de aves no son faciles de obtener, se pueden usar reconocimientos de pajaros carpinteros como una buena herramienta para evaluar la densidad de aves del bosque a escala de paisaje.