The Experts below are selected from a list of 180 Experts worldwide ranked by ideXlab platform

Michael F Allen - One of the best experts on this subject based on the ideXlab platform.

  • changes in n cycling and microbial n with elevated n in exotic Annual Grasslands of southern california
    Applied Soil Ecology, 2007
    Co-Authors: Abby G Sirulnik, Edith B Allen, T Meixner, Mark E Fenn, Michael F Allen
    Abstract:

    Abstract The impacts of nitrogen (N) fertilization and N deposition on N mineralization and microbial biomass were studied in exotic Annual Grasslands in southern California. The goal of the study was to understand how N deposition impacts N availability to the Grasslands by studying mineralization in plots in an urban area that has received chronic N deposition for 50 years compared with N fertilized and control plots in a rural area. Fertilized plots had higher net and gross rates of N cycling than did soils from the control. The effect of soil mineral N concentrations on microbial N varied between and within growing seasons. Lower microbial N corresponded to more net N release and higher microbial N corresponded to less net N release. Urban soils often had higher NO3− concentrations than did soils from the rural site but there was no difference in NH4+ concentrations. Urban soils also had lower mineral N concentrations than the fertilized soils and mineralization patterns in the high N deposition soils did not resemble those in the fertilized soils, indicating that the levels of N deposition at this site were well below the experimental fertilization rate. The levels of soil mineral N in the rural site were considerably higher than from other studies in the same plots in recent years. This corresponds with rapidly increasing suburbanization of the rural site and increasing N deposition, as suggested from a recent air pollution model. Although the urban and rural soils were not as different in mineral N concentrations as expected, soils in exotic Grasslands near urban areas across the region can have mineral N concentrations as high as the fertilized soils, indicating that increased N cycling and altered microbial N may occur under N deposition.

  • impacts of anthropogenic n additions on nitrogen mineralization from plant litter in exotic Annual Grasslands
    Soil Biology & Biochemistry, 2007
    Co-Authors: Abby G Sirulnik, Edith B Allen, T Meixner, Michael F Allen
    Abstract:

    Abstract Urban regions of southern California receive up to 45 kg N ha –1  y –1 from nitrogen (N) deposition. A field decomposition study was done using 15 N-labelled litter of the widespread exotic Annual grass Bromus diandrus to determine whether elevated soil N is strictly from N deposition or whether N mineralization rates from litter are also increased under N deposition. Tissue N and lignin concentrations, which are inversely related in field sites with high and low N deposition, determine the rate at which N moves from plant litter to soil and becomes available to plants. The effect of soil N on N movement from litter to soil was tested by placing litter on high and low N soil in a factorial experiment with two levels of litter N and two levels of soil N. The litter quality changes associated with N deposition resulted in faster rates of N cycling from litter to soil. Concentrations of litter-derived N in total N, NH 4 + , NO 3 − , microbial N and organic N were all higher from high N/low lignin litter than from low N/high lignin litter. Litter contributed more N to soil NH 4 + and microbial N in high N than low N soil. At the end of the study, N mineralized from high N litter on high N soil accounted for 46% of soil NH 4 + and 11% of soil NO 3 − , compared to 35% of soil NH 4 + and 6% of soil NO 3 − from low N litter on low N soil. The study showed that in high N deposition areas, elevated inorganic soil N concentrations at the end of the summer N deposition season are a result of N mineralized from plant litter as well as from N deposition.

  • soil biota responses to long term atmospheric co2 enrichment in two california Annual Grasslands
    Oecologia, 1999
    Co-Authors: Matthias C Rillig, Christopher B Field, Michael F Allen
    Abstract:

    Root, arbuscular-mycorrhizal (AM), soil faunal (protozoa and microarthropods), and microbial responses to field exposure to CO2 for six growing seasons were measured in spring 1997 in two adjacent grassland communities. The Grasslands showed contrasting root responses to CO2 enrichment: whereas root length was not affected in the sandstone grassland, it was greater in the serpentine grassland, as was specific root length. AM fungal hyphal lengths were greater in the sandstone, but were unaffected in the serpentine community. This lent support to the hypothesis that there may be a tradeoff in resource allocation to more fine roots or greater mycorrhizal extraradical hyphal length. AM root infection was greater in both communities at elevated CO2, as was the proportion of roots containing arbuscules. Our data on total hyphal lengths, culturable and active fungi, bacteria, and protozoa supported the hypothesis that the fungal food chain was more strongly stimulated than the bacterial chain. This study is one of the first to test these hypotheses in natural multi-species communities in the field.

Whendee L Silver - One of the best experts on this subject based on the ideXlab platform.

  • impacts of organic matter amendments on carbon and nitrogen dynamics in grassland soils
    Soil Biology & Biochemistry, 2014
    Co-Authors: Rebecca Ryals, Michael Kaiser, Margaret S Torn, Asmeret Asefaw Berhe, Whendee L Silver
    Abstract:

    Organic matter amendments have been proposed as a means to enhance soil carbon (C) stocks on degraded soils. However, only few data exist on rates of soil C sequestration or the fate of added C in grassland soils, which are generally thought to have high C storage potential. We measured changes in the amount of C and nitrogen (N) in soils and in the composition of soil organic matter (SOM) following a single application of composted organic matter in two Annual Grasslands from different bioclimatic zones (coastal and inland valley). There was a significant increase in bulk soil organic C content at the valley grassland, and a similar but non-significant trend at the coastal grassland. Physical fractionation of soil three years after organic matter amendment revealed increases in C and N in the free- and occluded light fractions in both the valley and coastal Grasslands. Amendments resulted in a greater relative increase in the N stored in light soil fractions compared to C, leading to lower C:N ratios. Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy showed an increase in the ratio of carboxyl and carbonyl functional groups to aliphatic methyl and methylene groups in the free- and occluded light fractions. These data show that the organic matter amendment was incorporated in the free light and occluded light fractions over three years. Our results indicate that a single application of compost to grassland soils can increase soil C and N storage in labile and physically protected pools over relatively short time periods and contribute to climate change mitigation.

  • a lifecycle model to evaluate carbon sequestration potential and greenhouse gas dynamics of managed Grasslands
    Ecosystems, 2013
    Co-Authors: Marcia S Delonge, Rebecca Ryals, Whendee L Silver
    Abstract:

    Soil amendments can increase net primary productivity (NPP) and soil carbon (C) sequestration in Grasslands, but the net greenhouse gas fluxes of amendments such as manure, compost, and inorganic fertilizers remain unclear. To evaluate opportunities for climate change mitigation through soil amendment applications, we designed a field-scale model that quantifies greenhouse gas emissions (CO2, CH4, and N2O) from the production, application, and ecosystem response of soil amendments. Using this model, we developed a set of case studies for grazed Annual Grasslands in California. Sensitivity tests were performed to explore the impacts of model variables and management options. We conducted Monte Carlo simulations to provide estimates of the potential error associated with variables where literature data were sparse or spanned wide ranges. In the base case scenario, application of manure slurries led to net emissions of 14 Mg CO2e ha−1 over a 3-year period. Inorganic N fertilizer resulted in lower greenhouse gas emissions than the manure (3 Mg CO2e ha−1), assuming equal rates of N addition and NPP response. In contrast, composted manure and plant waste led to large offsets that exceeded emissions, saving 23 Mg CO2e ha−1 over 3 years. The diversion of both feedstock materials from traditional high-emission waste management practices was the largest source of the offsets; secondary benefits were also achieved, including increased plant productivity, soil C sequestration, and reduced need for commercial feeds. The greenhouse gas saving rates suggest that compost amendments could result in significant offsets to greenhouse gas emissions, amounting to over 28 MMg CO2e when scaled to 5% of California rangelands. We found that the model was highly sensitive to manure and landfill management factors and less dependent on C sequestration, NPP, and soil greenhouse gas effluxes. The Monte Carlo analyses indicated that compost application to Grasslands is likely to lead to net greenhouse gas offsets across a broad range of potential environmental and management conditions. We conclude that applications of composted organic matter to Grasslands can contribute to climate change mitigation while sustaining productive lands and reducing waste loads.

  • effects of organic matter amendments on net primary productivity and greenhouse gas emissions in Annual Grasslands
    Ecological Applications, 2013
    Co-Authors: Rebecca Ryals, Whendee L Silver
    Abstract:

    Most of the world's Grasslands are managed for livestock production. A critical component of the long-term sustainability and profitability of rangelands (e.g., grazed grassland ecosystems) is the maintenance of plant production. Amending grassland soils with organic waste has been proposed as a means to increase net primary productivity (NPP) and ecosystem carbon (C) storage, while mitigating greenhouse gas emissions from waste management. Few studies have evaluated the effects of amendments on the C balance and greenhouse gas dynamics of Grasslands. We used field manipulations replicated within and across two rangelands (a valley grassland and a coastal grassland) to determine the effects of a single application of composted green waste amendments on NPP and greenhouse gas emissions over three years. Amendments elevated total soil respiration by 18% +/- 4% at both sites but had no effect on nitrous oxide or methane emissions. Carbon losses were significantly offset by greater and sustained plant production. Amendments stimulated both above- and belowground NPP by 2.1 +/- 0.8 Mg C/ha to 4.7 +/- 0.7 Mg C/ha (mean +/- SE) over the three-year study period. Net ecosystem C storage increased by 25-70% without including the direct addition of compost C. The estimated magnitude of net ecosystem C storage was sensitive to estimates of heterotrophic soil respiration but was greater than controls in five out of six fields that received amendments. The sixth plot was the only one that exhibited lower soil moisture than the control, suggesting an important role of water limitation in these seasonally dry ecosystems. Treatment effects persisted over the course of the study, which were likely derived from increased water-holding capacity in most plots, and slow-release fertilization from compost decomposition. We conclude that a single application of composted organic matter can significantly increase grassland C storage, and that effects of a single application are likely to carry over in time.

  • the sensitivity of Annual grassland carbon cycling to the quantity and timing of rainfall
    Global Change Biology, 2008
    Co-Authors: Wendy W Chou, Whendee L Silver, Randall D Jackson, Andrew W Thompson, Barbara Allendiaz
    Abstract:

    Global climate models predict significant changes to the rainfall regimes of the grassland biome, where C cycling is particularly sensitive to the amount and timing of precipitation. We explored the effects of both natural interAnnual rainfall variability and experimental rainfall additions on net C storage and loss in Annual Grasslands. Soil respiration and net primary productivity (NPP) were measured in treatment and control plots over four growing seasons (water years, or WYs) that varied in wet-season length and the quantity of rainfall. In treatment plots, we increased total rainfall by 50% above ambient levels and simulated one early- and one late-season storm. The early- and late-season rain events significantly increased soil respiration for 2‐4 weeks after wetting, while augmentation of wet-season rainfall had no significant effect. InterAnnual variability in precipitation had large and significant effects on C cycling. We observed a significant positive relationship between Annual rainfall and aboveground NPP across the study (P 50.01, r 2 50.69). Changes in the seasonal timing of rainfall significantly affected soil respiration. Abundant rainfall late in the wet season in WY 2004, a year with average total rainfall, led to greater net ecosystem C losses due to a � 50% increase in soil respiration relative to other years. Our results suggest that C cycling in Annual Grasslands will be less sensitive to changes in rainfall quantity and more affected by altered seasonal timing of rainfall, with a longer or later wet season resulting in significant C losses from Annual Grasslands. Abbreviations: WY 5 water year Rh 5 heterotrophic respiration Rs 5 soil respiration Rr 5 root respiration NPP 5 net primary productivity NEP 5 net ecosystem production RC 5 root contribution

Francisco M Azcarate - One of the best experts on this subject based on the ideXlab platform.

  • testing seed size predictions in mediterranean Annual Grasslands
    Seed Science Research, 2010
    Co-Authors: Francisco M Azcarate, Pablo Manzano, Begona Peco
    Abstract:

    On the basis of previous research, we predict that Mediterranean Grasslands should show larger-seeded Annuals in: (1) more-arid Grasslands; (2) more-fertile soils; (3) less-grazed Grasslands; and (4) Grasslands with lower intensities of seed predation by ants. To test these predictions, we set 29 sampling units of 50 m × 50 m in a 1000 km2 grassland area in Central Spain, and characterized them according to the former factors. We then recorded Annual vegetation using ten quadrats of 20 cm × 20 cm in each sampling unit. Seed size at the community level was described using six variables: (1) mean seed mass; (2) standard deviation of seed mass; (3) weighted mean seed mass (by species frequencies); (4) proportion of small-seeded Annuals; (5) proportion of medium-seeded Annuals; and (6) proportion of large-seeded Annuals. Most climate variables (mean Annual temperature, length of the summer drought, water balance and mean Annual precipitation) correlated with seed-size descriptors, showing that large-seeded Annuals increase in warmer and more-arid communities. Mean seed size was modelled as a function of mean Annual temperature and grazing pressure. According to this model, warmer and less-grazed communities tend to show a smaller mean seed size. These results confirm the importance of seed-size descriptors at the community level in Mediterranean Grasslands, and the role of climate and grazing as major drivers in these communities. Conversely, hypotheses about soil fertility and seed predation by ants were not supported by our results.

  • seed size and response to rainfall patterns in Annual Grasslands 16 years of permanent plot data
    Journal of Vegetation Science, 2009
    Co-Authors: Egona Peco, L Rico, Francisco M Azcarate
    Abstract:

    Question: Are seed size and plant size linked to species responses to inter-Annual variations in rainfall and rainfall distribution during the growing season in Annual Grasslands? Location: A 16-year data set on species abundance in permanent plots 15 km north of Madrid in a Quercus ilex subsp. ballota dehesa. Methods: At species level, a GLM was used to analyse the effects of various rainfall indices (total autumn rainfall, early autumn rainfall and spring drought) on species abundance residuals with respect to time and topography. We also assessed the importance of seed size and plant size in the species responses at community level using species as data points. Seed mass and maximum stem length were used as surrogates for seed size and plant size, respectively. Results: Seed mass and plant size may explain some of the fluctuations in the floristic composition of Annual species associated with autumn rainfall patterns. Species that are more abundant in dry autumns have greater seed mass than those species that are more abundant in wet autumns. Early autumn rainfall seems to favour larger plants. Conclusions: Our empirical results support the hypothesis that autumn rainfall patterns affect the relative establishment capacity of small and large seedlings in Annual species.

Begona Peco - One of the best experts on this subject based on the ideXlab platform.

  • testing the role of seed size in Annual legume seedling performance under experimental autumn moisture conditions
    Journal of Vegetation Science, 2012
    Co-Authors: Gabriel Arellano, Begona Peco
    Abstract:

    Question Previous studies show that large-seeded species increase their abundance in Mediterranean Annual Grasslands in growing seasons with dry autumns. One possible explanation is that large-seeded species have larger seedlings, which provide an advantage under drier conditions. We address the following questions: is seed mass correlated with seedling survival in Annual legumes? Is this correlation influenced by the watering regime? Can seedling growth characteristics explain the differential survival of small- and large-seeded species? Location Annual Mediterranean grassland, Central Spain. Methods An experiment was conducted with six grassland legume species of different seed sizes, subjected to six different watering regimes, monitoring survival and morphological variables (shoot and root growth) for 40 d. Results Large seeds provide an advantage for seedling survival, but in extreme drought conditions, seedling survival in small-seeded species equals that of seedlings from large-seeded species. Seedlings from larger seeds are larger than those of small-seeded species, but have a lower root/shoot biomass ratio, leading to greater potential evapotranspiration, which could explain their loss of relative advantage under extreme droughts. Conclusion The hypothesis that seedlings from large-seeded species survive better than small-seeded species under drought conditions was not supported. Germination behaviour seems to be a more plausible explanation for the increased abundance in the field of large-seeded species in growing seasons with dry autumns.

  • testing seed size predictions in mediterranean Annual Grasslands
    Seed Science Research, 2010
    Co-Authors: Francisco M Azcarate, Pablo Manzano, Begona Peco
    Abstract:

    On the basis of previous research, we predict that Mediterranean Grasslands should show larger-seeded Annuals in: (1) more-arid Grasslands; (2) more-fertile soils; (3) less-grazed Grasslands; and (4) Grasslands with lower intensities of seed predation by ants. To test these predictions, we set 29 sampling units of 50 m × 50 m in a 1000 km2 grassland area in Central Spain, and characterized them according to the former factors. We then recorded Annual vegetation using ten quadrats of 20 cm × 20 cm in each sampling unit. Seed size at the community level was described using six variables: (1) mean seed mass; (2) standard deviation of seed mass; (3) weighted mean seed mass (by species frequencies); (4) proportion of small-seeded Annuals; (5) proportion of medium-seeded Annuals; and (6) proportion of large-seeded Annuals. Most climate variables (mean Annual temperature, length of the summer drought, water balance and mean Annual precipitation) correlated with seed-size descriptors, showing that large-seeded Annuals increase in warmer and more-arid communities. Mean seed size was modelled as a function of mean Annual temperature and grazing pressure. According to this model, warmer and less-grazed communities tend to show a smaller mean seed size. These results confirm the importance of seed-size descriptors at the community level in Mediterranean Grasslands, and the role of climate and grazing as major drivers in these communities. Conversely, hypotheses about soil fertility and seed predation by ants were not supported by our results.

Michael G. Barbour - One of the best experts on this subject based on the ideXlab platform.

  • Typology and ecology of Californian serpentine Annual Grasslands
    Journal of Vegetation Science, 2001
    Co-Authors: Maria Pilar Rodríguez-rojo, Daniel Sánchez-mata, Rosario G. Gavilán, Salvador Rivas-martínez, Michael G. Barbour
    Abstract:

    A first classification for serpentine Annual Grasslands distributed throughout northern and central California is pro- posed. This study has followed the Braun-Blanquet phyto- sociological system based on floristical, biogeographical and bioclimatic features of the sampled areas. Numerical analyses of classification and ordination were applied to the floristic releves. Minimum Variance Clustering grouped releves into basic classification units that allowed us to define low-hierar- chical syntaxonomical units (associations) and 'communi- ties'. A Principal Coordinate Analysis was used to extract those ecological parameters related to the axes that separate those classification units from the previous dendrogram. The results showed that differences in species composition was mainly due to a continentality gradient and the shady effect of an overstory vegetation. On the basis of both analyses we propose a first syntaxonomic scheme on ultramafic (mainly serpentine) Annual plant communities of the biogeographical Californian Region that comprises four associations, two subassociations and some provisional communities.

  • syntaxonomical approach for classification of the californian serpentine Annual Grasslands
    Lazaroa, 2001
    Co-Authors: Maria Pilar Rodriguezrojo, Daniel Sanchezmata, Salvador Rivasmartinez, Michael G. Barbour
    Abstract:

    A preliminary syntaxonomical approach for the serpentine Annual Grasslands classification is presented. Our proposals include the phytosociological frame for the syntaxonomy of the Annual plant communities growing on ultramafic substrata and distributed throughout the territories of the Californian biogeographical region. All the formal phytosociological high units newly proposed are justified and legitimated on the basis of previous reports and our own data. These are collected in a new phytosociological class: V ulpio microstachyos-Hesperolinetea micranthi that includes, so far, one new order: Eriogono luteoli-Hesperolinetalia micranthi and four new alliances: Hesperevaco sparsiflorae-Hemizonion congestae , Hesperolinion clevelandii , Hesperolino micranthi-Navarretion filicaulis and Streptanthion polygaloidis .