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Berlin Brandenburg

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  • 1
    Language: English
    In: Science (New York, N.Y.), 04 May 2012, Vol.336(6081), pp.589-92
    Description: Plant diversity generally promotes biomass production, but how the shape of the response curve changes with time remains unclear. This is a critical knowledge gap because the shape of this relationship indicates the extent to which loss of the first few species will influence biomass production. Using two long-term (≥13 years) biodiversity experiments, we show that the effects of diversity on biomass productivity increased and became less saturating over time. Our analyses suggest that effects of diversity-dependent ecosystem feedbacks and interspecific complementarity accumulate over time, causing high-diversity species combinations that appeared functionally redundant during early years to become more functionally unique through time. Consequently, simplification of diverse ecosystems will likely have greater negative impacts on ecosystem functioning than has been suggested by short-term experiments.
    Keywords: Biodiversity ; Ecosystem ; Plants ; Poaceae
    ISSN: 00368075
    E-ISSN: 1095-9203
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  • 2
    Language: English
    In: Trends in Ecology & Evolution, June 2015, Vol.30(6), pp.357-363
    Description: In a review published over two decades ago I asserted that, along soil fertility gradients, plant traits change in ways that reinforce patterns of soil fertility and net primary productivity (NPP). I reevaluate this assertion in light of recent research, focusing on feedbacks to NPP operating through litter decomposition. I conclude that mechanisms emerging since my previous review might weaken these positive feedbacks, such as negative effects of nitrogen on decomposition, while others might strengthen them, such as slower decomposition of roots compared to leaf litter. I further conclude that predictive understanding of plant species effects on nutrient cycling will require developing new frameworks that are broadened beyond litter decomposition to consider the full litter–soil organic matter (SOM) continuum.
    Keywords: Decomposition ; Feedback ; Litter ; Nutrient Cycling ; Species Effects ; Environmental Sciences ; Biology ; Ecology
    ISSN: 0169-5347
    E-ISSN: 1872-8383
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  • 3
    Language: English
    In: Science (New York, N.Y.), 14 September 2018, Vol.361(6407)
    Description: Nie and colleagues suggest a key role for interannual climate variation as an explanation for the temporal dynamics of an unexpected 20-year reversal of biomass responses of C-C grasses to elevated CO However, we had already identified some climate-dependent differences in C and C responses to eCO and shown that these could not fully explain the temporal dynamics we observed.
    Keywords: Carbon Dioxide ; Poaceae
    ISSN: 00368075
    E-ISSN: 1095-9203
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  • 4
    Language: English
    In: Science (New York, N.Y.), 20 April 2018, Vol.360(6386), pp.317-320
    Description: Theory predicts and evidence shows that plant species that use the C photosynthetic pathway (C species) are less responsive to elevated carbon dioxide (CO) than species that use only the C pathway (C species). We document a reversal from this expected C-C contrast. Over the first 12 years of a 20-year free-air CO enrichment experiment with 88 C or C grassland plots, we found that biomass was markedly enhanced at CO relative to ambient CO in C but not C plots, as expected. During the subsequent 8 years, the pattern reversed: Biomass was markedly enhanced at CO relative to ambient CO in C but not C plots. Soil net nitrogen mineralization rates, an index of soil nitrogen supply, exhibited a similar shift: CO first enhanced but later depressed rates in C plots, with the opposite true in C plots, partially explaining the reversal of the CO biomass response. These findings challenge the current C-CCO paradigm and show that even the best-supported short-term drivers of plant response to global change might not predict long-term results.
    Keywords: Carbon Cycle ; Photosynthesis ; Carbon Dioxide -- Metabolism ; Poaceae -- Metabolism
    ISSN: 00368075
    E-ISSN: 1095-9203
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  • 5
    Language: English
    In: Science (New York, N.Y.), 10 August 2018, Vol.361(6402)
    Description: Wolf and Ziska suggest that soil and species attributes can explain an unexpected 20-year reversal of C-C grass responses to elevated CO This is consistent with our original interpretation; however, we disagree with the assertion that such explanations somehow render our results irrelevant for questioning a long-standing paradigm of plant response to CO based on C-C differences in photosynthetic pathway.
    Keywords: Carbon Dioxide ; Poaceae
    ISSN: 00368075
    E-ISSN: 1095-9203
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  • 6
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 16 July 2013, Vol.110(29), pp.11911-6
    Description: Anthropogenic drivers of environmental change often have multiple effects, including changes in biodiversity, species composition, and ecosystem functioning. It remains unknown whether such shifts in biodiversity and species composition may, themselves, be major contributors to the total, long-term impacts of anthropogenic drivers on ecosystem functioning. Moreover, although numerous experiments have shown that random losses of species impact the functioning of ecosystems, human-caused losses of biodiversity are rarely random. Here we use results from long-term grassland field experiments to test for direct effects of chronic nutrient enrichment on ecosystem productivity, and for indirect effects of enrichment on productivity mediated by resultant species losses. We found that ecosystem productivity decreased through time most in plots that lost the most species. Chronic nitrogen addition also led to the nonrandom loss of initially dominant native perennial C4 grasses. This loss of dominant plant species was associated with twice as great a loss of productivity per lost species than occurred with random species loss in a nearby biodiversity experiment. Thus, although chronic nitrogen enrichment initially increased productivity, it also led to loss of plant species, including initially dominant species, which then caused substantial diminishing returns from nitrogen fertilization. In contrast, elevated CO2 did not decrease grassland plant diversity, and it consistently promoted productivity over time. Our results support the hypothesis that the long-term impacts of anthropogenic drivers of environmental change on ecosystem functioning can strongly depend on how such drivers gradually decrease biodiversity and restructure communities.
    Keywords: Biogeochemistry ; Community Ecology ; Biodiversity ; Biomass ; Ecosystem ; Fertilizers ; Nitrogen -- Metabolism ; Poaceae -- Growth & Development
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 7
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 23 April 2013, Vol.110(17), pp.6889-94
    Description: Recent metaanalyses suggest biodiversity loss affects the functioning of ecosystems to a similar extent as other global environmental change agents. However, the abundance and functioning of soil organisms have been hypothesized to be much less responsive to such changes, particularly in plant diversity, than aboveground variables, although tests of this hypothesis are extremely rare. We examined the responses of soil food webs (soil microorganisms, nematodes, microarthropods) to 13-y manipulation of multiple environmental factors that are changing at global scales--specifically plant species richness, atmospheric CO2, and N deposition--in a grassland experiment in Minnesota. Plant diversity was a strong driver of the structure and functioning of soil food webs through several bottom-up (resource control) effects, whereas CO2 and N only had modest effects. We found few interactions between plant diversity and CO2 and N, likely because of weak interactive effects of those factors on resource availability (e.g., root biomass). Plant diversity effects likely were large because high plant diversity promoted the accumulation of soil organic matter in the site's sandy, organic matter-poor soils. Plant diversity effects were not explained by the presence of certain plant functional groups. Our results underline the prime importance of plant diversity loss cascading to soil food webs (density and diversity of soil organisms) and functions. Because the present results suggest prevailing plant diversity effects and few interactions with other global change drivers, protecting plant diversity may be of high priority to maintain the biodiversity and functioning of soils in a changing world.
    Keywords: Biodiversity ; Climate Change ; Food Chain ; Soil ; Poaceae -- Growth & Development
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 8
    In: Ecology, April 2013, Vol.94(4), pp.787-793
    Description: The relationship between plant diversity and productivity in grasslands could depend, partly, on how diversity affects vertical distributions of root biomass in soil; yet, no prior study has evaluated the links among diversity, root depth distributions, and productivity in a long‐term experiment. We used data from a 12‐year experiment to ask how plant species richness and composition influenced both observed and expected root depth distributions of plant communities. Expected root depth distributions were based on the abundance of species in each community and two traits of species that were measured in monocultures: root depth distributions and root‐to‐shoot ratios. The observed proportion of deep‐root biomass increased more than expected with species richness and was positively correlated with aboveground productivity. Indeed, the proportion of deep‐root biomass explained variation in productivity even after accounting for legume presence/abundance and greater nitrogen availability in diverse plots. Diverse plots had root depth distributions that were twice as deep as expected from their species composition and corresponding monoculture traits, partly due to interactions between C grasses and legumes. These results suggest that the productivity of diverse plant communities was partly dependent on belowground plant interactions that caused roots to be distributed more deeply in soil.
    Keywords: Aboveground Biomass ; C 4 Grass ; Complementarity ; Interspecific Interactions ; Legume ; Root Biomass ; Species Richness
    ISSN: 0012-9658
    E-ISSN: 1939-9170
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  • 9
    In: Ecology, April 2010, Vol.91(4), pp.1225-1236
    Description: The importance of litter decomposition to carbon and nutrient cycling has motivated substantial research. Commonly, researchers fit a single‐pool negative exponential model to data to estimate a decomposition rate (). We review recent decomposition research, use data simulations, and analyze real data to show that this practice has several potential pitfalls. Specifically, two common decisions regarding model form (how to model initial mass) and data transformation (log‐transformed vs. untransformed data) can lead to erroneous estimates of . Allowing initial mass to differ from its true, measured value resulted in substantial over‐ or underestimation of . Log‐transforming data to estimate using linear regression led to inaccurate estimates unless errors were lognormally distributed, while nonlinear regression of untransformed data accurately estimated regardless of error structure. Therefore, we recommend fixing initial mass at the measured value and estimating with nonlinear regression (untransformed data) unless errors are demonstrably lognormal. If data are log‐transformed for linear regression, zero values should be treated as missing data; replacing zero values with an arbitrarily small value yielded poor estimates. These recommendations will lead to more accurate estimates and allow cross‐study comparison of values, increasing understanding of this important ecosystem process.
    Keywords: Data Transformation ; Decomposition Rate ; Litterbag ; Model Fitting ; Regression
    ISSN: 0012-9658
    E-ISSN: 1939-9170
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  • 10
    Language: English
    In: 2012, Vol.7(9), p.e45140
    Description: Litter decomposition rate ( k ) is typically estimated from proportional litter mass loss data using models that assume constant, normally distributed errors. However, such data often show non-normal errors with reduced variance near bounds (0 or 1), potentially leading to biased k estimates. We compared the performance of nonlinear regression using the beta distribution, which is well-suited to bounded data and this type of heteroscedasticity, to standard nonlinear regression (normal errors) on simulated and real litter decomposition data. Although the beta model often provided better fits to the simulated data (based on the corrected Akaike Information Criterion, AIC c ), standard nonlinear regression was robust to violation of homoscedasticity and gave equally or more accurate k estimates as nonlinear beta regression. Our simulation results also suggest that k estimates will be most accurate when study length captures mid to late stage decomposition (50–80% mass loss) and the number of measurements through time is ≥5. Regression method and data transformation choices had the smallest impact on k estimates during mid and late stage decomposition. Estimates of k were more variable among methods and generally less accurate during early and end stage decomposition. With real data, neither model was predominately best; in most cases the models were indistinguishable based on AIC c , and gave similar k estimates. However, when decomposition rates were high, normal and beta model k estimates often diverged substantially. Therefore, we recommend a pragmatic approach where both models are compared and the best is selected for a given data set. Alternatively, both models may be used via model averaging to develop weighted parameter estimates. We provide code to perform nonlinear beta regression with freely available software.
    Keywords: Research Article ; Biology ; Computer Science ; Earth Sciences ; Mathematics ; Chemistry ; Computational Biology ; Computer Science ; Mathematics
    E-ISSN: 1932-6203
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