Browsing by Subject "grasslands"

Now showing 1 - 5 of 5
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    Biodiversity increases the resistance of ecosystem productivity to climate extremes
    (Nature Publishing Group, 2015) Isbell, Forest; Craven, Dylan; Connolly, John; Loreau, Michel; Schmid, Bernhard; Beierkuhnlein, Carl; Bezemer, T. Martijn; Bonin, Catherine; Bruelheide, Helge; de Luca, Enrica; Ebeling, Anne; Griffin, John N; Guo, Qinfeng; Hautier, Yann; Hector, Andy; Jentsch, Anke; Kreyling, Jürgen; Lanta, Vojtěch; Manning, Pete; Meyer, Sebastian T; Mori, Akira S.; Naeem, Shahid; Niklaus, Pascal A; Polley, H. Wayne; Reich, Peter B; Roscher, Christiane; Seabloom, Eric W; Smith, Melinda D; Thakur, Madhav P; Tilman, David; Tracy, Benjamin F; van der Putten, Wim H; van Ruijven, Jasper; Weigelt, Alexandra; Weisser, Wolfgang W; Wilsey, Brian; Eisenhauer, Nico
    It remains unclear whether biodiversity buffers ecosystems against climate extremes, which are becoming increasingly frequent worldwide. Early results suggested that the ecosystem productivity of diverse grassland plant communities was more resistant, changing less during drought, and more resilient, recovering more quickly after drought, than that of depauperate communities. However, subsequent experimental tests produced mixed results. Here we use data from 46 experiments that manipulated grassland plant diversity to test whether biodiversity provides resistance during and resilience after climate events. We show that biodiversity increased ecosystem resistance for a broad range of climate events, including wet or dry, moderate or extreme, and brief or prolonged events. Across all studies and climate events, the productivity of low-diversity communities with one or two species changed by approximately 50% during climate events, whereas that of high-diversity communities with 16-32 species was more resistant, changing by only approximately 25%. By a year after each climate event, ecosystem productivity had often fully recovered, or overshot, normal levels of productivity in both high- and low-diversity communities, leading to no detectable dependence of ecosystem resilience on biodiversity. Our results suggest that biodiversity mainly stabilizes ecosystem productivity, and productivity-dependent ecosystem services, by increasing resistance to climate events. Anthropogenic environmental changes that drive biodiversity loss thus seem likely to decrease ecosystem stability, and restoration of biodiversity to increase it, mainly by changing the resistance of ecosystem productivity to climate events.
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    CO2, nitrogen, and diversity differentially affect seed production of prairie plants
    (2009) Hillerislambers, J; Harpole, W S; Schnitzer, S; Tilman, D; Reich, Peter B
    Plant species composition and diversity is often influenced by early life history stages; thus, global change could dramatically affect plant community structure by altering seed production. Unfortunately, plant reproductive responses to global change are rarely studied in field settings, making it difficult to assess this possibility. To address this issue, we quantified the effects of elevated CO2, nitrogen deposition, and declining diversity on inflorescence production and inflorescence mass of 11 perennial grassland species in central Minnesota, USA. We analyzed these data to ask whether (1) global change differentially affects seed production of co-occurring species; (2) seed production responses to global change are similar for species within the same functional group (defined by ecophysiology and growth form); and (3) seed production responses to global change match productivity responses. We found that, on average, allocation to seed production decreased under elevated CO2, although individual species responses were rarely significant due to low power (CO2 treatment df = 2). The effects of nitrogen deposition on seed production were similar within functional groups: C4 grasses tended to increase while C3 grasses tended to decrease allocation to seed production. Responses to nitrogen deposition were negatively correlated to productivity responses, suggesting a trade-off. Allocation to seed production of some species responded to a diversity gradient, but responses were uncorrelated to productivity responses and not similar within functional groups. Presumably, species richness has complex effects on the biotic and abiotic variables that influence seed production. In total, our results suggest that seed production of co-occurring species will be altered by global change, which may affect plant communities in unpredictable ways. Although functional groups could be used to generalize seed production responses to nitrogen deposition in Minnesota prairies, we caution against relying on them for predictive purposes without a mechanistic understanding of how resource availability and biotic interactions affect seed production.
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    Impacts of global changes on leaf-level physiology of plant functional groups and ecosystem carbon storage
    (2020-08) Pastore, Melissa
    A key uncertainty in ecology is how concurrent global change factors will interact to affect terrestrial ecosystems. Humans have altered Earth’s carbon dioxide (CO2) concentrations, climate, nutrient levels, and biodiversity, all of which affect plant communities and ecosystem function. Yet, few multi-factor field studies exist to examine interactive effects of global changes on plants and ecosystems. I characterized the physiological responses of perennial grassland species from four plant functional groups (C3 grasses, C4 grasses, nitrogen-fixing leguminous forbs, and non-leguminous forbs) to single and interactive global changes including elevated carbon dioxide, increased soil nitrogen supply, reduced rainfall, and climate warming. I also determined how elevated CO2, increased soil nitrogen supply, and planted species richness affected total ecosystem carbon (C) storage over 19 years. These studies took place in the open-air, global change grassland ecosystem experiment, BioCON (Biodiversity x CO2 x Nitrogen), located at the Cedar Creek Ecosystem Science Reserve in Minnesota, USA. I present evidence that (1) the ability of plants to capture additional C as atmospheric CO2 rises via photosynthesis may be more limited than traditionally believed; (2) substantial, sustained declines in stomatal conductance and increases in water-use efficiency under elevated CO2 occur widely among grassland species; (3) global change factors interact in complex ways to affect photosynthesis, and how factors interact varies among grassland species; and (4) declines in biodiversity may influence ecosystem C storage more than a 50% increase in CO2 or high rates of nitrogen deposition in perennial grassland systems. These findings show that simple predictions of plant physiological responses to global changes based on theoretical expectations of isolated effects and on functional classifications of species are not sufficient – global changes and other environmental factors interact in complex ways to impact responses of species. These results also highlight the importance of biodiversity in promoting ecosystem function and call into question whether elevated CO2 will increase the C sink in grassland ecosystems and help to slow climate change.
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    Insecticide drift and impacts on arthropod prey resources of birds in public grasslands in Minnesota
    (2021-02) Goebel, Katelin
    Increasing evidence suggests that exposure to pesticides may be a considerable threat to grassland wildlife in agricultural landscapes. In Minnesota, many remaining grasslands are fragmented and surrounded by row crops, including soybeans that are routinely treated with foliar insecticides to control soybean aphids. These insecticides have been shown to be highly toxic to non-target organisms including birds and pollinators in laboratory settings; however, little information exists regarding the impact of spray drift on free-ranging wildlife. My objectives were to evaluate direct and indirect effects of soybean aphid insecticide applications on grassland birds and their insect food resources in the agricultural region of Minnesota. My treatment study sites were comprised of public grasslands bordering privately-owned soybean fields treated with foliar insecticides and non-treated control sites, and I collected samples during the summers of 2017 and 2018. I quantified chemical deposition to assess the extent of insecticide drift into public grasslands and surveyed the insect community pre- and post-application of insecticides to measure changes in abundance, biomass, and richness of insect food for grassland birds. I detected insecticides, primarily chlorpyrifos, in grasslands up to 400 m from field edges regardless of whether adjacent fields were sprayed with insecticides, and deposition was greatest within 25 m of field edges. I measured chlorpyrifos residues that were above the contact LD50 for honey bees up to 25 m from field edges in grasslands. The masses of chlorpyrifos that birds could consume in a day (if food items contained chlorpyrifos residues equivalent to those in my arthropod samples) were below the acute oral LD50 values for several grassland bird species. I used linear mixed models in a hierarchical selection approach to assess the importance of distance from field edge, spray method (plane or ground sprayer), and sampler height (mid-canopy or ground) in explaining insecticide deposition in grasslands. The best-supported model of deposition on passive sampling devices included an inverse association of distance from the field edge with deposition and positive association of samplers being placed at the mid-canopy level compared to ground level. Canopy cover of live vegetation had an inverse association with deposition. The best-supported model of insecticide deposition on arthropods included effects of air temperature and maximum height of vegetation. Short-term reductions in total arthropod abundance, bird prey abundance, and Coleopteran family richness occurred in grasslands bordered by fields sprayed with foliar insecticides. The total abundance of arthropods in grasslands bordering sprayed soybean fields was lower 3–5 days after insecticide applications. The abundance of arthropods important in grassland bird diets (specifically, Araneaens, Coleopterans, Orthopterans, and Lepidopteran larvae) was also lower after nearby spraying, with lower abundance measured in treatments sites 19–21 days post-spraying. Coleopteran family richness at treatment sites was lower than control sites 3–5 days after insecticide applications. Measures of total consumable dry biomass, bird prey biomass, family richness of Araneaens, family richness of Hemipterans, and family richness of Orthopterans were not different between treatment and control sites post-spraying. My findings suggest that spray drift from soybean aphid insecticides is occurring in grasslands in Minnesota and may be impacting food resources for grassland birds and other insectivorous wildlife. My results can inform land acquisition and management decisions to reduce impacts of insecticide spray drift on grassland wildlife in agricultural landscapes.
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    Species richness, but not phylogenetic diversity, influences community biomass production and temporal stability in a re-examination of 16 grassland biodiversity studies
    (Wiley, 2015) Venail, Patrick; Gross, Kevin; Oakley, Todd H; Narwani, Anita; Allan, Eric; Flombaum, Pedro; Isbell, Forest; Joshi, Jasmin; Reich, Peter B; Tilman, David; van Ruijven, Jasper; Cardinale, Bradley J
    Hundreds of experiments have now manipulated species richness (SR) of various groups of organisms and examined how this aspect of biological diversity influences ecosystem functioning. Ecologists have recently expanded this field to look at whether phylogenetic diversity (PD) among species, often quantified as the sum of branch lengths on a molecular phylogeny leading to all species in a community, also predicts ecological function. Some have hypothesized that phylogenetic divergence should be a superior predictor of ecological function than SR because evolutionary relatedness represents the degree of ecological and functional differentiation among species. But studies to date have provided mixed support for this hypothesis. Here, we reanalyse data from 16 experiments that have manipulated plant SR in grassland ecosystems and examined the impact on above-ground biomass production over multiple time points. Using a new molecular phylogeny of the plant species used in these experiments, we quantified how the PD of plants impacts average community biomass production as well as the stability of community biomass production through time. Using four complementary analyses, we show that, after statistically controlling for variation in SR, PD (the sum of branches in a molecular phylogenetic tree connecting all species in a community) is neither related to mean community biomass nor to the temporal stability of biomass. These results run counter to past claims. However, after controlling for SR, PD was positively related to variation in community biomass over time due to an increase in the variances of individual species, but this relationship was not strong enough to influence community stability. In contrast to the non-significant relationships between PD, biomass and stability, our analyses show that SR per se tends to increase the mean biomass production of plant communities, after controlling for PD. The relationship between SR and temporal variation in community biomass was either positive, non-significant or negative depending on which analysis was used. However, the increases in community biomass with SR, independently of PD, always led to increased stability. These results suggest that PD is no better as a predictor of ecosystem functioning than SR. Synthesis. Our study on grasslands offers a cautionary tale when trying to relate PD to ecosystem functioning suggesting that there may be ecologically important trait and functional variation among species that is not explained by phylogenetic relatedness. Our results fail to support the hypothesis that the conservation of evolutionarily distinct species would be more effective than the conservation of SR as a way to maintain productive and stable communities under changing environmental conditions.