Browsing by Subject "elevated CO2"

Now showing 1 - 6 of 6
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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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    The diversity and co-occurrence patterns of N2-fixing communities in a CO2-enriched grassland ecosystem
    (springer, 2016) Tu, Qichao; Zhou, Xishu; He, Zhili; Xue, Kai; Wu, Liyou; Reich, Peter B; Hobbie, Sarah; Zhou, Jizhong
    Diazotrophs are the major organismal group responsible for atmospheric nitrogen (N2) fixation in natural ecosystems. The extensive diversity and structure of N2-fixing communities in grassland ecosystems and their responses to increasing atmospheric CO2 remain to be further explored. Through pyrosequencing of nifH gene amplicons and extraction of nifH genes from shotgun metagenomes, coupled with co-occurrence ecological network analysis approaches, we comprehensively analyzed the diazotrophic community in a grassland ecosystem exposed to elevated CO2 (eCO2) for 12 years. Long-term eCO2 increased the abundance of nifH genes but did not change the overall nifH diversity and diazotrophic community structure. Taxonomic and phylogenetic analysis of amplified nifH sequences suggested a high diversity of nifH genes in the soil ecosystem, the majority belonging to nifH clusters I and II. Co-occurrence ecological network analysis identified different co-occurrence patterns for different groups of diazotrophs, such as Azospirillum/Actinobacteria, Mesorhizobium/Conexibacter, and Bradyrhizobium/Acidobacteria. This indicated a potential attraction of non-N2-fixers by diazotrophs in the soil ecosystem. Interestingly, more complex co-occurrence patterns were found for free-living diazotrophs than commonly known symbiotic diazotrophs, which is consistent with the physical isolation nature of symbiotic diazotrophs from the environment by root nodules. The study provides novel insights into our understanding of the microbial ecology of soil diazotrophs in natural ecosystems.
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    Elevated carbon dioxide is predicted to promote coexistence among competing species in a trait‐based model
    (Wiley, 2015) Ali, Ashehad A; Medlyn, Belinda E; Aubier, Thomas G; Crous, Kristine Y; Reich, Peter B
    Differential species responses to atmospheric CO2 concentration (Ca) could lead to quantitative changes in competition among species and community composition, with flow-on effects for ecosystem function. However, there has been little theoretical analysis of how elevated Ca (eCa) will affect plant competition, or how composition of plant communities might change. Such theoretical analysis is needed for developing testable hypotheses to frame experimental research. Here, we investigated theoretically how plant competition might change under eCa by implementing two alternative competition theories, resource use theory and resource capture theory, in a plant carbon and nitrogen cycling model. The model makes several novel predictions for the impact of eCa on plant community composition. Using resource use theory, the model predicts that eCa is unlikely to change species dominance in competition, but is likely to increase coexistence among species. Using resource capture theory, the model predicts that eCa may increase community evenness. Collectively, both theories suggest that eCa will favor coexistence and hence that species diversity should increase with eCa. Our theoretical analysis leads to a novel hypothesis for the impact of eCa on plant community composition. This hypothesis has potential to help guide the design and interpretation of eCa experiments.
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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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    The phylogenetic composition and structure of soil microbial communities shifts in response to elevated carbon dioxide
    (Nature Publishing Group, 2012) He, Zhili; Piceno, Yvette; Deng, Ye; Xu, Meiying; Lu, Zhenmei; DeSantis, Todd; Andersen, Gary; Hobbie, Sarah E; Reich, Peter B; Zhou1, Jizhong
    One of the major factors associated with global change is the ever-increasing concentration of atmospheric CO2. Although the stimulating effects of elevated CO2 (eCO2) on plant growth and primary productivity have been established, its impacts on the diversity and function of soil microbial communities are poorly understood. In this study, phylogenetic microarrays (PhyloChip) were used to comprehensively survey the richness, composition and structure of soil microbial communities in a grassland experiment subjected to two CO2 conditions (ambient, 368 p.p.m., versus elevated, 560 p.p.m.) for 10 years. The richness based on the detected number of operational taxonomic units (OTUs) significantly decreased under eCO2. PhyloChip detected 2269 OTUs derived from 45 phyla (including two from Archaea), 55 classes, 99 orders, 164 families and 190 subfamilies. Also, the signal intensity of five phyla (Crenarchaeota, Chloroflexi, OP10, OP9/JS1, Verrucomicrobia) significantly decreased at eCO2, and such significant effects of eCO2 on microbial composition were also observed at the class or lower taxonomic levels for most abundant phyla, such as Proteobacteria, Firmicutes, Actinobacteria, Bacteroidetes and Acidobacteria, suggesting a shift in microbial community composition at eCO2. Additionally, statistical analyses showed that the overall taxonomic structure of soil microbial communities was altered at eCO2. Mantel tests indicated that such changes in species richness, composition and structure of soil microbial communities were closely correlated with soil and plant properties. This study provides insights into our understanding of shifts in the richness, composition and structure of soil microbial communities under eCO2 and environmental factors shaping the microbial community structure.
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    Plant diversity, CO2 and N influence inorganic and organic N leaching in grasslands
    (2007) Dijkstra, Feike A; West, Jason B; Hobbie, Sarah E; Reich, Peter B; Trost, Jared
    In nitrogen (N)-limited systems, the potential to sequester carbon depends on the balance between N inputs and losses as well as on how efficiently N is used, yet little is known about responses of these processes to changes in plant species richness, atmospheric CO2 concentration ([CO2]), and N deposition. We examined how plant species richness (1 or 16 species), elevated [CO2] (ambient or 560 ppm), and inorganic N addition (0 or 4 g·m−2·yr−1) affected ecosystem N losses, specifically leaching of dissolved inorganic N (DIN) and organic N (DON) in a grassland field experiment in Minnesota, USA. We observed greater DIN leaching below 60 cm soil depth in the monoculture plots (on average 1.8 and 3.1 g N·m−2·yr−1 for ambient N and N-fertilized plots respectively) than in the 16-species plots (0.2 g N·m−2·yr−1 for both ambient N and N-fertilized plots), particularly when inorganic N was added. Most likely, loss of complementary resource use and reduced biological N demand in the monoculture plots caused the increase in DIN leaching relative to the high-diversity plots. Elevated [CO2] reduced DIN concentrations under conditions when DIN concentrations were high (i.e., in N-fertilized and monoculture plots). Contrary to the results for DIN, DON leaching was greater in the 16-species plots than in the monoculture plots (on average 0.4 g N·m−2·yr−1 in 16-species plots and 0.2 g N·m−2·yr−1 in monoculture plots). In fact, DON dominated N leaching in the 16-species plots (64% of total N leaching as DON), suggesting that, even with high biological demand for N, substantial amounts of N can be lost as DON. We found no significant main effects of elevated [CO2] on DIN or DON leaching; however, elevated [CO2] reduced the positive effect of inorganic N addition on DON leaching, especially during the second year of observation. Our results suggest that plant species richness, elevated [CO2], and N deposition alter DIN loss primarily through changes in biological N demand. DON losses can be as large as DIN loss but are more sensitive to organic matter production and turnover.