Browsing by Subject "global change"

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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.
Data from: Carbon cycling through plant and fungal herbarium specimens tracks the Suess effect over more than a century of environmental change
(2024-02-19) Michaud, Talia J; Hobbie, Erik A; Kennedy, Peter G; micha938@umn.edu; Michaud, Talia J; University of Minnesota Kennedy Lab
Although the anthropogenic decline in atmospheric carbon stable isotope ratios (d13C) over the last 150 years (termed the Suess effect) is well-studied, how different terrestrial trophic levels and modes reflect this decline remains unresolved. To evaluate the Suess effect as an opportunistic tracer of terrestrial forest carbon cycling, this study analyzed the d13C in herbarium specimens collected in Minnesota, USA from 1877-2019. Our results suggest that both broadleaf trees and ectomycorrhizal fungi relied on recent photosynthate to produce leaves and sporocarps, while saprotrophic fungi used carbon fixed from the atmosphere 32-55 years ago for sporocarp construction. The d13C values of saprotrophic fungal collections were also sensitive to the age of their plant C substrate, with sporocarps of twig specialists tracking changes in atmospheric d13C more closely than saprotrophs growing on wood. Collectively, this study indicated that natural history collections can quantitatively track carbon cycling among plants and fungi over time.
Historical plant and fungal nitrogen isotopes and concentrations from Minnesota, USA, 1871–2016
(2023-11-06) Michaud, Talia J; micha938@umn.edu; Michaud, Talia J; University of Minnesota Kennedy Lab
Historical declines in plant tissue nitrogen concentrations and d15N have been interpreted as evidence of declining terrestrial ecosystem nitrogen status. To test whether plant mycorrhizal type influences trajectories of plant nitrogen status, and whether fungi also exhibit declining nitrogen status, we analyzed herbarium collections made in MN, USA, from 1871–2016.
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.
Plant diversity effects on soil microbial functions and enzymes are stronger than warming in a grassland experiment
(Ecological Society of America, 2015) Steinauer, Katja; Tilman, G David; Wragg, Peter Douglas; Cesarz, Simone; Cowles, Jane M; Pritsch, Karin; Reich, Peter B; Weisser, Wolfgang W; Eisenhauer, Nico;
Anthropogenic changes in biodiversity and atmospheric temperature significantly influence ecosystem processes. However, little is known about potential interactive effects of plant diversity and warming on essential ecosystem properties, such as soil microbial functions and element cycling. We studied the effects of orthogonal manipulations of plant diversity (one, four, and 16 species) and warming (ambient, +1.5°C, and +3°C) on soil microbial biomass, respiration, growth after nutrient additions, and activities of extracellular enzymes in 2011 and 2012 in the BAC (biodiversity and climate) perennial grassland experiment site at Cedar Creek, Minnesota, USA. Focal enzymes are involved in essential biogeochemical processes of the carbon, nitrogen, and phosphorus cycles. Soil microbial biomass and some enzyme activities involved in the C and N cycle increased significantly with increasing plant diversity in both years. In addition, 16-species mixtures buffered warming induced reductions in topsoil water content. We found no interactive effects of plant diversity and warming on soil microbial biomass and growth rates. However, the activity of several enzymes (1,4-β-glucosidase, 1,4-β-N-acetylglucosaminidase, phosphatase, peroxidase) depended on interactions between plant diversity and warming with elevated activities of enzymes involved in the C, N, and P cycles at both high plant diversity and high warming levels. Increasing plant diversity consistently decreased microbial biomass-specific enzyme activities and altered soil microbial growth responses to nutrient additions, indicating that plant diversity changed nutrient limitations and/or microbial community composition. In contrast to our expectations, higher plant diversity only buffered temperature effects on soil water content, but not on microbial functions. Temperature effects on some soil enzymes were greatest at high plant diversity. In total, our results suggest that the fundamental temperature ranges of soil microbial communities may be sufficiently broad to buffer their functioning against changes in temperature and that plant diversity may be a dominant control of soil microbial processes in a changing world.
Response of boreal peatland ecosystems to global change: A remote sensing approach
(2017-08) McPartland, Mara
Global climate change is expected to result in anywhere from two to four degrees of warming, with consequences for terrestrial ecosystems. The rate of climate change is disproportionally greater at high latitudes, resulting in landscape-scale effects on the composition, structure, and function of arctic and boreal ecology. Remote sensing offers scientists the ability to track large-scale changes through the detection of biophysical processes occurring in terrestrial ecosystems. In this research, I measured the response of boreal peatland ecosystems to a suite of different climate-related drivers including increased temperature, elevated carbon dioxide levels, and hydrologic change. Working within large-scale ecosystem manipulation experiments, I used passive remote sensing to measure the response of two different types of boreal peatlands, a rich fen and an ombrotrophic bog, to simulated climate change. Chapter 1 describes my research on the use of hyperspectral remote sensing to examine changes in the composition and biodiversity of peatlands in response to long-term experimental manipulation. Chapter 2 details my findings on using simple remote sensing techniques to detect changes in peatland ecosystem productivity in response to warming, elevated carbon dioxide, and hydrologic change. Through this work, I demonstrate that remote sensing can be used to characterize the response of a range of different ecosystem properties to global change.
Species interactions in a changing environment: Elevated CO2 alters the ecological and potential evolutionary consequences of competition
(Evolutionary Ecology, 2010) Lau, Ja; Shaw, R G; Reich, Peter B; Tiffin, P
Question: How will global changes impact the ecological and evolutionary outcomes of competition? Hypothesis: Global changes that alter resource availability, such as rising atmospheric carbon dioxide (CO2) concentrations, will alter the effects of competition on mean fitness and patterns of natural selection. Because species exhibit different growth responses to elevated CO2 and because different traits may aid in competition against different taxa. these ecological and evolutionary effects may depend on the Identity of the competitor Organism: Arabidopsis thaliana grown under intraspecific competition or interspecific competition with the C3 grass Biomus inermis or the C4 grass Andropogon gerardu Field site: BioCON (Biodiversity, CO2, and Nitrogen) experiment at Cedar Creek Ecosystem Science Reserve. Minnesota, USA Methods: Manipulate the presence and type of competition experienced by A thaliana populations growing under ambient or elevated CO2 conditions. Measure the interactive effects of CO2 and competition on mean fitness and on patterns of natural selection Conclusions: Elevated CO2 reduces the effects of competition on mean fitness, alters the relative fitness effects of different competition treatments, and minimizes the strength of competition as a selective agent
Temperature and leaf nitrogen affect performance of plant species at range overlap
(Wiley, 2015) Fisichelli, Nicholas A; Stefanski, Artur; Frelich, Lee E; Reich, Peter B
Plant growth and survival near range limits are likely sensitive to small changes in environmental conditions. Warming temperatures are causing range shifts and thus changes in species composition within range-edge ecotones; however, it is often not clear how temperature alters performance. Through an observational field study, we assessed temperature and nitrogen effects on survival and growth of co-occurring temperate (Acer saccharum) and boreal (Abies balsamea) saplings across their overlapping range limits in the Great Lakes region, USA. Across sampled ranges of soil texture, soil pH, and precipitation, it appears that temperature affects leaf nitrogen for A. saccharum near its northern range limit (R2 = 0.64), whereas there was no significant leaf N ~ temperature relationship for A. balsamea. Higher A. saccharum leaf N at warm sites was associated with increased survival and growth. Abies balsamea survival and growth were best modeled with summer temperature (negative relationship); performance at warm sites depended upon light availability, suggesting the shade-tolerance of this species near its southern range limits may be mediated by temperature. The ranges of these two tree species overlap across millions of hectares, and temperature and temperature-mediated nitrogen likely play important roles in their relative performance.

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