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  1. Plants are subject to tradeoffs among growth strategies such that adaptations for optimal growth in one condition can preclude optimal growth in another. Thus, we predicted that a plant species that responds positively to one global change treatment would be less likely than average to respond positively to another treatment, particularly for pairs of treatments that favor distinct traits. We examined plant species abundances in 39 global change experiments manipulating two or more of the following: CO2, nitrogen, phosphorus, water, temperature, or disturbance. Overall, the directional response of a species to one treatment was 13% more likely than expected to oppose its response to a another single-factor treatment. This tendency was detectable across the global dataset but held little predictive power for individual treatment combinations or within individual experiments. While tradeoffs in the ability to respond to different global change treatments exert discernible global effects, other forces obscure their influence in local communities. 
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  2. Abstract

    Restoration in this era of climate change comes with a new challenge: anticipating how best to restore populations to persist under future climate conditions. Specifically, it remains unknown whether locally adapted or warm‐adapted seeds best promote native plant community restoration in the warmer conditions predicted in the future and whether local or warm‐adapted soil microbial communities could mitigate plant responses to warming. This may be especially relevant for biomes spanning large climatic gradients, such as the North American tallgrass prairie. Here, we used a short‐term mesocosm experiment to evaluate how seed provenances (Local Northern region, Non‐local Northern region, Non‐local Southern region) of 10 native tallgrass prairie plants (four forbs, two legumes, and four grasses) responded to warmer conditions predicted in the future and how soil microbial communities from those three regions influenced these responses. Warming and seed provenance affected plant community composition and warming decreased plant diversity for all three seed provenances. Plant species varied in their individual responses to warming, and across species, we detected no consistent differences among the three provenances in terms of biomass response to warming and few strong effects of soil provenance. Our work provides evidence that warming, in part, may reduce plant diversity and affect restored prairie composition. Because the southern provenance did not consistently outperform others under warming and we found little support for the “local is best” paradigm currently dominating restoration practice, identifying appropriate seed provenances to promote restoration success both now and in future warmer environments may be challenging. Due to the idiosyncratic responses across species, we recommend that land managers compare seeds from different regions for each species to determine which seed provenance performs best under warming and in restoration for tallgrass prairies.

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  3. Abstract

    The species pool concept has advanced our understanding for how biodiversity is coupled at local and regional scales. However, it remains unclear how species pool size, the number of species available to disperse to a site, influences community assembly across spatial scales. We provide one of the first studies that assesses diversity across scales after experimentally assembling grassland communities from species pools of different sizes. We show that species pool size causes scale‐dependent effects on diversity in grasslands undergoing restoration by altering the shape of the species–area relationship (SAR). Specifically, larger species pools increased the slope of the SAR, but not the intercept, suggesting that dispersal from a larger pool causes species to be more spatially aggregated. This increased aggregation appears to be caused by sampling effects due to fewer individuals arriving per species, rather than stronger species sorting across variation in soil moisture. These scale‐dependent effects suggest that studies evaluating species pools at a single, small scale may underestimate their effects, thereby contributing to uncertainty about the importance of regional processes for community assembly and their consequences for ecological restoration.

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  4. Forbs comprise most of the plant diversity in North American tallgrass prairie and provide vital ecosystem services, but their abundance in prairie restorations is highly variable. Restoration practitioners typically sow C4grasses in high abundances because they are inexpensive, provide fuel for prescribed fires, can dominate reference sites, and suppress weeds that suppress sown forbs. However, C4grasses can also suppress sown forbs, calling this practice into question. We evaluated how C4grasses influence the abundance and diversity of sown forbs in 78 restored prairies across Illinois, Indiana, and Michigan. We found that the direct negative effects of C4grasses on sown forbs outweighed indirect positive effects that occurred as C4grasses suppressed nonsown species, which in turn suppressed sown forbs. This pattern was especially strong for the C4grass big bluestem (Andropogon gerardii). Therefore, strategies to promote big bluestem and other C4grasses would not promote sown forbs. Although C4grass cover was not strongly related to two hypothesized drivers (time since fire or site age), seeding density of C4grasses increased their cover. Sown forb cover also increased with forb seeding density, increased indirectly with fire (through its negative effect on nonsown species), and decreased indirectly with soil water‐holding capacity (through its positive effect on nonsown species). These results highlight the complex interplay of species groups during grassland restoration and show how managers can promote sown forbs in restored prairies: increasing forb seeding density and reducing time since fire and the abundance of C4grasses and weeds.

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  5. Abstract

    There is strong evidence for a positive relationship between biodiversity and ecosystem functioning at local spatial scales. However, how different aspects of biodiversity relate to multiple ecosystem functions (multifunctionality) across heterogeneous landscapes, and how the magnitude of biodiversity, dominant species, and environmental effects on functioning compare, remain poorly understood. We compared relationships between plant phylogenetic, functional, and taxonomic diversity and ecosystem multifunctionality across 29 restored grasslands. Functional diversity was positively associated with multifunctionality, more strongly than other diversity measures; however, landscape composition explained nearly four times more variation in multifunctionality than did functional diversity, with plots within human‐modified landscapes supporting lower multifunctionality. Individual functions were typically more strongly correlated with environmental variables than with diversity. We also found that abundance of the dominant species,Andropogon gerardii, was positively correlated with multifunctionality. Plant diversity, dominant species, and underlying environmental conditions underpin ecosystem multifunctionality in grasslands, but how biodiversity is measured matters for the strength and direction of biodiversity–ecosystem function relationships. Finally, in natural systems environmental variation unrelated to local biodiversity is important for determining ecosystem functioning.

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  6. Summary

    Mutually beneficial resource exchange is fundamental to global biogeochemical cycles and plant and animal nutrition. However, there is inherent potential conflict in mutualisms, as each organism benefits more when the exchange ratio (‘price’) minimizes its own costs and maximizes its benefits. Understanding the bargaining power that each partner has in these interactions is key to our ability to predict the exchange ratio and therefore the functionality of the cell, organism, community and ecosystem.

    We tested whether partners have symmetrical (‘fair’) or asymmetrical (‘unfair’) bargaining power in a legume–rhizobia nitrogen‐fixing symbiosis using measurements of carbon and nitrogen dynamics in a mathematical modeling framework derived from economic theory.

    A model of symmetric bargaining power was not consistent with our data. Instead, our data indicate that the growth benefit to the plant (Medicago truncatula) has greater weight in determining trade dynamics than the benefit to the bacteria. Quantitative estimates of the relative power of the plant revealed that the plant's influence rises as soil nitrogen availability decreases and trade benefits to both partners increase.

    Our finding thatM. truncatulalegumes have more bargaining power than their rhizobial partner at lower nitrogen availabilities highlights the importance of context‐dependence for the evolution of mutualism with increasing nutrient deposition.

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