Diverse nitrogen fixation strategies and their ecosystem effects
Nitrogen fixing plants, and their associated bacteria, play a pivotal role in ecosystem functioning as the main source of nitrogen coming into ecosystems. While we know very little about how the interactions between plant and bacteria are regulated, the degree of nitrogen fixation regulation can determine the balance between the positive (carbon storage) and negative (greenhouse gas emissions due to nitrogen saturation) ecosystem effects of fixation. Along with Duncan Menge (Columbia), Jen Funk (Chapman), and Steve Perakis (USGS), we recently received a grant from the NSF to examine how nitrogen fixation is regulated along a gradient of nitrogen availability. Using a combination of field, greenhouse, and modeling experiments, we will be measuring nitrogen fixation rates and determine fixation strategies from the tropics to temperate regions. In previous work, we found that co-occurring legumes display a wide range of previously undescribed strategies to regulate nitrogen fixation, which could lead to divergent impacts on community and ecosystem processes (Menge, Wolf, and Funk 2015 Nature Plants).
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Effects of ant-plant interactions on resource availability, distribution, and heterogeneity
Many ant-plant mutualisms worldwide involve multiple species of ants, though the interactions between these ant species and their host plants can be highly varied. This project focuses on a multi-species ant-Acacia mutualism in the Kenyan savanna to examine nutrient exchange in plant-animal interactions and how these interactions affect nutrient dynamics at broad scales. Using a variety of experimental techniques including ant removal and enriched-15N isotope tracer studies, I have found that different species of mutualistic ants have divergent effects on their host trees, including leaf traits and resource use, leading to coherent suites of differences in trees inhabited by different ant species.
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Effects of realistic biodiversity loss on ecosystem functioning in serpentine grasslands
What happens when ecosystems lose species? How does the order in which species are lost influence how the remaining species interact with each other? This project addresses the effects of realistic species loss on ecosystem properties in California’s serpentine grasslands, and the mechanistic links between plant communities, ecosystem functioning, and interacting drivers of ecosystem change. We are finding that the effects of realistic diversity loss are generally larger than randomized diversity loss (Selmants, Zavaleta and Wolf 2014, Ecology), though these effects are influenced by environmental context (Wolf et al., in review). Our work on this system continues with analyses of diversity effects on belowground processes, multifunctionality, and flowering phenology (Wolf and Zavaleta 2015, Ecology).
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Plant-mediated effects of rising atmospheric CO2
Do plants mediate the effects of elevated atmospheric CO2 on belowground microbial processes? In collaboration with Pat Megonigal at the Smithsonian Environmental Research Center, we sought to assess the effects of changing atmospheric conditions on the persistence and functioning of wetland systems, which provide extremely important carbon sinks worldwide. Using natural-abundance isotope methods, we identified a positive feedback between higher soil oxygenation under elevated CO2 and rates of soil organic matter decomposition (Wolf et al. 2007, Global Change Biology). This increased decomposition rate may unlock other soil nutrients (Keller, Wolf et al. 2009, Biogeochemistry), a process that helps explain why progressive nitrogen limitation does not always dampen the CO2-fertilization effect in long-term CO2 experiments (Langley, McKinley, Wolf, et al. 2009, Soil Biology and Biochemistry). Additionally, this work suggests that coastal wetlands may be at greater risk from rising sea levels than otherwise predicted, as increased soil decomposition could lead to loss of wetland surface elevation.
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