Keiser Lab

soil and ecosystem ecology

Research

The lab’s research fits into four main themes.

1) Plant-microbe Interactions

??????????It is unresolved as to when and how plant communities shape soil microbial community function and how rapidly microbial communities respond to new resource inputs. We are broadly interested in how soil microbial community function, examined as carbon and nitrogen fluxes from decomposing leaf litters, respond to new above-ground inputs. Our research demonstrates that soil microbial communities from different resource histories (e.g. grassland vs. forest) are initially functionally dissimilar. Across time, these communities can dramatically increase function on a new resource while continuing to hold functional differences. In addition, the communities demonstrate a marked loss in function when placed in a new resource environment. These results reinforce the idea that resource history plays a significant role in structuring microbial community function. This research advances our understanding of microbial community function, and how function will change as resource inputs and climate conditions shift. Importantly, the results challenge the dominant decomposition paradigm (climate > litter quality > microbes). Understanding decomposer community function and its role within the larger decomposition paradigm is critical in creating realistic C and N budgets at local and regional scales. Changes in these budgets are also expected to impact essential ecosystem processes such as nutrient cycling in such a way that future terrestrial and aquatic community structure and function are altered.

 

2) Coupled Carbon-Nitrogen Dynamics

Nitrogen is an essential and limiting nutrient. Its availability for plant use is dependent upon supply as mediated through microbial transformations. We are interested in how changes to N supply, ranging from deposition to foliar inputs, alter microbial N transformations. From a watershed management approach, we conducted a field-based project examining landscape-level variation in net potential nitrification and mineralization. This project showed that the coupling of net N mineralization and nitrification was dependent upon the amount of soil carbon. We continue to explore coupled C & N dynamics though:

  1. A diverse set of ecosystems across the LTER Network
  2. Agricultural soils and the impacts of sustainable management practices on soil C – N storage and availability.

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3) Home-field advantage

A term borrowed from the sports literature, home-field advantage (HFA) within ecology indicates that a local population has greater fitness in its “home” habitat as opposed to any other environment. There was first evidence for HFA in ecosystem ecology when Hunt and colleagues (Ecology 1988) noticed that leaf litter decomposed faster than expected in its ecosystem of origin. Faster decomposition at home than away may be explained by the overall ability of a soil community to decompose litter as opposed to simply HFA. While HFA arises through a matching of a microbial community with its home environment, differences in ability may arise through mechanisms such as functional breadth or dispersal limitation. We developed theory to quantify microbial community function (ability) as well as HFA (see Keiser et al. J. of Ecology 2014), which we call the decomposer ability regression test (DART). The lab continues to explore the underlying drivers and occurrence of HFA across space and time. We are particularly interested in what factors contribute to the ability of microbial decomposers and how ability differences contribute to the biogeography and historical legacies of these important soil microorganisms.

 

 4) Invasive Species and Ecosystem Dynamics

Invasive plant species also interest me because as invaders, they inherently cause a shift in composition within the community. Once established, they are known to alter soil nutrient dynamics, but mechanistic pathways for these changes are still unknown. We have worked specifically with Microstegium vimineum, Japanese stiltgrass, which is a shade-tolerant, C-4 herb that has successfully invaded eastern forests. We have explored how stiltgrass alters nitrogen dynamics and plant-soil feedbacks as well as its dispersal. We continue to explore the impacts of invasive species on biogeochemical processes.

 

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