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New Mexico State University (2013)

Exploring the role soil-litter mixing on decomposition in dry-land ecosystems

Hewins, Daniel B

Titre : Exploring the role soil-litter mixing on decomposition in dry-land ecosystems

Auteur : Hewins, Daniel B

Université de soutenance : New Mexico State University

Grade : Doctor of Philosophy (PhD) 2013

Résumé
Leaf litter decomposition is a principle driver of carbon (C) and nutrient cycling globally. The current generation of predictive ecosystem models, which are accurate in mesic ecosystems, perpetually under predict rates of decomposition in dryland ecosystems. Subsequently, this limitation in our understanding of dryland decomposition has strong consequences for our ability to model biogeochemical cycles at local and global scales, because drylands cover >40% of the terrestrial surface of Earth. Recent investigations have sought to identify and test the role of overlooked drivers of decomposition such as soil-litter mixing (SLM) and photodegradation by solar radiation that may improve our understanding of decomposition in drylands. This dissertation presents results and interpretation of three experiments that aimed to investigate the ecology of SLM in shrub encroached drylands : 1. Does SLM accelerate decomposition in systems where grasses have been reduced to simulate the effects of shrub encroachment ? 2. Do coppice dune morphological characteristics (i.e., size and distribution), which control the redistribution of sediments in drylands, control SLM and subsequent decomposition ? 3. What are the abiotic and biotic consequences of SLM ? And how do these factors interact ? My results suggest that SLM is a process that occurs across many Chihuahuan Desert vegetation communities, that SLM and decomposition are strongly controlled by climate conditions namely episodic monsoon rains. I found strong interactions between the abiotic and biotic aspects of SLM in the development of soil microbial films and aggregates. These structures appear to be strongly related to soil-litter biological processes that occur as C and nutrients are converted during decomposition.

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