|Barnes, Paul -|
|Throop, Heather -|
|Hewins, Daniel -|
|Abbene, Michael -|
|Archer, Steven -|
Submitted to: Ecosystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 19, 2011
Publication Date: December 20, 2011
Citation: Barnes, P.W., Throop, H.L., Hewins, D.B., Abbene, M.L., Archer, S.R. 2011. Soil coverage reduce photodegradation and promotes the development of soil-microbial films on dryland leaf litter. Ecosystems. 15:311-321. Interpretive Summary: It is important to understand how plant organic material (such as leaves) breaks down in the environment in order to predict nutrient cycling and to understand how the environment will be affected by disturbances and climate change. In drylands, this decomposition is controlled both by sunlight (UV photodegredation) and by mixing with soil. This study found that decomposition is at first slow, resulting only from UV photodegredation, but then speeds up greatly when the organic material mixes with soil. When the material is completely buried, the decomposition rate slows down again. Both UV photodegredation and the degree of soil cover must be known in order to predict decomposition rates accurately.
Technical Abstract: Litter decomposition is a central focus of ecosystem science because of its importance to biogeochemical pools and cycling, but predicting dryland decomposition dynamics is problematic. Some studies indicate photodegradation by ultraviolet (UV) radiation can be a significant driver of dryland decomposition, whereas others suggest soil–litter mixing controls decomposition. To test the influence of soil coverage on UV photodegradation of litter, we conducted a controlled environment experiment with shrub (Prosopis velutina) leaf litter experiencing two UV levels and three levels of coverage with dry sterile soil. Under these conditions, decomposition over 224 days was enhanced by UV, but increasing soil coverage strongly and linearly diminished these effects. In a complementary study, we placed P. glandulosa leaf litter in different habitats in the field and quantified litter surface coverage by soil films. After 180 days, nearly half of the surface area of litter placed under shrub canopies was covered by a tightly adhering film composed of soil particles and fungal hyphae; coverage was less in grassy zones between shrubs. We propose a conceptual model for the shifting importance of photodegradation and microbial decomposition over time, and conclude that (1) soil deposition can ameliorate the direct effects of UV photodegradation in drylands and (2) predictions of C losses based solely on UV effects will overestimate the importance of this process in the C cycle. An improved understanding of how development of the soil–litter matrix mediates the shift from abiotic (photodegradation) to biotic (microbial) drivers is necessary to predict how ongoing changes in land cover and climate will influence biogeochemistry in globally extensive drylands.