Understanding litter decomposition in drylands: Is litter abrasion an important abiotic factor?
Abstract
Drylands comprise approximately 40% of global land cover and about 20% of global soil organic carbon (C) pool. Changes in dryland ecosystem processes, such as litter decomposition, could greatly influence global C cycling and climate change. Current models underestimate rates of litter decomposition in drylands, and little is known about the role and interactions of abiotic drivers in these systems. Research suggests leaf abrasion may play an important role on litter decomposition in drylands by increasing microbial activity or leaching. The Scrape Site at Jornada LTER was stripped of vegetation in 1991, leaving exposed soil that could serve as a source of sand particles to promote leaf abrasion on mesquite shrubs located downwind. This project examines the role that leaf abrasion, promoted in the field by wind erosion, and induced through laboratory simulations, will play in litter decomposition. We hypothesize that leaf abrasion will increase rates of litter decomposition due to facilitation of microbial colonization. Mesquite leaves were collected from two locations: down-wind from the Scrape Site and 80 meters away representing "field abraded" and "unabraded" treatments, respectively. For a "lab abraded" treatment, abrasion was performed by shaking leaves for 30 seconds with sand particles to simulate microscopic characteristics seen in "field abraded" treatment; this treatment resulted in an average leaf area loss of 3.267 %. Differences in decomposition rates among litter treatments were evaluated in a 16 week laboratory incubation. Litter was incubated at 22°C in airtight glass jars containing 50 g of soil (0.053 g water g-1 soil). Rapid colonization by fungi was apparent across treatments, but lab abraded litter showed the most abundant growth. Consequently, lab abraded litter treatment showed 20% and 30% times more accumulation of CO2 -C than field (P= 0.0008) and unabraded (P< 0.0001) litter treatments during the first 6 days of incubation. These results agree with a significant higher mass loss of lab abraded litter after one week of incubation, 4.6% and 4.8% higher than field abraded (P= 0.0005) and unabraded (P= 0.0004) litter, respectively. Results from litter mass loss showed an exponential decrease in all treatments during the first 4 weeks of incubation, where abraded treatments had higher decomposition decay constants than the unabraded leaves: 0.187, 0.170, and 0.164 for the lab abraded, field abraded and unabraded treatments, respectively. Interestingly, differences in the process of litter decomposition among treatments were pronounced during the first weeks of incubation and disappeared by the end of the incubation period where a similar rate of litter mineralization and a ca. 50% mass loss was reported by all litter treatments. Our results suggest that abrasion of leaf litter enhances early stages of decomposition perhaps by creating an exposed outer tissue suitable for microbial colonization. This is reflected by a higher initial accumulation of CO2-C and losses of litter mass in lab abraded litter. Influence of abrasion in litter decomposition was more evident on lab abraded leaves perhaps due to the faster and easier microbial colonization of recently abraded surfaces. Work is in progress to evaluate the amount of C transferred to the soil and the implications of our results on longer-term decomposition.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.B41A0257P
- Keywords:
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- 0400 BIOGEOSCIENCES;
- 0414 BIOGEOSCIENCES / Biogeochemical cycles;
- processes;
- and modeling;
- 0428 BIOGEOSCIENCES / Carbon cycling