Aggregate Mesquite Litter Chemistry Following Soil-litter Mixing and Decomposition in a Semi-arid Grassland on the Jornada Basin from 2010-2012

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Decomposition models typically under-predict decomposition relative to observed rates in drylands. This discrepancy indicates a significant gap in our mechanistic understanding of carbon and nutrient cycling in these systems. Recent research suggests that certain drivers of decomposition that are often not explicitly incorporated into models (e.g., photodegradation and soil-litter mixing; SLM) may be important in drylands, and their exclusion may, in part, be responsible for model under-predictions. To assess the role of SLM, litterbags were deployed in the Chihuahuan Desert and interrelationships between vegetation structure, SLM, and rates of decomposition were quantified. Vegetation structure was manipulated to simulate losses of grass cover from livestock grazing and shrub encroachment.

We hypothesized that (i) reductions in grass cover would destabilize soils and promote SLM, and (ii) that SLM would enhance microbial abundance and alter microbial community composition in ways that accelerate decomposition. To test our hypotheses, we quantified mass loss, and chemistry of litter incubated on sites with experimental reductions in grass cover (0 to 100% removals) over a 12-month period.  This dataset includes data pertaining to the percent carbon, percent nitrogen, and the carbon to nitrogen ratio. This study is complete.

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Litterbag contents (litter + accumulated soil) were separated using a 1 mm mesh sieve. Litter was then manually dusted using small brushes to remove additional soil from leaflets. The brushed litter was frozen at -80°C for 48 h, lyophilized for 48 h, weighed, and then ground to a fine powder using a ball mill (8000D Mixer/Mill, Spex Certiprep, Metuchen, NJ, USA). Subsamples of litter were combusted at 550°C for 6 h to determine the inorganic matter content (% ash). Mass loss and litter C and N content (elemental analyzer; ECS 4010, Costech Analytical Technologies, Valencia, CA, USA) are expressed on an ash-free basis.  The % ash was also used as a conservative index of soil accumulation that accounts only for soil adhering to litter surfaces after sieving and brushing (see Throop and Archer 2007). A large proportion of soil that infiltrates litterbags covers or mixes with litter, but does not adhere to litter surface. The mass of these ‘bulk’ soils entering or exiting litterbags is responsive to wind and water transport processes and is thus likely highly dynamic relative to that of the soil-litter films that form on litter surfaces. Quantifying the magnitude and dynamics of this ‘bulk’ component of the soil-litter matrix was beyond the scope of this study.

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data entry program validates entries for species code and acceptable range for cover.

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Site Location

JER Pasture 11A Okin exclosures (see Study 228)


Month interval from time of sample installation in field: 0, 1, 6, 12, 24, 30

0   = Apr 2010

1   = May 2010

6   = Oct 2010

12 = Apr 2011

24 = Apr 2012

30 = Oct 2012

This study is complete.

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