LTER Core Area: Organic Matter
Mesquite litter mass loss from decomposition associated with soil-litter mixing.
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. I hypothesized that reductions in grass cover would promote SLM and accelerate mass loss by improving conditions for microbial decomposition.
For more see: Hewins, D. B., S. R. Archer, G. S. Okin, R. L. McCulley, and H. L. Throop. 2013. Soil-litter mixing accelerates decomposition in a Chihuahuan Desert grassland. Ecosystems 16:183-195
The effect of vegetation structure on soil-litter mixing (SLM) and decomposition was explicitly tested in a litterbag experiment on a Chihuahuan Desert grassland site where vegetation cover was manipulated to simulate the progressive loss of grass cover accompanying livestock grazing and woody plant encroachment. We hypothesized that (i) reductions in grass cover would destabilize soi
The effect of vegetation structure on soil-litter mixing (SLM) and decomposition was explicitly tested in a litterbag experiment on a Chihuahuan Desert grassland site where vegetation cover was manipulated to simulate the progressive loss of grass cover accompanying livestock grazing and woody plant 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 is of the percent carbon, percent nitrogen, and the carbon to nitrogen ratio.
[John Anderson added the following from info provided by Justin Van Zee and edited by Michelle Buonopane.] Overview: In semiarid ecosystems the diversity of plant functional types ( grasses, shrubs, succulents, and so on) and of species may interact with the severe stresses imposed by the desert environment to influence ecosystem processes.
Erosion and transport of surface sediment by wind and water is one process that may be affected by the physical structure of the plant community. The Jornada plant diversity experiment, in which the diversity and structure of the plant community have been manipulated in large (25 m x 25 m) plots, offers the opportunity to examine the relative importance of vegetation characteristics and landscape position in determining rates of sediment movement within the plots. Soil erosion is also an important indicator of relative disturbance effects of the treatment manipulations. Each of the 48 plots of the plant diversity experiment contains 5 pans or trays on the downslope side; these accumulate sediments and plant litter that are moving within the plots (carried by wind or by water). Data have been collected on the amount of sediment accumulated in the pans during rainy and during dry seasons, with material sorted and weighed as fine (< 2 mm diameter) or coarse > 2 mm) mineral sediment, plant litter, or rabbit/jackrabbit pellets. Previous statistical analyses found that the mass of material collected per plot is explained only poorly by the treatment (plant community manipulation) of the plot and by block (a rough indication of location on the slope). Objectives: We will test the relative significance of the following variables in explaining plot-level accumulations of sediment and litter: treatment, block, position on slope (the row, from 1 (top of slope) to 10 (bottom), in which the plot is located), the treatment of the plot immediately upslope from the plot, and indices of plant cover and volume (total and by functional group) from the plot-level sampling of vegetation (using fall 1997 data). In addition, we will test the significance of the following variables in explaining the accumulation of sediment and litter in individual pans within a plot: all variables listed above for the plot, plus indices of the vegetative cover and volume located immediately upslope of the pan (weighted for distance from the pan itself).
Soil mineralization was examined on the control and fertilized treatment transects in association with the vegetation biomass study. Data set contains soil moisture correction factor, sample weight, total inorganic nitrogen (NO3+NO2-N), and nitrogen in ammonium (NH4-N) for Week F (field) of nitrogen mineralization potentials.
Soil mineralization was examined on the control and fertilized
treatment transects in association with the vegetation biomass
study. Data set contains soil moisture correction factor, sample
weight, total inorganic nitrogen (NO3+NO2-N), and nitrogen in
ammonium (NH4-N) for Week 0 of nitrogen mineralization potentials.
Data set includes bi-weekly records of number of termites observed within and beneath each of 4 rolls of toilet paper placed at each of 91 stations on treatment and control transects. Observations of presence of termite activity at each roll (paper eaten, cartons constructed) are also included.
*We designed a study to examine the long-term spatial and temporal patterns of mass loss, changes in nitrogen content and chemical composition during decomposition of roots in a desert watershed.
Because nitrogen availability has been hypothesized to affect decomposition rates of buried litter in deserts, we studied decomposition of roots along a transect on a desert watershed that had been fertilized with ammonium nitrate and compared these results with the decomposition of roots along a transect that had not been fertilized.
Rabbit pellets were collected from 24 5x5m plots at approximately 1 month intervals. Dry weight by date and plot was recorded. Pellets were subsampled and analyzed for Total N. Plots are located along LTER-1 Control and Treatment transects in creosotebush (around station C62 and T61) and upper basin slope.
(See site description.) Plots are located along LTER-1 Control and Treatment transects in creosotebush (around station C62 and T61) and upper basin slope. (See site description.)