Biophysical controls over concentration and depth distribution of soil organic carbon and nitrogen in desert playas

• Published in: Journal of geophysical research. Biogeosciences 2016-12, Vol.121 (12), p.3019-3029
• Main Authors: McKenna, Owen P., Sala, Osvaldo E.
• Format: Article
• Language: English
• Subjects: Allochthonous deposits; Arid zones; Biophysics; Carbon; Catchment area; Catchment areas; Clay; Clay soils; Climate; Climate change; Correlation; Depth; Deserts; Distribution; Drains; dry‐land catchments; Ecosystems; Grazing; Grazing intensity; Herbivores; Highlands; Jornada LTER; Mineral nutrients; Nitrogen; Organic carbon; Organic matter; Organic soils; Plant cover; Plants (botany); playa; Playas; Profiles; Ratios; Rooting; Sedimentation; Sedimentation & deposition; Soil; soil C/N ratio; soil nitrogen; soil organic carbon; Soil properties; Soil texture; Soils; Stocks; Storage; Texture; Vegetation; Vegetation cover
• ISSN: 2169-8953; 2169-8961
• DOI: 10.1002/2016JG003545

Playa wetlands are important areas of soil organic carbon and nutrient storage in drylands. We conducted this study to assess how catchment biophysical variables control soil organic carbon and nitrogen in playas and how playas function differently than upland ecosystems. We found that playa organic carbon and nitrogen corresponded primarily with catchment vegetation cover and secondarily with catchment area, slope, and soil texture. The effect of increased organic matter production associated with high catchment vegetation cover overshadowed the potential effect of reduced run‐on. We also found soil carbon and nitrogen profiles to be significantly shallower in playas than uplands. This trend is correlated with evidence of sedimentation and shallow‐rooted plants in playas. Upland soils had a deeper carbon and nitrogen profile, which correlated with organic matter being generated by deeply rooted vegetation. In playas, C:N ratios remained constant through depth but in uplands, C:N ratios increased through depth. We found evidence that differences in rooting depth distributions and soil texture may explain these C:N variations between uplands and playas. In uplands, clay concentration increased with depth, whereas in playas, clay concentration did not change with depth, which highlighted the important role of sedimentation in these ecosystems. Our results suggest that small changes in playa catchment vegetation cover in response to climate change or grazing intensity would greatly impact playa soil organic carbon and nitrogen stocks. This effect would be due to the playa soils dependence on allochthonous organic matter and the large upland area that drains into playas. Key Points Catchment vegetation cover was the most important predictor of soil carbon and nitrogen concentrations among playas Upland and playa soil C an N depth distribution correlated with differential rooting patterns Upland and playa soil C:N ratio through depth corresponded with soil clay content