Soil Texture and Carbon Dynamics in Savannah Vegetation Patches of Central Argentina

This study was intended to contribute information on the relation between soil texture and plant community composition, and the effect of interactions between texture and vegetation patch on soil C dynamics. Six sampling sites were chosen and a vegetation census and soil sampling were performed for between-canopy (BC) and under-canopy (UC) patches at each site, Shannon-Weaver diversity index (DI) was determined for herbaceous species, an relative abundance of forage species and avoided grasses were calculated. Soil data included texture, bulk density, total organic C (TOC), particulate organic C (POC), intermediate organic C (IOC), and fine organic C (FOC). Correspondence analysis showed that sandy and loamy sites did not share the same herbaceous species. We also found an interaction between vegetation patches and texture, with distinct vegetation composition in the same type of patch indifferent textures. The DI was lower in UC than BC patches (0.86 vs. 1-7), but no effect of texture was found. The TOC showed a positive relation with texture; the extremes were 9.0 vs. 16.3 g kg(-1) for a loamy sand and loam, respectively. Carbon fractions varied in their response to texture: while POC and IOC showed no clear trend with texture, FOC contents followed a textural gradient. Particulate organic C showed higher values in UC than BC (10.8 vs. 4.0 g kg(-1)). Differences between patches diminished with increasing clay contents. Intermediate organic C was similar to POC, while FOC showed no effect of patch but was related to texture. The high proportion of POC in sandy soils (50 vs. 35% in a loam) makes these more susceptible to changes in C balance and might thus render them less resilient under grazing.