The research area is a typical karst catchment subject to rocky desert ification in Huajiang Gorge

Guizhou Province. One representative soil sample was collected in each plot of strong

medium

light

or latent desertification grade. The research focused on soil organic carbon (SOC) and total nitrogen (TN) of physical fraction in the processes of rocky desertification. Results elucidated that the par ticulate organic carbon and nitrogen ( POC and PON) and light fraction organic carbon and nitrogen( LFOC and LFON) were higher than the mineral fraction in the process of rocky desertification. The C/ N values of part iculate fr action and light fraction were higher than those of total soil. The content sof POC

PON

LFOC

and LFON decreased with the increase of rocky desertification grade. The content of part iculate fraction and distribution ratio acted in accord with rocky desert if ication grade

while the above index of light fraction did not act in accord with rocky desert if ication grade. The enrichment and distribution ratios of POC and PON

as well as LFOC and LFON

were not the same. The decrease of POC and LFOC was faster than that of PON and LFON in the process of rocky desert if ication. Most POC in wood chopping sequence integrated with silt-clay particle to form organic-inorganic complex

with the integration way POC was protected and was diff icult to decompo se by microbe

while most POC in reclamation sequence integ rated with sand particle

with this kind of integr ation way SOC tended to be in a low humic degree and to be decomposed by microbe easily.