Karst Rocky Desertification Region Research Articles

Influence of bare rocks on surrounding soil moisture in the karst rocky desertification regions under drought conditions

A large number of bare rocks exposed in the field represent one of the most spectacular scenes of the Karst Rocky Desertification (KRD) process. The presence of bare rocks modifies the microenvironment. An understanding of soil moisture variability is necessary to characterize the linkages between a region's hydrology, ecology, and physiography. The objective of the study was to determine the influence of those exposed bare rocks on soil moisture in the surrounding area in a typical KRD region—the Forest Station of Sandoqing, in Fu'yuan County, Yun'nan Province, Southwest China. Dynamic soil moisture was quantified in Feb, 2010 during an extreme drought period. Results showed that during the drought period, soil moisture on the north side of the rocks was significantly higher than those on the east, west and south sides (p<0.01). Soil surface moisture increased with the above-ground height of the rocks. The size of the bare rocks was significantly correlated with soil moisture on the west and north sides of the rocks (p<0.01) and the east side of the rocks (p<0.05). Sharper rocks were associated with declining soil moisture on the east, west and north sides of the rocks. Soil moisture began to increase and then declined on the north, east and west sides, but showed a continued increase on the south side with the distance from the rocks. The soil moisture around the rocks increased gradually with depths of soil layers. During the drought period bare rocks created some shade, resulting in higher soil moisture on the north side of the rocks compared to the other three directions. The location at 15cm north of the rocks had the highest soil water content, thus becoming the most ideal site for establishing vegetation restoration in the KRD area under stressful environmental conditions. Results from this study can be used to assist in restoration of ecological system damaged by the KRD process.

Characterization of soil low-molecular-weight organic acids in the Karst rocky desertification region of Guizhou Province, China

Soil low-molecular-weight (LMW) organic acids play important roles in the soil-forming process and the cycling of nutrients in Karst regions. In this study, we quantified the contents of LMW organic acids (including lactate, acetate, formate, malate, and oxalate) in soil solution over the Karst region of Guizhou Province, China using ion chromatography. The concentration of total LMW organic acids in topsoil solution ranged from 0.358 to 1.823 μmol·g−1, with an average of 0.912 μmol·g−1. The mean concentrations of lactate, acetate, formate, malate, and oxalate were 0.212±0.089, 0.302±0.228, 0.301±0.214, 0.014±0.018 and 0.086±0.118 μmol·g−1, respectively. There were also significant difference in the contents of these acids among four phases of rocky desertification, and their concentrations decreased with the aggravation of rocky desertification. The concentrations of the LMW organic acids were significantly positive correlated each other. Significant positive correlations were also observed among individual LMW organic acids in soil solution, and between them and soil available P, available K, exchangeable Ca, respectively. Furthermore, the concentrations of LMW organic acids were significantly positively correlated with inorganic anions (chlorides, nitrates, and sulfates) in Karst topsoil solution. Therefore, the concentrations of soil LMW organic acids might be one of driving force in the Karst rock desertification process in Guizhou Province.