Rock outcrops (ROCs), either connected to bedrock or independent, are frequently visible in terrestrial landscapes. However, there has been insufficient research conducted on the effects of ROCs on the formation of soil water and nutrients heterogeneity in nearby soil patches. 

Prof. SHEN Youxin of Xishuangbanna Tropical Botanical Garden (XTBG) and his collaborators quantified rock outcrop emergence ratios in three karst ecosystems with ROCs covered by various types of vegetation.  

The researchers installed equipment to collect water from rock surfaces and atmospheric deposition, and determined the organic carbon, nitrogen (N), phosphorus (P), and potassium (K) content of each water sample. 

The researchers measured the rock occupancy ratio in a rock desertification ecosystem, an anthropogenic forest ecosystem, and a secondary forest ecosystem in Shilin, Southwest China.

They then quantified the water received by and subsequently funneled off by rock outcrops. Afterwards, the researchers determined their concentrations of the total organic carbon, nitrogen, phosphorus, and potassium. 

They found that rock outcrops received water, total organic carbon (TOC), N, P, K from rainfall/throughfall at different rate, and then subsequently funneled off them at different rate to the nearby soil patches. 

The receiving rates of rainfall/throughfall and funnel of water and P were not different, but TOC, N, K were different among the three ecosystems covered with different vegetation. 

The combined supply rate increased slowly at lower ROC emergency ratio, but sharply at the higher emergency ratio in the same ecosystem. 

The highest supply rate was several folds of the supply rate without ROC in the three ecosystems, thus created large supply heterogeneity. 

The supply rate also correlated with the receiving rates of rainfall/throughfall and funnel, thus factors that affect them can contribute to the soil heterogeneity in ROC+ soil combinations. 

"Our research could help to understand geomorphology, soil, flora diversity and other ecosystem characteristics in karst areas", said Dr. SHEN Youxin, principal investigator of the study.  

The study entitled "Large heterogeneity of water and nutrient supply derived from runoff of nearby rock outcrops in karst ecosystems in SW China" has been published in CATENA.