The Effect of Bedrock Differences on Plant Water Use Strategies in Typical Karst Areas of Southwest China

Abstract

Moisture conditions are important ecological factors limiting plant growth in karst areas. In karst areas, because bedrock exposure and permeability are significant and soils are dispersed—without spatial continuity—and shallow, the water storage required for plant uptake and growth in rock fissures as well as shallow soils is very limited, and therefore, water conditions are an important factor influencing plant growth. In order to discover the sources of water used by plants in the karst zone ecosystem of southwest China and the differences in plant water use under different lithological conditions, this study selected limestone and dolomite in the karst ecological test site of Maocun, Guilin, Guangxi, for comparison with the clastic rock area. By measuring the δD and δ18O composition of plant stem water and the potential water sources (soil water, groundwater and precipitation) of the dominant species in the study area, and using the IsoSource and soil water excess (SW-excess) models, we analyzed the proportion of water utilization by different vegetation types under different lithological conditions. The results showed that (1) the slope and intercept of the local rainfall line (LMWL) and soil water line (SWL) in the study area were smaller than those of the global rainfall line (GMWL), and also smaller than those of the local atmospheric precipitation line in Guilin (δD = 8.8δ18O + 17.96), indicating that the local rainfall is influenced by evaporation and is formed by nonequilibrium fractionation of isotopes; (2) in general, the plant water sources in the dolomite, limestone, and clastic areas were dominated by rainfall, groundwater, and soil water, respectively; and (3) the fluctuation range of SW-excess in karst areas was significantly greater than that in nonkarst areas, the xylem water of plants in karst areas was more depleted in δD than soil water, and groundwater was more enriched in δD than soil water, indicating that there might be an ecological–hydrological separation phenomenon in karst areas, i.e., the “two water worlds” hypothesis. The results of this study provide scientific data for hydrological regulation in the ecological restoration of karst areas.

Effects of Film-Mulched Rock Outcrops on Rainwater Redistribution and Maize Growth in the Cropland of a Rocky Karst Area

“…Water is a fundamental limitation for plant survival in karst areas [10,11]. Under natural conditions, the interconversion process between various links in the water cycle and precipitation recharges in karst areas is relatively complex, and this, along with the increasing influence of human activities on the regional water cycle, has resulted in contradictions between the supply and demand of water resources becoming increasingly prominent [12][13][14][15].…”

Effects of Soil–Rock Geomorphic Units on the Yield of Surface Runoff: A Case Study on Uncultivated Land of a Karst Area

“…Water is the lifeblood of karst vegetation [11,12]. Plants growing in karst areas are frequently affected by many environmental factors, but in karst areas, water is undoubtedly Water 2023, 15, 3224 2 of 13 the most important growth-limiting factor among them [13,14]. The karst area studied is located in the monsoon zone of the subtropics in southwest China where abundant rainfall provides the natural conditions for karst development [15,16].…”