Sources And Efficiency Of Water Use By Differences In Maocun,Guilin

The study of plant water use strategies under different lithological conditions provides scientific data for hydrological regulation during ecological restoration in karst areas and provides a basis for fragile karst ecological protection.In this study,the main plants under limestone and dolomite conditions in the karst underground river basin of Maocun,Guilin City,Guangxi Province were studied,and the main conclusions reached through the study of the sources and efficiency of water utilization of the main plants under different lithological conditions,in comparison with the clastic rock area,are as follows:（1）The trends of deuterium（δD）and oxygen(δ¹⁸O)isotope values of atmospheric precipitation in the study area are consistent,and generally show enrichment in the dry season and depletion in the rainy season.The overall variation ofδD andδ¹⁸O values of groundwater in the study area is small and insignificant with seasonal variations,and their groundwater pointδD andδ¹⁸O values are mainly distributed near the local precipitation line（LMWL）due to mixing effects,which also proves that atmospheric precipitation is an important source of groundwater recharge.（2）In November,theδ¹⁸O values of soil water showed a trend of depletion followed by enrichment as the depth of soil layer increased.The plant water source in the clastic zone was dominated by soil water;the tree water source in the dolomite zone was dominated by atmospheric precipitation,and the shrubs were dominated by soil water;most of the plant water sources in the limestone zone were groundwater.In June,theδ¹⁸O values of soil water showed enrichment with the increase of soil depth.The plant water source of the clastic rock sample site was dominated by soil water;most of the plant water sources of the dolomite sample site were dominated by soil water;most of the plant water sources of the limestone sample site were dominated by groundwater.（3）The excursions（SW-excess）of the soil water line in the xylem of plants in the study area were all less than 0.This indicates that the xylem water of plants in the study area is more depleted inδD than their soil water,while groundwater is more enriched inδD than soil water.This result is the same as that obtained by the bilinear method,suggesting that the"two water worlds"hypothesis（i.e.,"TWW"）may exist in the study area.（4）Overall,theδ¹³C values of plant leaves in non-karst areas were enriched than those of plant leaves in karst areas.The water use efficiency（WUE）of plants in June was significantly higher than that of plants in November in both karst and non-karst areas.The plant water use efficiency（WUE）in non-karst areas was significantly higher than that in karst areas,both in November and June.The differences among elements in plant leaves under different lithological conditions were large,in which the sample site with the highest TC content was the clastic rock sample site,which was significantly higher than the sample site in the karst area.There was a positive correlation between plant water use efficiency（WUE）and leaf TC and TN,and a negative correlation between leaf TP and TK.