Water Use Mechanism Of Typical Tree Species In Limestone Mountains Based On Stable Isotopes And Fluorescence Tracer

The mountain of limestone habitat with exposed bedrock and shallow soil,has resulted in low water holding capacity.Thus,the natural distribution of plants in limestone mountain habitats is symptomatic of their adaptation to soil moisture.Previous research suggests that deep-rooted plants absorb water from deep soils and rock crevices as the main adaptive strategy in limestone mountain habitats.However,the adaptation mechanism for the widespread distribution of shallow-rooted tree species in limestone habitat is unclear.In this study,Phyllostachys glauca was selected as the research object,which was a dominant species distributed in large areas in the limestone mountains of northwest Jiangxi Province.And we choose the accompanying species Phyllostachys heteroclada、Quercus fabri、Camellia oleifera and Phyllostachys glauca of non-limestone mountains as controls.During a high-frequency precipitation period with sufficient precipitation(June to August)and low-frequency precipitation period with poor precipitation(September to November),stable isotopes and fluorescence tracer techniques were used to study the adaptive mechanism of plant water sources,absorption and storage in limestone mountains.The main results were as follows:(1)According to the analysis of moisture source data,plants mainly utilize shallow soil(0-20cm)water during periods of high-frequency precipitation because of adequate soil moisture.The water use efficiency of P.glauca was higher than that of Q.fabri and Ca.oleifera in surface soil layer.Among them,the contribution rate of recent precipitation were higher than other plants.In the low-frequency precipitation period,plants used early precipitation,recent precipitation and soil water.Among them,the contribution rate of the rainfall one month ago was the highest,but the values were different.P.glauca mostly used the precipitation of one month ago and the recent precipitation of half a month ago,while Q.fabri basically used the precipitation of one month ago.Similar to P.glauca,P.heteroclada most use recent precipitation.C.oleifera changed the main water using source from soil water in high-frequency precipitation period to rainfall and soil water in low-frequency precipitation period.In terms of stem water content and absorption,the stem water content of bamboo plants was lower than that of oleifera and Q.fabri in both high-frequency and low-frequency precipitation periods.However,as to the amount of rainfall absorption,P.glauca and CK P.glauca were higher than the other three plants.(2)Based on high concentration 18O tracer experiments,it was found that under drought treatment,the plants of limestone mountain could all absorb water from the air,but the absorption capacity was different.After spraying the plant for 8 hours,the absorption rate and reverse transport rate(leaf water absorption to the root transport)of P.glauca were both higher than those of the other three plants,and each component also maintained the highest absorption rate to the fog.With the downstream transportation of fog,For bamboo plants,more water was transferred to bamboo root under drought treatment or non-drought treatment,while the accumulation of marked water was not detected in soil.Q.fabri transferred the labeled water to the soil through the root system.which indicated that the root system carried water to alleviate the drought.(3)The dynamics of water uptake in different plants vary according to leaf structure.According to the fluorescence tracer results,the fog water was absorbed from the lower epidermis of P.glauca and P.heteroclada,followed by the fog water made from HPTS(8-hydroxypyrene-1,3,6-trisulfonicacid)fluorescence reagent in the upper epidermis,lower epidermis,vascular bundle and vesicular cells.After tracing for 6 hours,the fluorescence intensity reached the highest in P.glauca,while it was 2hours later in P.heteroclada.The fluorescence tracer of C.oleifera and Q.fabri was also permeated from the lower epidermis first,and then HPTS solution was found in the glandular hair upper and lower epidermis,basic tissues,mechanical tissues,wood fibrocytes and xylem of C.oleifera,and the fluorescence effect reached the highest after 6 hours of tracing.HPTS solution was found in the parenchyma cells,wood fiber cells and xylem of Q.fabri,and the fluorescence effect reached the highest after 8hours.Based on the results of Schiff periodate and Sudan black staining,there were more hydrophilic polysaccharides and lipids in the leaves of P.glauca than in P.heteroclada,and the situation was similar between C.oleifera and Q.fabri.The dominant species P.glauca has strong water plasticity and movement ability.In the time of frequent rainfall,P.glauca,like other plants,gives priority to the use of soil moisture supplemented by abundant rainfall to reduce energy loss.In the drought period when the rainfall is deficient,the advantages of Pallorophora lutea are highlighted.It can store early precipitation to survive the drought,and its leaves can absorb more life-saving water from the air than other plants,transport it downward more quickly,and even transfer the water to the whip system.