Water eco-physiological adaptability of Hemiboea subcapitata in heterogeneous habitats in the Dehang karst valley
The Dehang canyon of Xiangxi UNESCO Global Geopark is cut by the runoff of streams.As a unique karst landform,it is an ideal area for studying plant species diversity and ecological adaptability.Collecting the clone plants,Hemiboea subcapitata,as samples from the Dehang karst valley in Xiangxi Global Geopark,this study measured their growth,morphology,and photosynthetic and water physiological indicators.On this basis,this study explored the water eco-physiological adaptability of the plants to three types of heterogeneous habitats formed during the evolution of the Dehang karst valley.These three habitats are canyon karst walls slightly weathering after water erosion without soil covering,bank weathered rocks with little soil covering and bank soil organic horizons highly weathering with soil covering.The results show as follows.(1)There was only a small difference(<2%)in the natural water content in ramet leaves of H.subcapitata in heterogeneous habitats,while there is no significant difference in terms of relative water content and natural saturation deficit.It is proved that they not only have a strong water maintenance mechanism but also have no obvious difference in their recovery ability after drought.The lowest water potential of canyon karst walls was-1.630±0.047 Mpa,and the highest water potential of bank soil organic horizons was-0.705±0.025 Mpa.It is obvious that,in heterogeneous habitats,the water demand of ramet leaves increased significantly with the decrease of the matrix water content,but the water potential of leaves decreased significantly.(2)There was a significant difference in ramet growth but no significant difference in total biomass.For example,the plant heights and leaf areas of ramets on the surfaces of canyon karst walls were significantly higher than those in bank soil organic horizons,but there was no significant difference in the cumulative height and leaf area of total population.(3)The morphological changes of ramets were significant.Values of lengths,diameters and root densities of stolons were listed as:canyon karst walls>bank weathered rocks>bank soil organic horizons.The leaf thickness on canyon karst walls was nearly 60 μm thicker than that in bank soil organic horizons,while the specific leaf area(SLA)decreased to 78.2%,and the stomatal density significantly reduced to 66%.The highest stomatal density was 2,299±158 mm2 in the habitats of bank soil organic horizons,and the lowest stomatal density was 1,518±98 mm2 in the habitats of canyon karst walls.(4)In terms of photosynthetic parameters,stomatal limit values of leaves increased significantly with the decrease of leaf water potential in different habitats,but stomatal conductance increased significantly at the same time,so the intercellular CO2 concentration did not change significantly.However,the net photosynthesis of ramet leaves on bank soil organic horizons only reached 69.6%of that in bank soil organic horizons.(5)The water use efficiency(WUE)of the habitats of bank soil organic horizons was the highest(4.134±0.333 μmol CO2·mmol-1 H2O).When the water deficit of leaves on canyon karst walls was the highest,the water use efficiency was the lowest(3.029±0.461 μmol CO2·mmol-1 H2O),only 73%of that in bank soil organic horizons.These results indicate that H.subcapitata can ensure the relative water stability of ramets in karst heterogeneous habitats through its own water maintenance mechanism.H.subcapitata can be adapted to the habitats of arid karst rock walls by increasing root density,stolon length,leaf thickness and weight,and by reducing stomatal density and other morphological plasticity.It can also keep intercellular CO2 concentration by increasing stomatal conductance to maintain transpiration pull.At last,it can be adapted to water heterogeneous habitats in karst river valleys by relatively stable growth with higher water consumption.
karst valleyHemiboea subcapitatawater use efficiency(WUE)water eco-physiological adaptability
万方数据
维普
