The response of the relationship between transpiration rate and leaf traits of Atriplex patens to population density in the national wetland park conservation areas in Qinwangchuan

The environmental response of plant relationships between transpiration rate and leaf traits is of vital significance to explore the ecophysiological mechanism of the coupling of plant carbohydrate metabolism and building modes for leaf traits. The objective of this study was to examine the relationship between atriplex(Atriplex patens) transpiration rate and vein density and midrib diameter under the influence of different population densities. The study site was located in the national wetland park conservation areas in Qinwangchuan, Gansu Province, China(36°27’59.6″ N, 103°39’5.6″ E). The study area was on a platform at the center of the wetland, gently transiting through the wetland community, in which atriplex was the single dominant species. The sample area was divided into 3 levels based on plant density, high(Ⅰ, 16-21 plant/m~2), medium(Ⅱ, 9-15 plant/m~2) and low(Ⅲ, < 9 plant/m~2), In order from bottom to top, six(2 m × 2 m) atriplex samples were selected per plot, numbering 24 samples(4 × 6) in all. Then, community traits(height and coverage) andsoil moisture were determined and 6 individuals of Atriplex patens were taken to the laboratory to measure the leaf thickness, leaf area, vein density, and midrib diameter. In addition, the leaf net photosynthetic rate(P_n), transpiration rate(T_r)and other parameters of the atriplex were measured in each plot. Quadrat survey methods were used to determine the relationship between transpiration rate and leaf traits of the atriplex. The results show that when the soil population density was decreased, the wetland vegetation community height and coverage presented increasing-decreasing changing trends;vein density(VD) and leaf transpiration rate(T_r) presented increasing trends, and the midrib diameter(MD) displayed a decreasing trend. There was a highly significant positive correlation(P < 0. 01) between T_rand VD, and there was a significant negative correlation(P 0.05) at plot(Ⅱ). In the high-density sample plot(Ⅰ), atriplex preferred a low vein density and a large midrib diameter to realize the low transpiration rate; in the low density sample plot(Ⅲ), atriplex preferred a large vein density and a small midrib diameter to achievea a higher transpiration rate; in the medium density sample plot(Ⅱ), atriplex chose an investment strategy of balanced vein density and midrib diameter to achieve a higher transpiration rate. T