不同放牧强度下羊草的光合特性日动态变化——以呼伦贝尔草甸草原为例

摘要

To explore the response of photosynthetic characteristics of Leymus ckinensis to different grazing intensities under continuous grazing, the diurnal dynamics of photosynthetic characteristics in five grazing plots and one enclosing plot were measured using Li-6400 Portable Photosynthesis System. The correlations between the traits of parameters and grazing intensities (R) were analyzed. Daily variation of net photosynthetic rate (Pn), transpiration rate (Tr), and stomataf conductance (Gs) appeared as a single peak curve and a double-peak curve in all plots on 16th August and 2nd September respectively, but intercellular CO2 concentration (Ci) showed a U shape trend. In the enclosed plot, Pn, Tr, and Gs were higher than those in the grazed plots. In addition, Pn, Tr, and Gs decreased with an increase in grazing intensity, but Ci increased. It is suggested that the variation range is greater under higher grazing intensities. There were significant negative correlations between Pn, Tr, Gs and R but Ci was significantly positively correlated with R. There were significant differences in Pn, Tr, Gs and Ci among 6 grazing intensities on the two dates. Hence, herding intensity and hydro-thermal conditions can inhibit photosynthesis fay L. chinensis.%在连续放牧方式下,探索羊草的光合特性对不同放牧强度的响应,利用Li-6400便携式光合测定仪对呼伦贝尔羊草草原1个封育对照试验区和5个不同放牧强度试验区内羊草叶片的光合特性进行日变化测定,并与放牧强度(R)进行相关性分析.研究结果表明,8月16日和9月2日,6个试验区内羊草叶片净光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Gs)的日变化既有单峰曲线也有双峰曲线变化,而胞间CO2浓度(Ci)日变化呈U字型.围封内羊草的Pn、Tr、Gs均高于放牧区;且羊草的Pn、Tr、Gs均随着放牧强度的增大而下降,Ci则升高;放牧强度越大,其降幅和增幅也越大.Pn、Tr、Gs与R之间均呈显著的负相关关系(P＜0.05),Ci与R呈显著的正相关关系(P＜0.05);而且6个放牧强度梯度下的Pn、Tr、Gs和Ci在2d之间有极显著差异(P＜0.01).因此,放牧胁迫和水热条件对羊草的光合作用有抑制作用.