阴山扁蓿豆光合特性对模拟牦牛、藏羊践踏和降水的短期响应

为明晰牦牛和藏羊践踏对阴山扁蓿豆光合特性的分异影响,在天祝高寒草地采用模拟降水和践踏双因子控制试验,研究了阴山扁蓿豆单叶面积、叶绿素含量、叶片气体交换参数变化对短期模拟牦牛、藏羊践踏和降水的响应。结果表明,随着模拟牦牛和藏羊践踏强度的增加、模拟降水量的降低,阴山扁蓿豆单叶面积、叶绿素含量、蒸腾速率(T_r)、叶片气孔导度(G_s)和净光合速率(P_n)均呈下降趋势,胞间CO₂浓度(C_i)呈上升趋势。相同降水量下,藏羊和牦牛轻度践踏强度下阴山扁蓿豆蒸腾速率、叶片气孔导度和净光合速率均高于对照,胞间CO₂浓度低于对照。与对照相比,牦牛重度践踏处理下阴山扁蓿豆单叶面积、叶绿素含量、蒸腾速率、叶片气孔导度和净光合速率的降幅和胞间CO₂浓度的升幅均大于藏羊重度践踏处理。单一的模拟降水或模拟践踏极显著地影响了各测定指标,且两者共同作用对阴山扁蓿豆单叶面积、蒸腾速率、叶片气孔导度、净光合速率和践踏末期叶绿素含量的影响达极显著水平。综合可得,牦牛和藏羊轻度践踏可促进阴山扁蓿豆光合作用,重度践踏严重抑制了阴山扁蓿豆光合作用,且牦牛践踏对阴山扁蓿豆光合能力的抑制作用大于藏羊践踏。

Short-term photosynthetic responses of Medicago ruthenia var.inschanicus to simulated yak and Tibetan sheep trampling and rainfall

To determine the effects of yak and Tibetan sheep trampling and rainfall on the photosynthetic characteristics of Medicago ruthenia var.inschanicus,the responses of single leaf area,chlorophyll content (SPAD value),and photosynthetic gas exchange parameters to short simulated yak and Tibetan sheep trampling and rainfall were studied with a two-factor (simulated trampling and rainfall) controlled experiment in a Tianzhu alpine meadow.The single leaf area,SPAD value,transpiration rate (Tr),stomatal conductance (Gs),and net photosynthetic rate (Pn) decreased with increasing yak and Tibetan sheep trampling intensity and declining rainfall,while the intracellular concentration of CO2 (Ci) increased.Under the same rainfall conditions,the Tr,Gs,and Pn were all higher under a light trampling intensity of Tibetan sheep and yaks than in the control (no trampling),while the Ci was lower than that in the control.The magnitude of decreases in the single leaf area,SPAD value,Tr,Gs,and Pn,and increases in Ci were greater under heavy trampling by yaks than under heavy trampling by Tibetan sheep.Simulated rainfall alone or simulated trampling alone significantly affected the tested indicators,and the interaction between simulated rainfall and simulated trampling had a significant effect on single leaf area,Tr,Gs,Pn,and SPAD value (at the final trampling stage) of M.ruthenia var.inschanicus.These results showed that the photosynthesis of M.ruthenia var.inschanicus was promoted by light trampling,but inhibited by heavy trampling by Tibetan sheep and yaks.Compared with Tibetan sheep,yaks had stronger inhibitory effects on the photosynthetic activity of M.ruthenia var.inschanicus.