Water is usually considered to be a key limiting factor for the growth and reproduction of steppe plants in the Xilin River Basin, Nei Mongol. Foliar delta C-13 values, an indicator of long-term intercellular carbon d...Water is usually considered to be a key limiting factor for the growth and reproduction of steppe plants in the Xilin River Basin, Nei Mongol. Foliar delta C-13 values, an indicator of long-term intercellular carbon dioxide concentration and thus of water-use efficiency (WUE) in plants, were measured on Leymus chinensis (Trin.) Tzvel. and Cleistogenes squarrosa (Trin.) Keng. in six communities of different habitats in die Xilin River Basin. The foliar delta C-13 values of both species tended to increase with decreasing soil water content (SWC) and a significant negative correlation was found between foliar delta C-13 Values and SWC in different soil layers, indicating that the two species could change WUE according to water availability. We also found relatively constant leaf water contents (LWC) of the two species in different habitats. Our results implied that the two steppe species might have adapted to different soil water regimes either through adjusting stomatal conductance to get a proper WUE, or through enhancing the osmosis-regulating ability to keep a relatively stable LWC. Our findings could partially explain why the two plant species have a wide distribution range and become dominant in the Xilin River Basin.展开更多
The present study was conducted to examine photosynthetic characteristics of three dominant grass species （Agropyron cristatum, Leymus chinensis, and Cleistogenes squarrosa） and their responses to burning and nitrog...The present study was conducted to examine photosynthetic characteristics of three dominant grass species （Agropyron cristatum, Leymus chinensis, and Cleistogenes squarrosa） and their responses to burning and nitrogen fertilization in a semiarid grassland in northern China. Photosynthetic rate （Pn）, stomatal conductance （gs）, and water use efficiency （WUE） showed strong temporal variability over the growing season. C. squarrosa showed a significantly higher Pn and WUE than A. cristatum and L. chinensis. Burning stimulated Pn of A. cristatum and L. chinensis by 24-59% （P 〈 0.05） in the early growing season, but not during other time periods. Light-saturated photosynthetic rate （Pmax） in A. cristatum and the maximum apparent quantum yield （Фmax） in A. cristatum and L. chinensis were significantly enhanced by burning （16-67%） in both the fertilized and unfertilized plots. The main effect of burning on Pn, Pmax and Фmax was not significant in C. squarrosa. The burning-induced changes in soil moisture could explain 51% （P= 0.01） of the burning-induced changes in Pn of the three species. All three species showed positive responses to N fertilization in terms of Pn, Pmax, and Фmax. The stimulation of Pn under N fertilization was mainly observed in the early growing season when the soil extractable N content was significantly higher in the fertilized plots. The N fertilization-induced changes in soil extractable N content could explain 66% （P = 0.001） of the changes in Pn under N fertilization. The photosynthetic responses of the three species indicate that burning and N fertilization will potentially change the community structure and ecosystem productivity in the semiarid grasslands of northern China.展开更多
文摘Water is usually considered to be a key limiting factor for the growth and reproduction of steppe plants in the Xilin River Basin, Nei Mongol. Foliar delta C-13 values, an indicator of long-term intercellular carbon dioxide concentration and thus of water-use efficiency (WUE) in plants, were measured on Leymus chinensis (Trin.) Tzvel. and Cleistogenes squarrosa (Trin.) Keng. in six communities of different habitats in die Xilin River Basin. The foliar delta C-13 values of both species tended to increase with decreasing soil water content (SWC) and a significant negative correlation was found between foliar delta C-13 Values and SWC in different soil layers, indicating that the two species could change WUE according to water availability. We also found relatively constant leaf water contents (LWC) of the two species in different habitats. Our results implied that the two steppe species might have adapted to different soil water regimes either through adjusting stomatal conductance to get a proper WUE, or through enhancing the osmosis-regulating ability to keep a relatively stable LWC. Our findings could partially explain why the two plant species have a wide distribution range and become dominant in the Xilin River Basin.
基金the National Natural Science Foundation of China (90511006)the Chinese Academy of Sciences (Hundred Talents Program).
文摘The present study was conducted to examine photosynthetic characteristics of three dominant grass species （Agropyron cristatum, Leymus chinensis, and Cleistogenes squarrosa） and their responses to burning and nitrogen fertilization in a semiarid grassland in northern China. Photosynthetic rate （Pn）, stomatal conductance （gs）, and water use efficiency （WUE） showed strong temporal variability over the growing season. C. squarrosa showed a significantly higher Pn and WUE than A. cristatum and L. chinensis. Burning stimulated Pn of A. cristatum and L. chinensis by 24-59% （P 〈 0.05） in the early growing season, but not during other time periods. Light-saturated photosynthetic rate （Pmax） in A. cristatum and the maximum apparent quantum yield （Фmax） in A. cristatum and L. chinensis were significantly enhanced by burning （16-67%） in both the fertilized and unfertilized plots. The main effect of burning on Pn, Pmax and Фmax was not significant in C. squarrosa. The burning-induced changes in soil moisture could explain 51% （P= 0.01） of the burning-induced changes in Pn of the three species. All three species showed positive responses to N fertilization in terms of Pn, Pmax, and Фmax. The stimulation of Pn under N fertilization was mainly observed in the early growing season when the soil extractable N content was significantly higher in the fertilized plots. The N fertilization-induced changes in soil extractable N content could explain 66% （P = 0.001） of the changes in Pn under N fertilization. The photosynthetic responses of the three species indicate that burning and N fertilization will potentially change the community structure and ecosystem productivity in the semiarid grasslands of northern China.
