Study On Growth And Development Response Of Leymus Chinensis To Main Global Climate Change Factors

Global climate change, caused primarily by greenhouse gas emission and other human activities and characterized by elevated CO2, warming, nitrogen deposition, and changes in the precipitation pattern, has become an unequivocal fact. Leymus chinensis is a highly palatable perennial C3grass that is rich in protein, minerals, and carbohydrates. Therefore, in the current paper, we investigated how climate changes alter biomass, photosynthesis, and clonal growth of L. chinensis from the perspective of both individual grasses and populations and, in addition, elaborated on its adaptive strategies to these environmental transformations. The primary objectives of this study are to explore how the productivity of L. chinensis responds to climate change while also determining how these productivity changes provide a theoretical basis for retaining the overall yield for this important grass. The main results and conclusions of our experiments are as follows:(1) Elevated CO2levels primarily enhance the biomass of the parent shoots and have very little effect on the biomass of the daughter shoots. Moreover, under low nitrogen conditions, elevated CO2has little effect on the aboveground biomass. Alternatively, high nitrogen conditions, in combination with elevated CO2, significantly increases the aboveground biomass, indicating that the effects of elevated CO2on biomass are likely mediated by nitrogen. In addition, we also found that elevated CO2causes an increase in the root biomass under low precipitation conditions and decreases the root biomass under normal and high precipitation(especially under high precipitation conditions), clearly showing that concentrations of high CO2can actually be beneficial under conditions with relative water shortages. Furthermore, the aboveground biomass increases with increasing precipitation. Results also show that summer nocturnal warming results in a decrease in the aboveground biomass under low precipitation (including both the parent and daughter shoot biomass) and an increase in the aboveground biomass as precipitation levels increase. Interestingly, nitrogen deposition was found to have a similar effect, implying that the effects of summer nocturnal warming and nitrogen deposition on the growth and development of L. chine sis is strongly limited by water.(2) Althouth L. chinensis undergoes "photosynthetic adaptation" under elevated CO2levels, its photosynthetic rate remains at high levels, due to higher substrate concentrations, and its respiration rate is lower than that at ambient CO2. Consistent with the data on the parent shoot biomass, the photosynthetic rate of L. chinensis gradually declines with elevated CO2concentrations and increasing precipitation levels, but increases under nitrogen deposition conditions. Furthermore, summer nocturnal warming was found to promote a depletion in the levels of leaf carbohydrates by enhancing their dark respiratory rate and promoting their net photosynthetic rate the next day. These factors in turn contribute to the accumulation of individual biomass; this effect was not seen during periods of low precipitation. Moreover, nitrogen deposition also enhances the photosynthetic rate of L. chinensis except under low precipitation. Therefore, the photosynthetic rate of L. chinensis is highest during periods of elevated CO2, summer nocturnal warming, and high precipitation conditions and is lowest during periods of relative drought. These phenomena led to an overall photosynthetic rate primarily dependent on the levels of precipitation, assuming all the other factors were the same. Consequently, we hypothesize that elevated CO2levels, in combination with summer nocturnal warming and nitrogen deposition, advances biomass accumulation by enhancing carbon absorption under favorable water conditions, but that only elevated CO2can enhance carbon absorption under low precipitation conditions.(3) Elevated CO2has little effect on the output of daughter shoots and rhizomatous extensions under conditions of normal and high precipitation. However, elevated CO2did significantly increase the number of daughter shoots and rhizome length during periods of low precipitation. These results suggest that elevated CO2primarily contributes to the biomass of L. chinensis via carbon absorption of individuals rather than by enhancing their asexual reproduction capacity and that elevated CO2advances clonal growth under nitrogen deposition conditions. We also found that the effect of summer nocturnal warming on clonal growth mainly depends on water conditions. Results indicate that when precipitation levels are below baseline, summer nocturnal warming causes a slight decrease in the number and biomass of daughter shoots; these values increase with increasing precipitation. Taken together, summer nocturnal warming promotes biomass accumulation in L. chinensis as a result of net carbon absorption via photosynthetic compensation and enhanced vegetative propagation. Moreover, nitrogen deposition has very little effect on clonal growth under low precipitation conditions. Consequently, the clonal growth of L. chinensis is depended on the water condition when periods of elevated CO2, summer nocturnal warming, and nitrogen deposition occur simultaneously. (4) Both the biomass and photosynthetic rate of L. chinensis increase with increasing levels of precipitation. Furthermore, we found that an extension in the precipitation interval results in a slight decrease in the stomal conductance, photosynthetic rate, and aboveground biomass when total precipitation remains unchanged. Rainfall frequency has no significant effect on root biomass. Therefore, we conclude that the precipitation interval is clearly not as important as precipitation quantity on the growth and development of L. chinensis during the summer.In short, in the context of climate change (elevated CO2, summer nocturnal warming, nitrogen deposition, and changes in the precipitation pattern) we found precipitation to be the most important factor in a semiarid grassland ecosystem. We conclude that the current productivity of L. chinensis will either:(1) improve if precipitation levels continue at the current level and/or increase,(2) be maintained if they decrease up to40%, or (3) decrease significantly if they decline beyond40%.