| Under the background of global warming,the annual average surface temperature in China has increased significantly,and the warming rate is slightly higher than the global average in the same period,especially in alpine regions.As the most important limiting factor of vegetation growth and development,the change of temperature will have a profound impact on plant physiology and ecology.At the same time,in recent decades,with the intensification of agriculture and industry,the consumption of chemical fertilizers and fossil fuels has increased sharply,resulting in a rapid increase in atmospheric nitrogen deposition rate worldwide.At present,China has become a hot spot of global atmospheric nitrogen deposition,and the amount of nitrogen deposition may increase cumulatively for a long time,which seriously threatens the stability of ecosystem structure and function.Studies have shown that nitrogen is the basic component of many important organic compounds in plants,and its supply level directly affects the physiological process of plant metabolism?In this study,the temperature rise was taken as the breakthrough point,and the OTCs system was used to simulate the way of temperature increase and exogenous nitrogen addition.The response characteristics of photosynthetic pigment content,osmotic adjustment substances and antioxidant system of dominant species Kobresia humilis,Kobresia tibetica and Carex Moorcroft ii in alpine wet meadow of Qinghai-Tibet Plateau to short-term warming,nitrogen application and their interaction were analyzed.The adaptability of three plants to warming and nitrogen application was comprehensively evaluated by principal component analysis and membership function method,trying to clarify the impact of climate change on alpine wet meadow plants and its adjustment and adaptation mechanism,revealing the response modes and differences of the three plants to temperature rise,and laying a theoretical foundation for predicting the impact of future climate change on alpine wet meadow plants and even the whole terrestrial ecosystem.The main conclusions are as follows:(1)under low warming,chlorophyll a of the three plants increased significantly(p<0.05),chlorophyll b did not change significantly(p>0.05),and carotenoids decreased significantly.Under high warming,chlorophyll b and carotenoids of three plants decreased significantly,chlorophyll a of Kobresia humilis and Carex Moorcroft ii decreased significantly,but Kobresia tibetica had no significant change.Under low nitrogen level,chlorophyll a of three kinds of plants increased significantly and carotenoids decreased significantly compared with the treatment without nitrogen addition,while chlorophyll b of three kinds of plants changed differently,Kobresia humilis did not change significantly,Kobresia tibetica increased significantly,and Carex Moorcroft ii decreased significantly.Under high nitrogen level,only Kobresia humilis chlorophyll a did not change significantly,while Kobresia tibetica and Carex Moorcroft ii increased significantly,while Kobresia tibetica chlorophyll b increased significantly,and carotenoids of the three plants decreased significantly.Under low nitrogen level,the chlorophyll content of leaves of three kinds of plants under low warming was significantly higher than that under no warming and high warming Under no nitrogen addition and high nitrogen treatment,the chlorophyll content of three kinds of plants decreased in high warming compared with low temperature treatment.Chlorophyll content of Kobresia humilis and Kobresia tibetica is extremely sensitive to nitrogen addition under the same warming condition,and chlorophyll content of three kinds of leaves reaches the maximum under low warming and high nitrogen treatment.In this study,it was found that under the same warming(nitrogen addition)treatment and different nitrogen addition(warming)treatments,the change trend of carotenoid content in leaves of three kinds of plants was different.(2)Under low warming,there was no significant change in proline and soluble protein of Kobresia humilis compared with Carex Moorcroft ii without warming,but the proline and soluble protein of Kobresia tibetica increased significantly,but there was no significant change in soluble sugar.Under high warming,the amino acids of the three plants increased significantly,while the soluble sugar and protein of Kobresia humilis and Carex Moorcroft ii decreased significantly,while the soluble sugar and protein of Kobresia tibetica increased significantly,but there was no significant change.Under low nitrogen level,proline content of three kinds of plants decreased significantly,soluble sugar content of Kobresia tibetica and Carex Moorcroft ii increased significantly,while soluble sugar content of Kobresia humilis decreased significantly,and soluble protein content of three kinds of plants increased significantly.Under high nitrogen level,proline content of three plants decreased significantly,and soluble sugar content of Kobresia humilis and Kobresia tibetica decreased significantly,while soluble sugar content of Carex Moorcroft ii had no significant change.Soluble protein of Kobresia humilis had no significant change,Kobresia tibetica increased significantly,while Carex Moorcroft ii decreased significantly.Under the treatment without nitrogen addition,the proline content of the leaves of the three plants reached the maximum value under the treatment of high warming,and was significantly higher than that under the treatment of no warming and low warming;Under low nitrogen treatment,the proline content of three kinds of plants has different trends.With the increase of temperature,the proline content of Kobresia humilis decreases,while that of Kobresia tibetica increases first and then decreases.However,under the interaction of low warming and low nitrogen addition,the proline content of three kinds of plants is not significantly different from that of the treatment without nitrogen addition,even significantly lower than that of the treatment without nitrogen addition.Without nitrogen addition,the soluble sugar content of Kobresia humilis and Carex qinghaiensis under warming was significantly lower than that under no warming,while that of Kobresia tibetica under high warming was significantly higher than that under no warming and low warming.Under low nitrogen and high nitrogen treatments,the soluble sugar content of the three plants was maintained at normal treatment or significantly lower than that without warming.Under the same treatment conditions,the change trend of soluble protein content of Kobresia tibetica and Carex Moorcroft ii was the same.Under the treatment without nitrogen addition,both plants reached the maximum value under the low warming.Under nitrogen addition treatment,the soluble protein content of Kobresia tibetica and Carex Moorcroft ii reached the maximum under high warming.Under no nitrogen addition treatment,the soluble protein of Kobresia humilis decreased with the increase of temperature,and reached the minimum value of experimental treatment under high temperature increase treatment.(3)Under low warming,the malondialdehyde of Kobresia humilis decreased significantly compared with Carex Moorcroft ii without warming,while Kobresia tibetica had no significant change.Under high warming,malondialdehyde(MDA)of Kobresia humilis and Kobresia tibetica decreased significantly,while Carex Moorcroft ii had no significant change.Peroxidase activity and superoxide dismutase of three plants showed different trends under different warming.Under low nitrogen level,the malondialdehyde content of Kobresia humilis and Carex Moorcroft ii decreased significantly compared with the treatment without nitrogen addition,while the peroxidase activity of Kobresia humilis and Carex Moorcroft ii increased significantly,while that of Kobresia tibetica decreased significantly,while the superoxide dismutase activity of Kobresia humilis and Carex Moorcroft ii did not change significantly,while Carex Moorcroft ii increased significantly.Under high nitrogen level,malondialdehyde content of Kobresia humilis and Kobresia tibetica decreased significantly,but there was no significant change,peroxidase activity of Kobresia humilis and Carex Moorcroft ii increased significantly,while that of Kobresia tibetica decreased significantly.Malondialdehyde content of the three plants reached the maximum under the interaction of high temperature increase and high concentration nitrogen addition.Under no nitrogen addition treatment,the malondialdehyde content of Kobresia tibetica and Carex Moorcroft ii reached the maximum under low temperature increase treatment,while Kobresia humilis decreased significantly under low temperature increase treatment compared with no temperature increase.Under no warming and low warming,the malondialdehyde content of the three plants was extremely sensitive to nitrogen addition,and the low concentration nitrogen addition did not have a positive effect on the plants,but aggravated the stress to a certain extent;Under high warming,high concentration of nitrogen promoted the synthesis of antioxidants and antioxidant enzymes in plants,which made the malondialdehyde content of the three plants significantly lower than that of low concentration of nitrogen.Under the same nitrogen treatment,the peroxidase activity of Kobresia humilis reached the maximum under low warming,and the peroxidase activity under high warming was higher than that under no warming,while the peroxidase activity of Kobresia tibetica and Carex qinghaiensis reached the maximum under low warming and high nitrogen treatment and high warming and low nitrogen treatment respectively.Under nitrogen treatment,superoxide dismutase(SOD)of Kobresia tibetica and Carex Moorcroft ii increased with the increase of temperature.(4)according to different conditions,the adaptability of the three plants to warming is as follows: Kobresia humilis > Carex Moorcroft ii > Kobresia tibetica;Under the warming condition,Carex qinghaiensis > Kobresia humilis > Kobresia tibetica.The adaptability of the three plants to nitrogen application,from strong to weak,did not change under different nitrogen addition conditions.The order was Kobresia humilis > Carex Moorcroft ii > Kobresia tibetica. |
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