Effect Of Nitrogen And P Hosp Horus Addition On Belowground Net Primary Productivity Of Kobresia Pygmaea Meadow

The grassland ecosystem is an important part of the terrestrial ecosystem.The Qinghai-Tibet Plateau,which is known as the most beautiful"third pole in the world"on the earth,has a very rich grassland ecosystem.Kobresia pygmaea meadows are located in high-altitude areas of the Qinghai-Tibet Plateau.There are abundant species resources.Although the soil contains a large amount of organic nitrogen and phosphorus,its utilization rate is low and plant growth is restricted.In recent years,with the global climate change and frequent human activities,the deposition of nitrogen in the atmosphere has been increasingly intensified.These environmental changes have contributed to the increase of available nutrients in Kobresia pygmaea meadow soil.Previous studies on the effects of nitrogen and phosphorus additions on plant productivity have focused on typical grasslands and above-ground parts of plants.Due to the limitations of geographical environment and technical conditions,the study on alpine meadows and underground parts of plants is relatively insufficient.Therefore,this experimental study is based on the comprehensive observation and research station for the ecological environment of Naqu in the Qinghai-Tibet Plateau,and uses the classic in-growth method to estimate the belowground net primary productivity of Kobresia pygmaea meadow for four consecutive months in the 2019 growing season.The effects of different nitrogen and phosphorus addition levels on the belowground net primary productivity of Kobresia pygmaea meadow were discussed,and the effects of different nitrogen and phosphorus addition levels on underground net primary productivity at different depths were also concerned.The results showed that:（1）Nitrogen addition alone has a significant effect on the net primary productivity of Kobresia pygmaea meadow.Under N1 treatment(7.5 g N m^-2y^-1),the net underground primary productivity of plants can be improved under N2 treatment(15 gN m^-2y^-1)significantly reduces underground primary net productivity（2）Phosphorus alone has no significant effect on the net primary productivity of Kobresia pygmaea meadow,and the best improvement effect is P3 treatment(30 g P m^-2y^-1);（3）The interaction of different levels of nitrogen and phosphorus has a significant effect on the net primary productivity of Kobresia pygmaea meadow,of which the best treatment effect is N1P1(7.5 g N-7.5 g P m^-2y^-1);（4）Nitrogen addition in different months has a significant effect on the net primary productivity of Kobresia pygmaea meadow.Generally speaking,the net underground primary productivity in September will reach the maximum value compared with the other three months.（5）Regarding the influence of different depths in different months on the underground net primary productivity of Kobresia pygmaea meadow,the overall trend will increase with the month,the deeper the depth,the greater the underground net primary productivity.