The Responses Of Belowground Net Primary Production And Biomass Allocation To Precipitation On The Songnen Grassland

Grassland ecosystem is an important ecological type that carbon sequestration accounts for one third of total terrestrial ecosystems carbon. Therefore grassland ecosystem plays importance role in carbon cycle and climate mediation. The most primary production of photosynthesis is allocated to root in perennial grassland ecosystems and root biomass is usually 2-5 times higher than aboveground biomass. The belowground net primary productivity (BNPP) is an important ecological variable to evaluate structure and function of grassland ecosystem. However the study of the response of BNPP to precipitation change is very weak in grassland ecosystems. Songnen grassland is located at Northest part of China and it is vital area for keeping regional climate and domesticated animal production. It is considered as national ecological security zone in the National Eleventh five-year Plan. Therefore quatification of BNPP and biomass allocation under climate change scenario is very important for accurate evaluation cological value of songnen grassland, e. g. potential reserves of grassland soil organic matter.Our objectives are as follows: How does plant net primary production (aboveground and belwoground) respond to precipitation change; How does biomass allocation respond to precipitation change.The experiment was conducted in Songnen grassland ecosystem research staion, southwest Changling county, Jilin Province. three rainfall treatments (30% increase of precipitation, 30% decrease of precipitation and the control) were cosidered. Aboveground (ANPP) and belowground net primary production, species composition and, soil water content were determined during the growing season in 2009.The main results showed:1) There is posivtive relationship between precipition and ANPP, increased 30% precipitation enhances ANPP by 56% and decreased 30% of precipitation reduces ANPP by 16%;2) There is also posivtive relationship between precipition and BNPP, increased 30% precipitation can enhance BNPP by 65% and decreased 30% of precipitation can reduce BNPP by 21.5%;3) Increased 30% precipitation significantly increased biomass allocation, whereas decreased 30% precipitation had no significant effects on biomass allocation.According to IPCC (2007) prediction, precipitation will increase in mid-latitude area in the next 50 years. From our results, increasing precipitation enhanced both above- and belowground net primary production which suggested Songnen grassland will benefit from plant and animal production point of view.