| It is exacerbated by human activities, especially the burning of fossil fuels, the extensive use of farmland ecosystem nitrogen and continuous development of animal husbandry that the nitrogen input level into ecosystem increased.The response between plant growth and the increased atmospheric concentrations of nitrogen oxides has become a hot topic. This paper took the Stipa aliena as a study. The nitrogen adding experiment was made at The Haibei Alpine Meadow Ecosystem Research Station of CAS. After the determination of leaf nitrogen content, chlorophyll content, photosynthetic CO2response curve as well as leaf area index and other indicators, we studiedthe Stipa aliena response of different leaf photosynthesis under different levels of nitrogen treatment. Then we used the indicators affected by nitrogen adding to model the gross primary productivity (GPP) changes. In the end this paper made a statistics of the functional relationship between the maximum carboxylation rate of plant and leaf nitrogen content. The data support for accurate simulation of ecosystem productivity was provided. Main conclusions are as follows:(1) The atmospheric nitrogen deposition increase would affect carbon, nitrogen and chlorophyll content of leaves, photosynthetic rate and leaf area index. With increasing amount of nitrogen, the plant leaf nitrogen content would increase under the low and high nitrogen treatment conditions. The leaf nitrogen content showed a certain degree of variability uner the middle nitrogen treatment in different years. With respect to the change in leaf nitrogen content of plants, the carbon content was stable. Therefore the change of carbon-nitrogen ratio was negatively correlated with the change of leaf nitrogen content. The different types of nitrogen fertilizer treatments had a different affect on the leaf nitrogen content. The leaf nitrogen content with the ammonia nitrogen fertilizer applied was much higher than that with nitrate fertilizer. The change of the maximum carboxylation rate of plant leaves (Vcmax), different maximum electron transfer rate (Jmax), and triose phosphate transfer rate (TPU) were different with the nitrogen fertilizer treatment in different years. The maximum carboxylation rate and the maximum electron transfer rate respectively decreased16.12%and0.23%under nitrogen treatment conditions in2012. The value of other photosynthetic parameters all increased. The statistical analysis showed that Vcmax,25and Na had a good correlation.(2) GPP under different nitrogen conditions were simulated by photosynthesis model. Using the different Vcmax,25and Jmax,25under different nitrogen conditions simulated the GPP. The results showed that nitrogen treated year amount of GPP were higher than the control. The increases are16.27%(LN),6.21%(MN), and31.82%(HN). Using the Vcmax,25inferred from Vcmax,25-Na relationship to simulate GPP, the values were lower12.77%(LN),4.55%(MN),22.97%(HN) than the Vcmax,25observed. Using LAI values under different nitrogen conditions to simulate GPP, the results showed that the year amount of GPP increased under the LN and HN conditions. The increases are39.49%and47.89%. The total GPP would slightly decreased under MN condition. The decrease was0.09%. Using Vcmax,25、Jmax,25and LAI to simulate GPP, the results showed that the year amount of GPP was higher than the control under different nitrogen conditions The increases are60.98%(LN),6.10%(MN) and86.88%(HN). Under the GPP factor sensitivity analysis, it showed that the total comprehensive factor had a greatest impact on GPP. The value of LAI, Vcmax,25and Jmax,25under different nitrogen levels played a crucial role on the final GPP simulation. If selecting a single parameter to simulate will produce large errors. Determining the proportion of different parameter values under different nitrogen levels to simulate GPP would improve the accuracy of the simulation model.(3) The relationship between Vcmax,25and Na varied with plant functional type, and the average slopes ranged from16.29to50.25μmol CO2g N-1s-1. Deciduous trees generally showed higher slope and photosynthetic nitrogen use efficiency than evergreen trees due to their differences in leaf mass per area(LMA) and nitrogen allocation to Rubisco. Relationships between Vcmax,25nd Na had seasonal and annual variations. In the year without water stress, the highest value of slopes mostly appeared in spring or summer. The change of slope was related to seasonal variations in LMA and nitrogen allocation in Rubisco. The slope increased in drought seasons or years. The slope of the linear relationshipbetween Vcmax,25and Na for perennial needle leaf reduced due to the decrease in Rubisco content with elevated CO2. The leaf maximum carboxylation rate, nitrogen content, and the slope of their linear relationship increased with increment of nitrogen application rate. |
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