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The paper selected three ecosystems, alpine meadow, swamp meadow and sandy grassland of Beiluhe in the hinterland of Qinghai-Tibet Plateau as the research object. Stable carbon isotope technique was used to determine the stable carbon and nitrogen isotope values (δ13C,δN /‰) of the major species of in the three different ecosystems from May to October, as well as the plant biomass, leaf weight, root weight, non-structural carbohydrates of leaf and non-structural carbohydrates of root.δ13C,δN /‰, compositive characteristics of non-structural carbohydrate and seasonal variation and its relationship with environmental factors of the major plants in different ecosystems were analysed in order to clarify the main factors infecting carbon, nitrogen isotopes non-structural carbohydrates of main plant species of the interior area of Tibetan Plateau. The research is designed to provide theoretical support for forecast of the responsive simulation of alpine grassland the carbon cycle under the future conditions of climate change in China and world. It is also to provide a scientific basis for the regional livestock management and sustainable development and ecological and environmental protection. The results show that:1.From early May to late October, leaf weight of the main plant species in the three kinds of ecosystems, meadow, swamp meadow and sandy grassland has gained to the maximum in early October; root weight increased gradually after the performance of the line gradually decreased; biomass of the three different ecosystems: sandy grassland>Alpine>swamp meadow; leaf weight: Alpine meadow>desertified grassland > swamp meadow; root weight: sandy grassland > Alpine > swamp meadow ; leaf / root ratio: Alpine meadow>swamp meadow>desertified grassland, mainly because of sandy grassland soil moisture is relatively low, and well-developed deep roots help absorb moisture, but also reflect that the water affect photosynthetic products distribution in the organs, which allocated more to roots, and less to leaves.2. Leaves of main plant species in alpine meadowδ13C values ranged between -27.99‰~ -24.73‰;δ13C of leaves of swamp meadow species ranged between -28.76‰~ -24.58‰;δ13C of leaves of the main plant species in the desertification of grassland ranged between -27.84‰~ -23.81‰. Species of meadow, swamp meadow and sandy grassland belonged to the main types of C3 photosynthetic pathway, and they all belonged to C3 plants.3. From May to September, average value ofδ13C, precipitation, 2m humidity, 20 cm soil water content were negatively correlated, with 2m temperature negatively correlated in the alpine meadow.The precipitation-related is not strong in marsh and meadow and 2m humidity, 20 cm soil water content were negatively correlated (p<0.05) with 2m temperature negatively related; in desertified grassland, precipitation also show correlation is not strong, and 2m humidity, 20 cm soil water content were negatively correlated (p<0.05) with 2m temperature negatively related. After analysis and comparison ofδ13C of the plants in the three ecosystem, although soil moisture were much different in the three kinds of ecosystems, the average value ofδ13C in the three ecosystem are -26‰, while the three ecosystems are very close because temperature, rainfall were little different. Through the analysis of environmental factors, it can be seen that in three different ecosystemsδ13C was influenced by precipitation, while mainly affected by temperature, which may be due to seasonal frozen soil temperature, permafrost melting layer to expand, thereby increasing soil moisture, plant growth in the region to provide sufficient water the studying area.4. The tested plantδN /‰in the distribution of interval in alpine meadow was between -1.418‰~ 11.158‰, in marsh meadow between -1.713‰~ 8.666‰, in desertification of grassland between -3.458‰~ 3.203‰, averaged 2.7443‰, 3.3233‰, -0.0764‰, which showsδN /‰is their common genetic traits and environmental factors combined.5. From May to September, in alpine meadow,δN /‰, 2m humidity and 2m temperature, were significantly positively related (p<0.05) with 20 cm soil water content related (p>0.05),δN /‰in swamp meadow and 20 cm soil water content were related, but did not reach significant level (p>0.05). And 2m temperature and other environmental factors were not strongly related (p> 0.05). In the sandy grasslandsδN /‰was negatively related with precipitation, but did not reach significant level (p>0.05). And temperature and other environmental factors is not strongly related (p>0.05). It can be seen thatδN/‰in the alpine meadow and marsh was not influenced by precipitation, while the principle of sandy grassland affected by precipitation. Comprehensive comparison values ofδN /‰in the three ecosystems was mainly affected by moisture, especially the impact of soil moisture.6. Starch, total soluble sugar, fructose and sucrose content showed that higher content in leaf than in root and plant roots in cold regions were library of the non-structural carbohydrate. Total soluble sugar, sucrose and fructose in the roots and leaves of different ecological changes are consistent, that is, sandy grassland>swamp meadow>alpine meadow. Leaf starch content: sandy prairie>marsh meadow>alpine meadow, and root starch content: Alpine meadow>swamp meadow>sandy grassland. Moderate water stress to plant leaves and roots increased soluble sugar content, starch content was significantly reduced. Starch content of root in decertified grassland was lower which shows that under the conditions of cold regions, some water restrictions accelerated the transformation of the roots of sugar, and also changed the storage form of sugar in order to maintain cell osmotic adjustment.7. From May to September, in three different ecosystems, for the NSC content of plant roots, NSC of the roots of plants in alpine meadow and 10cm soil moisture content were significantly positively related (p<0.05) and precipitation are related but did not reach significance level (p>0.05) and 2m humidity, 20 cm soil water content, 2m temperature dependence were not strong ly (p>0.05). NSC content of leaf moisture , 2m humidity, 10cm of soil moisture, 20cm of soil water content, 2m temperature were significantly positively related (p>0.05) and precipitation correlation was not strong (p>0.05). NSC content of plant roots of swamp meadow and the precipitation were significantly positively related (p<0.05) and 2m humidity, 10cm of soil water content, 20 cm soil water content, 2m temperature dependence is not strong (p>0.05), NSC content of leaf and precipitation, 2m humidity was negatively correlated (p<0.05) with 2m temperature significantly negatively related (p<0.05) and 10cm of soil water content, 20 cm soil moisture correlation is not strong.NSC content of plant roots and precipitation in the desertification of grassland, 20 cm soil water content, 2m humidity, 2m temperature were significantly positively related (p<0.05) and 10cm soil moisture correlation was not strong (p>0.05), and NSC content in plant leaves and precipitation were significantly negatively related (p<0.05), and 20cm soil moisture was a significantly positively related (p<0.05); 2m humidity, 2m temperature were related but did not reach significance level (p>0.05); 10cm soil moisture correlation is not strong (p>0.05). It can be seen that in the Qinghai-Tibet Plateau, water and temperature affect the plant roots, leaves NSC content of the dominant factors, which is also the result of many other environmental factors of climate interaction.
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