Global warming has led to significant vegetation changes especially in the past 20 years. Hulun Buir Grassland in Inner Mongolia, one of the world's three prairies, is undergoing a process of prominent warming and drying. It is essential to investigate the effects of climatic change (temperature and precipitation) on vegetation dynamics for a better understanding of climatic change. NDVI (Normalized Difference Vegetation Index), reflecting characteristics of plant growth, vegetation coverage and biomass, is used as an indicator to monitor vegetation changes. GIMMS NDVI from 1981 to 2006 and MODIS NDVI from 2000 to 2009 were adopted and integrated in this study to extract the time series characteristics of vegetation changes in Hulun Buir Grassland. The responses of vegetation coverage to climatic change on the yearly, seasonal and monthly scales were analyzed combined with temperature and precipitation data of seven meteorological sites. In the past 30 years, vegetation coverage was more correlated with climatic factors, and the correlations were dependent on the time scales. On an inter-annual scale, vegetation change was better correlated with precipitation, suggesting that rainfall was the main factor for driving vegetation changes. On a seasonal- interannual scale, correlations between vegetation coverage change and climatic factors showed that the sensitivity of vegetation growth to the aqueous and thermal condition changes was different in different seasons. The sensitivity of vegetation growth to temperature in summers was higher than in the other seasons, while its sensitivity to rainfall in both summers and autumns was higher, especially in summers. On a monthly-interannual scale, correlations between vegetation coverage change and climatic factors during growth seasons showed that the response of vegetation changes to temperature in both April and May was stronger. This indicates that the temperature effect occurs in the early stage of vegetation growth. Correlations between vegetation growth and precipitation of the month before the current month, were better from May to August, showing a hysteresis response of vegetation growth to rainfall. Grasses get green and begin to grow in April, and the impacts of temperature on grass growth are obvious. The increase of NDVI in April may be due to climatic warming that leads to an advanced growth season. In summary, relationships between monthly-interannual variations of vegetation coverage and climatic factors represent the temporal rhythm controls of temperature and precipitation on grass growth largely.

From July 2008 to August 2008, 72 leaf samples from 22 species and 81 soil samples in the nine natural forest ecosystems were collected, from north to south along the North-South Transect of Eastern China (NSTEC). Based on these samples, we studied the geographical distribution patterns of vegetable water use efficiency (WUE) and nitrogen use efficiency (NUE), and analyzed their relationship with environmental factors. The vegetable WUE and NUE were calculated through the measurement of foliar δ¹³C and C/N of predominant species, respectively. The results showed: (1) vegetable WUE, ranging from 2.13 to 28.67 mg C g^-1 H₂O, increased linearly from south to north in the representative forest ecosystems along the NSTEC, while vegetable NUE showed an opposite trend, increasing from north to south, ranging from 12.92 to 29.60 g C g^-1 N. (2) Vegetable WUE and NUE were dominantly driven by climate and significantly affected by soil nutrient factors. Based on multiple stepwise regression analysis, mean annual temperature, soil phosphorus concentration, and soil nitrogen concentration were responding for 75.5% of the variations of WUE (p<0.001). While, mean annual precipitation and soil phosphorus concentration could explain 65.7% of the change in vegetable NUE (p<0.001). Moreover, vegetable WUE and NUE would also be seriously influenced by atmospheric nitrogen deposition in nitrogen saturated ecosystems. (3) There was a significant trade-off relationship between vegetable WUE and NUE in the typical forest ecosystems along the NSTEC (p<0.001), indicating a balanced strategy for vegetation in resource utilization in natural forest ecosystems along the NSTEC. This study suggests that global change would impact the resource use efficiency of forest ecosystems. However, vegetation could adapt to those changes by increasing the use efficiency of shortage resource while decreasing the relatively ample one. But extreme impacts, such as heavy nitrogen deposition, would break this trade-off mechanism and give a dramatic disturbance to the ecosystem biogeochemical cycle.

On the Tibetan Plateau, the alpine meadow is the most widespread vegetation type. The alpine meadow has a low biological productivity and low vegetation coverage in the growing season. The daytime NEE between the atmosphere and the alpine meadow ecosystem was influenced by solar radiation. To analyze the characteristics of change in NEE and to calculate the parameters related to photosynthesis and respiration in different solar radiation environments, the NEE measurements were taken in Damxung from July to August in 2003, 2004, 2005 and 2006 using the eddy covariance technique. Solar radiation was grouped into three levels according to the net radiation, which was more than 155 W m^-2 d^-1 on clear days, 144±5 W m^-2 d^-1 on partly cloudy days and less than 134 W m^-2 d^-1 on cloudy days. The diurnal relationships between NEE and PAR varied with differences in solar radiation, which was a rectangular hyperbola form on clear days, two different concave curves on partly cloudy days and an irregular triangle form on cloudy days. The mean CO₂ absorption rate showed a decreasing trend with increasing solar radiation. The daytime absorption maximum occurred around 10:00 on clear days with an average of slightly less -0.2 mg m^-2 d^-1, around 11:00 on partly cloudy days with an average of about -0.2 mg m^-2 d^-1, and around 12:00 on cloudy days with an average of about -0.25 mg m^-2 d^-1. As solar radiation increased, the A_max and the Q₁₀ decreased. However, the R₁₀ increased and the maximum of the α occurred on partly cloudy days. The optimum net solar radiation was about 134-155 W m^-2 d^-1, which induced a PAR of about 1800-2000 μmol m^-2 s^-1 and soil temperature at a depth of 5 cm of about 14℃. Therefore, on the Tibetan Plateau, the alpine meadow ecosystem will have a higher carbon absorption potential while solar radiation decreases in the future.

Crop potential productivity is a key index of scientifically appraising crop production and land population-supporting capacity. This study firstly simulated the potential and waterlimited yield of summer maize in the Beijing-Tianjin-Hebei (BTH) region using WOFOST model with meteorological data of 40 years, and then analyzed yield gaps between the actual and potential yield based on statistical data at county level. The potential and water-limited yield of summer maize in the BTH region is 6854-8789 kg/hm² and 6434-8741 kg/hm², and the weighted average for whole region is 7861 kg/hm² and 7185 kg/hm², respectively. The simulated yields gradually decrease from northeast to southwest with changes in climatic conditions particularly temperature and precipitation. Annual variation of potential yield is higher in the central and southern parts than the northeastern part. Compared to potential yield, the water-limited yield has higher coefficient of variation (CV), because of precipitation effects. The actual yield of summer maize was 2537-8730 kg/hm², regionally averaged at 5582 kg/hm², about 70% of the potential yield, implying that the region has room to increase the yield by improving crop management and irrigation systems.