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In the present study, the response of spring wheat production and water use efficiency (WUE) to the elevated CO2 concentrations was investigated based on the open-top chamber (OTC) experiment platform in Dingxi, a typical semi-arid area. Three different CO2 concentrations (390 µmol·mol-1, 480 µmol·mol-1 and 570 µmol·mol-1) were involved. The results showed that the air temperature above plant canopy increased and the soil temperature at depth of 10 cm decreased by elevated CO2. The increased CO2 concentration substantially enhanced the total and each component biomass. The aboveground dry mass under the increased CO2 concentrations (480 and 570 µmol·mol-1) was increased by 20.6% and 41.5%, respectively, and the total dry mass was increased by 19.3% and 39.6%, respectively. The biomass enhacement was mainly due to the increases of dry mass of stems and leaves, which was strongly related to the material production capacity during the middle growth stage. The root/shoot ratio under the increased CO2 concentrations (480 and 570 µmol·mol-1) was decreased by 7.3% and 11.8%, respectively, indicating that the elevated CO2 affected the dry matter accumulation of aboveground more than that of belowground. The yields of spring wheat under the increased CO2 concentrations (480 and 570 µmol·mol-1) were higher than that of the control by 8.9% and 19.9%, respectively, mainly due to the increase of grains per spike. The long-term effect of elevated CO2 concentration on the photosynthesis of spring wheat was not obvious. The photosynthetic rate significantly increased, the transpiration rate decreased and the evapotranspiration reduced with the increases of CO2 concentration. WUE at the leaf, population, and yield levels increased under elevated CO2 concentration, with the increase range of WUE being the largest at the population level and the lowest at the yield level.

[Effects of air temperature increase and precipitation change on grain yield and quality of spring wheat in semiarid area of Northwest China].

In order to predict effects of climate changing on growth, quality and grain yields of spring wheat, a field experiment was conducted to investigate the effects of air temperature increases (0 °C, 1.0 °C, 2.0° C and 3.0°) and precipitation variations (decrease 20%, unchanging and increase 20%) on grain yields, quality, diseases and insect pests of spring wheat at the Dingxi Arid Meteorology and Ecological Environment Experimental Station of the Institute of Arid Meteorology of China Meteorological Administration (35°35' N ,104°37' E). The results showed that effects of precipitation variations on kernel numbers of spring wheat were not significant when temperature increased by less than 2.0° C , but was significant when temperature increased by 3.0° C. Temperature increase enhanced kernel numbers, while temperature decrease reduced kernel numbers. The negative effect of temperature on thousand-kernel mass of spring wheat increased with increasing air temperature. The sterile spikelet of spring wheat response to air temperature was quadratic under all precipitation regimes. Compared with control ( no temperature increase), the decreases of grain yield of spring wheat when air temperature increased by 1.0°C, 2.0°C and 3.0°C under each of the three precipitation conditions (decrease 20%, no changing and increase 20%) were 12.1%, 24.7% and 42.7%, 8.4%, 15.1% and 21.8%, and 9.0%, 15.5% and 22.2%, respectively. The starch content of spring wheat decreased and the protein content increased with increasing air temperature. The number of aphids increased when air temperature increased by 2.0°C , but decreased when air temperature increased by 3.0°CT. The infection rates of rust disease increased with increasing air temperature.

[Effects of increasng field temperature on growth, development and yield of spring wheat in semi-arid area].

A field infrared temperature-increasing simulation experiment was conducted to investi- gate the effects of air temperature increases (0, 1 and 2 °C ) on growth, development and yield of spring wheat at the Dingxi Arid Meteorology and Ecological Environment Experimental Station of the Institute of Arid Meteorology of China Meteorological Administration. The results showed that the growth period of spring wheat was shortened by 7-11 d when the temperature increased by 1-2 °C. The plant height and leaf area index increased at early growth stage, decreased after entering the jointing stage, and warming 2 °C had a higher effect than warming 1 °C. Warming treatment induced an obvious decrease in chlorophyll content, especially from late grain filling stage to milk ripe stage. Compared with the control, increasing temperature by 1-2 °C decreased the spring wheat yield by 25.4%-45.5%, mainly due to obvious decreases in number of grains and grain mass per panicle. Water consumption of 0-100 cm soil horizons increased with the increase of temperature, while the variation tendency of water consumption of 100-160 cm soil horizons was not obvious.

[Characteristics of evapotranspiration and crop coefficient of agroecosystems in semi-arid area of Loess Plateau, Northwest China].

Evapotranspiration (ET) is an important component of ground surface energy balance and water balance, and closely related to water cycle. By using eddy covariance technique, this paper studied the ET characteristics of agroecosystems in the semi-arid area of Loess Plateau in growth season (from April to September), 2010, and analyzed the relationships between crop coefficient and environmental factors. During the observation period, the diurnal variation of latent heat flux (LE) in each month was similar to single-peak curve, and the peak value (151.4 W x m(-2)) occurred in August. The daytime energy partitioning manner showed a significant seasonal variation, with LE/R(n) < H/R(n) (R(n) was net radiation, and H was sensible heat flux) from April to June, and LE/R(n) > H/R(n) from July to September. The daily ET rate also showed a significant seasonal variation, with the maximum of 4.69 mm x d(-1). The wind speed (W(s)), relative humidity (RH), soil water content (theta), and atmospheric vapor pressure deficit (D) were the major factors affecting the crop coefficient K(c) which was exponentially decreased with increasing W(s), exponentially increased with increasing RH and theta, and linearly decreased with increasing D.

[Effects of climate warming on oil flax growth and water use efficiency in semi-arid region of Loess Plateau, Northwest China].

By using the site-specific observation data of oil flax growth and related meteorological records in semi-arid region of Loess Plateau, this paper studied the effects of climate change on the oil flax growth, and analyzed the relationships between the oil flax water use efficiency and meteorological condition. In this region, the annual precipitation displayed a decreasing trend, and its climatic trend rate was -15.80 mm (10 a)(-1), with an annual periodic change of 3 a and 6 a, whereas the annual air temperature had an increasing trend, and its climatic trend rate was 0.36 degrees C (10 a)(-1). In crop growth period, the aridity index displayed a marked increasing trend, its climatic trend rate was 0.12 (10 a)(-1), and the aridity tendency was more obvious from the beginning of 1990s to the year 2009. From sowing to maturation, oil flax needed 120-150 d, 1700-2100 degrees C d of > or = 0 degrees C accumulated temperature, 200-250 mm precipitation, and 1000-1300 h sunshine hours. The main meteorological factors affecting the oil flax growth in the region were air temperature and precipitation. The increase of air temperature shortened the prophase vegetative growth stage, whereas the increase of air temperature and the decrease of precipitation extended the reproductive growth stage, causing the extension of the whole growth period of the oil flax. The air temperature in the oil flax whole growth period except at seeding stage and maturing stage had negative effect on the yield formation, being more obvious at squaring stage, whereas the precipitation in the whole growth period except at blooming stage had positive effect on the yield formation, being more obvious at seeding stage. The water use efficiency of the oil flax was significantly positively correlated with the air temperature and sunshine hours at seeding stage as well as the aridity index from squaring stage to maturing stage, and negatively correlated with the precipitation from squaring stage to maturing stage. In the study region, the aridity index from May to July was the key factor affecting the water use efficiency of oil flax.

[Effects of climate change on potato growth in semi-arid region of Loess Plateau, China].

Based on the 1988-2008 located observation and 2007-2008 encrypted observation of potato growth and the 1957-2008 meteorological observation in semi-arid region of Loess Plateau, this paper studied the effects of climate change on the potato growth in this region. In 1957-2008, the annual precipitation in this region had a descending trend, with a linear fitting rate of the annual precipitation change curves being - 13.359 mm x (10 a)(-1), while the annual mean temperature displayed an ascending trend, with a linear fitting rate of the annual mean temperature change curves being 0.239 degrees C x (10 a)(-1). During potato growth period, the aridity index displayed a marked ascending trend, and the linear fitting rate of the aridity index change curves was 0.102 x (10 a)(-1). The growth rate of potato tuber became faster from the 96th day after sowing, reached the maximum on the 110th day, and turned slower from the 124th day. The interval from sowing to seedling emergence was shortened by 1-2 d x (10 a)(-1), and that from inflorescence formation to reaping and of whole growth period was lengthened by 9-10 d x (10 a) (-1). In the study region, climate warming shortened the vegetative growth stage, but lengthened the reproductive growth stage and whole growth period of potato.

[Effects of air temperature change on spring wheat growth at different altitudes in northwest arid area].

Based on the 1981-2006 observation data from agricultural meteorological stations at Minle (high altitude) and Zhangye (low altitude) in northwest arid area, the effects of air temperature change at the two altitudes on the growth and yield of spring wheat were studied. It was shown that during study period, the air temperature at the two altitudes had an increasing trend, and the increment was greater at high altitude than at low altitude. At high altitude, the growth duration of spring wheat shortened but the grain yield increased; while at low altitude, the growth duration shortened and the yield decreased. When the mean daily air temperature during spring wheat growth period increased by 1 degrees C, the growth duration shortened by 8.3 days at high altitude and by 3.8 days at low altitude. The growth duration and grain yield of spring wheat at high altitude had a slight increase when the maximum air temperature during growth period was below 30.4 degrees C, but decreased when the maximum air temperature was above 30.4 degrees C.

[Responses of subalpine meadow Poa botryoides to climate change].

Based on the field plot observation and related meteorological data, the effects of climate change in 1985-2005 on the growth and development of subalpine meadow Poa botryoides in Maqu County of Gansu Province were analyzed. The results showed that during study period, the annual precipitation in the Maqu County had a decreasing trend, with a rate of -9.895 mm x (10 a)(-1) and a cycle of 3 years, while the annual air temperature had an increasing trend, with a rate of 0.341 degrees C x (10 a)(-1). The aridity index of P. botryoides in growth season had an obvious increasing trend, with a rate of 0.036 x (10 a)(-1), and the tendency was more markedly from the beginning of the 1990s to 2005. The period from reviving to ripeness of P. botryoides was 140-150 d, and the requirements of accumulated temperature above 0 degree C, precipitation, and sunshine duration in this period were 1000 degrees C-1200 degrees C, 400-450 mm, and 1000-1100 h, respectively. The growth rate of P. botryoides turned to higher at 54 d after reviving, reached the highest at 80 d after reviving, and became lower at 104 d after reviving. Under the effects of climate warming, the phenophase of P. botryoides was advanced by 15 d x (10 a)(-1) at heading stage, 7-8 d x (10 a)(-1) at flowering stage, 8-9 d x (10 a)(-1) at ripeness stage, and 3 d x (10 a)(-1) at withering stage. Climate change made the P. botryoides yield in study area have greater variation and higher unsteadiness.