Changes in vegetation phenology are key indicators of the response of ecosystems to climate change.Therefore,knowledge of growing seasons is essential to predict ecosystem changes,especially for regions with a fragile...Changes in vegetation phenology are key indicators of the response of ecosystems to climate change.Therefore,knowledge of growing seasons is essential to predict ecosystem changes,especially for regions with a fragile ecosystem such as the Loess Plateau.In this study,based on the normalized difference vegetation index(NDVI) data,we estimated and analyzed the vegetation phenology in the Loess Plateau from 2000 to 2010 for the beginning,length,and end of the growing season,measuring changes in trends and their relationship to climatic factors.The results show that for 54.84% of the vegetation,the trend was an advancement of the beginning of the growing season(BGS),while for 67.64% the trend was a delay in the end of the growing season(EGS).The length of the growing season(LGS) was extended for 66.28% of the vegetation in the plateau.While the temperature is important for the vegetation to begin the growing season in this region,warmer climate may lead to drought and can become a limiting factor for vegetation growth.We found that increasedprecipitation benefits the advancement of the BGS in this area.Areas with a delayed EGS indicated that the appropriate temperature and rainfall in autumn or winter enhanced photosynthesis and extended the growth process.A positive correlation with precipitation was found for 76.53% of the areas with an extended LGS,indicating that precipitation is one of the key factors in changes in the vegetation phenology in this water-limited region.Precipitation plays an important role in determining the phenological activities of the vegetation in arid and semiarid areas,such as the Loess Plateau.The extended growing season will significantly influence both the vegetation productivity and the carbon fixation capacity in this region.展开更多
Research for changes of soil water and salt is an important content of land sciences and agriculture sciences in arid and semi arid regions. In this paper, sampling in actual agricultural fields, laboratory analysis o...Research for changes of soil water and salt is an important content of land sciences and agriculture sciences in arid and semi arid regions. In this paper, sampling in actual agricultural fields, laboratory analysis of soil samples and statistical analysis methods are used to quantitatively analyze soil salinity changes under different ir- rigation methods throughout the cotton growing season in Shihezi reclamation area. The results show that irrigation methods play an important role in soil salt content in the surface soil （0-20 cm） and sub-deep soil （40-60 cm）, fol- lowed by deep soil layer （60-100 cm） and root soil layer （20-40 cm）. Furrow irrigation yields the maximum soil salt content in deep layer （60-100 cm） or sub-deep layer （40-60 cm） and the maximum salinity occurs in the first half of the cotton growing season （June or earlier）. In contrast, drip irrigation yields the maximum soil salinity in the root layer （20-40 cm） or sub-deep （40-60 cm）, and this usually appears in the second half growing season （July or af- ter）. The ratio of chloride ion to sulfate ion （Cl-/SO2- 4） and its change in the soil are on the rise under furrow irrigation while the value first increased and then decreased with a peak point in June under drip irrigation. This suggests that furrow irrigation may shift the type of soil salinization to chloride ion type moreso than drip irrigation. Potassium and sodium ion contents of the soil show that soil sodium＋potassium content will drop after the first rise under furrow irrigation and the value is manifested by fluctuations under drip irrigation. Potassium＋sodium content change is relatively more stable in the whole cotton growth period under irrigation methods. The maximum of sodium and potassium content of the soil usually occur in deep soil layer （60-100 cm） or sub-deep soil layer （40-60 cm） in most sample points under furrow irrigation while it is inconsistent in different sample points under drip irrigation. A non- parametric test for paired samples is used to analyze differences of soil salt content under different irrigation methods. This analysis shows that the impact of irrigation on soil salinity is most significant in July, followed by August, June, May, and April in most sample points. The most significant impact of irrigation methods occurs in the surface soil layer （0-20 cm）, followed by deep layer （60-100 cm）, root layer （20-40 cm） and sub-deep （40-60 cm）. These conclusions will be benefitial for mitigation of soil salinization, irrigation and fertilization and sustainable land use.展开更多
基金supported by the“Strategic Priority Research Program-Climate Change:Carbon Budget and Relevant Issues’’of the Chinese Academy of Sciences(Grant No.XDA05060104)
文摘Changes in vegetation phenology are key indicators of the response of ecosystems to climate change.Therefore,knowledge of growing seasons is essential to predict ecosystem changes,especially for regions with a fragile ecosystem such as the Loess Plateau.In this study,based on the normalized difference vegetation index(NDVI) data,we estimated and analyzed the vegetation phenology in the Loess Plateau from 2000 to 2010 for the beginning,length,and end of the growing season,measuring changes in trends and their relationship to climatic factors.The results show that for 54.84% of the vegetation,the trend was an advancement of the beginning of the growing season(BGS),while for 67.64% the trend was a delay in the end of the growing season(EGS).The length of the growing season(LGS) was extended for 66.28% of the vegetation in the plateau.While the temperature is important for the vegetation to begin the growing season in this region,warmer climate may lead to drought and can become a limiting factor for vegetation growth.We found that increasedprecipitation benefits the advancement of the BGS in this area.Areas with a delayed EGS indicated that the appropriate temperature and rainfall in autumn or winter enhanced photosynthesis and extended the growth process.A positive correlation with precipitation was found for 76.53% of the areas with an extended LGS,indicating that precipitation is one of the key factors in changes in the vegetation phenology in this water-limited region.Precipitation plays an important role in determining the phenological activities of the vegetation in arid and semiarid areas,such as the Loess Plateau.The extended growing season will significantly influence both the vegetation productivity and the carbon fixation capacity in this region.
基金National Natural Science Foundation of China(41171083/U1203181)
文摘Research for changes of soil water and salt is an important content of land sciences and agriculture sciences in arid and semi arid regions. In this paper, sampling in actual agricultural fields, laboratory analysis of soil samples and statistical analysis methods are used to quantitatively analyze soil salinity changes under different ir- rigation methods throughout the cotton growing season in Shihezi reclamation area. The results show that irrigation methods play an important role in soil salt content in the surface soil （0-20 cm） and sub-deep soil （40-60 cm）, fol- lowed by deep soil layer （60-100 cm） and root soil layer （20-40 cm）. Furrow irrigation yields the maximum soil salt content in deep layer （60-100 cm） or sub-deep layer （40-60 cm） and the maximum salinity occurs in the first half of the cotton growing season （June or earlier）. In contrast, drip irrigation yields the maximum soil salinity in the root layer （20-40 cm） or sub-deep （40-60 cm）, and this usually appears in the second half growing season （July or af- ter）. The ratio of chloride ion to sulfate ion （Cl-/SO2- 4） and its change in the soil are on the rise under furrow irrigation while the value first increased and then decreased with a peak point in June under drip irrigation. This suggests that furrow irrigation may shift the type of soil salinization to chloride ion type moreso than drip irrigation. Potassium and sodium ion contents of the soil show that soil sodium＋potassium content will drop after the first rise under furrow irrigation and the value is manifested by fluctuations under drip irrigation. Potassium＋sodium content change is relatively more stable in the whole cotton growth period under irrigation methods. The maximum of sodium and potassium content of the soil usually occur in deep soil layer （60-100 cm） or sub-deep soil layer （40-60 cm） in most sample points under furrow irrigation while it is inconsistent in different sample points under drip irrigation. A non- parametric test for paired samples is used to analyze differences of soil salt content under different irrigation methods. This analysis shows that the impact of irrigation on soil salinity is most significant in July, followed by August, June, May, and April in most sample points. The most significant impact of irrigation methods occurs in the surface soil layer （0-20 cm）, followed by deep layer （60-100 cm）, root layer （20-40 cm） and sub-deep （40-60 cm）. These conclusions will be benefitial for mitigation of soil salinization, irrigation and fertilization and sustainable land use.
