An increasing number of palaeo-climatic records have been reported to identify the Holocene climate history in the arid Xinjiang region of northwest China. However, few studies have fully considered the internal linka...An increasing number of palaeo-climatic records have been reported to identify the Holocene climate history in the arid Xinjiang region of northwest China. However, few studies have fully considered the internal linkages within the regional climate system, which may limit our understanding of the forcing mechanisms of Holocene climate change in this region. Here, we systematically consider three major issues of the moisture/precipitation, temperature and near-surface wind relevant to the Holocene climate history of Xinjiang. First, despite there still has debated for the Holocene moisture evolution in this region, more climatic reconstructions from lake sediments, loess, sand-dunes and peats support a long-term regional wetting trend. Second, temperature records from ice cores, peats and stalagmites demonstrate a long-term winter warming trend during the Holocene in middle-to high-latitudes of Asia. Third, recent studies of aeolian sedimentary sequences reveal that the near-surface winds in winter gradually weakened during the Holocene, whereas the winter mid-latitude Westerlies strengthened in the Tienshan Mountains. Based on this evidence, in the arid Xinjiang region we propose an early to middle Holocene relatively cold and dry interval, with strong near-surface winds;and a warmer, wetter interval with weaker near-surface winds in the middle to late Holocene during winter. Additionally,we develop a conceptual model to explain the pattern of Holocene climate changes in this region.From the early to the late Holocene, the increasing atmospheric COcontent and winter insolation,and the shrinking of high-latitude continental ice-sheets, resulted in increasing winter temperatures in middle to high latitudes in the Northern Hemisphere. Subsequently, the increased winter temperature strengthened the winter mid-latitude Westerlies and weakened the Siberian high-pressure system,which caused an increase in winter precipitation and a decrease in near-surface wind strength. This scenario is strongly supported by evidence from geological records, climate simulation results, and modern reanalysis data. Our hypothesis highlights the important contribution of winter temperature in driving the Holocene climatic evolution of the arid Xinjiang region, and it implies that the socio-economic development and water resources security of this region will face serious challenges presented by the increasing winter temperature in the future.展开更多
Erratic rainfalls and rise in temperature have become more frequent under the changing scenario of climate particularly in semiarid tropics. As a consequence of it, a drastic shift of chickpea diseases have been recor...Erratic rainfalls and rise in temperature have become more frequent under the changing scenario of climate particularly in semiarid tropics. As a consequence of it, a drastic shift of chickpea diseases have been recorded throughout the major chickpea growing regions in India and elsewhere. Dry root rot (DRR) caused by Rhizoctonia bataticola (Taub.) Butler [Pycnidial stage: Macrophomina phaseolina (Tassi) Goid] was found as a potentially emerging constraint to chickpea production than wilt (Fusarium oxysporum f. sp. ciceris). Increasing incidence of DRR indicate strong influence of climate change variables such as temperature and moisture on the development of disease. The present study therefore was conducted to quantify the role of temperature and soil moisture associated with infection, colonization and development of DRR under controlled environment. The DRR incidence was significantly affected by high temperature and soil moisture deficit. Out of five temperature regimes (15?C, 20?C, 25?C, 30?C and 35?C) and four moisture levels (40%, 60%, 80% and 100%), a combination of high temperature (35?C) and soil moisture content (60%) predisposes chickpea to DRR. The study clearly demonstrates that high temperature coupled with soil moisture deficit is the climate change variables predisposing chickpea to R. bataticola infection, colonization and development.展开更多
Increasing air temperatures are expected to continue in the future. The relation between soil moisture and near surface air temperature is significant for climate change and climate extremes. Evaluation of the relatio...Increasing air temperatures are expected to continue in the future. The relation between soil moisture and near surface air temperature is significant for climate change and climate extremes. Evaluation of the relations between soil moisture and temperature was performed by developing a quantile regression model, a wavelet coherency model, and a Mann-Kendall correlation model from 1950 to 2010 in the Mississippi River Basin. The results indicate that first, anomaly air temperature is negatively correlated to anomaly soil moisture in the upper and lower basin, and however, the correlation between them are mixed in the middle basin. The correlation is stronger at the higher quantile (90th) of the two variables. Second, anomaly soil moisture and air temperature show strong coherency in annual frequency, indicating that the two variables are interannually correlated. Third, annual air temperature is significant negatively related to soil moisture, indicating that dry (wet) soil leads to warm (cool) weather in the basin. These results have potential application to future climate change research and water resource management. Also, the strong relationship between soil moisture and air temperature at annual scale could result in improved temperature predictability.展开更多
Climate change is forecast to increase the frequency of extreme hot temperatures and dryer days and is anticipated to have profound impacts on the global carbon budget.Droughts are expected to alter soil respiration(R...Climate change is forecast to increase the frequency of extreme hot temperatures and dryer days and is anticipated to have profound impacts on the global carbon budget.Droughts are expected to alter soil respiration(R_(s))rates,but the scarcity of data preclude a reliable estimate of this response and its future trajectory.A field experiment using an automated soil respiration machinery(LI-8100A)was conducted in a natural forest and a plantation during a dry period in the Philippines,with the goal of quantifying Rsrates and their relationship with soil temperature and moisture,and air temperature.The natural forest(5.81μmol m^(-2)s^(-1))exhibited significantly higher Rsrates(p<0.0001)compared with the plantation(1.82μmol m^(-2)s^(-1))and control(3.23μmol m^(-2)s^(-1)).Rsrates showed significant negative relationships with air(-0.71)and soil temperatures(-0.62),indicating that as temperatures increase,the R_(s)rates decrease.In contrast,the R_(s)rates exhibited a significant positive relationship with soil moisture(0.65).Although the low R_(s)rates in the plantation and high Rsrates in the natural forest are indicators of sensitivities of these two types of tropical forests to warm,dry soil,this observation is only conclusive during the dry period,but not necessarily during wet periods.Further studies are needed to determine the trend of Rsrates during wet periods,considering different site conditions and types of vegetation.展开更多
Understanding the temperature and moisture sensitivity of soil organic matter (SOM) mineralization variations with changes in land cover is critical for assessing soil carbon (C) storage under global change scenar...Understanding the temperature and moisture sensitivity of soil organic matter (SOM) mineralization variations with changes in land cover is critical for assessing soil carbon (C) storage under global change scenarios We determined the differences in the amount of SOM mineralization and the temperature and moisture sensitivity of soils collected from six land-cover types, including an orchard, a cropland, and four forests, in subtropical south- eastern China. The responses of SOM mineralization to temperature (5, 10, 15, 20, and 25~C) and moisture (30%, 60%, and 90% of water-holding capacity [WHC]) were investigated by placing soil samples in incubators. Soil C mineralization rate and cumulative C mineralization were higher in orchard and cropland soils than in other forest soils. With increasing temperature, soil C mineralization rates and cumulative C mineralization increased with the rise of WHCo The temperature sensitivity of soil C mineralization was not affected by land-cover type and incubation moisture. All soil temperature treatments showed a similar response to moisture. Cropland soil was more respon- sive to soil moisture than other soils. Our findings indicate that cropland and orchard soils have a higher ability to emit CO2 than forest soils in subtropical southeastern China.展开更多
Background:Soil respiration(S_(R))is a critical process for understanding the impact of climatic conditions and land degradation on the carbon cycle in terrestrial ecosystems.We measured the S_(R) and soil environment...Background:Soil respiration(S_(R))is a critical process for understanding the impact of climatic conditions and land degradation on the carbon cycle in terrestrial ecosystems.We measured the S_(R) and soil environmental factors over 1 year in four land uses with varying levels of disturbance and different vegetation types viz.,mixed forest cover(MFC),Prosopis juliflora(Sw.)forest cover(PFC),agricultural field(AF),and vegetable field(VF),in a semi-arid area of Delhi,India.Our primary aim was to assess the effects of soil moisture(S_(M)),soil temperature(S_(T)),and soil microbial activity(S_(MA))on the S_(R).Methods:The S_(R) was measured monthly using an LI-6400 with an infrared gas analyser and a soil chamber.The S_(M) was measured using the gravimetric method.The S_(T)(10 cm)was measured with a probe attached to the LI-6400.The S_(MA) was determined by fluorescein diacetate hydrolysis.Results:The S_(R) showed seasonal variations,with the mean annual S_(R) ranging from 3.22 to 5.78μmol m^(−2) s^(−1) and higher S_(R) rates of~15-55%in the cultivated fields(AF,VF)than in the forest sites(MFC,PFC).The VF had significantly higher S_(R)(P<0.05)than the other land uses(AF,PFC,MFC),which did not vary significantly from one another in S_(R)(P<0.05).The repeated measures ANOVA evaluated the significant differences(P<0.05)in the S_(R) for high precipitation months(July,August,September,February).The S_(M) as a single factor showed a strong significant relationship in all the land uses(R^(2)=0.67-0.91,P<0.001).The effect of the S_(T) on the S_(R) was found to be weak and non-significant in the PFC,MFC,and AF(R^(2)=0.14-0.31;P>0.05).Contrasting results were observed in the VF,which showed high S_(R) during summer(May;11.21μmol m^(−2) s^(−1))and a significant exponential relationship with the S_(T)(R^(2)=0.52;P<0.05).The S_(R) was positively related to the SMA(R2=0.44-0.5;P<0.001).The interactive equations based on the independent variables S_(M),S_(T),and S_(MA) explained 91-95%of the seasonal variation in S_(R) with better model performance in the cultivated land use sites(AF,VF).Conclusion:S_(M) was the key determining factor of the S_(R) in semi-arid ecosystems and explained~90%of the variation.Precipitation increased S_(R) by optimizing the S_(M) and microbial activity.The S_(MA),along with the other soil factors S_(M) and S_(T),improved the correlation with S_(R).Furthermore,the degraded land uses will be more susceptible to temporal variations in S_(R) under changing climatic scenarios,which may influence the carbon balance of these ecosystems.展开更多
基金supported by the Second Tibetan Plateau Scientific Expedition and Research Program (STEP) (Grant No. 2019QZKK0602)the National Natural Science Foundation of China (Grant Nos. 41401046, 42067049)+1 种基金the Education Science and technology Innovation project of Gansu Province (2021QB-118)the Jiangxi Provincial Natural Science Foundation (Grant No. 20202BABL213035)。
文摘An increasing number of palaeo-climatic records have been reported to identify the Holocene climate history in the arid Xinjiang region of northwest China. However, few studies have fully considered the internal linkages within the regional climate system, which may limit our understanding of the forcing mechanisms of Holocene climate change in this region. Here, we systematically consider three major issues of the moisture/precipitation, temperature and near-surface wind relevant to the Holocene climate history of Xinjiang. First, despite there still has debated for the Holocene moisture evolution in this region, more climatic reconstructions from lake sediments, loess, sand-dunes and peats support a long-term regional wetting trend. Second, temperature records from ice cores, peats and stalagmites demonstrate a long-term winter warming trend during the Holocene in middle-to high-latitudes of Asia. Third, recent studies of aeolian sedimentary sequences reveal that the near-surface winds in winter gradually weakened during the Holocene, whereas the winter mid-latitude Westerlies strengthened in the Tienshan Mountains. Based on this evidence, in the arid Xinjiang region we propose an early to middle Holocene relatively cold and dry interval, with strong near-surface winds;and a warmer, wetter interval with weaker near-surface winds in the middle to late Holocene during winter. Additionally,we develop a conceptual model to explain the pattern of Holocene climate changes in this region.From the early to the late Holocene, the increasing atmospheric COcontent and winter insolation,and the shrinking of high-latitude continental ice-sheets, resulted in increasing winter temperatures in middle to high latitudes in the Northern Hemisphere. Subsequently, the increased winter temperature strengthened the winter mid-latitude Westerlies and weakened the Siberian high-pressure system,which caused an increase in winter precipitation and a decrease in near-surface wind strength. This scenario is strongly supported by evidence from geological records, climate simulation results, and modern reanalysis data. Our hypothesis highlights the important contribution of winter temperature in driving the Holocene climatic evolution of the arid Xinjiang region, and it implies that the socio-economic development and water resources security of this region will face serious challenges presented by the increasing winter temperature in the future.
文摘Erratic rainfalls and rise in temperature have become more frequent under the changing scenario of climate particularly in semiarid tropics. As a consequence of it, a drastic shift of chickpea diseases have been recorded throughout the major chickpea growing regions in India and elsewhere. Dry root rot (DRR) caused by Rhizoctonia bataticola (Taub.) Butler [Pycnidial stage: Macrophomina phaseolina (Tassi) Goid] was found as a potentially emerging constraint to chickpea production than wilt (Fusarium oxysporum f. sp. ciceris). Increasing incidence of DRR indicate strong influence of climate change variables such as temperature and moisture on the development of disease. The present study therefore was conducted to quantify the role of temperature and soil moisture associated with infection, colonization and development of DRR under controlled environment. The DRR incidence was significantly affected by high temperature and soil moisture deficit. Out of five temperature regimes (15?C, 20?C, 25?C, 30?C and 35?C) and four moisture levels (40%, 60%, 80% and 100%), a combination of high temperature (35?C) and soil moisture content (60%) predisposes chickpea to DRR. The study clearly demonstrates that high temperature coupled with soil moisture deficit is the climate change variables predisposing chickpea to R. bataticola infection, colonization and development.
文摘Increasing air temperatures are expected to continue in the future. The relation between soil moisture and near surface air temperature is significant for climate change and climate extremes. Evaluation of the relations between soil moisture and temperature was performed by developing a quantile regression model, a wavelet coherency model, and a Mann-Kendall correlation model from 1950 to 2010 in the Mississippi River Basin. The results indicate that first, anomaly air temperature is negatively correlated to anomaly soil moisture in the upper and lower basin, and however, the correlation between them are mixed in the middle basin. The correlation is stronger at the higher quantile (90th) of the two variables. Second, anomaly soil moisture and air temperature show strong coherency in annual frequency, indicating that the two variables are interannually correlated. Third, annual air temperature is significant negatively related to soil moisture, indicating that dry (wet) soil leads to warm (cool) weather in the basin. These results have potential application to future climate change research and water resource management. Also, the strong relationship between soil moisture and air temperature at annual scale could result in improved temperature predictability.
文摘Climate change is forecast to increase the frequency of extreme hot temperatures and dryer days and is anticipated to have profound impacts on the global carbon budget.Droughts are expected to alter soil respiration(R_(s))rates,but the scarcity of data preclude a reliable estimate of this response and its future trajectory.A field experiment using an automated soil respiration machinery(LI-8100A)was conducted in a natural forest and a plantation during a dry period in the Philippines,with the goal of quantifying Rsrates and their relationship with soil temperature and moisture,and air temperature.The natural forest(5.81μmol m^(-2)s^(-1))exhibited significantly higher Rsrates(p<0.0001)compared with the plantation(1.82μmol m^(-2)s^(-1))and control(3.23μmol m^(-2)s^(-1)).Rsrates showed significant negative relationships with air(-0.71)and soil temperatures(-0.62),indicating that as temperatures increase,the R_(s)rates decrease.In contrast,the R_(s)rates exhibited a significant positive relationship with soil moisture(0.65).Although the low R_(s)rates in the plantation and high Rsrates in the natural forest are indicators of sensitivities of these two types of tropical forests to warm,dry soil,this observation is only conclusive during the dry period,but not necessarily during wet periods.Further studies are needed to determine the trend of Rsrates during wet periods,considering different site conditions and types of vegetation.
基金Natural Sciences Foundation of China(31270519,31470506,31130009,31290221)
文摘Understanding the temperature and moisture sensitivity of soil organic matter (SOM) mineralization variations with changes in land cover is critical for assessing soil carbon (C) storage under global change scenarios We determined the differences in the amount of SOM mineralization and the temperature and moisture sensitivity of soils collected from six land-cover types, including an orchard, a cropland, and four forests, in subtropical south- eastern China. The responses of SOM mineralization to temperature (5, 10, 15, 20, and 25~C) and moisture (30%, 60%, and 90% of water-holding capacity [WHC]) were investigated by placing soil samples in incubators. Soil C mineralization rate and cumulative C mineralization were higher in orchard and cropland soils than in other forest soils. With increasing temperature, soil C mineralization rates and cumulative C mineralization increased with the rise of WHCo The temperature sensitivity of soil C mineralization was not affected by land-cover type and incubation moisture. All soil temperature treatments showed a similar response to moisture. Cropland soil was more respon- sive to soil moisture than other soils. Our findings indicate that cropland and orchard soils have a higher ability to emit CO2 than forest soils in subtropical southeastern China.
基金We thank Council of Scientific and Industrial Research(CSIR,Ref No.20-12/2009(ii)EU-IV),University Grants Commission(UGC,Ref No.20-6/2009(ii)EU-IV)and Science and Engineering Research Board(SERB),Department of Science and Technology(DST,SR/FT/LS-59/2012),India for financial supportWe also thank University of Delhi for providing Research and Development for providing grant for doctoral research program.
文摘Background:Soil respiration(S_(R))is a critical process for understanding the impact of climatic conditions and land degradation on the carbon cycle in terrestrial ecosystems.We measured the S_(R) and soil environmental factors over 1 year in four land uses with varying levels of disturbance and different vegetation types viz.,mixed forest cover(MFC),Prosopis juliflora(Sw.)forest cover(PFC),agricultural field(AF),and vegetable field(VF),in a semi-arid area of Delhi,India.Our primary aim was to assess the effects of soil moisture(S_(M)),soil temperature(S_(T)),and soil microbial activity(S_(MA))on the S_(R).Methods:The S_(R) was measured monthly using an LI-6400 with an infrared gas analyser and a soil chamber.The S_(M) was measured using the gravimetric method.The S_(T)(10 cm)was measured with a probe attached to the LI-6400.The S_(MA) was determined by fluorescein diacetate hydrolysis.Results:The S_(R) showed seasonal variations,with the mean annual S_(R) ranging from 3.22 to 5.78μmol m^(−2) s^(−1) and higher S_(R) rates of~15-55%in the cultivated fields(AF,VF)than in the forest sites(MFC,PFC).The VF had significantly higher S_(R)(P<0.05)than the other land uses(AF,PFC,MFC),which did not vary significantly from one another in S_(R)(P<0.05).The repeated measures ANOVA evaluated the significant differences(P<0.05)in the S_(R) for high precipitation months(July,August,September,February).The S_(M) as a single factor showed a strong significant relationship in all the land uses(R^(2)=0.67-0.91,P<0.001).The effect of the S_(T) on the S_(R) was found to be weak and non-significant in the PFC,MFC,and AF(R^(2)=0.14-0.31;P>0.05).Contrasting results were observed in the VF,which showed high S_(R) during summer(May;11.21μmol m^(−2) s^(−1))and a significant exponential relationship with the S_(T)(R^(2)=0.52;P<0.05).The S_(R) was positively related to the SMA(R2=0.44-0.5;P<0.001).The interactive equations based on the independent variables S_(M),S_(T),and S_(MA) explained 91-95%of the seasonal variation in S_(R) with better model performance in the cultivated land use sites(AF,VF).Conclusion:S_(M) was the key determining factor of the S_(R) in semi-arid ecosystems and explained~90%of the variation.Precipitation increased S_(R) by optimizing the S_(M) and microbial activity.The S_(MA),along with the other soil factors S_(M) and S_(T),improved the correlation with S_(R).Furthermore,the degraded land uses will be more susceptible to temporal variations in S_(R) under changing climatic scenarios,which may influence the carbon balance of these ecosystems.