Spatio-temporal variation of depth to groundwater level and its driving factors in arid and semi-arid regions of India

Climate change and increasing anthropogenic activities,such as over-exploitation of groundwater,are exerting unavoidable stress on groundwater resources.This study investigated the spatio-temporal variation of depth to groundwater level(DGWL)and the impacts of climatic(precipitation,maximum temperature,and minimum temperature)and anthropogenic(gross district product(GDP),population,and net irrigated area(NIA))variables on DGWL during 1994-2020.The study considered DGWL in 113 observation wells and piezometers located in arid western plains(Barmer and Jodhpur districts)and semi-arid eastern plains(Jaipur,Ajmer,Dausa,and Tonk districts)of Rajasthan State,India.Statistical methods were employed to examine the annual and seasonal patterns of DGWL,and the generalized additive model(GAM)was used to determine the impacts of climatic and anthropogenic variables on DGWL.During 1994-2020,except for Barmer District,where the mean annual DGWL was almost constant(around 26.50 m),all other districts exhibited increase in DGWL,with Ajmer District experiencing the most increase.The results also revealed that 36 observation wells and piezometers showed a statistically significant annual increasing trend in DGWL and 34 observation wells and piezometers exhibited a statistically significant decreasing trend in DGWL.Similarly,32 observation wells and piezometers showed an statistically significant increasing trend and 37 observation wells and piezometers showed a statistically significant decreasing trend in winter;33 observation wells and piezometers indicated a statistically significant increasing trend and 34 had a statistically significant decreasing trend in post-monsoon;35 observation wells and piezometers exhibited a statistically significant increasing trend and 32 observation wells and piezometers showed a statistically significant decreasing trend in pre-monsoon;and 36 observation wells and piezometers reflected a statistically significant increasing trend and 30 observation wells and piezometers reflected a statistically significant decreasing trend in monsoon.Interestingly,most of the observation wells and piezometers with increasing trends of DGWL were located in Dausa and Jaipur districts.Furthermore,the GAM analysis revealed that climatic variables,such as precipitation,significantly affected DGWL in Barmer District,and DGWL in all other districts was influenced by anthropogenic variables,including GDP,NIA,and population.As a result,stringent regulations should be implemented to curb excessive groundwater extraction,manage agricultural water demand,initiate proactive aquifer recharge programs,and strengthen sustainable management in these water-scarce regions.

Plastic-film-side seeding,as an alternative to traditional film mulching,improves yield stability and income in maize production in semi-arid regions

Planting under plastic-film mulches is widely used in spring maize production in arid-cold regions for water conservation and warming the soil.To ameliorate the associated issues such as plastic-film residues and additional labor during the“seedling release”in spring maize production,we have developed a plastic-film-side seeding(PSS)technology with the supporting machinery.In the semi-arid regions of Northwest China,a 7-year trial demonstrated that PSS increased plant number per hectare by 6547 and maize yield by 1686 kg ha–1compared with the traditional method of seeding under plastic-film mulch(PM).Two-year experiments were conducted in two semi-arid regions to further understand the effects of PSS on three important aspects of production:(i)the moisture and temperature of soil,(ii)maize development,yield output,and water use efficiency(WUE),and(iii)the revenue and plastic-film residuals in comparison with that of flat planting(CK)and PM.Continuous monitoring of the soil status demonstrated that,compared with CK,the PSS treatment significantly increased the temperature and moisture of the 0–20 cm soil in the seeding row at the early stage of maize development,and it also promoted grain yield(at 884–1089 kg ha^(–1))and WUE,achieving a similar effect as the PM treatment.Economically,the labor inputs of PSS were equal to CK,whereas the PM cost an additional 960 CNY ha–1in labor for releasing the seedlings from below the film.Overall,the PSS system increased profits by 5.83%(547 CNY ha^(–1)yr^(–1))and 8.16%(748 CNY ha^(–1)yr^(–1))compared with CK and PM,respectively.Environmentally,PSS achieved a residual film recovery rate of nearly 100%and eliminated 96 to 130 kg ha^(–1)of residual plastic-film in PM in 3–5 years of maize production.Collectively,these results show that PSS is an eco-friendly technique for improving yield stability and incomes for the sustainable production of maize in semi-arid regions.

Numerical Study of Impacts of Soil Moisture on the Diurnal and Seasonal Cycles of Sensible/Latent Heat Fluxes over Semi-arid Region

The semi-arid regions, as climatic and ecosystem transitional zones, are the most vulnerable to global environmental change. Earlier researches indicate that the semi-arid regions are characterized by strong landatmosphere coupling in which soil moisture is the crucial variable in land surface processes. In this paper, we investigate the sensitivity of the sensible/latent heat fluxes to soil moisture during the growing season based on the enhanced observations at Tongyu in the Jilin province of China, a reference site of international Coordinated Energy and Water Cycle Observations Project （CEOP） in the semi-arid regions, by using a sophisticated land surface model （NCAR_CLM3.0）. Comparisons between the observed and simulated sensible/latent heat fluxes indicate that the soil moisture has obvious effects on the sensible/latent heat fluxes in terms of diurnal cycle and seasonal evolution. Better representation of the soil moisture could improve the model performance to a large degree. Therefore, for the purpose of simulating the land-atmosphere interaction and predicting the climate and water resource changes in semi-arid regions, it is necessary to enhance the description of the soil moisture distribution both in the way of observation and its treatment in land surface models.

Can climate change influence agricultural GTFP in arid and semi-arid regions of Northwest China?

There are eight provinces and autonomous regions(Gansu Province,Ningxia Hui Autonomous Region,Xinjiang Uygur Autonomous Region,Inner Mongolia Autonomous Region,Tibet Autonomous Region,Qinghai Province,Shanxi Province,and Shaanxi Province)in Northwest China,most areas of which are located in arid and semi-arid regions(northwest of the 400 mm precipitation line),accounting for 58.74%of the country's land area and sustaining approximately 7.84×10^6 people.Because of drought conditions and fragile ecology,these regions cannot develop agriculture at the expense of the environment.Given the challenges of global warming,the green total factor productivity(GTFP),taking CO2 emissions as an undesirable output,is an effective index for measuring the sustainability of agricultural development.Agricultural GTFP can be influenced by both internal production factors(labor force,machinery,land,agricultural plastic film,diesel,pesticide,and fertilizer)and external climate factors(temperature,precipitation,and sunshine duration).In this study,we used the Super-slacks-based measure(Super-SBM)model to measure agricultural GTFP during the period 2000-2016 at the regional level.Our results show that the average agricultural GTFP of most provinces and autonomous regions in arid and semi-arid regions underwent a fluctuating increase during the study period(2000-2016),and the fluctuation was caused by the production factors(input and output factors).To improve agricultural GTFP,Shaanxi,Shanxi,and Gansu should reduce agricultural labor force input;Shaanxi,Inner Mongolia,Gansu,and Shanxi should decrease machinery input;Shaanxi,Inner Mongolia,Xinjiang,and Shanxi should reduce fertilizer input;Shaanxi,Xinjiang,Gansu,and Ningxia should reduce diesel input;Xinjiang and Gansu should decrease plastic film input;and Gansu,Shanxi,and Inner Mongolia should cut pesticide input.Desirable output agricultural earnings should be increased in Qinghai and Tibet,and undesirable output(CO2 emissions)should be reduced in Inner Mongolia,Xinjiang,Gansu,and Shaanxi.Agricultural GTFP is influenced not only by internal production factors but also by external climate factors.To determine the influence of climate factors on GTFP in these provinces and autonomous regions,we used a Geographical Detector(Geodetector)model to analyze the influence of climate factors(temperature,precipitation,and sunshine duration)and identify the relationships between different climate factors and GTFP.We found that temperature played a significant role in the spatial heterogeneity of GTFP among provinces and autonomous regions in arid and semi-arid regions.For Xinjiang,Inner Mongolia,and Tibet,a suitable average annual temperature would be in the range of 7℃-9℃;for Gansu,Shanxi,and Ningxia,it would be 11℃-13℃;and for Shaanxi,it would be 15℃-17℃.Stable climatic conditions and more efficient production are prerequisites for the development of sustainable agriculture.Hence,in the agricultural production process,reducing the redundancy of input factors is the best way to reduce CO2 emissions and to maintain temperatures,thereby improving the agricultural GTFP.The significance of this study is that it explores the impact of both internal production factors and external climatic factors on the development of sustainable agriculture in arid and semi-arid regions,identifying an effective way forward for the arid and semi-arid regions of Northwest China.

Emergy-based study on eco-economic system of arid and semi-arid region:a case of Gansu province,China

Taking Gansu province as a model case,this study provides an integrated analysis on the eco-economic system of arid and semi-arid region based on emergy synthesis theory. Through calculating the values of renewable emergy flow,non-renewable resources,imported emergy,exported emergy,waste emergy,and total emergy during the period of 1978-2007,the performance of Gansu eco-economic system was analyzed. The results indicated that the renewable emergy flow within the province basically remained steady state which was estimated at 2.99×1022 solar emjoules (sej) from 1978 to 2007. The imported emergy and exported emergy were estimated at 3.75×1017 sej and 2.99×1020 sej in 1978 and increased to 1.07×1022 sej and 1.44×1022 sej respectively in 2007. The nonrenewable emergy flow was estimated at 1.62×1022 sej and increased to 1.85×1023 sej,with annual growth rate of 8.7%,while the estimated total emergy was 4.58×1022 sej in 1978 and increased to 2.11×1023 sej in 2007,with annual growth rate of 5.41%. Our results indicate a deteriorate situation between economic development and environmental protection in the region. The rapid economic growth in the past thirty years was based on a great consumption of nonrenewable resource and caused continuous decrease in the capacity of sustainable development. The environmental loading ratio was 0.53 in 1978,increased to 6.06 in 2007,indicating a rapid degradation of the regional environment quality. We calculated that the actual population was 1.53 times the renewable resource population in 1978,increased to 7.06 times in 2007. During the period of 1978-2007,the emergy rose from 2.45×1015 sej/(capita·a) to 8.07×1015 sej/(capita·a). Our analysis revealed that the emergy density presented a trend of gradual increase,and then the emergy currency ratio in Gansu decreased from 7.08×1013 sej/Chinese Yuan to 7.82×1012 sej/Chinese Yuan.

Impact of rainfed and irrigated agriculture systems on soil carbon stock under different climate scenarios in the semi-arid region of Brazil

Understanding the dynamics of soil organic carbon(SOC) is of fundamental importance in land use and management, whether in the current researches or in future scenarios of agriculture systems considering climate change. In order to evaluate SOC stock of the three districts(Delmiro Gouveia, Pariconha, and Inhapi districts) in the semi-arid region of Brazil in rainfed and irrigated agriculture systems under different climate scenarios using the Century model, we obtained RCP4.5 and RCP8.5 climate scenarios derived from the Eta Regional Climate Model(Eta-Had GEM2-ES and Eta-MIROC5) from the National Institute for Space Research, and then input the data of bulk density, p H, soil texture, maximum temperature, minimum temperature, and rainfall into the soil and climate files of the Century model. The results of this study showed that the Eta-Had GEM2-ES model was effective in estimating air temperature in the future period. In rainfed agriculture system, SOC stock under the baseline scenario was lower than that under RCP4.5 and RCP8.5 climate scenarios, while in irrigated agriculture system, SOC stock in the almost all climate scenarios(RCP4.5 and RCP8.5) and models(Eta-Had GEM2-ES and Eta-MIROC5) will increase by 2100. The results of this study will help producers in the semi-arid region of Brazil adopt specific agriculture systems aimed at mitigating greenhouse gas emissions.

Evaluation of SEBS Algorithm for Estimation of Daily Evapotranspiration Using Landsat-8 Dataset in a Semi-Arid Region of Central Iran

Evapotranspiration is one the most important parameters in the hydrological cycle and plays a significant role in energy balance of the earth’s surface. Traditional field-based measurements approaches for calculation of daily evapotranspiration are valid only for local scales. Using advanced remote sensing technology, the spatial distribution of evapotranspiration may now be quantified more accurately. At the present study, daily evapotranspiration is estimated using Landsat 8 datasets based on the Surface Energy Balance System (SEBS) algorithm over the Zayanderud Dam area in central Iran. For this purpose, three Landsat 8 datasets in the years 2013, 2014 and 2015 covering the study area were atmospherically corrected using the FLAASH approach. The biophysical parameters of the earth’s surface for SEBS algorithm, such as normalized difference vegetation index (NDVI), Leaf area index (LAI), fractional vegetation cover (FC) were extracted from the visible and near infrared bands and land surface temperature was computed from thermal bands the Landsat 8 datasets. The spatial distribution of daily ET was provided separately for each year. In addition to the SEBS algorithm, the Penman-Monteith method was applied to estimate the daily ET from meteorological datasets which was obtained from two synoptic stations within the study area. Finally, the simulated daily ET values from both SEBS and Penman-Monteith method were compared to observed values obtained from a lysimeter within the study area. Although the estimated results from both SEBS and Penman-Monteith show a strong correlation with the observed values, the derived ET maps and following analysis demonstrated SEBS has higher accuracy and strength in estimation of daily ET in Zayanderud Dam region.

Comparisons of plant calcium fraction between two different vegetation zones in semi-arid region

To explore the characteristics of plant calcium(Ca) fraction, we analyzed 91 plant species in the Ningxia Habahu National Nature Reserve in Yanchi County of Ningxia and 84 plant species in Zhenglan Banner of Inner Mongolia. Results show that, for the two regions, there is no significant difference between Ca fraction for the same growth type, and between water soluble Ca content or between hydrochloric acid soluble Ca content for plants of the same ecosystem and between hydrochloric acid soluble Ca content for plants of the same family. In similar vegetation zones, there is a significant difference among hydrochloric acid soluble Ca content for different growth types in Yanchi County and Zhenglan Banner,which was the highest for annual herbs and the lowest for perennial herbs. There is a significant difference between acetic acid soluble Ca content and between hydrochloric acid soluble Ca content for sandy land and grassland ecosystems in Yanchi County. There is a significant difference among the same Ca fraction of different families in the same region. Thus, the characteristics of plant Ca fraction are results of long-term adaptation to the environment.

Runoff of arid and semi-arid regions simulated and projected by CLM-DTVGM and its multi-scale fluctuations as revealed by EEMD analysis

Runoff is a major component of the water cycle, and its multi-scale fluctuations are important to water resources management across arid and semi-arid regions. This paper coupled the Distributed Time Variant Gain Model （DTVGM） into the Community Land Model （CLM 3.5）, replacing the TOPMODEL-based method to simulate runoff in the arid and semi-arid regions of China. The coupled model was calibrated at five gauging stations for the period 1980-2005 and validated for the period 2006-2010. Then, future runoff （2010-2100） was simulated for different Representative Concentration Pathways （RCP） emission scenarios. After that, the spatial distributions of the future runoff for these scenarios were discussed, and the multi-scale fluctuation characteristics of the future annual runoff for the RCP scenarios were explored using the Ensemble Empirical Mode Decomposition （EEMD） analysis method. Finally, the decadal variabilities of the future annual runoff for the entire study area and the five catchments in it were investigated. The results showed that the future annual runoff had slowly decreasing trends for scenarios RCP 2.6 and RCP 8.5 during the period 2010-2100, whereas it had a non-monotonic trend for the RCP 4.5 scenario, with a slow increase after the 2050s. Additionally, the future annual runoff clearly varied over a decadal time scale, indicating that it had clear divisions between dry and wet periods. The longest dry period was approximately 15 years （2040-2055） for the RCP 2.6 scenario and 25 years （2045-2070） for the RCP 4.5 scenario. However, the RCP 8.5 scenario was predicted to have a long dry period starting from 2045. Under these scenarios, the water resources situation of the study area will be extremely severe. Therefore, adaptive water management measures addressing climate change should be adopted to proactively confront the risks of water resources.

Discussion on an Eco-Agriculture Model in the Semi-Arid Region of China

The semi-arid region of China covers an area of 2.2 x106km2. Water shortage in this region is the core but not the only one factor for the sustainable development of agriculture. Effective application of the energy and all kinds of resources and overall maintenance of the balance of ecological environment must be emphasized for sustainable development of the agriculture in the region. The extensive development of rural yard-economy is the only way to realize the intensive agricultural development there. A model is developed on the basis of our studies in recent years.

Influence of non-stationarity and auto-correlation of climatic records on spatio-temporal trend and seasonality analysis in a region with prevailing arid and semi-arid climate,Iran

Trend and stationarity analysis of climatic variables are essential for understanding climate variability and provide useful information about the vulnerability and future changes,especially in arid and semi-arid regions.In this study,various climatic zones of Iran were investigated to assess the relationship between the trend and the stationarity of the climatic variables.The Mann-Kendall test was considered to identify the trend,while the trend free pre-whitening approach was applied for eliminating serial correlation from the time-series.Meanwhile,time series stationarity was tested by Dickey-Fuller and Kwiatkowski-Phillips-Schmidt-Shin tests.The results indicated an increasing trend for mean air temperature series at most of the stations over various climatic zones,however,after eliminating the serial correlation factor,this increasing trend changes to an insignificant decreasing trend at a 95%confidence level.The seasonal mean air temperature trend suggested a significant increase in the majority of the stations.The mean air temperature increased more in northwest towards central parts of Iran that mostly located in arid and semiarid climatic zones.Precipitation trend reveals an insignificant downward trend in most of the series over various climatic zones;furthermore,most of the stations follow a decreasing trend for seasonal precipitation.Furthermore,spatial patterns of trend and seasonality of precipitation and mean air temperature showed that the northwest parts of Iran and margin areas of the Caspian Sea are more vulnerable to the changing climate with respect to the precipitation shortfalls and warming.Stationarity analysis indicated that the stationarity of climatic series influences on their trend;so that,the series which have significant trends are not static.The findings of this investigation can help planners and policy-makers in various fields related to climatic issues,implementing better management and planning strategies to adapt to climate change and variability over Iran.

The Analysis of Spring Precipitation in Semi-Arid Regions: Case Study in Iran

In this study, Zanjan from Iran has been chosen from among all the semi-arid regions of world, which has Synoptic station and statistical data since 1955. Spring and monthly precipitations are also provided in the period of 1956-2005. First, all data has been controlled by double mass method with the help of adjacent stations, and then it was normalized by the box-cox transformations method. The global SPI index was calculated for all months and spring, also drought and wet periods were determined and finally compared. In the drought category view, spring months have represented the great similarities. The moving averages are represented all months and spring’s precipitations such as three years, five years, seven years and nine years are shown. Statistical period was observed and analyzed based on five periods of ten years, and results precipitation with more than 5mm and 10mm has gradually decreased on April. However the number of days with precipitation has increased. The calculated spring precipitations and all of the atmospheric factors represented the dependence of this model to maximum average of spring temperature and relative humidity of spring and winter by the use of multi variable regression method. The predicted precipitation of spring also showed the gradual decline of precipitation in the next 30 years by the arima model.

Improvement of Supplementary Irrigation Water Quality for Rain-Fed Agriculture in the Semi-Arid Region Using Magnetization Techniques

Rain-fed agriculture depends on the groundwater as a supplementary source of irrigation. The poor quality of water from the hard rock area is applied to the crops to save the crop. Continuous irrigation leads to degradation of soil, drip irrigation system as well plants. This study assessed the damages on the drip irrigation system and soil, inflicted by the use of low-quality irrigation water. The quality of water was improved with reference to raw water in terms of pH (1.57% - 5.88%), EC (3.08% - 10.08%), ions (0.96% - 46%) by using magnetization method, without disrupting the existing irrigation system in the basaltic aquifer in semi-arid to the arid condition. This was demonstrated before the farmers in central India.

How to Build Artificial Grassland in the Cold and Semi-Arid Regions? ——A Case Study in Naqu

Construction of artificial grassland is a key factor to solve the shortage of grass and forage balance in cold and semi-arid areas of high plateau,and it is the key measure to ensure the sustainable development of grassland animal husbandry in this area. At present,the artificial grassland construction is neither reasonable nor scientific,which restricts the healthy and rapid development of artificial grassland in the cold and semi-arid areas of high plateau. In this research,with Naqu Area in Tibet as a case,problems and current status in construction process of artificial grassland are analyzed in cold and semi-arid areas of high plateau. Suitable artificial forage species in Nagqu are elaborated,and recommendations for the construction and development of artificial grassland are discussed.

Relationship between Rainfall Instability and Agricultural Production in the Brazilian Semi-arid Region

The study evaluated the synergy between the indicators of rainfall,vegetation cover,land productivity in crop production,livestock production and the relationship between the value of aggregate agricultural production and the gross domestic product of municipalities in the semi-arid region of the State of Ceará,Brazil.The data sources are:CearáMeteorology and Water Resources Foundation(FUNCEME)and Brazilian Institute of Geography and Statistics(IBGE)for the years 1996,2006 and 2017.The research used the methodology of factor analysis(FA),with decomposition into principal components,to construct the index of agricultural production preservation(IAPP).The results showed that 1996 had the best rainfall levels and the highest IAPP values compared to the other years studied.Year of 2017 was the last one of a draught period that extended in Cearáfrom 2012 to 2017.In that year the lowest values for IAPP were observed.The main conclusion is:there was the expected interaction between rainfall and agricultural preservation indicators applied in the semi-arid region of the state of Cearáin the years 1996,2006 and 2017.

A Review on Renewable Energy Systems for Irrigation in Arid and Semi-Arid Regions

The lack of water in arid and semi-arid regions has often limited agricultural production. Indeed, even where water is available for irrigation, the lack of electricity, as well as the high costs of diesel, has created constraints on small farmers. The purpose of this research is to review the renewable energy potential available in arid and semi-arid zones that can be used for irrigation as a substitute for fossil fuels. In this review, the solar thermal irrigation, solar photovoltaic (PV) irrigation, wind pumping and biomass pumping are discussed. The comparison of different hybrid pumping systems and analyses of renewable sources irrigation assessment in arid and semi-arid regions of Mozambique also are discussed. The results of this study showed that there are still certain technological limitations regarding the use of solar thermal energy for irrigation. As far as wind power is concerned, the analysis of the pumping water life cycle cost showed that the wind power water pumping system is more economical and viable compared to the diesel based system. However, the study concluded that photovoltaic solar energy has been shown to be more viable for pumping water for irrigation in arid and semi-arid regions.

陇中地区药用植物资源调查与分析

目的整理陇中地区药用植物名录,归纳该地区药用植物的种类及分布,为该地区中药资源的保护及开发利用等提供参考。方法通过中药资源普查数据库获得第四次全国中药资源普查数据,并参考《中国植物志》《黄土高原植物志》《甘肃中草药资源志》《甘肃省中药材标准》(2020年版)、《甘肃省中藏药材标准》(2020年版)等书籍及相关文献资料补充,对陇中地区药用植物资源种类及分布状况汇总,并对其进行分析。结果陇中地区药用植物资源共178科829属2101种,主要存在被子植物、裸子植物及蕨类植物等类群中,其中优势科主要集中在菊科、蔷薇科、豆科等,主要药用部位为全草类,以清热药为主,栽培药用植物51种,包括蒙古黄芪、玫瑰、忍冬等。结论陇中地区植物资源丰富,药用植物种类多,在保护的基础上应合理开发利用,并依据地理环境大力发展特色中药材产业。

传统村落的活态评价与适应性保护发展研究——以陇中黄土丘陵沟壑区3个典型传统村落为例

面对传统村落多维度失活,通过重新识别村落活态因子,研判失活、衰退主导因素,能够进一步为传统村落可持续发展提供新的思路。以陇中黄土丘陵沟壑区3个典型传统村落为例,立足本土地域环境,综合考虑村落活态发展因素,构建3层共28项活态性评价指标体系。研究发现:(1)3个传统村落均有失活现象,但在失活程度上有所分化。金崖和黄家庄村处于“微失活”,失活程度较轻,保护与发展的适应性、可持续性一般;古城村处于“失活”,失活现象较明显,保护与发展的适应性、可持续性较弱。(2)3个传统村落的村落治理、地域环境失活贡献率占比较高,对传统村落的活态发展影响较大;村落治理、经济发展和地域环境在失活指数上占比较高,对村落失活的影响较显著,可判断出陇中黄土丘陵沟壑区传统村落的适应性发展受村落治理、地域环境因素影响较大。(3)活态总分上,金崖村(71.63)>黄家庄村(68.58)>古城村(58.88),这与调研结果相吻合。村落失活是多因素综合、内外动力共同作用的结果,因此适应性、永续性的保护发展方式是村落振兴和活态化发展的关键。

陇中地区典型玉米农田生态系统呼吸作用对温湿度的响应研究

农田生态系统碳通量变化主要由作物光合作用和农田的呼吸作用引起。在陆地生态系统中,准确评估玉米农田生态系统的呼吸作用产生的碳排放量对全球碳通量的研究意义重大。使用甘肃省会宁县大山川村(属陇中半干旱区)玉米农田生态系统在2020年11月至2021年10月的涡度和土壤水分及温度监测数据,分析了玉米农田生态系统呼吸速率(R_(eco))的日平均变化和呼吸敏感性指数(Q_(10))在生长季内的月平均变化,探讨R_(eco)对温度的响应,并用不同模型进行拟合评估。陇中半干旱区玉米农田生态系统呼吸速率在年内呈单峰变化,日均最大呼吸速率11.49μmol/(m^(2)·s),相比呼吸速率对空气温度(Ta)与不同深度土壤温度(Ts)的响应,深度20 cm处的土壤温度(Ts_(20))对该地区R_(eco)全年拟合效果最佳。Q_(10)指数在生长季内表现出单峰型变化,最大值出现在8月(5.52μmol/(m^(2)·s)。通过各个模型拟合得出陇中地区玉米农田生态系统年呼吸碳排放量介于863.71~990.18 g C/m^(2),选择拟合效果最好的模型(Q_(10)模型),在考虑参数时变性对Q_(10)模型优化后,Q_(10)模型拟合精度得到大幅度提升,年碳排放量估计值由868.57 g C/m^(2)提高至1094.48 g C/m^(2),更加接近观测值(1110.28 g C/m^(2))。R_(eco)在土壤水分低于0.16 m^(3)/m^(3)时(出现在12-2月)受到抑制。

Intensified river salinization alters nitrogen-cycling microbial communities in arid and semi-arid regions of China

Freshwater salinization is receiving increasing global attention due to its profound influence on nitrogen cycling in aquatic ecosystems and the accessibility of water resources.However,a comprehensive understanding of the changes in river salinization and the impacts of salinity on nitrogen cycling in arid and semi-arid regions of China is currently lacking.A meta-analysis was first conducted based on previous investigations and found an intensification in river salinization that altered hydrochemical characteristics.To further analyze the impact of salinity on nitrogen metabolism processes,we evaluated rivers with long-term salinity gradients based on in situ observations.The genes and enzymes that were inhibited generally by salinity,especially those involved in nitrogen fixation and nitrification,showed low abundances in three salinity levels.The abundance of genes and enzymes with denitrification and dissimilatory nitrate reduction to ammonium functions still maintained a high proportion,especially for denitrification genes/enzymes that were enriched under medium salinity.Denitrifying bacteria exhibited various relationships with salinity,while dissimilatory nitrate reduction to ammonium bacterium(such as Hydrogenophaga and Curvibacter carrying nirB)were more inhibited by salinity,indicating that diverse denitrifying bacteria could be used to regulate nitrogen concentration.Most genera exhibited symbiotic and mutual relationships,and the highest proportion of significant positive correlations of abundant genera was found under medium salinity.This study emphasizes the role of river salinity on environment characteristics and nitrogen transformation rules,and our results are useful for improving the availability of river water resources in arid and semi-arid regions.