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1.
Drought-prone grasslands provide a critical resource for the millions of people who are dependent on livestock for food security.However,this ecosystem is potentially vulnerable to climate change(e.g.,precipitation)and human activity(e.g.,grazing).Despite this,the influences of precipitation and grazing on ecological functions of drought-prone grasslands in the Tianshan Mountains remain relatively unexplored.Therefore,we conducted a systematic field investigation and a clipping experiment(simulating different intensities of grazing)in a drought-prone grassland on the northern slopes of the Tianshan Mountains in China to examine the influences of precipitation and grazing on aboveground biomass(AGB),soil volumetric water content(SVWC),and precipitation use efficiency(PUE)during the period of 2014–2017.We obtained the meteorological and SVWC data using an HL20 Bowen ratio system and a PR2 soil profile hydrometer,respectively.We found that AGB was clearly affected by both the amount and seasonal pattern of precipitation,and that PUE may be relatively low in years with either low or excessive precipitation.The PUE values were generally higher in the rapid growing season(April–July)than in the entire growing season(April–October).Overall,moderate grazing can promote plant growth under water stress conditions.The SVWC value was higher in the clipped plots than in the unclipped plots in the rapid growing season(April–July),but it was lower in the clipped plots than in the unclipped plots in the slow growing season(August–October).Our findings can enhance the understanding of the ecological effects of precipitation and grazing in drought-prone grasslands and provide data that will support the effective local grassland management.  相似文献   

2.
The Palmer drought severity index(PDSI), standardized precipitation index(SPI), and standardized precipitation evapotranspiration index(SPEI) are used worldwide for drought assessment and monitoring. However, substantial differences exist in the performance for agricultural drought among these indices and among regions. Here, we performed statistical assessments to compare the strengths of different drought indices for agricultural drought in the North China Plain. Small differences were detected in the comparative performances of SPI and SPEI that were smaller at the long-term scale than those at the short-term scale. The correlation between SPI/SPEI and PDSI considerably increased from 1-to 12-month lags, and a slight decreasing trend was exhibited during 12-and 24-month lags, indicating a 12-month scale in the PDSI, whereas the SPI was strongly correlated with the SPEI at 1-to 24-month lags. Interestingly, the correlation between the trend of temperature and the mean absolute error and its correlation coefficient both suggested stronger relationships between SPI and the SPEI in areas of rapid climate warming. In addition, the yield–drought correlations tended to be higher for the SPI and SPEI than that for the PDSI at the station scale, whereas small differences were detected between the SPI and SPEI in the performance on agricultural systems. However, large differences in the influence of drought conditions on the yields of winter wheat and summer maize were evident among various indices during the crop-growing season. Our findings suggested that multi-indices in drought monitoring are needed in order to acquire robust conclusions.  相似文献   

3.
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4.
With the aid of analyses to landscape ecology in the highway region of the arid area in Xinjiang of China, vegetation type, soil type and land-use type were ascertained as environmental factors of highway landscape ecosystem fragility, and seasonal flood, blown-wind sand and alkali-salinization as disaster factors of highway engineering. All items of these factors constitute an objective hierarchy of evaluating landscape ecosystem risk of the highway region in the arid area. The weighted values of the items were determined according to the number of occupied area or length by them against each unit. The area or length was interpreted with the aids of GIS technology and gained by measuring in the highway reconnaissance. The results of the eco-environmental risk assessment of G315 Yitunbulake-Qiemo section in Xinjiang shows that eight units of landscape ecology can be sorted into four categories according to the differences of the fragility indices (Σxiwi) and the disaster indices (Σyiwj).  相似文献   

5.
Snow cover is an important water source for vegetation growth in arid and semi-arid areas,and grassland phenology provides valuable information on the response of terrestrial ecosystems to climate change.The Mongolian Plateau features both abundant snow cover resources and typical grassland ecosystems.In recent years,with the intensification of global climate change,the snow cover on the Mongolian Plateau has changed correspondingly,with resulting effects on vegetation growth.In this study,using MOD10A1 snow cover data and MOD13A1 Normalized Difference Vegetation Index(NDVI)data combined with remote sensing(RS)and geographic information system(GIS)techniques,we analyzed the spatiotemporal changes in snow cover and grassland phenology on the Mongolian Plateau from 2001 to 2018.The correlation analysis and grey relation analysis were used to determine the influence of snow cover parameters(snow cover fraction(SCF),snow cover duration(SCD),snow cover onset date(SCOD),and snow cover end date(SCED))on different types of grassland vegetation.The results showed wide snow cover areas,an early start time,a late end time,and a long duration of snow cover over the northern Mongolian Plateau.Additionally,a late start,an early end,and a short duration were observed for grassland phenology,but the southern area showed the opposite trend.The SCF decreased at an annual rate of 0.33%.The SCD was shortened at an annual rate of 0.57 d.The SCOD and SCED in more than half of the study area advanced at annual rates of 5.33 and 5.74 DOY(day of year),respectively.For grassland phenology,the start of the growing season(SOS)advanced at an annual rate of 0.03 DOY,the end of the growing season(EOS)was delayed at an annual rate of 0.14 DOY,and the length of the growing season(LOS)was prolonged at an annual rate of 0.17 d.The SCF,SCD,and SCED in the snow season were significantly positively correlated with the SOS and negatively correlated with the EOS and LOS.The SCOD was significantly negatively correlated with the SOS and positively correlated with the EOS and LOS.The SCD and SCF can directly affect the SOS of grassland vegetation,while the EOS and LOS were obviously influenced by the SCOD and SCED.This study provides a scientific basis for exploring the response trends of alpine vegetation to global climate change.  相似文献   

6.
C3 plant Reaumuria soongorica and C4 plant Salsola passerina are super xerophytes and coexist in a mixed community in either isolated or associated growth, and interspecific facilitation occurs in associated growth. In the present study, the root traits including root distribution, root length(RL), root surface area(RSA), root weight(RW) and specific root length(SRL) of both species in two growth forms were investigated to clarify their response to facilitation in associated growth. Six isolated plants of each species, as well as six associated plants similar in size and development were selected during the plant growing season, and their roots were excavated at 0–10, 10–20, 20–30, 30–40 and 40–50 cm soil depths at the end of the growing season. All the roots of each plant were separated into the two categories of fine roots(2 mm diameter) and coarse roots(≥2 mm diameter). Root traits such as RL and RSA in the fine and coarse roots were obtained by the root analyzing system WinRHIZO. Most of the coarse roots in R. soongorica and S. passerina were distributed in the top 10 cm of the soil in both growth forms, whereas the fine roots of the two plant species were found mainly in the 10–20 and 20–30 cm soil depths in isolated growth, respectively. However, the fine roots of both species were mostly overlapped in 10–20 cm soil depth in associated growth. The root/canopy ratios of both species reduced, whereas the ratios of their fine roots to coarse roots in RL increased, and both species had an increased SRL in the fine roots in associated growth. In addition, there was the increase in RL of fine roots and content of root N for S. passerina in associated growth. Taken together, the root growth of S. passerina was facilitated for water and nutrient exploration under the interaction of the overlapped roots in both species in associated growth, and higher SRL allowed both species to more effectively adapt to the infertile soil in the desert ecosystem.  相似文献   

7.
Ecological restoration by Tamarix plants on semi-arid saline lands affects the accumulation, distribution patterns and related mechanisms of soil water content and salinity. In this study, spatio-temporal variations of soil water content and salinity around natural individual Tamarix ramosissima Ledeb. were invetigated in a semi-arid saline region of the upper Yellow River, Northwest China. Specifically, soil water content, electrical conductivity(EC_e), sodium adsorption ratio(SAR_e), and salt ions(including Na~+, K~+, Ca~(2+), Mg~(2+) and SO_4~(2–)) were measured at different soil depths and at different distances from the trunk of T. ramosissima in May, July, and September 2016. The soil water content at the 20–80 cm depth was significantly lower in July and September than in May, indicating that T. ramosissima plants absorb a large amount of water through the roots during the growing period, leading to the decreasing of soil water content in the deep soil layer. At the 0–20 cm depth, there was a salt island effect around individual T. ramosissima, and the EC_e differed significantly inside and outside the canopy of T. ramosissima in May and July. Salt bioaccumulation and stemflow were two major contributing factors to this difference. The SAR_e at the 0–20 cm depth was significantly different inside and outside the canopy of T. ramosissima in the three sampling months. The values of SAR_e at the 60–80 cm depth in May and July were significantly higher than those at the 0–60 cm depth and higher than that at the corresponding depth in September. The distribution of Na~+ in the soil was similar to that of the SAR_e, while the concentrations of K~+, Ca~(2+), and Mg~(2+) showed significant differences among the sampling months and soil depths. Both season and soil depth had highly significant effects on soil water content, EC_e and SAR_e, whereas distance from the trunk of T. ramosissima only significantly affected EC_e. Based on these results, we recommend co-planting of shallow-rooted salt-tolerant species near the Tamarix plants and avoiding planting herbaceous plants inside the canopy of T. ramosissima for afforestation in this semi-arid saline region. The results of this study may provide a reference for appropriate restoration in the semi-arid saline regions of the upper Yellow River.  相似文献   

8.
Phenological events for desert plants were recorded and rainfall and temperature data were gathered over a three-year time scale at a gravel plain in the eastern region of the United Arab Emirates. Variations of phenological periods were analyzed and correlations between phenological periods and climate factors were discussed. The study showed that the growth and flowering of therophytes were significantly correlated with air temperature. The timing and abundance of rainfall came to be another factor significantly correlated with the onset and duration of chamaephyte flowering as well as the duration of therophyte growth and flowering. The variation in rainfall did not affect the onset of flowering in phanerophytes. Peak growing seasons were from November to March and flowering from November to December(also February to March depending on the availability of rainfall). Flowering in phanerophytes and chamaephytes occurs 4–6 weeks and in therophytes 4–8 weeks after rain. The results showed that variations in growth and phenology between species were correlated with environmental factors, such as temperature and rainfall or, maybe, differences in life form and photosynthetic pathways, each being adapted for utilizing a particular phase of the seasonally and yearly variable rainfall. The sequence of flowering for the species under study was more or less constant despite the difference in the amount of rainfall. The fruiting patterns of most of the species were also found parallel to their flowering patterns. Our results emphasized the need to study multiple species at many sites for the understanding and forecast of regional changes in phenology.  相似文献   

9.
Precipitation chemistry analysis is essential to evaluate the atmospheric environmental quality and identify the sources of atmospheric pollutants. In this study, we collected a total of 480 precipitation samples at 6 sampling sites in the northern and southern slopes of Wushaoling Mountain from May 2013 to July 2014 to analyze the chemical characteristics of precipitation and to identify the main sources of ions in precipitation. Furthermore, we also explored the indicative significance for sand dust events in the northern and southern slopes of Wushaoling Mountain based on the precipitation chemistry analysis.During the sampling period(from May 2013 to July 2014), the p H values, EC(electrical conductivity)values and concentrations of cations(Ca~(2+), Mg~(2+), Na~+, K~+ and NH_4~+) and anions(SO_4~(2–), NO_3~–, Cl~–, NO_2~– and F~–) in precipitation were different in the northern and southern slopes at daily and seasonal time scales, with most of the values being higher in the northern slope than in the southern slope. The chemical type of precipitation in the southern and northern slopes was the same, i.e.,SO_4~(2–)-Ca~(2+)-NO_3~–-Na~+. The concentrations of ions in precipitation were mainly controlled by terrigenous material and anthropogenic activities(with an exception of Cl~–). The concentration of Cl~– in precipitation was mainly controlled by the sea salt fraction. The concentrations of Na+ and Cl~– showed an increasing trend after the occurrence of sand dust events both in the northern and southern slopes. In addition, after the occurrence of sand dust events, the concentrations of K~+, Mg~(2+), SO_4~(2–), NO_3~– and Ca~(2+) showed an increasing trend in the southern slope and a decreasing trend in the northern slope. It is our hope that the results may be helpful to further understand the atmospheric pollution caused by sand dust events in the Wushaoling Mountain and can also provide a scientific basis for the effective prevention of atmospheric pollution.  相似文献   

10.
Rui WANG 《干旱区科学》2017,9(6):850-864
Detecting near-surface soil freeze-thaw cycles in high-altitude cold regions is important for understanding the Earth's surface system, but such studies are rare. In this study, we detected the spatial-temporal variations in near-surface soil freeze-thaw cycles in the source region of the Yellow River(SRYR) during the period 2002–2011 based on data from the Advanced Microwave Scanning Radiometer for the Earth Observing System(AMSR-E). Moreover, the trends of onset dates and durations of the soil freeze-thaw cycles under different stages were also analyzed. Results showed that the thresholds of daytime and nighttime brightness temperatures of the freeze-thaw algorithm for the SRYR were 257.59 and 261.28 K, respectively. At the spatial scale, the daily frozen surface(DFS) area and the daily surface freeze-thaw cycle surface(DFTS) area decreased by 0.08% and 0.25%, respectively, and the daily thawed surface(DTS) area increased by 0.36%. At the temporal scale, the dates of the onset of thawing and complete thawing advanced by 3.10(±1.4) and 2.46(±1.4) days, respectively; and the dates of the onset of freezing and complete freezing were delayed by 0.9(±1.4) and 1.6(±1.1) days, respectively. The duration of thawing increased by 0.72(±0.21) day/a and the duration of freezing decreased by 0.52(±0.26) day/a. In conclusion, increases in the annual minimum temperature and winter air temperature are the main factors for the advanced thawing and delayed freezing and for the increase in the duration of thawing and the decrease in the duration of freezing in the SRYR.  相似文献   

11.
Pappophorum vaginatum is the most abundant C4perennial grass desirable to livestock in rangelands of northeastern Patagonia,Argentina.We hypothesized that(1)defoliation reduce net primary productivity,and root length density and weight in the native species,and(2)root net primary productivity,and root length density and weight,are greater in P.vaginatum than in the other,less desirable,native species(i.e.,Aristida spegazzinii,A.subulata and Sporobolus cryptandrus).Plants of all species were either exposed or not to a severe defoliation twice a year during two growing seasons.Root proliferation was measured using the cylinder method.Cylindrical,iron structures,wrapped up using nylon mesh,were buried diagonally from the periphery to the center on individual plants.These structures,initially filled with soil without any organic residue,were dug up from the soil on 25April 2008,after two successive defoliations in mid-spring 2007.During the second growing season(2008–2009),cylinders were destructively harvested on 4 April 2009,after one or two defoliations in midand/or late-spring,respectively.Roots grown into the cylinders were obtained after washing the soil manually.Defoliation during two successive years did reduce the study variables only after plants of all species were defoliated twice,which supported the first hypothesis.The greater root net primary productivity,root length density and weight in P.vaginatum than in the other native species,in support of the second hypothesis,could help to explain its greater abundance in rangelands of Argentina.  相似文献   

12.
High salinity in soil can prevent root growth of most plants. To investigate soil salinity dynamics under drip irrigation with mulch film(DI) and its effects on cotton root length, we conducted field experiments in saline soil based on a monolith method using flooding irrigation with mulch film(FI) as a control at the Korla Experimental Station of the Xinjiang Academy of Agricultural Sciences, China in 2009 and 2010. The results showed that the total root length decreased 120 days after sowing(DAS) under DI, and was mainly centered in the 0–30 cm soil layer and at distances of 30–70 cm from the drip-lines. There was almost complete overlap in the area of root length decline and salt accumulation. In the soil depth of 0–30 cm and at distances of 30–70 cm from the drip-lines at 110 to 160 DAS in 2009 and 171 DAS in 2010, the electrical conductivity(EC) in all soil samples was at least 3 mS/cm and in some cases exceeded 5 mS/cm under DI treatment. However, EC barely exceeded 3 mS/cm and no reduc- tion in root length was observed under FI treatment. Correlation analysis of soil EC and root length density indicated that the root length declined when the soil EC exceeded 2.8 mS/cm. The main reason for the decrease of root length in cotton under DI was localized accumulation of salinity.  相似文献   

13.
Grazing can modulate the feedback between vegetation and soil nutrient dynamics(carbon and nitrogen),altering the cycles of these elements in grassland ecosystems.For clarifying the impact of grazing on the C and N in plants and soils in the desert grassland of Ningxia,China,we examined the plant biomass,SOC(soil organic carbon),total soil N and stable isotope signatures of plants and soils from both the grazed and ungrazed sites.Significantly lower aboveground biomass,root biomass,litter biomass and vegetation coverage were found in the grazed site compared to the ungrazed site,with decreases of 42.0%,16.2%,59.4% and 30.0%,respectively.The effects of grazing on plant carbon,nitrogen,?15N and ?13C values were uniform among species.The levels of plant carbon and nitrogen in grasses were greater than those in the forbs(except for the carbon of Cynanchum komarovii and Euphorbia esula).Root 15 N and 13 C values increased with grazing,while the responses of root carbon and nitrogen to grazing showed no consistent patterns.Root 15 N and 13 C were increased by 79.0% and 22.4% in the grazed site compared to the ungrazed site,respectively.The values of SOC and total N were significantly lower in the grazed than in the ungrazed sites for all sampling depths(0–10 and 10–20 cm),and values of SOC and total N at the surface(0–10 cm) were lower than those in the deeper soils(10–20 cm).Soil ?15N values were not affected by grazing at any sampling depth,whereas soil ?13C values were significantly affected by grazing and increased by 19.3% and 8.6% in the soils at 0–10 and 10–20 cm,respectively.The soil ?13C values(–8.3‰ to –6.7‰) were higher than those for roots(–20.2‰ to –15.6‰) and plant tissues(–27.9‰ to –13.3‰).Our study suggests that grazing could greatly affect soil organic carbon and nitrogen in contrast to ungrazed grassland and that grazing appears to exert a negative effect on soil carbon and nitrogen in desert grassland.  相似文献   

14.
ManHou XU 《干旱区科学》2015,7(2):189-204
Climate warming and livestock grazing are known to have great influences on alpine ecosystems like those of the Qinghai-Tibetan Plateau(QTP) in China. However, it is lacking of studies on the effects of warming and grazing on plant and soil properties in these alpine ecosystems. In this study, we reported the related research from manipulative experiment in 2010–2012 in the QTP. The aim of this study was to investigate the individual and combined effects of warming and clipping on plant and soil properties in the alpine meadow ecosystem. Infrared radiators were used to simulate climate warming starting in July 2010, while clipping was performed once in October 2011 to simulate the local livestock grazing. The experiment was designed as a randomized block consisting of five replications and four treatments: control(CK), warming(W), clipping(C) and warming+clipping combination(WC). The plant and soil properties were investigated in the growing season of the alpine meadow in 2012. The results showed that W and WC treatments significantly decreased relative humidity at 20-cm height above ground as well as significantly increases air temperature at the same height, surface temperature, and soil temperature at the depth of 0–30 cm. However, the C treatment did not significantly decrease soil moisture and soil temperature at the depth of 0–60 cm. Relative to CK, vegetation height and species number increased significantly in W and WC treatment, respectively, while vegetation aboveground biomass decreased significantly in C treatment in the early growing season. However, vegetation cover, species diversity, belowground biomass and soil properties at the depth of 0–30 cm did not differ significantly in W, C and WC treatments. Soil moisture increased at the depth of 40–100 cm in W and WC treatments, while belowground biomass, soil activated carbon, organic carbon and total nitrogen increased in the 30–50 cm soil layer in W, C and WC treatments. Although the initial responses of plant and soil properties to experimental warming and clipping were slow and weak, the drought induced by the downward shift of soil moisture in the upper soil layers may induce plant belowground biomass to transfer to the deeper soil layers. This movement would modify the distributions of soil activated carbon, organic carbon and total nitrogen. However, long-term data collection is needed to further explain this interesting phenomenon.  相似文献   

15.
The vegetation ecosystem of the Qinghai–Tibet Plateau in China,considered to be the′′natural laboratory′′of climate change in the world,has undergone profound changes under the stress of global change.Herein,we analyzed and discussed the spatial-temporal change patterns and the driving mechanisms of net primary productivity(NPP)in the Qinghai–Tibet Plateau from 2000 to 2015 based on the gravity center and correlation coefficient models.Subsequently,we quantitatively distinguished the relative effects of climate change(such as precipitation,temperature and evapotranspiration)and human activities(such as grazing and ecological construction)on the NPP changes using scenario analysis and Miami model based on the MOD17A3 and meteorological data.The average annual NPP in the Qinghai–Tibet Plateau showed a decreasing trend from the southeast to the northwest during 2000–2015.With respect to the inter-annual changes,the average annual NPP exhibited a fluctuating upward trend from 2000 to 2015,with a steep increase observed in 2005 and a high fluctuation observed from 2005 to 2015.In the Qinghai–Tibet Plateau,the regions with the increase in NPP(change rate higher than 10%)were mainly concentrated in the Three-River Source Region,the northern Hengduan Mountains,the middle and lower reaches of the Yarlung Zangbo River,and the eastern parts of the North Tibet Plateau,whereas the regions with the decrease in NPP(change rate lower than–10%)were mainly concentrated in the upper reaches of the Yarlung Zangbo River and the Ali Plateau.The gravity center of NPP in the Qinghai–Tibet Plateau has moved southwestward during 2000–2015,indicating that the increment and growth rate of NPP in the southwestern part is greater than those of NPP in the northeastern part.Further,a significant correlation was observed between NPP and climate factors in the Qinghai–Tibet Plateau.The regions exhibiting a significant correlation between NPP and precipitation were mainly located in the central and eastern Qinghai–Tibet Plateau,and the regions exhibiting a significant correlation between NPP and temperature were mainly located in the southern and eastern Qinghai–Tibet Plateau.Furthermore,the relative effects of climate change and human activities on the NPP changes in the Qinghai–Tibet Plateau exhibited significant spatial differences in three types of zones,i.e.,the climate change-dominant zone,the human activity-dominant zone,and the climate change and human activity interaction zone.These research results can provide theoretical and methodological supports to reveal the driving mechanisms of the regional ecosystems to the global change in the Qinghai–Tibet Plateau.  相似文献   

16.
The distribution of stable isotopes and ions in precipitation in the Shule River Basin,northwestern China,were investigated to understand the regional water cycle and precipitation input to groundwater recharge.The study found that the mean annual concentrations of Ca2+,Na+,SO42–,Cl–,Mg2+,NO3–,and K+ in the basin were lower than those in other arid areas of northwestern China.The average concentrations of ions in the lower reaches of the Shule River were higher than those in the upper reaches.The results showed that the main ionic concentrations decreased with the increase of precipitation amount,indicating that heavy precipitation cannot only wash crustal aerosols out of the atmosphere,but also create a dilution effect.Cl– and Na+ in precipitation had a strong and positive correlation,suggesting a common origin for the two ions.However,the excess of Na+,combined with non-marine SO42– and NO3–,indicated that some ions were contributed by terrestrial origins.In the extremely arid regions of northwestern China,the evaporation process obviously changes the original relationship between δ2H and δ18O in precipitation,and leads to dexcess values 8‰.δ18O and temperature were significantly correlated,suggested that temperature strongly affected the characteristics of isotopes in the study area.The δ18O value indicates a dominant effect of westerly air masses and southwest monsoon in warm months,and the integrated influence of westerly and Siberian-Mongolian polar air masses in cold months.The d-excess values were generally lower in warm months than those in cold months,indicating that post-condensation processes played a significant role in the water cycle.The results provide reliable precipitation input information that can be used in future groundwater recharge calculations in the study area.  相似文献   

17.
Most soil respiration measurements are conducted during the growing season.In tundra and boreal forest ecosystems,cumulative,non-growing season soil CO2 fluxes are reported to be a significant component of these systems' annual carbon budgets.However,little information exists on soil CO2 efflux during the non-growing season from alpine ecosystems.Therefore,comparing measurements of soil respiration taken annually versus during the growing season will improve the accuracy of estimating ecosystem carbon budgets,as well as predicting the response of soil CO2 efflux to climate changes.In this study,we measured soil CO2 efflux and its spatial and temporal changes for different altitudes during the non-growing season in an alpine meadow located in the Qilian Mountains,Northwest ChinaField experiments on the soil CO2 efflux of alpine meadow from the Qilian Mountains were conducted along an elevation gradient from October 2010 to April 2011.We measured the soil CO2 efflux,and analyzed the effects of soil water content and soil temperature on this measure.The results show that soil CO2 efflux gradually decreased along the elevation gradient during the non-growing season.The daily variation of soil CO2 efflux appeared as a single-peak curve.The soil CO2 efflux was low at night,with the lowest value occurring between 02:00-06:00.Then,values started to rise rapidly between 07:00-08:30,and then descend again between 16:00-18:30.The peak soil CO2 efflux appeared from 11:00 to 16:00.The soil CO2 efflux values gradually decreased from October to February of the next year and started to increase in March.Non-growing season Q10(the multiplier to the respiration rate for a 10℃ increase in temperature) was increased with raising altitude and average Q10 of the Qilian Mountains was generally higher than the average growing season Q10 of the Heihe River Basin.Seasonally,non-growing season soil CO2 efflux was relatively high in October and early spring and low in the winter.The soil CO2 efflux was positively correlated with soil temperature and soil water content.Our results indicate that in alpine ecosystems,soil CO2 efflux continues throughout the non-growing season,and soil respiration is an important component of annual soil CO2 efflux.  相似文献   

18.
This paper analyzed the data of temperature and precipitation in Minqin,typical desert area in north-west China,during the period of 1961 2007 by linear regression.The result indicated that the increasing rate of the mean annual temperature in Minqin was higher than that of the average of China;and the temperature in February increased by 3.01oC averagely in the past 47 years.The climate in Minqin displayed an evident warming trend.However,there was no evidently increasing trend of precipitation in the past 47 years,and drought occurred during the whole growing season.  相似文献   

19.
Jing YANG 《干旱区科学》2017,9(4):622-634
Climate change in mountainous regions has significant impacts on hydrological and ecological systems. This research studied the future temperature, precipitation and snowfall in the 21~(st) century for the Tianshan and northern Kunlun Mountains(TKM) based on the general circulation model(GCM) simulation ensemble from the coupled model intercomparison project phase 5(CMIP5) under the representative concentration pathway(RCP) lower emission scenario RCP4.5 and higher emission scenario RCP8.5 using the Bayesian model averaging(BMA) technique. Results show that(1) BMA significantly outperformed the simple ensemble analysis and BMA mean matches all the three observed climate variables;(2) at the end of the 21~(st) century(2070–2099) under RCP8.5, compared to the control period(1976–2005), annual mean temperature and mean annual precipitation will rise considerably by 4.8°C and 5.2%, respectively, while mean annual snowfall will dramatically decrease by 26.5%;(3) precipitation will increase in the northern Tianshan region while decrease in the Amu Darya Basin. Snowfall will significantly decrease in the western TKM. Mean annual snowfall fraction will also decrease from 0.56 of 1976–2005 to 0.42 of 2070–2099 under RCP8.5; and(4) snowfall shows a high sensitivity to temperature in autumn and spring while a low sensitivity in winter, with the highest sensitivity values occurring at the edge areas of TKM. The projections mean that flood risk will increase and solid water storage will decrease.  相似文献   

20.
HUANG Jin 《干旱区科学》2016,8(3):341-349
Soil respiration(SR) in crop field is affected by environmental factors, agronomic practices and crop types. To clarify how planting density affects the SR dynamics in switchgrass(Panicum virgatum L.) field on the semi-arid Loess Plateau, this research investigated diurnal and seasonal changes of soil respiration rate(RS) under three different row-spacing treatments(20, 40 and 60 cm) in the fourth growing year of switchgrass. Results showed that RS presented a pronounced seasonality under all row-spacing treatments. The highest daily average RS values appeared in August, while the lowest(P0.05) were in September for each row-spacing. Diurnal variations of RS exhibited single-peak curves in each month. Daily average RS increased significantly as row-spacing enlarged during May and August but there was no significant difference among row-spacing treatments in September. Soil water storage in the depth of 0–100 cm had no significant difference(P0.05) among the row-spacing treatments, and similar results were found for soil temperature in 0–15 cm soil depth. Soil respiration temperature sensitivity(Q_(10)) values were 1.0–3.7 during the growing months, which were strongly correlated with air temperature in May and June and the soil temperature at 15 cm depth in August. Higher aboveground biomass production and lower RS in most growth months indicated that 20 cm row-spacing treatment was beneficial for increasing the carbon fixation in switchgrass field. Results also implied that it is necessary to take into account the influence of phenology and root growth of switchgrass on soil respiration for accurately evaluating the carbon cycle in the region.  相似文献   

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