Soil respiration （SR） is the second-largest flux in ecosystem carbon cycling. Due to the large spatio-temporal variability of environmental factors, SR varied among different vegetation types, thereby impeding accur...Soil respiration （SR） is the second-largest flux in ecosystem carbon cycling. Due to the large spatio-temporal variability of environmental factors, SR varied among different vegetation types, thereby impeding accurate estimation of CO2 emissions via SR. However, studies on spatio-temporal variation of SR are still scarce for semi-arid regions of North China. In this study, we conducted 12-month SR measurements in six land-use types, including two secondary forests （Populus tomentosa （PT） and Robinia pseudoacacia （RP））, three artificial plantations （Armeniaca sibirica （AS）, Punica granatum （PG） and Ziziphusjujuba （Z J）） and one natural grassland （GR）, to quantify spatio-temporal variation of SR and distinguish its controlling factors. Results indicated that SR exhibited distinct sea- sonal patterns for the six sites. Soil respiration peaked in August 2012 and bottomed in April 2013. The temporal coefficient of variation （CI0 of SR for the six sites ranged from 76.98% to 94.08%, while the spatial CV of SR ranged from 20.28% to 72.97% across the 12-month measurement. Soil temperature and soil moisture were the major controlling factors of temporal variation of SR in the six sites, while spatial variation in SR was mainly caused by the differences in soil total nitrogen （STN）, soil organic carbon （SOC）, net photosynthesis rate, and fine root biomass. Our results show that the annual average SR and Q10 （temperature sensitivity of soil respira- tion） values tended to decrease from secondary forests and grassland to plantations, indicating that the conversion of natural ecosystems to man-made ecosystems may reduce CO2 emissions and SR temperature sensitivity. Due to the high spatio-temporal variation of SR in our study area, care should be taken when converting secondary forests and grassland to plantations from the point view of accurately quantifying C02 emissions via SR at regional scales.展开更多
Hydrological service is a hot issue in the current researches of ecosystem service, particularly in the upper reaches of mountain rivers in dry land areas, where the Qilian Mountain is a representative one. The Qilian...Hydrological service is a hot issue in the current researches of ecosystem service, particularly in the upper reaches of mountain rivers in dry land areas, where the Qilian Mountain is a representative one. The Qilian Mountain, where forest, shrubland and grassland consist of its main ecosystems, can provide fresh water and many other ecosystem services, through a series of eco-hydrological process such as precipitation interception, soil water storage, and fresh water provision. Thus, monitoring water regulation and assessing the hydrological service of the Qilian Mountain are meaningful and helpful for the healthy development of the lower reaches of arid and semi-arid areas. In recent 10 years, hydrological services have been widely researched in terms of scale and landscape pattern, including water conservation, hydrological responses to afforestation and their ecological effects. This study, after analyzing lots of current models and applications of geographical information system（GIS） in hydrological services, gave a scientific and reasonable evaluation of mountain ecosystem in eco-hydrological services, by employing the combination of international forefronts and contentious issues into the Qilian Mountain. Assessments of hydrological services at regional or larger scales are limited compared with studies within watershed scale in the Qilian Mountain. In our evaluation results of forest ecosystems, it is concluded that long-term observation and dynamic monitoring of different types of ecosystem are indispensable, and the hydrological services and the potential variation in water supplement on regional and large scales should be central issues in the future research.v展开更多
As one critical source of water for maintaining ecosystems in arid and semi-arid regions, rainfall replenishment to soil water can determine vegetation growth and ecosystem functions. However, the limited rainfall res...As one critical source of water for maintaining ecosystems in arid and semi-arid regions, rainfall replenishment to soil water can determine vegetation growth and ecosystem functions. However, the limited rainfall resources were often not used effectively in the semi-arid loess hilly areas due to random temporal and spatial distribution of rainfall and specific vegetation features. Thus, it is highly significant to determine the threshold and efficiency of rainfall replenishment to soil water under different vegetation types. The threshold and efficiency can offer scientific evidence for rehabilitating vegetation and improving efficiency of using rainfall resources. In this study, the efficiency and threshold of rainfall replenishment to soil water were determined under natural grassland, wheat, artificial grassland, sea buckthorn shrubland and Chinese pine forestland based on consecutive measurements. The results indicated that the lag-time, rate, efficiency of rainfall replenishment to soil water were closely related to vegetation type, with significant differences existing among different vegetation types. The lag-time for natural grassland in the soil horizon of 20 cm was the shortest one （26.4 h）, followed by wheat （27.8 h）, sea buckthorn （41.8 h）, artificial grassland （50.0 h） and Chinese pine （81.8 h）.The value of replenishment rate, followed the order of wheat （0.40 mm h-l）〉 natural grassland （0.30 mm h-~）〉 sea buckthorn （0.17 mm h-t）〉 artificial grassland （0.14 mm h-l）〉 Chinese pine （0.09 mm fit）. As for the efficiency of rainfall replenishment to soil water, natural grassland was the most efficient one （35.1%）, followed by wheat （29.2%）, sea buckthorn （16.8%）, artificial grassland （11.5%）, Chinese pine （4.2%）. At last, it was found that wheat had the lowest threshold （6.8 mm） of rainfall replenishment to soil water, which was followed by natural grassland （10.5 mm）, sea buckthorn （20.5 mm）, artificial grassland （22.6 mm） and Chinese pine （26.4 mm）. These results implied that soil water in natural grassland was sensitive to rainfall and easily to be replenished, while soil water in Chinese pine was harder to be replenished by rainfall compared to other vegetation types.展开更多
Sporadic rain events that occur during summer play an important role in the initiation of biological activity of semi-arid grasslands.To understand how ecosystem processes of a buffel grass(Cenchrus ciliaris L.)-domin...Sporadic rain events that occur during summer play an important role in the initiation of biological activity of semi-arid grasslands.To understand how ecosystem processes of a buffel grass(Cenchrus ciliaris L.)-dominated grassland respond to summer rain events,an LI 6 400 gas exchange system was used to measure the leaf gas exchange and plant canopy chambers were used to measure net ecosystem CO2exchange(NEE) and ecosystem respiration(Reco), which were made sequentially during periods before rain(dry) and after rain(wet). Gross ecosystem photosynthesis(GEP) was estimated from NEE and Reco fluxes, and light use efficiency parameters were estimated using a rectangular hyperbola model. Prior to the monsoon rain, grassland biomass was non-green and dry exhibiting positive NEE(carbon source) and low GEP values during which the soil water became increasingly scarce. An initial rain pulse(60 mm) increased the NEE from pre-monsoon levels to negative NEE(carbon gain) with markedly higher GEP and increased green biomass. The leaf photosynthesis and leaf stomatal conductance were also improved substantially. The maximum net CO2uptake(i.e.,negative NEE) was sustained in the subsequent period due to multiple rain events. As a result, the grassland acted as a net carbon sink for 20 d after first rain. With cessation of rain(drying cycle), net CO2 uptake was reduced to lower values. High sensitivity of this grassland to rain suggests that any decrease in precipitation in summer may likely affect the carbon sequestration of the semiarid ecosystem.展开更多
The decomposition of plant litter is a major process of equivalent status to primary production in ecosystem functioning.The spatiotemporal changes in the composition and dynamics of litter fungal community along a cl...The decomposition of plant litter is a major process of equivalent status to primary production in ecosystem functioning.The spatiotemporal changes in the composition and dynamics of litter fungal community along a climate gradient ranging from arid desert to humid-Mediterranean regions in Israel was examined using wheat straw litter bags placed at four selected sites along the climate gradient,arid,semi-arid,Mediterranean,and humid-Mediterranean sites.Litter samples were collected over a two-year decomposition period to evaluate litter weight loss,moisture,C:N ratio,fungal composition,and isolate density.The litter decomposition rate was found to be the highest during the first year of the study at the Mediterranean and arid sites.Although the Shannon-Wiener index values of the fungal communities in the litter samples were the highest at the humid-Mediterranean site,the number of fungal species was not significantly different between the four study sites.Different fungal groups were found to be related to different study sites:Basidiomycota,Mucoromycotina,and teleomorphic Ascomycota were associated with the humid-Mediterranean site,while Coelomycetes were mostly affected by the arid site.Our results indicate that climate factors play an important role in determining the structure of saprotrophic fungal communities in the decomposing litter and in mediating plant litter decomposition processes.展开更多
Based on the carbon fluxes measured over the grassland ecosystems in Inner Mongolia （UG79 site）, Loess Plateau （SACOL site）, and Tongyu, Jilin Province （TY site） in the semiarid areas from 2007 to 2008 with the ...Based on the carbon fluxes measured over the grassland ecosystems in Inner Mongolia （UG79 site）, Loess Plateau （SACOL site）, and Tongyu, Jilin Province （TY site） in the semiarid areas from 2007 to 2008 with the eddy covariance method, we have investigated the carbon exchange processes over semiarid grassland ecosystem and its main affecting environmental variables. The precipitations at UG79 and TY sites in 2007 were below the historical average, especially for TY site, which was 50% be- low the historical average annual precipitation. The precipitation in SACOL site was close to average in 2007 but below average in 2008. The variation of monthly diurnal average NEE showed that the diurnal mean NEE decreased in the order of TY site, UG79 site, and SACOL site. However, a longer net carbon uptake period was observed at SACOL site. The diurnal course of NEE at UG79 site was similar between 2007 and 2008. The diurnal average NEE remained large during July and August in growing sea- son （May to September） at UG79 site, with maximum values approaching 0.08 mg C m^-2 s^-1 in August of 2008. The diurnal av- erage NEE of 2007 was larger than 2008 at SACOL site, with maximum values of 0.07 mg C m^-2 sq in September of 2007. A shorter carbon uptake period was recorded in 2007 at TY site, lasting from July to August. A larger diurnal average NEE oc- curred in 2008 at TY site, with maximum values of 0.12 mg C m^-2 s^-1. The ecosystem respirations of three sites were controlled by both soil temperature and soil volumetric water content （at a depth of 5 cm below the land surface）. Both UG79 site and SACOL site acted as a carbon sink during the growing periods of 2007 and 2008. Annual NEE in the growing seasons of 2007 and 2008 ranged from -68 to -50 g C m^-2 at UG79 site and from -109 to -55 g C m^-2at SACOL site. Alternation between car- bon source and carbon sink was found at TY site, with respective values of annual NEE in the growing seasons of 0.32 g C m^-2 and -73 g C m^-2 in 2007 and 2008. The magnitude and duration of carbon uptake depended mainly on the amount and timing of precipitation and the timing of the first effective rainfall during the growing season in semiarid grassland ecosystems.展开更多
基金Under the auspices of Strategic Priority Research Program of Chinese Academy of Sciences(No.XDA05060600)National Natural Science Foundation of China(No.51378306)
文摘Soil respiration （SR） is the second-largest flux in ecosystem carbon cycling. Due to the large spatio-temporal variability of environmental factors, SR varied among different vegetation types, thereby impeding accurate estimation of CO2 emissions via SR. However, studies on spatio-temporal variation of SR are still scarce for semi-arid regions of North China. In this study, we conducted 12-month SR measurements in six land-use types, including two secondary forests （Populus tomentosa （PT） and Robinia pseudoacacia （RP））, three artificial plantations （Armeniaca sibirica （AS）, Punica granatum （PG） and Ziziphusjujuba （Z J）） and one natural grassland （GR）, to quantify spatio-temporal variation of SR and distinguish its controlling factors. Results indicated that SR exhibited distinct sea- sonal patterns for the six sites. Soil respiration peaked in August 2012 and bottomed in April 2013. The temporal coefficient of variation （CI0 of SR for the six sites ranged from 76.98% to 94.08%, while the spatial CV of SR ranged from 20.28% to 72.97% across the 12-month measurement. Soil temperature and soil moisture were the major controlling factors of temporal variation of SR in the six sites, while spatial variation in SR was mainly caused by the differences in soil total nitrogen （STN）, soil organic carbon （SOC）, net photosynthesis rate, and fine root biomass. Our results show that the annual average SR and Q10 （temperature sensitivity of soil respira- tion） values tended to decrease from secondary forests and grassland to plantations, indicating that the conversion of natural ecosystems to man-made ecosystems may reduce CO2 emissions and SR temperature sensitivity. Due to the high spatio-temporal variation of SR in our study area, care should be taken when converting secondary forests and grassland to plantations from the point view of accurately quantifying C02 emissions via SR at regional scales.
基金Under the auspices of Ministry of Science and Technology of China(No.2012BAC08B01)
文摘Hydrological service is a hot issue in the current researches of ecosystem service, particularly in the upper reaches of mountain rivers in dry land areas, where the Qilian Mountain is a representative one. The Qilian Mountain, where forest, shrubland and grassland consist of its main ecosystems, can provide fresh water and many other ecosystem services, through a series of eco-hydrological process such as precipitation interception, soil water storage, and fresh water provision. Thus, monitoring water regulation and assessing the hydrological service of the Qilian Mountain are meaningful and helpful for the healthy development of the lower reaches of arid and semi-arid areas. In recent 10 years, hydrological services have been widely researched in terms of scale and landscape pattern, including water conservation, hydrological responses to afforestation and their ecological effects. This study, after analyzing lots of current models and applications of geographical information system（GIS） in hydrological services, gave a scientific and reasonable evaluation of mountain ecosystem in eco-hydrological services, by employing the combination of international forefronts and contentious issues into the Qilian Mountain. Assessments of hydrological services at regional or larger scales are limited compared with studies within watershed scale in the Qilian Mountain. In our evaluation results of forest ecosystems, it is concluded that long-term observation and dynamic monitoring of different types of ecosystem are indispensable, and the hydrological services and the potential variation in water supplement on regional and large scales should be central issues in the future research.v
基金supported by the National Natural Science Foundation of China(Grant No.41401209)National Key Research and Development Program of China(Grant No.2016YFC0501701)
文摘As one critical source of water for maintaining ecosystems in arid and semi-arid regions, rainfall replenishment to soil water can determine vegetation growth and ecosystem functions. However, the limited rainfall resources were often not used effectively in the semi-arid loess hilly areas due to random temporal and spatial distribution of rainfall and specific vegetation features. Thus, it is highly significant to determine the threshold and efficiency of rainfall replenishment to soil water under different vegetation types. The threshold and efficiency can offer scientific evidence for rehabilitating vegetation and improving efficiency of using rainfall resources. In this study, the efficiency and threshold of rainfall replenishment to soil water were determined under natural grassland, wheat, artificial grassland, sea buckthorn shrubland and Chinese pine forestland based on consecutive measurements. The results indicated that the lag-time, rate, efficiency of rainfall replenishment to soil water were closely related to vegetation type, with significant differences existing among different vegetation types. The lag-time for natural grassland in the soil horizon of 20 cm was the shortest one （26.4 h）, followed by wheat （27.8 h）, sea buckthorn （41.8 h）, artificial grassland （50.0 h） and Chinese pine （81.8 h）.The value of replenishment rate, followed the order of wheat （0.40 mm h-l）〉 natural grassland （0.30 mm h-~）〉 sea buckthorn （0.17 mm h-t）〉 artificial grassland （0.14 mm h-l）〉 Chinese pine （0.09 mm fit）. As for the efficiency of rainfall replenishment to soil water, natural grassland was the most efficient one （35.1%）, followed by wheat （29.2%）, sea buckthorn （16.8%）, artificial grassland （11.5%）, Chinese pine （4.2%）. At last, it was found that wheat had the lowest threshold （6.8 mm） of rainfall replenishment to soil water, which was followed by natural grassland （10.5 mm）, sea buckthorn （20.5 mm）, artificial grassland （22.6 mm） and Chinese pine （26.4 mm）. These results implied that soil water in natural grassland was sensitive to rainfall and easily to be replenished, while soil water in Chinese pine was harder to be replenished by rainfall compared to other vegetation types.
基金supported by Deutscher Akademischer Austausch Dienst(DAAD),Germanythe University of Bayreuth,Germany.the logistic support provided by Dr.Sudhakar SWAMY and technical staff from Madurai Kamaraj University,India
文摘Sporadic rain events that occur during summer play an important role in the initiation of biological activity of semi-arid grasslands.To understand how ecosystem processes of a buffel grass(Cenchrus ciliaris L.)-dominated grassland respond to summer rain events,an LI 6 400 gas exchange system was used to measure the leaf gas exchange and plant canopy chambers were used to measure net ecosystem CO2exchange(NEE) and ecosystem respiration(Reco), which were made sequentially during periods before rain(dry) and after rain(wet). Gross ecosystem photosynthesis(GEP) was estimated from NEE and Reco fluxes, and light use efficiency parameters were estimated using a rectangular hyperbola model. Prior to the monsoon rain, grassland biomass was non-green and dry exhibiting positive NEE(carbon source) and low GEP values during which the soil water became increasingly scarce. An initial rain pulse(60 mm) increased the NEE from pre-monsoon levels to negative NEE(carbon gain) with markedly higher GEP and increased green biomass. The leaf photosynthesis and leaf stomatal conductance were also improved substantially. The maximum net CO2uptake(i.e.,negative NEE) was sustained in the subsequent period due to multiple rain events. As a result, the grassland acted as a net carbon sink for 20 d after first rain. With cessation of rain(drying cycle), net CO2 uptake was reduced to lower values. High sensitivity of this grassland to rain suggests that any decrease in precipitation in summer may likely affect the carbon sequestration of the semiarid ecosystem.
文摘The decomposition of plant litter is a major process of equivalent status to primary production in ecosystem functioning.The spatiotemporal changes in the composition and dynamics of litter fungal community along a climate gradient ranging from arid desert to humid-Mediterranean regions in Israel was examined using wheat straw litter bags placed at four selected sites along the climate gradient,arid,semi-arid,Mediterranean,and humid-Mediterranean sites.Litter samples were collected over a two-year decomposition period to evaluate litter weight loss,moisture,C:N ratio,fungal composition,and isolate density.The litter decomposition rate was found to be the highest during the first year of the study at the Mediterranean and arid sites.Although the Shannon-Wiener index values of the fungal communities in the litter samples were the highest at the humid-Mediterranean site,the number of fungal species was not significantly different between the four study sites.Different fungal groups were found to be related to different study sites:Basidiomycota,Mucoromycotina,and teleomorphic Ascomycota were associated with the humid-Mediterranean site,while Coelomycetes were mostly affected by the arid site.Our results indicate that climate factors play an important role in determining the structure of saprotrophic fungal communities in the decomposing litter and in mediating plant litter decomposition processes.
基金supported by the National Basic Research Program of China (Grant Nos.2010CB951801and 2006CB400501)the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (Grant No.41021004)
文摘Based on the carbon fluxes measured over the grassland ecosystems in Inner Mongolia （UG79 site）, Loess Plateau （SACOL site）, and Tongyu, Jilin Province （TY site） in the semiarid areas from 2007 to 2008 with the eddy covariance method, we have investigated the carbon exchange processes over semiarid grassland ecosystem and its main affecting environmental variables. The precipitations at UG79 and TY sites in 2007 were below the historical average, especially for TY site, which was 50% be- low the historical average annual precipitation. The precipitation in SACOL site was close to average in 2007 but below average in 2008. The variation of monthly diurnal average NEE showed that the diurnal mean NEE decreased in the order of TY site, UG79 site, and SACOL site. However, a longer net carbon uptake period was observed at SACOL site. The diurnal course of NEE at UG79 site was similar between 2007 and 2008. The diurnal average NEE remained large during July and August in growing sea- son （May to September） at UG79 site, with maximum values approaching 0.08 mg C m^-2 s^-1 in August of 2008. The diurnal av- erage NEE of 2007 was larger than 2008 at SACOL site, with maximum values of 0.07 mg C m^-2 sq in September of 2007. A shorter carbon uptake period was recorded in 2007 at TY site, lasting from July to August. A larger diurnal average NEE oc- curred in 2008 at TY site, with maximum values of 0.12 mg C m^-2 s^-1. The ecosystem respirations of three sites were controlled by both soil temperature and soil volumetric water content （at a depth of 5 cm below the land surface）. Both UG79 site and SACOL site acted as a carbon sink during the growing periods of 2007 and 2008. Annual NEE in the growing seasons of 2007 and 2008 ranged from -68 to -50 g C m^-2 at UG79 site and from -109 to -55 g C m^-2at SACOL site. Alternation between car- bon source and carbon sink was found at TY site, with respective values of annual NEE in the growing seasons of 0.32 g C m^-2 and -73 g C m^-2 in 2007 and 2008. The magnitude and duration of carbon uptake depended mainly on the amount and timing of precipitation and the timing of the first effective rainfall during the growing season in semiarid grassland ecosystems.
