In the arid and semi-arid areas of China, rainfall and drought affect the growth and photosynthetic activities of plants.Gross primary productivity(GPP) is one of the most important indices that measure the photosynth...In the arid and semi-arid areas of China, rainfall and drought affect the growth and photosynthetic activities of plants.Gross primary productivity(GPP) is one of the most important indices that measure the photosynthetic ability of plants.This paper focused on the GPP of two representative grassland species(Stipa krylovii Roshev.and Allium polyrhizum Turcz.ex Regel) to demonstrate the effect of a temporal rainfall on the two species.Our research was conducted in a temperate grassland in New Barag Right Banner, Hulun Buir City, Inner Mongolia Autonomous Region of China, in a dry year 2015.We measured net ecosystem productivity(NEP) and ecosystem respiration flux(ER) using a transparent chamber system and monitored the photosynthetically active radiation(PAR), air and soil temperature and humidity simultaneously.Based on the measured values of NEP and ER, we calculated the GPP of the two species before and after the rainfall.The saturated GPP per aboveground biomass(GPPAGB) of A.polyrhizum remarkably increased from 0.033(±0.018) to 0.185(±0.055) μmol CO2/(gdw·s) by 5.6-fold and that of S.krylovii decreased from 0.068(±0.021) to 0.034(±0.011) μmol CO2/(gdw·s) by 0.5-fold on the 1st and 2nd d after a 9.1 mm rainfall event compared to the values before the rainfall at low temperatures below 35℃.However, on the 1st and 2nd d after the rainfall, both of the saturated GPPAGB values of S.krylovii and A.polyrhizum were significantly lower at high temperatures above 35℃(0.018(±0.007) and 0.110(±0.061) μmol CO2/(gdw·s), respectively) than at low temperatures below 35℃(0.034(±0.011) and 0.185(±0.055) μmol CO2/(gdw·s), respectively).The results showed that the GPP responses to the temporal rainfall differed between S.krylovii and A.polyrhizum and strongly negative influenced by temperature.The temporal rainfall seems to be more effective on the GPP of A.polyrhizum than S.krylovii.These differences might be related to the different physiological and structural features, the coexistence of the species and their species-specific survival strategies.展开更多
To describe the biodiversity patterns of plants along an altitudinal gradient on the Qinghai-Tibetan Plateau and to clarify the bias in plant specimen records at high altitude.Methods We conducted a large-scale invest...To describe the biodiversity patterns of plants along an altitudinal gradient on the Qinghai-Tibetan Plateau and to clarify the bias in plant specimen records at high altitude.Methods We conducted a large-scale investigation of vegetation at a wide range of altitudes,focusing on a high-altitudinal range(3200-5200 m)at different locations on the Qinghai-Tibetan Plateau.We then compared the altitudinal distribution of plant species obtained from our field investigation with that in plant specimen records from published sources and an online database.Important Findings Our data provide evidence that altitude plays a large role in regulating species composition on the Qinghai-Tibetan Plateau.We could not,however,detect a clear relationship between altitude and species richness,although a weak monotonically increasing trend of richness was detected with increasing altitude.According to specimen records,most species have been sampled at a wide range of altitudes,and the average range of 145 species is>2000 m.Despite this wide range,more than half of the species we observed were at higher altitudes than the specimen records indicate.High-altitude areas have probably been so poorly sampled that only a small fraction of the resident species has been recorded.This study clearly shows the regional bias of specimen records in the Qinghai-Tibetan Plateau.展开更多
Aims Recent studies have recognized the alpine grasslands on the Qinghai-Tibetan plateau as a significant sink for atmospheric CO_(2).The carbon-sink strength may differ among grassland ecosystems at various altitudes...Aims Recent studies have recognized the alpine grasslands on the Qinghai-Tibetan plateau as a significant sink for atmospheric CO_(2).The carbon-sink strength may differ among grassland ecosystems at various altitudes because of contrasting biotic and physical environments.This study aims(i)to clarify the altitudinal pattern of ecosystem CO_(2) fluxes,including gross primary production(GPP),daytime ecosystem respiration(Redaytime)and net ecosystem production(NEP),during the period with peak above-ground biomass;and(ii)to elucidate the effects of biotic and abiotic factors on the altitudinal variation of ecosystem CO_(2) fluxes.Methods Ecosystem CO_(2) fluxes and abiotic and biotic environmental factors were measured in an alpine grassland at four altitudes from 3600 to 4200 m along a slope of the Qilian Mountains on the northwestern Qinghai-Tibetan Plateau during the growing season of 2007.We used a closed-chamber method combined with shade screens and an opaque cloth to measure several carbon fluxes,GPP,Redaytime and NEP,and factors,light-response curve for GPP and temperature sensitivity of Redaytime.Above-and below-ground biomasses and soil C and N contents at each measurement point were also measured.Important Findings(i)Altitudinal pattern of ecosystem CO_(2) fluxes:The maximum net ecosystem CO_(2) flux(NEPmax),i.e.the potential ecosystem CO_(2) sink strength,was markedly different among the four altitudes.NEPmax was higher at the highest and lowest sites,ap proximately7.460.9 and6.760.6 lmol CO_(2) m^(-2)s^(-1)(mean 6 standard error),respectively,but smaller at the intermediate altitude sites(3800 and 4000 m).The altitudinal pattern of maximum gross primary production was similar to that of NEPmax.The Redaytime,however,was significantly higher at the lowest altitude(3.460.3 lmol CO_(2) m^(-2)s^(-1))than at the other three altitudes.(ii)Altitudinal variation of vegetation biomass:The aboveground biomass was higher at the highest altitude(154627 g DW m2)than at the other altitudes,which we attribute mainly to the large biomass in cushion plants at the highest altitude.The small above-ground biomass at the lower altitudes was probably due to heavy grazing during the growing season.(iii)Features of ecosystem CO_(2) fluxes:Redaytime and GPP were positively correlated with above-ground biomass.The low ratio of Redaytime to GPP at either the measurement point or the site level suggests that CO_(2) uptake efficiency tends to be higher at higher altitudes,which indicates a high potential sink strength for atmospheric CO_(2) despite the low temperature at high altitudes.The results suggest that the effect of grazing intensity on ecosystem carbon dynamics,partly by decreasing vegetation biomass,should be clarified further.展开更多
Aims Kobresia meadows,the dominant species of which differ in different habitats,cover a large area of alpine grassland on the QinghaiTibetan Plateau and act as potential CO_(2) sinks.Kobresia meadows with different d...Aims Kobresia meadows,the dominant species of which differ in different habitats,cover a large area of alpine grassland on the QinghaiTibetan Plateau and act as potential CO_(2) sinks.Kobresia meadows with different dominant species may differ in carbon sink strength.We aimed to test the hypothesis and to clarify the differences in CO_(2) sink strength among three major Kobresia meadows on the plateau and the mechanisms underlying these differences.Methods We measured the net ecosystem exchange flux(NEE),ecosystem respiration flux(ER),aboveground biomass(AGB)and environmental variables in three Kobresia meadows,dominated by K.pygmaea,K.humilis,or K.tibetica,respectively,in Haibei,Qinghai.NEE and ER were measured by a closed-chamber method.Environmental variables,including photosynthetic photon flux density(PPFD),air and soil temperature and air and soil moisture,were monitored during the above flux measurements.Important findings The measured peak AGB increased with soil water content and was 365,402 and 434 g dry weight m2 for K.pygmaea,K.humilis and K.tibetica meadow,respectively.From the maximum ecosystem photosynthetic rate in relation to PPFD measured during the growing season,we estimated gross ecosystem photosynthetic potential(GEPmax)as 22.2,29.9 and 37.8 lmol CO_(2) m2 s1 for K.pygmaea,K.humilis and K.tibetica meadow,respectively.We estimated the respective gross primary production(GPP)values as 799,1063 and 1158 g C m^(-2) year^(-1) and ER as 722,914 and 1011 g C m^(-2) year^(-1).Average net ecosystem production(NEP)was estimated to be 76.9,149.4 and 147.6 g C m^(-2) year^(-1) in K.pygmaea,K.humilis and K.tibetica meadows,respectively.The results indicate that(i)the three meadows were CO_(2) sinks during the study period and(ii)Kobresia meadows dominated by different species can differ considerably in carbon sink strength even under the same climatic conditions,which suggests the importance of characterizing spatial heterogeneity of carbon dynamics in the future.展开更多
Aims Recent studies have shown that alpine meadows on the Qinghai-Tibetan plateau act as significant CO_(2)sinks.On the plateau,alpine shrub meadow is one of typical grassland ecosystems.The major alpine shrub on the ...Aims Recent studies have shown that alpine meadows on the Qinghai-Tibetan plateau act as significant CO_(2)sinks.On the plateau,alpine shrub meadow is one of typical grassland ecosystems.The major alpine shrub on the plateau is Potentilla fruticosa L.(Rosaceae),which is distributed widely from 3200 to 4000 m.Shrub species play an important role on carbon sequestration in grassland ecosystems.In addition,alpine shrubs are sensitive to climate change such as global warming.Considering global warming,the biomass and productivity of P.fruticosa will increase on Qinghai-Tibetan Plateau.Thus,understanding the carbon dynamics in alpine shrub meadow and the role of shrubs around the upper distribution limit at present is essential to predict the change in carbon sequestration on the plateau.However,the role of shrubs on the carbon dynamics in alpine shrub meadow remains unclear.The objectives of the present study were to evaluate the magnitude of CO_(2)exchange of P.fruticosa shrub patches around the upper distribution limit and to elucidate the role of P.fruticosa on ecosystem CO_(2)fluxes in an alpine meadow.Methods We used the static acrylic chamber technique to measure and estimate the net ecosystem productivity(NEP),ecosystem respiration(Re),and gross primary productivity(GPP)of P.fruticosa shrub patches at three elevations around the species’upper distribution limit.Ecosystem CO_(2)fluxes and environmental factors were measured from 17 to 20 July 2008 at 3400,3600,and 3800 m a.s.l.We examined the maximum GPP at infinite light(GPPmax)and maximum Re(Remax)during the experimental time at each elevation in relation to aboveground biomass and environmental factors,including air and soil temperature,and soil water content.Important Findings Patches of P.fruticosa around the species’upper distribution limit absorbed CO_(2),at least during the daytime.Maximum NEP at infinite light(NEPmax)and GPPmax of shrub patches in the alpine meadow varied among the three elevations,with the highest values at 3400 m and the lowest at 3800 m.GPPmax was positively correlated with the green biomass of P.fruticosa more strongly than with total green biomass,suggesting that P.fruticosa is the major contributor to CO_(2)uptake in the alpine shrub meadow.Air temperature influenced the potential GPPat the shrub-patch scale.Remax was correlated with aboveground biomass and Remax normalized by aboveground biomass was influenced by soil water content.Potentilla fruticosa height(biomass)and frequency increased clearly as elevation decreased,which promotes the large-scale spatial variation of carbon uptake and the strength of the carbon sink at lower elevations.展开更多
Aims The aims of this study were to compare the fungal communities developing on cotton strips at three different altitudes on the Tibetan Plateau and to assess the environmental variables influencing them.Methods Cot...Aims The aims of this study were to compare the fungal communities developing on cotton strips at three different altitudes on the Tibetan Plateau and to assess the environmental variables influencing them.Methods Cotton strips that had been buried in soil for a year were sampled at three sites at different altitudes(4500,4950 and 5200 m)located on a southeast-facing slope on the Nyainqentanglha Mountains near Damxung.The fungi on the cotton strips were isolated using a modified washing method.The decomposition abilities and colony growth properties of the major species cultured in pure-culture conditions were investigated and compared.Canonical correspondence analysis(CCA)was used to evaluate the relationships between fungal community composition and environmental variables(altitude,soil depth,soil water content[SWC],plant root mass and gravel content).Important Findings A total of 24 species were isolated from the cotton strips,and 12 species occurred frequently and were regarded as major species.The number of fungal species was lower at the 4950-m altitude site than at the other two sites,indicating that not only altitude but also other factors affected the number of species present.All of the major species were able to decompose the cotton strips.In the CCA ordination,automatic forward selection revealed that altitude,SWC and plant root mass significantly affected fungal species composition.Our results suggest thatspecies numberandthecomposition ofcellulolytic fungal communities are highly correlated with environmental variables as well as altitude in the alpine meadow on the Tibetan Plateau.展开更多
基金jointly supported by the National Natural Science Foundation of China (31470504, 31670455)the Grant-in-Aid for Scientific Research by the Japan Society for the Promotion of Science (grant 23405001)the National Key Research and Development Program of China (2016YFC0500908)
文摘In the arid and semi-arid areas of China, rainfall and drought affect the growth and photosynthetic activities of plants.Gross primary productivity(GPP) is one of the most important indices that measure the photosynthetic ability of plants.This paper focused on the GPP of two representative grassland species(Stipa krylovii Roshev.and Allium polyrhizum Turcz.ex Regel) to demonstrate the effect of a temporal rainfall on the two species.Our research was conducted in a temperate grassland in New Barag Right Banner, Hulun Buir City, Inner Mongolia Autonomous Region of China, in a dry year 2015.We measured net ecosystem productivity(NEP) and ecosystem respiration flux(ER) using a transparent chamber system and monitored the photosynthetically active radiation(PAR), air and soil temperature and humidity simultaneously.Based on the measured values of NEP and ER, we calculated the GPP of the two species before and after the rainfall.The saturated GPP per aboveground biomass(GPPAGB) of A.polyrhizum remarkably increased from 0.033(±0.018) to 0.185(±0.055) μmol CO2/(gdw·s) by 5.6-fold and that of S.krylovii decreased from 0.068(±0.021) to 0.034(±0.011) μmol CO2/(gdw·s) by 0.5-fold on the 1st and 2nd d after a 9.1 mm rainfall event compared to the values before the rainfall at low temperatures below 35℃.However, on the 1st and 2nd d after the rainfall, both of the saturated GPPAGB values of S.krylovii and A.polyrhizum were significantly lower at high temperatures above 35℃(0.018(±0.007) and 0.110(±0.061) μmol CO2/(gdw·s), respectively) than at low temperatures below 35℃(0.034(±0.011) and 0.185(±0.055) μmol CO2/(gdw·s), respectively).The results showed that the GPP responses to the temporal rainfall differed between S.krylovii and A.polyrhizum and strongly negative influenced by temperature.The temporal rainfall seems to be more effective on the GPP of A.polyrhizum than S.krylovii.These differences might be related to the different physiological and structural features, the coexistence of the species and their species-specific survival strategies.
基金The Second Tibetan Plateau ScientificExpeditionand Research(STEP)program(2019QZKK0106)the National Natural Science Foundation of China(91837312)Postdoctoral Science Foundation of China(2019M660751).
文摘To describe the biodiversity patterns of plants along an altitudinal gradient on the Qinghai-Tibetan Plateau and to clarify the bias in plant specimen records at high altitude.Methods We conducted a large-scale investigation of vegetation at a wide range of altitudes,focusing on a high-altitudinal range(3200-5200 m)at different locations on the Qinghai-Tibetan Plateau.We then compared the altitudinal distribution of plant species obtained from our field investigation with that in plant specimen records from published sources and an online database.Important Findings Our data provide evidence that altitude plays a large role in regulating species composition on the Qinghai-Tibetan Plateau.We could not,however,detect a clear relationship between altitude and species richness,although a weak monotonically increasing trend of richness was detected with increasing altitude.According to specimen records,most species have been sampled at a wide range of altitudes,and the average range of 145 species is>2000 m.Despite this wide range,more than half of the species we observed were at higher altitudes than the specimen records indicate.High-altitude areas have probably been so poorly sampled that only a small fraction of the resident species has been recorded.This study clearly shows the regional bias of specimen records in the Qinghai-Tibetan Plateau.
基金One Hundred Talent Project(0429091211)Scientific Research from the Japan Society for the Promotion of Science(JSPS+1 种基金No.18710017)JSPS-KOSEF-NSFC A3 Foresight Program(Quantifying and Predicting Terrestrial Carbon Sinks in East Asia:Toward a Network of Climate Change Research).
文摘Aims Recent studies have recognized the alpine grasslands on the Qinghai-Tibetan plateau as a significant sink for atmospheric CO_(2).The carbon-sink strength may differ among grassland ecosystems at various altitudes because of contrasting biotic and physical environments.This study aims(i)to clarify the altitudinal pattern of ecosystem CO_(2) fluxes,including gross primary production(GPP),daytime ecosystem respiration(Redaytime)and net ecosystem production(NEP),during the period with peak above-ground biomass;and(ii)to elucidate the effects of biotic and abiotic factors on the altitudinal variation of ecosystem CO_(2) fluxes.Methods Ecosystem CO_(2) fluxes and abiotic and biotic environmental factors were measured in an alpine grassland at four altitudes from 3600 to 4200 m along a slope of the Qilian Mountains on the northwestern Qinghai-Tibetan Plateau during the growing season of 2007.We used a closed-chamber method combined with shade screens and an opaque cloth to measure several carbon fluxes,GPP,Redaytime and NEP,and factors,light-response curve for GPP and temperature sensitivity of Redaytime.Above-and below-ground biomasses and soil C and N contents at each measurement point were also measured.Important Findings(i)Altitudinal pattern of ecosystem CO_(2) fluxes:The maximum net ecosystem CO_(2) flux(NEPmax),i.e.the potential ecosystem CO_(2) sink strength,was markedly different among the four altitudes.NEPmax was higher at the highest and lowest sites,ap proximately7.460.9 and6.760.6 lmol CO_(2) m^(-2)s^(-1)(mean 6 standard error),respectively,but smaller at the intermediate altitude sites(3800 and 4000 m).The altitudinal pattern of maximum gross primary production was similar to that of NEPmax.The Redaytime,however,was significantly higher at the lowest altitude(3.460.3 lmol CO_(2) m^(-2)s^(-1))than at the other three altitudes.(ii)Altitudinal variation of vegetation biomass:The aboveground biomass was higher at the highest altitude(154627 g DW m2)than at the other altitudes,which we attribute mainly to the large biomass in cushion plants at the highest altitude.The small above-ground biomass at the lower altitudes was probably due to heavy grazing during the growing season.(iii)Features of ecosystem CO_(2) fluxes:Redaytime and GPP were positively correlated with above-ground biomass.The low ratio of Redaytime to GPP at either the measurement point or the site level suggests that CO_(2) uptake efficiency tends to be higher at higher altitudes,which indicates a high potential sink strength for atmospheric CO_(2) despite the low temperature at high altitudes.The results suggest that the effect of grazing intensity on ecosystem carbon dynamics,partly by decreasing vegetation biomass,should be clarified further.
基金Integrated Study for Terrestrial Carbon Management of Asia in the 21st Century Based on Scientific AdvancementsEarly Detection and Prediction of Climate Warming Based on the LongTerm Monitoring of Alpine Ecosystems on the Tibetan Plateau.
文摘Aims Kobresia meadows,the dominant species of which differ in different habitats,cover a large area of alpine grassland on the QinghaiTibetan Plateau and act as potential CO_(2) sinks.Kobresia meadows with different dominant species may differ in carbon sink strength.We aimed to test the hypothesis and to clarify the differences in CO_(2) sink strength among three major Kobresia meadows on the plateau and the mechanisms underlying these differences.Methods We measured the net ecosystem exchange flux(NEE),ecosystem respiration flux(ER),aboveground biomass(AGB)and environmental variables in three Kobresia meadows,dominated by K.pygmaea,K.humilis,or K.tibetica,respectively,in Haibei,Qinghai.NEE and ER were measured by a closed-chamber method.Environmental variables,including photosynthetic photon flux density(PPFD),air and soil temperature and air and soil moisture,were monitored during the above flux measurements.Important findings The measured peak AGB increased with soil water content and was 365,402 and 434 g dry weight m2 for K.pygmaea,K.humilis and K.tibetica meadow,respectively.From the maximum ecosystem photosynthetic rate in relation to PPFD measured during the growing season,we estimated gross ecosystem photosynthetic potential(GEPmax)as 22.2,29.9 and 37.8 lmol CO_(2) m2 s1 for K.pygmaea,K.humilis and K.tibetica meadow,respectively.We estimated the respective gross primary production(GPP)values as 799,1063 and 1158 g C m^(-2) year^(-1) and ER as 722,914 and 1011 g C m^(-2) year^(-1).Average net ecosystem production(NEP)was estimated to be 76.9,149.4 and 147.6 g C m^(-2) year^(-1) in K.pygmaea,K.humilis and K.tibetica meadows,respectively.The results indicate that(i)the three meadows were CO_(2) sinks during the study period and(ii)Kobresia meadows dominated by different species can differ considerably in carbon sink strength even under the same climatic conditions,which suggests the importance of characterizing spatial heterogeneity of carbon dynamics in the future.
基金JSPS-KOSEF-NSFC A3 Foresight Program(Quantifying and Predicting Terrestrial Carbon Sinks in East Asia:Toward a Network of Climate Change Research).
文摘Aims Recent studies have shown that alpine meadows on the Qinghai-Tibetan plateau act as significant CO_(2)sinks.On the plateau,alpine shrub meadow is one of typical grassland ecosystems.The major alpine shrub on the plateau is Potentilla fruticosa L.(Rosaceae),which is distributed widely from 3200 to 4000 m.Shrub species play an important role on carbon sequestration in grassland ecosystems.In addition,alpine shrubs are sensitive to climate change such as global warming.Considering global warming,the biomass and productivity of P.fruticosa will increase on Qinghai-Tibetan Plateau.Thus,understanding the carbon dynamics in alpine shrub meadow and the role of shrubs around the upper distribution limit at present is essential to predict the change in carbon sequestration on the plateau.However,the role of shrubs on the carbon dynamics in alpine shrub meadow remains unclear.The objectives of the present study were to evaluate the magnitude of CO_(2)exchange of P.fruticosa shrub patches around the upper distribution limit and to elucidate the role of P.fruticosa on ecosystem CO_(2)fluxes in an alpine meadow.Methods We used the static acrylic chamber technique to measure and estimate the net ecosystem productivity(NEP),ecosystem respiration(Re),and gross primary productivity(GPP)of P.fruticosa shrub patches at three elevations around the species’upper distribution limit.Ecosystem CO_(2)fluxes and environmental factors were measured from 17 to 20 July 2008 at 3400,3600,and 3800 m a.s.l.We examined the maximum GPP at infinite light(GPPmax)and maximum Re(Remax)during the experimental time at each elevation in relation to aboveground biomass and environmental factors,including air and soil temperature,and soil water content.Important Findings Patches of P.fruticosa around the species’upper distribution limit absorbed CO_(2),at least during the daytime.Maximum NEP at infinite light(NEPmax)and GPPmax of shrub patches in the alpine meadow varied among the three elevations,with the highest values at 3400 m and the lowest at 3800 m.GPPmax was positively correlated with the green biomass of P.fruticosa more strongly than with total green biomass,suggesting that P.fruticosa is the major contributor to CO_(2)uptake in the alpine shrub meadow.Air temperature influenced the potential GPPat the shrub-patch scale.Remax was correlated with aboveground biomass and Remax normalized by aboveground biomass was influenced by soil water content.Potentilla fruticosa height(biomass)and frequency increased clearly as elevation decreased,which promotes the large-scale spatial variation of carbon uptake and the strength of the carbon sink at lower elevations.
基金Academic Frontier’Project for Private Universities:a matching fund subsidy from MEXT(Ministry of Education,Culture,Sports,Science,and Technology of Japan)2007–2010.This study was part of a joint research project between the National Institute for Environmental Studies,Japan,and the Northwest Institute of Plateau of Biology,China,and was supported by the‘Early Detection and Prediction of Climate Warming Based on the Long-Term Monitoring of Alpine Ecosystems on the Tibetan Plateau’project.
文摘Aims The aims of this study were to compare the fungal communities developing on cotton strips at three different altitudes on the Tibetan Plateau and to assess the environmental variables influencing them.Methods Cotton strips that had been buried in soil for a year were sampled at three sites at different altitudes(4500,4950 and 5200 m)located on a southeast-facing slope on the Nyainqentanglha Mountains near Damxung.The fungi on the cotton strips were isolated using a modified washing method.The decomposition abilities and colony growth properties of the major species cultured in pure-culture conditions were investigated and compared.Canonical correspondence analysis(CCA)was used to evaluate the relationships between fungal community composition and environmental variables(altitude,soil depth,soil water content[SWC],plant root mass and gravel content).Important Findings A total of 24 species were isolated from the cotton strips,and 12 species occurred frequently and were regarded as major species.The number of fungal species was lower at the 4950-m altitude site than at the other two sites,indicating that not only altitude but also other factors affected the number of species present.All of the major species were able to decompose the cotton strips.In the CCA ordination,automatic forward selection revealed that altitude,SWC and plant root mass significantly affected fungal species composition.Our results suggest thatspecies numberandthecomposition ofcellulolytic fungal communities are highly correlated with environmental variables as well as altitude in the alpine meadow on the Tibetan Plateau.