Variation of soil-plant-atmosphere continuum stable isotope and water source in Qinghai spruce forest of the eastern Qilian Mountains

Understanding the hydrogen and oxygen stable isotope composition and characteristics of different water bodies in soil-plant-atmosphere continuum is of significance for revealing regional hydrological processes and water cycle mechanisms.In this study,we analyzed the stable isotopic composition,relationship and indicative significance of precipitation,soil water(0~100 cm depth)and xylem water of Qinghai spruce(Picea crassifolia)forest in the eastern Qilian Mountains,and explored the circulation process among different water bodies.The results show that the stable isotopes of precipitation vary greatly during the entire observation period.The values ofδ2H andδ^(18)O in the precipitation in the warm season are richer than those in the cold season,and the slope and intercept of local meteoric water line(LMWL,δ2H=6.79δ18O+7.13)are both smaller than global meteoric water line(GMWL,δ2H=8.17δ18O+10.56).The stable isotopes of soil water at different depths underwent different degrees of evaporative fractionation,and theδ18O andδ2H of shallow soil water varied greatly,while the deep soil water tended to be similar.The topsoil(0~10 cm)can respond quickly to precipitation,and the response of the deep soil has a time lag.In the whole growing season,0~30 cm and 60~100 cm soil water are the main water sources of Qinghai spruce.The water source of Qinghai spruce was from all soil layers in May and September,mainly from the shallow soil layer(0~30 cm)in August and October,and mainly from the deep soil layer(60~100 cm)in June and July.

Estimating distribution of water uptake with depth of winter wheat by hydrogen and oxygen stable isotopes under different irrigation depths

Crop root system plays an important role in the water cycle of the soil-plant-atmosphere continuum. In this study, com- bined isotope techniques, root length density and root cell activity analysis were used to investigate the root water uptake mechanisms of winter wheat （Triticum aesfivum L.） under different irrigation depths in the North China Plain. Both direct inference approach and multisource linear mixing model were applied to estimate the distribution of water uptake with depth in six growing stages. Results showed that winter wheat under land surface irrigation treatment （Ts） mainly absorbed water from 10-20 cm soil layers in the wintering and green stages （66.9 and 72.0%, respectively）; 0-20 cm （57.0%） in the jointing stage; 0-40 （15.3%） and 80-180 cm （58.1%） in the heading stage; 60-80 （13.2%） and 180-220 cm （35.5%） in the filling stage; and 0-40 （46.8%） and 80-100 cm （31.0%） in the ripening stage. Winter wheat under whole soil layers irrigation treatment （Tw） absorbed more water from deep soil layer than Ts in heading, filling and ripening stages. Moreover, root cell activity and root length density of winter wheat under TW were significantly greater than that of Ts in the three stages. We concluded that distribution of water uptake with depth was affected by the availability of water sources, the root length density and root cell activity. Implementation of the whole soil layers irrigation method can affect root system distribution and thereby increase water use from deeper soil and enhance water use efficiency.

Stable isotopes of water as a tracer for revealing spatial and temporal characteristics of groundwater recharge surrounding Qinghai Lake,China

Studying spatial and temporal characteristics of regional groundwater recharge will guide the scientific management and sustainable development of regional water resources.This study investigated stable isotopes(δ^(18)O and δ^(2) H)of precipitation,groundwater,river water and lake water during 2019-2020 in Qinghai Lake Basin to reveal the spatial and temporal characteristics of groundwater recharge.The local meteoric water line was simulated using ordinary least squares regression(δ^(2) H=7.80δ^(18)O+10.60).The local evaporation lines of the river water,lake water and groundwater were simulated asδ^(2) H=6.21δ^(18)O-0.72,δ^(2) H=5.73δ0-3.60 and δ^(2) H=6.59δ0+1.76,respectively.The δ^(2) H and δ^(18)O of river water and groundwater were in more depleted values due to the recharge by precipitation at high altitudes or precipitation effects,and theδ^(2) H andδ^(18)O of the lake water were in more enriched values because of evaporation.The relationship between the δ^(2) H and δ^(18)O of groundwater and river water was not significantly different,indicating a strong hydrological connection between the groundwater and river water surrounding Qinghai Lake.Additionally,the maximum values of δ^(18)O and the minimum values of lc-excess of groundwater in most regions were both in August,and the minimum values of δ^(18)O and the maximum values of lc-excess of groundwater in most regions were both in October.Therefore,the groundwater was recharged by soil water with strong evaporation in August and recharged by precipitation at high altitudes in October.The recharge rate of groundwater was relatively fast in areas with large slopes and large hydraulic gradients(e.g.,south of Qinghai Lake),and in areas with strong hydrological connections between the groundwater and river water(e.g.,the Buha River Valley).Those results can provide data support for protection and utilization of water resources in Qinghai Lake Basin,and provide reference for groundwater research in closed lake basins on the Qinghai-Tibet Plateau.

A Pilot Study of Trophic Level and Human Origins at the Xiaoshuangqiao Site, China(ca. 1400 BC) Using 8D Values of Collagen

We present here a pilot study to examine trophic level effects and migration patterns at the middle Shang Dynasty site of Xiaoshuangqiao in Henan Province using δD results combined with δ^13C and δ^15N values. A total of 33 specimens（17 humans, 7 cattle, 5 pigs, 3 sheep, 1 dog） of bone collagen were isotopically analyzed for δ^13C, δ^15N, and dD values. A strong positive correlation（R^2 = 0.94）between mean δ^15N and δD values of herbivores（cattle and sheep）, omnivores（pig）, carnivores（dog）and humans was observed. The δD results were found to increase by -10‰ to 20‰ from herbivores to omnivores to carnivorous, evidence that collagen δD results are a useful indicator for the study of trophic levels and dietary patterns at archaeological sites. The δD results were also used to examine the origins of two different groups of individuals buried at Xiaoshuangqiao. Individuals buried in sacrificial pits of district V had mean δD values（-47.0 ± 2.9‰, n = 11） that were significantly（p =0.049） elevated compared to the people buried in the stratigraphy of district IX（-51.3 ± 3.3‰, n = 3）,indicating that they were ingesting water from different locations. In addition, the D values of the people buried in the stratigraphy were similar to the pigs（-54.5 ± 4.2‰, n = 5） at Xiaoshuangqiao,suggesting that they were most probably of the local population, and that the individuals buried in the sacrificial pits were most possibly from the coast and prisoners of the Dongyi（“东夷”）people. Thus,δD results have the potential to examine human origins and migration patterns and should be increasingly used in conjunction with δ^13C and δ^15N values at archaeological sites.

Water sources of plants and groundwater in typical ecosystems in the lower reaches of the Heihe River Basin

Stable oxygen and hydrogen isotopic compositions （δ18O and δD） of soil water and shallow groundwater of a riparian forest, an artificial shrub forest, and Gobi of the lower reaches of the Heihe River Basin are used to study the recharge water sources of those ecosystems. IsoSource software is used to determine the δ180 values for root water of Populous euphratica and Tamarix ramosissima in the riparian forest ecosystem, Haloxylon ammodendron in the artificial shrub forest, and Reaumuria soongorica in the Gobi, as well as for local soil water and groundwater, and precipitation in the upper reaches of the Heihe River Basin. Our results showed that soil water and shallow groundwater of the riparian forest and the artificial shrub forest were recharged by river water which originated from precipitation in the upper reaches, and strong evaporation occurred in the artificial shrub forest. Soil water of the Gobi was not affected by Heihe River water due to this area being far away from the river channel. The main water sources of Populous euphratica were from 40-60-cm soil water and groundwater, and of Tamarix ramosissima were from 40-80-cm soil water in the riparian forest ecosystem. In the artificial forest, Haloxylon ammodendron used 200-cm saturated-layer soil water and shallow groundwater. The Reaumuria soongorica mainly used soil water from the 175-200-cm depth in the Gobi. Therefore, soil water and groundwater are the main water sources which maintain survival and growth of the plants in the extremely arid regions of the lower reaches of the Heihe River Basin.

Study on Change Rules and Influencing Factors of Soil Moisture in Huaibei Plain

[Objectives]To study the relationship between soil water,groundwater burial depth,and precipitation for summer maize in Huaibei Plain.[Methods]The atmospheric precipitation,soil water and groundwater for the growth period of summer maize in Huaibei Plain were analyzed using the 26-year long series of data from the Wudaogou Hydrological Experimental Station,combined with the hydrogen and oxygen stable isotope tracing method.[Results]The average soil moisture content of summer maize in different growth periods showed a trend of first decreasing,then increasing and then decreasing with the increase of soil depth.The average soil moisture content was the lowest at the surface soil layer.From the characteristic values of hydrogen and oxygen isotopes of atmospheric precipitation,soil water and groundwater,it can be known that the average values ofδ18O andδD of soil water decreased with the increase of soil depth,indicating that soil moisture evaporation leads to the enrichment of soil heavy isotopes,and the degree of enrichment decreased from the surface layer to the deep layer of the soil.The seasonal variation of the stable isotope of hydrogen and oxygen in soil water declined with the increase of soil depth.The soil water changes at 30 cm and 50 cm soil depths were the most obvious.The soil was easily recharged by precipitation,and soil evaporation was relatively strong.[Conclusions]The research results are favorable for in-depth understanding of the regional water cycle process,and are expected to provide a certain scientific basis for realizing the efficient and sustainable use of regional groundwater.

Differential water use strategies among selected rare and endangered species in West Ordos Desert of China

Aims West Ordos Desert(WOD)in Inner Mongolia of China is charac-terized by unique geographical and ecological features to avoid the direct invasion of Quaternary Continental Glaciation,so it hosts many endangered relic species such as Tetraena mongol-ica,Ammopiptanthus mongolicus and Potaninia mongolica from Tertiary.However,how these plants utilize available water sources remains unknown.The objective of this study was to investigate the water utilization strategies of selected rare and endangered plant species in WOD by comparing hydrogen isotope ratios between their xylem water and possible water sources following four rainfall events of varying-intensities.Methods We measured the hydrogen isotope ratios of xylem water from T.mongolica,A.mongolicus and P.mongolica and an accom-panying species Sarcozygium xanthoxylum and potential water sources(including precipitation and soil water in different soil layers from 0 to 150 cm)over 9 days following each of four varying-intensity rainfall events during the summer of 2012.And then calculated the percentage utilization of potential water sources by each species after each rainfall events using the linear mixing model.We also made the measurements of soil moisture and root biomass in favor of interpretation of plant water use strategies.Important Findings Tetraena mongolica,A.mongolicus and S.xanthoxylum primarily relied on deep soil water,whereas P.mongolica depended predomi-nantly on rainwater.These rare and endangered desert plants had differential utilizations of available water sources,so some com-petition for limited water existed among some species.Tetraena mongolica had a competitive relationship in absorption of soil moisture with the same family species S.xanthoxylum,suggesting that T.mongolica and S.xanthoxylum should be restored separately at different areas in the WOD.Overall,this study provides a better understanding of water use strategies of these four plants and scien-tific evidence for protecting rare and endangered plants,maintain-ing regional species diversity,and developing effective vegetation restoration plans in the WOD.

艾比湖流域典型荒漠植被水分利用来源研究

In arid and semi-arid environments,desert vegetation plays an important role in preventing soil erosion by wind and helps maintain the stability of desert and oasis ecosystems.Four types of typical desert vegetation,namely Populus euphratica,Haloxylon ammodendron,Nitraria sibirica,and Halostachs caspica,corresponding to different habitats(i.e.,river bank,sand dune,desert,and salt marsh)were chosen as the model vegetation in this research.Theδ^(2)H andδ^(18)O for rainwater,soil water,and plant water were applied to identify the water sources and quantify the proportions of different water sources used over the entire plant growth period(from March to October).The results showed that the precipitationδ^(2)H andδ^(18)O in the Ebinur Lake basin varied from-142.5‰to-0.6‰and from-20.16‰to 1.20‰,respectively.The largestδ^(2)H andδ^(18)O values occurred in summer and the smallest in winter.The soil waterδ^(2)H andδ^(18)O of the four habitats decreased gradually with increasing depth.Theδ^(2)H andδ^(18)O values of water extracted from the stems of the four plants had similar variation trends,that is,the maximum was observed in spring and the minimum in summer.Among the four plants,H.caspica had the highest stable isotopic values in the stem water,followed by N.sibirica,H.ammodendron,and P.euphratica.The water sources and utilization ratios of desert vegetation varied across different growth stages.Throughout the growing period,H.ammodendron mainly used groundwater,whereas the water source proportions used by N.sibirica varied greatly throughout the growing season.In spring,plants mainly relied on surface soil water,with a contribution rate of 80%-94%.However,in summer,the proportion of deep soil water used was 31%-36%;and in autumn,the proportion of middle soil water used was 33%-36%.H.caspica mainly relied on topsoil water in spring and autumn,and the proportion of soil water in the middle layer slightly increased to 20%-36%in summer.P.euphratica mainly used intermediate soil water in spring with a utilization rate of 53%-54%.In summer,groundwater was the main source,with a utilization rate of 72%-88%,and only 2%-5%came from river water,whereas in autumn,the river water utilization rate rose to 11%-21%.The results indicated that there were significant differences in water use sources during the growing period for desert vegetation in arid areas.This research provides a theoretical basis for understanding water use mechanisms,water adaptation strategies,and vegetation restoration and management in arid areas.