Responses of Tamarix ramosissima ABA accumulation to changes in groundwater levels and soil salinity in the lower reaches of Tarim River, China

The Tarim River, located in central Xinjiang Uygur Autonomous Region, is situated north of the Taklimakana Desert. A reduction in groundwater levels and a concomitant increase in soil salinity have reduced vegetation in lower reaches of the river. Tamarix ramosissima is one of the dominant plant species in this riparian system. This species provides a buffer between the desert and the riparian zone, and contributes significantly to the function of the ecosystem and the maintenance of the biodiversity. Thus, an understanding of how T. ramosissima responds to changes in groundwater levels and soil salinity is necessary for ecological and economic management of this riparian system. We found a positive correlation (Pearson Correlation Coefficient = 0.80305) between T. ramosissima Abscisic Acid (ABA) and groundwater levels, and a negative correlation between ABA and soil salinity levels (Pearson Correlation Coefficient = –0.00961). From these relationships between ABA and groundwater/salinity we concluded that subsurface groundwater level of 3.12 m and soil salinity of 0.96 g/L can limit the normal growth and development of T. ramosissima; subsurface groundwater level of larger than 5.59 m and soil salinity of higher than 1.61 g/L will strongly impede the normal development of T. ramosissima. So we should take into account the resistance of plants to environmental stressors such as drought and salinity to keep the levels of salinity and groundwater on both sides of the main river within a range, in which trees, shrubs and herbs can grow well, and perform various ecological functions. Such conservation practice will not only avoid waste of water resources, but also contribute to efficient artificial water-recharge, helping to maintain the riparian zone of Tarim River and to promote “green corridor” maintenance.     

Water sources of dominant species in three alpine ecosystems on the Tibetan Plateau, China

Plant water sources were estimated by two or three compartment linear mixing models using hydrogen and oxygen isotope （δD and δ^18O） values of different components such as plant xylem water, precipitation and river water as well as soil water on the Tibetan Plateau in the summer of 2005. Four dominant species （Quercus aquifolioides, Pinus tabulaeformis, Salix rehderiana and Nitraria tangutorum） in three typical ecosystems （forest, shrub and desert） were investigated in this study. Stable isotope ratios of the summer precipitations and the soil water presented variations in spatial and temporal scales. δ^18O values of N. tangutorum xylem water were constant in the whole growth season and very similar to those of deep soil water. Water sources for all of the plants came from both precipitations and soil water. Plants switched rapidly among different water sources when environmental water conditions changed. Rainwater had different contributions to the plants, which was influenced by amounts of precipitation. The percentage of plant xylem water derived from rainwater rose with an increase in precipitation. Water sources for broad-leaved and coniferous species were different although they grew in the same environmental conditions. For example, the broad-leaved species Q. aquifolioides used mainly the water from deep soil, while 92.5% of xylem water of the coniferous species P. tabulaeformis was derived from rainwater during the growth season. The study will be helpful for us to fully understand responses of species on the Tibetan Plateau to changes in precipitation patterns, and to assess accurately changes of vegetation distribution in the future.     

Responses of Tamarix ramosissima ABA accumulation to changes in groundwater levels and soil salinity in the lower reaches of Tarim River, China

The Tarim River, located in central Xinjiang Uygur Autonomous Region, is situated north of the Taklimakana Desert. A reduction in groundwater levels and a concomitant increase in soil salinity have reduced vegetation in lower reaches of the river. Tamarix ramosissima is one of the dominant plant species in this riparian system. This species provides a buffer between the desert and the riparian zone, and contributes significantly to the function of the ecosystem and the maintenance of the biodiversity. Thus, an understanding of how T. ramosissima responds to changes in groundwater levels and soil salinity is necessary for ecological and economic management of this riparian system. We found a positive correlation (Pearson Correlation Coefficient = 0.80305) between T. ramosissima Abscisic Acid (ABA) and groundwater levels, and a negative correlation between ABA and soil salinity levels (Pearson Correlation Coefficient = –0.00961). From these relationships between ABA and groundwater/salinity we concluded that subsurface groundwater level of 3.12 m and soil salinity of 0.96 g/L can limit the normal growth and development of T. ramosissima; subsurface groundwater level of larger than 5.59 m and soil salinity of higher than 1.61 g/L will strongly impede the normal development of T. ramosissima. So we should take into account the resistance of plants to environmental stressors such as drought and salinity to keep the levels of salinity and groundwater on both sides of the main river within a range, in which trees, shrubs and herbs can grow well, and perform various ecological functions. Such conservation practice will not only avoid waste of water resources, but also contribute to efficient artificial water-recharge, helping to maintain the riparian zone of Tarim River and to promote “green corridor” maintenance.     

The influences of surface water-overflowing disturbance on the fluctuations of Tamarix ramosissima community in Western China

The main purpose of this study is to examine the fluctuation characteristics of Tamarix ramosissima community from the year of 2007–2008 in desert riparian forest under human surface water-overflowing disturbance in the lower reaches of Tarim River, China. In this paper, community structure, species diversity and dominant species were chosen as the indicators which could reflect the characteristics of community fluctuation. The representative sampling method was used to investigate and measure the fluctuation process of Comm. T. ramosissima. The main results showed that species numbers of the community increased 66.7% under the surface water-overflowing disturbance within two years comparing with it under non-disturbance. The Sorensen similarity coefficient of plant species is 0.75 in community under the disturbance and non-disturbance, indicating that species composition is very similar and main structure of the community has not changed on these two different treatments. Species diversity index of Comm. T. ramosissima changed a lot under the disturbance. Compared with it under non-disturbance, species richness and species diversity have been increasing while species evenness declined slightly under the disturbance. The numbers and kinds of dominant species also changed in community under the disturbance, of which the dominance of T. ramosissima is significantly increased. Compared with the river channel water disturbance, surface water-overflowing disturbance could enhance seed germination and plant growth through the effect of shallow soil moisture and its physic-chemical properties. And it improved the germination of plant seed in the soil and promoted the clone growth of plant reproductive body. As a result, species diversity was increased and species composition happened significantly changed in Comm. T. ramosissima influenced by the water-overflowing disturbance. In addition, community hierarchical structure was getting more complex. And then, it was concluded that water-overflowing disturbance is an effective way to positively affect the fluctuation of Comm. T. ramosissima in the lower reaches of Tarim River. Thus, it can make up for the insufficient effectiveness of river channel water disturbance to restore damaged vegetation.     

The influences of surface water-overflowing disturbance on the fluctuations of Tamarix ramosissima community in Western China

The main purpose of this study is to examine the fluctuation characteristics of Tamarix ramosissima community from the year of 2007–2008 in desert riparian forest under human surface water-overflowing disturbance in the lower reaches of Tarim River, China. In this paper, community structure, species diversity and dominant species were chosen as the indicators which could reflect the characteristics of community fluctuation. The representative sampling method was used to investigate and measure the fluctuation process of Comm. T. ramosissima. The main results showed that species numbers of the community increased 66.7% under the surface water-overflowing disturbance within two years comparing with it under non-disturbance. The Sorensen similarity coefficient of plant species is 0.75 in community under the disturbance and non-disturbance, indicating that species composition is very similar and main structure of the community has not changed on these two different treatments. Species diversity index of Comm. T. ramosissima changed a lot under the disturbance. Compared with it under non-disturbance, species richness and species diversity have been increasing while species evenness declined slightly under the disturbance. The numbers and kinds of dominant species also changed in community under the disturbance, of which the dominance of T. ramosissima is significantly increased. Compared with the river channel water disturbance, surface water-overflowing disturbance could enhance seed germination and plant growth through the effect of shallow soil moisture and its physic-chemical properties. And it improved the germination of plant seed in the soil and promoted the clone growth of plant reproductive body. As a result, species diversity was increased and species composition happened significantly changed in Comm. T. ramosissima influenced by the water-overflowing disturbance. In addition, community hierarchical structure was getting more complex. And then, it was concluded that water-overflowing disturbance is an effective way to positively affect the fluctuation of Comm. T. ramosissima in the lower reaches of Tarim River. Thus, it can make up for the insufficient effectiveness of river channel water disturbance to restore damaged vegetation.     

Changes in plant biomass and species composition of alpine <Emphasis Type="Italic">Kobresia</Emphasis> meadows along altitudinal gradient on the Qinghai-Tibetan Plateau

Alpine Kobresia meadows are major vegetation types on the Qinghai-Tibetan Plateau. There is growing concern over their relationships among biodiversity, productivity and environments. Despite the importance of species composition, species richness, the type of different growth forms, and plant biomass structure for Kobresia meadow ecosystems, few studies have been focused on the relationship between biomass and environmental gradient in the Kobresia meadow plant communities, particularly in relation to soil moisture and edaphic gradients. We measured the plant species composition, herbaceous litter, aboveground and belowground biomass in three Kobresia meadow plant communities in Haibei Alpine Meadow Ecosystem Research Station from 2001 to 2004. Community differences in plant species composition were reflected in biomass distribution. The total biomass showed a decrease from 13196.96±719.69 g/m2 in the sedge-dominated K. tibetica swamp to 2869.58±147.52 g/m2 in the forb and sedge dominated K. pygmaea meadow, and to 2153.08±141.95 g/m2 in the forbs and grasses dominated K. humilis along with the increase of altitude. The vertical distribution of belowground biomass is distinct in the three meadow communities, and the belowground biomass at the depth of 0-10 cm in K. tibetica swamp meadow was significantly higher than that in K. humilis and K. pygmaea meadows (P＜0.01). The herbaceous litter in K. tibetica swamp was significantly higher than those in K. pygnaeca and K. humilis meadows. The effects of plant litter are enhanced when ground water and soil moisture levels are raised. The relative importance of litter and vegetation may vary with soil water availability. In the K. tibetica swamp, total biomass was negatively correlated to species richness (P＜0.05); aboveground biomass was positively correlated to soil organic matter, soil moisture, and plant cover (P＜0.05); belowground biomass was positively correlated with soil moisture (P＜0.05). However, in the K. pygnaeca and K. humilis meadow communities, aboveground biomass was positively correlated to soil organic matter and soil total nitrogen (P＜0.05). This suggests that the distribution of biomass coincided with soil moisture and edaphic gradient in alpine meadows.     

Physiological Responses of Three Contrasting Plant Species to Groundwater Level Changes in an Arid Environment

Plants growing on both sides of the Tarim River in western China serve as a natural barrier containing the deserts and protecting the oasis, and their growth is greatly affected by water conditions In their local habitat. We studied the physiological responses of three different types plants （i.e. Populus euphratlca Oliver, Tamarix ramosissima L., and Apocynum venetumas Linn） to changing groundwater levels by analyzing changes in chlorophyll, soluble sugar, proline （Pro）, malondialdehyde （MDA）, superoxlde dlsmutase （SOD）, peroxidase （POD）, indoleacetic acid （IAA）, giberellic acid, abscisic acid （ABA） and cytokinin （CK）. Relationships between these physiological characteristics and groundwater levels were analyzed in order to assess the drought tolerance of the three plant species based on the values of average membership function. We found that MDA, SOD and ABA were more susceptible to changes in groundwater level, followed by POD, IAA and CK. Among the three plant species, Populus euphratica responded physiologically less to changing groundwater level than T. ramosissima and A. venetumas.     

Soil water use strategy of dominant species in typical natural and planted shrubs in loess hilly Region北大核心CSCD

Aims Artemisia gmelinii is a dominant specie naturally established after abandonment of cultivated lands in the Loess Plateau, and Caragana korshinskii is one of the main planted shrub species to control soil erosion. Improved understanding of water use strategies of these two species is of great significance to evaluate the sustainable development of the Loess Plateau under the trend of climate warming and increasing drought events. Methods Stable oxygen-18 isotope was used to determine seasonal variations in the water sources of native A. gmelinii communities established after abandonment of cultivated lands for 7 and 30 years and planted C. korshinskii after 30 years. The contributions of soil water from different depths to water uptake were estimated by the MixSIR Bayesian mixing model. The geometric mean regression method was used to fit the line of precipitation to get the local meteoric water line (LWML). Important findings The stable hydrogen isotope rate (δD) and stable oxygen isotope rate (δ18O) of soil water and xylem water plotted to the right side of the LWML, indicating that the isotopic compositions of soil water were enriched due to evaporation. The native A. gmelinii communities established after abandonment of cultivated lands for 7 years and planted C. korshinskii after 30 years showed plasticity in switching water sources from different soil layers, extracting water from shallow soil (0-40 cm) when soil water was available, but deeper soil (40-80 cm) when shallow soil water was dry. In contrast, A. gmelinii growing in site after cultivation abandonment for 30 years mainly relied on water from the surface soil (0-10 cm) throughout the growing season. Our results suggest that the ability of A. gmelinii to compete for soil water reduces with aging of the community while the planted C. korshinskii will have competitive advantage under the condition of increasing frequency of drought events in the future.     

Nitrogen released from different plant residues of the Loess Plateau and their additions on contents of microbial biomass carbon, nitrogen in soil

An incubation method was used to investigate the nitrogen release characteristics from the residue of ten plant species which commonly grow in the northern part of the Loess Plateau. The effect of the residue on soil microbial biomass carbon (SMBC) and soil microbial biomass nitrogen (SMBN) was also determined. There were significant differences in the total N content and the C/N ratios among the different types of plant residue. The total N content of the residues ranged from 6.61 to 32.78 g kg^?1. The C/N ratio of the residue ranged from 14 to 65. There was an immediate increase in soil N after alfalfa, erect milkvetch, and korshinsk peashrub residue was added to the soil. In contrast, soil N decreased after elm, sea buckthorn, and wild peach residue was added to the soil. The soil N content remained relatively low for 14–34 days and then increased. This indicated that N immobilization occurred during the early portion of the incubation period when elm, sea buckthorn and wild peach residue was added to the soil. Soil N levels were low during the entire incubation period when simon poplar, locust, Stipa bungeana, and old world bluestem residue were added to the soil. The addition of plant residue significantly increased SMBC and SMBN in all treatments. The SMBC and SMBN values were greatest in treatments containing plant residue with high total N content and low C/N ratios. The C/N ratios of korshinsk peashrub, sea buckthorn, and wild peach residues were similar, but the amount of N released from these residues and the effects of the residue on SMBC and SMBN in soil were significantly different. This indicates that not only the C/N ratio but also the chemical composition of the plant residue affected decomposition. It is important to consider C and N release characteristics from plant residue in order to adjust the C and N balance of soil when revegetating degraded ecosystems.     

Soil moisture ecological environment of artificial vegetation on steep slope of loess region in North Shaanxi Province, China

By means of fixed-point monitoring and comparative analysis, soil water deficient situation, soil moisture dynamic variation laws, soil aridization and soil water compensation features under condition of different artificial vegetations were studied on 35–45° steep slope of loess region in North Shaanxi Province, China. The results showed that soil water was extremely deficient under condition of perennial artificial vegetation on steep slope, soil water storage (0–10 m) was only equal to 26.2%–42.0% of the field capacity in dry years, and in rainy years it was also only equal to 27.0%–43.3% of the field capacity. The order of soil water deficit was Caragana microphylla > locust > alfalfa > Chinese arborvitae > poplar > Chinese pine > wild land > apricot > Chinese date > farm land. Annual variations of soil moisture with the same vegetation were weakened with soil depth increasing, and occurred mainly in 0–200 cm soil layers. In the same growth season, all CVs (coefficients of variation) of soil moisture under condition of different vegetations were bigger and concentrated comparatively in 0–120 cm soil layers, but difference of CVs in different vegetations was small. Below 120 cm soil layers, CVs were smaller, but difference of CVs in different vegetations was bigger. Permanent dry soil layers always occurred under condition of perennial vegetation on steep slope, but the difference of soil aridization intensity was obvious among different vegetations and growth years. Soil water compensation and recovery depths in rainy seasons were 1.0–1.4 m, but the soil water storage increment and compensation degree in different vegetations were dramatically different. Soil water compensation depth in the same vegetation in rainy years was over 60 cm more than that in dry years, while the soil water storage increment in 5 m soil layers increased over 3 times. Under natural precipitation, the soil water deficit in artificial vegetation on steep slope cannot be ameliorated, and the soil aridization also can't be relieved.     

Changes in plant biomass and species composition of alpine Kobresia meadows along altitudinal gradient on the Qinghai-Tibetan Plateau

Alpine Kobresia meadows are major vegetation types on the Qinghai-Tibetan Plateau. There is growing concern over their relationships among biodiversity, productivity and environments. Despite the im-portance of species composition, species richness, the type of different growth forms, and plant bio-mass structure for Kobresia meadow ecosystems, few studies have been focused on the relationship between biomass and environmental gradient in the Kobresia meadow plant communities, particularly in relation to soil moisture and edaphic gradients. We measured the plant species composition, her-baceous litter, aboveground and belowground biomass in three Kobresia meadow plant communities in Haibei Alpine Meadow Ecosystem Research Station from 2001 to 2004. Community differences in plant species composition were reflected in biomass distribution. The total biomass showed a de-crease from 13196.96±719.69 g/m2 in the sedge-dominated K. tibetica swamp to 2869.58±147.52 g/m2 in the forb and sedge dominated K. pygmaea meadow, and to 2153.08±141.95 g/m2 in the forbs and grasses dominated K. humilis along with the increase of altitude. The vertical distribution of below-ground biomass is distinct in the three meadow communities, and the belowground biomass at the depth of 0-10 cm in K. tibetica swamp meadow was significantly higher than that in K. humilis and K. pygmaea meadows (P<0.01). The herbaceous litter in K. tibetica swamp was significantly higher than those in K. pygnaeca and K. humilis meadows. The effects of plant litter are enhanced when ground water and soil moisture levels are raised. The relative importance of litter and vegetation may vary with soil water availability. In the K. tibetica swamp, total biomass was negatively correlated to species richness (P<0.05); aboveground biomass was positively correlated to soil organic matter, soil moisture, and plant cover (P<0.05); belowground biomass was positively correlated with soil moisture (P<0.05). However, in the K. pygnaeca and K. humilis meadow communities, aboveground biomass was posi-tively correlated to soil organic matter and soil total nitrogen (P<0.05). This suggests that the distribu-tion of biomass coincided with soil moisture and edaphic gradient in alpine meadows.     

Effect of Seasonality on Distribution of Macroalgae in a Stream System （Xin＇an Spring）in Shanxi Province, North China

A survey of the seasonal distribution of macroalgae in a stream system in Shanxi Province, north China, was undertaken from July 2004 to April 2005. The relative abundance and percentage cover of macroalgae, and several environmental factors were monitored along a 20-m stretch at each of four sites, at intervals of approximately three months （one sampling per season）. Several stream conditions were relatively constant over the sampling period （pH, maximum width and maximum depth）, whereas others exhibited a distinct seasonal pattern （water temperature and specific conductance）, and some fluctuated with no discernable seasonal pattern （current velocity and dissolved oxygen）. Forty-two species of macroalgae were found, with a predominance of Chlorophyta （26 species, 61.9%）. Rhodophyts and Charophyta represented the smallest proportion （1 species each, 2.38%）. Six macroalgae species were the most widespread, occurring in all four sampling sites. Twelve species were found at only one site each. In terms of seasonality, eight species occurred throughout the year, whereas 16 species were found in only one season each. The macroalgal community at Xin＇an Spring was species rich relative to other streams. Species richness per sampling site was negatively correlated with pH. Principal component analysis revealed that no single variable had much influence on the macroalgal seasonal dynamics. We calculated Sorensen similarity indices to compare our study with other continent-wide surveys of stream macroalgae, but the similarity indices were all very low. This study also shows that macroalgae in different locations have significant reproductive isolation.     

Effects of deep soil desiccation on artificial forestlands in different vegetation zones on the Loess Plateau of China

Deep soil desiccations are increasingly threatening artificial forests on the Loess Plateau of China. Soil moisture in 0–1000 cm soil layers of 23 kinds of tree and shrub forestlands was measured. Average soil moisture in 0–1000 cm soil profile of the forestlands was 10.84%, obviously lower than soil moisture in local natural grasslands and soil stable moisture. Average soil desic-cation intensity reached a medium level. Maximum soil water use depth was close to or over 1000 cm, and the thickness of desic-cated soil layers in forestlands reached or passed 800 cm.     

Nitrogen released from different plant residues of the Loess Plateau and their additions on contents of microbial biomass carbon, nitrogen in soil

An incubation method was used to investigate the nitrogen release characteristics from the residue of ten plant species which commonly grow in the northern part of the Loess Plateau. The effect of the residue on soil microbial biomass carbon (SMBC) and soil microbial biomass nitrogen (SMBN) was also determined. There were significant differences in the total N content and the C/N ratios among the different types of plant residue. The total N content of the residues ranged from 6.61 to 32.78 g kg^?1. The C/N ratio of the residue ranged from 14 to 65. There was an immediate increase in soil N after alfalfa, erect milkvetch, and korshinsk peashrub residue was added to the soil. In contrast, soil N decreased after elm, sea buckthorn, and wild peach residue was added to the soil. The soil N content remained relatively low for 14–34 days and then increased. This indicated that N immobilization occurred during the early portion of the incubation period when elm, sea buckthorn and wild peach residue was added to the soil. Soil N levels were low during the entire incubation period when simon poplar, locust, Stipa bungeana, and old world bluestem residue were added to the soil. The addition of plant residue significantly increased SMBC and SMBN in all treatments. The SMBC and SMBN values were greatest in treatments containing plant residue with high total N content and low C/N ratios. The C/N ratios of korshinsk peashrub, sea buckthorn, and wild peach residues were similar, but the amount of N released from these residues and the effects of the residue on SMBC and SMBN in soil were significantly different. This indicates that not only the C/N ratio but also the chemical composition of the plant residue affected decomposition. It is important to consider C and N release characteristics from plant residue in order to adjust the C and N balance of soil when revegetating degraded ecosystems.     

Estimation of evaporation rate from soil surface using stable isotopic composition of throughfall and stream water in a tropical seasonal rain forest of Xishuangbanna, Southwest China

Xishuangbanna is located at the northern edge of the distribution of tropical forests in Southeast Asia, and it has a very high frequency of radiation fog, especially during the dry season (November-April). In this study, rainwater, throughfall, intercepted fog water (fog drip) by forest canopy, and stream water were collected in January 2002 and December 2003 for stable isotopic analysis at a tropical seasonal rain forest site in Xishuangbanna, Southwest China. The objective of the study is to estimate the evaporation rate from the forest floor. The stable hydrogen (δD) and oxygen isotope composition (δ¹⁸O) of rainwater, throughfall, fog drip, and stream water was determined using an isotope ratio mass spectrometer. Stream water during the non-storm runoff period was considered to reflect the effect of evaporation from the forest floor. The evaporation rates from the forest floor were estimated using isotope composition values in stream water and the total throughfall was estimated using the Rayleigh distillation equation under equilibrium conditions. The results indicated that the annual weighted means of δD and δ¹⁸O in fog drip were consistently more enriched than those of rainwater and stream water, and the fog drip was thought to contain water that had evaporated and recycled. The weighted means of δD and δ¹⁸O in stream water during the non-storm runoff period were 5.69% and 0.39% more enriched than those of the total throughfall (rain throughfall fog drip) in 2002, while in 2003 these were 5.05% and 0.28%, respectively. Evapotranspiration in the humid year 2002 and the dry year 2003, computed from the water balance, was 1186 mm and 987 mm, respectively, which was quite low when compared with the values reported in some humid tropical forests. Consequently, the evaporation rate from the forest floor was 5.1% of the evapotranspiration in 2002, and 3.1% in 2003. The lower evaporation rate was thought to be mainly a result of the influence of the high frequency of heavy radiation fog on the rain forest during the night in the dry season (November-April).     

Estimation of evaporation rate from soil surface using stable isotopic composition of throughfall and stream water in a tropical seasonal rain forest of Xishuangbanna, Southwest China

Xishuangbanna is located at the northern edge of the distribution of tropical forests in Southeast Asia, and it has a very high frequency of radiation fog, especially during the dry season (November-April). In this study, rainwater, throughfall, intercepted fog water (fog drip) by forest canopy, and stream water were collected in January 2002 and December 2003 for stable isotopic analysis at a tropical seasonal rain forest site in Xishuangbanna, Southwest China. The objective of the study is to estimate the evaporation rate from the forest floor. The stable hydrogen (δD) and oxygen isotope composition (δ¹⁸O) of rainwater, throughfall, fog drip, and stream water was determined using an isotope ratio mass spectrometer. Stream water during the non-storm runoff period was considered to reflect the effect of evaporation from the forest floor. The evaporation rates from the forest floor were estimated using isotope composition values in stream water and the total throughfall was estimated using the Rayleigh distillation equation under equilibrium conditions. The results indicated that the annual weighted means of δD and δ¹⁸O in fog drip were consistently more enriched than those of rainwater and stream water, and the fog drip was thought to contain water that had evaporated and recycled. The weighted means of δD and δ¹⁸O in stream water during the non-storm runoff period were 5.69% and 0.39% more enriched than those of the total throughfall (rain throughfall + fog drip) in 2002, while in 2003 these were 5.05% and 0.28%, respectively. Evapotranspiration in the humid year 2002 and the dry year 2003, computed from the water balance, was 1186 mm and 987 mm, respectively, which was quite low when compared with the values reported in some humid tropical forests. Consequently, the evaporation rate from the forest floor was 5.1% of the evapotranspiration in 2002, and 3.1% in 2003. The lower evaporation rate was thought to be mainly a result of the influence of the high frequency of heavy radiation fog on the rain forest during the night in the dry season (November-April).     

Modeling the spatial–temporal dynamics of water use efficiency in Yangtze River Basin using IBIS model

Climate change alters regional water and carbon cycling, which has been a hot study point in the filed of climatology and ecology. As a traditionally “water-rich” region of China, Yangtze River Basin plays an important role in regional economic development and ecosystem productivity. However, the mechanism of the influence of climate change on water and carbon cycling has been received little attention. As a coupling indicator for carbon and water, the water use efficiency (WUE) is widely used, which indicates the water consumption for carbon sequestration in watershed and regional scale. A lot of studies showed that climate change has significantly affected the water resource and production of the ecosystems in Yangtze River Basin during the period of 1956–2006, when great climate variations were occurred. To better understand the alternation pattern for the relationship between water and carbon cycling under climate change at regional scale, the WUE and the spatiotemporal variations patterns were simulated in the study area from 1956 to 2006 by using the Integrated Biosphere Simulator (IBIS). The results showed that the WUE spatial pattern had the annual and seasonal variations. In general, the average annual WUE value per square meter was about 0.58 g C/kg H₂O in Yangtze River Basin. The high WUE levels were mainly distributed in the eastern area of Sichuan, western area of Jiangxi and Hunan, and the highest value reached 0.88 g C/kg H₂O. The lowest WUE’s were mainly located in the western area of Sichuan and Qinghai with the lowest values reaching to 0.36 g C/kg H₂O. The WUE in other regions mostly ranged from 0.5 to 0.6 g C/kg H₂O. For the whole study area, the annual WUE slowly increased from 1956 to 2006. The WUE in the upper reaches of Yangtze River increased based on the simulated temporal trends, which mainly located in the western area of the Sichuan Basin; the WUE of the middle reaches of Yangtze River had increased slightly from 1987 to 1996, and then decreased from 1996 to 2006; the lower reaches of Yangtze River always had smaller WUE’s than the average from 1956 to 2006. The spatiotemporal variability of the WUE in the vegetation types was obvious in the Yangtze River Basin, and it was depended on the climate and soil conditions, and as well the disturbance in its distribution areas. The temporal variations of WUE among different vegetation types had similar trends but different in values. The forest type had higher WUE than any other vegetation types ranging from 0.65 to 0.8 g C/kg H₂O. The WUE of shrubland ranged from 0.45 to 0.6 g C/kg H₂O. The WUE of tundra was the lowest, indicating the differences in plant physiology. The consistence of the spatial pattern of WUE with the NPP indicated that the regional production of Yangtze River Basin increased based on the water resources prompted and vegetation restoration. We found the drought climate was one of critical factor that impacts the alteration of WUE in Yangtze River Basin in the simulation.     

Photosynthesis and Water Use Efficiency of Platycladus Orientalis and Robinia Pseudoacacia Saplings under Steady Soil Water Stress during Different Stages of Their Annual Growth Period

A simulated drought experiment was conducted in a rain-free shed to test the physiological response of Platycladus orientalis and Robinia pseudoacacia saplings to steady soil water stress during different stages. The five soil water treatments were： 100%, 87.84%, 70%, 52.16% and 40% of field capacity. The results showed that the net photosynthetic rate of R. pseudoacacia decreased as soil water potential decreased in the range between -0.041 MPa and -0.292 MPa. The threshold value at which the net photosynthetic rate changed significantly was -0.12 MPa. The relationship between net photosynthetic rate of P. orientalis and soil water potential could be described as a quadratic parabola in the range between -0.041 MPa and -0.648 MPa. Analysis of variance showed significant differences in the net photosynthetic rate of P. orientalis between soil water potentials of -0.061 MPa ~, -0.648 MPa. Average water use efficiency （WUE） increased as soil water potential decreased, but the influence mechanism of soil water stress on leaf WUE and photosynthetic rate for the two species were different evidently.     

Modeling the spatial–temporal dynamics of water use efficiency in Yangtze River Basin using IBIS model

Climate change alters regional water and carbon cycling, which has been a hot study point in the filed of climatology and ecology. As a traditionally “water-rich” region of China, Yangtze River Basin plays an important role in regional economic development and ecosystem productivity. However, the mechanism of the influence of climate change on water and carbon cycling has been received little attention. As a coupling indicator for carbon and water, the water use efficiency (WUE) is widely used, which indicates the water consumption for carbon sequestration in watershed and regional scale. A lot of studies showed that climate change has significantly affected the water resource and production of the ecosystems in Yangtze River Basin during the period of 1956–2006, when great climate variations were occurred. To better understand the alternation pattern for the relationship between water and carbon cycling under climate change at regional scale, the WUE and the spatiotemporal variations patterns were simulated in the study area from 1956 to 2006 by using the Integrated Biosphere Simulator (IBIS). The results showed that the WUE spatial pattern had the annual and seasonal variations. In general, the average annual WUE value per square meter was about 0.58 g C/kg H₂O in Yangtze River Basin. The high WUE levels were mainly distributed in the eastern area of Sichuan, western area of Jiangxi and Hunan, and the highest value reached 0.88 g C/kg H₂O. The lowest WUE’s were mainly located in the western area of Sichuan and Qinghai with the lowest values reaching to 0.36 g C/kg H₂O. The WUE in other regions mostly ranged from 0.5 to 0.6 g C/kg H₂O. For the whole study area, the annual WUE slowly increased from 1956 to 2006. The WUE in the upper reaches of Yangtze River increased based on the simulated temporal trends, which mainly located in the western area of the Sichuan Basin; the WUE of the middle reaches of Yangtze River had increased slightly from 1987 to 1996, and then decreased from 1996 to 2006; the lower reaches of Yangtze River always had smaller WUE’s than the average from 1956 to 2006. The spatiotemporal variability of the WUE in the vegetation types was obvious in the Yangtze River Basin, and it was depended on the climate and soil conditions, and as well the disturbance in its distribution areas. The temporal variations of WUE among different vegetation types had similar trends but different in values. The forest type had higher WUE than any other vegetation types ranging from 0.65 to 0.8 g C/kg H₂O. The WUE of shrubland ranged from 0.45 to 0.6 g C/kg H₂O. The WUE of tundra was the lowest, indicating the differences in plant physiology. The consistence of the spatial pattern of WUE with the NPP indicated that the regional production of Yangtze River Basin increased based on the water resources prompted and vegetation restoration. We found the drought climate was one of critical factor that impacts the alteration of WUE in Yangtze River Basin in the simulation.     

Responses of soil N2O emissions to experimental warming regulated by soil moisture in an alpine Steppe北大核心CSCD

Aims Nitrous oxide (N2O) is one of the most important greenhouse gases, which contributes a lot to global warming. However, considerable variations are observed in the responses of soil N2O emissions to experimental warming, and the underlying microbial processes remain unknown. Methods A warming experiment based on open-Top chambers (OTCs) was set up in a typical alpine steppe on the Qinghai-Xizang Plateau. The static chamber combined gas chromatography method was applied to investigate soil N2O flux under control and warming treatments during the growing seasons in 2014 and 2015. Gene abundances of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) were quantified using quantitative real-Time PCR. Important findings Our results showed that the warming treatments increased soil temperature by 1.7 and 1.6 °C and decreased volumetric water content by 2.5% and 3.3% respectively during the growing season (May to October) in 2014 and 2015. However, there were no significant differences in other soil properties. Our results also revealed that, the magnitude of soil N2O emissions exhibited substantial variations between the two experi mental years, which were 3.23 and 1.47 μg·m-2·h-1 in 2014 and 2015, respectively, but no significant difference in N2O fluxes was observed between control and warming treatments. AOA and AOB abundances are 15.2 × 107 and 10.0 × 105 copies·g-1 in 2014, and 5.0 × 107 and 4.7 × 105 copies·g-1 in 2015, with no significant differences between control and warming treatments during the experimental period. Furthermore, warming-induced changes in N2O emissions had no significant relationship with the changes in soil temperature, but showed a significant positive correlation with the changes in soil moisture at seasonal scale. Overall, these results demonstrate that soil moisture regulates the responses of N2O emissions to experimental warming, highlighting the necessity to consider the warming-induced drying effect when estimating the magnitude of N2O emissions under future climate warming. © 2018 Editorial Office of Chinese Journal of Plant Ecology. All rights reserved.