Effects of environmental conditions and leaf area index changes on seasonal variations in carbon fluxes over a wheat-maize cropland rotation.

Environmental conditions (EV) changes not only affect temporal variations in carbon fluxes directly, but affect them indirectly by impacting plant biotic traits. Investigating the extent of the effects of EV and biotic changes can help deepen our understanding of ecosystem carbon cycling. Therefore, we partitioned and quantified the contributions of EV and biotic changes' effects on seasonal variations in carbon fluxes (net ecosystem carbon exchange (NEE), and its components, i.e., gross ecosystem carbon exchange (GEE) and ecosystem respiration (RE)) in a (winter) wheat-(summer) maize rotation ecosystem from 2010 to 2012. A path analysis accompanied by Granger causality tests (GCTs), which filtered out several variables that were not causal for dependent variables, was used to calculate their respective contributions by integrating path coefficients. The seasonal variations in NEE, RE, and GEE were significantly and jointly affected by EV and the leaf area index (LAI) with R2 values ranging from 0.63 to 0.94 after the GCT. The path analysis indicated that the seasonal variations of carbon fluxes were dominated by the effects of EV changes (induced from varying EV for different fluxes, crops, and years), which contributed 60.7% (mean of two years), 64.5%, and 58.2% to wheat NEE, RE, and GEE, respectively, and 62.5%, 82.3%, and 58.1% to maize NEE, RE, and GEE, respectively. Overall, our study provided a new basis that future climatic changes may have important impacts on carbon exchanges in this rotation cropland.

Regional variation in the temperature sensitivity of soil organic matter decomposition in China's forests and grasslands.

How to assess the temperature sensitivity (Q10 ) of soil organic matter (SOM) decomposition and its regional variation with high accuracy is one of the largest uncertainties in determining the intensity and direction of the global carbon (C) cycle in response to climate change. In this study, we collected a series of soils from 22 forest sites and 30 grassland sites across China to explore regional variation in Q10 and its underlying mechanisms. We conducted a novel incubation experiment with periodically changing temperature (5-30 °C), while continuously measuring soil microbial respiration rates. The results showed that Q10 varied significantly across different ecosystems, ranging from 1.16 to 3.19 (mean 1.63). Q10 was ordered as follows: alpine grasslands (2.01) > temperate grasslands (1.81) > tropical forests (1.59) > temperate forests (1.55) > subtropical forests (1.52). The Q10 of grasslands (1.90) was significantly higher than that of forests (1.54). Furthermore, Q10 significantly increased with increasing altitude and decreased with increasing longitude. Environmental variables and substrate properties together explained 52% of total variation in Q10 across all sites. Overall, pH and soil electrical conductivity primarily explained spatial variation in Q10 . The general negative relationships between Q10 and substrate quality among all ecosystem types supported the C quality temperature (CQT) hypothesis at a large scale, which indicated that soils with low quality should have higher temperature sensitivity. Furthermore, alpine grasslands, which had the highest Q10 , were predicted to be more sensitive to climate change under the scenario of global warming.

A global synthesis of the rate and temperature sensitivity of soil nitrogen mineralization: latitudinal patterns and mechanisms.

Soil net nitrogen (N) mineralization (Nmin ) is a pivotal process in the global N cycle regulating the N availability of plant growth. Understanding the spatial patterns of Nmin, its temperature sensitivity (Q10 ) and regulatory mechanisms is critical for improving the management of soil nutrients. In this study, we evaluated 379 peer-reviewed scientific papers to explore how Nmin and the Q10 of Nmin varied among different ecosystems and regions at the global scale. The results showed that Nmin varied significantly among different ecosystems with a global average of 2.41 mg N soil kg-1  day-1 . Furthermore, Nmin significantly decreased with increasing latitude and altitude. The Q10 varied significantly among different ecosystems with a global average of 2.21, ranging from the highest found in forest soils (2.43) and the lowest found for grassland soils (1.67) and significantly increased with increasing latitude. Path analyses indicated that Nmin was primarily affected by the content of soil organic carbon (C), soil C:N ratio, and clay content, where Q10 was primarily influenced by the soil C:N ratio and soil pH. Furthermore, the activation energy (Ea ) of soil N mineralization was significantly and negative correlated with the substrate quality index among all ecosystems, indicating the applicability of the carbon quality temperature hypothesis to soil N mineralization at a global scale. These findings provided empirical evidence supporting that soil N availability, under global warming scenarios, is expected to increase stronger in colder regions as compared with that low-latitude regions due to the higher Q10 . This may alleviate the restriction of N supply for increased primary productivity at higher latitudes.

Dew water isotopic ratios and their relationships to ecosystem water pools and fluxes in a cropland and a grassland in China.

Dew formation has the potential to modulate the spatial and temporal variations of isotopic contents of atmospheric water vapor, oxygen and carbon dioxide. The goal of this paper is to improve our understanding of the isotopic interactions between dew water and ecosystem water pools and fluxes through two field experiments in a wheat/maize cropland and in a short steppe grassland in China. Measurements were made during 94 dew events of the D and (18)O compositions of dew, atmospheric vapor, leaf, xylem and soil water, and the whole ecosystem water flux. Our results demonstrate that the equilibrium fractionation played a dominant role over the kinetic fractionation in controlling the dew water isotopic compositions. A significant correlation between the isotopic compositions of leaf water and dew water suggests a large role of top-down exchange with atmospheric vapor controlling the leaf water turnover at night. According to the isotopic labeling, dew water consisted of a downward flux of water vapor from above the canopy (98%) and upward fluxes originated from soil evaporation and transpiration of the leaves in the lower canopy (2%).

Limiting resource and leaf functional traits jointly determine distribution patterns of leaf intrinsic water use efficiency along aridity gradients.

Intrinsic water use efficiency (iWUE) is a critical eco-physiological function allowing plants to adapt to water- and nutrient-limited habitats in arid and semi-arid regions. However, the distribution of iWUE in coexisting species along aridity gradients and its controlling factors are unknown. We established two transects along an aridity gradient in the grasslands of Losses Plateau (LP) and Inner Mongolia Plateau (MP) to elucidate the patterns and underlying mechanisms of iWUE distribution in coexisting species along aridity gradient. We determined leaf carbon (δ13C) and oxygen (δ18O) stable isotopes, functional traits related to carbon fixation, and limiting resources. Bulk leaf δ13C and δ18O were used as proxies for time-integrated iWUE and stomatal conductance (gs) during the growing season. Our results showed that variability in iWUE within transect was primarily controlled by species, sampling sites and an interactive effect between species and sampling sites. Mean values of iWUE (iWUEMean) increased and coefficient of variation (CV) in iWUE (iWUECV) decreased with an increase in aridity, demonstrating that increases in aridity lead to conservative and convergent water use strategies. Patterns of iWUEMean and iWUECV were controlled primarily by the ratio of soil organic carbon to total nitrogen in LP and soil moisture in MP. This revealed that the most limited resource drove the distribution patterns of iWUE along aridity gradients. Interspecific variation in iWUE within transect was positively correlated with Δ18O, indicating that interspecific variation in iWUE was primarily regulated by gs. Furthermore, relationship between iWUE and multi-dimensional functional trait spectrum indicated that species evolved species-specific strategies to adapt to a harsh habitat by partitioning limiting resources. Overall, these findings highlighted the interactive effects of limiting resources and leaf functional traits on plant adaptation strategies for iWUE, and emphasized the importance of considering biological processes in dissecting the underlying mechanisms of plant adaptation strategies at large regional scales.

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Photosynthesis and respiration are two important components of net ecosystem exchange (NEE). NEE can be directly observed by eddy covariance (EC) technique, and statistically separated into ecosystem assimilation and respiration based on the statistical flux partitioning of temperature response function or light-response curves. However, these methods would result in auto-correlation between assimilation and respiration, and overestimate daytime respiration. Recently-developed isotope ratio infrared spectroscopy permits high-resolution measurement of atmospheric CO2 and its stable carbon isotope composition (δ13C) under field conditions, and achieves diurnal and seasonal partitioning of ecosystem photosynthesis and respiration by matching with NEE measurements from EC. We expounded the fundamental theories and assumptions of isotopic flux partitioning of ecosystem photosynthesis and respiration, elaborated the development and application advance of techniques in isotopic flux measurement, summarized the advance of isotopic flux partitioning to provide new insight into the assimilation and respiration processes, and prospected the uncertainty of isotopic flux partitioning theory and the necessity of comparative researches of various methods.

Effects of reclaimed wastewater irrigation on soil-crop systems in China: A review.

Reclaimed wastewater (RW) use represents a substantial opportunity to alleviate the growing scarcity of water for irrigation of agricultural crops in China. However, insufficient understanding of the effects and fates of possible contaminants in RW promotes concerns over crop safety and prevents the extensive incorporation of RW in agriculture. We reviewed the characteristics of contaminants in RW, the fate of contaminants in soil-crop systems, and the effects of RW irrigation on soil quality and crop growth in China. We found that concentrations of heavy metals in RW were higher than the permissible limits in some areas. The total concentrations and main categories of emerging contaminants and pathogens in RW varied markedly among municipal wastewater treatment plants, and the greatest risks of contamination were posed by ofloxacin, sulfamethoxazole, and erythromycin, the most frequently observed compounds with risk quotients >1. The negative effects of salts and nutrients in RW on soil quality and crop growth were minor and manageable. The accumulation of heavy metals and emerging contaminants in soils irrigated with RW did not pose an immediate risk to soils and crops. Changes in soil microbial populations, diversity, and activity caused by RW irrigation increased crop yields and protected crops against contaminants. However, attention is necessary to the risks of bioaccumulation in soils and crops of heavy metals, emerging contaminants, intermediate metabolites, and pathogens, and their effects on human health with long-term RW irrigation. We recommend irrigation practices, crop screening, soil treatments, prioritizing the risks of contaminants, and comprehensive management to increase safety in RW used for agricultural irrigation.

Terrestrial carbon sinks in China and around the world and their contribution to carbon neutrality.

Enhancing the terrestrial ecosystem carbon sink (referred to as terrestrial C sink) is an important way to slow down the continuous increase in atmospheric carbon dioxide (CO2) concentration and to achieve carbon neutrality target. To better understand the characteristics of terrestrial C sinks and their contribution to carbon neutrality, this review summarizes major progress in terrestrial C budget researches during the past decades, clarifies spatial patterns and drivers of terrestrial C sources and sinks in China and around the world, and examines the role of terrestrial C sinks in achieving carbon neutrality target. According to recent studies, the global terrestrial C sink has been increasing from a source of (-0.2±0.9) Pg C yr-1 (1 Pg=1015 g) in the 1960s to a sink of (1.9±1.1) Pg C yr-1 in the 2010s. By synthesizing the published data, we estimate terrestrial C sink of 0.20-0.25 Pg C yr-1 in China during the past decades, and predict it to be 0.15-0.52 Pg C yr-1 by 2060. The terrestrial C sinks are mainly located in the mid- and high latitudes of the Northern Hemisphere, while tropical regions act as a weak C sink or source. The C balance differs much among ecosystem types: forest is the major C sink; shrubland, wetland and farmland soil act as C sinks; and whether the grassland functions as C sink or source remains unclear. Desert might be a C sink, but the magnitude and the associated mechanisms are still controversial. Elevated atmospheric CO2 concentration, nitrogen deposition, climate change, and land cover change are the main drivers of terrestrial C sinks, while other factors such as fires and aerosols would also affect ecosystem C balance. The driving factors of terrestrial C sink differ among regions. Elevated CO2 concentration and climate change are major drivers of the C sinks in North America and Europe, while afforestation and ecological restoration are additionally important forcing factors of terrestrial C sinks in China. For future studies, we recommend the necessity for intensive and long term ecosystem C monitoring over broad geographic scale to improve terrestrial biosphere models for accurately evaluating terrestrial C budget and its dynamics under various climate change and policy scenarios.

Soil properties mediate ecosystem intrinsic water use efficiency and stomatal conductance via taxonomic diversity and leaf economic spectrum.

The interactions between plants and soils lead to complex feedbacks that regulate intrinsic water use efficiency (iWUE) and stomatal conductance (gs) at ecosystem level and reflect water constraints on plant productivity. However, the relationships among soil properties, biodiversity, and leaf functional traits contributing to the variability in ecosystem iWUE and gs remain largely unknown. To elucidate these relationships, we used principal component analysis to reduce soil properties to a fertility spectrum and a limiting-resource spectrum across grassland, and early-, mid- and late-successional forests in a karst catchment. Leaf functional traits at community level were calculated based on leaf biomass, and were reduced to an economic spectrum and a limiting-resource spectrum. Leaf carbon (δ13C) and oxygen (δ18O) stable isotopes at community levels were used as proxies for ecosystem iWUE and gs. The effects of soil properties, biodiversity (taxonomic, functional and phylogenetic diversity) and leaf traits on δ13C and δ18O were evaluated using structural equation models. Our results showed that variability in ecosystem iWUE and gs was determined overwhelmingly by indirect effects of soil properties via two different pathways: the soil fertility spectrum, determining the number of coexisting species (taxonomic diversity) and turnover of species (leaf economic spectrum), and the soil limiting-resource spectrum, shaping the specific phylogenetic lineages (phylogenic diversity). In addition, δ13C and δ18O were constrained by the interactive effects of leaf economic spectrum, and taxonomic and phylogenic diversity; total effects of biodiversity on δ13C and δ18O were larger than those of leaf economic spectrum. Our study highlighted the critical role of the evaluating interaction relationships between leaf functional traits, biodiversity metrics and soil properties in understanding the mechanisms of ecosystem function responding to environmental change.

Interannual variability in net ecosystem carbon production in a rain-fed maize ecosystem and its climatic and biotic controls during 2005-2018.

Interannual variability (IAV) in net ecosystem carbon production (NEP) plays an important role in the processes of the carbon cycle, but the long-term trends in NEP and the climatic and biotic control of IAV in NEP still remain unclear in agroecosystems. We investigated interannual variability in NEP, expressed as annual values and anomalies, and its climatic and biotic controls using an eddy-covariance dataset for 2005-2018 for rain-fed spring maize in northeastern China. Average annual NEP was 270±31 g C m-2yr -1, with no significant changes over time. The effects on interannual variability in NEP of gross ecosystem productivity (GEP) that was mainly controlled by soil water content (SWC) and leaf area index (LAI), were more than those of respiration (RE) that was controlled by temperature and LAI. Further, maximum daily NEP (NEPmax) that was dominated by summer vapor pressure deficit explained the largest fraction of annual anomalies in NEP, followed by carbon dioxide uptake period (CUP) that was defined by the beginning date (BDOY) and the end date (EDOY) of CUP. The variability in BDOY was mainly determined by spring precipitation and the effective accumulated temperature, and the variability in EDOY was determined by autumn precipitation, SWC and LAI. NEP may decrease with declining precipitation in the future due to decreasing GEP, NEPmax, or CUP, and irrigation and residues cover may be useful in efforts to maintain current NEP levels. Our results indicate that interannual variability in NEP in agroecosystems may be more sensitive to changes in water conditions (such as precipitation, SWC and VPD) induced by climate changes, while temperature may be an important indirect factor when VPD is dominated.

Contribution of soil microbial necromass to SOC stocks during vegetation recovery in a subtropical karst ecosystem.

Carbon sequestration is a key soil function, and an increase in soil organic carbon (SOC) is an indicator of ecosystem recovery because it underpins other ecosystem services by acting as a substrate for the soil microbial community. The soil microbial community constitutes the active pool of SOC, and its necromass (microbial residue carbon, MRC) contributes strongly to the stable SOC pool. Therefore, we propose that the potential for restoration of degraded karst ecosystems lies in the abundance of soil microbial community and the persistence of its necromass, and may be measured by changes in its contribution to the active and stable SOC pools during recovery. We investigated changes in SOC stocks using an established space-for-time chronosequence along a perturbation gradient in the subtropical karst ecosystem: sloping cropland < abandoned cropland < shrubland < secondary forest < primary forest. Microbial biomarkers were extracted from soil profiles from surface to bedrock and used to measure the contributions of the soil microbial community composition (using phospholipid fatty acids, PLFAs) and MRC (using amino sugars) to SOC stocks at each recovery stage. The results showed that the SOC stocks ranged from 10.53 to 31.77 kg m-2 and increased with recovery stage, with total MRC accounting for 17-28% of SOC. Increasing PLFAs and MRC abundances were positively correlated with improved soil structure (decreased bulk density) and organic carbon, nitrogen and phosphorus nutrient. Bacterial MRC contributes more to SOC stocks than fungal residue carbon during vegetation recovery. The PLFA analysis indicated that Gram positive bacteria were the largest microbial group and were relatively more abundant in deeper soils, and biomarkers for saprophytic and ectomycorrhizal fungi were more abundant in soils under woody vegetation. In conclusion, this study suggests that the soil microbial community in karst soils have the potential to adapt to changing soil conditions and contribute substantially to building SOC stocks after abandonment of agriculture in degraded karst landscapes.

Sediment carbon short-term response to water carbon content change in a large floodplain-lake system.

After carbon (C) enters a lake through surface runoff and atmospheric deposition, most of it, being influenced by the environmental conditions of the basin, is deposited into lake sediment, thus, becoming one of the most important C pools in the world. Therefore, it is critical to understand sediment response characteristics under the context of increasing C concentrations in lake water. Based on the changes of sediment C concentration at different depths in Poyang Lake, belonging to China's large floodplain-lake system, we revealed the sediment C short-term response characteristics to changes in lake water C concentrations as well as their associated impacting factors. We found that dissolved total carbon (DTC) concentrations increased by 25.78% in winter compared to spring, while total carbon (TC) sediment concentrations increased by only 4.37% during the corresponding period. Specifically, we found that there was a hysteresis effect in the response of sediment C to the increase of water C concentration in the short term. When DTC concentrations in water were below a threshold value (12.50 mg/L), sediment TC concentrations were generally maintained at approximately 5.79 mg/kg. We also believed that biological and environmental factors and sediment stratification characteristics collectively resulted in this sediment C hysteresis effect. Among these factors and characteristics, phytoplankton can affect sediment C response by changing C absorption and utilization in water or cause a synergistic effect along with environmental factors, which is the key link that causes this C sediment hysteresis effect to occur. Furthermore, we found that the combined effect of sediment C from different depths also resulted in a hysteresis effect in C deposition.

Increased CO2 emissions surpass reductions of non-CO2 emissions more under higher experimental warming in an alpine meadow.

It is well documented that warming can accelerate greenhouse gas (GHG) emissions, further inducing a positive feedback and reinforcing future climate warming. However, how different kinds of GHGs respond to various warming magnitudes remains largely unclear, especially in the cold regions that are more sensitive to climate warming. Here, we concurrently measured carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes and their total balance in an alpine meadow in response to three levels of warming (ambient, +1.5 °C, +3.0 °C). We found warming-induced increases in CH4 uptake, decreases in N2O emissions and increases in CO2 emissions at the annual basis. Expressed as CO2-equivalents with a global warming potential of 100 years (GWP100), the enhancement of CH4 uptake and reduction of N2O emissions offset only 9% of the warming-induced increase in CO2 emissions for 1.5 °C warming, and only 7% for 3.0 °C warming. CO2 emissions were strongly stimulated, leading to a significantly positive feedback to climate system, for 3.0 °C warming but less for 1.5 °C warming. The warming with 3.0 °C altered the total GHG balance mainly by stimulating CO2 emissions in the non-growing season due to warmer soil temperatures, longer unfrozen period, and increased soil water content. The findings provide an empirical evidence that warming beyond global 2 °C target can trigger a positive GHG-climate feedback and highlight the contribution from non-growing season to this positive feedback loop in cold ecosystems.

[Transport Characteristics of Phosphorus Sources at the Multi-scale Watershed and the Associated Ecological Effects on Poyang Lake].

In this study, a cascaded watershed system in the Poyang Lake area was selected as the study site, which ranged from the primary tributaries to the lake area (Xiangxi River→Jiazhu River→Ganjiang River→Poyang Lake). The aims of the study were to monitor the P wet deposition and runoff process in the Poyang Lake area and discuss the P transport characteristics at the multi-scale watershed and its impact on phytoplankton community structure in the Poyang Lake. The results showed that the P concentration in the Poyang Lake area exhibited significant seasonal changes. Apart from the Xiangxi River watershed, the concentrations of total phosphorus (TP), dissolved total phosphorus (DTP), and orthophosphate(PO43-) were higher in the low flow period than in the high flow period at other watersheds. There was a significant correlation between TP concentration and diatom density during the high flow period, and between TP concentration and cryptophyta during the low flow period. The order of the amounts of TP and PO43- transport by runoff under different rain intensities is as follows:light rain > moderate rain > heavy rain. There is a significant difference in the deposition flux between the wet season and the dry season with seasonal change, in which the flux during the wet years was about 2.8 times higher than in the dry years. The export flux of P was also shown to be higher in the high flow than in the low flow period. As watershed size increased, the contribution rate of P export did not increase, indicating that P transported at different scales was not the main source of P in each watershed.

Prioritizing environmental risks of pharmaceuticals and personal care products in reclaimed water on urban green space in Beijing.

Pharmaceuticals and personal care products (PPCPs) in reclaimed water can enter into soil, groundwater, and air during the irrigation of urban green spaces, leading to potential risks due to their negative effects of feminization, on root elongation, and as carcinogens. In this study, a validated HYDRUS-1D model by field experiments and an exposure model were used to simulate the distributions of 67 PPCPs detected in the effluent from municipal wastewater treatment plants of Beijing under two scenarios (1, uniform irrigation concentrations; 2, detected irrigation concentrations) in soil, groundwater, and air. To determine the priority ranks of the 67 PPCPs, the effect values of the PPCPs in soil, groundwater, and air were calculated on the basis of distributions and toxicity data, and then weighted and scored. Under scenario 1, roxithromycin, medroxyprogesterone acetate, and megestrol acetate, characterized by high adsorption and low volatilization and degradation, had the highest accumulations in soil, and ofloxacin, characterized by the lowest degradation and adsorption, had the highest leaching to groundwater. The highest volatilization was observed for galaxolide abbalide, tonalid, and dioctyl phthalate. Under scenario 2, based on their overall scores and priority ranks, the 67 PPCPs were divided into three groups: I, high priority; II, moderate priority; III, low priority. Of the 67 PPCPs, 17 were classified in group I, with the highest priority rankings for ofloxacin, 17α-ethynylestradiol, dibutyl phthalate, dioctyl phthalate, and sulfamethoxazole. In group III (total 33 PPCPs), 28 of the PPCPs were not of urgent concern under reclaimed water irrigation in Beijing.

Effects of sky conditions on net ecosystem productivity of a subtropical coniferous plantation vary from half-hourly to daily timescales.

The dynamic changes of solar radiation have received wide attention in global change studies, but there are controversies about the influence of diffuse radiation on ecosystem carbon sequestration. Using eddy covariance measurements from 2010 to 2012, the effects of sky conditions extracted from adjacent sunny, cloudy, and overcast days on net ecosystem productivity (NEP) of a subtropical coniferous plantation were examined from half-hourly to daily scales. Half-hourly NEP responded to the changing radiation more efficiently on overcast days compared to sunny days, but such response did not differ obviously between cloudy and sunny days. Compared with sunny conditions, apparent quantum yield (α) under overcast (cloudy) conditions changed 282.4% (41.7%) in spring, 140.3% (-4.2%) in summer, 218.5% (38.9%) in autumn, and 146.2% (0.5%) in winter, respectively; annually, α under overcast (cloudy) conditions increased by 225.9% (19.8%) in 2010, 189.8% (6.0%) in 2011, and 159.5% (21.4%) in 2012, respectively. Moreover, the potential NEP at the light intensity of 150 and 750 W m-2 was improved due to increased diffuse fraction. However, both daytime NEP and daily NEP were significantly lower under overcast skies than under sunny and cloudy skies. Compared with sunny days, daily NEP on overcast days decreased by 127.7% in spring, 126.4% in summer, 121.8% in autumn, and 100.6% in winter, respectively; annually, daily NEP decreased by 122.5% in 2010, 141.7% in 2011, and 109.9% in 2012, respectively. Diurnal patterns of daily NEP were quite similar between sunny and cloudy days. Both path analysis and multiple regression showed that solar radiation, especially diffuse radiation, was responsible for the variations of NEP under different skies across seasons, but this effect may be weakened by seasonal droughts. This study implies that the effects of sky conditions on NEP are timescale dependent and should be paid more attention in ecosystem carbon cycle study.

[Effects of Water Vapor Source and Local Evaporation on the Stable Hydrogen and Oxygen Isotopic Compositions of Precipitation].

Stable hydrogen and oxygen isotopic compositions in precipitation are good tracers and can provide unique information about the water cycle. Precipitation samples were collected at the Nanjing, Liyang, Yixing, and Dongshan sites in 2016, and the HDO and H218O compositions of precipitation were measured. The temporal variability of HDO and H218O compositions and deuterium-excess of precipitation were analyzed, and the influence of the water vapor source and local evaporation on stable isotopic composition of precipitation were discussed. The results indicated that:① Seasonal variations in the HDO composition, H218O composition, and deuterium-excess of precipitation occurred due to different water vapor sources during the summer and winter monsoon seasons. The HDO and H218O compositions were depleted during the summer monsoon season and enriched during the winter monsoon season. The deuterium-excess during the summer monsoon season was lower compared to the winter monsoon season. ② During the summer monsoon, the evaporation of Lake Taihu made the deuterium-excess of downwind precipitation and the downwind intercept of the local meteoric water line higher. During the winter monsoon season, local evaporation had little influence on HDO and H218O components in precipitation. ③ Both of the intercepts and slopes of the local meteoric water line were higher than those of the global meteoric water line, due to moisture recycling during the winter monsoon season and different water vapor sources between the summer and winter monsoon seasons.

Internet of Things to network smart devices for ecosystem monitoring.

Smart, real-time, low-cost, and distributed ecosystem monitoring is essential for understanding and managing rapidly changing ecosystems. However, new techniques in the big data era have rarely been introduced into operational ecosystem monitoring, particularly for fragile ecosystems in remote areas. We introduce the Internet of Things (IoT) techniques to establish a prototype ecosystem monitoring system by developing innovative smart devices and using IoT technologies for ecosystem monitoring in isolated environments. The developed smart devices include four categories: large-scale and nonintrusive instruments to measure evapotranspiration and soil moisture, in situ observing systems for CO2 and δ13C associated with soil respiration, portable and distributed devices for monitoring vegetation variables, and Bi-CMOS cameras and pressure trigger sensors for terrestrial vertebrate monitoring. These new devices outperform conventional devices and are connected to each other via wireless communication networks. The breakthroughs in the ecosystem monitoring IoT include new data loggers and long-distance wireless sensor network technology that supports the rapid transmission of data from devices to wireless networks. The applicability of this ecosystem monitoring IoT is verified in three fragile ecosystems, including a karst rocky desertification area, the National Park for Amur Tigers, and the oasis-desert ecotone in China. By integrating these devices and technologies with an ecosystem monitoring information system, a seamless data acquisition, transmission, processing, and application IoT is created. The establishment of this ecosystem monitoring IoT will serve as a new paradigm for ecosystem monitoring and therefore provide a platform for ecosystem management and decision making in the era of big data.

A global database of water vapor isotopes measured with high temporal resolution infrared laser spectroscopy.

The isotopic composition of water vapour provides integrated perspectives on the hydrological histories of air masses and has been widely used for tracing physical processes in hydrological and climatic studies. Over the last two decades, the infrared laser spectroscopy technique has been used to measure the isotopic composition of water vapour near the Earth's surface. Here, we have assembled a global database of high temporal resolution stable water vapour isotope ratios (δ18O and δD) observed using this measurement technique. As of March 2018, the database includes data collected at 35 sites in 15 Köppen climate zones from the years 2004 to 2017. The key variables in each dataset are hourly values of δ18O and δD in atmospheric water vapour. To support interpretation of the isotopologue data, synchronized time series of standard meteorological variables from in situ observations and ERA5 reanalyses are also provided. This database is intended to serve as a centralized platform allowing researchers to share their vapour isotope datasets, thus facilitating investigations that transcend disciplinary and geographic boundaries.

Co-regulation of photosynthetic capacity by nitrogen, phosphorus and magnesium in a subtropical Karst forest in China.

Leaf photosynthetic capacity is mainly constrained by nitrogen (N) and phosphorus (P). Little attention has been given to the photosynthetic capacity of mature forests with high calcium (Ca) and magnesium (Mg) in the Karst critical zone. We measured light-saturated net photosynthesis (Asat), photosynthetic capacity (maximum carboxylation rate [Vcmax], and maximum electron transport rate [Jmax]) as well as leaf nutrient contents (N, P, Ca, Mg, potassium [K], and sodium [Na]), leaf mass per area (LMA), and leaf thickness (LT) in 63 dominant plants in a mature subtropical forest in the Karst critical zone in southwestern China. Compared with global data, plants showed higher Asat for a given level of P. Vcmax and Jmax were mainly co-regulated by N, P, Mg, and LT. The ratios of Vcmax to N or P, and Jmax to N or P were significantly positively related to Mg. We speculate that the photosynthetic capacity of Karst plants can be modified by Mg because Mg can enhance photosynthetic N and P use efficiency.