Cadmium (Cd) contamination in farmland poses a significant threat to food security in staple crops, especially rice. Using a mix of hydroponic and soil culture methods, stable isotope tracers, and advanced analytical techniques, this study elucidated the mechanisms of Cd uptake, translocation, and accumulation in rice throughout different growth stages. Despite a notable linear correlation between soil DTPA (diethylene-triaminepentaacetic acid)-Cd and the total Cd concentration of rice, our findings showed that the influence of soil Cd level on the proportion of Cd in grain was negligible. The study highlighted the dynamic response of Cd distribution within plant nodes to changes in DTPA-extractable Cd. Heading stage (HS) and mature stage (MS) were critical for Cd uptake and upward transport in rice, and the contribution of Cd absorption in brown rice was 28.61% and 40.16%, respectively. Moreover, the distribution of Cd in nodes showed how important nodes are for controlling and redistributing Cd in rice. In the HS, the lower node had a function in re-transporting, whereas in the MS, there was a considerable redistribution of Cd in the upper node. These insights can help us understand rice Cd dynamics and develop agronomic techniques and rice cultivars that minimize Cd accumulation.

The successful utilization of stable carbon isotope approaches in investigating forest carbon dynamics has relied on the assumption that the carbon isotope compositions (δ13C) therein have detectable temporal variations. However, interpreting the δ13C signal transfer can be challenging, given the complexities involved in disentangling the effect of a single environmental factor, the isotopic dilution effect from background CO2, and the lack of high-resolution δ13C measurements. In this study, we conducted continuous in-situ monitoring of atmospheric CO2 (δ13Ca) across a canopy profile in an old-growth temperate forest in northeast China during the normal year 2020 and the wet year 2021. Both years exhibited similar temperature conditions in terms of both seasonal variations and annual averages. We tracked the natural carbon isotope composition from δ13Ca to photosynthate (δ13Cp) and to ecosystem respiration (δ13CReco). We observed significant differences in δ13Ca between the two years. Contrary to in 2020, in 2021 there was a δ13Ca valley in the middle of the growing season, attributed to surges in soil CO2 efflux induced by precipitation, while in 2020 values peaked during that period. Despite substantial and similar seasonal variations in canopy photosynthetic discrimination (Δ13Ccanopy) in the two years, the variability of δ13Cp in 2021 was significantly lower than in 2020, due to corresponding differences in δ13Ca. Furthermore, unlike in 2020, we found almost no changes in δ13CReco in 2021, which we ascribed to the imprint of the δ13Cp signal on above-ground respiration and, more importantly, to the contribution of stable δ13C signals from soil heterotrophic respired CO2. Our findings suggest that extreme precipitation can impede the detectability of recent photosynthetic δ13C signals in ecosystem respiration in forests, thus complicating the interpretation of above- and below-ground carbon linkage using δ13CReco. This study provides new insights for unravelling precipitation-related variations in forest carbon dynamics using stable isotope techniques.

Identifying and quantifying water nitrate pollution is crucial for managing aquatic environment of a bay. Dongshan Bay, a significant semi-enclosed bay in the southeastern coastal area of Fujian Province, features mangrove and coral reef ecosystems at its estuary and bay mouth, respectively. Dongshan Bay is impacted by human activities such as mariculture. We quantified and analyzed nitrate pollution status in the surface waters of Dongshan Bay by measuring physicochemical parameters, stable isotopes (δ15N-NO3-, δ18O-NO3- and δ15N-NH4+) of the surface waters, and using statistical methods including the MixSIAR isotope mixing model. The results showed that the concentrations of chlorophyll a and dissolved inorganic nitrogen in the surface waters exhibited a noticeable gradient change, decreasing from the estuary of the Zhangjiang River to the mouth of Dongshan Bay. The maximum concentrations of chlorophyll a, NH4+, NO3- and NO2- were 45.2 μg·L-1, 52.67 μmol·L-1, 379.2 μmol·L-1 and 3.93 μmol·L-1, respectively. The nitrogen and oxygen isotope values of NH4+ and NO3- in the surface waters showed significant spatial variations. According to the MixSIAR model results, nitrogen sources in the surface waters of Dongshan Bay were mainly freshwater inputs of the Zhangjiang River estuary, aquaculture wastewater, and groundwater. The freshwater input from the Zhangjiang River estuary contributed the most (25.2%), while aquaculture wastewater, groundwater and urban sewage accounted for 24.6%, 19.0%, and 15.1%, respectively. It is evident that freshwater input from the Zhangjiang River estuary is the primary source of nitrate in the surface waters of Dongshan Bay.
识别和量化海湾水体硝态氮污染,对管理海湾水体环境至关重要。东山湾是福建省东南沿海重要的半封闭海湾,湾头漳江河口和湾口分别存在红树林和珊瑚礁生态系统,同时也伴随着海水养殖等人类活动影响。本研究通过测定海湾表层水体理化参数、稳定同位素(δ15N-NO3-、δ18O-NO3-和δ15N-NH4+),结合MixSIAR同位素混合模型等统计方法,定量化分析漳州东山湾表层水体硝态氮污染。结果表明: 东山湾表层水体叶绿素a和溶解无机氮浓度呈现较为明显的梯度变化,表现为由漳江河口向东山湾湾口方向逐渐下降,叶绿素a、NH4+、NO3-和NO2-浓度的最大值分别为45.2 μg·L-1、52.67 μmol·L-1、379.2 μmol·L-1和3.93 μmol·L-1;表层水体NH4+和NO3-的氮、氧同位素值则表现为明显的空间异质性。MixSIAR模型结果显示,东山湾表层水体潜在氮源主要来源于漳江河口的淡水输入、养殖废水以及地下水等,其中漳江河口淡水输入的贡献最大,占25.2%,养殖废水、地下水以及城市污水分别占24.6%、19.0%和15.1%。可见,漳江河口淡水输入是东山湾表层水体硝酸盐最主要的来源。.

To understand the adaptation of water use strategy of plant community to habitat heterogeneity, we measured the δD and δ18O values of xylem water of shrubs and potential water sources (soil water in different layers or groundwater) of Ammopiptanthus mongolicus communities on sand dune and Gobi from April to September in 2021 in the Ulan Buh Desert. Employing the MixSIAR model, we examined the seasonal dynamics of water source of each shrub by quantifying the contribution of different potential water sources. The results showed that A. mongolicus and Artemisia xerophytica on sand dune mainly used soil water of 10-25 cm in April and May after heavy rain in early spring, whereas Artemisia ordosica mainly used soil water of 10-200 cm. During the drought event within summer from June to August, A. mongolicus increasingly used soil water of 100-200 cm and groundwater, but A. xerophytica and A. ordosica increased the usage of 50-200 cm soil water. After the moderate rain in September, A. mongolicus evenly used soil water in all layers and groundwater, whereas two Artemisia shrubs preferred soil water of 10-50 cm. On Gobi, A. mongolicus and Nitraria sphaerocarpa evenly used soil water in all layers in April and May, mainly used 50-150 cm soil water from June to August and used 10-50 cm soil water in September. Convolvulus tragacanthoides mainly used soil water of 10-50 cm (from April to May), 25-150 cm (from June to August), and 10-25 cm (in September), separately. There were seasonal differences in water use of three shrubs on sand dune and Gobi A. mongolicus communities. During drought, A. mongolicus on sand dune could use deep soil water and groundwater, and that on Gobi relied only on deep soil water, which was more sensitive to rainfall.
为了解植物群落水分利用过程对生境异质性的适应,2021年4—9月测定乌兰布和沙漠沙丘和戈壁沙冬青群落不同灌木的木质部水和潜在水源(各层土壤水或地下水)的δD和δ18O值,通过MixSIAR模型量化不同潜在水源的贡献比例,明确各水分来源的季节动态。结果表明: 早春大雨后4月和5月沙丘的沙冬青和旱蒿对10～25 cm土壤水利用较多,黑沙蒿主要利用10～200 cm土壤水;6—8月干旱时,沙冬青对100～200 cm土壤水和地下水的利用增加,旱蒿和黑沙蒿对50～200 cm土壤水的利用增加;9月中雨后沙冬青对各层土壤水和地下水的利用比例类似,旱蒿和黑沙蒿对10～50 cm土壤水的利用增加。戈壁的沙冬青和泡泡刺4月和5月对各层土壤水的利用比例类似,6—8月和9月它们分别主要利用50～150 cm和10～50 cm土壤水;刺旋花则分别主要利用10～50 cm(4—5月)、25～150 cm(6—8月)和10～25 cm土壤水(9月)。两个沙冬青群落不同灌木的水分利用过程存在季节差异。干旱时,沙丘的沙冬青能够利用深层土壤水和部分地下水,而戈壁的沙冬青仅依赖深层土壤水,对降雨更加敏感。.

To investigate the variation and fractionation of stable isotopes from irrigation water to soil, grapes, and wine, δ2H, δ18O, and δ17O in different samples from 10 regions in China were determined using a water isotope analyser. The values were significantly different among regions according to the chemometric analysis. All isotopes were significantly and positively correlated with irrigation water-soil and grape-wine. A significant water isotopic fractionation effect was observed from the irrigation water to the soil, grapes, and wine. Stable isotope distribution characteristics correlated with longitude, latitude, altitude, temperature, precipitation, station pressure and wind speed. The linear discriminant analysis (LDA), random forest (RF), support vector machine (SVM), and feed-forward neural network (FNN) models 58.33-100 %, 80-100 %, 53.33-100 %, and 73.33-100 % accurate for distinguishing the geographical origins of all samples from training and test data, respectively. These findings provide a theoretical basis for authenticating the geographic origin of Chinese wines using stable isotope analysis.

Long-term pure forest (PF) management and successive planting has result resulted in \"low-efficiency artificial forests\" in large areas. However, controversy persists over the promoting effect of introduction of broadleaf tree species on production efficiency of PF. This study hypothesised that introduced broadleaf tree species can significantly promote both water-nutrient use efficiency and gross primary productivity (GPP)of PF. Tree ring chronologies, water source, water use efficiency and GPP were analysed in coniferous Cunninghamia lanceolata and broadleaved Phoebe zhennan growing over the past three decades. The introduction of P. zhennan into C. lanceolata plantations resulted in inter-specific competition for water, probably because of the similarity of the main water source of these two tree species. However, C. lanceolata absorbed more water with a higher nutrient level from the 40-60-cm soil layer in mixed forests (MF). Although the co-existing tree species limited the basal area increment and growth rates of C. lanceolata in MF plots, the acquisition of dissolved nutrients from the fertile topsoil layer were enhanced; this increased the water use efficiency and GPP of MF plots. To achieve better ecological benefits and GPP, MFs should be constructed in southern China.

Bivalves are often employed for biomonitoring contaminants in marine environments; however, in these large-scale programs, unavoidably, using multiple species presents a significant challenge. Interspecies differences in contaminant bioaccumulation can complicate data interpretation, and direct comparisons among species may result in misleading conclusions. Here, we propose a robust framework based on toxicokinetic measurements that accounts for interspecies differences in bioaccumulation. Specifically, via a recently developed double stable isotope tracer technique, we determined the toxicokinetics of cadmium (Cd)─a metal known for its high concentrations in bivalves and significant interspecies bioaccumulation variability─in six widespread bivalve species including mussels (Perna viridis, Mytilus unguiculatus, Mytilus galloprovincialis) and oysters (Magallana gigas, Magallana hongkongensis, Magallana angulata). Results show that oysters generally have higher Cd uptake rate constants (ku: 1.18-3.09 L g-1 d-1) and lower elimination rate constants (ke: 0.008-0.017 d-1) than mussels (ku: 0.21-0.64 L g-1 d-1; ke: 0.018-0.037 d-1). The interspecies differences in tissue Cd concentrations are predominantly due to Cd uptake rather than elimination. Utilizing toxicokinetic parameters to back-calculate Cd concentrations in seawater, we found that the ranking of Cd contamination levels at the six sites markedly differs from those based on tissue Cd concentrations. We propose that this approach will be useful for interpreting data from past and future biomonitoring programs.

Golden cuttlefish play a significant role in the food web of the East and Yellow Seas and are a valuable fishery resource in Chinese coastal waters. Samples of golden cuttlefish were obtained from the northern East China Sea between September 2021 and March 2022, and stable isotope methods were utilized in this study to examine the variations in the forage ecology of golden cuttlefish. Our findings reveal dynamic shifts in carbon and nitrogen stable isotopes (δ13C and δ15N), highlighting intricate foraging strategies tailored to growth and environmental changes. A notable trend emerges: an initial growth-linked rise in δ13C and δ15N enrichment, followed by seasonal fluctuations mirroring seasonal food availability. The ontogenetic niche evolution displays striking habitat shifts and trophic level escalation in small mantle length stages, transitioning to niche overlap and subtle trophic shifts later on. Sex-specific differences emerge, with females occupying higher trophic levels than males in most samples. This comprehensive study underscores the complexity and adaptability of golden cuttlefish feeding ecology, inviting further inquiry into their intricate relationships within the marine ecosystem.

Chlorinated pollutants may follow distinct degradation pathways in anaerobic environments compared to aerobic settings. However, the understanding of the behaviors and fate of dichlorodiphenyltrichloroethanes (DDTs) under anaerobic conditions remains limited. To address this knowledge gap, we conducted a study on flooded soil samples collected from three typical paddy fields in China using an integrated approach of enantiomer-specific analysis and compound-specific stable carbon isotope analysis. It is unexpected that the dichlorodiphenyldichloroethane /dichlorodiphenyldichloroethylene ratios (DDD/DDE=(o,p\'-DDD+p,p\'-DDD)/(o,p\'-DDE+p,p\'-DDE)) were below 1 in over 90 % of the samples. This might be attributed to the higher recalcitrance of p,p\'-DDE, which concentrations were found to be 36 times higher than p,p\'-DDD on average. There were 71.7 % of the samples showing enantiomeric fractions (EFs) of o,p\'-DDT below 0.5, indicating a preferential accumulation of the (-)-enantiomer. The δ13C values of the anaerobic metabolite o,p\'-DDD (-24.76 ± 1.35 ‰ to -34.39 ± 0.20 ‰) all deviated negatively from the initial product, while those of the aerobic metabolite o,p\'-DDE (-23.61 ± 0.48 ‰ to -38.95 ± 0.81 ‰) displayed either negative or positive deviations. This demonstrates that o,p\'-DDD is the primary metabolite of o,p\'-DDT under anaerobic conditions. However, no clear correlations were observed between the δ13C and EF of o,p\'-DDT. This study underscores the importance of such an integrated methodology in unraveling the fate and behaviors of DDTs in complex environmental systems.

Ophiuroids, as an important group of echinoderms, are widely distributed in marine benthic habitats. Previous studies have identified two primary feeding types of ophiuroids in the Yellow Sea, including carnivorous (Ophiura sarsii vadicola and Stegophiura sladeni) and suspension feeders (Ophiopholis mirabilis). Despite their ecological role in the benthic food webs, little is known about their accumulation of trace metal elements (TMEs). In this study, the content of TMEs (Pb, As, Cd, Hg, Cr, Cu, Zn), methylmercury (MeHg) and δ15N value of three ophiuroids species from the North Yellow Sea were determined. Our results showed that the contents of some TMEs (As, Cd, Cr, Cu and Zn) and MeHg were significantly different in three species of ophiuroid (p < 0.05). There were significant correlations between the accumulations of trace metal elements (Pb, Cd and Zn) and the δ15N value of the ophiuroids (p < 0.05). Additionally, As and Zn exhibited opposite correlations in ophiuroid with two feeding types, which may be related to their host species and different feeding habits. This study provided fundamental data for understanding the distribution of trace metal elements in echinoderms.