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AIMS: Stable isotopes of oxygen and hydrogen are often used to determine plant water uptake depths. We investigated whether and to what extend soil moisture, clay content, and soil calcium carbonate influences the water isotopic composition. METHODS: In the laboratory, dried soil samples varying in clay content were rewetted with different amounts of water of known isotopic composition. Further, we removed soil carbonate from a subset of samples prior to rewetting. Water was extracted from samples via cryogenic vacuum extraction and analysed by mass spectrometry. RESULTS: The isotopic composition of extracted soil water was similarly depleted in both ¹⁸O and ²H with decreasing soil moisture and increasing clay and carbonate content. Soil carbonate changed the δ¹⁸O composition while δ²H was not affected. CONCLUSIONS: Our results indicate that soil carbonate can cause artifacts for ¹⁸O isotopic composition of soil water. At low soil moisture and high carbonate content this could lead to conflicting results for δ¹⁸O and δ²H in plant water uptake studies.

Overgrazing significantly affects alpine meadows in ways similar to grasslands in other areas. Fencing to exclude grazers is one of the main management practices used to protect alpine meadows. However, it is not known if fencing can improve soil properties and soil organic carbon storage by restraining grazing in alpine meadows. We studied the long-term (nine-year) effects of fencing on soil properties, soil organic carbon and nitrogen storage compared with continued grazing in an alpine swamp meadow of the Qinghai-Tibetan Plateau, NW China. Our results showed that fencing significantly improved vegetation cover and aboveground biomass. There were significant effects of fencing on pH value, soil bulk density, and soil moisture. Long-term fencing favored the increase of soil total nitrogen, soil organic matter, soil organic carbon, soil microbial biomass carbon and soil carbon storage compared with grazed meadows. Our study suggests that long-term fencing to prevent disturbance could greatly affect soil organic carbon and nitrogen storage with regard to grazed meadows. Therefore, it is apparent from this study that fencing is an effective restoration approach of with regard to the soil's storage ability for carbon and nitrogen in alpine meadow of the Qinghai-Tibetan Plateau.

Asymmetric transport behavior of Cd in soils can result from sorption nonlinearity or rate-limited sorption, of which the relative significance is difficult to be discerned by transport modeling alone. Multiple approaches incorporating batch, sequential extraction, and miscible displacement experiments were therefore used in this study. Batch isotherm was used to indicate the range of Cd concentration where sorption became nonlinear. It is noteworthy that batch kinetics illustrated a shorter apparent equilibrium time of sorption at a higher Cd concentration, which presumably correlates with the significance of rate-limited sorption. In addition, sequential extraction results indicated that the relative contribution of rate-limited specific sorption to total sorption became negligible with increasing Cd concentration. Since the rate-limited specific sorption appears to be of low capacity, it is only important for sorption at low concentration. In miscible displacement experiments, Cd transport at 10-5 M could only be simulated using a nonequilibrium model, whereas a nonlinear model was necessary for describing Cd transport at 10-3 M. Therefore, this study demonstrated that transport behavior is predominantly influenced by rate-limited sorption at sufficiently low concentration, while by sorption nonlinearity at sufficiently high concentration. Additionally, sequential extraction can be a useful tool to illustrate the significance of rate-limited specific sorption and the corresponding chemical nonequilibrium transport behavior.

Buttress trees are prominent in tropical rainforests, providing mechanical support for canopy trees. Other ecological functions of these structures remain unclear. Here we demonstrate that buttresses are physical structures that regulate soil moisture, soil nutrient status and seedling diversity near tree trunks. We monitored soil moisture over a year in plots on the uphill, downhill and lateral sides of buttresses on a tropical seasonal rainforest slope in Xishuangbanna, Southwest China. Soil nutrient status was examined in dry and rainy season and seedlings were identified and counted in the plots. Leaf litter accumulation was sampled at the end of the study. Higher levels of soil moisture were maintained uphill of the buttresses throughout the year and leaf litter accumulation was also much higher. Total soil carbon, total N, and hydrolysable N were much higher on the uphill side but other nutrient concentrations did not differ significantly. Seedling species composition varied significantly among different locations with the densest and most diverse seedling assemblages on the uphill side. This study illustrates an important function of buttress trees in providing soil heterogeneity and promoting seedling diversity in rainforests.