Defoliation, trampling and nutrient return differentially influence grassland productivity by modulating trait-dependent plant community composition: insights from a simulated grazing experiment.

Ungulate grazing involves multiple components, including defoliation, dung and urine return, and trampling, which supply offsetting or synergistic effects on plant community composition and productivity (ANPP), but these effects have not been fully studied. Plant functional traits may reflect the response of plants to disturbance and their impact on ecosystem functions. Species turnover and intraspecific trait variation (ITV) are important drivers of community trait composition. We conducted a simulated grazing experiment in a steppe grassland in northern China to examine the effects of defoliation, dung and urine return, and trampling on community-weighted mean (CWM), functional diversity (FD) and ANPP, and to disentangle the roles of species turnover and ITV in driving these changes. We found that defoliation had a dominant effect on CWMs and FDs of all four traits through species turnover and ITV, respectively, resulting in a convergence of traits towards as more resource-acquisitive strategy. Dung-urine return resulted in more resource-acquisitive community traits mainly through ITV, whereas there were no significant effects on FDs except for leaf C/N. Trampling increased CWM of leaf dry matter content primarily driven by ITV, and had no significant effect on FDs. Furthermore, our simulated grazing positively affected ANPP, primarily due to nutrient additions from dung and urine, and ITV largely explained the variation in ANPP. These findings highlight the multifaceted effects of grazing components on community structure and ANPP, and the significance of ITV in shaping grassland plant communities and productivity.

Coupling Hydrazine Oxidation with Seawater Electrolysis for Energy-Saving Hydrogen Production over Bifunctional CoNC Nanoarray Electrocatalysts.

Seawater electrolysis is a promising method to produce H2 without relying on scarce freshwater resource, but its high energy consumption and inevitable accompany of competitive chlorine oxidation reaction (ClOR) are still great technological challenges. Herein, a metal-organic framework (MOF)-templated pyrolysis strategy to prepare uniform cobalt/nitrogen-codoped carbon nanosheet arrays on carbon cloth (CC@CoNC) as highly-efficient but low-cost bifunctional electrocatalysts for hydrazine-assisted seawater electrolysis is explored. The optimized CoNC nanosheet arrays can be used as an efficient bifunctional electrocatalyst to catalyze hydrazine oxidation reaction and hydrogen evolution reaction, remarkably reducing the energy consumption and nicely overcome the undesired anodic corrosion problems caused by ClOR. Impressively, a hydrazine-assisted water electrolysis system is successfully assembled by using the optimized CC@CoNC as both cathode and anode, which only needs an ultra-low cell voltage of 0.557 V and an electricity consumption of 1.22 kW h per cubic meter of H2 to achieve 200 mA cm-2 . Furthermore, the optimized CC@CoNC can also show greatly improved stability in the hydrazine-assisted seawater electrolysis system for H2 production, which can work steadily for above 40 h at ≈10 mA cm-2 . This study may offer great opportunities for obtaining hydrogen energy from infinite ocean resource by an eco-friendly method.

Controllable Synthesis of Ultrathin Defect-Rich LDH Nanoarrays Coupled with MOF-Derived Co-NC Microarrays for Efficient Overall Water Splitting.

Water electrolysis has attracted immense research interest, nevertheless the lack of low-cost but efficient bifunctional electrocatalysts for both hydrogen and oxygen evolution reactions greatly hinders its commercial applications. Herein, the controllable synthesis of ultrathin defect-rich layered double hydroxide (LDH) nanoarrays assembled on metal-organic framework (MOF)-derived Co-NC microarrays for boosting overall water splitting is reported. The Co-NC microarrays can not only provide abundant nucleation sites to produce a large number of LDH nuclei for favoring the growth of ultrathin LDHs, but also help to inhibit their tendency to aggregate. Impressively, five types of ultrathin bimetallic LDH nanoarrays can be electrodeposited on the Co-NC microarrays, forming desirable nanoarray-on-macroarray architectures, which show high uniformity with thicknesses from 1.5 to 1.9 nm. As expected, the electrocatalytic performance is significantly enhanced by exploiting the respective advantages of Co-NC microarrays and ultrathin LDH nanoarrays as well as the potential synergies between them. Especially, the optimal Co-NC@Ni2 Fe-LDH as both cathode and anode can afford the lowest cell voltage of 1.55 V at 10 mA cm-2 , making it one of the best earth-abundant bifunctional electrocatalysts for water electrolysis. This study provides new insights into the rational design of highly-active and low-cost electrocatalysts and facilitates their promising applications in the fields of energy storage and conversion.

Shoot δ13 C values as an indicator of cumulative stress: The role of re-watering during drought and salinity stress.

RATIONALE: The carbon stable isotope composition (δ13 C value) of a plant can reflect prolonged drought and salinity, as different isotopic signals resulting from drought and salinity can be retained in plant tissue. Commonly, drought and salinity are interrupted by intermittent precipitation or irrigation. It remains unclear whether the δ13 C values reflect the cumulative duration of intermittent drought or salinity stress. METHODS: Drought (5% and 10% polyethylene glycol) and salinity (35 mM and 85 mM NaCl) were imposed on annual ryegrass consistently or cyclically; throughout the treatments, the stress duration for cyclic drought/salinity was half that of the corresponding prolonged stress treatment. The shoot δ13 C values were measured using isotope ratio mass spectrometry. RESULTS: Prolonged drought restrained growth and increased shoot δ13 C values relative to the control group. However, the shoot biomass was even lower under cyclic drought than under prolonged drought. Furthermore, the shoot δ13 C value under cyclic drought was close to that of the control group. The low NaCl concentration treatment actually enhanced shoot growth. The shoot δ13 C value varied with both duration and intensity of salinity across all groups. CONCLUSIONS: The shoot δ13 C value in annual ryegrass did indicate cumulative stress from cyclic low salinity, but not that from cyclic drought, in a manner that was mediated by the effect of re-watering on the mass and allocation of the photosynthates produced during stress.

Growth and carbohydrate dynamic of perennial ryegrass seedlings during PEG-simulated drought and subsequent recovery.

Due to the increasing occurrence of drought events, drought recovery has become equally important as drought resistance for long-term growth and survival of plants. However, information regarding the mechanism that controls growth recovery of herbaceous perennials is not available. In this study, perennial ryegrass (Lolium perenne) was rewatered after eight-day exposure to three drought intensities simulated by polyethylene glycol-6000. The growth, nonstructural carbohydrates (NSC, i.e. sucrose, glucose, fructose and starch), shoot δ13C, and activities of enzymes for sucrose conversion were monitored for 24 days after rewatering, allowing investigation of the dynamic of NSCs and its relation with growth in the recovery phase. In response to drought, growth and NSC content decreased mainly in shoot rather than root, and the total dry matter was negatively correlated to shoot δ13C. After rewatering, the growth of drought-treated groups still lagged behind that of control (CK) group for more than 16 days, but it was no longer correlated to shoot δ13C, suggesting that the limited growth is caused by non-stomatal factors related to photosynthesis. On day 24 after rewatering, the final growth of drought-treated groups caught up or even exceeded that of CK group, and was accompanied by higher dry weight root to shoot ratio (R/S) and root NSC content, which may facilitate water and nutrient acquisition and emergency of new tillers, respectively. During drought and subsequent recovery, the variation of R/S and root NSC content mainly attributed to root acid invertase rather than leaf sucrose phosphate synthase activity.