Low carbon storage of woody debris in a karst forest in southwestern China

The properties of woody debris(WD) vary across different forests under various soil conditions.Owing to the relatively shallow and low amounts of soils on karst terrains, it is necessary to determine the WD carbon inventory of karst forests. In this study, we recorded WD with a basal diameter for standing snags and the largeend diameter for fallen logs of ≥ 1 cm. The carbon density of WD in a secondary karst mixed evergreen and deciduous broad-leaved forest that had been clear-cut 55 years ago in southwestern China were inventoried in a 2 ha plot. Woody debris carbon density calculated using specific gravity and carbon concentration was 4.07 Mg C ha^-1. Woody debris with diameters ≥ 10 cm(coarse WD) constituted 53.8% of total carbon storage whereas WD < 10 cm in diameters(fine WD) accounted for more pieces of WD(89.9%).Lithocarpus confinis contributed the most WD carbon(26.5%). Intermediate decayed WD was relatively more abundant, but WD with final decay contributed the least to the total pieces of WD(6.7%). The contribution of WD to carbon storage of karst forest was low compared to other forests worldwide. Significant positive correlations were found between WD carbon and biodiversity(R^2= 0.035,p < 0.01) and elevation(R^2= 0.047, p < 0.01) and negative correlations was found in outcrop coverage(R^2= 0.034, p <0.01). Further studies are needed to elucidate the ecological functions of WD to better understand their roles in maintaining biodiversity, enhancing productivity, and controlling vegetation degradation in karst forest ecosystems.

Experimental and Numerical Analysis of High-Strength Concrete Beams Including Steel Fibers and Large-Particle Recycled Coarse Aggregates

In order to study the performances of high-strength concrete beams including steel fibers and large-particle recycled aggregates,four different beams have been designed,tested experimentally and simulated numerically.As varying parameters,the replacement rates of recycled coarse aggregates and CFRP(carbon fiber reinforced polymer)sheets have been considered.The failure mode of these beams,related load deflection curves,stirrup strain and shear capacity have been determined through monotonic loading tests.The simulations have been conducted using the ABAQUS finite element software.The results show that the shear failure mode of recycled concrete beams is similar to that of ordinary concrete beams.The shear carrying capacity of high-strength concrete beams including steel fibers and large-particle recycled coarse aggregates grows with an increase in the replacement rate of recycled coarse aggregates.Reinforcement with CFRP sheets can significantly improve the beam’s shear carrying capacity and overall resistance to deformation.

Formation of the Huajiang Grand Canyon (southwestern China) driven by the evolution of a Late Pleistocene tiankeng

Collapse is a common geomorphic process in karst areas,especially on the Yunnan-Guizhou Plateau,which has a tectonic background of integral uplift.The frequent occurrence of collapse processes in karst underground caves and canyons indicates that collapses play an important role in the formation of canyons.Through an analysis of the morphology of a semicircular cliff in the Huajiang Grand Canyon and an investigation of sediments at the bottom of the cliff,a large-scale collapse event was found to have occurred.U-series dating of secondary calcium carbonate cement in the collapse breccias indicates that collapse processes occurred approximately 200 ka.According to the geomorphological evolution of the Huajiang Grand Canyon,the following geomorphic evolutionary process is proposed:underground river-cave hall-collapse of a tiankeng-tiankeng degradation-canyon formation.These findings also show that the dating of collapsed breccia cement can be effectively used to determine the development times of karst canyons and the formation ages of tiankengs.

Forest carbon storage in Guizhou Province based on field measurement dataset

Accurate estimation of forest carbon storage is crucial in understanding global and regional carbon cycles and projecting future ecological and economic scenarios.Guizhou is the largest karst landform province in China;61.9% of its land area is characterized as karst. However,monitoring its field biomass and carbon storage is difficult.This study synthesized and analyzed a comprehensive database of direct field observations of forest vegetation and soil carbon storage in Guizhou Province by using data from existing literature. The total vegetation carbon storage in Guizhou Province was 488.170 TgC, the average vegetation carbon density(VCD) was 27.866 MgC hm^(-2), the total amount of soil organic carbon(SOC)(20 cm) was 1017.364 TgC, and the average SOC density was 58.074 MgC hm^(-2). Among all vegetation types, needleleaf forest had the highest vegetation carbon stocks, and scrub presented the highest SOC storage. The vegetation and SOC storage values of the karst landform were 282.352 and 614.825 TgC, respectively, which were higher than thoseof the non-karst landform. VCD was concentrated at 10–40 MgC hm^(-2), and SOC density was concentrated at 40–60, 60–80, and 80–100 MgC hm^(-2). This comprehensive regional data synthesis and analysis based on direct field measurement of vegetation and soil will improve our understanding of the forest carbon cycle in karst landforms under a changing climate.

Enhanced nitrate removal from groundwater using a conductive spacer in flow-electrode capacitive deionization

Flow-electrode capacitive deionization(FCDI)represents a promising approach for ion separation from aqueous solutions.However,the optimization of spacer,particularly for nitrate-contaminated groundwa-ter systems,has often been overlooked.This research comprehensively investigates the influence of using a conductive(carbon cloth,CC)spacer on nitrate removal performance within FCDI system,comparing it to a non-conductive(nylon net,NN)spacer.In both CC and NN FCDI systems,it is unsurprisingly that nitrate removal efficiency improved notably with the increasing current density and hydraulic retention time(HRT).Interestingly,the specific energy consumption(SEC)for nitrate removal did not show obvious fluctuations when the current density and HRT varied in both systems.Under the auspiciously optimized process parameters,CC-FCDI attained a 20%superior nitrate removal efficiency relative to NN-FCDI,ac-companied by a notably diminished SEC for CC-FCDI,registering at a mere 28%of NN-FCDI.This great improvement can be primarily attributed to the decrement in FCDI internal resistance after using con-ductive spacer,which further confirmed by electrochemical tests such as linear sweep voltammetry(LSV)and electrochemical impedance spectroscopy(EIS).Upon prolonged continuous nitrate removal at the optimized conditions,the CC-FCDI system achieved a consistent 90%nitrate removal efficiency with a low SEC of 2.7-7.8 kWh/kg NO_(3)-N,underscoring its steady performance.Overall,this study highlights the pivotal importance of careful spacer design and optimization in realizing energy-efficient groundwater treatment via FCDI.

Control of Leaf Senescence by an MeOH- Jasmonates Cascade that Is Epigenetically Regulated by OsSRT1 in Rice

Although considerable progress has been made in identifying the genes regulating accumulation of hormones that are involved in leaf senescence, only a few studies have focused on natural variations in jasmonates content and much less on the underlying genetic basis. Moreover, the epigenetic regulation of jasmonate-mediated leaf senescence remains largely unknown, in this study, we carried out metabolic profiling of a worldwide collection of rice accessions and demonstrated that there are substantial variations in jasmonate levels among these accessions. A subsequent metabolite-based genornewide association study identified candidates for two major quantitative genes （QTGs）, OsPME1 and OsTSD2, affecting the content of jasmonates. Further investigations using a series of relevant mutants and transgenic lines revealed the MeOH-jasmonata cascade plays an important role in regulating leaf senescence. Moreover, we showed that OsSRT1, one of the two Sir2 （silent information regugator 2） homologs in rice, negatively regulates leaf senescence by repressing expression of the biosynthetic genes of this metabolic cascade and at least particiaUy through histone H3K9 deacetylation of OsPME1. Taken together, our results indicate that the MeOH-jasmonates cascade and its epigenetic regulation are crucial for controlling leaf senescence process in rice.