Changes in the seasonal precipitation regime induced by global climate change may alter moisture and the dynamics of related microbes and enzymes, thereby significantly affecting forest litter decomposition; however, the specific mechanisms remain unclear. Hence, a precipitation manipulation experiment including the treatments of control (CK), decreased precipitation in the dry season with extremely increased precipitation in the wet season (IE) and decreased precipitation in the dry season with proportionally increased precipitation in the wet season (IP) was performed from October 2020 to October 2021 in a subtropical evergreen broad-leaved forest in China. The moisture, chemical properties, microbial biomass, enzyme activity, and decomposition rates of two dominant shrub species foliar litter, Phyllostachys violascens and Alangium chinense, were measured at six stages during the dry and wet seasons. The results showed that both IE and IP significantly increased the litter decomposition rates (more than 2.0% for P. violascens and more than 4.7% for A. chinense, respectively), while the effects of IE were the most significant, which was mainly related to the precipitation availability and the frequency of dry-wet cycle. Furthermore, the IE and IP increased the wet season’s contribution to the annual total decomposition regardless of litter species, and more significant effects were also observed in IE. Additionally, the results of structural equation model indicated that the seasonal precipitation regime could regulate the decomposition process directly by changing moisture and the contents of elements and refractory substances, as well as indirectly by influencing the related microbial biomass and enzyme activity. These results deepen the understanding of the biogeochemical cycle in forest ecosystems under the global climate change scenarios.
Coastal wetland resources are abundant in Jiangsu Province.The area of salt marsh has declined since the 1980s,due to human activities(such as reclamation)and the invasion of alien species.Based on Landsat re-mote sensing images and the application of Digital Shoreline Analysis System(DSAS),we examined the variations of the reclamation area and salt marsh vegetation area in the tidal flat vegetation zone of coastal wetlands in Jiangsu Province from 1985 to 2020,the relationships between their changes,as well as the vegetation effects of reclama-tion scale.The results showed that:(1)From 1985 to 2020,the vegetation zone shifted seawards significantly,spatially corresponding an increase of reclamation area.The change hotspot area gradually moved southward,from Sheyang Estuary-Beiling Estuary in 1985 to Liangtuo Estuary-Yaowang Port after 2015.(2)The areas of salt mar-shes and reclamation varied greatly among different bank sections.The ratio of reclamation area to salt marshes in-creased rapidly,increasing from 0.017∶1 in 1985 to 5.59∶1 in 2020.The reclamation area was significantly nega-tively correlated with the salt marsh area.(3)With the gradual decline of the salt marsh vegetation zone,the corre-lation between the area of salt marshes and the extension rate of tidal flat vegetation shifted from significant positive to non-significant,indicating that the scale of salt marsh vegetation area played a certain role in promoting tidal flat vegetation zone extending to the sea.
Water is a key factor limiting the improvement of both quality and yield of walnut industry in arid areas.The effects of different water supply amounts on physiology,growth,and fruit quality of walnut trees remain unclear.We conducted an irrigation experiment with three treatments,i.e.,deficit(DI),conventional(CI),and excess irrigation(EI).We measured leaf hydraulic traits,photosynthetic physiological characteristics,soluble sugar content,leaf area,branch growth,fruit morphology and no kernel or deflated kernel rate at different canopy heights of'Wen 185'walnut trees.The results showed that:(1)Midday leaf water potential decreased significantly with de-creasing irrigation and increasing canopy height.Midday leaf water potential at the upper canopy was significantly lower than that at the lower canopy.(2)Different irrigation amounts did not affect light compensation point,light saturation point,maximum net photosynthetic rate,maximum photochemical efficiency,and chlorophyll SPAD.(3)Irrigation treatments did not significantly affect soluble sugar content of leaves and fine roots,but the soluble sugar content of walnut kernels was significantly increased with decreasing irrigation and accumulated with increas-ing canopy height.(4)Leaf area was significantly decreased and Huber value was significantly increased with the reduction of irrigation.The reduction of irrigation did not affect fruit morphology,but increased the no kernel or deflated kernel rate,with a rate being 87.9％higher in the DI group than in the EI group.The no kernel or deflated kernel rate at the upper canopy was 41.8％higher than that at the lower canopy.Our results indicated that walnut trees resist drought by increasing Huber value and decreasing leaf area to maintain stable photosynthesis,but the hydraulic restriction caused by increasing canopy height will aggravate the drought stress of plants,resulting in an increase in the no kernel or deflated kernel rate.
Habitat selection is the process that animals actively select suitable habitats to escape predators,repro-duce,and forage,reflecting the ecological needs of animals.Land covers and seven habitat variables of Jiangsu Dafeng Milu National Nature Reserve were investigated by unmanned aerial vehicle(UAV)remote sensing and field surveys in spring,summer,and autumn of 2019.The Vanderploeg selection coefficient and Scavia selection index were calculated,and statistical test and principal component analysis were performed.The results showed that:(1)in spring,Pere David's deer preferred to select the habitats of Spartina alterniflora,Imperata cylindrica,and Carex scabrifolia communities with vegetation coverage less than 30％,vegetation density less than 150 plants· m 2,aboveground biomass less than 100 g·m 2,and the distance to water source less than 210 m(P＜0.05);(2)in summer,they preferred the habitats of S.alterniflora and I.cylindrica communities with aboveground bio-mass less than 40 g·m-2(P＜0.05);and(3)in autumn,they preferred to select the habitats of I.cylindrica,S.alterniflora and Suaeda glauca communities with vegetation height less than 4 cm and vegetation density more than 30 plants·m-2(P＜0.05).Key factors affecting habitat selection of Père David's deer in different seasons were feeding factor,food abundance factor,and water source factor,respectively.Through revealing the differences in habitat selection by Père David's deer in spring,summer,and autumn,our results provided the reference for the conservation and restoration of Père David's deer and their habitats in Dafeng Milu National Nature Reserve.
Using artificial water supplementation and natural water control methods,we measured the light response process of photosynthetic physiological parameters of potato leaves under different water conditions and further ana-lyzed the threshold effects for the responses to soil water.Soil moisture was set as 55％,65％and 75％field water-holding capacity for drought stress treatments,80％field water-holding capacity for control treatment and 85％field water-holding capacity for waterlogging treatment.The results showed that net photosynthetic rate(Pn),water use efficiency(WUE),and light response parameters of potato leaves had obvious water critical effects.The apparent quantum efficiency(AQY),maximum net photosynthetic efficiency(Pnmax),and light saturation point(LSP)in-creased first and then decreased with increasing soil water content,while light compensation point(LCP)and dark respiration rate(Rd)first decreased and then increased.Under waterlogging or drought stress,the ability of light absorption and conversion of potato leaves under weak light was reduced,the utilization of strong light and weak light was inhibited,and dry matter accumulation was maintained by reducing respiratory consumption.With increa-sing soil moisture,Pn and WUE increased first and then decreased,but the critical values of moisture were different.The relative soil water content(Wr)at 56.7％was the critical point of stomatal limitation in potato leaves.The Wr at 96.3％was water saturation point of Pn,andWrat 70.1％was the high effiiciency point of WUE.Photosynthetic capacity of potato leaves under waterlogging was higher than that under drought stress.The moisture threshold of po-tato in semi-arid area was determined by mathematical model.The Wr value between 70.1％and 96.3％was high-yield and high-efficiency water,in which the photosynthetic productivity and water use efficiency of potato were higher.Therefore,Wr between 70.1％and 96.3％is suitable for potato growth in semi-arid area.Photosynthetic capacity of potatoes under waterlogged conditions is significantly higher than that under drought stress in semi-arid area.
