Root tensile strength of terrace hedgerow plants in the karst trough valleys of SW China:Relation with root morphology and fiber content

Root tensile strength is commonly affected by root morphology and fiber content,which combinedly affect the effectiveness of terrace hedgerow on controlling soil erosion in sloping farmland.However,the relationships between these root characteristics are still elusive.This study aimed to compare the root tensile strength,root morphologies,and root fiber contents,and quantify their differences among different plant species.Complete root systems of three terrace hedgerow plant species,i.e.,O.bodinieri,V.villosa,and D.lablab L.were sampled for detecting root morphologies and fiber contents at different slope positions on a representative hillslope in karst trough valley.Single root specimens were collected to measure root tensile properties for these three plant species.Results showed that most root morphological parameters were the highest in O.bodinieri,followed by D.lablab L.Three plant species presented the same dominant diameter class as<1.0 mm,and root volumes as<1.50 cm3.Cellulose with contents closing to 50%was the main fiber type,and increased significantly linearly with the increasing root diameter in both O.bodinieri and V.villosa.The highest tensile strength and Young's modulus were found in D.lablab L.,while the best ultimate tensile force and ultimate elongation were displayed in O.bodinieri.Root diameter showed negative power relationships with tensile strength and Young's modulus,a positive power relationship with ultimate tensile force,and a positive linear relationship with ultimate elongation.Our results will deepen the understanding of the terrace hedgerow functions for controlling soil erosion worldwide.

Human activity and climate change triggered the expansion of rocky desertification in the karst areas of Southwestern China

It is conducive to the sustainable development of human beings in karst regions to research the mechanism of karst rocky desertification(KRD)expansion.Whether the large-scale KRD in southwestern China is caused by climate change or human activities is still controversial.In this study,the evolution of the KRD in southwestern China over the past 2000 years was reconstructed through the high-precisionδ^(13)C record of stalagmites from Shijiangjun(SJJ)Cave,Guizhou Province,China.Theδ^(13)C of the stalagmites from SJJ Cave exhibited heavy values from the Medieval Warm Period(MWP)to the Little Ice Age(LIA).Furthermore,theδ^(13)C records of other stalagmites and tufa from southwestern China also showed the same significant heavy trend.Because the stalagmiteδ^(13)C could record the change of ecological environment,it indicated that the consistent change of the stalagmitesδ^(13)C may record the process of KRD expansion in the karst regions of southwestern China.During the MWP,the stronger Asian summer monsoon and the northward movement of the rain belt led to a dry period in southwestern China and a wet period in northern China.In contrast,it was wet in southwestern China and dry in northern China during the LIA.In addition,after the Jing-Kang event(JK event,AD1127)occurred at the end of the Northern Song dynasty,the political and economic center of China migrated to southern China for the first time,which changed the population distribution pattern of larger population in the north and smaller population in the south.Therefore,the expansion of KRD in southwestern China was exacerbated in the MWP due to the change of climate in southwestern China,the migration of a large number of people,wars,the large-scale reclamation of arable land,and the cultivation of large areas of crops.

Feedback and contribution of vegetation, air temperature and precipitation to land surface temperature in the Yangtze River Basin considering statistical analysis

Land surface temperature(LST),especially day-night LST difference(LSTd-LSTn),is a key variable for the stability of terrestrial ecosystems,affected by vegetation and climate change.Quantifying the contribution and feedback of vegetation and climate to LST changes is critical to developing mitigation strategies.Based on LST,Normalized vegetation index(NDVI),land use(LU),air temperature(AT)and precipitation(Pre)from 2003 to 2021,partial correlation was used to analyze the response of LST to vegetation and climate.The feedback and contribution of both to LST were further quantifed by using spatial linear relationships and partial derivatives analysis.The results showed that both interannual LST(LSTy)and LSTd-LSTn responded negatively to vegetation,and vegetation had a negative feedback effect in areas with significantly altered.Vegetation was also a major contributor to the decline of LSTd-LSTn.With the advantage of positive partial correlation area of 94.99%,AT became the main driving factor and contributor to LSTy change trend.Pre contributed negatively to both LSTy and LSTd-LSTn,with contributions of-0.004℃/y and-0.022℃/y,respectively.AT played a decisive role in LST warming of YRB,which was partially mitigated by vegetation and Pre.The present research contributed'to,the,detection,of LST changes and improved understanding of the driving mechanism.

Future variation of land surface temperature in the Yangtze River Basinbasedon CMIP6 model

In recent years,past changes in global and regional land surface temperatures(LST)have been well studied,however,future LST changes have been largely ignored owing to data limitations.In this study,three climate variables of CMIP6,namely air temperature(AT),precipitation(Pre),and leaf area index(LAl),were spatially corrected using the Delta downscaling method.On this basis,by combining MODIS LST,elevation,slope and aspect,a random forest(RF)model was built to calculate the LST from 2022 to 2100.The absolute variability(AV)and Mann-Kendall(M-K)tests were used to quantitatively detect interannual and seasonal LST changes in different Shared Socioeconomic Pathways(SSPs)scenarios.The results showed that the AV value increased successively from SSP1-2.6 to SSP2-4.5 and then to SSP5-8.5.Compared with the base period(2003-2021),the increment in interannual,spring,summer and autumn LST during 2022-2100 was mainly between 1 and 2°℃under threescenarios.The interannual and seasonal LST were spatially characterized by significant warming over large areas,and the increasing was the fastest under SSP5-8.5.These results indicate that,in the future,LST will increase further over large areas,especially in winter.

Geochemical characterization of major elements in desert sediments and implications for the Chinese loess source

Mineral dust released from the desert is one of the important components of atmospheric aerosols. Arid and semi-arid deserts, sandy lands in northern China and their adjacent Gobi Desert lands in northern China and neighboring Mongolia(hereinafter referred to as Gobi) are potential sources of mineral dust in Asia. However, there is currently a lack of systematic studies on the characteristics of major elements in the potential mineral dust source area. This study investigates the major elements of 310 surficial sand samples in the stabilized and semi-stabilized dune fields from 12 deserts/sandy land and Gobi in northern China and southern Mongolian Gobi and compiles published data. We identify four regions with distinct geochemical characteristics:(1) Taklimakan, Kumtag and Qaidam deserts in western China;(2) Badain Jaran, Tengger, Hobq, and Mu Us deserts in the central and western regions of northern China;(3) Hulun Buir, Onqin Daga and Horqin sandy lands in northeast China;and(4) Gobi and Gurbantunggut deserts. The spatial distributions of the SiO2 and CaO contents in Chinese deserts are highly variable. The average content of SiO2 generally reflects an increasing trend from west to east, while the average content of CaO shows a decreasing trend from west to east. We demonstrate that the spatial variation of major elements is likely controlled by two key scenarios: the composition of source rocks and the mineral maturity caused by the supply of fresh materials. The SiO2/(Al2O3+K2O+Na2O) ratio of desert sediments is relatively lower in western China and may be caused by high ferricmagnesia and high carbonate minerals;this ratio is relatively higher in the northeast sandy lands and may be linked to a lack of fresh material supply and the presence of high K-feldspar minerals in source rocks. The deserts can be further distinguished by ternary diagrams with SiO2/10-CaO-Al2O3,(K2O+Na2O)-CaO-Fe2O3 and CaO-Na2O-K2O. The comparison of major elements between desert sediments and loess suggests that the western and/or central deserts in China may be the potential provenances of loess on the Loess Plateau.

Movement of lateral hyporheic flow between stream and groundwater

The hyporheic zone plays an important role in groundwater and stream water quality protection. To investigate the stream-groundwater interaction mechanisms in the lateral hyporheic zone, this study examined Ma'an Creek in Chongqing during the dry season from December 2015 to April 2016. The water level, water temperature, pH and Cl. concentration in the hyporheic zone and groundwater were monitored in situ. The sediment permeability coefficient, stable isotopes of hydrogen and oxygen and concentration of DOC were analyzed. The results show that the water level changes of hyporheic zone and the movement of hyporheic flow were influenced significantly by the permeability coefficient of sediment. The hyporheic flow approximately10 cm from the stream bank was clearly affected by precipitation infiltration and evapotranspiration. During the study period,the groundwater recharged the stream, and the impact of groundwater on the hyporheic flow gradually decreased with the flow path. The hyporheic flow approximately 30 cm from the stream bank was still mainly affected by groundwater. Approximately10–30 cm from the stream bank, the mixing of groundwater with precipitation and stream water intensified. Due to the sediment properties, moisture accumulated approximately 10 cm from the stream bank and drained into the stream via hyporheic flow, with potential impacts on stream water quality.

重庆市关键生态系统服务对土地利用和气候变化的多维响应--时间、空间及地形

Mountainous landscapes are particularly vulnerable and sensitive to climate change and human activities,and a clear understanding of how ecosystem services(ES)and their relationships continuously change over time,across space,and along altitude is therefore essential for ecosystem management.Chongqing,a typical mountainous region,was selected to assess the long-term changes in its key ES and their relationships.From 1992 to 2018,the temporal variation in water yield(WY)revealed that the maximum and minimum WYs occurred in 1998 and 2006,which coincided with El Ni?o-Southern Oscillation and severe drought events,respectively.Soil export(SE)and WY were consistent with precipitation,which reached their highest values in 1998.During this period,carbon storage(CS)and habitat quality(HQ)both decreased significantly.ES in Chongqing showed large variations in altitude.Generally,WY and SE decreased with increasing altitude,while CS and HQ increased.For spatial distribution,WY and SE showed positive trends in the west and negative trends in the east.In regard to CS and HQ,negative trends dominated the area.Persistent tradeoffs between WY and soil conservation(SC)were found at all altitude gradients.The strong synergies between CS and HQ were maintained over time.