Abstract:【Objective】As the most dynamic and bioavailable fraction of the soil carbon pool, dissolved organic matter (DOM) plays important roles in a wide range of biogeochemical processes in the environment. The interaction of soil minerals with DOM would induce structural fractionation of the DOM at the mineral/water interface, thereby influencing long-term preservation and biogeochemical processes of the DOM in the soil. Ferrihydrite, a poorly crystalline iron oxide, is known to be highly reactive to DOM in the soil owing to its high specific surface area and abundant reactive binding sites. it is widespread in the environment and can associate with DOM through either adsorption or co-precipitation. However, so far, few studies have been reported on structural fractionation of DOM at the ferrihydrite/water interface induced by co-precipitation at the molecular level. 【Method】To explore molecular fractionation of DOM at the ferrihydrite/water interface during its co-precipitation process, this study prepared ferrihydrite-DOM complex separately in solutions different in C/Fe ratio via co-precipitation and adopted the technology of combining ultraviolet (UV) spectrum with electrospray ionization Fourier transform ion cyclotron resonant mass spectrometry (ESI-FT-ICR-MS) to probe changes in DOM composition after co-precipitation ended. Species of carbon and Fe in the complex were determined with the aid of X-ray photoelectron spectroscopy (XPS) and Fe K edge XAS.【Result】Results show that Fe in the complex existed mainly in the form of ferrihydrite, of which the proportion gradually decreased from 95.9% to 68.0% with the increase in initial carbon/iron (C/Fe) ratio of the solution. UV and ESI-FT-ICR-MS analysis collectively revealed that during the co-precipitation process, ferrihydrite fixed in priority aromatic components high in molecular weight and rich in oxygen (mainly combustion-derived condensed polycyclic aromatic- and vascular plant-derived polyphenols-like substances) in the DOM, leaving aliphatic components in the solution. The lower the solution in C/Fe ratio, the higher the molecular fractionation in degree. This feature is basically consistent with what has been reported about the fractionation induced by adsorption, which indicates that no matter whether in the process of adsorption or co-precipitation, ferrihydrite tends to fix DOM components high in molecular weight and aromaticity, thus leading to changes in chemical composition of the DOM as well as surface properties of the ferrihydrite, which will in turn affect sorption, transportation and transformation processes of the contaminants therein. In addition, this study was the first to find that ferrihydrite varied dynamically with the reaction in time in selectivity to structure of the DOM, that is, combustion-derived condensed polycyclic aromatics were preferentially fixed in the ferrihydrite-DOM complex, and with the reaction going on, vascular plant-derived polyphenols-like substances followed.【Conclusion】The findings in this study are expected to be able to help understand in depth the mechanism of molecular fractionation that affects geochemical behavior of DOM in the environment via co-precipitation during the process of ferrihydrite formation.

Abstract:The Sanjiang Plain is located in the northern part of the mid-temperate zone of China. In recent years, climate warming and cultivated land use have been changing significantly. So it is of great significance in protecting food security and stability to analyze responses of cultivated land use to regional climate change. As cultivated land is a kind of artificial vegetation, its NDVI value reflects certain crop information, like growth and yield. Therefore, by analyzing impacts of climate factors on cultivated land NDVI, information relevant to response of regional cultivated land use to climate change can be obtained.[Objective] Based on the data of cultivated land use, ten-day climatic data, and ten-day normalized difference vegetation indexes (NDVI) of the Sanjiang Plain during the farming period (May~September) of the years from 2000 to 2015, temporal changes in climatic factors and spatial variation of NDVI of the cultivated land were obtained through analysis and furthermore, information about delayed response of cultivated land NDVI to regional climate change was acquired.[Method] In this research, methods, like variation coefficient analysis, trend coefficient analysis and time-delay cross correlation analysis were adopted.[Result] Results show:(1)The interannual variability of temperature was more stable than that of precipitation during the farming period of the Sanjiang Plain, while the intermonthly variabilities of the two tended to be more regular; (2)The cultivated land NDVI did vary much between years, with the vegetation coverage being the highest in September; spatial variation of the cultivated land NDVI during the 16 years exhibited a trend of being low-unstable-increasing in value, representative in the western part of the region and being high-stable-decreasing in value, representative in the eastern part; (3)Maximum unbiased correlation coefficients of the ten-day NDVIs and ten-day mean temperatures of the cultivated land varied mostly in the range between 0.931 and 0.992, and delayed response was observed for 2 ten-day periods. Maximum unbiased correlation coefficients of the ten-day NDVI and ten-day precipitation of the cultivated land varied in the range between 0.778 and 0.927, and delayed response was observed for 1 ten-day period only. The cultivated land NDVI of the Sanjiang Plain, except for Fuyuan County, Raohe County and Tongjiang City, responded more slowly to air temperature than to precipitation. The cultivated land NDVI responded quite slowly to regional climate change in Jiamusi City and Shuangyashan City, while it did rather quickly in Mishan City, Baoqing County, and Hulin City. Moreover, it responded faster to change in air temperature and slower to change in precipitation in Fuyuan County and Muling City; and (4) The maximum unbiased correlation coefficients of dry land ten-day NDVI and ten-day mean temperature were both 0.942, and that of the paddy fields was 0.962. Delayed response of NDVI to mean temperature in dry land was observed for 2.026 ten-day periods, and that in paddy field for 1.633 ten-day period. The mean maximum unbiased correlation coefficient between ten-day NDVI and ten-day precipitation was 0.809 in dry land, and 0.765 in paddy field, and the mean time lag of NDVI to precipitation was 1.323 ten-day period in dry land, and 1.045 ten-day periods in paddy field.[Conclusion] Change in regional temperature impacts cultivated land NDVI more than change in precipitation does. The lag of NDVI responding to air temperature of cultivated land is longer than that to precipitation in most counties. Temperature is a major factor affecting regional paddy field NDVI; the lag of dry land NDVI responding to regional climate change is longer than that of paddy fields. The findings in the research may provide a scientific basis for guiding farming production of the region to cope with climate change and ensure food security.

Abstract:Phosphorus is a nutrient element essential to plant growth and a key one linking biological and abiotic interactions in ecosystems. An in-depth knowledge of sorption mechanism of phosphate on mineral surface is helpful to understanding the speciation, translocation, transformation, and bioavailability of phosphate in terrestrial and aquatic environments. In this paper, a review is presented of progresses in researches on phosphate sorption on mineral surface and its mechanism. Various analytical techniques or methods, such as quantitative analysis of OH- released, Zeta potential measurement (electrophoretic mobility measurement), isothermal titration calorimetry, atomic force microscopy, X-ray photoelectron spectroscopy, infrared spectroscopy, nuclear magnetic resonance spectroscopy, X-ray absorption spectroscopy, surface complexation model, and quantum chemical calculation have been used to analyze adsorption mechanism of phosphate on mineral surface from different angles. Adsorption of phosphate on the surface of minerals (e.g., iron and aluminum oxides) is usually accompanied by exchange of aqueous and hydroxyl groups. It is generally believed that phosphate mainly forms bidentate binuclear, monodentate mononuclear inner-sphere complexes on the surface of minerals, which is greatly affected by pH. Both pH and adsorption density of phosphate on the surface of minerals affect its protonation state. Under special conditions (i.e., low pH, high phosphorus concentration, high reaction temperature, long adsorption duration, and adsorption by weak crystalline mineral), phosphate adsorbed on the surface of minerals may transform into phosphate-containing surface precipitates, thus resulting in mineral dissolution and conversion, and further decrease of phosphate bioavailability. In the end, prospects are discussed about hot spots and orientation of future researches related to phosphate sorption on the surface of minerals.

Abstract:【Objective】In order to explore temporal variation of stable isotopes in soil water and distribution in soil profile, and to characterize the soil water line (SWL) in the monsoon region, this research project was launched, which was expected to be conducive to a better knowledge of redistribution processes of soil water. 【Method】 In this study, monitoring was carried out of stable isotopes in ground water in the soil profile (0-130 cm), precipitation and groundwater, and relevant environmental factors (including soil water content, soil temperature and meteorological variables), in a Cinnamomum camphora forest in Changsha from March 2017 to February 2019, and the monitoring data were collated and analyzed to determine variation of stable isotopes in soil water and rain water and its influencing factors. 【Result】 Stable isotopic composition of the soil water in the 0-60 cm soil layer varied significantly with the season, and the variation lagged by a varying degree behind that in rain water. The mean monthly maximum hydrogen stable isotope ratios (δ2H) in soil water regardless of soil depth all appeared all in May, and the mean monthly minimum one did in the period from September to December. However, no obvious seasonal variations were observed in the soil water and ground water below 60 cm in depth. All the above findings suggest that rain water may directly affect the soil water in the 0-60 cm soil layer and the soil water in the soil layers below and groundwater may preserve more data of stable isotopes in rain water accumulated from preceding rainfall events. Difference of the δ2H in soil water from the local meteoric water line (LMWL) increased in mean lc (Line-conditioned excess) with soil depth, decreased in standard deviation and gradually leveled off, which suggests that evaporation of soil water gradually decreases with soil depth. Significant and positive relationships were found between lc andδ2H in soil water at all soil depths. That is to say, the higher the δ2H in soil water, the lower the deviation degree of δ2H in soil water from the LMWL, and the weaker the evaporation of soil water; and likewise the lower the δ2H in soil water, the higher the deviation degree of δ2H in soil water from the LMWL, and the stronger the evaporation of soil water. Correlation analyses of lc in soil water at various soil depths with accumulated atmospheric evaporation (∑E) and accumulated atmospheric temperature (∑TA) in the preceding period shows that the latters significantly affected lc in soil water in the 0-60 cm soil layer, but insignificantly in soil layers below 60 cm in depth. Moreover, a certain relationship was found between soil water content (θ) and lc in soil water. The study also shows that relatively low stable isotope ratios in soil water in all soil layers were observed mostly during warm seasons relatively high in ∑E and ∑TA, and during the seasons evaporation enrichment grew stronger, while lc in soil water did lower, thus making scatter points of stable isotopes in soil water deviate further from LMWL; while relatively high stable isotope ratios in soil water in all soil layers appeared mostly during cold seasons, relatively low in ∑E and ∑TA, and relatively weak evaporation enrichment and relatively high lc in soil water during the seasons made scatter points of stable isotopes in soil water close to LMWL. Therefore, the slope of SWL was higher than that of LMWL in all soil layers in this study area. 【Conclusion】Stable isotopes contained in atmospheric precipitation are a direct factor affecting stable isotopes in soil water. Abundance of the stable isotopes in soil water is related to atmospheric heat and humidity in the preceding period. The cause why the slope of SWL is higher than that of LMWL in all soil layers is negatively and seasonally related to stable isotopes in precipitation and evaporation enrichment intensity of stable isotopes in soil water.

Abstract:The content of total organic carbon in soil is a major indicator reflecting the content of total organic matter and further on soil fertility. There are numerous factors that affect accumulation of organic carbon in soil. Among them, iron plays an essential role in capturing organic carbon and forming rust sink, thus promoting accumulation of soil organic carbon. A number of scholars have studied stabilizing mechanisms of soil organic carbon. In this paper, attempts were made to summarize the studies that had been done. It is found that the stabilizing mechanisms mainly include physical preservation of aggregates, chemical preservation of minerals, biological preservation of microorganisms and preservation of organic carbon per se. Among the four mechanisms, the first two are the main ones. Iron is closely involved in the mechanisms of physical, chemical and biological preservations. In physical preservation, iron promotes formation of soil aggregates. In chemical preservation, iron adsorbs and precipitates with organic carbon. At the same time, iron affects activity of soil microorganisms in biological preservation. All indicate that iron plays an important role in soil organic carbon accumulation. And the protective effect of organic carbon per se is mainly reflected in the anti-decomposition of a certain portion of organic carbon. In the end, the authors put forward several suggestions. More attention should be paid to the mechanisms of organic carbon sequestration and functional recovery of the carbon sink in the soil systems that are active in oxidation reduction and remarkable in ecological service function, to quantitative researches on and comparison between the different mechanisms in importance, and to simulation experiments, so as to better realize the goal of theory serving practice.

Abstract:【Objective】Papers available in the literature show that loess dust precipitation exists generally in North China, becoming an important source of topsoil in the region. It brings in a large amount of fine mineral particles and nutrient elements, especially, CaCO3, to the soil. CaCO3 is an important component of the soils in arid, semi-arid and semi-humid regions, and hence a major indicator reflecting development degree of a soil. The purpose of this paper is to study vertical distribution of CaCO3 content and its characteristics in the mountainous soil of North China, in an attempt to explain causes of this phenomenon from the perspective of soil genesis. 【Method】A total of 257 soil profiles of various soil series in Beijing and Shanxi Province were investigated for mechanical composition, CaCO3 content and lime reaction and statistic analysis was performed of the data. On such a basis, vertical distributions of CaCO3 content and lime reaction in the mountainous soils of North China and their characteristics were summarized, and causes of the phenomena explained with the theory of soil genesis.【Result】Results show that the topsoil in North China is mainly composed of silt, which is similar to loess, indicating that loess dust precipitation is an important source of soil minerals, bringing in CaCO3 to the topsoils of the mountainous soils in North China. As soil humidity varies sharply from area to area due to difference in elevation, soil CaCO3 content does too. In areas above 1 500 meters in elevation, the soils are quite high in humidity (varying in the humid and damp regime)_due to relatively high precipitation (mean annual precipitation of over 600 mm) and relatively low temperature (varying in the gelic or cryic soil temperature regime), and good to vegetation, which in turn reduces surface runoff, but enhances downward leaching of CaCO3. As a result CaCO3 is leached out of the soil, no matter what it is derived from, and no lime reaction is detected throughout the solum. So in these areas, bio-climatic conditions play a leading role affecting soil CaCO3 content and lime reaction. However, in areas ranging between 500 and 1 500 meters in elevation, the soils are relatively low in soil humidity (varying in the semi-arid-humid/humid regime) due to relatively low precipitation (mean annual precipitation of < 600 mm) and higher soil temperature (varying in the frigid/temperate regime), and hence not so good to vegetation, As a result, CaCO3 leaching is weakened and lime reaction could be found almost everywhere. Therefore in these areas bio-climate conditions descend from the leading role to a major role, following behind the role of parent material. Whatever, no obvious characteristic of the distribution of soil CaCO3 content and lime reaction could be summarized in areas below 500 meters in elevation.【Conclusion】In conclusion, the characteristics of the vertical distribution of soil CaCO3 content / lime reaction caused by leaching process, strong or weak, is one of the typical soil genetic characteristics of the mountainous soils in North China.

Abstract:Terrestrial water cycling encompasses mainly three factors, including precipitation, evapotranspiration and runoff, and dry or wet of the climate mainly depends on precipitation and evapotranspiration. Crop evapotranspiration is a major index to take into account in assessing climate drought degree, crop potential productivity, vegetation water consumption, and water resources supply and demand balance. And it may also provide a scientific basis for calculating crop water requirement, evaluating agricultural water resources, and developing reasonable irrigation schemes. It is generally believed that rising temperature will speed up surface evapotranspiration, and aggravate surface drought degree, while precipitation will increase will supplement the soil with water and relieve the surface droughtiness to a certain extent. So research and analysis on precipitation and evapotranspiration is of certain reference value to evaluating surface soil moisture conditions. The Huaihe River Basin, located between the Yangtze River basin and the Yellow River basin in the east part of China,, is a transitional zone between the north and south climates in this country, and belongs to the warm temperate semi-humid monsoon climatic region. Because of its special geographical position, the complexity and variability of its climate and frequent subjection to the impacts of convergence of cold and warm fronts from the north and south, precipitation varies frequenly and sharply, thus often leading to occurrence of droughts or flooding in this region. In the context of global warming, whether the climate in this region will change as affected by the factors mentioned above, how it will change, and what the development trend will be, are problems that call for systematic research. So analysis of changes in surface soil moisture content of the region will be of some practical significance. The precipitation data of the region monitored day by day were calculated and analyzed, and potential evapotranspiration and relative humidity at each station during that period of time were worked out using the Penman-Monteith formula. The interannual and decadal variation trends of precipitation, relative humidity index and potential evapotranspiration were analyzed through statistics. The analysis mainly used wavelet function of the Matlab software for cycle analysis and the Mann-Kendall test to analyze saltation of the variation trends. In which UF stands for clockwise standard normal distribution curve, while UB for counter-clockwise standard normal distribution curve. AcrGIS 10.1 was used to analyze spatial distributions of precipitation, potential evapotranspiration and relative humidity index The interpolation method used the inverse distance weighting(IDW) method, which set the distance between the interpolation point and the sample point as weight for calculate of weighted mean. The advantage of this method lies in being relatively intuitive and rapid in operation and applicable to dataset with sample points evenly and densely distributed. On such a basis, further study was done on characteristics of the spatio-temporal distribution and variation trend of soil moisture regime in the region, so as to provide some reference or basis for precautions to prevent flood, drought and other disasters in the Huaihe River Basin. Results show that: (1) in temporal distribution, the precipitation displayed an almost invisible slowly rising trend, and within the past 53 years, it showed 6-year primary cycles and 14-year secondary cycles, while in spatial distribution, the precipitation showed standard latitudinal difference, being relatively high in the south and low in the north; (2) the potential evaporation was on a downward trend in temporal distribution and in the past 53 years, it showed 11-year primary cycles and 4-year secondary cycles, while in spatial distribution, it displayed a trend mostly reverse to that of the precipitation; (3) in temporal distribution the relative humidity index was also on a slowly rising trend, with steady fluctuation range and frequency, while in spatial distribution. the relative humidity index in most of the region followed the same trend as the precipitation showed; and (4) the variation of the surface soil moisture regime of the region was the result of the combined effect of various meteorological factors. It is not difficult to draw the conclusion that precipitation is a positive factor and potential evapotranspiration a negative one affecting soil moistureregime.

Abstract:The alpine region in the Tibetan Plateau, characterized by sharp contrasts in topographpy and bioclimate, accounts for about one-fifth of China’s total land area. Due to limited field observation and high spatial heterogeneity, distribution of soil organic and inorganic carbon in the alpine region remains unclear. A better understanding of the distributions of soil organic and inorganic carbon and their controlling factors in this region is critical for accurate assessment of terrestrial carbon storage and important in implication for dealing with global climatic change. In this study, investigations were conducted of vertical distribution of soil organic and inorganic carbon along two toposequences in the middle Qilian Mountains on the northeastern edge of the Tibetan Plateau, one on the shady or north slope, the Hulugou watershed and the other on the sunny or south slope, the Shitougou watershed. Each toposequence consists of five typical soil profiles, and soil samples were collected by soil genetic horizons. The objectives of this study were to examine changes in vertical distribution of soil organic and inorganic carbon along the two toposequences, and to identify main controlling factors for the variations of soil organic and inorganic carboncontent at the slope scale in a relatively small region. Results show that organic carbon content decreased with soil depth in both toposequences, but the rate was much higherin the sunny slope (66% to 91%) than in the shady slope (31% to 77%). In the soil profiles along the shady slope, inorganic carbon was found distributed quite evenly (< 5.0 g kg-1) due to the strong leaching of carbonate, while in the soil profiles along the sunny slope, inorganic carbon in B horizons was two-fold as high as that in A horizons, which demonstrates that evident enrichment of inorganic carbon in the B horizons of the soil profiles on the sunny slope. Soil carbon in the topmost 1 meter soil layer did not vary much in density between the north and south slopes (16.1 to 33.9 kg m-2 and 11.8 to 32.8 kg m-2 respectively), but did in composition. In the north slope, the soil carbon was dominated by organic carbon accounting for 82% to 99% in density, however, the soil organic and inorganic carbon in the south slope varied sharply in density, accounting for 27% to 81% and 19% to 73% of the soil total, respectively. Therefore, it may be concluded that slope aspect plays an important role in the vertical distribution as well as composition of soil carbon in the alpine region. In addition, precipitation and vegetation are also major factors affecting spatial variability of soil carbon along the toposequences. With the mean annual precipitation increasing by 1 mm, soil organic carbon within the 0~20 cm soil layer increased by 0.4 g kg-1, while inorganic carbon within the 40~80 cm soil layer declined by 0.2 g kg-1. And vegetation type also had some effect on enrichment of soil organic carbon. All the findings in this study demonstrate that the study on soil carbon cycling and the estimation of soil carbon stocks in the alpine region should take into account the influence of micro-topography, especially slope aspect, on distribution, composition and spatial variation of soil carbon at the slope scale.

Abstract:Soil temperature is an important soil physical property. Seasonal and regional variations of soil temperature affect growth, propagation and distribution of soil organisms, which are closely related to agriculture and eco-environment. Based on the data of mean monthly soil temperature and air temperature and precipitation in China from 1971 to 2000, seasonal and regional variations of soil temperature in China and impacts of air temperature and precipitation on soil temperature were analyzed. Results indicate that seasonal variation of soil temperature in China was distinct. It was the most distinct from spring to summer, when the 20℃ contour line jumped up beyond 25℃ in latitude from south to north, and the mildest from winter to spring. The seasonal variation differed significantly from region to region. The relationships of soil temperature with air temperature and precipitation also varied with the region. In the temperate zone and the Qinghai-ibet Plateau, soil temperature was mainly affected by air temperature, while in the tropical and subtropical zones, both air temperature and precipitation contributed to the seasonal variation of soil temperature.

Abstract:The indicators are analyzed for the samples taken from 6 typical soil profiles, including Ah and AB horizons on the eastern vertical spectrum of soil in Mt. Hengshan. The results show:1) In the past 20 years, these soils developed on weathering materials of granite have experienced different levels of acidification, which is recognized by such indicators as increase in exchangeable acid, especially exchangeable Al3+ as well as decrease in pH, total of exchangeable base, base saturation percentage, and especially soil acid-buffer ability and soil acid-damage capacity. 2) By contrast, acidification is more evident for the perudic luvisol at the top of the mountain and the udic ferrisol at the foot of the mountain while the process of acidification is slow for the perrudic ferrisol on the slopes of the mountain and slower for the perudic cambisol at the upper part of the mountain, suggesting that soil acidification is related not only to the amount of acid precipitation to soil but also type of the soil.