水溶性有机物在土壤中的化学行为及其对环境的影响

水溶性有机物(Dissolved organic matter,DOM)是能够溶解于水的有机化合物的统称。尽管目前对于陆地生态系统中DOM的研究尚不完善,对其性质、组成和分类方法等问题的看法还没有达成一致,但现有研究结果已经表明DOM是一种十分活跃的重要化学组分。DOM进入土壤后将发生吸附、解吸、迁移、转化等一系列化学过程,进而对土壤及环境产生一系列重要影响:一方面,DOM可以与土壤胶体结合,形成有机无机结合体,从而改善土壤性质,DOM还可以通过其自身的分解产生养分离子,从而提高土壤肥力;另一方面,DOM也可能亲合土壤中原来与土壤胶体结合的养分,使之与DOM一起进入土壤溶液,从而增加土壤中养分离子被淋失的风险,并造成土壤养分的损失以及水体的富营养化,DOM还有可能活化土壤中重金属离子,增加土壤中重金属离子的毒性,并使土壤中的重金属离子向地下水迁移。由于其对土壤和环境的多种效应,水溶性有机物近年来已经逐渐成为土壤学、环境科学、生态学等学科的研究热点之一。     

模拟酸雨对龙眼落果及果实品质的影响研究

试验研究模拟酸雨对 8年生龙眼落果及果实品质的影响结果表明 ,pH≤ 3 5的酸雨处理显著增加落果率 ,果实可溶性固形物、固酸比和糖酸比显著下降。pH为 2 5的酸雨处理果实出现伤斑 ,单果重和可食率显著降低。     

菜心对邻苯二甲酸酯(PAEs)吸收途径的初步研究

采用玻璃室处理和污染土壤覆盖原土壤来控制PAEs来源进行盆栽试验，应用GC/MS联机检测技术初步研究了菜心对PAEs的吸收途径。结果表明：污染土壤处理与污染土壤上覆盖原土壤处理相比，前者菜心茎叶中DBP和DEHP的含量均高于后者，但相差不大，表明菜心茎叶可以吸收污染土壤中挥发出来的DBP和DEHP，而根系吸收运移是菜心茎叶中DBP和DEHP的主要来源途径。玻璃室处理增加了菜心茎叶和根系中DBP的含量，而对DEHP的影响趋势不明显。DBP与DEHP相比，前者更易被菜心根系吸收并向地上部(茎叶)运移，后者主要滞留在根部。     

The sensitivity of water extractable soil organic carbon fractions to land use in three soil types

Soil organic carbon (SOC) has a high impact on the sustainability of ecosystems, global environmental processes, soil quality and agriculture. Long-term tillage usually leads to SOC depletion. The purpose of this study was to determine the impact of different land uses on water extractable organic carbon (WEOC) fractions and to evaluate the interaction between the WEOC fractions and other soil properties. Using an extraction procedure at 20°C and 80°C, two fractions were obtained: a cold water extractable organic carbon (CWEOC) and a hot water extractable organic carbon (HWEOC). The results suggest that there is a significant impact from different land uses on WEOC. A lower relative contribution of WEOC in SOC and a lower concentration of labile WEOC fractions are contained in arable soil compared to forestlands. Chernozem soil was characterized by a lower relative contribution of WEOC to the SOC and thus higher SOC stability in contrast to Solonetz and Vertisol soils. Both CWEOC and HWEOC are highly associated with SOC in the silt and clay fraction (<53 µm) and were slightly associated with SOC in the macroaggregate classes. The WEOC fractions were highly and positively correlated with the SOC and mean weight diameter.     

Clay dispersion and its relation to surface charge in a paddy soil of the Red River Delta,Vietnam

Dispersion is an important issue for clay leaching in soils. In paddy soils of the Red River Delta (RRD), flooding with fresh water and relatively high leaching rates can accelerate dispersion and the translocation of clay. For the clay fraction of the puddled horizon of a typical paddy soil of the RRD, the effect of various cations and anions as well as humic acid (HA) at different pH values on the surface charge (SC) were quantified and the dispersion properties were determined in test tubes and described by the C₅₀ value. In the <2 µm fraction, dominated by illite, the proportion of 2:1 vs. 1:1 clay minerals is 5:1. The organic‐C content of the clay fraction is 2.2%. Surface charge was found to be highly pH‐dependent. At pH 8 values of –32 and at pH 1 of –8 mmol_c kg^–1 were obtained. Complete dispersion was observed at pH > 4, where SC is > –18 mmol_c kg^–1. The flocculation efficiency of Ca strongly depends on the pH. At pH 4, the C₅₀ value is 0.33, 0.66 at pH 5, and 0.90 mmol L^–1 at pH 6. At pH 6, close to realistic conditions of paddy soils, the effect of divalent cations on the SC and flocculation decreases in the order: Pb > Cu > Cd > Fe^II > Zn > Ca > Mn^II > Mg; Fe^II was found to have a slightly stronger effect on flocculation than Ca. An increase in concentrations of Ca, Mn^II, and Mg from 0 to 1 mmol L^–1 resulted in a change in SC from –25 to approx. –15 mmol_c kg^–1. In comparison, the divalent heavy‐metal cations Pb, Cu, Cd, and Zn were found to neutralize the SC more effectively. At a Pb concentration of 1 mmol L^–1, the SC is –2 mmol_c kg^–1. From pH 3 to 5, the dispersion of the clay fraction is facilitated rather by SO than by Cl^–, which can be explained by the higher affinity of SO to the positively charged sites. With an increase of the amount of HA added, the SC continuously shifts to more negative values, and higher concentrations of cations are needed for flocculation. At pH 3, where flocculation is usually observed, the presence of HA at a concentration of 40 mg L^–1 resulted in a dispersion of the clay fraction. While high anion concentrations and the presence of HA counteract flocculation by making the SC more negative, Fe^II and Ca (C₅₀ at pH 6 = 0.8 and 0.9 mmol L^–1, respectively) are the main factors for the flocculation of the clay fraction. For Fe^II and Ca, the most common cations in soil solution, the C₅₀ values were found to be relatively close together at pH 4, 5, and 6, respectively. Depending on the specific mineralogical composition of the clay fraction, SC is a suitable measure for the determination of dispersion properties and for the development of methods to keep clay particles in the soil in the flocculated state.     

翻埋与覆盖林木枝条改善宁夏沙化土壤性质

土地沙漠化一直是影响宁夏生态建设和农业生产的主要问题之一。为探讨林木枝条对沙化土壤的改良效果,以当地农田防护林所产生的林木枝条为原料,在2011年10月至2013年10月期间研究了土壤翻埋杨树粉碎枝条(chips incorporation,CI)、覆盖杨树粉碎枝条(chips mulch,CM)、翻埋杨树粉碎枝条+覆盖未粉碎的柳树枝条(chips incorporation plus branches mulch,CI+BM)和不做任何处理的对照(control,CK)对宁夏沙化土壤理化性状和生物学特性的影响。结果表明,CI和CI+BM与CK相比,2012年和2013年均增加了土壤总孔隙度、田间持水率、有机碳、有效磷和速效钾含量(P0.05),提高了土壤呼吸强度、微生物数量(细菌、真菌和放线菌)和酶活性(脲酶、过氧化氢酶)(P0.05),降低了土壤密度(P0.05);2013年CI和CI+BM进一步增加了土壤全氮、全磷和水解氮含量(P0.05),但同时也增加了土壤全盐含量(P0.05)。CM与CK相比,2012年和2013年均显著增加了土壤有效磷和速效钾含量(P0.05),提高了土壤呼吸强度和酶活性(P0.05);2013年CM处理的土壤p H值、全氮和水解氮含量亦显著增加(P0.05)。相关分析结果显示,沙化土壤性质的改善与土壤中有机碳含量的增加密切相关,处理间土壤有机碳含量CI+BMCICMCK,表征土壤质量的综合指数表现出同样的趋势:2012年分别为0.907、0.678、0.259和0.105,2013年分别为0.926、0.828、0.258和0.136。该研究为当地及中国北方干旱半干旱地区沙地生态治理及农业生产提供了可借鉴的案例,同时也为促进林木废弃物的资源化利用提供理论基础。     

洱海缓冲带土壤特性的空间分布

[目的]了解洱海缓冲带内土壤特性空间分布状况,进而为缓冲带面源污染治理、精细农业与植被布局等提供参考。[方法]采集80个缓冲带表层土壤样品,测定其含水率、有机质、全磷、全氮、氨氮和硝氮的含量,并应用传统统计学和地统计学方法对数据进行分析。[结果](1)土壤中含水率、有机质、全磷、全氮、氨氮和硝氮各项统计特性均通过K—S检验,呈正态分布;(2)洱海缓冲带土壤中养分水平较高;氨氮和硝氮的变异系数大于100%,属强变异性;(3)有机质南部略低,东西向呈东西高,中部低,全氮、全磷南北向呈南北低,中部高,东西向变化不大;(4)有机质表现出强烈的空间相关性,而全氮和全磷空间相关性弱。[结论]缓冲带农田格局和迁移转化是影响土壤特性空间分布的两个重要因素。     

Differences Among Rice Cultivars in their Adaptation to Low Ionic Strength Solution with Toxic Level of Aluminum that Mimics Tropical Acid Soil Conditions

Nutrient deficiencies are often an additional growth-limiting factor in tropical acid soils. Considering the potential interactions between Al stress and low-nutrient stress, differences among rice cultivars for Al tolerance, low-nutrient tolerance, and combined stress tolerance were investigated. The main objective of this study was to identify the predominant growth-limiting factor in tropical acid soils. Tolerance to low nutrient stress and combined stress did not show any relationship with aluminum (Al) tolerance indicating that these stress factors act independently. Al-tolerant cv. Rikuu-132 was tolerant to combined stress. Conversely, highly Al-sensitive cv. BR34 was most tolerant to combined and low nutrient stress. Combined stress tolerance of shoot was positively correlated with calcium (Ca) content of shoot. The results indicate that Al tolerance alone is not adequate for superior performance on most acid soils. Tolerance to combined stress factors would be needed to improve productivity of rice on low fertility acid soils.     

可变电荷土壤对酸雨敏感度的影响因子

The sensitivity of a large number of variable charge soils to acid rain was evaluated through examining pH-H₂SO₄ input curves. Two derivative parameters, the consumption of hydrogen ions by the soil and the acidtolerant limit as defined as the quantity of sulfuric acid required to bring the soil to pH 3.5 in a 0.001mol L^-1 Ca(NO₃)₂ solution, were used. The sensitivity of variable charge soils was higher than that of constant charge soils, due to the predominance of kaolinite in clay mineralogical composition. Among these soils the sensitivity was generally of the order lateritic red soil > red soil > latosol. For a given type of soil within the same region the sensitivity was affected by parent material, due to differences in clay minerals and texture. The sensitivity of surface soil may be lower or higher than that of subsoil, depending on whether organic matter or texture plays the dominant role in determining the buffering capacity. Paddy soils consumed more acid within lower range of acid input when compared with upland soils, due to the presence of more exchangeable bases, but consumed less acid within higher acid input range, caused by the decrease in clay content.     

Organic matter status and the size,activity and metabolic diversity of the soil microflora as indicators of the success of rehabilitation of mined sand dunes

The effectiveness of the rehabilitation of mined sand dunes on the northern coast of KwaZulu–Natal, South Africa, was assessed based on measurements of the total and labile organic matter content and the size, activity and metabolic diversity of the soil microflora. Soil was sampled (0–10 cm) after 0, 5, 10, 20 and 25 years of rehabilitation and compared with soil under undisturbed native forest and under long-term commercial pine forest. Following topsoil removal, stockpiling and respreading on reformed dunes, there was a massive loss of organic C such that, at time zero, organic C content was only 24% of that present under native forest. Soil organic C content increased progressively during rehabilitation until, after 25 years, it represented 93% of that present under native forest. The pattern of change in light-fraction C, KMnO₄-extractable C, water-soluble C, microbial biomass C, basal respiration and arginine ammonification rate was broadly similar to that for organic C, but the extent of the initial loss and the magnitude of the subsequent increase differed. Microbial biomass C, water-soluble C and KMnO₄-extractable C, expressed as a percentage of organic C, declined during rehabilitation as humic substances progressively accumulated. Principal component (PC) analysis of catabolic response profiles to 36 substrates revealed that the catabolic diversity of microbial communities differed greatly between native forest, commercial pine forest, 0 years and 10 years of rehabilitation. On the PC1 axis, values for soils under native forest and after 25 years rehabilitation were similar, but there was still separation on the PC2 axis. The main factor explaining variation in response profiles on the PC1 axis was organic C content; and the greatest catabolic diversity occurred in soils under native forest and after 25 years of rehabilitation.