小兴安岭两种森林类型土壤有机碳库及周转

采用室内培养法测定了不同温度下(8、18、28 ℃)小兴安岭原始阔叶红松林和阔叶次生林土壤有机碳的矿化速率和矿化量,并用三库一级动力学模型对有机碳各库进行拟合.结果表明： 基于单位干土质量的阔叶次生林土壤有机碳矿化速率和累计矿化量均大于原始红松林,但有机碳累计矿化量占总有机碳的比率小于原始红松林.2种森林类型土壤活性碳库和缓效碳库随土层加深而减小,其占总有机碳的比例增加.尽管阔叶次生林土壤活性和缓效碳库均大于原始红松林,但其占总有机碳的比例却小于原始红松林,而土壤惰性碳库及其比例均大于原始红松林,表明阔叶次生林土壤有机碳整体上更稳定.土壤活性碳库平均驻留时间(MRT)为9～24 d,且随土层加深而缩短,而缓效碳库MRT为7～42 a,且随土层加深而延长.土壤活性碳库及其占总有机碳的比例随温度升高而线性增加,缓效碳库则降低;原始红松林土壤活性碳随温度的增速大于阔叶次生林,表明原始红松林土壤有机碳库对温度变化反应更敏感.     

喀斯特森林植被自然恢复过程中土壤可矿化碳库特征

2011年9月,采用空间代替时间方法,研究了茂兰自然保护区喀斯特森林自然恢复过程中土壤可矿化碳库的特征.结果表明: 研究期间,喀斯特森林自然恢复过程中不同深度土壤的总有机碳含量、可矿化碳含量和矿化速率随土层加深而减少,随恢复的进程而增加;累积矿化排放量及其速率随恢复的进程增加,其速率随培养时间延长而减小;矿化率随恢复的进程增加,而随土层加深的变化不明显;qCO₂值随恢复的进程和土层加深而递减;土壤可矿化碳与凋落物现存量及其分解质量损失率分别呈负相关(r=-0.796)和正相关(r=0.924);土壤生境由早期干扰强烈转向中后期日趋稳定,土壤的固碳能力由早期差、潜力大转向中后期强、潜力小.     

水分状况与不同形态氮添加对亚热带森林土壤氮素净转化速率及N2O排放的影响

通过室内模拟试验,研究40%、70%和110%土壤饱和持水量(WHC)下,不同形态氮(硝态氮和铵态氮)添加对亚热带森林红壤氮素转化的影响.结果表明:70%WHC下土壤净矿化和氨化速率最高,40%WHC下最低;与对照相比,70%WHC下添加硝态氮使土壤净矿化和氨化速率分别降低56.1%和43.0%,110%WHC下分别降低68.2%和19.0%,但提高了氨化速率占矿化速率的比例,表明添加硝态氮抑制了硝化.110%WHC下,添加硝态氮后,土壤净硝化速率最低,但氧化亚氮(N2O)浓度最高,最大值出现在第3~7天,表明N2O产生自反硝化途径,硝态氮也在同时段降低;而40%WHC和70%WHC下,N2O浓度在培养初期最大,即使在铵态氮和硝态氮添加处理下,试验后期N2O浓度也没有显著变化,表明自氧硝化是试验前期N2O产生的主要途径.40%WHC下,土壤可溶性有机碳含量增加最多,且在铵态氮添加处理下增加最多,可见添加铵态氮促进土壤有机质矿化,增加可溶性有机碳,但是土壤水分含量增多不利于有机质矿化.在40%WHC和110%WHC下,铵态氮添加处理土壤可溶性有机氮(SON)变化速率分别显著高于对照73.6%和176.6%,而在硝态氮添加处理下,只有40%WHC下显著高于对照78.7%,表明高水分条件和添加铵态氮有利于SON的形成.     

武夷山不同海拔植被土壤易氧化碳

土壤有机质的短暂波动主要发生在易氧化部分,而易氧化碳作为土壤有机碳的敏感因子,可以指示土壤有机质的早期变化.采用高锰酸钾氧化法,分析了福建武夷山自然保护区不同海拔高度具有代表性的中亚热带常绿阔叶林(200～1 000 m)、针叶林(1 350～1 750 m)、亚高山矮林(1 750～1 900 m)以及高山草甸(1 700～2 158 m)土壤中易氧化碳的变化特征,分析其与微生物量碳、土壤总有机碳、土壤含水量、全氮之间的关系.结果表明:不同群落土壤中的易氧化碳含量随海拔上升而增加,随土层深度的增加而减少;易氧化碳和土壤总有机碳、微生物量碳、土壤湿度、全氮间呈极显著的相关;土壤易氧化碳占总有机碳比例为8.69%～14.73%,是微生物量碳占总有机碳比例的3.32～11.41倍;沿海拔梯度,易氧化碳含量受到土壤总有机碳、土壤湿度和温度的显著影响.     

黄土高原沟壑区森林带不同植物群落土壤氮素含量及其转化

为了探讨在黄土高原退耕还林还草过程中植物群落对土壤氮素含量及形态分布的影响,本文选择退耕历史较长的黄土高原沟壑区——安塞县洞子沟流域8种典型植物群落下0-10cm和10-20cm的土壤为对象,测定了土壤中有机氮、矿化氮、微生物量氮、硝态氮和铵态氮的含量。结果表明,从草本群落到乔灌草群落,土壤各形态氮素含量均增加,整体表现为乔灌草群落>灌草群落>草本群落。然而人工刺槐林的土壤氮素水平远低于自然恢复的乔灌草群落,甚至低于灌草群落。0-10cm 土层各形态氮素均高于10-20cm 土层。硝态氮对植物群落的变化最为敏感,可作为土壤氮素水平的敏感指标。土壤有机质、pH、容重与氮素含量极显著相关,各种氮素间极显著正相关。各种氮素占总氮的比例对总氮的变化有着不同的响应,有机氮、可矿化氮和微生物量氮占总氮的比例相对稳定,硝态氮占总氮的比例随总氮含量的增加而增加,铵态氮占总氮的比例随总氮含量的增加而降低。     

长期施肥对水稻土颗粒有机碳和矿物结合态有机碳的影响

在23a的田间定位试验区,研究了长期施肥对水稻土颗粒有机碳和矿物结合态有机碳的影响.结果表明,在不施肥(CK)、无机肥(NPK)、有机肥(猪粪 紫云英绿肥)(OM)和无机肥与有机肥配施(NPKM)处理中,A层游离态和闭蓄态颗粒有机物含量比P层高,随着土层的加深呈下降的趋势;而矿物态有机物呈相反的趋势.增施有机肥(NPKM,OM处理)有利于提高土壤中游离态和闭蓄态颗粒有机物及其有机碳的含量以及占土壤有机碳的比例.团聚体中颗粒有机物占土壤团聚体重量的比例及颗粒有机物的有机碳含量均随着团聚体粒径的减小而明显增加.增施有机肥显著提高了团聚体特别是微团聚体(<0.25mm)中颗粒有机物及其有机碳的含量.团聚体中颗粒有机物的有机碳含量显著高于容积土壤中颗粒有机物的有机碳含量.这些结果表明微团聚体对颗粒有机物具有富集和保护作用. 和闭蓄态颗粒有机物含量比P层高,随着土层的加深呈下降的趋势;而矿物态有机物呈相反的趋势.增施有机肥(NPKM,OM处理)有利于提高土壤中游离态和闭蓄态颗粒有机物及其有机碳的含量以及占土壤有机碳的比例.团聚体中颗粒有机物占土壤团聚体重量的比例及颗粒有机物的有机碳含量均随着团聚体粒径的减小而明显增加. 施有机肥显著提高了团聚体特别是微团聚体(<0.25mm)中颗粒有机物及其有机碳的含量.团聚体中颗粒有机物的有机碳含量显著高于容积土壤中颗粒有机物的有机碳含量.这些结果表明微团聚体对颗粒有机物具有富集和保护作用. 和闭蓄态颗粒有机物含量比P层高,随着土层的加深呈下降的趋势;而矿物态有机物呈相反的趋势.增施有机肥     

川西亚高山-高山土壤表层有机碳及活性组分沿海拔梯度的变化

青藏高原东缘亚高山-高山地带土壤碳被认为是我国重要的土壤碳库,作为高海拔低温生态系统,土壤碳对土壤暖化的响应可能也更加敏感。该区域亚高山森林一般分布在海拔3200 m以上,上缘接高山树线和灌丛草地,土壤有机碳含量高。海拔梯度上变化的土壤环境因子是主要土壤温度,海拔梯度上高寒土壤有机碳及活性有机碳组的分布格局,可体现海拔梯度上温度因子对土壤碳动态的影响。对沿海拔3200 m(亚高山针叶林)、3340 m(亚高山针叶林)、3540 m(亚高山针叶林)、3670 m(亚高山针叶林)、3740 m(亚高山针叶林)、3850 m(高山林线)、3940 m(高山树线)、4120 m(高山草地)的土壤表层(0-20 cm)有机碳和活性有机碳组分含量进行分析,结果表明在该海拔范围内,表层土壤总有机碳含量随着海拔的升高而增加,显示高海拔有利于土壤碳的固存;土壤活性有机碳组分中,颗粒态有机碳含量及其占总有机碳比例与海拔呈显著正相关,在海拔最高的4120 m含量和占有机碳总量比例分别达到50.81 g/kg和56.52%。在该海拔范围内海拔越高颗粒态有机碳占有机碳比例越高,显示高海拔土壤有机碳更多以土壤颗粒态碳形式贮存。微生物量碳、水溶性碳、轻组分有机碳与海拔高度没有明显的相关性,表明这些活性有机碳组分受海拔因素影响不大;易氧化有机碳含量与海拔高度显著正相关。因此,颗粒态有机碳含量及其比例可作为高海拔地带土壤活性有机碳库动态的特征指标,表征高海拔地带土壤有机碳动态与贮量受温度影响的指标。     

不同形态有机碳的有效性在两种重金属污染水平下水稻土壤中的差异

调查分析了两块不同重金属污染水平下的水稻田土壤有机碳活性组分的含量,以评价重金属胁迫条件下有机碳基质的微生物有效性。结果显示,重污染水稻土的总有机碳(TOC)、0·5mol·L-1K2SO4溶解态有机碳(K2SO4-C)、微生物生物量碳(MBC)、1~7d(CO2-C1~7d)和8~28d矿化的有机碳(CO2-C8~28d)的含量均显著低于轻污染土壤(p<0·001)。碳有效性指标中,微生物商(MBC/TOC比)和8~28d的有机碳矿化率(CO2-C8~28d·TOC-1d-1))在轻污染土壤中较高,而K2SO4-C/TOC和代谢商(qCO2)在重污染土壤较高(p<0·001)。1~7d的有机碳矿化率(CO2-C1~7d·TOC-1d-1)在两种土壤中差异不显著。两种土壤培养初期的有机碳矿化率远高于培养后期(p<0·001)。逐步回归分析显示,CO2-C1~7d与活性组分K2SO4-C和MBC显著相关(r2=0·83,p<0·001),而CO2-C8~28d只与TOC显著相关(r2=0·70,p<0·001)。研究表明,尽管K2SO4溶解态有机碳在供试的重金属污染的水稻土中是较易被分解的活性碳基质,但重金属污染抑制了微生物数量及其呼吸活性,降低了活性有机碳库的矿化率,这是导致土壤中K2SO4溶解态碳积累的原因。溶解性有机碳又能提高重金属的有效性,进一步抑制微生物对有机碳的矿化。因此,评价重金属污染的水稻土有机碳的有效性,应当综合考虑不同有机碳库的活性、微生物的矿化能力和碳基质在不同阶段的供应潜力。     

藏东南色季拉山西坡土壤有机碳库研究

土壤碳是森林生态系统最大的碳库,是其碳循环的极其重要组分.土壤微生物生物量是陆地生态系统碳循环的重要组成部分.为探讨不同森林植被类型对土壤活性有机碳库的影响,以西藏色季拉山(西坡)的高山灌丛(Alpine shrub,AS)、杜鹃林(Rhododendron forest,RF)、急尖长苞冷杉林(Abies georgei var.smithii forest,AGSF)和林芝云杉林(Picea likiangensis var.linzhiensis forest,PLLF)为试验对象,研究了林地土壤有机碳、总氮含量及微生物生物量.结果表明:高海拔植被类型具有较高的土壤活性有机碳含量和分配比例.土壤总有机碳表现在0-10cm均差异显著;在10-20cm和20-40cm无规律性(P＜0.05).土壤全氮表现在0-10cm AS均差异显著,而RF、AGSF和PLLF差异不显著;在10-20cm AS、RF、AGSF与PLLF均相差显著;在20-40cm AS、RF、AGSF与PLLF均相差不显著(P＜0.05).土壤微生物量碳含量与土壤总有机碳含量关系密切,呈显著的正相关.土壤微生物生物量氮含量和比例随微生物生物量碳含量和比例增加而增加.色季拉山土壤微生物量碳含量均随海拔升高而增加.在不同植被类型的生态系统中,土壤总有机碳含量、土壤颗粒有机碳和土壤易氧化碳含量均呈现出随土层深度增加而递减的变化趋势.土壤颗粒有机碳含量占土壤总有机碳含量和土壤易氧化有机碳含量占土壤总有机碳含量的比率范围不同,且随土层深度增加比率减小.土壤活性有机碳与土壤总有机碳显著相关,土壤易氧化有机碳与颗粒有机碳的相关系也比较显著(P＜0.05).     

土地利用方式转变对赣中地区土壤活性有机碳的影响

选取江西省安福县15年撂荒地和3种林地(毛竹林人工林、木荷次生林、杉木人工林),研究土地利用方式改变对土壤有机碳库以及活性有机碳的影响.结果表明：不同样地的土壤总有机碳、微生物生物量碳、热水浸提有机碳和易氧化态碳均表现为毛竹人工林>杉木人工林>木荷次生林>撂荒地;与对照(撂荒地)相比,3种林地的土壤有机碳含量、碳储量及活性有机碳含量均随土壤深度增加而递减,表层富集现象明显;不同土壤活性有机碳的分配比例明显不同,其中,土壤易氧化态碳占总有机碳的比例最大,微生物生物量碳所占比例最小,土壤总有机碳、微生物生物量碳、热水浸提有机碳和易氧化态碳间的相关性均达到极显著水平.后三者表征了土壤中活性较高部分碳的含量,对土地利用方式的响应较敏感,可以作为评价赣中地区土壤质量和肥力的指标之一.     

有机肥连续施用对菜田重金属行为的影响——基于地球化学模型研究

2017年起,农业部连续多年出台化肥减量增效行动工作方案,要求适当增加有机肥投入,发展循环农业。但连续施用的有机肥进入土壤后,会对土壤pH、有机质和重金属含量等产生影响,改变土壤重金属行为。科学评估有机肥料施用的影响至关重要。仅通过总含量评估重金属污染风险被认为是片面的,不同化学提取剂提取的重金属含量不能完全代表实际污染状况。地球化学模型具有良好的适用性,比传统的提取方法能够更全面地解释重金属的行为。在集约化农业种植区黄淮海平原,多次施用不同比例的粪源有机肥于旱地菜田,并引入地球化学模型,结合pH依赖性浸出试验,明确连续施肥对菜田土壤重金属行为的主要影响机制。研究发现,有机肥中的铜锌含量远高于土壤中的含量,施用后,它们在土壤中的淋溶浓度随着施用比例增加而显著增加,最多可超过十倍以上,并且活性大大增加,与施肥后溶解性有机物含量的升高呈正相关。不同处理条件下的土壤重金属浸出趋势相似：在中性pH下浸出浓度最低,然后逐渐向强酸和强碱增加,呈现出V型变化。地球化学模型LeachXS展示出较好的模拟结果,其模拟值与实测浓度具有良好的相关性(71.02%)。模拟结果显示,有机肥的施用不会明显改变重金...     

Anthropogenic N deposition increases soil organic matter accumulation without altering its biochemical composition

Accumulating evidence indicates that future rates of atmospheric N deposition have the potential to increase soil C storage by reducing the decay of plant litter and soil organic matter (SOM). Although the microbial mechanism underlying this response is not well understood, a decline in decay could alter the amount, as well as biochemical composition of SOM. Here, we used size‐density fractionation and solid‐state ¹³C‐NMR spectroscopy to explore the extent to which declines in microbial decay in a long‐term (ca. 20 yrs.) N deposition experiment have altered the biochemical composition of forest floor, bulk mineral soil, as well as free and occluded particulate organic matter. Significant amounts of organic matter have accumulated in occluded particulate organic matter (~20%; oPOM); however, experimental N deposition had not altered the abundance of carboxyl, aryl, alkyl, or O/N‐alkyl C in forest floor, bulk mineral soil, or any soil fraction. These observations suggest that biochemically equivalent organic matter has accumulated in oPOM at a greater rate under experimental N deposition, relative to the ambient treatment. Although we do not understand the process by which experimental N deposition has fostered the occlusion of organic matter by mineral soil particles, our results highlight the importance of interactions among the products of microbial decay and the chemical and physical properties of silt and clay particles that occlude organic matter from microbial attack. Because oPOM can reside in soils for decades to centuries, organic matter accumulating under future rates of anthropogenic N deposition could remain in soil for long periods of time. If temperate forest soils in the Northern Hemisphere respond like those in our experiment, then unabated deposition of anthropogenic N from the atmosphere has the potential to foster greater soil C storage, especially in fine‐texture forest soils.     

Increase in pH stimulates mineralization of ‘native’ organic carbon and nitrogen in naturally salt-affected sandy soils

Large amounts of terrestrial organic C and N reserves lie in salt-affected environments, and their dynamics are not well understood. This study was conducted to investigate how the contents and dynamics of ‘native’ organic C and N in sandy soils under different plant species found in a salt-affected ecosystem were related to salinity and pH. Increasing soil pH was associated with significant decreases in total soil organic C and C/N ratio; particulate (0.05–2 mm) organic C, N and C/N; and the C/N ratio in mineral-associated (<0.05 mm) fraction. In addition, mineral-associated organic C and N significantly increased with an increase in clay content of sandy soils. During 90-day incubation, total CO₂-C production per unit of soil organic C was dependent on pH [CO₂-C production (g kg⁻¹ organic C) = 22.5 pH – 119, R ² = 0.79]. Similarly, increased pH was associated with increased release of mineral N from soils during 10-day incubation. Soil microbial biomass C and N were also positively related to pH. Metabolic quotient increased with an increase in soil pH, suggesting that increasing alkalinity in the salt-affected soil favoured the survival of a bacterial-dominated microbial community with low assimilation efficiency of organic C. As a result, increased CO₂-C and mineral N were produced in alkaline saline soils (pH up to 10.0). This pH-stimulated mineralization of organic C and N mainly occurred in particulate but not in mineral-associated organic matter fractions. Our findings imply that, in addition to decreased plant productivity and the litter input, pH-stimulated mineralization of organic matter would also be responsible for a decreased amount of organic matter in alkaline salt-affected sandy soils.     

Interactions between Carbon and Nitrogen Mineralization and Soil Organic Matter Chemistry in Arctic Tundra Soils

We used long-term laboratory incubations and chemical fractionation to characterize the mineralization dynamics of organic soils from tussock, shrub, and wet meadow tundra communities, to determine the relationship between soil organic matter (SOM) decomposition and chemistry, and to quantify the relative proportions of carbon (C) and nitrogen (N) in tundra SOM that are biologically available for decomposition. In all soils but shrub, we found little decline in respiration rates over 1 year, although soils respired approximately a tenth to a third of total soil C. The lack of decline in respiration rates despite large C losses indicates that the quantity of organic matter available was not controlling respiration and thus suggests that something else was limiting microbial activity. To determine the nature of the respired C, we analyzed soil chemistry before and after the incubation using a peat fractionation scheme. Despite the large losses of soil C, SOM chemistry was relatively unchanged after the incubation. The decomposition dynamics we observed suggest that tundra SOM, which is largely plant detritus, fits within existing concepts of the litter decay continuum. The lack of changes in organic matter chemistry indicates that this material had already decomposed to the point where the breakdown of labile constituents was tied to lignin decomposition. N mineralization was correlated with C mineralization in our study, but shrub soil mineralized more and tussock soil less N than would have been predicted by this correlation. Our results suggest that a large proportion of tundra SOM is potentially mineralizable, despite the fact that decomposition was dependent on lignin breakdown, and that the historical accumulation of organic matter in tundra soils is the result of field conditions unfavorable to decomposition and not the result of fundamental chemical limitations to decomposition. Our study also suggests that the anticipated increases in shrub dominance may substantially alter the dynamics of SOM decomposition in the tundra. Received 31 January 2002; accepted 16 July 2002.     

酸性矿山废水污染的水稻田土壤中重金属的微生物学效应

采样调查了广东大宝山地区受酸性采矿废水长期污染的亚热带水稻田的土壤理化性质 ,重金属 Cu、Pb、Zn、Cd的全量及其 DTPA浸提量 ,以及微生物生物量及其呼吸活性等指标。利用主成分和逐步回归分析了影响土壤重金属的有效性及其微生物学效应的因素。结果表明 :土壤高含硫 ,强酸性 ,有机碳、全氮较低 ,4种金属的全量普遍超标。DTPA可提取态金属含量较高 ,不仅与其全量呈显著正相关 ,而且与土壤酸度和粘粒含量正相关 ,和 Mn含量负相关。过量的金属显著降低了土壤微生物生物量 C、N、微生物商、生物量 N/全 N比 ,并抑制了微生物呼吸强度和对有机碳的矿化率 ,导致了土壤 C/N比的升高。同时 ,金属对微生物群落及生理代谢指标 ,如微生物生物量 C/N比和代谢商的影响不显著。 DTPA可提取态金属 ,特别是 DTPA- Cu是导致微生物生物量和活性指标变化的主要因素。以有机碳 (或全氮 )为基数的复合微生物指标降低了土壤性质差异造成的干扰 ,较单一指标更能准确指示微生物对金属胁迫的反应。土壤硫没有对金属有效性和微生物指标产生明显影响 ,但其氧化过程可能引起酸化和金属离子的释放     

Particulate organic carbon in the estuarine turbidity maxima of the Gironde,Loire and Seine estuaries: origin and lability

A study of the particulate organic carbon (POC) in the estuarine turbidity maxima (ETMs) of the three major French macrotidal estuaries shows that the average contents are 1.5, 3.3 and 3.1% (expressed in % of dry suspended sediment) in the Gironde, Loire and Seine Estuaries, respectively. There is no seasonal variation of POC contents in the Gironde Estuary, whereas, they often increase in the Loire and the Seine Estuaries in spring and summer. The lability of the estuarine particulate organic matter was estimated by two analyses: 1/labile organic matter was measured as the organic carbon loss during incubation tests over one month; 2/ the hydrolysable organic fraction was determined after 6N HCl digestion. The organic fractions of the ETMs are mainly refractory. Any increase in the amount of POC as compared to the background levels (cited above) is always correlated to an increase of organic matter lability. The yearly average fluvial contributions by various particulate organic pools (soil and litter organic matter; organic matter of phytoplanktonic and human origin) that enter the three estuaries were quantified. In the Garonne River, soil and litter are the major (90%) POC sources. In the Loire system, due to the eutrophication of the river water, phytoplankton contributes up to 50% of the total POC load. In the Seine river, soil and litter contribute 70% of the total POC input; POC of human origin is also significant (10%), due to the impact of the City of Paris (10 million inhabitants). The lability of the different types of organic matter ranks as follows: phytoplankton ∼litter > human-origin organic matter >> soil. By combining the POC budgets and the lability of each type of organic fraction, it was possible to explain why the POC of the three ETMs is different and characterizes its refractory vs. labile nature.     

Depth-dependent effects of ericoid mycorrhizal shrubs on soil carbon and nitrogen pools are accentuated under arbuscular mycorrhizal trees

Plant mycorrhizal associations influence the accumulation and persistence of soil organic matter and could therefore shape ecosystem biogeochemical responses to global changes that are altering forest composition. For instance, arbuscular mycorrhizal (AM) tree dominance is increasing in temperate forests, and ericoid mycorrhizal (ErM) shrubs can respond positively to canopy disturbances. Yet how shifts in the co-occurrence of trees and shrubs with different mycorrhizal associations will affect soil organic matter pools remains largely unknown. We examine the effects of ErM shrubs on soil carbon and nitrogen stocks and indicators of microbial activity at different depths across gradients of AM versus ectomycorrhizal (EcM) tree dominance in three temperate forest sites. We find that ErM shrubs strongly modulate tree mycorrhizal dominance effects. In surface soils, ErM shrubs increase particulate organic matter accumulation and weaken the positive relationship between soil organic matter stocks and indicators of microbial activity. These effects are strongest under AM trees that lack fungal symbionts that can degrade organic matter. In subsurface soil organic matter pools, by contrast, tree mycorrhizal dominance effects are stronger than those of ErM shrubs. Ectomycorrhizal tree dominance has a negative influence on particulate and mineral-associated soil organic matter pools, and these effects are stronger for nitrogen than for carbon stocks. Our findings suggest that increasing co-occurrence of ErM shrubs and AM trees will enhance particulate organic matter accumulation in surface soils by suppressing microbial activity while having little influence on mineral-associated organic matter in subsurface soils. Our study highlights the importance of considering interactions between co-occurring plant mycorrhizal types, as well as their depth-dependent effects, for projecting changes in soil carbon and nitrogen stocks in response to compositional shifts in temperate forests driven by disturbances and global change.     

粉煤灰滤泥混合物对土壤性质、萝卜产量与品质的影响

粉煤灰和滤泥以1：1（w/w）比例混合并添加少量化肥配制成混合物,通过盆栽试验研究该混合物农用对土壤生物化学性质、萝卜产量和品质的影响以及重金属在土壤和萝卜中的富集状况。结果表明,该混合物中Dd、Pb、Cr、As和Hg含量均明显低于国家农用粉煤灰中污染物控制标准;施用一定数量的该混合物未见导致重金属在土壤和萝卜中的明显富集作用,重金属污染指数均＜1;土壤细菌数量显著增加;脲酶、磷酸酶和纤维素酶的活性增强;促进了萝卜的生长发育和代谢作用,萝卜的生物产量、经济产量、还原糖和维生素C的含量均明显提高,因此,适量施用该混合物未见导致重金属对土壤和萝卜的明显污染,且具有较明显的改土培肥、增产和提高萝卜品质的效果。     

Dynamics of C,N, P and S in grassland soils: a model

We have developed a model to simulate the dynamics of C, N, P, and S in cultivated and uncultivated grassland soils. The model uses a monthly time step and can simulate the dynamics of soil organic matter over long time periods (100 to 10,000 years). It was used to simulate the impact of cultivation (100 years) on soil organic matter dynamics, nutrient mineralization, and plant production and to simulate soil formation during a 10,000 year run. The model was validated by comparing the simulated impact of cultivation on soil organic matter C, N, P, and S dynamics with observed data from sites in the northern Great Plains. The model correctly predicted that N and P are the primary limiting nutrients for plant production and simulated the response of the system to inorganic N, P, and S fertilizer. Simulation results indicate that controlling the C:P and C:S ratios of soil organic matter fractions as functions of the labile P and S levels respectively, allows the model to correctly simulate the observed changes in C:P and C:S ratios in the soil and to simulate the impact of varying the labile P and S levels on soil P and S net mineralization rates.     

Nitrogen mineralization dynamics in grass monocultures

Although Wedin and Tilman (1990) observed large differences in in situ N mineralization among monocultures of five grass species, the mechanisms responsible were unclear. In this study, we found that the species did not change total soil C or N, and soil C: N ratio (range 12.9–14.1) was only slightly, but significantly, changed after four years. Nor did the species significantly affect the total amount of N mineralized (per g soil N) in year-long aerobic laboratory incubations. However, short-term N mineralization rates in the incubations (day 1–day 17) differed significantly among species and were significantly correlated with annual in situ mineralization. When pool sizes and turnover rates of potentially mineralizable N (N_o) were estimated, the best model treated N_o as two pools: a labile pool, which differed among species in size (N_l, range 2–3% of total N) and rate constant (h, range 0.04–0.26 wk^–1), and a larger recalcitrant pool with a constant mineralization rate across species. The rate constant of the labile pool (h) was highly correlated with annual in situ N mineralization (+0.96). Therefore, plant species need only change the dynamics of a small fraction of soil organic matter, in this case estimated to be less than 3%, to have large effects on overall system N dynamics.