Soil restoration under pasture after topsoil removal: Some factors influencing C and N mineralization and measurements of microbial biomass

Factors influencing rates of C and N mineralization of soil and plant materials, and the reliability of different procedures for estimating microbial biomass, were measured in a soil (Typic Dystrochrept) that had been restored under grazed pasture in a temperate environment for 10–11 years after 20 cm of the original topsoil had been removed by stripping. Rates of net N mineralization were appreciably lower, but CO₂-C production higher, in the stripped than in the unstripped soil. These activities were not influenced directly by levels of soil mineral-N, but they were influenced by differences in plant composition. Herbage and litter, and roots, from the stripped plots were generally mineralized more readily to CO₂-C, but more slowly to net mineral-N, than were the corresponding materials from the unstripped plots. Rates of mineralization of herbage and litter, or roots, were mainly indistinguishable in stripped and unstripped soil, whereas rates of mineralization of all standing dead material were lower in stripped soil. Measurements of extractable-C flush, and of CO₂-C flush (using a fumigated soil control) and mineral-N flush by fumigation-incubation procedures, indicated that microbial biomass in stripped soil had recovered to at least 88 percent of the levels in unstripped soil. Substrate-induced respiration also generally indicated high levels of recovery of microbial biomass. The fumigation-incubation procedure appeared to under-estimate microbial biomass markedly in stripped soil when unfumigated soil controls were used; the used of a large soil inoculum (20 percent w/w) only sometimes overcame this problem. Possible reasons for apparent anomalies in estimation of microbial C are discussed.     

苏南丘陵地区栓皮栎次生林与火炬松人工林土壤有效碳

采用重复熏蒸-培养法研究了苏南丘陵地区具有代表性的栓皮栎次生林和火炬松人工林土壤有效碳的变化特征。结果表明:栓皮栎次生林土壤中的有效碳和微生物量碳含量均显著高于火炬松人工林,而火炬松人工林土壤有效碳占总有机碳比率(4.7%)及土壤微生物量碳含量占土壤有效碳比率(54.3%)分别高于栓皮栎次生林(2.9%和40.9%);去除森林凋落物后,2种林分土壤有效碳含量均显著降低;土壤有效碳与土壤微生物量碳以及土壤总有效碳显著相关。重复熏蒸-培养法是估测该地区森林土壤有效碳的一种简单有效的方法。与火炬松人工林相比,天然次生栓皮栎林土壤含有较多的活性有机碳,可能对区域碳平衡产生较大的影响。     

Dynamics of viable nitrifier community, N-mineralization and nitrification in seasonally dry tropical forests and savanna

The study was conducted in Vindhyan region, to assess the N-mineralization, nitrification and size of viable community of ammonium- and nitrite-oxidizing bacteria as affected by different sites and seasons. Six different ecosystems (four forests and two savannas), which differ in terms of topography, vegetation and moisture status, were selected for the present study. The soils of the study sites differ significantly in its physico-chemical properties. The savanna site had significantly higher pH (7.2), bulk density (1.37 g cm(-3)) and silt content (67.80%) but lower water holding capacity (1.37%), total-C (16,356 microg g(-1) dry soil), N (1090 microg g(-1) dry soil) and P (213 microg g(-1) dry soil) than forest sites. The soil moisture content, N-mineralization, nitrification rates and numbers of ammonium- and nitrite-oxidizing bacteria were highest in the wet season and lowest in dry season, while the size of mineral-N (NH4(+)-N and NO3(-)-N) showed a reverse trend at the sites. The N-mineralization, nitrification and nitrifier population size differ significantly across the site and season. The numbers of free-living cells of ammonium- and nitrite-oxidizing bacteria were significantly related to each other and to N-mineralization, nitrification, soil moisture and mineral-N components. The N-mineralization, nitrification and the viable number of nitrifying cells were consistently higher for forest soils compared to savanna sites. It was concluded that soil microbial process (N-mineralization and nitrification) and nitrifier population size were dependent on site topography, vegetation cover and soil moisture status.     

The Impact of Storage of Soils during Opencast Mining on the Microbial Community: A Strategist Theory Interpretation

The microbial community in a soil stripped and stored during opencast coal mining was analyzed. There were significant effects of soil disturbance on the microbial community: in particular, there were large decreases in the total microbial biomass, as determined by ATP analysis, and numbers of fungal propagules as a result of the store construction process, but there was no significant effect on the numbers of bacteria. During the subsequent months of storage there was a flush in the numbers of bacteria, with gram-negative bacteria showing an increase of nearly 700% in comparison to the control. During this time there was a steady accumulation in the amount of ammonium in the deepest part of the soil store, indicating the onset of anaerobiosis. These changes may be interpreted in terms of lifestyle strategy theory (Grime 1979). The bacteria exhibit behavior typical of R-strategists, or ruderal species, taking advantage of the nutrients made available by the death of fungal biomass during store construction. Fungi respond as C-strategists, or competitors, and they are severely affected by store construction-and unable to persist deep in the anaerobic part of the store. In contrast, anaerobes, S-strategists or stresstolerators, are able to survive under the same conditions. These changes have serious implications for the restoration of systems using stored topsoil as a resource. The microbial population has been altered in terms of its size and composition. Many of the fungi required for adequate breakdown and incorporation of organic matter will be absent, and the soils will be generally poor in microbial biomass. This will lead to inadequate nutrient cycling and poor soil structural stability, two factors essential for the restoration of a self-sustaining ecosystem.     

西宁南山4种灌木根际和非根际土壤微生物、酶活性和养分特征

西宁南山区植被退化情况严重,人工造林植被恢复被看作是最有效的恢复手段,其中选择合适造林树种尤为关键。选择人工种植的唐古特白刺Nitraria tangutorum、柠条Caragana korshinskii、西北小蘗Berberis vernae和短叶锦鸡儿Caragana brevifolia共4种灌木树种造林试验区为研究对象,通过测定根际和非根际土壤微生物数量、酶活性及养分含量,综合比较种植4种灌木树种根际和非根际土壤肥力差异,科学评价其对土壤的改善效果。研究表明:(1)土壤微生物数量和酶活性总体呈现出根际高于非根际的规律,仅放线菌数量和脲酶活性出现了根际低于非根际现象。(2)土壤养分方面,4种灌木根际土壤和非根际土壤p H值、全N、全P、全K含量差异不显著,有机质、有效P、速效K含量均呈现出根际非根际,而碱解N则是根际非根际。(3)土壤酶活性与土壤微生物数量相关性不显著,土壤有机质含量与土壤细菌、真菌数量呈极显著正相关,有效P含量与土壤细菌、真菌和放线菌数量呈极显著正相关,速效K含量与过氧化氢酶、酸性磷酸酶活性呈显著正相关,全N、碱解N含量均与脲酶活性呈显著正相关。(4)从土壤肥力综合水平来看,根际非根际,其中根际土壤中西北小蘗柠条短叶锦鸡儿唐古特白刺,研究结果表明西北小蘗和柠条能大幅提高土壤肥力,改良土壤效果较好。     

高寒草甸不同植被土壤微生物数量及微生物生物量的特征

用稀释平板法和氯仿熏蒸法研究了藏嵩草草甸、小嵩草草甸、矮嵩草草甸、禾草草甸、杂类草草甸及金露梅灌丛土壤的微生物数量、生物量及有机质的变化特征.结果表明:0～40 cm土层细菌和放线菌数量、微生物生物量碳和土壤有机质含量均以藏嵩草草甸最高,其微生物生物量及土壤有机质显著高于其它5种植被;真菌数量以金露梅灌丛最高;由表层到深层,随着土壤深度的增加以上各项指标均呈下降趋势.通径分析表明:土壤各生物环境因子之间存在着不同程度的相关性;土壤微生物数量、生物量及土壤有机质含量均与土壤水分含量存在显著的相关关系,说明土壤水分是调节高寒草甸生态系统土壤微生物代谢及物质转化的关键因子.     

采煤沉陷区不同造林树种恢复土壤酚酸物质对土壤微生物的影响

酚酸物质是影响微生物群落和结构的最重要因子之一,研究酚酸物质在不同造林树种土壤中的变化规律及其与微生物群落结构的关系,有助于更好地了解和揭示采煤沉陷区恢复造林条件下微生物群落变化的机制.本研究在双鸭山宝山采煤沉陷区的撂荒地基础上营造三针一阔(红松、落叶松、樟子松和杨树)人工林,测定这4种造林地土壤酚类物质、11种酚酸物质和微生物群落结构.结果表明: 复合态酚含量总体表现为人工林显著高于撂荒地,其中,落叶松人工林和杨树人工林的复合态酚含量较高,落叶松人工林和红松人工林的总酚含量显著高于撂荒地,红松人工林的水溶性酚含量显著高于撂荒地;在11种酚酸物质中,阿魏酸、松香酸、β-谷甾醇、齐墩果酸、莽草酸、亚油酸和硬脂酸的含量在人工林土壤中较高.土壤酚类物质与土壤微生物生物量不存在显著的相关关系,个别的酚酸物质与土壤微生物的相关关系显著,其中,阿魏酸、松香酸和β-谷甾醇对土壤微生物生物量有明显的促进作用,与真菌和真菌/细菌存在显著的正相关关系.杨树人工林的酚酸物质含量较高,说明营造杨树人工林对采煤沉陷区的土壤恢复有益.     

Soil Carbon, Nitrogen and Phosphorus Dynamics as Affected by Solarization Alone or Combined with Organic Amendment

Soil solarization, alone or combined with organic amendment, is an increasingly attractive approach for managing soil-borne plant pathogens in agricultural soils. Even though it consists in a relatively mild heating treatment, the increased soil temperature may strongly affect soil microbial processes and nutrients dynamics. This study aimed to investigate the impact of solarization, either with or without addition of farmyard manure, in soil dynamics of various C, N and P pools. Changes in total C, N and P contents and in some functionally-related labile pools (soil microbial biomass C and N, K₂SO₄-extractable C and N, basal respiration, KCl-exchangeable ammonium and nitrate, and water-soluble P) were followed across a 72-day field soil solarization experiment carried out during a summer period on a clay loam soil in Southern Italy. Soil physico-chemical properties (temperature, moisture content and pH) were also monitored. The average soil temperature at 8-cm depth in solarized soils approached 55 °C as compared to 35 °C found in nonsolarized soil. Two-way ANOVA (solarization×organic amendment) showed that both factors significantly affected most of the above variables, being the highest influence exerted by the organic amendment. With no manure addition, solarization did not significantly affect soil total C, N and P pools. Whereas soil pH, microbial biomass and, at a greater extent, K₂SO₄-extractable N and KCl-exchangeable ammonium were greatly affected. An increased release of water-soluble P was also found in solarized soils. Yet, solarization altered the quality of soluble organic residues released in soil as it lowered the C-to-N ratio of both soil microbial biomass and K₂SO₄-extractable organic substrates. Additionally, in solarized soils the metabolic quotient (qCO₂) significantly increased while the microbial biomass C-to-total organic C ratio (microbial quotient) decreased over the whole time course. We argued that soil solarization promoted the mineralization of readily decomposable pools of the native soil organic matter (e.g. the microbial biomass) thus rendering larger, at least over a short-term, the available fraction of some soil mineral nutrients, namely N and P forms. However, over a longer prospective solarization may lead to an over-exploitation of labile organic resources in agricultural soils. Manure addition greatly increased the levels of both total and labile C, N and P pools. Thus, addition of organic amendments could represent an important strategy to protect agricultural lands from excessive soil resources exploitation and to maintain soil fertility while enhancing pest control.     

Extractable N and P in relation to microbial biomass in UK acid organic soils

Summary Samples of peat and mor humus were treated with CHCl₃ to kill microbial cells and the amounts of C as CO₂, N as soluble- and mineral-N, and P as inorganic-P released by the treatment were compared with estimates of the microbial biomass by the Anderson and Domsch test and ATP determination. Increased amounts of soluble-N and inorganic-P, extracted with 1M KCl and 0.01M CaCl₂ respectively, were detected immediately after the fumigation treatment. However, the subsequent rates of production of CO₂–C and mineral-N measured during a 10-day incubation period at 25°C were low and variable, resulting in anomalously low estimates of microbial biomass. The flush of inorganic-P was more consistent and, in mor humus, generally related to biomass-C as measured by the Anderson and Domsch test.     

人工油松林（Pinus tabulaeformis）恢复过程中土壤微生物生物量C、N的变化特征

采用时空替代法,选取15a（PF15）、25a（PF25）、30a（PF30）的人工油松林作为样地,并选取灌丛作为参考植被,研究了植被恢复过程中土壤微生物生物量C、N以及土壤养分的变化特征,同时探讨了它们之间的相互关系。研究结果表明随着恢复的进行,土壤质量得到了改善,主要表现为有机碳、全氮、粘粒含量、土壤含水量的上升和pH值、容重的下降。土壤微生物生物量C、N分别在155.00~885.64mg/kg和33.73~237.40mg/kg的范围内变化。土壤微生物生物量C、N在植被恢复的初期显著低于灌丛,而后随着恢复的进行逐步增长。土壤微生物生物量C、N与植被恢复时间的相关性没有达到统计学上的显著水平,但是土壤微生物生物量C与土壤有机碳、全氮、全磷呈显著正相关,这表明植被恢复过程中土壤微生物生物量与土壤养分状况关系密切,植被恢复通过改善土壤养分状况间接地影响土壤微生物生物量的变化。Cmic/TOC在1.38%~4.75%的范围内变化。Cmic/TOC随着植被恢复不断下降,Cmic/TOC与植被恢复时间和土壤有机碳呈显著负相关,这表明植被恢复过程中,惰性有机质积累导致供应土壤微生物的活性有机质减少,Cmic/TOC同时受土壤有机质的数量和质量影响。     

白桦和落叶松苗木对其纯林土壤养分的生物检测

利用35年生白桦、落叶松纯林土壤分别栽植白桦、落叶松1年生苗木,通过对苗木生长、生物量、叶片养分及土壤养分变化的研究,对两种土壤的肥力进行评价,探讨白桦、落叶松混交林种间互作机制.结果表明:白桦纯林土壤全氮、碱解氮含量显著高于落叶松纯林土壤(P<0.05),落叶松纯林土壤全磷、全钾、速效磷含量显著高于白桦纯林土壤(P<0.05).盆栽第1年,白桦纯林土壤上的白桦苗木苗高、地径和生物量分别比在落叶松纯林土壤上增加69%、52%和65%(P<0.05),落叶松苗木分别增加12%、8%和37%(P>0.05).以白桦纯林土壤为基质时,白桦、落叶松苗木叶片氮浓度高于落叶松纯林土壤,而磷浓度低于落叶松纯林土壤.白桦凋落量大且分解速度快,落叶松对土壤磷具有活化作用,导致白桦纯林土壤氮素有效性较高,落叶松纯林土壤有效磷含量较高.推测两树种混交时,土壤氮、磷的互补作用可能对林分产量产生有益的作用.     

库布齐沙漠不同人工固沙灌木林土壤微生物量与土壤养分特征

在库布齐沙漠东段选取人工油蒿+杨柴半灌木混交林、人工柠条锦鸡儿灌木林和人工沙柳灌木林3种人工固沙灌木林为对象,以流动沙地为对照,研究了不同人工固沙灌木林土壤微生物生物量碳和氮、土壤微生物数量、土壤养分变化特征及其相互间的关系,并运用综合指数法对不同人工固沙灌木林的土壤恢复效果进行评价.结果表明: 与流动沙地相比,3种人工固沙灌木林土壤有机质、全氮、全磷、速效氮、速效磷含量均有不同程度的提高,表现为油蒿+杨柴林地＞柠条锦鸡儿林地＞沙柳林地,且均随土层加深而依次降低;3种人工固沙灌木林土壤微生物数量、微生物生物量碳和氮均较流动沙地有不同程度的提高,油蒿+杨柴林地土壤微生物生物量碳氮和细菌相对数量高于柠条锦鸡儿林地和沙柳林地,而真菌与放线菌相对数量则表现为柠条锦鸡儿林地＞沙柳林地＞油蒿+杨柴林地;影响3种人工固沙灌木林土壤细菌相对数量、微生物生物量碳和氮的因素是土壤有机质、全氮、全磷、速效氮、速效磷含量及C/N,而放线菌、真菌相对数量主要受土壤全磷、速效氮和速效磷含量的影响;不同人工固沙灌木林土壤质量排序为:油蒿+杨柴林地＞柠条锦鸡儿林地＞沙柳林地＞流动沙地,表明不同人工固沙灌木林的建植均能提高沙漠土壤质量,其中营造油蒿+杨柴半灌木混交林对提高土壤综合质量效果最好.     

Biochemical properties of soils of undisturbed and disturbed mangrove forests of South Andaman (India)

Studies on soil quality of mangrove forests would be of immense use in minimizing soil degradation and in adopting strategies for soil management at degraded sites. Among the various parameters of soil quality, biological and biochemical soil properties are very sensitive to environmental stress and provide rapid and accurate estimates on changes in quality of soils subjected to degradation. In this study, we determined the general and specific biochemical characteristics of soils (0-30 cm) of inter-tidal areas of 10 undisturbed mangrove forest sites of S. Andaman, India. In order to determine the effects of disturbance, soils from the inter-tidal areas of 10 disturbed mangrove forest sites were also included in the study. The general biochemical properties included all the variables directly related to microbial activity and the specific biochemical parameters included the activities of extracellular hydrolytic enzymes that are involved in the carbon, nitrogen, sulfur and phosphorus cycles in soil. The pH, clay, cation exchange capacity, Al₂O₃ and Fe₂O₃ levels exhibited minimum variation between the disturbed and undisturbed sites. In contrast, organic C, total N, Bray P and K levels exhibited marked variation between the sites and were considerably lower at the disturbed sites. The study also revealed marked reductions in microbial biomass and activity at the disturbed sites. In comparison to the undisturbed sites, the levels of all the general biochemical parameters viz., microbial biomass C, microbial biomass N, N flush, basal respiration, metabolic quotient (qCO₂), ATP, N mineralization rates and the activities of dehydrogenase and catalase were considerably lower at the disturbed sites. Similarly, drastic reductions in the activities of phosphomonoesterase, phosphodiesterase, ß-g1ucosidase, urease, BAA-protease, casein-protease, arylsulfatase, invertase and carboxymethylcellulase occurred at the disturbed sites due mainly to significant reductions in organic matter/substrate levels. The data on CO₂ evolution, qCO₂ and ATP indicated the dominance of active individuals in the microbial communities of undisturbed soils and the ratios of biomass C:N, ATP:biomass C and ergosterol:biomass C ratios indicated low N availability and the possibility of fungi dominating over bacteria at both the mangrove sites. Significant and positive correlations between soil variables and biochemical properties suggested that the number and activity of soil microorganisms depend mainly on the quantity of mineralizable substrate and the availability of nutrients in these mangrove soils.     

油田外排水对干旱戈壁区人工湿地土壤微生物生物量的影响

为研究油田外排水对干旱戈壁区人工湿地土壤微生物生物量的影响,选择干旱戈壁区某油田外排水形成的湿地内坝内、内外坝间、外坝边缘土壤,及不受排水影响的对照土壤,采用磷脂脂肪酸(PLFA)方法,分析外排水对土壤细菌、真菌、放线菌生物量的影响。结果表明:湿地内坝内、内外坝间、外坝边缘土壤与对照土壤的pH和容重均无显著差异,内外坝间的土壤含水量、电导率、溶解性全盐和全碳含量最高,显著高于内坝内土壤;除含水量外,对照土壤的主要物理性质和养分特征与湿地内坝内、内外坝间、外坝边缘的土壤无显著差异。土壤总微生物量、细菌和真菌生物量从湿地内坝内至外坝边缘逐渐增加。土壤总微生物量、细菌、真菌、放线菌与全氮含量均呈显著正相关,丛枝菌根真菌与全碳呈显著正相关,真菌、丛枝菌根真菌与总石油烃呈显著正相关。研究结果表明,油田外排水增加了湿地外坝边缘的土壤微生物量。     

有机物料在维持土壤微生物体氮库中的作用

采用室内和田间培养试验,研究了有机物料矿化过程中土壤微生物体氮的变化,测定结果表明,有机物料对矿化过程和微生物体氮的影响,既与有机物料本身性质和组成有关,也与土壤肥力水平和施氮与否有关。加入Ｃ／Ｎ比高的有机物料后,微生物对矿质氮的净固定持续时间长,而加入Ｃ／Ｎ比小的则固定时间短;高肥力土壤上的固定时间比低肥力土壤短。不同有机物料对土壤微生物体氮的影响不同。从加绿豆茎叶、小麦茎叶、未腐解马粪、腐熟马粪、腐熟猪粪到厩肥,土壤微生物体氮依次减小,提供的有效能源物质丰富（如绿豆茎叶）或Ｃ／Ｎ比较高（如小麦茎叶）时影响效果突出。土壤肥力不同,有机物料对微生物体的影响效果不同,在低肥力土壤的效果突出,约为高肥力土壤的４倍,因此,在评价有机物料对土壤微生物体氮的影响时,既考虑有有机物料的性质和组成,也考虑土壤力水平、矿质氮含量和培养时期。     

Temporal variations in some plant and soil P pools in two pasture soils of widely different P fertility status

Temporal variations in plant production, plant P and some soil P (and N) pools were followed over 21 months in two New Zealand pasture soils of widely different P fertility status. Plant growth rates, and herbage composition at the high-fertility site, were closely linked to soil water use, with growth rates falling when soil water deficits exceeded 60 mm. Herbage P concentrations reflected P fertility, and varied with season, being generally higher in winter and lower in summer. A similar temporal pattern was also observed for labile organic P (NaHCO₃-extractable P₀) in both soils. In the low-fertility soil in spring, net mineralization was especially strong, but from early winter net immobilization occurred. Surprisingly, Olsen P also changed temporally in the high-fertility soil. The microbial biomass remained fairly constant throughout the year, whereas the P content of the biomass varied seasonally. Although microbial biomass was not a useful index of soil fertility, highest microbial P₀ contents coincided with periods of maximum labile P₀ mineralization, when herbage production was also at a peak. Net N-mineralization in the low-fertility soil, in contrast to the high-fertility soil, was low but varied seasonally, under standardised incubation conditions. Soil P and N dynamics were apparently synchronised in the low-fertility soil through soil microbial processes, with mineral N being negatively correlated with microbial P₀ in samples collected two months later. The results of this investigation suggest that the demands of rapid and sustained pasture growth in spring and early summer can best be met by maximising the build-up of organic matter during the preceding autumn and winter. This practice could help to alleviate the common problem of feed shortage in North Island hill country pastures in late winter-early spring.     

Mycorrhizal colonization and microbial community structure in the rhizosphere of annual ryegrass grown in pyrene‐amended soils

In an 182‐d lightroom experiment, annual ryegrass (Lolium multiflorum Lam.) was grown in two soils under conditions of high and low fertility to examine the effect of pyrene (500 mg kg^‐1) on plant shoot biomass, mycorrhizal colonization, and soil microbial community structure. Treatments were destructively sampled every 14 d. Plant shoot biomass remained relatively unaffected by pyrene in either soil. Mycorrhizal colonization was only briefly affected by pyrene in one soil, but was unaffected in the other. Changes in soil microbial community structure were measured with whole soil fatty acid methyl ester (FAME) profiles. Differences in soil microbial community structure were observed between planted and nonplanted treatments at both fertility levels, but these differences were unrelated to the presence of pyrene. The bulk soil was associated primarily with fatty acid biomarkers for Gram‐positive bacteria, while the rhizosphere was associated primarily with the fatty acid biomarkers associated with protozoa. Differences in microbial community structure were observed between the two soils. Methylene chloride‐extractable pyrene decreased in nonplanted and planted treatments of one soil, but decreased only in nonplanted treatments of the other soil. These results suggest the potential for phytoremediation to differ among soils.     

改变碳输入对亚热带人工林土壤微生物生物量和群落组成的影响

通过在亚热带杉木(Cunninghamia lanceolata)和米老排(Mytilaria laosensis)人工林中设置互换凋落物、去除凋落物、去除凋落物+去除根系和对照处理来分析改变地上、地下碳输入对人工林土壤微生物生物量和群落组成的影响。结果显示,改变地上、地下碳输入对土壤微生物生物量碳、氮的影响因树种而异。在米老排林中,土壤微生物生物量不受碳源的限制。而在杉木林中,加入米老排凋落物、去除凋落物和去除凋落物+去除根系3种处理中土壤微生物生物量碳、氮具有明显增加的趋势。磷脂脂肪酸分析结果显示,杉木林中,添加高质量的米老排凋落物后,革兰氏阳性细菌、阴性细菌、丛枝菌根真菌、放线菌和真菌群落生物量分别显著增加了24%、24%、53%、25%、28%,革兰氏阴性细菌和丛枝菌根真菌的相对丰度均有显著增加。与对照相比,杉木林中去除凋落物后革兰氏阳性细菌、阴性细菌、丛枝菌根真菌、放线菌和真菌群落生物量分别显著增加了22%、29%、44%、25%、52%,真菌与细菌比值显著增加了21%。但是,去除凋落物+去除根系处理对两个树种人工林土壤微生物群落组成均无显著影响。米老排和杉木林土壤微生物生物量碳、氮的季节变化格局不同,土壤养分有效性可能是驱动土壤微生物生物量季节变化的主要因子。未来研究需要关注凋落物和根系在不同树种人工林中对土壤微生物群落的相对贡献。     

土壤微生物学特性对土壤健康的指示作用

土壤健康是陆地生态系统可持续发展的基础。作者通过概述土壤微生物学特性(土壤微生物群落结构、土壤微生物生物量、土壤酶活性)与土壤质量的关系, 阐明了土壤微生物对土壤健康的生物指示功能。研究表明: 土壤中细菌、真菌和放线菌的组成及其所占比率在一定程度上反映了土壤的肥力水平: 在土壤性质和肥水条件较好的土壤中, 细菌所占比率较高。土壤微生物生物量与土壤有机质含量密切相关, 而且土壤微生物生物量碳与土壤有机碳的比值(C_mic : C_org)和土壤微生物代谢熵(qCO2)的变化在一定程度上反映了土壤有机碳的利用效率。一般情况下, 土壤酶活性高的土壤中, 土壤微生物生物量碳、氮含量也高。因此, 土壤微生物学特性可以反映土壤质量的变化, 并可用作评价土壤健康的生物指标。     

The preservation unaltered,of mineral nitrogen in tropical soils and soil extracts

Summary Experiments have been conducted on different methods of storing soils and soil extracts to preserve the mineral-N status unaltered. Neither the addition of chemicals at the rates used nor storage at sub-zero temperatures were found to preserve the mineral-N status of the soils completely unaltered over short periods of time. Furthermore, evidence was found to show that storage at sub-zero temperatures can effect subsequent mineralization of nitrogen during incubation.The mineral-N content of soil extracts prepared with an acidified K₂SO₄ reagent was not preserved over short periods by the addition of chemicals, by storing the extracts at sub-zero temperatures or by the addition of copper ions to the extracting solution. The mineral-N content of soil extracts prepared with a neutral KCl reagent could be preserved during storage at subzero temperatures but the addition of copper ions to the extracting reagent was not effective.Changes in the mineral-N content of both soils and soil extracts during storage were not consistent and in the soils appeared to be related to biological activity and the concentration of mineral N present. In soil extracts changes appeared to be related to the concentration of mineral-N present and to some other factor(s).Part of a thesis submitted for the degree of Ph. D in the University of East Africa.