Microbial degradation of geogenic organic C and N in mine spoils

Many mine spoils present at the surface of reclamation sites in the Lower Lusatian mining district are carboniferous substrates, i.e. contain geogenic organic matter. Depending on its susceptibility to microbial degradation, geogenic organic matter might influence the establishment of a carbon requiring microflora in mine spoils. As geogenic organic matter contains substantial amounts of organic nitrogen it is also a potential source for plant available N. The objective of the present study was to quantify C and N mineralisation and microbial biomass in geogenic organic matter present at reclamation sites in Lower Lusatia. We also studied, whether these properties can be influenced by raising the originally low pH to near neutral conditions. In laboratory incubation studies, the rates of CO₂ evolution and net N mineralisation were determined in geogenic organic matter and carboniferous mine spoil with and without addition of lime. At the same time, microbial biomass carbon was estimated. As a reference, soil organic matter originating from the humus layer of a 60-year-old Pinus sylvestris stand was used. As indicated by the initial rates of C mineralisation, geogenic carbon was microbially available but to a lower extent than soil organic carbon. During incubation, C mineralisation remained constant or tended to increase with time, depending on the origin of the sample, while it decreased in soil organic matter. Unlike in soil organic matter, in geogenic organic matter and carboniferous mine spoil, C mineralisation was not consistently promoted by lime addition. Prior to incubation, microbial biomass in geogenic organic matter and carboniferous mine spoil was about 10-fold lower than in soil organic matter and tended to increase with incubation time while it decreased in soil organic matter. Similar to C mineralisation, microbial biomass in geogenic organic matter increased after liming, while it declined in carboniferous mine spoil immediately after lime addition. Rates of net N mineralisation were very low in geogenic organic matter and carboniferous mine spoil regardless of the length of incubation and could not be enhanced by raising the pH. It was concluded, that in mine spoils where accumulation of soil organic matter has not yet occurred, geogenic organic matter can be favourable for the establishment of a heterotrophic microflora. However, in the short term, geogenic matter is no source for plant available N in mine spoils. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date.     

The management of populations of vesicular-arbuscular mycorrhizal fungi in acid-infertile soils of a savanna ecosystem

Topsoil stockpiled for 4 years resulted in an accumulation of NH₄-N at depths of 1m or more in mound, as measured by an ammonia gas-sensing electrode. When leached with water these soils were also found to contain high concentrations of dissolved organic C below 1m. Both NH₄-N and DOC were products of microbial mineralisation of soil organic matter that accumulated under anaerobic conditions. When these soils were restored a flush of decomposition took place, fuelled by labile organic matter and soluble nitrogen.Stockpiled soil which underwent an ammonium-rich perfusion regime in the laboratory indicated that in-mound soils rapidly attained greater nitrification potential than surface mound soils and also had greater potential for further mineralisation of organic matter to NH₄-N. This further production was seen as a contribution from the bacterial flush, stimulated by the large labile-C pool already present.As the bulk of stored soil was anaerobic, restored soils were seen as potentially wasteful of their N-reserves; the fate of nitrogen and soluble carbon compounds in restored soils is discussed.     

Implications of increased carbon dioxide levels for carbon input and turnover in soils

The complexity of the plant-soil system in its interaction with the changing climate is discussed. It is shown that processes at the level of organic matter inputs into the soil and the fluxes and pools involved in the global cycle are not known in sufficient detail to allow an estimation of the future quantitative shifts. Even the direction in which the level of stored carbon in the soil organic matter pool will develop is not clear. The importance of the nitrogen cycle, which is intimately coupled to the carbon cycle through the turnover of soil organic matter is underlined. In its turn, the mineralisation of soil organic matter takes place at a rate which is highly dependent on the nature of inputs and the availability of mineral nutrients.Aspects of shifts in temperature, changes in cultivation practices (reduced tillage) and unintended spreading of inputs in chemical N-fertilizers are of great importance at a regional and global scale.The complexity of the interactions in the process of mineralisation do require further studies to clarify the point whether a substantial and durable additional storage of carbon in soil organic matter is likely, or that shifts in temperature will cause an overriding acceleration of the mineralisation, and trigger a corresponding net release of carbon.     

Soil organic matter dynamics in tiger bush (Niamey,Niger). Preliminary results

Some typical features of soil organic matter dynamics and soil texture were studied to discuss the particular spatial pattern of tiger bush in Niger and its dynamics. The soil texture through silt and clay contents showed a high variability in the vegetation arc as well as in the bare area. These variations were clearly linked to water/wind erosion and termite activity. Tiger bush soils showed a high capacity to store soil organic matter despite a moderate primary production, even in the bare area where the input of plant debris has been nil for many decades. The carbon content was higher within the vegetation arc (0.93 %) than within the bare area (0.45 %). Additionally, potential carbon mineralisation significantly varied in relation to the total carbon content and thus to primary production. Then, the vegetation arcs can be viewed as `fertility islands' as in many arid ecosystems. The measurements of δ¹³C showed a dominant contribution of C₃ plants to the soil organic matter pool. Nevertheless, the contribution of C₄ plants was not negligible. Two hypotheses could be proposed: a different mineralisation rate between C₃ and C₄ plants; or (ii) a better physical protection of C₄ compounds against biodegradation. The soil variables depending totally or partly on biological factors, such as carbon and nitrogen contents, carbon isotopic composition, carbon potential mineralisation, did not show any symmetry in their variations along the studied transects. It was expected in the vegetation arc because the vegetation cover does not show symmetry in its specific composition and spatial structure. In the bare area, a clear asymmetry was observed on some of the variables: carbon content, fine material content and natural abundance of ¹³C. This supports the hypothesis that the vegetation arcs move upslope, and weakens the hypothesis of the alternance of contraction and spreading periods of the vegetation cover.     

Regulation of amino acid utilization in Neurospora crassa: effect of nmr-1 and ms-5 mutations.

The effect of the nmr-1 and ms-5 mutations, which lead to insensitivity to glutamine-mediated nitrogen metabolite repression, was examined with respect to extracellular deaminase production by Neurospora crassa. Deaminase production normally requires nitrogen limitation, but these mutations eliminated this requirement and allowed production of deaminase activity under nitrogen metabolite repressing conditions. Demonstration of normal glutamine transport by both strains eliminated the possibility that these mutations exerted their effects through repressor exclusion. We have proposed a new working model for nitrogen regulation in Neurospora based on the findings that these mutations affected a nitrogen-regulated activity in addition to those activities originally reported and that the mutations are genetically very closely linked and likely allelic.     

Short-term carbon and nitrogen mineralisation in soil amended with winery and distillery organic wastes

The aim of this work was to study the influence of the organic wastes derived from the winery and distillery industry (grape stalk (GS), grape marc (GM), wine lees (WL) and exhausted grape marc (EG)) and the soil type (clayey-loam (S1), loam (S2) and sandy textured (S3)) on different soil characteristics, especially the carbon and nitrogen mineralisation. The evolution of C mineralisation fitted a first-order kinetic for all amended soils. An initial increase was observed in the specific respiration (qCO(2)) at the beginning of the experiment. However, afterwards, the evolution in the qCO(2) was to tend towards the values of the control soil due to the pattern of the soil to recover its initial equilibrium status. The addition of these materials in the soils produced a slight increase of the inorganic nitrogen content, except in the case of GS and EG in most of the studied soils. The use of GS as amendment produced an inhibition in the N mineralisation in the three types of soils studied. Organic matter mineralisation was probably influenced by soil type, the sandy soil favouring more the N and C mineralisation processes than the clayey-loam and loam soils.     

Mineralisationsuntersuchungen in der Malcolmia cephallenica-und der cerastiumarabis verna-assoziation auf Kephallinia

Zusammenfassung Aus den vorliegenden Befunden geht hervor, daß in einem humusreichen Substrat die Mineralisation bodeneigenen Materials infolge des hier sehr regen Mikroorganismenlebens schneller erfolgt, als in Böden, die arm an organischer Substanz sind. Die Fruchtbarkeit eines Kohlenstoff-reichen Bodens zeigt sich innerhalb der Malcolmia cephallenica-Assoziation deutlich in der größeren Zahl von Pflanzenarten. Wird jedoch in einen humusreichen Boden organische Substanz inkubiert, so verlaufen die Mineralisationsvorgänge sehr viel langsamer als in humusarmen Substraten.

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Summary Soil samples from four places under two plant associations (Malcolmia cephallenica-and Cerastium-Arabis vernaass.) were taken on the Greek island of Kephallinia. The mineralisation of carbon, nitrogen and phosphorus was studied by laboratory measurements.The highest production of CO₂ was found in the soil with the highest amount of humus and nitrogen. In this soil was also the best mineralisation of nitrogen. The incubation of organic matter added to soil samples caused a high activity just in such soils which had the lowest amount of C and N. The decomposition and mineralisation of added pepton and lecithin was better in the poor than in the rich soils.

     

Simulation of C and N mineralisation during crop residue decomposition: A simple dynamic model based on the C:N ratio of the residues

C and N mineralisation kinetics obtained in laboratory incubations during decomposition of crop residues under non-limiting nitrogen conditions were simulated using a simple dynamic model. This model includes three compartments: the residues, microbial biomass and humified organic matter. Seven parameters are used to describe the C and N fluxes. The decomposed C is either mineralised as CO₂ or assimilated by the soil microflora, microbial decay producing both C humification and secondary C mineralisation. The N dynamics are governed by the C rates and the C:N ratio of the compartments which remain constant in the absence of nitrogen limitation. The model was parameterised using apparent C and N mineralisation kinetics obtained for 27 different residues (organs of oilseed rape plants) that exhibited very wide variations in chemical composition and nitrogen content. Except for the C:N ratio of the residues and the soil organic matter, the other five parameters of the model were obtained by non-linear fitting and by minimising the differences between observed and simulated values of CO₂ and mineral N. Three parameters, namely the decomposition rate constant of the residues, the biomass C:N ratio and humification rate, were strongly correlated with the residues C:N ratio. Hyperbolic relationships were established between these parameters and the residues C:N ratio. In contrast, the other two parameters, i.e. the decay rate of the microbial biomass and the assimilation yield of residue-C by the microbial biomass, were not correlated to the residues C:N ratio and were, therefore, fixed in the model. The model thus parameterised against the residue C:N ratio as a unique criterion, was then evaluated on a set of 48 residues. An independent validation was obtained by taking into account 21 residues which had not been used for the parameterisation. The kinetics of apparent C and N mineralisation were reasonably well simulated by the model. The model tended to over-estimate carbon mineralisation which could limit its use for C predictions, but the kinetics of N immobilisation or mineralisation due to decomposition of residues in soil were well predicted. The model indicated that the C:N ratio of decomposers increased with the residue C:N ratio. Higher humification was predicted for substrates with lower C:N ratios. This simple dynamic model effectively predicts N evolution during crop residue decomposition in soil.     

Effects of afforestation on phosphorus dynamics and biological properties in a New Zealand grassland soil

Selected chemical, biochemical and biological properties of mineral soil (0–30 cm) were measured under a 19 year old forest stand (mixture of Pinus ponderosa and Pinus nigra) and adjacent unimproved grassland at a site in South Island, New Zealand. The effects of afforestation on soil properties were confined to the 0–10 cm layer, which reflected the distribution of fine roots (< 2 mm) in the soil profile. Concentrations of organic C, total N and P and all organic forms of P were lower under the forest stand, while concentrations of inorganic P were higher under forest compared with grassland, supporting the previously described suggestion that afforestation may promote mineralisation of soil organic matter and organic P. On the other hand, microbial biomass C and P, soil respiration and phosphatase enzyme activity were currently all lower and the metabolic quotient was higher in soil under forest compared with grassland, which is inconsistent with increased mineralisation in the forest soil. Reduced biological fertility by afforestation may be mainly attributed to changes in the quantity, quality and distribution of organic matter, and reduction in pH of the forest soil compared with the grassland soil. We hypothesize that the lower levels of C, N and organic P found in soil under forest are due to enhanced microbial and phosphatase activity during the earlier stages of forest development. Forest floor material (L and F layer) contained large amounts of C, N and P, together with high levels of microbial and phosphatase enzyme activity. Thus, the forest floor may be an important source of nutrients for plant growth and balance the apparent reduction in C, N and P in mineral soil through mineralisation and plant uptake. This revised version was published online in June 2006 with corrections to the Cover Date.     

广西中南部耕地土壤有机质和全氮变化的遥感监测

以1981年、2011年土壤数据为基础,以AVHRR和MODIS遥感影像为数据源,通过研究广西中南部土壤有机质、全氮及其变化与归一化差异植被指数(NDVI)、植被覆盖度、植被净初级生产力(NPP)等遥感因子之间的耦合关系,建立表层土壤有机质、全氮含量变化的遥感监测模型。研究表明:近30年来,研究区土壤有机质、全氮变化均呈极显著上升趋势,分别增加了5.43g/kg和0.21g/kg;1981—2011年间,NDVI、植被覆盖度和NPP 3个遥感因子变化趋势一致,均呈现缓慢上升趋势,且遥感因子变化与有机质、全氮变化均具有显著正相关关系;利用逐步线性回归方法,建立土壤有机质、全氮变化的遥感监测模型,分别能够解释有机质、全氮变化的16.9%和20.3%;根据所建模型对研究区耕地土壤有机质、全氮变化可进行空间预测制图。结果表明,研究区内耕地土壤表层有机质、全氮分别上升了6.65g/kg和0.31g/kg,验证结果显示遥感模型能够反映出不同区域土壤有机质和全氮长期变化的空间特征。     

太原市农业土壤全氮和有机质的空间分布特征及其影响因素

利用GPS定位,2005年在山西省太原市主要农业用地采集土样1821个,分析了全氮和有机质的含量.应用传统统计学和地质统计学方法对数据进行了分析.结果表明,按照1980年全国第二次土壤普查养分分级标准,土壤全氮和有机质的平均含量均属中等水平.通过半方差函数分析,土壤全氮和有机质在一定范围内存在空间相关性;它们的空间相关距离分别为122.4 km和75.6 km;全氮的空间变异主要受结构性因素的影响,而土壤有机质的空间变异是由结构性因素和随机性因素共同作用引起的.太原市土壤全氮含量的空间分布呈现由西南向东北逐渐降低的趋势,而有机质的分布规律较为复杂,它们的空间分布主要受土壤类型、海拔高度、土地利用方式和人类生产活动等因素的影响.土壤全氮与有机质的空间分布存在很大的差异,这与娄烦县、古交市当地土壤受煤粉尘污染严重以及所处地形地貌密切相关.研究揭示了在自然和社会条件十分复杂的情况下太原市土壤全氮和有机质的空间变异规律及其影响因素,为实现土壤肥力评价和养分资源精准管理提供了科学依据.     

Nitrogen mineralisation in soils of varying texture,moisture and organic matter

Summary Estimates of nitrogen availability based on the nitrogen mineralisation potential,N ₀, and the mineralisation rate constant,k, increased within the sequence, loamy sand, coarse sandy loam and loam, and were consistently higher in the high labile organic matter counterparts of the soils. There was a similar trend in the production of inorganic nitrogen at ambient temperatures. Under these conditions, an increase between mid-April and the end of May was followed by a trough in June and July and a second increase from early August to the end of September. Nitrogen production was generally higher where soil moisture was allowed to fluctuate widely in the available range, compared with a moisture regime near field capacity. Results of short-term incubations indicated that net mineralisation was minimal or negative in June and July.There was a significant relationship between values calculated fromN ₀ andk and those obtained near field capacity in the second period of mineralisation when soil temperature was relatively constant, but not in the first period when soil temperature was rising.The time required for mineralisation of 50% ofN ₀ indicated that less than half the potential value would become available in a normal temperature growing season.     

模拟践踏和降水对高寒草甸土壤养分和酶活性的影响

为明晰牦牛和藏羊践踏对高寒草甸的分异影响,通过2年模拟践踏和降水双因子控制试验,研究了践踏和降水对高寒草甸土壤养分和酶活性的影响。研究结果表明,践踏处理提高了0—20 cm土层土壤速效氮和速效钾含量,降低了0—20 cm全磷、脲酶和0—10 cm速效磷、碱性磷酸酶和有机质含量,且适度践踏促进了全氮的矿化。随降水强度的增加,0—30 cm土层土壤全氮和0—20 cm全磷和脲酶活性呈单峰曲线的变化态势,在平水下达到峰值;降水显著降低了0—30 cm土层土壤速效氮、磷、钾和0—10 cm土层土壤全钾含量,对土壤有机质含量无显著影响(P0.05)。同一放牧强度下,藏羊践踏区的土壤养分和酶活性优于牦牛践踏区,但差异不显著(P0.05)。综合可得,家畜的践踏作用促进了土壤氮和钾的矿化,抑制了磷的累积且加速了表层土壤有机质的耗竭,降低了土壤脲酶和碱性磷酸酶活性;适度降水提高了土壤全氮、全磷含量及酶活性,降水过多则相反。适度的家畜践踏与降水相耦合下草地土壤的养分循环和酶活性要优于重度践踏和不践踏小区。在对草地的适度放牧利用前提下,应注重土壤含水量和放牧畜种对草地的影响。草地干旱或土壤含水量过高时,应适当减少放牧畜种中牦牛比例增加藏羊比例,以期使草地得到健康可持续发展。     

长期施肥对设施菜田土壤酶活性及土壤理化性状的影响

利用沈阳农业大学蔬菜长期定位施肥试验田,研究了长期施肥对设施菜田土壤酶活性及土壤理化性状的影响.结果表明:长期施用有机肥或有机肥与氮肥配合施用可明显提高土壤有机质和氮、磷、钾养分含量,改善土壤物理性状,增强土壤转化酶、脲酶和中性磷酸酶的活性;而长期单施氮肥造成土壤pH值和土壤酶活性降低.土壤酶活性与土壤养分因子的相关分析表明,转化酶活性与土壤有机质、全磷含量呈显著正相关;脲酶活性与土壤有机质、全磷和速效钾含量呈极显著正相关,与碱解氮和速效磷含量呈显著正相关;中性磷酸酶活性与土壤有机质、全磷和速效钾含量呈显著正相关;脱氢酶活性与土壤各养分因子均无明显相关性.     

氮沉降对毛竹林土壤可溶性有机质数量与光谱学特征的影响

中国亚热带是受氮沉降影响最严重的地区之一.土壤可溶性有机质(DOM)被认为是土壤有机质的重要指标,氮沉降可能通过改变微生物活性导致土壤DOM质量和数量的变化.本研究以亚热带毛竹林为研究对象,设置对照、低氮和高氮3个水平,进行为期3年的施氮处理,探究氮添加对土壤DOM含量、光谱学特征和微生物胞外酶活性的影响.结果表明: 与对照相比,施氮后土壤pH、可溶性有机碳、可溶性有机氮含量和芳香化指数无显著变化,而腐殖化指数随施氮量的增加显著增加,微生物酶活性也随着施氮量的增加呈现先升高后下降的趋势.傅里叶红外光谱结果显示,土壤DOM在7个区域的相似位置存在吸收峰,其中,1000～1260 cm^-1的吸收峰最强,表明施氮处理后,土壤中多糖类、醇类、羧酸类及酯类物质增加.三维荧光光谱结果表明,施氮处理后,土壤DOM结构有显著改变,表现在低分子物质如类蛋白质物质和微生物代谢产物减少,而高分子物质如类腐殖质物质显著增加.总的来说,施氮使得土壤氮与微生物需求相适应,促进微生物分解DOM中易降解的物质,土壤DOM结构更加复杂,短期氮沉降可能有利于土壤肥力的改善.     

武夷山不同海拔森林表层土壤轻组有机质特征

土壤轻组有机质是土壤有机质的重要组分,研究轻组有机质在不同森林生态系统土壤中的变化规律对理解土壤有机质形成与转换具有重要意义。以福建省武夷山国家级自然保护区不同海拔的常绿阔叶林（海拔600 m）、针阔混交林（海拔1000 m）和针叶林（海拔1400 m）为研究对象,利用密度分组方法分离了表层（0-5 cm和5-10 cm）土壤轻组有机质,研究了不同海拔森林土壤轻组有机质特征及其影响因素。结果表明：针阔混交林表层土壤的轻组有机质含量大于针叶林和常绿阔叶林（P < 0.05）,并且轻组有机碳的含量变化亦是如此（P < 0.05）,而轻组有机氮的含量无显著差异（P > 0.05）。表层土壤对应土层的轻组C：N大于土壤C：N,针阔混交林轻组C：N和土壤C：N均大于其他林分类型。0-5 cm与5-10 cm土层针阔混交林的轻组有机碳、氮储量均大于针叶林和常绿阔叶林（P < 0.05）,并且针阔混交林的轻组有机碳、氮储量所占土壤有机碳与总氮的比重均大于其余两种林分。0-10 cm土层针叶林土壤有机碳与总氮含量与储量最高,并随海拔降低而减小,但差异不显著（P > 0.05）。相关分析结果表明,轻组有机碳、氮储量与SOC、DOC、MBC和细根生物量具有显著相关关系（P < 0.05）,而与年凋落物量无关（P > 0.05）,说明地下细根可能是土壤轻组有机质的重要来源。因此,在未来气候和植被变化共同作用下,地下细根对土壤轻组有机质的形成可能具有不可忽视的作用。     

呼伦贝尔典型退化草原土壤理化与微生物性状

以内蒙古克鲁伦河流域呼伦贝尔典型草原为对象,设置了轻度、中度和重度退化3种类型样地,研究不同程度退化草原的物种组成、地上生物量、土壤理化性状、土壤微生物数量和酶活性,以及微生物生物量的变化.结果表明: 中度退化样地的群落物种丰富度最大,轻度退化样地的地上生物量显著高于重度退化样地.退化样地的土壤水分、养分(有机质、全氮),微生物量碳、氮,以及微生物数量和酶活性显著下降,土壤容重显著增加.退化样地的土壤微生物生物量碳、氮在128～185和5.6～13.6 g·kg^-1,土壤脱氢酶和脲酶活性均与土壤容重呈显著负相关,与土壤全氮、有机质、微生物数量以及微生物生物量碳、氮呈显著正相关,地上生物量与土壤细菌和真菌数量呈不同程度的正相关.     

Soil nitrogen patterns induced by colonization of Polygonum cuspidatum on Mt. Fuji

Summary The spatial pattern of soil nitrogen was analyzed for a patchy vegetation formed by the colonization of Polygonum cuspidatum in a volcanic desert on Mt. Fuji. Soils were sampled radially from the bare ground to the center of the patch, and analyses were done for bulk density, water content, soil acidity, organic matter, organic nitrogen, and ammonium and nitrate nitrogen. The soils matured with succession from the bare ground through P. cuspidatum to Miscanthus oligostachyus and Aster ageratoides sites: bulk density decreased, and water content, organic matter, organic nitrogen, and ammonium nitrogen increased. Nitrate nitrogen showed the highest values at the P. cuspidatum site. Application of principal component analysis to the soil data discriminated two component factors which control the variation of soil characteristics: the first factor is related to soil formation and the second factor to nitrogen mineralization and nitrification. The effect of soil formation on nitrogen mineralization and nitrification was analyzed with a first-order kinetic model. The decreasing trends with soil formation in the ratios of mineral to organic nitrogen and of nitrate to ammonium nitrogen could be accounted for by the higher activity of immobilization by microorganisms and uptake by plants in the more mature ecosystem.     

Effect of a legume on soil nitrogen mineralisation and percentage nitrogen in grasses

Summary The percentage nitrogen in three mature grasses,Pennisetum purpureum, Tripsacum laxum andPanicum maximum was significantly increased when grown in association with a legumeDesmodium uncinatum. When the grasses were grazed and cut back a similar but non-significant effect occurred in the regrowth material. Soil analyses showed that the legume effectively increased the surface organic horizon and the amount of nitrogen mineralised in the underlying soil. The surface layer also produced large amounts of nitrate on mineralisation. Both with the soil and the organic surface mineralisation was greatest at the start of the rains when the influence of the legume on the percentage nitrogen in the grass was most apparent.