Soil microbial biomass and activity in organic tomato farming systems: Effects of organic inputs and straw mulching

Organic farming is rapidly expanding worldwide. Plant growth in organic systems greatly depends on the functions performed by soil microbes, particularly in nutrient supply. However, the linkages between soil microbes and nutrient availability in organically managed soils are not well understood. We conducted a long-term field experiment to examine microbial biomass and activity, and nutrient availability under four management regimes with different organic inputs. The experiment was initiated in 1997 by employing different practices of organic farming in a coastal sandy soil in Clinton, NC, USA. Organic practices were designed by applying organic substrates with different C and N availability, either in the presence or absence of wheat-straw mulch. The organic substrates used included composted cotton gin trash (CGT), animal manure (AM) and rye/vetch green manure (RV). A commercial synthetic fertilizer (SF) was used as a conventional control. Results obtained in both 2001 and 2002 showed that microbial biomass and microbial activity were generally higher in organically than conventionally managed soils with CGT being most effective. The CGT additions increased soil microbial biomass C and activity by 103-151% and 88-170% over a period of two years, respectively, leading to a 182-285% increase in potentially mineralizable N, compared to the SF control. Straw mulching further enhanced microbial biomass, activity, and potential N availability by 42, 64, and 30%, respectively, relative to non-mulched soils, likely via improving C and water availability for soil microbes. The findings that microbial properties and N availability for plants differed under different organic input regimes suggest the need for effective residue managements in organic tomato farming systems.     

Effects of pasture improvement and intensive cultivation on microbial biomass,enzyme activities,and composition and size of earthworm populations

We investigated the quantity and distribution of organic C, microbial biomass C, protease, arylsulphatase and arylphosphatase activity, and earthworm numbers and biomass in the soil from a 37-year-old grazed pasture supplied with superphosphate at rates of 0, 188, and 376 kg ha^-1 annually. The results were compared with a non-irrigated wilderness site which had not been used for agriculture and an arable site that had been intensively cultivated for 11 consecutive years. In the 0- to 5-cm layer, organic C followed the trend arableAporrectodea caliginosa (77–89% of total numbers) although Lumbricus rubellus made an increasing contribution to the population with increasing superphosphate rates. In the unirrigated wilderness site the population consisted of 56% A. caliginosa and 44% L. rubellus. While Octolasion cyaneum and A. rosea made up a small proportion of the population in the improved pasture sites, they were not present in the wilderness or arable sites. A. caliginosa was the only species present in the arable site. The mean fresh weight of individuals followed the order arable相似文献   

Effect of lithological substrate on microbial biomass and enzyme activity in brown soil profiles in the northern Apennines (Italy)

The aim of the present study was to investigate the microbial activity along forest brown soil profiles sequence developed on different lithological substrates (carbonate or non-carbonated cement in sandstone formations) at different altitudes. The main question posed was: does carbonate affect the biochemical activity of brown soil profiles at different altitudes? For the purpose of this study, four soil profiles with different amounts and compositions of SOM developed on different lithological substrates were selected: two with carbonate (MB and MZ) and the other two with non-carbonated cement in the sandstone formations (MF1 and MF2). Chemical and biochemical properties of soil were analysed along soil profiles in order to assess the SOM quantity and quality, namely total organic C (C_org), water extractable organic C (WEOC) and humification indices (HI, DH, HR). Microbial biomass (C_mic and N_mic) content, as well as the specific activities of acid phosphatase, β-glucosidase and chitinase enzymes were chosen as indicators of biochemical activity. The soil biochemical properties provided evidence of better conditions for microorganisms in MB than in MF1, MF2 and MZ soil profiles, since patterns of microbial biomass content and activity might be expected in response to the amount and quality of organic substances. The different lithological substrates did not show any clear effect on soil microbial biomass content, since similar values were obtained in MF1, MF2 (with non-carbonated cement) and MZ (with carbonate). However, the specific activities of acid phosphatase (per unit of C_org and per unit of C_mic) were higher in soils with no carbonate (MF1 and MF2) than in soils with carbonate (MB and MZ). In conclusion, the biochemical activity along brown soil profiles was mainly regulated by different soil organic matter content and quality, while the two different lithological substrates (with carbonate or non-carbonated cement in the sandstone formations) did not show any direct effect on microbial biomass and its activity. However, the activity of acid phosphatase per unit of C was particularly enhanced in soil with non-carbonate cement in the sandstone formations.     

The significance of microbial biomass sulphur in soil

The soil microbial biomass S fraction of total organic S in soil is considered to be relatively labile and the most active S pool for S turnover in soil. Its significance has been demonstrated in studies of S deficiency in agronomic situations and in those of S pollution from high atmospheric inputs. The utility of the CHCl₃ fumigation-extraction technique for the measurement of microbial S has been proved for a range of soils and conditions. The various methodologies currently available are discussed, including the need for determination of the conversion (K _s) factor. Microbial S values, summarized from the available literature, ranged from 3 to 300 g S g^-1 dry weight soil. They were generally greater in grassland than in arable systems, though the greatest values were obtained in the few examples from forest and peatland soil systems. Microbial S values showed direct relationships with both microbial C and with total soil organic S. Again, there were significant differences between arable and grassland systems. The effect of factors such as organic and inorganic inputs as well as soil physical conditions on microbial S are described. Microbial S turnover rates were estimated from seasonal, ³⁵S-labelling and modelling studies. These rates varied between an approximately annual turnover rate in undisturbed soils up to 80 year^-1 following the addition of readily available substrates. Prospective future research areas are also outlined.     

Soil organic matter,microbial properties,and aggregate stability under annual and perennial pastures

The use of annually sown pastures to provide winter forage is common in dairy farming in many regions of the world. Loss of organic matter and soil structural stability due to annual tillage under this management may be contributing to soil degradation. The comparative effects of annual ryegrass pastures (conventionally tilled and resown each year), permanent kikuyu pastures and undisturbed native vegetation on soil organic matter content, microbial size and activity, and aggregate stability were investigated on commercial dairy farms in the Tsitsikamma region of the Eastern Cape, South Africa. In comparison with soils under sparse, native grassy vegetation, those under both annual ryegrass and permanent kikuyu pasture had higher soil organic matter content on the very sandy soils of the eastern end of the region. By contrast, in the higher rainfall, western side, where the native vegetation was coastal forest, there was a loss of organic matter under both types of pasture. Nonetheless, soil organic C, K₂SO₄-extractable C, microbial biomass C, basal respiration, arginine ammonification and fluorescein diacetate hydrolysis rates and aggregate stability were less under annual than permanent pastures at all the sites. These results reflect the degrading effect of annual tillage on soil organic matter and the positive effect of grazed permanent pasture on soil microbial activity and aggregation. Soil organic C, microbial biomass C, K₂SO₄-extractable C, basal respiration and aggregate stability were significantly correlated with each other. The metabolic quotient and percentage of organic C present as microbial biomass C were generally poorly correlated with other measured properties but negatively correlated with one another. It was concluded that annual pasture involving conventional tillage results in a substantial loss of soil organic matter, soil microbial activity and soil physical condition under dairy pastures and that a system that avoids tillage needs to be developed.     

Impact of agricultural practices on the size and activity of the microbial biomass in a long-term field experiment

The Dehérain long-term field experiment was initiated in 1875 to study the impact of fertilization on a wheat-sugarbeet rotation. In 1987, the rotation was stopped to be replaced by continuous maize. Crop residues were soil-incorporated and the mineral fertilization was doubled in some plots. The impact of those changes on the microbial biomass and activity are presented. In spring 1987, the soil was still in a steady-state condition corresponding to the rotation. The microbial biomass was correlated with total organic C and decreased in the order farmyard manure>mineral NPK>unfertilized control. Microbial specific respiratory activity was higher in the unfertilized treatments. The soil biomass was closely related to soil N plant uptake. In 1989, after 2 years of maize and crop residue incorporation, the steady-state condition corresponding to the previous agricultural practices disappeared. So did the relationship between the biomass and total organic C, and the soil N plant uptake. Biomass specific respiratory activity increased because of low efficiency in the use of maize residues by microbes under N stress.     

长期施肥处理对玉米生长期潮土微生物生物量和活度的影响

以1989年建立的中国科学院封丘农田生态系统国家试验站的长期定位试验为平台,研究经18a连续不同施肥处理后玉米季土壤微生物生物量碳氮和微生物活度的动态变化及其与土壤有机碳之间的相互关系,并探讨施肥措施对土壤微生物及其活性的影响。施肥处理包括:(1)有机肥(OM);(2)1/2化肥和1/2有机肥(1/2OM+1/2NPK);(3)氮磷钾肥(NPK);(4)氮磷肥(NP);(5)磷钾肥(PK);(6)氮钾肥(NK);(7)不施肥,即对照(CK)7个处理。结果表明,微生物生物量碳氮和微生物活度在玉米生长期内均有明显的时间变异性,其中微生物生物量碳与微生物活度的动态变化比较一致,其间的极显著相关关系表明潮土微生物生物量碳的变化可以在很大程度上代表土壤微生物活度的变化。施肥制度显著影响微生物生物量碳氮和微生物活度的变化,总体趋势为OM1/2OM+1/2NPKNPKNPPKNKCK,表明OM有利于保持土壤的生物化学环境及促进土壤的生物学活性;与OM处理相比,化学肥料的长期施用有降低土壤微生物生物量和微生物活度的趋势,尤其是缺素处理的表现更为明显,其中以缺磷处理的表现最为严重。土壤微生物生物量碳氮、微生物活度与土壤有机碳变化均呈极显著正相关。     

Effects of irrigation-induced salinity and sodicity on soil microbial activity

The effects of irrigation-induced salinity and sodicity on the size and activity of the soil microbial biomass in vertic soils on a Zimbabwean sugar estate were investigated. Furrow-irrigated fields were selected which had a gradient of salinity and sugarcane yield ranging from good cane growth at the upper ends to dead and dying cane at the lower ends. Soils were sampled under dead and dying cane, poor, satisfactory and good cane growth and from adjacent undisturbed sites under native vegetation. Electrical conductivity (EC) and sodium adsorption ratio (SAR) of saturation paste extracts was measured, as well as the exchangeable sodium percentage (ESP). There was a significant negative exponential relationship between EC and microbial biomass C, the percentage of organic C present as microbial biomass C, indices of microbial activity (arginine ammonification and fluorescein diacetate hydrolysis rates) and the activities of the exocellular enzymes β-glucosidase, alkaline phosphatase and arylsulphatase but the negative relationships with SAR and ESP were best described by linear functions. By contrast, the metabolic quotient increased with increasing salinity and sodicity, exponentially with EC and linearly with SAR and ESP.Potentially mineralizable N, measured by aerobic incubation, was also negatively correlated with EC, SAR and ESP. These results indicate that increasing salinity and sodicity resulted in a progressively smaller, more stressed microbial community which was less metabolically efficient. The exponential relationships with EC demonstrate the highly detrimental effect that small increases in salinity had on the microbial community. It is concluded that agriculture-induced salinity and sodicity not only influences the chemical and physical characteristics of soils but also greatly affects soil microbial and biochemical properties.     

不同碳氮比有机肥对有机农业土壤微生物生物量的影响

有机肥能提高土壤微生物活性, 改善土壤品质。碳氮比是影响有机肥肥效的重要因素。本试验以无肥处理为对照(CK), 设置4个有机肥碳氮比处理(20︰1、15︰1、10︰1、5︰1), 在温室中进行茄子盆栽试验, 定期采集土壤样品, 用熏蒸提取法测定土壤微生物生物量碳(SMBC)、氮(SMBN), 研究等氮条件下不同碳氮比有机肥料对土壤生物活性的影响。试验结果表明, 不同碳氮比的有机肥均能提高土壤的SMBC和SMBN含量, 具体表现为SMBC: 20︰1>10︰1≈15︰1>5︰1>CK, SMBN: 15︰1>10︰1>20︰1>5︰1>CK。SMBC/SMBN的比率反映土壤氮素生物活性, 其值越低, 生物活性越大, 氮素损失越少, 本试验SMBC/SMBN表现为: 15︰1<10︰1<20︰1≈5︰1相似文献   

Soil microbial biomass, activity and potential nitrogen mineralization in a pasture: Impact of stock camping activity

Grazing animals recycle a large fraction of ingested C and N within a pasture ecosystem, but the redistribution of C and N via animal excreta is often heterogeneous, being highest in stock camping areas, i.e., near shade and watering sources. This non-uniform distribution of animal excreta may modify soil physical and chemical attributes, and likely affect microbial community eco-physiology and soil N cycling. We determined microbial population size, activity, N mineralization, and nitrification in areas of a pasture with different intensity of animal excretal deposits (i.e., stock camping, open grazing and non-grazing areas). The pasture was cropped with coastal bermudagrass (Cynodon dactylon L.) and subjected to grazing by cattle for 4 y. Soil microbial biomass, activity and N transformations were significantly higher at 0-5 cm than at 5-15 cm soil depth, and the impacts of heterogeneous distribution of animal excreta were more pronounced in the uppermost soil layer. Microbial biomass, activity and potential net N mineralization were greater in stock camping areas and were significantly correlated (r²≈0.50, P<0.05) with the associated changes in total soil C and N. However, gross N mineralization and nitrification potential tended to be lower in stock camping areas than in the open grazing areas. The lower gross N mineralization, combined with greater net N mineralization in stock camping areas, implied that microbial N immobilization was lower in those areas than in the other areas. This negative association between microbial N immobilization and soil C is inconsistent with a bulk of publications showing that microbial N immobilization was positively related to the amount of soil C. We hypothesized that the negative correlation was due to microbial direct utilization of soluble organic N and/or changes in microbial community composition towards active fungi dominance in stock camping areas.     

Size and activity of the soil microbial biomass under grass and arable management

 The effects of 5 years of continuous grass/clover (Cont grass/clover) or grass (Cont grass) pasture or 5 years of annual grass under conventional (Ann grass CT) or zero tillage (Ann grass ZT) were compared with that of 5 years of continuous barley (LT arable) on a site which had previously been under arable crops for 11 years. For added comparison, a long-term grass/clover pasture site (LT past) nearby was also sampled. Soil organic C (C_org) content followed the order LT arable=Ann grass CT<Ann grass ZT<Cont grass=Cont grass/clover<LTpast. Trends with treatment for microbial biomass C (C_mic), basal respiration, flourescein diacetate (FDA) hydrolytic activity, arginine ammonification rate and the activities of dehydrogenase, protease, histidase, acid phosphatase and arylsulphatase enzymes were broadly similar to those for C_org. For C_mic, FDA hydrolysis, arginine ammonification and the activities of histidase, acid phosphatase and arylsulphatase, the percentage increase caused by 5 years of continuous pasture (in comparison with LT arable) was 100–180%, which was considerably greater than that for organic C (i.e. 60%). The microbial metabolic quotient (qCO₂) was higher for the two treatments which were mouldboard ploughed annually (LT arable and Ann grass CT) than for the undisturbed sites. At the undisturbed sites, C_org declined markedly with depth (0–15 cm) and there was a similar stratification in the size and activity of C_mic and enzyme activity. The microbial quotient (C_mic/C_org) declined with depth whilst qCO₂ tended to increase, reflecting a decrease in the proportion of readily available substrate with depth. Received: 7 July 1998     

Enzyme activities and microbial biomass in topsoil layer during spontaneous succession in spoil heaps after brown coal mining

Changes in the activity of extracellular enzymes (cellobiohydrolase, β-glucosidase, β-xylosidase, chitinase, arylsulfatase and phosphatases) and the changes in microbial community and abiotic properties in the topsoil layer, as well as soil abiotic properties during primary succession were investigated in a brown coal mine deposit area near Sokolov, Czech Republic. The study considered the chronosequence of 4 post-mining plots, 4-, 12-, 21- and 45-year old. The 4-year old site had no vegetation cover. Herbs and grasses (mainly Calamagrostis epigeios) were present on the 12-year old plot, shrubs (Salix caprea) occurred on the 21-year old plot and tree cover (Betula spp. and Populus tremuloides) developed on the 45-year old plot. Soil pH gradually decreased with site age, while the content of P, K, C and N peaked in the 21-year old site, being significantly lower in the 45-year old site and much lower in the 4- and 12-year old sites. Phosphatase activities were strongly affected by seasonality while the activities of all the other enzymes measured were more influenced by the effects of succession age and soil layer than by seasonality. Succession age was also the most important factor affecting the total and bacterial PLFA contents, followed by the effects of soil layer and season while for the fungal biomass content-related properties (ergosterol, fungal PLFA and the fungal/bacterial PLFA ratio), season was the most important. Activities of individual enzymes in the topsoil (0–5 cm depth) were significantly affected by both site age and season. Cellobiohydrolase and β-xylosidase were more affected by site age while chitinase and phosphatases were more affected by season. Enzyme activity increased with succession age. Comparison of the effect of site and season on enzyme activity showed that season played a principal role in the enzyme activity of the entire 0–5 cm component of topsoil, as well the soil layers when evaluated separately.     

Organic matter accumulation and fertilizer-induced acidification interact to affect soil microbial and enzyme activity on a long-term sugarcane management experiment

The effects of crop residue management and fertilizer applications on the size and activity of the microbial community and the activity of exocellular enzymes involved in mineralization of C, N, P and S were examined on a long-term (60 years) field trial under sugarcane situated at Mount Edgecombe, South Africa. Treatments at the site included pre-harvest burning with harvest residues removed (B), burning with harvest residues (unburnt tops) left on the soil surface (B_t) and green cane harvesting with retention of a trash blanket (T). Plots were either fertilized annually with N, P and K or unfertilized. The size and activity of the microbial community and the activity of soil enzymes assayed increased with increasing inputs of crop residues (B < B_t < T) and this effect was evident to a depth of 30 cm. The metabolic quotient was decreased by inputs of both crop residues and fertilizers. Annual fertilizer additions did not affect basal respiration, increased fluorescein diacetate (FDA) hydrolysis rate and acid phosphatase, invertase and protease activities and decreased arginine ammonification rate and dehydrogenase, alkaline phosphatase, arylsulphatase and histidase activities. These effects were attributed to an interaction between the positive effect of fertilizer in increasing the size of the microbial biomass and the negative effect of fertilizer-N-induced soil acidification on microbial activity and on the activity of exocellular enzymes. Such results demonstrate the importance of using a range of measurements of microbial and enzyme activity when determining the effects of management on soil microbial and biochemical properties.     

接种蚯蚓和食细菌线虫对红壤性状及花生产量的影响

通过温室花生盆栽试验研究了接种有益土壤动物(蚯蚓和食细菌线虫)对旱地红壤生物学性质(微生物生物量碳氮、基础呼吸、微生物熵、脲酶和酸性磷酸酶活性)、土壤速效养分(碱解氮和速效磷)及花生产量的影响.试验包含4个处理:不接种处理(CK)、仅接种蚯蚓(E)、仅接种食细菌线虫(N)、联合接种蚯蚓和食细菌线虫(EN).结果表明:①蚯蚓和食细菌线虫均提高了土壤微生物生物量碳氮的含量,线虫对微生物生物量碳的贡献大于蚯蚓.②除花生成熟期的接种蚯蚓处理外,接种蚯蚓和食细菌线虫后土壤基础呼吸均有所增加,且食细菌线虫的影响也大于蚯蚓.③除花生结荚期无显著性差异外,蚯蚓和食细菌线虫均极显著提高了土壤脲酶和酸性磷酸酶活性(P＜0.05).④蚯蚓和食细菌线虫均能增加土壤速效磷和碱解氮含量.⑤接种蚯蚓和食细菌线虫后花生产量的增幅为17％～ 20％.总之,在4个花生生长时期,相对于不接种的对照处理,接种蚯蚓和食细菌线虫能明显改善红壤性状并最终提高花生产量.     

Soil microbial biomass, activity and nitrogen transformations in a turfgrass chronosequence

Understanding the chronological changes in soil microbial properties of turfgrass ecosystems is important from both the ecological and management perspectives. We examined soil microbial biomass, activity and N transformations in a chronosequence of turfgrass systems (i.e. 1, 6, 23 and 95 yr golf courses) and assessed soil microbial properties in turfgrass systems against those in adjacent native pines. We observed age-associated changes in soil microbial biomass, CO₂ respiration, net and gross N mineralization, and nitrification potential. Changes were more evident in soil samples collected from 0 to 5 cm than the 5 to 15 cm soil depth. While microbial biomass, activity and N transformations per unit soil weight were similar between the youngest turfgrass system and the adjacent native pines, microbial biomass C and N were approximately six times greater in the oldest turfgrass system compared to the adjacent native pines. Potential C and N mineralization also increased with turfgrass age and were three to four times greater in the oldest vs. the youngest turfgrass system. However, microbial biomass and potential mineralization per unit soil C or N decreased with turfgrass age. These reductions were accompanied by increases in microbial C and N use efficiency, as indicated by the significant reduction in microbial C quotient (qCO₂) and N quotient (qN) in older turfgrass systems. Independent of turfgrass age, microbial biomass N turnover was rapid, averaging approximately 3 weeks. Similarly, net N mineralization was ∼12% of gross mineralization regardless of turfgrass age. Our results indicate that soil microbial properties are not negatively affected by long-term management practices in turfgrass systems. A tight coupling between N mineralization and immobilization could be sustained in mature turfgrass systems due to its increased microbial C and N use efficiency.     

The influence of tillage on the proportion of organic carbon and nitrogen in the microbial biomass of medium-textured soils in a humid climate

Summary Microbial biomass C and N respond rapidly to changes in tillage and soil management. The ratio of biomass C to total organic C and the ratio of mineral N flush to total N were determined in the surface layer (0–5 cm) of low-clay (8–10%), fine sandy loam, Podzolic soils subjected to a range of reduced tillage (direct drilling, chisel ploughing, shallow tillage) experiments of 3–5 years' duration. Organic matter dynamics in the tillage experiments were compared to long-term conditions in several grassland sites established on the same soil type for 10–40 years. Microbial biomass C levels in the grassland soils, reduced tillage, and mouldboard ploughing treatments were 561, 250, and 155 g g^-1 soil, respectively. In all the systems, microbial biomass C was related to organic C (r=0.86), while the mineral N flush was related to total N (r=0.84). The average proportion of organic C in the biomass of the reduced tillage soils (1.2) was higher than in the ploughed soils (0.8) but similar to that in the grassland soils (1.3). Reduced tillage increased the average ratio of mineral N flush to total soil N to 1.9, compared to 1.3 in the ploughed soils. The same ratio was 1.8 in the grassland soils. Regression analysis of microbial biomass C and percent organic C in the microbial biomass showed a steeper slope for the tillage soils than the grassland sites, indicating that reduced tillage increased the microbial biomass level per unit soil organic C. The proportion of organic matter in the microbial biomass suggests a shift in organic matter equilibrium in the reduced tillage soils towards a rapid, tillage-induced, accumulation of organic matter in the surface layer.     

不同利用方式下红壤微生物生物量及代谢功能多样性的变化

研究了不同农林利用方式下红壤微生物生物量和代谢功能多样性等土壤质量指标的变化.结果表明:不同利用方式对土壤质量各指标造成了显著的影响;稻田的微生物生物量碳、氮最高,林地和草地微生物生物量次之,旱地的微生物生物量碳、氮最低(分别是稻田利用方式的4.3% 和 13.7%);稻田的微生物代谢功能多样性最高,旱地、林地和草地的细菌代谢功能多样性较低,旱地的真菌代谢功能多样性最低;微生物生物量和代谢功能多样性可以作为反映土壤质量变化的早期敏感的指标,用来衡量管理措施的改变对土壤质量造成的影响.     

Soil microbial biomass activation by trace amounts of readily available substrate

The soil microbial biomass survives as a largely dormant population for long periods without fresh substrates, depending for growth upon a rapid uptake of substrates when they become available. Currently, little investigation has been made into the mechanisms involved in the transition from dormancy to activity. We found that additions of trace amounts of different simple and complex substrates (glutamic acid, amino acids mixture, glucose, protein hydrolysates, carbohydrates, compost extract), even at very low application rates (5-μg C g⁻¹ soil), caused an immediate and significant activation (measured as increased CO₂-C evolved) of the soil microbial biomass. The different substrates caused different intensities of respiration response, which were related to the substrates’ composition, complexity, and degradability. The difference between the CO₂-C evolved from the amended soil minus that evolved from a similarly incubated but non-amended soil ranged from 80 to 160% of the humified carbon C added as substrate, with most of the substrates causing a positive priming effect, in agreement with previous findings. The activation ended after 5–70 h, depending on the substrate, but the microbial biomass could be reactivated with further additions. It seems that the microbial biomass first responds to traces of substrate by increasing its metabolic activity in anticipation of a larger ‘food event’. Overall, these results indicate that soil micro-organisms have evolved metabolic and physiological strategies that allow them to survive and growth in the generally poor-substrate soil environment.Contribution presented at the Exploratory Workshop: ‘Non-molecular manipulation of soil microbial communities’, held at the University of Udine, Udine, Italy from 17 to 20 October, 2004. The workshop was funded by the European Science Foundation and the University of Udine.     

无机氮和葡萄糖添加对土壤微生物生物量和活性的影响

以黄淮海平原潮土为研究对象,通过室内恒温恒湿培养方法,比较研究了土壤中纤维素是否存在时,外源无机氮和葡萄糖添加对土壤微生物生物量及其活性的影响变化。实验设8个处理,包括不加任何物质的对照(CK)、添加无机氮(N)、葡萄糖(G)、纤维素(C)处理及葡萄糖和无机氮同时添加(G+N)处理,以及在纤维素存在基础上添加无机氮(C+N)、葡萄糖(C+G)、葡萄糖和无机氮同时添加(C+G+N)处理。在33天培养时间内,分别在不同的时间间隔内测定了土壤CO2累积释放量、微生物生物量碳(Cmic)、及脱氢酶(DHD)、β-葡萄糖苷酶(GLU)、过氧化氢酶(CAT)、碱性磷酸酶(APH)活性。结果表明,所有测定的微生物性质在CK与C处理间均没有显著性差异。与CK和C处理相比,其他所有处理的土壤CO2累积释放量均显著增加,其中C+G+N处理达最大值;G、G+N、C+G、C+G+N处理的土壤Cmic含量及DHD和APH活性显著提升,尤其在培养的前14天,而N和C+N处理则与CK处理相似,表示添加葡萄糖可显著增加上述处理生物活性水平,而添加无机氮则不能。添加无机氮和葡萄糖对GLU和CAT的影响不明显,大部分情况下它们在处理间没有表现出显著性差异。相关性分析表明,CO2释放速率始终与APH活性成显著正相关,但与Cmic和其他酶活性之间的相关关系则随着培养时间的不同而发生变化,这可能与不同培养时间的微生物组成或微生物利用底物的模式发生改变有关。聚类分析结果进一步表明,8个处理的土壤微生物活性水平可明显分成3组,其中活性水平最高的组只包含C+G+N处理,该结果提示在难分解纤维素存在时,无机氮和易利用有机碳的同时添加对提升土壤微生物活性的重要性。     

Effects of long-term waste water irrigation on soil organic matter, soil microbial biomass and its activities in central Mexico

 The effect of long-term waste water irrigation (up to 80 years) on soil organic matter, soil microbial biomass and its activities was studied in two agricultural soils (Vertisols and Leptosols) irrigated for 25, 65 and 80 years respectively at Irrigation District 03 in the Valley of Mezquital near Mexico City. In the Vertisols, where larger amounts of water have been applied than in the Leptosols, total organic C (TOC) contents increased 2.5-fold after 80 years of irrigation. In the Leptosols, however, the degradability of the organic matter tended to increase with irrigation time. It appears that soil organic matter accumulation was not due to pollutants nor did microbial biomass:TOC ratios and qCO₂ values indicate a pollutant effect. Increases in soil microbial biomass C and activities were presumably due to the larger application of organic matter. However, changes in soil microbial communities occurred, as denitrification capacities increased greatly and adenylate energy charge (AEC) ratios were reduced after long-term irrigation. These changes were supposed to be due to the addition of surfactants, especially alkylbenzene sulfonates (effect on denitrification capacity) and the addition of sodium and salts (effect on AEC) through waste water irrigation. Heavy metals contained in the sewage do not appear to be affecting soil processes yet, due to their low availability. Detrimental effects on soil microbial communities can be expected, however, from further increases in pollutant concentrations due to prolonged application of untreated waste water or an increase in mobility due to higher mineralization rates. Received: 28 April 1999