The influence of different types of urban land use on soil microbial biomass and functional diversity in Beijing,China

Soil microbes in urban ecosystems are affected by a variety of abiotic and biotic factors resulting from changes in land use. However, the influence of different types of land use on soil microbial properties and soil quality in urban areas remains largely unknown. Here, by comparing five types of land use: natural forest, park, agriculture, street green and roadside trees, we examined the effects of different land uses on soil microbial biomass and microbial functional diversity in Beijing, China. We found that soil properties varied with land uses in urban environments. Compared to natural forest, soil nutrients under the other four types of urban land use were markedly depleted, and accumulation of Cu, Zn, Pb and Cd was apparent. Importantly, under these four types of land use, there was less microbial biomass, but it had greater functional diversity, particularly in the roadside‐tree soils. Furthermore, there were significant correlations between the microbial characteristics and physicochemical properties, such as organic matter, total nitrogen and total phosphorus (P < 0.05), suggesting that lack of nutrients was the major reason for the decrease in microbial biomass. In addition, the larger C/N ratio, Ni concentration and pool of organic matter together with a higher pH contributed to the increase in microbial functional diversity in urban soils. We concluded that different land uses have indirect effects on soil microbial biomass and microbial community functional diversity through their influence on soil physicochemical properties, especially nutrient availability and heavy metal content.     

Soil management modifies micro-scale abundance and function of soil microorganisms in a Mediterranean ecosystem

The present study tests whether soil management (tillage and fertilizer) modified the small-scale abundance and function of soil microorganisms in response to changes in organic matter quantity and quality. The experimental field, located in the coastal hills of Marche (central Italy), was planted in rotation with Triticum durum in winter and Zea mais in summer. Soil samples were collected in the maize-field soil, in conventional and no-tillage (NT) systems, and in fertilized and unfertilized soil. We analysed total organic C (TOC), total nitrogen (TN) microbial biomass C (MBC), enzymes involved in C- (β-glucosidase, α-glucosidase, β-cellobiohydrolase, β-xylosidase), N- (leucine-aminopeptidase and N-acetyl-β-glucosaminidase), P- (acid phosphatase) and S-cycling (arylsulphatase), as well as functional diversity in the bulk soil, coarse sand, fine sand, silt and clay fractions. Micro-scale investigations revealed great microbial abundance in smaller fractions because of protection offered by microaggregates, whereas the distribution of enzymes reflected the availability of their corresponding substrates. No-tillage treatment significantly increased organic input, mainly in the coarser fractions, enhancing enzyme activities and the functional diversity of the microbial community. This effect was even larger in the absence of fertilizer. At the particle-size level of resolution, adding fertilizer stimulated nutrient cycling. Our results confirmed the hypothesis that no-tillage enlarges the content of particulate organic matter in the coarse sand fraction and stimulates microbial decomposition. In the smaller fractions the enlarged microbial pool and increased soil organic matter with small C/N ratio under NT confirm that this management practice is effective in increasing soil C sequestration capacity.     

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.     

Isoelectric focusing of β-glucosidase humic-bound activity in semi-arid Mediterranean soils under management practices

Changes in β-glucosidase enzyme–humic complexes and conventional parameters (pH, total organic C, total N, water-soluble C, and bulk density) were studied in an almond-cropped soil prone to erosion under a rehabilitation practice. The experimental plan included three soil slopes (0%, 2%, and 6%) and two type of fertilization (organic and mineral), with sampling of rhizosphere and inter-row soils. The enzyme humic complexes were extracted by pyrophosphate, purified by ultrafiltration of the organic extracts on molecular mass exclusion membranes (mol wt > 10⁴) and fractionated by isoelectric focusing technique (IEF). The IEF on polyacrylamide rod gels with a restricted pH gradient ranging between 6.0 and 4.0 gave five humic bands on the basis of the little differences of their electric charges (pI). Under both organic and mineral fertilization, β-glucosidase activity bound to the fractionated humic substances, especially in the pH range 4.5–4.2 of the rhizosphere soil, was higher than that of the inter-row soil. This also occurred in 6% slope where the enzyme activity was lower than in soil with lower slopes. The higher number of the β-glucosidase active humic bands in rhizosphere than inter-row soil, particularly for the 0% slope, may be due to the presence of humic molecules capable of preserving the enzyme molecules in the active form, other than to the higher microbial activity synthesizing and releasing the tested enzymes.     

Microbial performance under increasing nitrogen availability in a Mediterranean forest soil

In forest ecosystems, the external nitrogen (N) inputs mainly involve wet and dry depositions that potentially alter inorganic N availability in the soil and carbon (C) turnover. This study assesses the effect of a slow increase of inorganic N availability on microbial community activity and functionality in a Mediterranean forest soil. A four-month incubation experiment was performed with soil collected from the organic layer of a forest site and fertilized with a solution of ammonium nitrate. The fertilizer was supplied at an equivalent of 0, 10, 25, 50 and 75 kg N ha⁻¹ (0, 0.3, 0.7, 1.3 and 2 mg N g⁻¹ for control N0 and treatments N1, N2, N3 and N4, respectively). The incubation was carried out under optimal conditions, with the addition of the nutritive solution in small aliquots once a week to mimic the phenomenon of N deposition. In order to isolate the effect of N, the pH of the NH₄NO₃ solutions was adjusted to soil pH, and phosphorus was added in order to prevent any nutrient limitation effect. Inorganic N, C-mineralization, the activity of one oxidative enzyme (o-diphenol oxidase) and 8 hydrolitic enzymes (α-glucosidase, β-glucosidase, N-acetyl-β-d-glucosaminidase, cellulase, leucine amino-peptidase, acid phosphatase, butyric esterase and β-xylosidase) and the community level physiological profile (CLPP) were measured and analyzed during the whole incubation and at the end of the experiment as a proxy for microbial decomposition activity. In the first month, the highest N availability (N4) repressed the microbial respiration activity but stimulated microbial enzymatic activity, suggesting a change of C-pathways from spilling to enzymes and biomass investment. The treatments N1, N2 and N3 had no effect in the same period. Throughout the incubation, a general stress condition affected all the treated soils. As a consequence, treated soils exhibited higher respiration rates than the control. This was accompanied by a loss of functional diversity and an end-detected decline in biomass C. Although at the end of incubation most of the soil features showed a clear correlation with the inorganic N pool, the organic C content was strongly affected by different patterns of microbial activity during the experiment: the highest N treatment (N4) showed a lower C loss than the N3 treatment. Overall, the experiment showed how inorganic N availability can potentially alter the C cycle in a Mediterranean forest soil. The effect is non linear, depending on microbial community dynamics, on the community’s ability to adapt given the time scale of the process, and on N supply amount. Our study also revealed a common pattern in the short-term response to N addition in other, similar ecosystems with different climatic conditions.     

有机和常规生产模式下菜田土壤酶活性差异研究

通过对露地及温室环境下有机和常规蔬菜栽培土壤采样,测定分析了5种参与土壤碳氮循环的酶活性,及其与土壤相关理化性质之间的关系。结果显示:温室及露地土壤EC值在有机生产中相应低于常规生产12%和16%;有机生产土壤微生物碳氮含量显著高于常规生产;不同生产模式下土壤酶活性差异显著,有机生产土壤中的蛋白酶、脲酶、脱氢酶、β-葡糖苷酶活性高于常规生产,而硝酸还原酶活性较常规生产低;有机与常规栽培对蛋白酶活性影响极显著(P=0.006 8),对脲酶活性影响程度达显著水平(P=0.012 4)。除脱氢酶以外,不同栽培模式环境对土壤中另外4种酶活性均有显著影响,温室栽培环境中的蛋白酶、脲酶和硝酸还原酶活性高于露地。除硝酸还原酶外,其他4种酶活性与可溶性全氮、微生物碳、微生物氮相关系数达到显著水平。分析表明,土壤酶活性受到栽培方式以及环境的影响,并且有机生产能够提高参与土壤碳氮循环的酶活性。土壤蛋白酶、脲酶、脱氢酶和β-葡糖苷酶活性能够作为表征土壤碳氮循环以及微生物活性的指标。     

Effects of harvester ant (<Emphasis Type="Italic">Messor</Emphasis> spp.) activity on soil properties and microbial communities in a Negev Desert ecosystem

Harvester ants (Messor spp.) function as an essential link between aboveground resources and below-ground biota such as the microbial community. We examined changes in soil microbial biomass and functional diversity resulting from harvester ant (Messor spp.) activity in the Negev Desert, Israel. Abiotic and biotic soil parameters were recorded during two seasons—wet and dry—also representing food availability periods for the ants (low and high seed availability, respectively). Soil samples were collected monthly from the 0- to 10- and 10- to 20-cm soil layers: (1) near the nest entrance, (2) under chaff piles, and (3) at a 2-m radius from the nest entrance (control). Harvester ant activity increased the percentage of organic matter, total soluble nitrogen, and microbial activity in nest-modified soils in comparison to the control soils. Higher CO₂ evolution was recorded in the low-seed season in ant nest soils than in the control soils. During the high-seed season, higher carbon dioxide evolution was recorded only at the nest entrance locations. There were no differences in microbial biomass between the low- and high-seed seasons, but highest microbial biomass was found under chaff in low-seed season and in nest soils in high-seed season. Microbial functional diversity was higher in nest-modified soils than in the control soils. This study suggests that the effect of harvester ant nests on soil fertility is due to increased microbial biomass and microbial activity in ant nest-modified soils.     

The effects of N and P additions on soil microbial properties in paired stands of temperate secondary forests and adjacent larch plantations in Northeast China

The conversion of secondary forests to larch plantations in Northeast China has resulted in a significant decline in soil available nitrogen (N) and phosphorus (P), and thus affects plant productivity and ecosystem functioning. Microbes play a key role in the recycling of soil nutrients; in turn, the availability of soil N and P can constrain microbial activity. However, there is little information on the relationships between available soil N and P and the microbial biomass and activity in larch plantation soil. We studied the responses of soil microbial respiration, microbial biomass and activity to N and P additions in a 120-day laboratory incubation experiment and assessed soil microbial properties in larch plantation soil by comparing them with the soil of an adjacent secondary forest. We found that the N-containing treatments (N and N + P) increased the concentrations of soil microbial biomass N and soluble organic N, whereas the same treatments did not affect microbial respiration and the activities of β-glucosidase, N-acetyl-β-glucosaminidase and acid phosphatase in the larch plantation. In addition, the concentration of microbial biomass P decreased with N addition in larch plantation soil. In contrast, N and N + P additions decreased microbial respiration, and N addition also decreased the activity of N-acetyl-β-glucosaminidase in the secondary forest soil. The P treatment did not affect microbial respiration in either larch plantation or secondary forest soils, while this treatment increased the activities of β-glucosidase and acid phosphatase in the secondary forest soil. These results suggested that microbial respiration was not limited by available P in either secondary forest or larch plantation soils, but microbial activity may have a greater P demand in secondary forest soil than in larch plantation soil. Overall, there was no evidence, at least in the present experiment, supporting the possibility that microbes suffered from N or P deficiency in larch plantation soil.     

The response of organic matter mineralisation to nutrient and substrate additions in sub-arctic soils

Global warming in the Arctic may alter decomposition rates in Arctic soils and therefore nutrient availability. In addition, changes in the length of the growing season may increase plant productivity and the rate of labile C input below ground. We carried out an experiment in which inorganic nutrients (NH₄NO₃ and NaPO₄) and organic substrates (glucose and glycine) were added to soils sampled from across the mountain birch forest-tundra heath ecotone in northern Sweden (organic and mineral soils from the forest, and organic soil only from the heath). Carbon dioxide production was then monitored continuously over the following 19 days. Neither inorganic N nor P additions substantially affected soil respiration rates when added separately. However, combined N and P additions stimulated microbial activity, with the response being greatest in the birch forest mineral soil (57% increase in CO₂ production compared with 26% in the heath soil and 8% in the birch forest organic soil). Therefore, mineralisation rates in these soils may be stimulated if the overall nutrient availability to microbes increases in response to global change, but N deposition alone is unlikely to enhance decomposition. Adding either, or both, glucose and glycine increased microbial respiration. Isotopic separation indicated that the mineralisation of native soil organic matter (SOM) was stimulated by glucose addition in the heath soil and the forest mineral soil, but not in the forest organic soil. These positive ‘priming’ effects were lost following N addition in forest mineral soil, and following both N and P additions in the heath soil. In order to meet enhanced microbial nutrient demand, increased inputs of labile C from plants could stimulate the mineralisation of SOM, with the soil C stocks in the tundra-heath potentially most vulnerable.     

Effects of a humic deposit (gyttja) on soil chemical and microbiological properties and heavy metal availability

The influence of a humic deposit (Gyttja, G) alone (applied at 25 kg ha⁻¹) and in combination with mineral fertilizer (G + NP) on soil organic matter content, pH, electrical conductivity, total N content, calcium carbonate content, enzyme activities (urease, β-glucosidase, arylsulphatase, and alkaline phosphatase), microbial biomass C, soil respiration, and availability of Cd, Pb, Ni, and Zn was examined through a 180-day incubation period and compared with the behavior of no treatment (control) and NP treatment. A significant increase in organic matter content was observed in soils treated with G + NP. Compared with G and NP alone, the G + NP-amended soils showed higher values of the selected microbiological properties.Diethylenetriaminepentaacetic-acid-extractable Cd, Pb, Ni, Cu, and Zn increased significantly with increasing rates of NP, but the addition of G + NP resulted in a considerable decrease in the amount of extractable metals during the incubation period (P<0.05). Based on these results, it can be concluded that the organic matter applied in the gyttja led to an increase in the metal adsorption capacity of the amended soils. This material can be used to reduce the availability and mobility of heavy metals in the soils intensively amended with mineral fertilizers. A combination of G with NP can, therefore, be considered as an alternative approach in the applications of organomineral fertilization.     

Land use effects on microbial biomass C, β-glucosidase and β-glucosaminidase activities,and availability,storage, and age of organic C in soil

Microbial biomass, β-glucosidase and β-glucosaminidase activities, and availability, storage, and age of soil organic C were investigated after 26 years of conversion from sugarcane (Saccharum officinarum) to forest (Eucaliptus robusta or Leucaena leucocephala), pasture (mixture of tropical grasses), and to vegetable cropping (agriculture) in a vertisol in Puerto Rico. Soil organic C (SOC) at 0–100 cm was similar under Leucaena (22.8 kg C/m²), Eucalyptus (18.6 kg C/m²), and pasture (17.2 kg C/m²), which were higher than under agriculture (13.0 kg C/m²). Soil organic N (SON) at 0–100 cm was similar under the land uses evaluated which ranged from 1.70 (under agriculture) to 2.28 kg N/m² (under Leucaena forest). Microbial biomass C (MBC) and N (MBN) of the 0–15-cm soil layer could be ranked as: pasture > Leucaena = Eucalyptus > agriculture. The percentages of SOC and SON present as MBC and MBN, respectively, were nearly 1% in pasture and less than 0.50% in forest under Leucaena or Eucalyptus and agricultural soil. The activity of β-glucosidase of the 0–15-cm soil layer could be ranked as: Leucaena = Eucalyptus > pasture > agriculture; while β-glucosaminidase activity was ranked as: Eucalyptus > Leucaena = pasture > agriculture. The soil δ ¹³C changed from 1996 to 2006 in forest under Eucalyptus (18.7‰ to 21.2‰), but not under Leucaena (20.7‰ to 20.8‰). The soil under Leucaena preserved a greater proportion of old C compared to the forest under Eucalyptus; the former had an increased soil mineralizable C from the current vegetation inputs. The soil under agriculture had the lowest enzyme activities associated with C cycling, lowest percentage of SOC as MBC, highest percentage of SOC present as mineralizable C, and highest percentage of MBC present as mineralizable C compared to the other land uses.     

Catabolic and genetic microbial indices,and levels of nitrate,ammonium and organic carbon in soil from the black locust (<Emphasis Type="Italic"> Robinia pseudo-acacia</Emphasis>) and tulip poplar (<Emphasis Type="Italic"> Liriodendron tulipifera</Emphasis>) trees in a Pennsylvania forest

Soil samples were collected from the upper soil horizon within 4 m of black locust ( Robinia pseudo-acacia) and tulip poplar trees ( Liriodendron tulipifera) from the same mixed forest in south-central Pennsylvania. The soil samples were analyzed for organic C levels, pH, NO₃ ^-, NH₄ ⁺, catabolic diversity (Shannon diversity index; catabolic H), catabolic evenness (Simpson-Yule index; catabolic E), genetic H, and genetic E. The catabolic H and genetic H of microbes in these soils were found to correlate well with the levels of mineralized N, organic C, and pH. Significant variations in these parameters were found between the soils from near black locust and tulip poplar trees. Conditions in the soil near the black locust trees were more favorable to nitrification as indicated by the elevated pH, organic C, NO₃ ^-, and total mineral N levels, along with lower NH₄ ⁺ levels. The microbial genetic H and E were greater and the catabolic H and E were lower in the black locust soils than in the tulip poplar soils. This suggests that a more specialized environment exists in the soil near the black locust trees which selects for enhanced nitrification and the use of fewer, but preferred catabolic pathways by a more genetically diverse group of microbes that grow to a greater biomass. Conversely, the soils from near the tulip poplar trees are such that they do not select for some dominant catabolic pathways, rather they allow for the use of a greater variety of catabolic pathways by a less diverse microbial population, which appear to grow to a lower biomass. We believe that the combined application of the microbial genetic and catabolic diversity analyses, microbial biomass estimates, and traditional physico-chemical characteristics in soil studies provides information not easily available that can be useful during assessment of soil processes in different terrestrial habitats.     

Dynamics of soil properties and organic carbon pool in topsoil of zokor-made mounds at an alpine site of the Qinghai–Tibetan Plateau

The population of burrowing plateau zokors (Myospalax baileyi) was markedly increased in the Qinghai–Tibetan Plateau. The objective of this study was to investigate the effects of zokor foraging and mound-making disturbance on topsoil properties and organic C pools at an alpine site of the Qinghai–Tibetan Plateau. Surface (0–15 cm) soil samples were collected from mounds with different ages (3 months and 3, 6, and 15 years) and from undisturbed grassland. Above- and below-ground plant biomasses were depleted by zokors in newly created mounds (3 months). Plant cover and root biomass gradually recovered thereafter, but were still lower in the 15-year-old mounds than in the undisturbed soils. Organic C contents of coarse (>2 mm), soil (<2 mm), particulate (2–0.05 mm) fractions, and microbial biomass, organic C mineralization, β-glucosidase activity, urease activity, alkaline phosphatase activity, acid phosphatase activity, and soil aggregation were significantly lower in the 3, 6, and 15-year-old mound soils than in the undisturbed soils or newly created mound soils. Fifteen years after mound creation, the soil had only 12% of root biomass, 35% of coarse organic C, 83% of particulate organic C, 58% of microbial biomass C, 57% of 30-day respired C, and 45% of water-stable aggregate mean weight diameter, compared to values of the undisturbed soils. Our results suggested that foraging and mound-making by zokors have negative impacts on properties and organic matter content of the topsoil.     

Soil biochemical and microbial indices in wet tropical forests: Effects of deforestation and cultivation

Little information is available about the long‐term effects of deforestation and cultivation on biochemical and microbial properties in wet tropical forest soils. In this study, we evaluated the general and specific biochemical properties of soils under evergreen, semi‐evergreen, and moist deciduous forests and adjacent plantations of coconut, arecanut, and rubber, established by clear felling portions of these forests. We also examined the effects of change in land use on microbial indices and their interrelationships in soils. Significant differences between the sites occurred for the biochemical properties reflecting soil microbial activity. Microbial biomass C, biomass N, soil respiration, N mineralization capacity, ergosterol, levels of adenylates (ATP, AMP, ADP), and activities of dehydrogenase and catalase were, in general, significantly higher under the forests than under the plantations. Likewise, the activities of various hydrolytic enzymes such as acid phosphomonoesterase, phosphodiesterase, casein‐protease, BAA‐protease, β‐glucosidase, CM‐cellulase, invertase, urease, and arylsulfatase were significantly higher in the forest soils which suggested that deforestation and cultivation markedly reduced microbial activity, enzyme synthesis and accumulation due to decreased C turnover and nutrient availability. While the ratios of microbial biomass C : N and microbial biomass C : organic C did not vary significantly between the sites, the ratios of ergosterol : biomass C and ATP : biomass C, qCO2 and AEC (Adenylate Energy Charge) levels were significantly higher in the forest sites indicating high energy requirements of soil microbes at these sites.     

农业土壤中频繁施用有机质提高土壤抑菌作用

Soil-borne plant pathogens are among the most important limiting factors for the productivity of agro-ecosystems.Fungistasis is the natural capability of soils to inhibit the germination and growth of soil-borne fungi in the presence of optimal abiotic conditions.The objective of this study was to assess the effects of different soil managements,in terms of soil amendment types and frequency of application,on fungistasis.For this purpose,a microcosm experiment was performed by conditioning a soil with frequent applications of organic matter with contrasting biochemical quality (i.e.,glucose,alfalfa straw and wheat straw).Thereafter,the fungistasis response was assessed on four fungi (Aspergillus niger,Botrytis cinerea,Pyrenochaeta lycopersici and Trichoderma harzianum).Conditioned soils were characterized by measuring microbial activity (soil respiration) and functional diversity using the BIOLOG EcoPlatesTM method.Results showed that irrespective of the fungal species and amendment types,frequent applications of organic matter reduced fungistasis relief and shortened the time required for fungistasis restoration.The frequent addition of easily decomposable organic compounds enhanced soil respiration and its specific catabolic capabilities.This study demonstrated that frequent applications of organic matter affected soil fungistasis likely as a result of higher microbial activity and functional diversity.     

Microbial biomass in agricultural topsoils after 6 years of bare fallow

Inherent soil properties have an influence on microbial activity. These effects were measured in a field trial at Weihenstephan with 30 agricultural and 2 vineyard soils from different sites in Bavaria which had been kept under bare fallow for 6 years. The soils represented a wide range of arable soils from a temperate climate. Unaffected by recent differences in climatic conditions or cropping managements, they were used to assess the relationship between microbial biomass C and a broad spectrum of soil physical and chemical properties (clay content 5–63%, pH 4.5–7.5, organic C 0.55–2.93%). Microbial C was measured using the substrate-induced respiration method. In addition, soil catalase activity and the abundance and biomass of earthworms were determined. Among the soil properties, microbial C was most strongly correlated with organic C (r=0.86, n=29). In a comparison of linear regressions between microbial biomass C and organic C for different cropping managements, the slope under bare fallow was lowest, followed by monoculture and crop rotation. The microbial: organic C ratio ranged from 1.1 to 4.3% and was significantly correlated with soil pH (r=0.66). A positive relationship between microbial C and the clay content (r=0.66) was significantly improved when soils with more than 25% clay were excluded (r=0.80). Partial correlation analysis indicated that clay had a direct influence, hardly affected by an intercorrelation with organic C. Catalase activity was highly correlated with microbial C (r=0.95) and, because a rapid and sensitive method of determination is available, was considered suitable for estimating relative amounts of active microbial biomass. A positive relationship between microbial C and the abundance of earthworms indicated interactions between microorganisms and mesofauna.     

Soil organic carbon distribution drives microbial activity and functional diversity in particle and aggregate-size fractions

Chemical and functional characterizations of particle-size and aggregate fractions of soils were performed to investigate whether accessibility and decomposability of organic matter regulate functions and diversity of the soil microbial community at the micro-habitat scale. Soils were physically fractionated into particle size fractions, free-particulate organic matter (F-POM), macro-aggregates (250–2000 μm) and micro-aggregates (53–250 μm). Organic C was enriched in silt and clay, micro-aggregates and F-POM fractions. Enzymes showed the greatest activity in the fine fractions (silt and clay) and F-POM, and were largely influenced by organic C content. MicroResp-CLPP (Community Level Physiological Profile) showed the lowest catabolic responses in the sand and the highest in the fine fraction and micro-aggregates. In general, organic C availability drove soil activity and functional diversity: soils with the higher amount of organic C showed the higher catabolic activity. However, this response was variable within soil fractions, where organic C accessibility, as well as microbial selection and distribution, affected functional diversity.     

Short-term effects of organic municipal wastes on wheat yield,microbial biomass,microbial activity,and chemical properties of soil

The objectives of this work were to (a) investigate the short-term effects of applications of mineral fertilizer, municipal solid waste (MSW) compost, and two sewage sludges (SSs) subjected to different treatments (composting and thermal drying) on microbial biomass and activity of soil by measuring microbial biomass C, adenosine 5′-triphosphate content, basal respiration, and dehydrogenase, catalase, urease, phosphatase, β-glucosidase, and N-α-benzoyl-l-argininamide-hydrolyzing activities and (b) explore the relationships between soil microbiological, biochemical, and chemical properties and wheat yields under semiarid field conditions by principal component analysis. The additions of MSW compost, SS compost, and thermally dried SS did not affect significantly soil microbial biomass, as compared to mineral fertilization and no amendment. However, microbial activity increased in organically amended soils, probably due to the stimulating effect of the added decomposing organic matter. Changes in soil microbiological and biochemical properties showed no significant relationships with wheat yields, probably because plant growth was primarily water-limited, as typically occurs in semiarid regions.     

Effect of differently post-treated dewatered sewage sludge on β-glucosidase activity,microbial biomass carbon,basal respiration and carbohydrates contents of soils from limestone quarries

This work has evaluated the effects of thermally dried (TDS) or composted (CDS) dewatered sewage sludge on β-glucosidase activity, total (TCH) and extractable (ECH) carbohydrate content, microbial biomass carbon and basal respiration of soils from limestone quarries under laboratory conditions. Two doses (low and high) of the dewatered sludge (DS) or of the respective TDS or CDS were applied to a clayey and a sandy soil, both coming from working quarries. The soil mixtures and the controls (soils with no added sludge) were incubated for 9 months at 25°C and 30% of field capacity. The addition of sludge increased all the studied soil parameters, and the increase depended on the amount of sludge. Except in the case of TCH and ECH, the enhancing effect decreased with time, but at the end of incubation, parameters of the treated soils were higher than those of the control. The rank order of the initial stimulating effect was soil–TDS ≥ soil–DS ≥ soil–CDS, and probably, this order depended on the proportion of stable organic matter, which was the lowest in the TDS. Values of metabolic quotient (qCO₂) were higher at the lower dose, and they did not change during incubation in the CDS-treated soils. Both TCH and ECH were the parameters with the greatest significant sludge and dose effects. Basal respiration, microbial biomass carbon and β-glucosidase activity were the best measured parameters in distinguishing the long-term effects of the three sludge types over the soils.     

Microbial and soil parameters in relation to N mineralization in soils of diverse genesis under differing management systems

 Oregon soils from various management and genetic histories were used in a greenhouse study to determine the relationships between soil chemical and biological parameters and the uptake of soil mineralized nitrogen (N) by ryegrass (Lolium perenne L.). The soils were tested for asparaginase, amidase, urease, β-glucosidase, and dipeptidase activities and fluorescein diacetate hydrolysis. Microbial biomass carbon (C) and N as well as metabolic diversity using Biolog GN plates were measured, as were total soil N and C, pH, and absorbance of soil extracts at 270 nm and 210 nm. Potentially mineralizable N (N₀) and the mineralization rate constant (k) were calculated using a first order nonlinear regression model and these coefficients were used to calculate the initial potential rate of N mineralization (N₀ k). Except for Biolog GN plates, the other parameters were highly correlated to mineralized N uptake and each other. A model using total soil N and β-glucosidase as parameters provided the best predictor of mineralized N uptake by ryegrass (R ² =0.83). Chemical and biological parameters of soils with the same history of formation but under different management systems differed significantly from each other in most cases. The calculated values of the initial potential rate of mineralization in some cases revealed management differences within the same soil types. The results showed that management of soils is readily reflected in certain soil chemical and biological indicators and that some biological tests may be useful in predicting N mineralization in soils. Received: 31 January 1997