Soil microbial biomass and selected soil enzyme activities: Effect of fertilization and cropping practices

Selected microbiological properties of soils receiving different fertilizer management regimes were studied from adjoining wheat farms in the highly productive Palouse region of eastern Washington. Since 1909, the only N input to the soil of Farm Management System 1 has been through leguminous green manure crops consisting most recently of Austrian winter peas (Pisum sativum ssp. arvense L., Poir), plus native soil fertility for N and all other plant nutrients. The soil of Farm Management System 2 received regular applications of anhydrous ammonia, P and S at recommended rates for the last 30 yr. There were no differences in numbers of soil microorganisms as determined by plate counts; however, soil from management system 1 had significantly higher levels of urease, phosphatase and dehydrogenase at all three samplings and significantly higher soil microbial biomass at the first two samplings. The data indicate that management system 1 soil had a larger and more active soil microflora.     

Spatial variation of soil enzyme activities and microbial functional diversity in temperate alley cropping systems

Spatially dependent patterns in microbial properties may exist in temperate alley cropping systems due to differences in litter quality and microclimate in areas under trees compared to those in the alleys. The effect of tree row location was evaluated for its impact on soil enzyme activities and Biolog substrate use patterns. Soils were sampled to a depth of 30 cm at the tree row and at the middle of the alley at two sites: a 21-year-old pecan (Carya illinoinensis)/bluegrass (Poa trivials) intercrop (Pecan site) and a 12-year-old silver maple (Acer saccharinum)/soybean (Glycine max)–maize (Zea mays) rotation (Maple site). Sampling was done in fall 2001 and summer 2002. β-Glucosidase activities, Biolog patterns expressed as average well color (AWC), substrate richness, and Shannon diversity index, and total Kjeldahl nitrogen (TKN) were significantly higher (P<0.05) in the tree row than at the middle of the alley for surface soils at the Pecan site. Fluorescein diacetate (FDA) hydrolytic activity was also higher at the tree row for soils sampled in the fall, but did not differ significantly for soils sampled in the summer. At the Maple site, AWC and substrate richness were significantly higher at the tree row for soils sampled in 2001. Soil volumetric water content and temperature were generally lower in the tree row at the Maple site. The results of this study suggest that functionally different microbial populations may be present under pecan trees compared to cropped alleys which may promote disparities in nutrient availability necessitating differential long-term nutrient management in such alley cropping systems.     

Plant roots and species moderate the salinity effect on microbial respiration,biomass, and enzyme activities in a sandy clay soil

The aim of this study was to determine the effects of plant absence or presence on microbial properties and enzyme activities at different levels of salinity in a sandy clay soil. The treatments involved five salinity levels—0.5 (control), 2.5, 5, 7.5, and 10 dS m^?1 which were prepared using a mixture of chloride salts—and three soil environments (unplanted soil, and soils planted with either wheat or clover) under greenhouse conditions. Each treatment was replicated three times. At the end of the experiment, soil microbial respiration, substrate-induced respiration (SIR), microbial biomass C (MBC), and enzyme activities were determined after plant harvest. Increasing salinity decreased soil microbial properties and enzyme activities, but increased the metabolic quotient (qCO₂) in both unplanted and planted soils. Most microbial properties of planted soils were greater than those of unplanted soils at low to moderate salinity levels, depending upon plant species. There was a small or no difference in soil properties between the unplanted and planted treatments at the highest salinity level, indicating that the indirect effects of plant presence might be less important due to significant reduction of plant growth. The lowered microbial activity and biomass, and enzyme activities were due to the reduction of root activity and biomass in salinized soils. The lower values of qCO₂ in planted than unplanted soils support the positive influence of plant root and its exudates on soil microbial activity and biomass in saline soils. Nonetheless, the role of plants in alleviating salinity influence on soil microbial activities decreases at high salinity levels and depends on plant type. In conclusion, cultivation and growing plant in abandoned saline environments with moderate salinity would improve soil microbial properties and functions by reducing salinity effect, in particular planting moderately tolerant crops. This helps to maintain or increase the fertility and quality of abandoned saline soils in arid regions.     

Mobile and readily available C and N fractions and their relationship to microbial biomass and selected enzyme activities in a sandy soil under different management systems

Within different land‐use systems such as agriculture, forestry, and fallow, the different morphology and physiology of the plants, together with their specific management, lead to a system‐typical set of ecological conditions in the soil. The response of total, mobile, and easily available C and N fractions, microbial biomass, and enzyme activities involved in C and N cycling to different soil management was investigated in a sandy soil at a field study at Riesa, Northeastern Germany. The management systems included agricultural management (AM), succession fallow (SF), and forest management (FM). Samples of the mineral soil (0—5, 5—10, and 10—30 cm) were taken in spring 1999 and analyzed for their contents on organic C, total N, NH₄⁺‐N and NO₃^—‐N, KCl‐extractable organic C and N fractions (Corg_(KCl) and Norg_(KCl)), microbial biomass C and N, and activities of β‐glucosidase and L‐asparaginase. With the exception of Norg_(KCl), all investigated C and N pools showed a clear relationship to the land‐use system that was most pronounced in the 0—5 cm profile increment. SF resulted in greater contents of readily available C (Corg_(KCl)), NH₄⁺‐N, microbial biomass C and N, and enzyme activities in the uppermost 5 cm of the soil compared to all other systems studied. These differences were significant at P ≤ 0.05 to P ≤ 0.001. Comparably high C_mic:C_org ratios of 2.4 to 3.9 % in the SF plot imply a faster C and N turnover than in AM and FM plots. Forest management led to 1.5‐ to 2‐fold larger organic C contents compared to SF and AM plots, respectively. High organic C contents were coupled with low microbial biomass C (78 μg g^—1) and N contents (10.7 μg g^—1), extremely low C_mic : C_org ratios (0.2—0.6 %) and low β‐glucosidase (81 μg PN g^—1 h^—1) and L‐asparaginase (7.3 μg NH₄‐N g^—1 2 h^—1) activities. These results indicate a severe inhibition of mineralization processes in soils under locust stands. Under agricultural management, chemical and biological parameters expressed medium values with exception for NO₃^—‐N contents which were significantly higher than in SF and FM plots (P ≤ 0.005) and increased with increasing soil depth. Nevertheless, the depth gradient found for all studied parameters was most pronounced in soils under SF. Microbial biomass C and N were correlated to β‐glucosidase and L‐asparaginase activity (r ≥ 0.63; P ≤ 0.001). Furthermore, microbial biomass and enzyme activities were related to the amounts of readily mineralizable organic C (i.e. Corg_(KCl)) with r ≥ 0.41 (P ≤ 0.01), suggesting that (1) KCl‐extractable organic C compounds from field‐fresh prepared soils represent an important C source for soil microbial populations, and (2) that microbial biomass is an important source for enzymes in soil. The Norg_(KCl) pool is not necessarily related to the size of microbial biomass C and N and enzyme activities in soil.<?show $6#>     

利用复合方法对不同耕作系统中的土壤微生物活性进行分析

Cropping activities may affect soil microbial activities and biomass,which would affect C and N cycling in soil and thus the crop yields and quality.In the present study,a combination of microcalorimetric,enzyme activity(sucrase,urease,catalase,and fluorescein diacetate hydrolysis),and real-time polymerase chain reaction(RT-PCR) analyses was used to investigate microbial status of farmland soils,collected from 5 different sites in Huazhong Agriculture University,China.Our results showed that among the 5sites,both positive and negative impacts of cropping activities on soil microbial activity were observed.Enzyme activity analysis showed that cropping activities reduced soil sucrase and urease activities,which would influence the C and N cycles in soil.Much more attentions should be given to microbial status affected by cropping activities in future.According to the correlation analysis,fluorescein diacetate hydrolysis showed a significantly(P 0.05) negative correlation with the time to reach the maximum power output(R ——0.898),but a significantly(P 0.05) positive correlation with bacterial gene copy number(R = 0.817).Soil catalase activity also showed a significantly(P 0.05) positive correlation with bacterial gene copy number(R = 0.965).Using combined methods would provide virtual information of soil microbial status.     

长期不同施肥条件下土壤微生物量及 土壤酶活性的季节变化特征

研究长期不同施肥条件下褐潮土微生物量碳（SMBC）、微生物量氮（SMBN）和土壤酶活性随季节的变化特征。结果表明,长期施肥条件下土壤SMBC、SMBN含量及土壤酶活性均表现出一定的季节变化。SMBC、SMBN含量在各施肥处理中的顺序为:化肥与猪厩肥配施处理（NPKM）化肥配施玉米秸秆处理（NPKS）单施化肥处理（NPK）不施肥处理（CK）,各处理之间差异显著(P0.05);施肥还显著提高了土壤脲酶、转化酶、碱性磷酸酶活性,有机无机配施的高于单施化肥的。除过氧化氢酶活性随季节变化显著下降外,SMBC、SMBN、酶活性的值一般在夏季（6月到8月）较高。通过双因素单变量方差分析表明,不同施肥制度与季节变化对SMBC、SMBN与酶活性的影响分别达极显著水平（P0.01）,不同施肥制度的SMBC、SMBN与酶活性的季节波动有极显著不同（P0.01）。     

菌肥对混播牧草土壤酶活性及微生物的影响

为研究菌肥与混播对土壤酶活性及微生物生物量的影响,本试验以苜蓿和饲用高粱为研究对象,设8个处理,分别为苜蓿单播(N1)、饲用高粱单播(N2)、苜蓿与饲用高粱同行混播(N3)、苜蓿与饲用高粱间行混播(N4)以及分别施入微生物菌肥(T1、T2、T3与T4)。在饲草生长的苗期、旺盛期与收获期分别取0～20、20～40和40～60 cm土样并测定土壤脲酶、蔗糖酶、过氧化氢酶活性以及微生物生物量碳、氮含量。结果表明:菌肥及混播各处理土壤酶活性及微生物生物量均显著高于未施菌肥及饲草单播各处理,且混播配施菌肥效果更优。土壤酶活性随土层深入逐渐降低,随生育期推进,过氧化氢酶和蔗糖酶活性呈现先降低后升高趋势;土壤脲酶活性呈现先升后降趋势,微生物生物量碳、氮的规律与脲酶相同。混播配施菌肥有利于增加有益酶活性,提高土壤微生物生物量,增强土壤生产力的可持续性,从而达到保护和改善土壤环境的效果,为内蒙古地区马铃薯提供倒茬作物,提供充足饲草,对农业与畜牧业发展意义重大。     

Evaluation of soil enzyme activities and microbial communities in tomato continuous cropping soil treated with jerusalem artichoke residues

ABSTRACT

Jerusalem artichoke (JY) (Helianthus tuberosus L.) has been reported to have a strong inhibitory effect on weed growth and root knot nematodes, but little information is available on the effects on soil ecosystems, especially soil microorganisms and soil enzyme activities. Understanding the dynamics of soil microbes and soil enzyme activities in cropping systems can help determine how agricultural practices influence soil processes mediated by JY residues. This study used a pot experiment, with five-year continuous cropping soil of tomato plants as the experimental material and 2% (w/w) JY residue as the treatment material in the soil. The treatment was compared to continuously monocropped tomato soil that was not treated with JY residues. The results of 16S high-throughput sequencing showed that both fungal and bacterial community structure and composition varied significantly at each stage of JY treatment. The analysis showed that the major phyla in the soil fungal community included Ascomycota, Zygomycota and Basidiomycota. Chytridiomycota was dominant in only the JY-treated soil. At the genus level, the abundances of Mortierella, Cephaliophora, Cryptococcus and Fusarium notably changed at each stage of JY treatment. In the bacterial community in the JY-treated group, the abundance of Proteobacteria increased significantly, while that of Firmicutes decreased significantly, compared to the control group. JY enhanced the activity of soil sucrase and urease. In addition, the soil sucrase activity showed a strong negative correlation with Fusarium and Bacillus. Overall, our results revealed that JY residues changed both the soil bacterial and fungal community composition and the soil enzyme activities.     

Microbial community structure and functionality under peanut-based cropping systems in a sandy soil

Little information is available on soil microbial and biochemical properties, important for understanding nutrient cycling and organic matter dynamics, as affected by different peanut cropping systems and how they relate to soil functioning. Thus, we studied a Tifton loamy sand (fine-loamy, kaolinitic, thermic Plinthic Kandiudults) in Georgia, which is first in peanut production in USA, after 5 and 8 years under continuous cotton (Gossypium hirsutum, L) (CtCtCt), cotton–cotton–peanut (CtCtPt), corn (Zea mays L.)–peanut–cotton (CrPtCt), peanut–peanut–cotton (PtPtCt), and continuous peanut (PtPtPt). Soil organic carbon (OC) at 0–20 cm was already higher under PtPtPt (average, 8.7 g C kg⁻¹ soil), PtPtCt (average, 7.7 g C kg⁻¹ soil), and CrPtCt (average, 7.8 g C kg⁻¹ soil) compared with CtCtPt (average, 4.7 g C kg⁻¹ soil) and CtCtCt (average, 3.3 g C kg⁻¹ soil). Similarly, alkaline phosphatase, acid phosphatase, and phosphodiesterase as a group showed higher activities under PtPtPt, PtPtCt, and CrPtCt than under CtCtPt and CtCtCt. The activities of glycosidases (α-galactosidase, β-glucosidase, and β-glucosaminidase) as a group were more sensitive to the cropping systems than phosphastases and showed a distinctive cropping system separation as follows: PtPtPt = CrPtCt > PtPtCt > CtCtPt > CtCtCt. Similar to OC and microbial biomass C trends, distinctive differences were found in the microbial community structure of this sandy soil after 8 years between peanut-based cropping systems (CrPtCt, PtPtCt, and PtPtPt) and cotton-based cropping systems (CtCtCt and CtCtPt) as indicated by the fatty acid methyl esters profiles. Trade names and company names are included for the benefit of the reader and do not infer any endorsement or preferential treatment of the product by USDA-ARS.     

Grazing and plant-canopy effects on semiarid soil microbial biomass and respiration

The major objectives of this study were to determine the influence of grazing on the soil microbial biomass and activity in semiarid grassland and shrubland areas and to quantify the canopy effect (the differences in soil microbial biomass and activities between soils under plant canopies and soils in the open between plants). We also quantified changes in microbial biomass and activity during seasonal transition from dry to moist conditions. Chronosequences of sites withdrawn from grazing for 0, 11, and 16 years were sampled in a grassland (Bouteloua spp.) area and a shrubland (Atriplex canescens) area on and near the Sevilleta National Wildlife Reguge in central New Mexico, USA. Samples were obtained from beneath the canopies of plants (Yucca glauca in the grassland and A. canescens in the shrubland) and from open soils; they were collected three times during the spring and summer of a single growing season. Organic C, soil microbial biomass C, and basal respiration rates (collectively called the soil C triangle) were measured. We also calculated the microbial: organic C ratio and the metabolic quotient (ratio of respiration to microbial C) as measures of soil organic C stability and turnover. Although we had hypothesized that individual values of the soil C triangle would increase and that the ratios would decrease with time since grazing, differences in microbial parameters between sites located along the chronosequences were generally not significant. Grazing did not have a consistion effect on organic C, microbial C, and basal respiration in our chronosequences. The microbial: organic C ratio and the metabolic quotient generally increased with time since grazing on the shrubland chronosequence. The microbial: organic C ratio decreased with time since grazing and the metabolic quotient increased with time since grazing on the grassland chronosequence. The canopy effect was observed at all sites in nearly all parameters including organic C, microbial C, basal respiration, the microbial: organic C ratio, and the metabolic quotient which were predominantly higher in soils under the canopies of plants than in the open at all sites. Microbial biomass and activity did not increase during the experiment, even though the availability of moisture increased dramatically. The canopy effects were approximately equal on the shrubland and grassland sites. The microbial: organic C ratios and the metabolic quotients were generally higher in the shrubland soils than in the grassland soils.     

Effect of the addition of municipal solid-waste compost on microbial biomass and enzyme activities in soil

Summary Changes in the content of C, N, P, and S in the soil biomass and in phosphatase, urease, protease, deaminase, and arylsulphatase activity, induced by amendment with municipal solid-waste compost, were determined in a clay loam soil during 1 year of incubation at 25° and 35°C.In the unenriched soil (control) decreasing trends in biomass C, biomass N, and biomass S were observed at both temperatures. In the enriched soil, these values increased, reaching a maximum after 1 month. Biomass P, probably due to a slower process of P immobilization, showed different trends. Alkaline phosphomonoesterase, phosphodiesterase, and deaminase activity remained constant after reaching maximum values (3–5 months). Arylsulphatase, urease, and protease activity tended to return to baseline after reaching a maximum (2–3 months).Atrazine, though applied at a dose that was 10 times higher than the recommended field rate, did not modify the chemical and biochemical properties of either the control or the enriched soil.Significant positive and negative correlations between changes in biomass values and changes in enzyme activity were found. The negative correlations are attributed to the delay in the enzymatic response compared with the changes in microbial biomass.     

不同种植时间菜园土壤微生物生物量和酶活性变化特征

土壤生物学指标能够反映土壤质量在各种自然和人为作用下的微小变化,是敏感的土壤质量指标。本文以太湖地区高强度开发为背景,研究了不同利用年限的菜园土壤微生物生物量C和酶活性的变化特征。研究结果表明,菜园土壤随着利用年限的不断增加,土壤养分逐渐升高,土壤脲酶活性、土壤微生物生物量C与土壤有机质、全N、全P之间具有良好的线性关系,土壤纤维素酶活性随菜地利用时间增加有上升的趋势,它们能较好地区别不同利用年限的菜地土壤,可以作为敏感的土壤生物学指标。但土壤转化酶活性与土壤养分的变化没有明显的相关性。     

不同耕作方式对土壤有机碳、微生物量及酶活性的影响

【目的】依托8年长期(2005~2012)固定道定位试验,研究不同耕作方式对土壤有机碳、土壤微生物量、土壤酶活性在0—90 cm土层的分布特征,为优化中国西北干旱区的耕作方式提供理论依据。【方法】试验包括固定道垄作(PRB)、固定道平作(PFT)与传统耕作(CT)三种耕作模式下的土壤有机碳土壤总有机碳(TOC)、颗粒有机碳(POC)、土壤微生物量碳(MBC)、土壤微生物量氮(MBN)、土壤微生物量磷(MBP)、蔗糖酶、过氧化氢酶、脲酶及小麦产量进行了测定和分析。【结果】在0—90 cm土层,不同耕作方式下的TOC、POC、MBC、MBN、MBP、蔗糖酶活性、脲酶活性均随着土层的增加呈下降趋势,过氧化氢酶活性呈先下降后增大的分布特征;在0—60 cm,固定道保护性耕作能够显著增加心土层作物生长带土壤有机碳储量,有机碳储量大小为PRBPFTCT;PRB、PFT较CT可以显著增加0—10 cm作物生长带TOC、POC、MBC、MBN、MBP含量、蔗糖酶、脲酶活性,其大小为PRBPFTCT;耕作方式对过氧化氢酶活性影响不显著;TOC、POC、MBC、MBN、MBP、蔗糖酶活性、脲酶活性、过氧化氢酶活性之间均达到了显著或极显著相关。【结论】PRB较PFT、CT能够提高耕作层(0—10 cm)土壤有机碳含量、土壤微生物量、土壤酶活性, 增加作物产量, 增大0—60 cm土层有机碳储量,耕作方式(PRB、PFT及CT)对10 cm以下土层土壤环境改善作用不明显。     

Changes in enzyme activities and microbial biomass after “in situ” remediation of a heavy metal-contaminated soil

Microbial properties such as microbial biomass carbon (MBC), arylsulfatase, β-glucosidase and dehydrogenase activities, and microbial heterotrophic potential, together with several chemical properties such as pH, CaCl₂ soluble heavy metal concentrations, total organic carbon and hydrosoluble carbon were measured to evaluate changes in soil quality, after “in situ” remediation of a heavy metal-contaminated soil from the Aznalcóllar mine accident (Southern Spain, 1998). The experiment was carried out using containers, filled with soil from the affected area. Four organic amendments (a municipal waste compost, a biosolid compost, a leonardite and a litter) and an inorganic amendment (sugarbeet lime) were mixed with the top soil at the rate of 100 Mg ha⁻¹. Unamended soil was used as control. Agrostis stolonifera L. was sown in the containers. The soil was sampled twice: one month and six months after amendment application. In general, these amendments improved the soil chemical properties: soil pH, total organic carbon and hydrosoluble carbon increased in the amended soils, while soluble heavy metal concentrations diminished. At the same time, higher MBC, enzyme activities and maximum rate of glucose mineralization values were found in the organically amended soils. Plant cover was also important in restoring the soil chemical and microbial properties in all the soils, but mainly in those that were not amended organically. As a rule, remediation measures improved soil quality in the contaminated soils.     

Soil compaction and forest floor removal reduced microbial biomass and enzyme activities in a boreal aspen forest soil

Soil enzymes are linked to microbial functions and nutrient cycling in forest ecosystems and are considered sensitive to soil disturbances. We investigated the effects of severe soil compaction and whole-tree harvesting plus forest floor removal (referred to as FFR below, compared with stem-only harvesting) on available N, microbial biomass C (MBC), microbial biomass N (MBN), and microbial biomass P (MBP), and dehydrogenase, protease, and phosphatase activities in the forest floor and 0–10 cm mineral soil in a boreal aspen (Populus tremuloides Michx.) forest soil near Dawson Creek, British Columbia, Canada. In the forest floor, no soil compaction effects were observed for any of the soil microbial or enzyme activity parameters measured. In the mineral soil, compaction reduced available N, MBP, and acid phosphatase by 53, 47, and 48%, respectively, when forest floor was intact, and protease and alkaline phosphatase activities by 28 and 27%, respectively, regardless of FFR. Forest floor removal reduced available P, MBC, MBN, and protease and alkaline phosphatase activities by 38, 46, 49, 25, and 45%, respectively, regardless of soil compaction, and available N, MBP, and acid phosphatase activity by 52, 50, and 39%, respectively, in the noncompacted soil. Neither soil compaction nor FFR affected dehydrogenase activities. Reductions in microbial biomass and protease and phosphatase activities after compaction and FFR likely led to the reduced N and P availabilities in the soil. Our results indicate that microbial biomass and enzyme activities were sensitive to soil compaction and FFR and that such disturbances had negative consequences for forest soil N and P cycling and fertility.     

Response of soil microbial biomass and enzyme activities to the transient elevation of carbon dioxide in a semi-arid grassland

Although elevation of CO₂ has been reported to impact soil microbial functions, little information is available on the spatial and temporal variation of this effect. The objective of this study was to determine the microbial response in a northern Colorado shortgrass steppe to a 5-year elevation of atmospheric CO₂ as well as the reversibility of the microbial response during a period of several months after shutting off the CO₂ amendment. The experiment was comprised of nine experimental plots: three chambered plots maintained at ambient CO₂ levels of 360 μmol mol⁻¹ (ambient treatment), three chambered plots maintained at 720 μmol mol⁻¹ CO₂ (elevated treatment) and three unchambered plots of equal ground area used as controls to monitor the chamber effect.Elevated CO₂ induced mainly an increase of enzyme activities (protease, xylanase, invertase, alkaline phosphatase, arylsulfatase) in the upper 5 cm of the soil and did not change microbial biomass in the soil profile. Since rhizodeposition and newly formed roots enlarged the pool of easily available substrates mainly in the upper soil layers, enzyme regulation (production and activity) rather than shifts in microbial abundance was the driving factor for higher enzyme activities in the upper soil. Repeated soil sampling during the third to fifth year of the experiment revealed an enhancement of enzyme activities which varied in the range of 20-80%. Discriminant analysis including all microbiological properties revealed that the enzyme pattern in 1999 and 2000 was dominated by the CO₂ and chamber effect, while in 2001 the influence of elevated CO₂ increased and the chamber effect decreased.Although microbial biomass did not show any response to elevated CO₂ during the main experiment, a significant increase of soil microbial N was detected as a post-treatment effect probably due to lower nutrient (nitrogen) competition between microorganisms and plants in this N-limited ecosystem. Whereas most enzyme activities showed a significant post-CO₂ effect in spring 2002 (following the conclusion of CO₂ enrichment the previous autumn, 2001), selective depletion of substrates is speculated to be the cause for non-significant treatment effects of most enzyme activities later in summer and autumn, 2002. Therefore, additional belowground carbon input mainly entered the fast cycling carbon pool and contributed little to long-term carbon storage in the semi-arid grassland.     

Spatial variability of enzyme activities and microbial biomass in the upper layers of Quercus petraea forest soil

Extracellular lignocellulose-degrading enzymes are responsible for the transformation of organic matter in hardwood forest soils. The spatial variability on a 12 × 12 m plot and vertical distribution (0–8 cm) of the ligninolytic enzymes laccase and Mn-peroxidase, the polysaccharide-specific hydrolytic enzymes endoglucanase, endoxylanase, cellobiohydrolase, 1,4-β-glucosidase, 1,4-β-xylosidase and 1,4-β-N-acetylglucosaminidase and the phosphorus-mineralizing acid phosphatase were studied in a Quercus petraea forest soil profile. Activities of all tested enzymes exhibited high spatial variability in the L and H horizons. Acid phosphatase and 1,4-β-N-acetylglucosaminidase exhibited low variability in both horizons, while the variability of Mn-peroxidase activity in the L horizon, and endoxylanase and cellobiohydrolase activities in the H horizon were very high. The L horizon contained 4× more microbial biomass (based on PLFA) and 7× fungal biomass (based on ergosterol content) than the H horizon. The L horizon also contained relatively more fungi-specific and less actinomycete-specific PLFA. There were no significant correlations between enzyme activities and total microbial biomass. In the L horizon cellulose and hemicellulose-degrading enzymes correlated with each other and also with 1,4-β-N-acetylglucosaminidase and acid phosphatase activities. Laccase, Mn-peroxidase and acid phosphatase activities correlated in the H horizon. The soil profile showed a gradient of pH, organic carbon and humic compound content, microbial biomass and enzyme activities, all decreasing with soil depth. Ligninolytic enzymes showed preferential localization in the upper part of the H horizon. Differences in enzyme activities were accompanied by differences in the microbial community composition where the relative amount of fungal biomass decreased and actinomycete biomass increased with soil depth. The results also showed that the vertical gradients occur at a small scale: the upper and lower parts of the H horizon only 1 cm apart were significantly different with respect to seven out of nine activities, microbial biomass content and community composition.     

Perennial energy cropping systems affect soil enzyme activities and bacterial community structure in a South European agricultural area

In recent decades, perennial rhizomatous grasses have been introduced in the Po Valley (Northern Italy), not only to produce bioenergy, but also to face the loss of soil organic carbon due to intensive crop management. Given the dual purpose of perennial energy crops, this work was intended to evaluate changes induced by the introduction of these crops on soil microbial community structure and on soil functionality. We compared a 9 year-old land conversion to two perennial energy crops, giant Miscanthus (Miscanthus sinensis × giganteus) and giant reed (Arundo donax L.), with two 40-year old annual arable systems, continuous wheat and maize/wheat rotation. The structure of the bacterial community was studied by the fingerprinting method of denaturing gradient gel electrophoresis (PCR-DGGE) amplifying 16S rRNA fragments, while the functional aspects of soil were investigated through the determination of three soil enzyme activities involved in soil carbon, nitrogen, and phosphorous cycles (β-glucosidase, urease, and alkaline phosphatase, respectively). Introduction of perennial energy crops positively stimulated the three soil enzymes, especially in the shallow soil layer (0–0.15 m), where accumulation of carbon and nitrogen was stronger. Enzyme activities were also positively correlated with organic carbon, apart from β-glucosidase. A significant but weaker correlation was also observed between enzyme activities and total nitrogen. The DGGE profiles revealed the relationship between crop types and soil microbial communities. Community richness was higher in perennial than in annual crops, but no effect of soil depth was observed. In opposition, Shannon index of diversity was not influenced by crop type, but only by soil depth with a 32% increase in the shallow layer. We conclude that the introduction of perennial energy crops in a South European soil increases both soil biochemical activity and microbial diversity, related to the ability of these crops to stabilize organic matter in soil. It is thereby evidenced that perennial rhizomatous grasses for energy uses could represent a sustainable choice for the recovery of soils depleted by intensive agricultural management.     

Soil microbial biomass carbon and nitrogen as affected by cropping systems

 The impacts of crop rotations and N fertilization on microbial biomass C (C_mic) and N (N_mic) were studied in soils of two long-term field experiments initiated in 1978 at the Northeast Research Center (NERC) and in 1954 at the Clarion-Webster Research Center (CWRC), both in Iowa. Surface soil samples were taken in 1996 and 1997 from plots of corn (Zea mays L.), soybeans (Glycine max (L.) Merr.), oats (Avena sativa L.), or meadow (alfalfa) (Medicago sativa L.) that had received 0 or 180 kg N ha^–1 before corn and an annual application of 20 kg P and 56 kg K ha^–1. The C_mic and N_mic values were determined by the chloroform-fumigation-extraction method and the chloroform-fumigation-incubation method, respectively. The C_mic and N_mic values were significantly affected (P<0.05) by crop rotation and plant cover at time of sampling, but not by N fertilization. In general, the highest C_mic and N_mic contents were found in the multicropping systems (4-year rotations) taken in oats or meadow plots, and the lowest values were found in continuous corn and soybean systems. On average, C_mic made up about 1.0% of the organic C (C_org), and N_mic contributed about 2.4% of the total N (N_tot) in soils at both sites and years of sampling. The C_mic values were significantly correlated with C_org contents (r≥0.41**), whereas the relationship between C_mic and N_tot was significant (r≤0.53***) only for the samples taken in 1996 at the NERC site. The C_mic : N_mic ratios were, on average, 4.3 and 6.4 in 1996, and 7.6 and 11.4 in 1997 at the NERC and CWRC sites, respectively. Crop rotation significantly (P<0.05) affected this ratio only at the NERC site, and N fertilization showed no effect at either site. In general, multicropping systems resulted in greater C_mic : C_org (1.1%) and N_mic : N_tot (2.6%) ratios than monocropping systems (0.8% and 2.1%, respectively). Received: 9 February 1999