Phosphomonoesterase,phosphodiesterase, phosphotriesterase,and inorganic pyrophosphatase activities in forest soils in an alpine area: effect of pH on enzyme activity and extractability

We investigated different types of phosphatase activity (phosphomono-, phosphodi-, phosphotriesterase, inorganic pyrophosphatase) in five forest soils in Vorarlberg, Austria. Phosphatase activity was determined both in soils and in soil extracts prepared with different solutions (distilled water, 0.1M sodium pyrophosphate at pH 7, 0.1M sodium phosphate buffer/1M KCl at pH 6.5, and a modified universal buffer at pH 4, 6.5, 9, and 11). High phosphomonoesterase activity in these soils indicated a severe deficiency in available P. Acidic phosphomonoesterase prevailed over alkaline phosphomonoesterase activity. Phosphodiesterase was highest in the least acidic soil but no general trend towards an optimum pH was recognized. Phosphotriesterase activity was observed in only two of the five soils and favoured an alkaline optimum pH; this activity was not detected in strongly acid soils. Inorganic pyrophosphatase activity was high in soils with no phosphotriesterase. Phosphomonoesterase, phosphodiesterase and inorganic pyrophosphatase activities were much lower in soil extracts than in soils.     

Phosphorus limitation in microorganisms leads to high phosphomonoesterase activity in acid forest soils

We addressed the mechanistic basis for a negative correlation between soil pH and phosphomonoesterase activity, often found in various soils. Also in the present study, a significant negative correlation was observed between soil pH and phosphomonoesterase activity measured at pH 6.5 in Japanese acidic forest soils (3 Inceptisols, 3 non-allophanic Andisols, and 2 allophanic Andisols). A hypothesis that higher activity of phosphomonoesterase in acid forest soils results from increased synthesis of phosphomonoesterase by microorganisms in response to P limitation was tested. Soils with lower pH showed a lower optimum pH for phosphomonoesterase activity and greater activity at the optimum pH than other soils. To assess nutrient limitations of the soil microbial community, the effects of addition of C, N, or P on phosphomonoesterase and dehydrogenase activities, which is an intracellular enzyme and the activity of which reflects overall microbial activity, were examined in the soil samples. Addition of P increased dehydrogenase activity in some forest soils. Also, microorganisms in some soils were co-limited by C, N, and P. Response ratios (RR) of phosphomonoesterase and dehydrogenase activities in P-amended soil to their activity in non-amended soil were used to evaluate the response of soil microorganisms to P limitation. The ratio of RR-dehydrogenase to RR-phosphomonoesterase was strongly correlated with phosphomonoesterase activity at the optimum pH (P < 0.01). The results indicate that P limitation accounts for higher phosphomonoesterase activity in the more acid forest soils.     

Phosphatase activity and phosphorus fractions in Karri (Eucalyptus diversicolor F. Muell.) forest soils

Summary Karri forest soils contain negligible concentrations of labile-P, low concentrations of total P and more P in organic forms than inorganic. The ratio of organic P to inorganic P was lowest (1:2) in recently burnt surface soils and greatest (7:1) at depth in soil that had been undisturbed for long periods of time. Phosphomonoesterase and phosphodiesterase activities (to 10 cm depth, phosphomonoesterase 700–1300; phosphodiesterase 2000–2400 g nitrophenol released h^-1 g^-1 fresh weight) were comparable to those in other, organically rich forest soils. The optimum pH for phosphatase activities were within 1–2 units of soil pH (6) and little reduction in activity was observed over the pH range 4–8. Phosphatase activity was reduced by air-drying (up to 20-fold reduction) and was almost entirely absent in soils that were heat-affected as a result of logging/burning operations. Neither phosphomonoesterase nor phosphodiesterase were directly related to soil P fractions or total P. A reduction in P demand is postulated as the cause of reduced phosphatase activity and the increased concentration of organic P with increasing soil depth.     

土壤磷酸酶活性对施肥-种植-耕作制度的响应

植物所需的磷素营养,主要来源于土壤内源、外源无机磷。而大量存在的有机磷类化合物在土壤磷酸酶的作用下催化水解为无机磷,不仅是土壤内源无机磷的主要来源,也是土壤磷素循环的一个重要的环节。土壤磷酸酶在土壤中主要以吸附态的形式存在,其活性受到施肥、种植和耕作制度的影响。本文对国内外不同施肥方式、种植及耕作制度下土壤磷酸酶(酸性磷酸酶、中性磷酸酶、碱性磷酸酶、磷酸二酯酶、磷酸三酯酶、焦磷酸酶)活性响应进行综述,拟为不同农业管理制度下土壤磷酸酶活性的调节提供依据。     

Global patterns of soil phosphatase responses to nitrogen and phosphorus fertilization

Hydrolysis of organic phosphorus(P) by soil phosphatases is an important process of P cycling in terrestrial ecosystems, significantly affected by nitrogen(N) and/or P fertilization. However, how soil acid phosphatase(ACP) and alkaline phosphatase(ALP) activities respond to N and/or P fertilization and how these responses vary with climatic regions, ecosystem types, and fertilization management remain unclear. This knowledge gap hinders our ability to assess P cycling and availability from a glo...     

Response of phosphomonoesterases in soils to chloroform fumigation

The chloroform fumigation technique has been successfully employed to quantify intracellular and extracellular urease and arylsulfatase activities in soil. In this study, the same approach was evaluated for its ability to differentiate between various pools of phosphomonoesterase activities in soils and reference proteins purified from plant and microbial sources. The activities of acid and alkaline phosphatases were assayed in 10 surface soils and reference proteins at their optimal pH values before and after chloroform fumigation and in the presence and absence of toluene. Chloroform fumigation decreased the activities of acid and alkaline phosphatases in soils, on average, by 6 and 8%, respectively. Similarly, the activities of two purified reference enzyme proteins were decreased after fumigation, with acid and alkaline phosphatase activities exhibiting a reduction of 17 and 8%, respectively. Toluene treatment caused an increase in the activities of acid and alkaline phosphatases by 8 to 18% in nonfumigated soils, but showed no effect in the fumigated soils. Average enzyme protein concentrations, calculated for the 10 soils based on the activity values of the soils and the specific activity of the purified enzymes (i.e., activity values per mg protein), were 22.5 and 2.1 mg protein (kg soil)^—1 for acid and alkaline phosphatase, respectively. The decrease in enzyme activity by the fumigant was either by direct denaturing of the periplasmic and extracellular portion of the particular protein after lysis of the microbial cell membrane, by absorption and/or inhibition of the released phosphomonoesterases by organic and inorganic constituents or by degradation of the protein by soil proteases. The ratios of acid phosphatase protein concentrations relative to organic C in six soils were significantly, but negatively correlated with soil organic C, suggesting differences in organic C quality. Comparison of the activity values of soil phosphatases with those of the protein concentrations present in soils indicated that alkaline phosphatase has greater catalytic efficiency than does acid phosphatase.     

Annual dynamics of phosphatase activities in an evergreen oak litter: influence of biotic and abiotic factors

As part of a study of the processes involved in litter biodegradation, we considered the variations over 1 year of the phosphatase activities in sclerophyllous evergreen oak litter (Quercus ilex L.). Evergreen oak is representative of tree species in the forests of the French Mediterranean area. Acid (E.C. 3.1.3.2.) and alkaline (E.C. 3.1.3.1.) phosphatases, were measured over 13 months in the forest litter, along with several biotic and abiotic variables, potentially involved in the regulation of these enzymes. These comprised moisture, temperature, pH, water-extractable inorganic P (P_I), fungi, culturable heterotrophic bacteria and protein concentrations. Moisture considerably affected the production of proteins and acid phosphatases, probably formed by litter microorganisms. This result corroborated the study of Criquet et al. [Soil Biology and Biochemistry 34 (2002) 1111] which indicated that rainfall was the most important factor regulating the production and the activity of numerous enzymes in sclerophyllous forest litter. However, it appeared that moisture cannot alone predict all of the variations in phosphatase activities and the mineralisation rate of organic P (P_O). Indeed, principal component analyses (PCA) and multiple regressions showed that temperature and bacterial communities were also implicated in phosphatase dynamics and P_O mineralisation. Acid phosphatases were negatively correlated with the temperature, whilst alkaline phosphatases were positively correlated with this variable. The significant correlation obtained between bacteria and P_I concentrations, and the lack of correlation between bacteria and both acid and alkaline phosphomonoesterases, suggest that other important phosphatase types, such as phosphodiesterases, must be strongly implicated in P_O mineralisation of the litter and in the regulation of P microbial metabolism.     

Phosphatases in soils

Most studies on phosphatase activity in soils have been concerned with acid phosphatase. This study was conducted to determine the activity of phosphomonoesterases (acid and alkaline phosphatases), phosphodiesterase, and “phosphotriesterase”. The results indicate that acid phosphatase is predominant in acid soils and that alkaline phosphatase is predominant in alkaline soils. With universal buffer, the pH optima of phosphodiesterase and phosphotriesterase were at pH 10. The activities of these phosphatases in soils were much lower than those of the acid and alkaline phosphatases. Studies on the effects of various soil treatments on the activity of phosphatases in soils indicated that air-drying increased the activity of acid phosphatase and phosphotriesterase, decreased the activity of alkaline phosphatase, but did not affect the activity of phosphodiesterase. Steam sterilization of soils at 121 C for 1 h inactivated alkaline phosphatase, phosphodiesterase, and phosphotriesterase, but did not completely inactivate acid phosphatase. Addition of toluene to the incubation mixture did not markedly affect the activity of acid phosphatase, alkaline phosphatase, phosphodiesterase, but increased the activity of phosphotriesterase in soils.Studies of the kinetic parameters of phosphatases in the soils studied showed that the K_m values ranged from 1.11 to 3.40 mm for acid phosphatase. from 0.44 to 4.94 mm for alkaline phosphatase, and from 0.25 to 1.25 mm for phosphodiesterase. Expressed as μg p-nitrophenol released·h^?1·g^?1 soil, the V_max values ranged from 200 to 625 for acid phosphatase, from 124 to 588 for alkaline phosphatase, and from 46 to 127 for phosphodiesterase. The substrate of phosphotriesterase (tris-p-nitrophenyl phosphate) is insoluble in water; hence, the K_m and V_max values of this enzyme in soils could not be determined.     

Characterization of extracellular phosphatase activities in periphytic biofilm from paddy field

Periphytic biofilms exist widely in paddy fields, but their influences on the hydrolysis of organic phosphorus(P) have rarely been investigated. In this study,a periphytic biofilm was incubated in a paddy soil solution, and hydrolysis kinetic parameters(half-saturation constant(Km) and maximum catalytic reaction rate(Vmax)), optimal environmental conditions, substrate specificity, and response to different P regimes of the phosphatase activities in the periphytic biofilm were determined, in order to characterize extracellular phosphatase activities in periphytic biofilms from paddy fields. The results indicated that the periphytic biofilm could produce an acid phosphomonoesterase(PMEase), an alkaline PMEases, and a phosphodiesterase(PDEase). These three phosphatases displayed high substrate affinity, with Km values ranging from 141.03 to 212.96 μmol L^-1. The Vmax/Km ratios for the phosphatases followed the order of alkaline PMEase > acid PMEase > PDEase, which suggested that the PMEases, especially the alkaline PMEase, had higher catalytic efficiency. The optimal pH was 6.0 for the acid PMEase activity and 8.0 for the PDEase activity, and the alkaline PMEase activity increased with a pH increase from 7.0 to 12.0. The optimal temperature was 50℃ for the PMEases and 60℃ for the PDEase. The phosphatases showed high catalytic efficiency for condensed P over a wide pH range and for orthophosphate monoesters at pH 11.0, except for inositol hexakisphosphate at pH 6.0. The inorganic P supply was the main factor in the regulation of phosphatase activities. These findings demonstrated that the periphytic biofilm tested had high hydrolysis capacity for organic and condensed P,especially under P-limited conditions.     

Hydrolases extracted from soil: Their properties and activities

The pH optima and stabilities of some hydrolases extracted by pyrophosphate from two different soils were determined for phosphatase, urease, casein and benzoylargininamide-hydrolysing proteases. Hydrolases activities of soil extracts were more resistant to thermal denaturation than their respective commercial preparations. Extracted phosphatases exhibited a marked stability to temperature and to proteolysis.By exhaustively ultrafiltering soil extracts against 0.1 M pyrophosphate at pH 7.1 fractions of mol. wt higher and lower than 100,000 were obtained. Ultrafiltration increased the total activities of extracted ureases and phosphatases while those of casein and benzoylargininamide-hydrolysing proteases were decreased. Both on an organic C and an N basis, specific activities of ureases and phosphatases increased after ultrafiltration.     

芦苇根际土壤有机磷组分的季节变化及与磷酸酶活性的关系

通过野鸭湖湿地一年实验研究了芦苇根际土壤中各组分有机磷含量随植物生长的变化规律,分析了不同有机磷组分与磷酸单酯酶、磷酸二酯酶活性间的关系。结果表明:有机磷含量分布为活性有机磷(L-OP)中活性有机磷(ML-OP)中稳定性有机磷(MR-OP)高稳定性有机磷(HR-OP),各组分含量均随芦苇生长先降低后升高。在芦苇对养分需求最大的旺盛生长期,L-OP、ML-OP含量达到最低值,分别为2.46、3.27 mg/kg;在此阶段,MR-OP、HR-OP含量也有所降低。在有机磷矿化过程中,HR-OP一定程度上可转化为ML-OP,ML-OP与MR-OP主要转化为L-OP。磷酸单酯酶与磷酸二酯酶活性均随芦苇生长先降低后升高,在其旺盛生长期达到最低值,分别为Ph OH 0.37 mg/(g·h)和PN 62?g/(g·h)。磷酸酶活性均与L-OP、ML-OP、HR-OP含量呈极显著或显著正相关,活性磷含量的高低对磷酸酶活性有明显的影响作用,两种磷酸酶在一定程度上也可水解转化稳定性高的有机磷组分。衰亡期的芦苇,其衰败的老根及脱落物可间接促进磷酸酶活性。     

葡萄糖添加对不同演替阶段森林土壤微生物及酶化学计量特征的影响

糖类作为一种重要的根系分泌物,如何影响土壤微生物及酶化学计量特征目前尚不清楚,制约着人们对上述过程的认识。为探究糖类对森林生态系统中土壤微生态环境和酶活性的影响,以黄土高原子午岭地区森林演替先锋(山杨林)、中期(油松林)和气候顶级群落(辽东栎林)为研究对象,通过野外土壤采样、添加3种不同浓度的葡萄糖(0.1,0.5,1 g/kg干土),和室内培养的方法,研究了葡萄糖添加对土壤微生物量和酶活性及化学计量的影响。结果表明:(1)随着森林演替,土壤中速效磷(SAP)、硝态氮(NO^-₃-N)等速效养分显著降低。在葡萄糖影响下,3种林地土壤全氮(TN)降低,山杨林土壤C/N值显著大于油松林和辽东栎林。(2)随着森林演替,山杨林和辽东栎林微生物碳(MBC)和微生物氮(MBN)的值显著大于油松林,均为先减小后增加。随葡萄糖浓度增加,3种林地MBC和MBN均增加,微生物(MBP)呈波动趋势。(3)山杨林和辽东栎林土壤酶活性均显著大于油松林。随葡萄糖浓度增加,油松林和辽东栎林4种酶活性均为先增加后减小。BG/(LAP+NAG)、BG/AP和(LAP+NAG)/AP辽东栎林的值最大,山杨林和辽东栎林的值显著大于油松林。(4)RDA分析表明,土壤酶、微生物量及其酶活性分别与有机质(SOC),MBC有着显著性正相关关系,土壤酶活性(除NAG)与pH值均呈显著负相关。本研究说明碳输入增加了3种林分土壤的激发效应,土壤微生物量增加,降低了土壤TN含量,改变了土壤养分化学计量,进而加剧了油松林地微生物N限制和辽东栎林地微生物P限制,影响根际土壤有机质分解和养分代谢等过程,从而影响了森林演替过程。     

根际pH对玉米利用磷酸单酯和双酯盐的影响

【目的】土壤有机磷在土壤全磷中占有很大比重,是植物潜在的有效磷源,但必须通过磷酸酶的水解作用释放出无机磷才能被植物利用。土壤中有机磷的主要形式为磷酸单酯和磷酸双酯。本研究中,我们探讨了无菌条件下不同形态的氮源引起的根际pH变化如何影响植物对这两种有机磷的活化利用。【方法】采用琼脂无菌培养体系种植玉米,向玉米植株供应两种形态的氮源和磷源, 氮源为硝态氮和铵态氮,磷源为植酸钙和卵磷脂,植酸钙属于磷酸单酯盐,卵磷脂属于磷酸双酯盐。不同的供氮形态会导致根际pH变化,进而研究根际pH变化对磷酸单酯盐和磷酸双酯盐的活化利用所产生的影响。【结果】当给玉米供应铵态氮时,根际pH从5.5降至4.0; 供应硝态氮时,根际pH升至6.6。测定玉米根际的琼脂中根系分泌的磷酸单酯酶和磷酸双酯酶活性发现,磷酸单酯酶活性在pH 6.0~7.0之间最高,磷酸双酯酶活性在pH 7.0~8.0之间达到最高。无论以植酸钙还是卵磷脂为有机磷源,相对于铵态氮处理,硝态氮处理能够使根际保持较高的磷酸单酯酶或磷酸双酯酶活性。有机磷的水解过程由磷酸酶活性和底物有效性两个因素控制,而植酸钙的水解受根际pH影响很大,在一定pH范围内,植酸钙的溶解度随根际pH值降低而升高,有效态磷浓度的增加,使得磷酸酶的底物有效性提高。在供应铵态氮时,根际pH值降低,玉米对植酸钙的利用效率高于硝态氮处理,尽管供硝态氮时磷酸单酯酶活性更高。同时,在供应铵态氮条件下,植株对植酸钙的利用率要显著高于卵磷脂,原因在于虽然磷酸双酯酶和磷酸单酯酶活性较低,由于植酸钙的溶解度较大,它的底物有效性更高。因此,植酸钙处理中植株的磷含量更高。相反,在供应硝态氮时,植酸钙溶解度减小而两种磷酸酶活性较高,卵磷脂处理中植株的磷含量更高。【结论】土壤中有机磷的水解过程由磷酸酶活性和有机磷底物有效性两个因素控制,酶活性与根际pH密切相关。本研究说明土壤有机磷的活化必须首先转化为溶解于水溶液中的状态,才能作为磷酸酶的底物被催化水解。我国长期施用化肥导致北方土壤大范围酸化,这种酸化无疑对土壤固有或随有机物料进入农田的有机磷的活化利用是具有重要贡献的,应该在北方土壤养分管理中应加以考虑。     

Hydrogen oxidation activities in soil as influenced by pH,temperature, moisture,and season

Summary Hydrogen oxidation in soil was measured at low (1 ppmv) and high (300 ppmv) H₂ concentrations to distinguish between the activities of abiontic soil hydrogenases and Knallgas bacteria, respectively. The two activities also showed distinctly different pH optima, temperature optima, and apparent activation energies. The pH optima for the soil hydrogenase activities were similar to the soil pH in situ, i.e., pH 8 in an slightly alkaline garden soil (pH 7.3) and pH 5 in an acidic cambisol (pH 4.6–5.4). Most probable number determinations in the alkaline acidic soils showed that Knallgas bacterial populations grew preferentially in neutral or acidic media, respectively. However, H₂ oxidation activity by Knallgas bacteria in the acidic soil showed two distinct pH optima, one at pH 4 and a second at pH 6.4–7.0. The soil hydrogenase activities exhibited temperature optima at 35–40°C, whereas the Knallgas bacteria had optima at 50–60°C. The apparent activation energies of the soil hydrogenases were lower (11–23kJ mol^-1) than those of the Knallgas bacteria (51–145 kJ mol^-1). Most of the soil hydrogenase activity was located in the upper 10 cm of the acidic cambisol and changed with season. The seasonal activity changes were correlated with changes in soil moisture and soil pH.     

Quantitative assessment of hydrolase production and persistence in soil

The aim of this work was to calculate indices of hydrolase production (Pr) and persistence (Pe) through simple arithmetical calculations. Changes in acid and alkaline phosphomonoesterase, phosphodiesterase, urease, protease, and β-glucosidase activities were monitored under controlled conditions in seven soils with a wide range of properties, in which microbial growth was stimulated by adding glucose and nitrogen. Glucose mineralization was monitored by CO₂–C evolution, and microbial growth was quantified by determining the soil adenosine triphosphate (ATP) content. Hydrolase Pr and Pe indices were numerically quantified by the following relationships: Pr = H / t _H and Pe = (r / H)Δt, respectively, where H indicates the peak value of each measured hydrolase activity, t _H is the time of the peak value, r indicates the residual activity value, and Δt is the time interval t _r − t _H, where t _r is the time of the residual activity value. Addition of glucose and N-stimulated soil respiration increased ATP content and stimulated the production of the measured hydrolase activities in all soils; the measured variable reached a maximum value and then decreased, returning to the value of the control soil. Apart from β-glucosidase activity, whose activity was not stimulated by glucose and N addition, the other measured hydrolase activities showed a trend that allowed us to calculate the Pr and Pe indices using the above-mentioned equations. Acid phosphomonoesterase and protease Pr values were significantly higher in soils under forest or set aside management; the alkaline phosphomonoesterase and phosphodiesterase Pr values were generally higher in the neutral and alkaline soils, and the urease Pr values showed no obvious relationships with soil pH or management. Concerning the persistence of enzyme activities, Pe values of the acid phosphomonoesterase activity were significantly higher in the acidic soils, and those of urease activity were higher in acidic soils and the Bordeaux neutral soil. No relationships were observed between Pe values of alkaline phosphomonoesterase, phosphodiesterase, or protease activities and soil pH or management. The different responses of hydrolases were discussed in relation to soil properties, microbial growth, and regulation at the enzyme molecular level.     

浑河上游河岸带土壤微生物数量及酶活性特征

为了研究浑河上游河岸带土壤质量现状,采用实地调查与实验室分析相结合的方式,测定了其天然灌木草地、次生林、人工松林和玉米地的土壤微生物数量和酶活性特征。结果表明,土壤微生物数量呈现出在天然灌木草地和次生林中最多,人工松林次之,玉米地最少的趋势;细菌在土壤微生物类群中占绝对优势,比例为99.87%~99.94%;土壤蔗糖酶、脲酶、磷酸酶、多酚氧化酶、过氧化氢酶活性变化范围分别为12.95~76.43,0.35~1.80,1.32~6.39,0.35~1.61 mg/(g·d)及0.93~3.27 ml/(g·20 min);5种土壤酶活性呈现出在天然灌木草地和次生林中最多,人工松林次之,玉米地最少的趋势;相关性分析中,细菌数量与5种酶活性显著正相关,放线菌数量与除了过氧化氢酶之外的其他4种酶活性显著正相关,真菌和蔗糖酶、磷酸酶和多酚氧化酶活性显著正相关。4种植被河岸带中,天然灌木草地和次生林具有最高的微生物数量和土壤酶活性,土壤质量高,是很好的河岸带形式。     

Relationships between soil properties and feeding activity of soil fauna in acid forest soils

We investigated the relationships between soil chemical properties, humus form, and feeding activity in eight forest sites in Northrhine‐Westphalia, Germany. The study sites varied in forest type (oak, oak‐hornbeam, spruce, and pine). Three study sites were located under the same climatic conditions, and five study sites were distributed all over Northrhine‐Westphalia. We determined humus form, soil chemical properties, and feeding activity in three replication plots per site. We used the bait‐lamina test to determine feeding activity of soil fauna. Independent of forest type, all study sites were very acid with pH(CaCl₂) values in the Ah horizon between 2.8 and 4.0. The three study sites located under the same climatic conditions showed very homogenous soil chemical properties (pH in Ah: 2.9–3.0), whereas the five other sites varied significantly due to their soil chemical parameters (pH in Ah: 2.8–4.0). All single sites presented feeding activities with a very low spatial heterogeneity. Forest types and climatic conditions were not related to activity of soil fauna. Feeding activity and thickness of the O layer were strongly negatively correlated, whereas the activity was strongly positively correlated to soil pH in the five study sites with a wide range of soil chemical parameters. The three extremely acid forest sites presented significant differences in feeding activities that were not related to soil chemical properties.     

浙江省凤阳山不同林分类型土壤酶活性研究

在浙江省凤阳山自然保护区选取海拔相近的6个典型林分类型(常绿阔叶林、针叶林、针阔混交林、杉木林、毛竹林以及柳杉林),在其林下采集土壤样品,分析了脲酶、蔗糖酶、酸性磷酸酶和过氧化氢酶、蛋白酶5种主要土壤酶活性的变化。结果表明,在6个林分类型中,常绿阔叶林土壤脲酶、过氧化氢酶、酸性磷酸酶活性均较高柳杉林分土壤蔗糖酶活性较高而针叶林则表现出土壤蛋白酶活性最高杉木林则表现出土壤脲酶、蔗糖酶活性较低土壤酶活性具有明显的垂直分层分布,土层越深,土壤酶活性越低同时该地区土壤酶活性与土壤理化性质指标相关性较高,尤其是pH值和有机质含量与土壤酶活性关系最为密切。     

丛枝菌根真菌群落对白三叶草植株生物量磷吸收和土壤磷酸单酯酶活性的影响

丛枝菌根真菌（AMF）在土壤与植物的磷素循环中发挥着关键的作用。采用盆栽实验研究了丛枝菌根真菌群落对白三叶草植株生物量、磷吸收和土壤磷酸单酯酶活性的影响。结果表明,接种不同AMF群落均能显著地促进白三叶草植株的生长及其对磷素的吸收,提高根际土壤磷酸单酯酶的活性。Mnp处理中,白三叶草生物量最大,白三叶草总生物量、茎叶生物量和根系生物量分别比对照处理（-M）提高64.48%、61.48%和84.91%。不同菌根处理中,Mck处理显著地提高白三叶草磷吸收和土壤磷酸单酯酶活性,白三叶草磷吸收总量和茎叶磷吸收量分别比对照（-M）提高107.18%和91.91%,土壤碱性磷酸单酯酶和酸性磷酸单酯酶活性相对对照（-M）分别提高54.33%和138.43%。碱性磷酸单酯酶活性与AMF群落中的Acaullospora属孢子数呈显著的正相关关系,而酸性磷酸单酯酶活性则主要受Paraglomus属孢子数的影响。说明接种AMF群落可显著地影响土壤的磷酸单酯酶活性,从而影响白三叶草的生长及其对磷素的吸收。     

Activity of carbohydrases in the gut of Bibionidae (Diptera) larvae

Dipteran larvae play an important role in the soil of some deciduous forests. They can consume a considerable part of the annual litter fall and produce a large amount of faecal pellets, which are forming an important part of the fermentation horizon of forest soils. We measured the pH changes and assayed the activities and pH optima of saccharolytic enzymes in the digestive tracts of the larvae of Bibio pomonae and Penthetria holosericea (Bibionidae). The pH of the litter offered as a food was about 5. The gut content became highly alkaline (pH about 10) in the anterior part of the midgut and the pH decreased posteriorly and in the hindgut. Excrements were neutral or had slightly alkaline pH (7.5–8.0) in both species. The alkaline pH optima of amylase (9.5–10.0) and maltase (8.0), trehalase and cellobiase (7.0) were the same in both species. Saccharolytic activity showed an optimum at pH 7 in B. pomonae and at pH 8 in P. holosericea. Though there are previously published reports of high assimilation efficiency of bibionid larvae fed in litter (46–76% in B. pomonae), activities of both exo and endocellulases were below the detection limit of saccharolytic and chromolytic assays along a wide pH range (5–10). Possible explanations are discussed.