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1.
To describe the compartmentalization of the gut and the microbial activity in the digestive tract, the histology of the gut wall, enzymatic activity, pH of the gut content, abundance and composition of the microbial community (direct counts, plate counts on various media, and phospholipid fatty acid analyses—PLFA) were studied in the Penthetria holosericea larvae. The highest secretion activity was observed in the caeca and in the part of the anterior midgut before caeca openings. A strong increase in pH (10.5) was observed in the anterior part of the midgut. Some enzymes produced in the caeca might have their maximum activity in a different part of the gut as a result of their pH optimum; e.g. amylase was most active in the strongly alkaline anterior part of the mesenteron. Maltase, hydrolyzing products of starch degradation, was most active in the posterior part of the gut and in the ectoperithrophic space. The microbial community was reduced in the anterior part of the midgut. In the posterior part of the gut, bacterial numbers increased and peaked in excrements. Caeca had an abundant microbial community.  相似文献   

2.
The fungus Ulocladium botrytis was isolated from Scutia buxifolia leaf litter and its growth was evaluated on both liquid and solid medium with sodium-carboxy-methylcellulose (CMC, 0.5%) as sole C source at a pH range between 4.0 and 10.0 and the synthesis of cellulose-degrading enzymes on litter. Growth on CMC-agar medium was maximum at pH 6.0, while in liquid CMC cultures, the highest biomass levels were found at pH 8.0 in both cases after 7 days of incubation. Cellulose-degrading enzyme activities such as β-glucosidase (2.40 U dry leaf g−1), cellobiohydrolase (3.92 10−3 U dry leaf g−1), and endoglucanase (2.01 U dry leaf g−1) activities were detected in water-soluble fractions of inoculated leaves after 30 days of incubation. Endoglucanase activity was maximum at pH 6.0 and relatively stable as the pH increase, being 100 and 60% stable at pH 7 and 8, respectively. As a consequence of these enzyme activities, leaf mass was reduced by 5.8%. Our findings suggest that U. botrytis contains a cellulose-degrading enzyme complex that, unlike other cellulolytic systems, can degrade recalcitrant plant litter under alkaline conditions.  相似文献   

3.
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.  相似文献   

4.
Lipases are glycerol ester hydrolases (EC 3.1.1.3) produced by a wide range of microorganisms. They catalyse the hydrolysis of different esters depending on the water content of the reaction medium. Here, we developed a simple methodology to quantify lipase hydrolysis activities using two different litters: a litter of Quercus pubescens (QP) and a litter of both Q. pubescens and Q. ilex. Different p-nitrophenyl esters were used to test hydrolysis in a reaction medium with an organic solvent (heptane). We showed that these activities depended on the amount of litter, the incubation time and the substrate concentration and that they increased with temperature. Furthermore, the lipases from the studied litters were still active after 2 h at 70 °C. These activities showed common properties of lipases: the highest activities were obtained with a medium-acyl chain substrate, p-nitrophenyl laurate. Moreover abiotic hydrolysis with short-chain acyl substrates was observable. The following parameters are recommended to quantify hydrolysis activities of lipases in litters: 10 mM of p-nitrophenyl laurate in 2 ml of heptane, 1 g of litter, 2 ml of water incubated at 30 °C for 2 h.  相似文献   

5.
In a Mediterranean climate, water stress is one of the principal constraints on proper forest ecosystem functioning. Drought influences rates of organic matter degradation by affecting microbial growth and enzyme activities. The objectives of this study were: (i) to evaluate the effect of repeated drying-rewetting cycles on cellulase, alkaline phosphatase and fluorescein diacetate (FDA) hydrolase activities of three distinct Quercus ilex L. litter layers, and (ii) to investigate the effect of these cycles on γ-irradiated litters in order to distinguish the abiotic influence on the fluctuations observed. Results, for all three layers, showed high correlations between litter water content and enzyme activities. Under mesocosm conditions, and using non-sterilized litter samples, cellulase, alkaline phosphatase, and FDA activities significantly decreased or increased during drying or rewetting cycles respectively. Significant differences were also found when evaluating the effect of litter depth on enzyme activities, the intermediate depth (OLv layer) generally being the most active. For γ-sterilized samples, FDA activity still fluctuated with drying-rewetting cycles. Assays showed that pre-humidification of γ-irradiated litter increased FDA activity two-fold in the first 30 min. All these results have shown that, following drying-rewetting cycles, some of the fluctuations occur independently of microbial growth, suggesting abiotic interactions, such as desorption, in combination with both solvatation status and conformational changes of enzymes.  相似文献   

6.
Species of Trichoderma typical of cool geographic regions possessed lower temperature optima and maxima than species from warm climatic regions. T. viride Pers. ex S.F. Gray and T. polysporum (Link ex Pers.) Rifai had temperature maxima ranging from 28–31°C and grew much better than other species at 7°C. The temperature maxima of T. koningii Oud. ranged from 32–35°C, T. hamatum (Bon.) Bain. from 30–35°C, T. harzianum Rifai from 30–38°C and T. pseudokoningii Rifai and T. saturnisporum Hammill from 40–41°C.Isolates of Trichoderma varied in their responses to CO2-enriched atmospheres and the response was pH dependent. The largest responses were obtained on a medium of pH 7.5 as compared to an acid medium of pH 4.4. As the CO2 level increased from 2 to 10 per cent, growth was reduced on an acid medium and increased on the alkaline medium as compared to cultures incubated in air. In air the optimum pH for Trichoderma ranged between 3–7 and 4.7. However, as the CO2 concentration was increased to 10 per cent, growth was nearly as good at pH 7.5 as at pH 4.4.The addition of HCO3? to an alkaline medium strongly inhibited Trichoderma while having little effect on fungi isolated from roots or a strongly alkaline habitat. Low moisture content of litter was shown to have a variable effect on Trichoderma species and may be important in the ecology of Trichoderma. Salt (NaCl) concentration is not considered to be an important ecological factor.  相似文献   

7.
《Applied soil ecology》2007,35(3):553-565
The underlying influences of soil flooding, pH level and soil-inhabiting Diaprepes abbreviatus (L.) root weevil larval feeding in citrus were examined in two separate greenhouse studies, rootstock × flooding × Diaprepes-larvae (RFD) and liming × rootstock × flooding × Diaprepes-larvae (LRFD). Our objectives were to determine the combined effects of soil flooding and pH level on survival and growth of Diaprepes root weevil larvae to gain insights of insect-environmental relations for the weevil control. We used a Floridana sandy loam (pH 4.8) from a citrus grove infested by Diaprepes root weevil in center Florida. The RFD experiment consisted of two citrus rootstocks (Swingle and Smooth Flat Seville), three flooding durations (0, 20, and 40 days) and two larval infestation rates (0 and 5 larvae) for 40-day feeding. The LRFD experiment consisted of two citrus rootstocks (Swingle and Carrizo), three pH levels (non-limed control, and target pH 6 and 7), two flooding durations (0 and 40 days), and two larval rates (0 and 5 larvae) for 56-day feeding. Dolomite (54% CaCO3 and 46% MgCO3) was used for soil liming in the LRFD. Treatments were arranged with 15 replicates in a completely randomized design. In the RFD, flooded soil pH was 0.3 units higher than non-flooded soil and larval survival was the lowest in the longest flooded treatment (P < 0.05). In the LRFD, soil pH increased 0.5–0.9 units for the target pH 6, and 0.7–1.1 units for the target pH 7. The effects of rootstock, liming and flooding treatments and their interactions were significant on soil pH and larval survival (P < 0.05). Larval survival decreased from 80% to 60% with increasing soil pH from 4.8 to 5.7. Total larval weight per seedling decreased significantly from 0.060 g to 0.012 g when the soil pH increased from 5.1 to 5.7. Flooding reduced larval survival and growth, and increasing acidic soil pH by 1 unit would be an option for controlling soil acidity and for promoting integrated management of Diaprepes root weevil in citrus.  相似文献   

8.
Phenol oxidase, peroxidase and organic matter dynamics of soil   总被引：2，自引：0，他引：2  
Extracellular enzymes mediate the degradation, transformation and mineralization of soil organic matter. The activity of cellulases, phosphatases and other hydrolases has received extensive study and in many cases stoichiometric relationships and responses to disturbances are well established. In contrast, phenol oxidase and peroxidase activities, which are often uncorrelated with hydrolase activities, have been measured in only a small subset of soil enzyme studies. These enzymes are expressed for a variety of purposes including ontogeny, defense and the acquisition of carbon and nitrogen. Through excretion or lysis, these enzymes enter the environment where their aggegrate activity mediates key ecosystem functions of lignin degradation, humification, carbon mineralization and dissolved organic carbon export. Phenol oxidases and peroxidases are less stable in the environment than extracellular hydrolases, especially when associated with organic particles. Activities are also affected, positively and negatively, by interaction with mineral surfaces. High spatiotemporal variation obscures their relationships with environmental variables and ecological process. Across ecosystems, phenol oxidase and peroxidase activities generally increase with soil pH, a finding not predicted from the pH optima of purified enzymes. Activities associated with plant litter and particulate organic matter often correlate with decomposition rates and potential activities generally increase with the lignin and secondary compound content of the material. At the ecosystem scale, nitrogen amendment alters the expression of phenol oxidase and peroxidase enzymes more broadly than culture studies imply and these responses correlate with positive and negative changes in litter decomposition rates and soil organic matter content. At the global scale, N amendment of basidiomycete-dominated soils of temperate and boreal forest ecoystems often leads to losses of oxidative enzyme activity, while activities in grassland soils dominated by glomeromycota and ascomycetes show little net response. Land use that leads to loss of soil organic matter tends to increase oxidative activities. Across ecosystems, soil organic matter content is not correlated with mean potential phenol oxidase and peroxidase activities. A multiple regression model that includes soil pH, mean annual temperature, mean annual precipitation and potential phenol oxidase activity accounts for 37% of the variation in soil organic matter (SOM) content across ecosystems (n = 63); a similar model for peroxidase activity describes 32% of SOM variance (n = 43). Analysis of residual variation suggest that suites of interacting factors create both positive and negative feedbacks on soil organic matter storage. Soils with high oxygen availability, pH and mineral activity tend to be substrate limited: high in situ oxidative activities limit soil organic matter accumulation. Soils with opposing characteristics are activity limited: low in situ oxidative activities promote soil organic matter storage.  相似文献   

9.
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 (PI), 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 (PO). Indeed, principal component analyses (PCA) and multiple regressions showed that temperature and bacterial communities were also implicated in phosphatase dynamics and PO 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 PI 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 PO mineralisation of the litter and in the regulation of P microbial metabolism.  相似文献   

10.
The dispersal ability, home range size and habitat preference of sixth instar larvae of the widespread cantharid species Cantharis fusca (L.) and C. livida (L.) were studied in a mark–recapture experiment in a meadow–field (winter grain) area between autumn and spring in 1999/2000. The main results and conclusions were: (i) The mean dispersal velocity of C. fusca/C. livida larvae was 1.4/1.6 m d–1 with a maximum of 3.2/2.3 m d–1. The larvae were able to disperse more than 100 m during their larval development, demonstrating that larvae and not only adults contribute to spreading. (ii) The average home range area of seven C. fusca individuals was 12.9 m2 (minimum 8 m2/maximum 19 m2). The low number of multiple recaptures and the large distances larvae can cover indicate that the real home range size was underestimated. (iii) C. fusca larvae significantly preferred the meadow area compared to the bare ground of the field. This can be explained by the meadow's higher plant cover and humidity C. livida specimens that were released one month later and recaptured only in low numbers showed no such preference. (iv) Due to the high dispersal ability of soldier beetle larvae, immigration from meadows and grass bulks of boundary strips into the crop margins and inner field areas is possible; it can be augmented by creating constant plant cover, e.g. through winter grain or cover crops.  相似文献   

11.
Litter decomposition is an important process of C and N cycling in the soil. Variation in the response of litter decomposition to nitrogen (N) addition (positive, negative or neutral) has been observed in many field studies. However, mechanism about variability in individual fungal species response to N addition has not yet been well demonstrated in the literature. Therefore, the objective of this study was to investigate the effects of N addition and litter chemistry properties on litter decomposition and enzyme activities of individual fungi. Three fungal species (Penicillium, Aspergillus, and Trichoderma) were isolated from a subtropical mixed forest soil. An incubation experiment was conducted using the individual fungi with two types of litter (leaf of Pinus massoniana and needle of Cryptocarya chinensis) and different N addition levels (0, 50 and 100 for N-deficient treatments, and 500 and 1000 μg N for N-excessive treatments). Cumulative CO2-C, enzyme activities, and lignin and cellulose loss were measured during the incubation period of 60 days. Litter decomposition and enzyme activities significantly varied with the fungal species, while the N addition and litter types greatly affected fungal enzyme activities. The N treatments significantly increased lignin-rich needle decomposition by lignocellulose decomposers (Penicillium and Aspergillus) but did not affect their leaf decomposition. On the contrary, The N treatments stimulated leaf decomposition by cellulolytic species (Trichoderma) but did not affect its needle decomposition. Correlation analysis showed that lignin in the litter was the key component to affect litter decomposition. Activities of N-acetyl-β-glucosaminidase and phenol oxidase were both positively correlated to litter decomposition. The fungi (Penicillium and Aspergillus) with higher production of N-acetyl-β-glucosaminidase showed higher litter decomposition ability. The low N addition levels stimulated Penicillium and Aspergillus litter decomposition, but they still required more N source (e.g., litter N source) to support decomposition. Depressed fungal litter N uptake (lower N-acetyl-β-glucosaminidase activities) only occurred at the highest N addition level. Litter decomposition of Trichoderma depended more on external N and its litter decomposition capability was the lowest among the three species.  相似文献   

12.
《Soil biology & biochemistry》2001,33(4-5):659-665
We tested whether elevated UV-B radiation applied to Quercus robur, a principal climax species of northern Europe, would influence concentrations of polyphenolics (Folin–Denis tannins and lignin), phenylpropanoid moieties of lignin, carbohydrates (monosaccharides and holocellulose), or nutrient elements (K, Ca, Mg, P and N) in recently-abscised leaf litter. Saplings of Q. robur were exposed for 2 years at an outdoor facility in the UK to a 30% elevation above the ambient amount of erythemally-weighted UV-B (280–315 nm) radiation under arrays of fluorescent lamps with cellulose diacetate filters, which transmitted both UV-B and UV-A (315–400 nm) radiation. Saplings were also exposed to elevated UV-A alone under arrays of lamps with polyester filters and to ambient radiation under non-energised arrays of lamps. We found little evidence that elevated UV-B radiation influenced leaf litter quality. Data pooled for both years indicated an 8% increase in vanillic acid concentration in litter from polyester-filtered lamp arrays, relative to non-energised arrays, and 8% and 6% increases, respectively, in concentrations of acetovanillone in litter from polyester- and cellulose diacetate-filtered lamp arrays, relative to non-energised lamp arrays. Arabinose concentration in litter from cellulose diacetate-filtered lamp arrays was 3% higher than in litter from polyester-filtered arrays, and glucose concentration in litter from cellulose-diacetate filtered lamp arrays was increased by 6%, relative to non-energised arrays. There were no main effects of elevated UV on the concentrations of holocellulose, polyphenolics or nutrient elements. We conclude that exposure to elevated UV-B does not substantially influence the initial chemical composition of Q. robur leaf litter and that any increases in UV-B radiation arising from ozone depletion over northern mid-latitudes will be unlikely to affect nutrient cycling and decomposition in Quercus woodlands through effects on litter quality alone.  相似文献   

13.
Soil-dwelling insect herbivores are significant pests in many managed ecosystems. Because eggs and larvae are difficult to observe, mathematical models have been developed to predict life-cycle events occurring in the soil. To date, these models have incorporated very little empirical information about how soil and drought conditions interact to shape these processes. This study investigated how soil temperature (10, 15, 20 and 25 °C), water content (0.02 (air dried), 0.10 and 0.25 g g?1) and pH (5, 7 and 9) interactively affected egg hatching and early larval lifespan of the clover root weevil (Sitona lepidus Gyllenhal, Coleoptera: Curculionidae). Eggs developed over 3.5 times faster at 25 °C compared with 10 °C (hatching after 40.1 and 11.5 days, respectively). The effect of drought on S. lepidus eggs was investigated by exposing eggs to drought conditions before wetting the soil (2–12 days later) at four temperatures. No eggs hatched in dry soil, suggesting that S. lepidus eggs require water to remain viable. Eggs hatched significantly sooner in slightly acidic soil (pH 5) compared with soils with higher pH values. There was also a significant interaction between soil temperature, pH and soil water content. Egg viability was significantly reduced by exposure to drought. When exposed to 2–6 days of drought, egg viability was 80–100% at all temperatures but fell to 50% after 12 days exposure at 10 °C and did not hatch at all at 20 °C and above. Drought exposure also increased hatching time of viable eggs. The effects of soil conditions on unfed larvae were less influential, except for soil temperature which significantly reduced larval longevity by 57% when reared at 25 °C compared with 10 °C (4.1 and 9.7 days, respectively). The effects of soil conditions on S. lepidus eggs and larvae are discussed in the context of global climate change and how such empirically based information could be useful for refining existing mathematical models of these processes.  相似文献   

14.
In a previous study, we demonstrated that Suillus granulatus exhibits positive growth responses to added litter. From this, we hypothesized that this positive growth response (increased number of EM root tips) would be accompanied by increased activities of enzymes that enable EM fungi to utilize litter as a nutrient source. We tested this hypothesis by adding sterile litter in replicate treatment/control blocks, and assaying cellulase, laccase and phosphatase activities in the dominant fungal species, S. granulatus. We used healthy, growing EM roots for both treatment and control assays. Activities of all enzymes increased significantly in response to litter addition (P < 0.05 laccase; P < 0.01 cellulase; P < 0.001 phosphatase). Hence, litter accumulation apparently causes functional as well as structural changes to the EM fungal community that would significantly affect carbon cycling in forest ecosystems.  相似文献   

15.
Enchytraeidae were studied at spruce forest sites (Harz, Germany) differing in their exposure and soil acidity affected by acid deposition. Total density ranged between 38 000 and 59 000 ind. m–2 and biomass between 0.5 and 1 g m–2 d.m. (annual means). Of the seven species recorded, Cognettia sphagnetorum, Marionina clavata, and Achaeta camerani were dominant. The site affected most by acidification had the highest densities and lowest species number. Population dynamics and vertical distributions were affected by climate. Field and laboratory data provide evidence for sexual reproduction in C. sphagnetorum. Substrate preference experiments showed this species to prefer spruce litter from the OL-Horizon to that from the OH-Horizon, and spruce litter to beech litter.  相似文献   

16.
《Applied soil ecology》2006,31(1-2):32-42
Microcosm and litterbag experiments were conducted to determine the effects of litter quality, soil properties and microclimate differences on soil carbon (C) and nitrogen (N) mineralization in alley cropping systems. Bulk soils were collected from 0 to 20 cm depth at three sites: a 21-year old pecan (Carya illinoinensis)/bluegrass (Poa trivialis) intercrop (Pecan site) in north-central Missouri, a 12-year old silver maple (Acer saccharinum)/soybean (Glycine max)–maize (Zea mays) rotation (Maple site) in northeastern Missouri and a restored prairie site (MDC site) in southwestern Missouri. Seven tree and crop litters with varying composition were collected, including pecan, silver maple, chestnut and walnut leaf litter (tree litter) and maize, soybean and bluegrass residues (crop litter). Aerobic microcosm incubations were maintained at 25 °C and a soil water potential of −47 kPa. Unamended MDC soil mineralized 24 and 18% more CO2 than the Pecan and Maple soils, respectively. Soil amended with crop litter mineralized on average 32% more CO2 than when amended with tree litter. Net N mineralization from soybean litter was 40 mg kg−1, while all other litter immobilized N for various durations. A double pool and a single pool model best described C and N mineralization from amended soils, respectively. Cumulative CO2 mineralized, labile C fraction (C1) and potentially mineralizable C (C0) were correlated to litter total N and lignin contents and to (lignin + polyphenol):N ratio. In the field, bluegrass litter decomposed and released N twice as fast as pecan leaf litter. Soybean, maize and silver maple litter released 84, 75 and 63% of initial N, respectively, 308 days after field placement, while no differences in mass loss was observed among the three litter materials. At the Maple site, mass and N remaining, 308 days after field placement was lower at the middle of the alley, corresponding to higher soil temperature and water content. No differences in mass loss and N release patterns were observed at the Pecan site. Microclimate and litter quality effects can lead to differences in nutrient availability in alley cropping systems.  相似文献   

17.
Purpose

Although litter decomposition and nutrient release patterns have been studied in cocoa agroforestry systems in general, studies focusing on organic and conventional cocoa systems are lacking which is critical as organic farms are particularly dependent on nutrient returns from decomposing litter.

Materials and methods

Dynamics in leaf litter decomposition and the mineralisation of macro- and micro-nutrients in organic and conventional cocoa agroforestry systems were studied using the litterbag technique for 12 months.

Results

The average monthly mass loss was more than two times higher on organic farms (9.2–14.4 g month?1) compared to conventional farms (4.2–7.3 g month?1) in the first five months. The annual rate of decomposition (k) was higher on organic farms (1.9) compared to conventional systems (1.4). The time required for 50% (t50) and 99% (t99) decomposition of leaf litter was both lower on organic farms (t50?=?0.4 years, t99?=?2.6 years) than conventional farms (t50?=?0.5 years, t99?=?3.5 years). The estimated k values for macro- and micro-nutrients on organic cocoa systems ranged from 2.3 for calcium to 4.5 for potassium compared to 1.6 (Ca) to 2.8 (K) on conventional farms. The k values of all nutrients (except nitrogen and phosphorus) were significantly greater on organic farms than conventional systems. The estimated k values for both litter decomposition and nutrient mineralisation correlated with soil pH and moisture content, but not initial litter chemistry.

Conclusions

Organic management of smallholder cocoa agroforestry systems enhanced leaf litter decomposition and nutrient mineralisation through improved soil conditions. Thus, organic management of cocoa agroforestry systems may contribute to sustainable cocoa production in smallholder systems through enhanced nutrient return from litter decomposition.

  相似文献   

18.
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.  相似文献   

19.
Periodic swarming by adult train millipedes Parafontaria laminata (Attems, 1909) occurs in central Japan on an 8-year cycle, and the emergence of new adults is highly predictable. Millipede biomass reaches a maximum and feeding habits change upon the emergence of adults. Larvae are geophagous while adults feed on both litter and soil. We hypothesized that the shift in the developmental stages of P. laminata influenced the carbon dynamics in the soil and conducted a field mesocosm experiment in a larch plantation forest over 2 years (1999 and 2000) using three developmental stages: sixth- and seventh-instar larvae and adults. By experimentally manipulating millipede density at four levels, we obtained the following results: larvae were geophagous, while adults consumed both litter and soil (mixed-feeding) and consequently showed stronger density effects on litter decomposition rates than larvae; adult activities in the high-density treatment increased soil microbial biomass but not at low adult densities or at the larval stages; and adults increased the carbon accumulation in soil layers especially at high densities due to their mixed-feeding on litter and soil. We determined that due to synchronized postembryonic development with high densities and changes in feeding habits, the train millipede periodically sequestered carbon in this forest.  相似文献   

20.
Condensed tannins (CT) can strongly affect litter decomposition, but their fate during the decomposition process, in particular as influenced by detritivore consumption, is not well understood. We tested the hypothesis that litter CT are reduced by the gut passage of two functionally distinct detritivores of Mediterranean forests, the millipede Glomeris marginata, and the land snail Pomatias elegans, as a fixed proportion of initial litter CT, but more so in Pomatias since snails are known to have a more efficient enzymatic capacity. Contrary to our hypothesis, both detritivore species reduced litter CT to near zero in their faecal pellets irrespective of the wide range in initial leaf litter CT concentrations of 9-188 mg g−1 d m among three Mediterranean tree species (Pistacia terebinthus, Quercus ilex, Alnus glutinosa) and different decomposition stages of their litter. The almost complete disappearance of CT even from some litter types highly concentrated in CT, due to either degradation by gut microorganism or complexation of CT into insoluble high molecular weight structures, suggests a high “de-tanning” efficiency across functionally distinct detritivore species. The transformation of CT-rich litter into virtually CT-free faecal pellets by detritivores might be highly relevant for the subsequent decomposition process in ecosystems with a high macrofauna abundance and CT-rich plant species such as Mediterranean forests.  相似文献   

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