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1.
The mycelial biomass of fungi decomposing plant materials may be estimated by use of a chitin (hexosamine) assay technique. A method is described together with a discussion of its limitations; whatever the sensitivity of the chemical analysis the validity of the biomass estimate rests on the reliability of the conversion from chitin determination to mycelial dry weight. Estimates made on mycelium of Coriolus versicolor during decay of sawdust from Castanea sativa show a constant increase in biomass. The economic coefficient derived is 47 per cent which is similar to that for the utilization of glucose in liquid culture. Estimates of production are not possible due to lack of information concerning rates of hyphal death and autolysis. The estimated extents of mineral nutrient immobilization are 39% for N, 37% for P and 95% for K.  相似文献   

2.
The side effects of fluazifop-butyl on soil fungal populations and oxygen uptake were studied by incubating soil samples with a range of fluazifop-butyl concentrations (0, 0.6, 3 and 6 μg g?1) over 8 weeks. Cellulose decomposition in soil was also studied in laboratory experiments with the herbicide which was either incorporated in soil or sprayed onto calico squares which were buried in soil. The mycelial dry weight of six fungal species under the effect of the herbicide was also examined. Fluazifop-butyl had no significant effect on total fungal propagule populations at 0.6 μg g?1. At 3 and 6 μg g?1, it caused temporary reduction in fungal populations observed after 1 and 2-wk of incubation. The herbicide had no significant effect on OZ uptake. The decay of calico buried in herbicide-treated soil was generally stimulated, while the decomposition of herbicide-treated calico, buried in untreated soil, was temporary delayed. The mycelial dry weight yields of Aspergillus favus (at 2 and 12 μg mL?1 of fluazifop-butyl) and Cunninghamella echinulata (at 12 μg mL?1) were significantly increased. At 24 μg mL?1 the mycelial dry weight of A. flavus and Alternaria alternata was significantly reduced.  相似文献   

3.
Aboveground biomass, litterfall, leaf weight loss during decomposition, nutrient return and water balance have been estimated in a Scots pine plantation (Pinus sylvestris L.) in the Sierra de la Demanda, Spain, a Mediterranean climatic zone. The aboveground biomass was estimated by cutting and weighing seven trees according to diameter classes, recording the categories of trunk, branches and leaves. The carbon and nitrogen content in the different fractions were also analysed. The results indicate a total biomass of 152.1 Mg·ha–1. The litterfall was 5.8 Mg·ha–1·yr–1, although variations from year to year were observed mostly due to water stress in summer. Greater decomposition constants were obtained for total litter than for needle litter alone. It is possible that the mean soil humidity was not a limiting factor in the decomposition process, which would be due to the distribution of rainfall rather than to the total amount of precipitation together with elevated temperature. The values of precipitation reaching the soil fluctuated monthly, depending on the rainfall characteristics. Important fluctuations in concentration were observed for Ca2+, PO4–3-P, and NO3–-N.  相似文献   

4.
The heterogeneity of nutrients in forest soils is governed by many biotic and abiotic factors. The significance of nutrient patchiness in determining soil processes remains poorly understood. Some saprotrophic basidiomycete fungi influence nutrient heterogeneity by forming large mycelial networks that enable translocation of nutrients between colonized patches of dead organic matter. The effect of mycophagous soil fauna on these networks and subsequent nutrient redistribution has, however, been little studied. We used a soil microcosm system to investigate the potential effects of a mycophagous collembola, Protaphorura armata, on nutrient transfer within, and nutrient loss from, the mycelium of a saprotrophic basidiomycete fungus, Phanerochaete velutina. A 15N label, added to central mycelium, was used to track nitrogen movement within the microcosms across 32 days. Although collembola grazing had little impact on δ15N values, it did alter the partitioning of 15N between different regions of mycelia. Less 15N was transferred to new mycelial growth in grazed systems than in ungrazed systems, presumably because collembola reduced fungal growth rate and altered mycelial morphology. Surprisingly, collembola grazing did not increase the mineralization of N from mycelium into the bulk soil. Overall, our results suggest that mycophagous soil fauna can alter nutrient flux and partitioning within fungal mycelium; this has the potential to affect the dynamics and spatial heterogeneity of forest floor nutrients.  相似文献   

5.
The energy content of the mycoparasite Sporidesmium sclerotivorum mycelium was 18,389 J g?1 and 16,334 J g?1 for macroconidia on a dry weight basis. The energy content of Sclerotinia minor sclerotia, the host of the mycoparasite, was 16,485 J g?1. In liquid culture, the economic coefficient for the conversion of glucose to mycelium (mycelial dry wt ÷ glucose consumed × 100) was 51–60 whereas the mycelial energy coefficient, [mycelial energy (J) ÷ substrate energy (J) × 100] was 65–75. In soil, the conidial energy coefficient [conidial energy (J) ÷ substrate energy (J) × 100] for the conversion of host sclerotial energy to the macroconidia of the mycoparasite was 19.8, which was 2–9 times that for the conversion of glucose in liquid culture. The conidial energy coefficient when grown on a liquid medium on vermiculite was 23.0. S. sclerotivorum, as an obligate parasite of sclerotia in soil, was most efficient in the conversion of energy in a system where there was a high surface: energy ratio. In liquid culture S. sclerotivorum is more efficient than most other fungi.  相似文献   

6.
Saprotrophic microorganisms in soils have traditionally been assumed to be carbon (C) limited, since additions of readily assimilable carbohydrates usually result in increased respiration. In many forest soils, however, rapid nitrogen (N) immobilization and increased microbial growth in response to N addition indicate N limitation. Here we test whether this apparent contradiction could be explained by changes in C allocation between microbial growth and respiration (i.e. changed C-use efficiency) under controlled conditions in laboratory microcosms. Respiration, mycelial production and needle mass loss were monitored after application of glucose or ammonium sulphate to Pinus sylvestris needles inoculated with the litter decomposer fungus Mycena epipterygia. Addition of ammonium resulted in a 32% increase in respiration, 31% increase in needle mass loss and increased mycelial production, indicating that both growth and activity of the fungus were N limited. In spite of N limitation, additions of glucose resulted in a 19% increase in respiration but had no effect on mycelial production and led to a 17% decrease in needle mass loss, indicating a reduced C-use efficiency of the fungus. The capacity of individual fungi to adapt their C-use efficiency to C availability implies that additions of labile C could increase respiration even under N-limited conditions.  相似文献   

7.
Combining decomposition data with process-based biogeochemical models is essential to quantify the turnover of organic carbon (C) in surface litter and soil organic matter (SOM). Long-term decomposition may be suitably analyzed by linear models (i.e., all fluxes defined by first-order kinetics), which allow the derivation of analytical expressions to estimate the loss of C and the overall apparent decay rate (kapp) through time. Here we compare eight linear models (four discrete-compartment models with one or two C pools, two models with a single time-dependent decay rate, and two models based on a continuous distribution of decay rates) and report their analytical solutions for two types of decomposition experiments: i) studies that evaluate the decomposition of a single input of fresh litter (i.e., a single cohort, as in litterbag and C labeling experiments), and ii) studies that evaluate the decomposition of soil samples with compounds of different ages (i.e., multiple cohorts, as in long-term incubations or isotope dilution experiments). We fitted analytical mass loss functions to both types of datasets and evaluated the performance of the models. For single-cohort data, continuous-decay models provide the best balance between accuracy and parsimony (R2 = 0.99, lowest Akaike and Bayesian information criteria), while for multiple-cohort data the two-pool models tend to perform better (R2 = 0.96), perhaps because of the strong separation of time scales in the decomposition data considered. Differences among some models are marginal, suggesting that decomposition data alone do not point to a single ‘best’ model. All models resulted in apparent decay rates that decreased markedly through time, in contrast with the assumption of constant k adopted in the single-pool exponential decay model. We also show how model parameters estimated from single cohort samples can be used to model multiple cohort decomposition, unifying both types of experimental data in one theory. Based on our results, it is possible to distinguish the temporal changes in C loss that are attributable to initial chemical composition or abiotic factors, from those associated with the presence of multiple ages in the substrate.  相似文献   

8.
The decomposition of oak leaf litter was studied by means of a litterbag experiment in an oak forest in the Netherlands. The contribution of microbial activity and leaching to weight loss and element dynamics during the first 6 weeks of decomposition was investigated by means of frequent respiration measurements and extractions of the litter and by a qualitative comparison of throughfall and litter percolation water chemistry. The oak-leaf litter lost 9.3% of its initial dry weight during the first 6 weeks. In total, 90% of this observed weight loss was explained by the processes studied. About 5.9% (64% of the total) of this weight loss was attributed to microbial tespiration and 0.5% (5%) to the loss of inorganic solutes. Leaching of dissolved organic compounds was estimated to account for 2.0% (21%). The results indicated a fast leaching of K and Cl out of the fresh litter during the first 2 weeks, while Mg, Fe, Mn, Si, ortho P, and dissolved organic N were released at a much lower rate. At the same time, small amounts of H+, NH inf4 sup+ and NO inf3 sup- were retained in the litter.  相似文献   

9.
A streptomycin-resistant variant, of CB756 was used as seed inoculum to follow population changes in rhizosphere and soil of black gram (Vigna mungo cv. Regur) by direct plating onto an antibiotic agar medium. The number of viable rhizobia decreased from the initial level added to the soil at sowing. There was a further decrease during the early stages of root development, which was followed by a substantial increase in the rhizosphere population, and this increase continued for the duration of the experiment. Very little consistent change in soil numbers occurred until after plant senescence and nodule and root decay, which coincided with an increase in the soil numbers of CB756strr. Movement of the inoculum strain in the soil and rhizosphere from the seed inoculum was estimated by measuring lateral and vertical distribution of nodules on the root system.  相似文献   

10.
Uptake and rapid translocation of 32P-orthophosphate to Pinus radiata mycorrhizas from soil by mycelial strands of Rhizopogon luteolus was demonstrated. In greenhouse material, translocation occurred from soil for at least 12 mm and some 30–80 per cent of phosphate absorbed from 5 × 10?6M as KH2PO4 was translocated. In the field, translocation occurred for 12 cm. Uptake by excised mycelial strands was metabolically mediated. Translocation occurred more rapidly when the untreated ends of strands were placed in an osmoticum: polarity in translocation was also observed. It was concluded that uptake and translocation by mycelial strands (as distinct from individual hyphae) provide an effective method for mycorrhizal exploitation of large inter-root soil volumes and assist the plants in competition for nutrients.Large differences occurred between strains of the same species in mycelial strand growth in soil. Mycelial strands of R. luteolus grew through the test soil at 1.3-2.9 mm/day and along P. radiata roots at 1.7 mm/day at 25°C day and 16°C night temperatures.  相似文献   

11.
A thorough assessment of Canadian exposure to mercury (Hg) has not been undertaken since 1970. A multimedia approach was used to update estimates of Hg exposure to members of the general population in Canada, based on currently available information. Adult Canadians have an estimated intake of all Hg species via all routes of 7.7μg/day (0.11μg/kg body weight/day), which equated to an absorbed dose of 5.3μg/day (0.076μg/kg bw/day). Fish consumption accounts for much of this exposure (27% of intake, 40% of absorbed dose), in the form of methylmercury. However, dental amalgam appears to account for a greater proportion of total Hg exposure than fish consumption. Exposure from amalgam was estimated for intake and absorbed doses (of Hg0) at 2.81 and 2.25μg/day, respectively. This represents 36% of total Hg intake and 42% of absorbed dose. Hg2+ arises principally from foods other than fish. Intake of Hg2+ by adults was determined to be 1.82μg/day and absorbed dose only 0.18μg/day. Exposures for four other age groups of the population were also evaluated.  相似文献   

12.
Studies were conducted to compare the main‐stem and branch yield component distribution of two soybean [Glycine max (L.) Merr.] lines differing in architecture and growth habit, and to relate the partitioning of carbon assimilates during pod filling and seed filling stages. An indeterminate line (MI) and a determinate line (MD) were planted in early May on a fine, mixed mesic Udic Haplustalf soil in southwestern France. For the N treatment, N fertigation was applied at the end of the vegetative phase and the early stages of reproductive growth. Pod production on branches was stimulated in response to N application for the determinate line, and N also enhanced the weight of seeds located on branches for both lines. At different stages during pod setting and seed filling, mid‐canopy‐level leaves were allowed to assimilate 14CO2 and 24 h after exposure, radioactivity was measured in different organs and levels of the whole plant. 14C‐assimilates appeared to be preferentially transferred to the lower level of the main‐stem in MI and to the lower level and branches in the MD line. For N‐treated plants, radiocarbon accumulation was particularly marked in pods located on the lower level and on branches; this was consistent with the yield component distribution patterns seen at harvest.  相似文献   

13.
Soil factors affecting growth of mycelial strands from ectomycorrhizas into surrounding soil were studied experimentally. Treated soil cores were inserted into root boxes for 4–6 weeks, then infiltrated with gelatin, sectioned, and mycelial strands harvested. Very large differences in mycelial strand growth (measured by weight) occurred between different soils, some soils completely inhibiting growth of strands of the mycorrhizal fungus Rhizopogon luteolus. Compaction of soil reduced mycelial strand penetration greatly e.g. by 80 per cent in one experiment. Soil sterilization ameliorated compaction effects. High soil phosphorus tended to increase strand growth but nitrogen level and Pseudomonas fluorescens. a common soil bacterium, had small or inconsistent effects.  相似文献   

14.
A two-year (2008–2009) field experiment was conducted to determine the effect of irrigation management and weed control on yield and yield components of safflower. The experiment was conducted as a split-split plot arranged in a randomized blocks design with three replications. There were two treatments (weedy and weed free) and four irrigation interval water managements (7 days for all stages, 15, 22 and 28 days after six-leaf stages). The results indicated that grain yield was 29% higher in weed-free plots than in weedy plots. Weed competition reduced yield components such as primary branches, petal weight and number of capitulum per plant. Increasing the irrigation interval to 15 days at the six-leaf stage had no significant effects on grain yield, but grain yield decreased by 18 and 29.8% with increases in the irrigation interval to 22 and 28 days, respectively. An increased irrigation interval >15 days had negative effects on yield components like number of capitulum per plant, petal weight and number of primary branches. The highest grain yield (3703 kg ha?1) was obtained in the weed-free plot, and there was no significant difference between 7- and 15-day irrigation intervals.  相似文献   

15.
The decomposition and nutrient content of litter was studied for 2 years in regrowth Eucalyptus diversicolor forest to which N (0, 200 kg ha-1 year-1) and P (0, 30, 200 kg ha-1) had been applied. The P addition increased, and the N addition decreased, the rate of dry weight loss of decomposing litter. Analysis of the coefficients of a double exponential decay model with components describing the release of labile and resistant fractions indicated that decomposition of the resistant component of litter was most affected by the fertilizer additions. Treatment with N reduced the rate of loss of this component and increased its half-life by approximately 30%, whereas P treatment increased its rate of decay and decreased its half-life by approximately 30%. P accumulated in litter during decomposition. P uptake and retention was greater in P-treated than untreated plots. The application of N reduced P accumulation in litter. An accumulation of N also occurred during decomposition, the amount of N imported into litter being greater on plots treated with N fertilizer. Treatment with N affected the amount of S in decomposing litter. Litter on N-treated plots either accumulated more S or released it more slowly than litter on plots not treated with N. The application of N as NH4NO3 decreased forest-floor litter pH, increased litter layer mass (by 15%), and increased the amount of N (by 34%) and S (by 32%) stored in the forest floor. Treatment with P reduced the amount of N (by 22%) stored in the litter layer. The application of 200 kg P ha-1 in the absence of N increased the store of P in the litter layer by 80%, but when N and P were applied together the amount of P in the litter was not significantly different between P treatments.  相似文献   

16.
Ammonia fluxes from application of anaerobically-digested slurry (ADS) and chemical fertilizer (CF) to flooded forage rice (Oryza sativa L.) in Japan were measured using a dynamic flow-through chamber method in lysimeters. The CF was applied at a rate of 300 N ha?1 (three times) as ammoniacal-N fertilizer, and the ADS was applied to the lysimeters at total rates equivalent to 75, 100 and 150 kg N ha?1, by broadcasting uniformly into the floodwater at three or six times (equal splits) between 17th June and 17th November, 2005. The emission fluxes for the first 2 days after application were very high from ADS, the highest values being 679 compared with a maximum of 156 mg N m?2 d?1 from CF. Most (61–93%) of the ammonia loss occurred during the first 5 days after each application of fertilizer. The total N loss as ammonia from ADS (29.6–51.7%) was much higher than from CF (12.2%). The highest fluxes were observed in August (2005) when air temperature was highest. More ammonia was lost from the ADS applied at the early stages (i.e. root taking, tiller stages) than at later stages (i.e. elongation, fruiting stages) of rice growth.  相似文献   

17.
The present study aimed to elucidate the atmosphere–forest exchange of ammoniacal nitrogen (NHX-N) at a young larch ecosystem. NHX-N exchanges were measured at a remote site in northernmost Japan where 4-year-old larches were growing after a pristine forest had been clear-cut and subsequent dense dwarf bamboo (Sasa) had been strip-cut. The site was a clean area for atmospheric ammonia with mean concentrations of 0.38 and 0.11 μg N m?3 in snowless and snow seasons, respectively. However, there was a general net emission of NHX-N. The annual estimated emission of NHX-N of 4.8 kg N ha?1 year?1 exceeded the annual wet deposition of 2.4 kg N ha?1 year?1, but the weekly exchange fluxes may have been underestimated by 28–60%. The main cause of the ammonia loss from the young larch ecosystem was probably enhanced nitrogen supply stimulated by the cutting of the pristine forest and Sasa, in particular, the Sasa.  相似文献   

18.
Estimating carbon (C) and nitrogen (N) stocks in deadwood in forests nationwide is required for understanding large-scale C and N cycling. To do so requires estimated values of wood density and C and N concentrations. Additionally, parameters that show variation should be examined. In this study, we clarified the estimated values and the variation in three parameters in each decay class of each of two tree species and examined whether dead log diameter and region contribute to variation in the parameters. Data were collected from 73 Chamaecyparis obtusa (Sieb. et Zucc.) Endl. plantations and 66 Cryptomeria japonica D. Don plantations throughout Japan. Wood densities decreased from 386 to 188?kg?m?3 for C. obtusa and from 334 to 188?kg?m?3 for C. japonica in decay classes 1–4. The variation in wood density increased with decay class, and the coefficient of variance increased from 13.9% to 46.4% for C. obtusa and from 15.2% to 48.1% for C. japonica. The N concentrations increased from 1.04 to 4.40?g?kg?1 for C. obtusa and from 1.11 to 2.97?g?kg?1 for C. japonica in decay classes 1–4. The variation in N concentration increased with decay class, and the coefficient of variance increased from 51.9% to 76.7% for C. obtusa and from 50.3% to 70.4% for C. japonica. Log diameter and region contributed to variations in wood density and N concentration in decay classes 1 and 2 for C. obtusa and C. japonica. However, no relationship was observed between regional climates and the two parameters. In contrast, C concentrations ranged from 507 to 535?g?kg?1 and were stable with much lower coefficients of variance throughout the decay classes for both tree species. Thus, we recommend that the same C concentration can be adapted for all decay classes of both tree species.  相似文献   

19.
The impact of soil (1, 2 kg ha?1) and foliar (100, 200 mg L?1) boron (B) with control (no B) was evaluated on phenology and yield formation of Camelina each applied at stem elongation and flowering stages. Foliar (200 mg L?1) or soil B (2 kg ha?1) resulted in earlier flowering and maturity, increased fruit bearing branches (19.68%), number of siliqua, seeds per siliqua (4.6%), biological yield (15%), seed yield (24%), harvest index (11.4%) and oil contents (23%) than no B. Increased fruit bearing branches, seed filled siliqua or seed numbers, harvest index and oil quality can be attributed to changes in dry matter accumulated of stem with simultaneous increase in siliqua dry weight with foliar or soil applied B. In crux, foliar (200 mg L?1) or soil applied (2 kg ha?1) B seems promising to improve seed and oil yield, harvest index of Camelina sativa under B deficient condition.  相似文献   

20.
Soil erosion contributes negatively to agricultural production, quality of source water for drinking, ecosystem health in land and aquatic environments, and aesthetic value of landscapes. Approaches to understand the spatial variability of erosion severity are important for improving landuse management. This study uses the Kelani river basin in Sri Lanka as the study area to assess erosion severity using the Revised Universal Soil Loss Equation (RUSLE) model supported by a GIS system. Erosion severity across the river basin was estimated using RUSLE, a Digital Elevation Model (15 × 15 m), twenty years rainfall data at 14 rain gauge stations across the basin, landuse and land cover, and soil maps and cropping factors. The estimated average annual soil loss in Kelani river basin varied from zero to 103.7 t ha-1 yr−1, with a mean annual soil loss estimated at 10.9 t ha−1 yr−1. About 70% of the river basin area was identified with low to moderate erosion severity (<12 t ha−1 yr−1) indicating that erosion control measures are urgently needed to ensure a sustainable ecosystem in the Kelani river basin, which in turn, is connected with the quality of life of over 5 million people. Use of this severity information developed with RUSLE along with its individual parameters can help to design landuse management practices. This effort can be further refined by analyzing RUSLE results along with Kelani river sub-basins level real time erosion estimations as a monitoring measure for conservation practices.  相似文献   

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