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1.
For examining the probability of increase in the occupation ratio of inoculated rhizobium in nodules, various Rj-soybean cultivars including the Rj 2 Rj 3 Rj 4-lines of soybean were grown in a field of the Kyushu University Farm. Bradyrhizobium japonicum USDA110 that carries uptake hydrogenase (Hup+) was used as an inoculum. The relative efficiency of nitrogen fixation generally increased by the inoculation. However, there were no significant differences in the effects among the genotypes of the host plants. The occupation ratio of serogroup USDA110 in the nodules on the taproot of the inoculated plants was in the range of 77–100%, suggesting that the B. japonicum strain USDA110 infected taproots immediately after inoculation. The occupation ratios in the nodules on the lateral roots were 53–67, 40–86, 63–83, and 62–77% in inoculated plants of the non-Rj-, Rj 2 Rj 3-, Rj 4-, and Rj 2 Rj 3 Rj 4-genotypes, respectively, and they decreased in all the genotypes with the progression of growth. At the time of the first sampling, the occupation ratios on the lateral roots of these Rj 2 Rj 3 Rj 4-genotypes showed values intermediate between those of IAC-2 (Rj 2 Rj 3) and Hill (Rj 4) , which were the parent cultivars of the Rj 2 Rj 3 Rj 4-lines, B340, B349, and C242. The reduction in the occupation ratio of the serogroup USDA110 for about 1 month after the first sampling was the lowest (0.13–0.16) in the Rj 2 Rj 3 Rj 4-genotypes, excluding B349, followed by the non-Rj- and Rj 2 Rj 3-genotypes and highest (0.52–0.69) in the Rj 4-genotypes, excluding Hill. Therefore, it was considered that the population of compatible rhizobia with host soybean plants increased in the rhizosphere with the progression of the development and growth. The results showed that with the expansion of the root area of host plants, the occupation ratio of type A rhizobia including the serogroup USDA110 was high. Therefore, the Rj 2 Rj 3 Rj 4-genotypes were superior to other Rj-genotypes in terms of the inoculation effects of nodulation type A rhizobium, B. japonicum USDA110. However, the preference of the Rj 2 Rj 3 Rj 4-genotype for serogroup USDA110 is not sufficient to rule out the competition with the other serogroups in this study. Therefore, the study should be centered on the isolation of more efficient (Hup+) and highly compatible rhizobial strains with the Rj 2 Rj 3 Rj 4- genotypes.  相似文献   

2.
Denitrification and fermentation in plant-residue-amended soil   总被引：1，自引：0，他引：1  
Summary Nitrous oxide production (denitrification) during anaerobic incubation of ground-alfalfa-, red-clover-, wheat-straw-, and cornstover-amended soil was positively related to the initial water-soluble C content of the residue- amended soil. The water-soluble C concentration decreased in all treatments during the first 2 days, then increased in the alfalfa-, red-clover-, and wheat-straw-amended soil until the end of the experiment at 15 days. An accumulation of acetate, propionate, and butyrate was partly responsible for the increased water-soluble C concentration. Denitrification rates were much higher in the alfalfa-and red-clover-amended soil, but NO 3 – was not fully recovered as N2O in these treatments. Supported by earlier experiments in our laboratory, we conclude that some of the NO 3 – was reduced to NH 4 + through fermentative NO 3 – reduction, otherwise known as dissimilatory NO 3 – reduction to NH 4 + . Acetate, the primary product of anaerobic fermentation, accumulated in the alfalfa- and red-clover-amended soil in the presence of NO 3 – , supporting previous observations that the processes of denitrification and fermentation occur simultaneously in C-amended soil. The partitioning of NO 3 – between denitrification and fermentative NO 3 – reduction to NH 4 + depends on the activity of the denitrifying and fermentative bacterial populations. NO2 concentration may be a key in the partitioning of NO 3 – between these two processes.  相似文献   

3.
Knowledge on anisotropy of saturated hydraulic conductivity can improve the understanding of transport phenomena in soil. We hypothesized that saturated hydraulic conductivity (Ks) in the upper part of the root zone of an agricultural sandy loam soil was anisotropic at different soil depths and times after tillage. Ks was measured on undisturbed 100 cm3 core samples taken in the horizontal and vertical directions in up to four soil layers (Surf: surface layer (0–5 cm); Top: topsoil (10–15 cm); Trans: transition layer between topsoil and subsoil; Sub: subsoil (40–60 cm)) 1, 8 and 32 months, respectively, after mouldboard ploughing and drilling. The ratio between estimated geometric mean values for Ks in the vertical and the horizontal directions (Kms,v/Kms,h) was used to test the hypotheses. A total of 669 soil samples were analysed.Kms,v/Kms,h varied with time after tillage and between soil layers. One month after ploughing, Kms,v/Kms,h was <0.23 (P = 0.975) in the Trans layer with an average value of 0.084, i.e. Kms,h was 12 times larger than Kms,v. Anisotropy could not be documented in this layer 8 or 32 months after ploughing, i.e. Kms,v/Kms,h was not significantly different from 1.0. For the Surf and Top layers 32 months after ploughing, Kms,v/Kms,h was in the intervals 1.4–50 and 3.1–77, respectively, (P = 0.95) with average values of 8.4 and 15, respectively. Thus, Kms,v was 8.4 respectively 15 times larger than Kms,h in the two layers. Anisotropy was not found in these layers 1 or 8 months after tillage. Strong anisotropy was found in the Sub layer with Kms,v/Kms,h averaging to 14 and 32, respectively, 8 and 32 months after tillage. Kms,v and Kms,h generally decreased with time in the Surf, Top and Trans layers, except in the vertical direction in the Top layer between 8 and 32 months after ploughing, and in the Trans layer between 1 and 8 months after ploughing. Overall, the geometric means of Ks varied between 10−4.0 and 10−7.1 m s−1.The results may reflect systematic effects of soil settlement and drying/wetting phenomena coupled with biological activity and the existence of stable, vertically oriented biopores in the subsoil. It appears to be necessary to consider anisotropy of Ks and its variation in the analysis and modelling of water flow and chemical transport in agricultural soils, particularly to explain heterogeneous flow phenomena at the plot and field scales.  相似文献   

4.
不同供氮水平对广藿香产量与品质的影响   总被引：2，自引：1，他引：1  
为探讨不同供氮水平对广藿香产量和品质的影响,采用砂培试验,研究了广藿香在3、 6、 12、 18、 24 mmol/L 5种不同氮水平下（用N1、 N2、 N3、 N4、 N5表示）氮营养、 生长性状、 产量、 挥发油含量和品质的变化。结果表明,随着供氮水平的提高,广藿香生长性状参数、 氮营养、 植株鲜（干）重量、 挥发油含量增加,茎和叶的油分含量下降。在广藿香的茎挥发油中,N1和N2处理的12种成分含量均显著高于N4与N5。-广藿香烯、 -愈创木烯、 苦橙油醇、 -愈创木烯、 反式-丁香烯、 广藿香醇、 广藿香酮含量以N1处理最高。刺蕊草烯、 -广藿香烯、 -愈创木烯、 -榄香烯、 异石竹烯含量在N2处理最高。在广藿香叶挥发油所测定的成分中,除了-广藿香烯外, N1和N2 处理的其他成分含量均显著高于N4与N5。-广藿香烯、 -愈创木烯、 -愈创木烯、 -荜澄茄烯、 异石竹烯、 -愈创木烯、 反式-丁香烯、 广藿香醇、 广藿香酮含量在N1处理最高。刺蕊草烯、 -广藿香烯、 -榄香烯含量以N2处理最高。广藿香茎和叶挥发油所测定的12种有效成分N1与N2及N4与N5处理之间无显著差异。总之提高氮水平有利于增加挥发油含量,但油分含量降低。  相似文献   

5.
Investigation of spatial patterns of adenylate kinase, catalase, endopeptidase and fructose-1,6-diphosphatase encoding genes (Ak, Cat1, Cat2, Ep, Fdp) allelic variation in Aegilops tauschii was carried out. About 300 accessions, representing all the species range were taken for the study. Cat2 and Fdp loci are completely monomorphic in ssp. strangulata and in the western part of ssp. tauschii range, as well. Both Cat2 and Fdp are highly polymorphic in the eastern part of ssp. tauschii range, with the patterns of this polymorphism being discordant in these two loci. Ak 108, a rare allele with sporadical spatial occurrence, was found in ssp. tauschii only. On the contrary, Ak 92 is absent in ssp. tauschii: it is the most common Ak allele in ssp. strangulata in Precaspian Iran, the most moist part of the area, and is very rare in other parts of ssp. strangulata area. Ep is a highly polymorphic locus with the highest level of variation in the west of Ae. tauschii area, where this species had originated. Ep allele variation patterns are rather similar in ssp. tauschii and ssp. strangulata. The data reveal the adaptive nature of Ak, Cat2, and Fdp allele variation, while Ep polymorphism seems to be mostly neutral.  相似文献   

6.
Estimation of sediment load from Himalayan basins is of considerable importance for the planning, designing, installation and operation of hydro-power projects, including management of reservoirs. In the present study, an assessment of physical and chemical load, sediment yield and erosion rate has been undertaken at eight different locations in the Sainj and Tirthan watersheds. The analysis revealed that the maximum load was transferred during the monsoon season. Moreover, the estimated average chemical erosion rate of the Sainj (83 t km− 2 yr− 1) and Tirthan (80 t km− 2 yr− 1) watersheds were higher than that of the Indian average (69 t km− 2 yr− 1) representing all the rivers. Both watersheds were eroding physically and chemically at a faster rate than that of the world global average erosion rate (185 t km− 2 yr− 1). The flattish nature of the channels in some segments of these watersheds showed a lower transport of sediments, where as the constricted segments having steep bed slopes increased the velocity of flow and the sediment transport rate. These findings have important implications for water resource management in the context of sediments mobilization, erosion, channel management, ecological functions and operation of the hydro-power projects in the Lesser Himalayan region.  相似文献   

7.
Here we provide evidence that the form of carbon compound and O2 concentration exert an inter-related regulation on the production and reduction of N2O in soil. 6.7 mM d-glucose, 6.7 mM D-mannitol, 8 mM L-glutamic acid or 10 mM butyrate (all equivalent to 0.48 g C l−1) were applied to slurries of a sandy loam soil. At the start of the experiment headspace O2 concentrations were established at ∼2%, 10% and 21% O2 v/v for each C treatment, and 2 mM K15NO3 (25 atom % excess 15N) was applied, enabling quantification of 15N-N2 production, 15N-(N2O-to-N2) ratios and DNRA. The form of C compound was most important in the initially oxic (21% O2 v/v) soils, where addition of butyrate and glutamic acid resulted in greater N2O production (0.61 and 0.3 μg N2O-N g−1 soil for butyrate and glutamic acid, respectively) than the addition of carbohydrates (glucose and mannitol). Although, there was no significant effect of C compound at low initial O2 concentrations (∼2% O2 v/v), production of 15N-N2 was greatest where headspace O2 concentrations were initially, or fallen to, ∼2% O2 v/v, with greatest reduction of N2O and lowering 15N-(N2O-to-N2) ratios (∼0-0.27). This may reflect that the effect of C is indirect through stimulation of heterotrophic respiration, lowering O2 concentrations, providing sub-oxic conditions for dissimilatory nitrate reduction pathways. Addition of carbohydrates (glucose and mannitol) also resulted in greatest recovery of 15N in NH4+ from applied 15N-NO3−, indicative of the occurrence of DNRA, even in the slurries with initial 10% and 21% O2 v/v concentrations. Our 15N approach has provided the first direct evidence for enhancement of N2O reduction in the presence of carbohydrates and the dual regulation of C compound and O2 concentration on N2O production and reduction, which has implications for management of N2O emissions through changing C inputs (exudates, rhizodeposition, residues) with plant species of differing C traits, or through plant breeding.  相似文献   

8.
The difficulties in using complicated models of carbon mineralization and the poor performance of simple ones call for new models that are simple in use and robust in performance. We have developed a model for the mineralization of carbon from experimental data in which the organic matter is treated as a single component. The logarithm of the average relative mineralization rate, K, or rate constant, of a substrate considered as a whole was found to be linearly related to the logarithm of time, t, provided prevailing soil conditions remained unchanged. The equation is: logK = logR–S logt, or K = R t–S, in which R (dimension tS ? 1) represents K at t = 1, and S (dimensionless, 1 ≥ S≥ 0) is a measure of the rate at which K decreases over time, also called the speed of ‘ageing’ of the substrate. The quantity of the remaining substrate, Yt, is calculated by Yt = Y0 exp(–Rt1 – S), where Y0 is the initial quantity of the substrate. The actual relative mineralization rate, k, at time t is proportional to K, according to k = (1 ? S)K. The model was tested against an assembly of 136 sets of data collected from trials conducted in 14 countries all over the world. They cover materials ranging from glucose, cellulose and plant residues, to farmyard manure, peat and soil organic matter. The results lead to the conclusion that the model describes well the dynamics of organic matter in soil over time varying from months to tens of years, provided major environmental conditions remain unchanged. It can easily be applied in practice and is attractive because of its modest input requirements.  相似文献   

9.
鸡粪腐解过程不同溶解性腐殖物质结合形态锌的动态   总被引：2，自引：0，他引：2  
以鸡粪为材料,添加不同比例的铜锌进行腐解试验,研究了腐解过程中不同溶性（水溶性、氢氧化钠溶性、氢氧化钠-焦磷酸钠混合液溶性）腐殖物质结合形态锌浓度的动态变化、受铜含量的影响及其与有效锌的关系。结果表明,粪肥原样水溶性锌（H2O-Zn）占其全锌量的0.74%,在腐解过程中逐渐下降;随着粪肥中添加锌量的增加（Cu/Zn为1: 1、1: 2、1: 3处理）,H2O-Zn含量也相应增加,但平均含量占其全锌的比例低于对照处理,同时也随着腐解时间延长呈减少趋势。铜含量的增加对H2O-Zn提取有促进作用。腐解初期,粪肥原样中NaOH浸提取锌含量占其全锌量的62.41%,在腐解过程其比例大幅度下降;NaOH腐殖物质结合态锌（NaOH-Zn）随着加入锌的增大而有所增加,随着铜含量增加,NaOH溶性腐殖物质结合态锌的含量也有增加趋势,而随着腐解时间呈下降趋势。粪肥原样中NaOH-Na4P2O7提取腐殖物质络合锌含量占其全锌量的13.59%,随腐解时间推移呈增加趋势;NaOH-Na4P2O7提取腐殖物质络合态锌（NaOH-Na4P2O7-Zn）的量随着加入锌量的增加,其变化不大,且铜含量对NaOH-Na4P2O7提取腐殖物质络合态锌的量影响很小。在堆腐前,在各个处理样中,50%～85%的可溶性锌分配在NaOH的溶液,10%～50%分配在碱性混合液,0～5%在水溶液;至腐解后期,58%～92%分配在NaOH-Na4P2O7溶液,6%～41%分配在NaOH的溶液,0～2%分配在水溶液。随着锌含量增加,H2O-Zn和NaOH-Zn的分配比例逐渐增加,而NaOH-Na4P2O7-Zn的分配比例减少。在堆腐粪肥中,水溶性锌、NaOH溶性腐殖物质结合态锌与有效锌浓度之间显极正显著或正显著相关,而NaOH-Na4P2O7-Zn溶性腐殖物质络合态锌与水溶性锌,NaOH溶性腐殖物质结合态锌及有效锌浓度都显极负显著或负显著相关。  相似文献   

10.
The composition of the soil atmosphere is an indicator of biological processes, and soil CO2 gradients have been used to estimate CO2 efflux from the surface. Soil atmosphere samplers, constructed with gas-permeable materials, have been used to quantify soil CO2 concentrations. The type of material used can influence the perceived real-time concentrations of CO2 in the soil. Previous works have not directly compared different types of materials under the same conditions. The objective of this study was to determine the diffusion coefficient (D) and time of 95% equilibrium (teq) of CO2 through several materials, and to evaluate the effect of long-term soil burial (183 days) on diffusion characteristics. Materials tested included silicone, expanded Teflon (ePTFE), and ultra high molecular weight polyethylene (PE) tubing. The D of each material was determined using a closed-loop system consisting of a CO2-enriched (7800 ppm) chamber, a CO2 analyzer and an inner tube (experimental tubing) placed inside the chamber. Air was re-circulated through the inner tube, and as CO2 diffused from the chamber into the tubing, the analyzer recorded the increase in concentration. The silicone tubes had values of D ranging from 8.64 to 5.80×10−6 cm2 s−1 with corresponding teq between 3.9 and 9.7 h. Diffusion coefficients of the ePTFE (1.25×10−4 cm2 s−1) and PE (7.70×10−4 cm2 s−1) materials were 2 orders of magnitude greater, with teq<6 min. Exposure to the soil environment for 183 days did not visibly deteriorate the materials or significantly affect the D or teq values. Use of the ePTFE or PE materials, over the silicone materials, may allow for better characterization of dynamic CO2 concentrations in the soil based on the greater D and lesser teq values of these materials.  相似文献   

11.
 The effects of a large species of anecic earthworm, Martiodrilus carimaguensis Jiménez and Moreno, on soil C and N dynamics were investigated in a native savanna and a man-made pasture of the eastern plains of Colombia. We compared, across time (11 months), the total C, total N, NH+ 4 and NO– 3 contents in the earthworm casts, the underlying soil and the adjacent soil. Additional sampling of root biomass and macrofauna was performed. In the two management systems, the total C and N contents were higher in casts (4.33–7.50%) than in the bulk soil (2.81–4.08%), showing that the earthworms selected food substrates with high organic contents. In general, C contents significantly increased during cast ageing (+100%), possibly because of CO2 fixation processes, dead root accumulation and/or macrofaunal activities in casts. In fresh casts, NH+ 4 levels were very high (294.20–233.98 μg g–1 dry cast) when compared to the soil (26.96–73.95 μg g–1 dry soil), due to the intense mineralisation processes that occurred during the transit of soil and organic matter through the earthworm gut. During the first week of cast ageing, NH+ 4 levels sharply decreased, while NH– 3 levels showed successive peaks in the casts, the underlying soil and the adjacent soil. These results suggested the rapid production of NO– 3 by nitrification processes in the fresh casts, followed by diffusion to the nearby soil, first vertically, then horizontally. After 2 weeks of cast ageing, NH+ 4 and NO– 3 levels only showed slight variations, likely because of organic matter protection in stable dry casts. The root biomass was higher (1.6–4.7 times) below the old earthworm casts. The ecological significance of these results is discussed. Received: 22 October 1998  相似文献   

12.
A method is proposed which follows Darrah's experimental procedure and takes advantage of a mathematical solution provided by Carslaw & Jaeger to estimate the diffusion coefficients of adsorbed and non-adsorbed solutes in soil. The method requires only the values of the concentration of the solute at the input face of a uniform column of soil, Cs, and of the total amount, Qt, that has entered the soil after a specified time during which the surface of the block is in contact with a thin porous pad containing a known initial amount of solute, Q0, at concentration C0, expressed in the same units as Cs. In the Cs/C0 vs. Qt/Q0 space there is a unique relationship between the effective diffusion coefficient, De, of the solute in the soil and the contact conductance for this solute, h, between the pad and the soil surface. The proposed procedure is firstly to determine De, and h for a non-adsorbed solute in the experimental soil using the experimental values of Cs/C0 and Q/Q for that solute. This value of De, gives the diffusion impedance factor for the solute in the soil, f, which is assumed also to apply to adsorbed solutes. A first estimate of the effective diffusion coefficient of an adsorbed solute, 1Dea, is then made using f and the diffusion coefficient of the free solute in water, DL, obtained from the literature (i.e. 1Dea= DLf). Only if the solute is weakly adsorbed will the values of Cs/C0, and Qt/Q0 lie in Cs/C0, vs. Qt/Q0, space as defined by 1Dea and the contact conductance, h. Instead a second space relating Cs/C0 and Qt/Q0, is now constructed from nominated values of h and De, where De, is defined in terms of 1Dea, the adsorption coefficient, F , and the volumetric moisture content of the soil, θ. The position of the experimental values of Cs/C0, and Qt/Q0 within this new space defines h and the actual De, and F of the solute as it diffuses and is adsorbed in the soil. The advantages and limitations of the method are discussed. In particular, the method assumes that the adsorption process is linear and reversible.  相似文献   

13.
The distribution coefficient (K d) between the soil solid phase and the liquid phase is a commonly used parameter to evaluate radionuclide behavior in soil. For reliable evaluation, the variability of the K ddue to changes of environmental conditions should be clarified. In the present study, applicability of electrical conductivity (EC) to estimate effects of competing ions on K dwas examined in batch experiments. The K dof five radionuclides (60Co, 54Mn, 85Sr, 137Cs, 65Zn) were found to be in inverse proportion to the supernatant EC. The K dof 60Co and 54Mn were increasing at 7 days and no stable K dcould be determined. For 85Sr, 137Cs, and 63Zn, the regression equations obtained between the K dof the equilibrium state and the supernatant EC were validated in another experiment; it is expected that their K ds can be determined accurately using the EC. Because of its simplicity in measurements, using EC should be very practical for estimating effects of competing ions on K dof selected radionuclides.  相似文献   

14.
为探明河西绿洲区塑料大棚甘蓝适宜的水肥管理模式,通过田间小区试验,设定3个施肥量(F_1:N、P_2O_5、K_2O含量为320,160,210kg/hm~2;F_2:N、P_2O_5、K_2O含量为260,120,157.5kg/hm~2,F_3:N、P_2O_5、K_2O含量为200,80,105kg/hm~2)和2个灌水频率(H_1:6d/次,H_2:9d/次),共6个处理,分析甘蓝农艺性状、产量、品质和叶球养分吸收及水肥利用效率对不同施肥量和灌水频率的响应规律。结果表明:H_1处理水平下叶球全氮、磷、钾含量随施肥量增加逐渐升高,H_2处理水平下氮、磷含量随施肥量增加先升高后降低,而钾含量却在随施肥量增加逐渐升高,同一灌水条件下肥料偏生产力随施肥量的减少而升高;同一施肥水平下,叶球中的全氮、磷、钾含量及吸收量高灌水频率大于低灌水频率处理,而肥料偏生产力的变化则相反。水肥耦合作用下,甘蓝叶球纵横径、生物产量和干物质量均H_2F_1处理最高,叶球紧实度、干鲜重比、单球重、经济产量和经济系数均H_2F_2最大,而叶球中心柱长和帮叶比H_2F_3处理最小。灌溉频率和施肥量对甘蓝叶球品质影响显著,且两因素的交互作用达到显著水平,其中硝酸盐含量H_1F_1最高、可溶性糖含量H_2F_1最高、Vc含量H_2F_2处理最大。水肥耦合后全氮和全磷含量及两者吸收量均以H_2F_2最大,全钾及吸收量H_2F_1最高。随着施肥量的增加,水分利用效率也逐渐升高,H_2F_1水分利用效率显著高于其他处理。综合分析表明,水肥耦合对河西绿洲区塑料大棚甘蓝叶球的农艺性状、产量、品质和养分吸收及水分利用率的影响显著,且灌溉频率的影响大于施肥量。H_2F_2处理(灌水频率9d/次,施肥量N、P_2O_5、K_2O为260,120,157.5kg/hm~2)是河西绿洲区塑料大棚甘蓝农艺性状、产量、品质、养分吸收以及水肥利用效率方面最佳的水肥组合模式。  相似文献   

15.
To measure the contribution of root respiration (Rr) to total soil respiration (Rt) in arid cotton fields, eighteen plots, nine for girdling and nine control, were built in an arid cotton field in the Aksu National Experimental Station of Oasis Farmland Ecosystem, Xinjiang of China. Given the difference of soil respiration between girdled plots and non-girdled control plots, the components of soil respiration, root respiration (Rr) and respiration originating from decomposition (Rd) were divided. The temperature sensitivities of R r and R d were analyzed, respectively. The results showed that the average contribution of R r to R t in arid cotton field was about 32% during the study period. The temperature-response curve of R r differed from that of Rd . The dynamic variation of R d was more related to the change of soil temperature as compared to Rr . Rr and Rd had different responses to the variation of environment, and thus new models capable of differentiating between Rr and Rd are needed for evaluating the different factors controlling these two components of soil respiration in arid cotton field.  相似文献   

16.
三峡库区典型农业小流域次降雨产沙过程及其影响因素   总被引：1，自引：1，他引：0  
为探究引起三峡库区农业小流域土壤侵蚀的主要次降雨因子,通过天然降雨观测资料,分析忠县石盘丘小流域2019年侵蚀性降雨年内分布特征和典型次降雨条件下A和B 2个集水区产沙过程的变化规律,采用相关性分析方法,揭示次降雨产沙的主要影响因素。结果表明:(1)全年119场降雨资料中,有19场为侵蚀性降雨。全年侵蚀性中雨共发生10次,是侵蚀性降雨中最常见的降雨类型。暴雨及以上降雨是造成研究区产沙量最大的降雨类型。(2)在典型中雨、大雨和暴雨产沙事件中,B集水区产沙量分别是A集水区的5.13,1.66,7.56倍。对3场典型次降雨产沙过程进行分析发现,B集水区产沙过程线随降雨历时的延长,变化程度更剧烈。(3)各PIn因子与研究区产沙量的相关性系数大小排序为PI30>PI10>PI15>PI60>PI5>PI90>PI。对各类降雨因子与研究区的产沙量进行相关性分析,系数大小排序为P>PIn>In>I>T。A、B集水区产沙量与次降雨量P和PI30均存在极显著正相关性。总之,在三峡库区开展水土保持工作时,要加强对暴雨及以上降雨造成农业小流域水土流失的监测与预警响应能力;P和PI30能较好地反映三峡库区天然次降雨对农业小流域侵蚀产沙的影响;对天然降雨条件下的次降雨侵蚀力进行估算时,可将PI30作为主要参考因子;农林水复合生态系统与结构简单的传统农耕模式相比,具有更丰富多元的层次结构,不仅能全面开发利用小流域的农业资源,更有利于保持水土,且其对降雨环境变化的适应性也更强。  相似文献   

17.
Despite the substantial interest to ecologists of the relationship between species diversity and ecosystem functioning, little is known about how the high species richness of decomposer (saprotrophic) fungi and their relative frequencies of occurrence influence the decomposition of organic matter. Three experiments were conducted to test the ability of culturable saprotrophic fungal isolates to utilise a range of artificial and more natural substrates that occur in organic matter, with the aims of (1) characterising the functional potential of ‘common’ and ‘occasional’ taxa in an upland grassland soil and (2) determining whether there was a high degree of apparent functional redundancy in these communities. ‘Function’ was defined as the ability of a fungal isolate to utilise broad categories of substrates (e.g. sugars, cellulose, lignin) that occur in organic matter and which change in proportion during decomposition. The terms ‘common/abundant/frequent’ and ‘occasional/infrequent’ usually referred here to the frequencies of occurrence of taxa estimated using Warcup soil plates. Accepting the difficulties of sampling fungi in soil, this appeared to be the most useful isolation method to produce a general picture of the microfungal community with an estimate of frequency of occurrence for every taxon obtained, and to provide cultures for use in function tests. The influence of this technique on the interpretation of the results is discussed.Forty-eight fungal isolates, obtained from an upland grassland in Roxburghshire, UK, were selected to cover the most ‘abundant’ taxa and a range of ‘occasionals’. Pure cultures of anamorphic fungi and members of the Zygomycota, Ascomycota and Basidiomycota were tested. Although there was apparently a high degree of functional redundancy (equivalence) in assemblages of culturable decomposer fungi, with ‘frequent’ and ‘infrequent’ taxa largely utilising the same substrates, the ‘infrequent’ taxa played important roles in decomposition. ‘Infrequent’ microfungi tested were potentially more active in decomposition than the ‘frequent’ taxa, i.e. several had a higher overall activity, were able to utilise a wider range of substrates and were more combative than the ‘abundant’ taxa. When ‘abundant’ and ‘occasional’ taxa from the same putative guild were inoculated together on grass litter, there was slight evidence of ‘positive’ indirect effects on decomposition and cellulose degradation. Some ‘negative’ effects on lignin degradation, probably as a result of combat, were observed.It is possible that the ‘occasional’ taxa increased the temporal resilience of the ecosystem process of decomposition, and were ‘waiting in the wings’ to replace the abundant taxa. Nevertheless, greater functional diversity could be associated with the uncultured taxa not studied here.  相似文献   

18.
石灰性土壤交换性盐基组成的测定,通行的方法是采用70%乙醇溶液反复洗盐,再经pH 8.50.1 mol L-1氯化铵-70%乙醇(CH3CH2OH)溶液进行多次交换处理,测定交换液中的K+、Na+、Ca2+、Mg2+浓度。但此方法常常受操作步骤繁琐,以及土壤中碳酸盐的溶解量因多次浸提而增加的困扰,最终导致测定结果偏高。基于上述原因,选择不同浓度、不同pH的NH4OAc和NH4Cl 10种交换剂,对比分析10种交换剂中的碳酸盐溶解度和土壤交换性钙镁含量。结果表明,pH=8.5 1 mol L-1氯化铵-70%乙醇(CH3CH2OH)溶液较适合石灰性土壤交换性盐基的测定。此新方法是先经70%乙醇(CH3CH2OH)溶液洗盐,再用pH8.5 1 mol L-1氯化铵(NH4Cl)-70%乙醇(CH3CH2OH)溶液进行一次性交换处理,然后测定交换液的K+、Na+、Ca2+、Mg2+浓度,简化了操作程序的同时有效抑制了土壤碳酸盐的溶解,降低了测定结果的偏差。  相似文献   

19.
 The composition of soil microbiota in four heated (350  °C, 1 h) soils (one Ortic Podsol over sandstone and three Humic Cambisol over granite, schist or limestone) inoculated (1.5 μg chlorophyll a g–1 soil or 3.0 μg chlorophyll a g–1 soil) with cyanobacteria (Oscillatoria PCC9014, Nostoc PCC9025, Nostoc PCC9104, Scytonema CCC9801, and a mixture of the four) was studied by cultural methods. The aims of the work were to investigate the potential value of cyanobacteria as biofertilizers for accelerating soil recolonization after fire as well as promoting microbiotic crust formation and to determine the microbial composition of such a crust. The inoculated cyanobacteria proliferated by 5 logarithmic units in the heated soils which were colonized very quickly and, after 2 months of incubation, the cyanobacterial filaments and associated fungal hyphae made up a matrix in which surface soil particles were gathered into crusts of up to 1.0 cm in thickness. These crusts were composed, on average, of 2.5×1010 cyanobacteria, 2.8×106 algae, 6.1×1010 heterotrophic bacteria (of which 1.2×108 were acidophilic, 1.3×106 were Bacillus spp. and 1.5×108 were actinomycetes) and 77.8 m fungal mycelium (1.4×106 were fungal propagules) g–1 crust. Counts of most microbial groups were positively correlated to cyanobacterial numbers. The efficacy of treatment depended on both the class of inoculum and the type of soil. The best inoculum was the mixture of the four strains and, whatever the inoculum used, the soil over lime showed the most developed crust followed by the soils over schist, granite and sandstone; however, the latter was comparatively the most favoured by the amendment. In the medium term there were no significant differences between the two inocula rates used. Biofertilization increased counts of cyanobacteria by 8 logarithmic units while heterotrophic bacteria, actinomycetes, algae and fungal propagules rose by >4 logarithmic units, acidophilic bacteria and Bacillus spp. by around 3 logarithmic units and fungal mycelia showed an 80-fold increase. The results showed that inoculation of burned soils with particle-binding diazotrophic cyanobacteria may be a means of both improving crust formation and restoring microbial populations. Received: 8 March 2000  相似文献   

20.
The present study was conducted to determine the spatial heterogeneity of bulk density, soil moisture, inorganic N, microbial biomass C, and microbial biomass N in the ridge tillage system of Turiel compared to conventional mouldboard ploughing on three sampling dates in May, July, and August. The soil sampling was carried out under vegetation representing the ridge in a high spatial resolution down the soil profile. Bulk density increased with depth and ranged from 1.3 g cm−3 at 10 cm depth to 1.6 g cm−3 at 35 cm in ploughed plots and from 1.0 g m−3 at 5 cm to 1.4 g m−3 at 35 cm in the ridges. In the ploughed plots, the contents of microbial biomass C and microbial biomass N remained roughly constant at 215 and 33 μg g−1 soil, respectively, throughout the experimental period. The microbial biomass C/N ratio varied in a small range around 6.4. In the ridged plots, the contents of microbial biomass C and microbial biomass N were 5% and 6% higher compared to the ploughed plots. Highest microbial biomass C contents of roughly 300 μg g−1 soil were always measured in the crowns in July. The lowest contents of microbial biomass C of 85–137 μg g−1 soil were measured in the furrows. The ridges showed strong spatial heterogeneity in bulk density, soil water content, inorganic nitrogen and microbial biomass.  相似文献   

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