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The agar-film method was used to assess fungal biomass and standing crop in several analogous decomposition stages of two leaf species (the fast decomposing Michelia nilagirica and the slow decomposing Semecarpus coriaceae), both from an upper montane rainforest in Sri Lanka. At all decomposition stages the fungal biomass on Michelia litter was significantly higher (P<0.001) than for Semecarpus and had developed much more rapidly (17.04 mg g−1 at the first decomposition stage compared with 4.39 mg g−1 for Semecarpus). These figures are considerably higher than those for a cool temperate deciduous forest, but when the data are given as fungal biomass per area the reverse is true. Data are given on the contribution of different hyphal types showing a trend for change (hyaline to dark hyphae) during the course of decomposition. The mass of dead hyphae is considerably lower than data from temperate forests. Data on immobilization of C and of plant nutrients (N, P, K, Ca, Mg and Na) are provided plus hyphal nutrient contents expressed as % of total contents in the leaf litter. These data are comparable to those from temperate forests. 相似文献
3.
《Applied soil ecology》2005,28(1):37-46
The availability of nutrients in the soil is key to the potential response of a plant to elevated CO2 and is central to correctly predicting the response of terrestrial communities to climate change. In order for a plant to fully realise the potential of increased atmospheric CO2, it must increase its nutrient uptake for the increased production of biomass as well as biochemical compounds. In this study the stable isotope 15N was used to follow the fate of nitrogen contained in litter in order to determine the effect elevated atmospheric CO2 had on the loss of nitrogen from decomposing litter and the eventual re-use of this nitrogen. During the decomposition study, on a mass basis more 15N was transferred from the litter despite the litter grown in elevated CO2 initially having a lower 15N signal. This was primarily related to a higher decomposition rate of the elevated CO2 grown litter. Despite more nitrogen entering the below-ground community under elevated atmospheric CO2, the additional N did not stay within the terrestrial community and was not exploited by the plants. The results confirm previous suggestions that Lolium perenne plants growing in elevated CO2 have to derive at least a proportion of their nitrogen from a source external to either added fertiliser or decomposing litter 相似文献
4.
Mo, V, and U are mobilized as anions by aerobically decomposing plant matter; the behaviour of the dissolved metals differs in several respects from what would be expected in inorganic systems. With respect to dialysis through cellophane, between pH I and 4 the mobilized Mo is fixed by colloidal organic decomposition products, with maximum retention at pH 1.5; V is retained between pH 1.5 and 7.0, with a maximum at pH 3. The specific fixation of Mo and V by soil organic matter was considerably less, and persisted over wider pH ranges–1.5-6.5 and 1.0-9.0 respectively. The fixation of U by both forms of humified organic matter increased sharply to a maximum around pH 4-5, and thereafter decreased slightly up to pH 8. The anionic forms of the three elements persisted when MOO:2-4, VO;-3 and UO, were incubated with anaerobically decomposing plant matter; under these conditions V(V) was probably reduced to V(IV), and it seems that an anionic V(IV) complex was formed. Although the molecular size of the colloidal decomposition products of lucerne was somewhat less than that of organic matter extracted from Rothamsted top soil, acid hydrolysates of the two humic acids contained the same twenty-three amino acids, in much the same relative proportions. 相似文献
5.
Effect of climate, soil type and earthworm activity on nitrogen transfer from a nitrogen-15-labelled decomposing material under field conditions 总被引：4，自引：0，他引：4
N transfer from 15N-labelled decomposing material into the microbial biomass and inorganic N forms was studied for more than 2 years at three
experimental sites differing in climatic conditions and earthworm abundance. The 15N-labelled decomposing material was mixed with low-elevation soil (LES), mid-elevation soil (MES) and high-elevation soil
(HES). The amended soils were put into two kinds of plastic cylinders closed on both sides with nets preventing (0.1 cm mesh)
and allowing (0.5 cm mesh) access by earthworms, and were buried in soil (20 cm depth) to monitor the transfer of N from the
15N-labelled decomposing material. Climate and soil type play an important role in the release of N from decomposing material.
LES transplanted to more humid sites (mid- and high-elevation sites) showed an increase in most of its biological activities
(N atom % excess, and microbial biomass C and N). Furthermore, LES was a sandy soil in which the 15N-labelled decomposing material was less bound than in MES and HES, which contained more silt and clay. This resulted in faster
organic matter turnover when climatic conditions were favourable. The presence of earthworms greatly increased the quantity
of inorganic N (mainly NH4
+) in the soils and enhanced the release of N from the 15N-labelled decomposing material and the native organic matter, compared to soil without earthworms.
Received: 21 January 1999 相似文献
6.
During cultivation of legumes soil is acidified due to proton release from roots. As a consequence of proton release, plants accumulate organic anions which may, if returned and decomposed in the soil, neutralize the soil acids. Until now the detailed processes responsible for the change in soil pH after incorporation of plant material have not been completely understood. Using a pot experiment we studied the changes in acid and base in soil during growth of field beans (Vicia faba L. cv. Alfred) and after incorporation of the plant material into the soil. Soil pH was significantly decreased by field beans from 6.00 to 5.64 in a cultivation period of 45 days. Proton release amounted to 32.7 mmol H+ pot-1, which was approximately equivalent to the accumulated alkalinity in the plant shoots (34.4 mmol). Return of field bean shoots caused a significant soil pH increase from 5.64 to 6.29. Within 7 days more than 90% of the added alkalinity was released. After 307 days incubation, soil pH decreased to 5.86 due to nitrification. In a second experiment, maize leaves (Zea mays L.), containing various concentrations of nitrogen and at various alkalinities, were incorporated into the soil. Soil pH change was positively correlated to alkalinity and malate concentration and negatively correlated to total nitrogen and water-soluble organic nitrogen of incorporated leaves. It is concluded that the soil acidification caused by legume cultivation can be partly compensated for if crop residues are returned to the soil. Addition of plant material may initially cause an increase in soil pH due to decomposition of organic anions and organic nitrogen. Soil pH may decrease if nitrification is involved. The concentrations of nitrogen and alkalinity of added plant material are decisive factors controlling soil pH change after incorporation of plant material.Dedicted to Professor J.C.G. Ottow on the occasion of his 60th birthday 相似文献
7.
Mineralization of carbon and nitrogen from cowpea leaves decomposing in soils with different levels of microbial biomass 总被引：2，自引：0，他引：2
Kathrin Franzluebbers Richard W. Weaver Anthony S. R. Juo Alan J. Franzluebbers 《Biology and Fertility of Soils》1995,19(2-3):100-102
Soils with greater levels of microbial biomass may be able to release nutrients more rapidly from applied plant material. We tested the hypothesis that the indigenous soil microbial biomass affects the rate of decomposition of added green manure. Cowpea (Vigna unguiculata L.) Walp.] leaves were added to four soils with widely differing microbial biomass C levels. C and N mineralization of the added plant material was followed during incubation at 30°C for 60 days. Low levels of soil microbial biomass resulted in an initially slower rate of decomposition of soil-incorporated green manure. The microbial biomass appeared to adjust rapidly to the new substrate, so that at 60 days of incubation the cumulative C loss and net N mineralization from decomposing cowpea leaves were not significantly affected by the level of the indigenous soil microbial biomass. 相似文献
8.
The decomposition of 14C, 14N-labelled medic (Medicago littoralis) material and the net formation and decay of isotope-labelled biomass have been measured in four South Australian soils in the field over 4 yr. The field sites were in similar climatic zones but two sites received about twice as much rainfall as the others. The soils were calcareous and of similar pH, but differed in texture and organic matter content. The decomposition of the organic-14C and organic-15N residues were, for a given site, similar. Initially, the concentrations of labelled residues decreased rapidly, then very slowly. Decomposition rates in a heavy clay soil were significantly less than in the other soils during the first 16 weeks after incorporation of plant material, but thereafter, rates of decomposition in all soils were similar, despite differences in soil texture and climate. More than 50% of the medic-14C had disappeared from all soils after 4 weeks of decomposition and only 15–20% of the medic-14C remained as organic residues after 4 yr. Of the medic-15N 60–65% remained as organic residues after 32 weeks decomposition; the percentage decreased to 45–50% after 4 yr.The amounts of 14C, 14N-labelled biomass, formed from decomposing plant material, were maximal 4–8 weeks after incorporation of plant material into the soils. In samples taken at 8 weeks from the sandy Roseworthy soil, biomass-14C and -15N accounted for 14 and 22% respectively of the total organic-14C and -15N residues present. Thereafter in this soil, the concentrations of biomass-14C and -15N decreased, rapidly at first then more slowly. Nevertheless, throughout most of the decomposition the rates of decrease in the concentrations of biomass-14C and -15N exceeded those of the non-biomass, labelled organic residues.The proportions of 14C, 15N-labelled materials accounted for in the labelled biomass varied between soils. Soils of higher clay content generally retained higher proportions of residual organic-14C and -14N in the biomass, even though the net rates of decomposition of total labelled residues did not differ significantly between soils during most of the decomposition. 相似文献
9.
Sara Elfstrand Jan Lagerlöf Katarina Hedlund Anna Mårtensson 《Soil biology & biochemistry》2008,40(10):2530-2539
This field experiment investigated how C from fresh organic amendments and from a growing leek crop was allocated into different soil microbial and faunal groups in an arable field. A 13C-enriched red clover green manure was incorporated in one treatment, while the growing leek crop was pulse labelled with 13CO2 in another. Incorporation of 13C into microbial fatty acids, micro- and macroarthropods, enchytraeids and earthworms was determined on several occasions during the growing season in order to determine whether different groups or species of microorganisms and fauna were specialised on either the decomposing green manure material or root-derived C. Compound-specific stable isotope ratio analysis showed fatty acid markers of actinomycetes and Gram-positive bacteria to be more strongly linked to C originating from the decomposing green manure material, whereas the marker for arbuscular mycorrhizal fungi was more linked to C from the growing leek crop. In contrast, several markers for Gram-negative bacteria were the most 13C-enriched and had incorporated more 13C than the other phospholipid fatty acids in both treatments, indicating a general dominance irrespective of C source. Most soil fauna seemed to derive their C directly or indirectly from the decomposing plant material, while C from the growing crop appeared to be of secondary importance in this agroecosystem. 相似文献
10.
土壤中水溶性有机物质的数量、性质及其变化 总被引：2，自引：0，他引：2
水溶性有机物质的数量可因绿肥种类、土壤和时间而异。该物质是一类分子量低、带不同电荷(正、负电荷)和等电点的物质,并含有羧基和胺基。其中的某些性质随时间而变。该物质的数量与Eh的相关系数显著。其还原性因绿肥种类而异。工作中应用了凝胶层析、红外、可见光谱分析和等电聚焦技术。 相似文献
11.
Bernard Nicolardot Lamia Bouziri Fabiola Bastian Lionel Ranjard 《Soil biology & biochemistry》2007,39(7):1631-1644
The effects of location (soil surface vs. incorporated in soil) and nature of plant residues on degradation processes and indigenous microbial communities were studied by means of soil microcosms incubation in which the different soil zones influenced by decomposition i.e. residues, soil adjacent to residues (detritusphere) and distant soil unaffected by decomposition (bulk soil) were considered. Plant material decomposition, organic carbon assimilation by the soil microbial biomass and soil inorganic N dynamics were studied with 13C labelled wheat straw and young rye. The genetic structure of the community in each soil zone were compared between residue locations and type by applying B- and F-ARISA (for bacterial- and fungal-automated ribosomal intergenic spacer analysis) directly to DNA extracts from these different zones at 50% decomposition of each residue. Both location and biochemical quality affected residue decomposition in soil: 21% of incorporated 13C wheat straw and 23% left at the soil surface remained undecomposed at the end of incubation, the corresponding values for 13C rye being 1% and 8%. Residue decomposition induced a gradient of microbial activity with more labelled C incorporated into the microbial biomass of the detritusphere. The sphere of influence of the decomposing residues on the dynamics of soluble organic C and inorganic N in the different soil zones showed particular patterns which were influenced by both residue location and quality. Residue degradation stimulated particular genetic structure of microbial community with a gradient from residue to bulk soil, and more pronounced spatial heterogeneity for fungal than for bacterial communities. The initial residue quality strongly affected the resulting spatial heterogeneity of bacteria, with a significance between-zone discrimination for rye but weak discrimination between the detritusphere and bulk soil, for wheat straw. Comparison of the different detrituspheres and residue zones (corresponding to different residue type and location), indicated that the genetic structure of the bacterial and fungal communities were specific to a residue type for detritusphere and to its location for residue, leading to conclude that the detritusphere and residue corresponded to distinct trophic and functional niches for microorganisms. 相似文献
12.
Effect of different 15N labeled sources on the estimation of N2 fixation was investigated. The combination of 15N labeled ammonium sulfate, 15N labeled plant material, and 15N labeled ammonium sulfate with unlabeled plant material, was examined in pot experiments. Two cultivars of soybean (Glycine max) and one of mungbean (Vigna radiata) were used. No significant difference was observed among the treatments for the estimation of N2 fixation. This was due to the homogeneity and stability of the 15N abundance in soil which resulted in a similar N uptake from the soil by the N2 fixing and reference crops. The plant yield, total N uptake and amount of N2 fixed were higher in the Yellow Soil than in the Andosol. The amount of N2 fixed was strongly influenced by the plant growth and consequently it affected the plant yield. The slow decomposition of plant material in the Andosol resulted in a low yield in both the N2 fixing and reference crops. Thus, the artificial decrease of the available N content in soil, by application of plant material, did not stimulate N, fixation but suppressed plant growth and N2 fixation. 相似文献
13.
Mingrelia España Frank Rasche Ellen Kandeler Belkis Rodriguez Georg Cadisch 《Pedobiologia》2011,54(3):187-193
As limited information is available about the relationship between microbial processes and community structure in tropical soils, we used 15N-DNA stable isotope probing (15N-DNA-SIP) to identify bacteria actively involved in decomposition of plant residues of different biochemical quality. 15N-labeled (90 atom%) and unlabeled (control) maize (C-to-N ratio: 32; cellulose content: 24.9%) and soybean (15; 15.5%) leaf residues were incubated in a tropical Vertisol for 15 days. Soil DNA was isolated, subjected to 15N-DNA-SIP and buoyant density-resolved DNA fractions were analyzed by 16S rRNA gene-based denaturing gradient gel electrophoresis (DGGE) analysis and sequencing of selected DGGE bands. Residue addition induced new bands and changed relative intensity of already existing bands in 15N-enriched SIP fractions. Phylogenetic analysis of selected, cloned DGGE bands from ‘heaviest’ 15N-enriched fractions (57.8 atom% (maize), 87.1 atom% (soybean)) revealed that soils treated with maize residues were dominated by Pseudonocardia sp., while Arthrobacter sp. and Streptomyces sp. were found in the soybean residue treated soils. Sequences related to Bacillus sp. and Saccharopolyspora sp. were found in both organic residue treatments. Our study gave clear evidence that 15N-DNA-SIP combined with 16S rRNA gene-based community fingerprinting of density-resolved fractions and an unlabeled control was suited for detecting active bacteria involved in decomposition of complex maize and soybean residues. In conclusion, we could show that residue quality, inducing contrasting N assimilation by decomposing bacteria, was a substantial determinant of certain decomposing community members assayed in this study. 相似文献
14.
Slavka Georgieva Søren Christensen Karen Stevnbak 《Soil biology & biochemistry》2005,37(10):1763-1774
The quality of plant material affects the vigor of the decomposition process and composition of the decomposer biota. Root residues from hairy vetch (Vicia villosa Roth), rye (Secale cereale L.) and vetch+rye, packed in litterbags were placed in pots of soil at 15 C and the content of the bags was analyzed after 2, 4, 8 and 12 weeks. Bacterial biomass did not differ between residues with contrasting composition. Among bacterivores groups of nematodes that require high bacterial production dominated in fast decomposing resources whereas flagellates with smaller requirements prevail in slower decomposing resources. Biomass of bacterial feeding nematodes correlated positively with early phase (0-2 wk) decomposition that increased in the order: rye< vetch+rye<vetch. Bacterial biomass therefore seems to be under top-down (predation) control during early decomposition. In contrast, the fungal biomass differed between resources with highest values for rye. Moreover, this increase in fungal biomass occurred later during succession and was correlated with decomposition activity for rye in that period. Fungal biomass therefore seems to be under bottom-up (resource) control. The composition of the nematode assemblages (composed of 25 taxa) showed a clear relationship to initial plant resource quality as well as decomposition phase. Early successional microbivorous nematodes vary according to resource quality with demanding bacterivores+predators (Neodiplogasteridae) dominating in vetch and less demanding bacterivores (Rhabditidae) and fungivores (Aphelenchus) being equally common in vetch and rye. Later in the succession (2-4 wk) bacterivorous Cephalobidae and fungivorous Aphelenchoides prevailed similarly on the different root materials whereas bacterivorous protozoa and the amoebal fraction thereof dominated in rye. At week 12 no species dominated the nematode assemblages that were similar between the resources. The differences between nematode assemblages among plant resources at 2 week were similar to the results of a field study sampled after 6 weeks with the same soil and plant resources. This lends support to the relevance of the successional patterns observed in this incubation study. 相似文献
15.
It is generally accepted that during the early stages of residue decomposition, easily available compounds are decomposed, leading to a relative increase in more recalcitrant compounds in the later stages of decomposition and that these changes in substrate availability are associated with changes in microbial community composition. However most studies on residue decomposition are conducted over several weeks or months; little is known about the changes in microbial community composition in the first weeks of decomposition. To address this knowledge gap, we incubated wheat residues inoculated with a microbial suspension in mesh bags buried in sand for 30 days, with sampling on days 0, 2, 4, 6, 8, 10, 15, 20, 25 and 30. Of the C added with the residues, 10, 18 and 25% had been respired on days 10, 20 and 30, respectively. The sum of PLFAs (phospholipid fatty acids), as an indicator of microbial biomass, increased strongly in the first 4 days and then decreased. The concentration of bacterial fatty acids was maximal on days 2 and 4, whereas the concentration of fungal fatty acids peaked on day 15. Microbial community composition (based on PLFA patterns) changed rapidly, with significant changes in the first 8 days and from day 8 to day 20. There were no significant changes in microbial community composition after day 20. The concentration of water-soluble C decreased strongly in the first 8 days, suggesting that the rapid changes in microbial community in this period are related to the changes in water-soluble C. Residue C chemistry, assessed by 13C NMR spectroscopy, changed little during the incubation period. This study showed that microbial community composition in decomposing residues changes rapidly in the first 1-2 weeks, which is, at least partly, the result of competition for the easily available compounds in the water-soluble fraction. After depletion of the water-soluble compounds, the microbial community composition changes more slowly. 相似文献
16.
Edward Ayres Heidi Steltzer Rodney T. Simpson Matthew D. Wallenstein William J. Parton Diana H. Wall 《Soil biology & biochemistry》2009,41(3):606-610
Several leaf litter decay studies have indicated that decomposition occurs more rapidly when litter is placed beneath the plant species from which it had been derived than beneath a different plant species (i.e. home-field advantage, HFA), although support for this notion has not been universal. We provide the first quantification of HFA in relation to leaf litter decomposition using published litter mass loss data from forest ecosystems in North America, South America, and Europe. Our findings indicate that HFA is widespread in forest ecosystems; on average litter mass loss was 8% faster at home than away. We hypothesize that HFA results from specialization of the soil biotic community in decomposing litter derived from the plant above it. Climate and initial litter quality data can be used to explain about 70% of the variability in litter decomposition at a global scale, leaving about 30% unexplained. We suggest that HFA be recognized as a factor that explains some of this remaining variability. 相似文献
17.
《Communications in Soil Science and Plant Analysis》2012,43(3-4):574-586
Abstract Nitrogen (N) management may be improved by a thorough understanding of the nutrient dynamics during previous‐crop residue decomposition and its impact on fertilizer N fate in the soil–plant system. An experiment was conducted in the Argentine Pampas to evaluate the effect of maize and soybean as previouscrops and plow‐till and no‐till methods on N dynamics and 15N‐labeled fertilizer uptake during a wheat growing season. Maize and soybean residues released N under both tillage treatments, but N release was faster from soybean residues and when residues were buried by tillage. Net immobilization of N on decomposing residues was not detected. A regression model that accounted for 92% of remaining N variability included time, previous crop, and tillage treatment as independent variables. The rapid residue decomposition with N release was attributed to the high temperatures of the agroecosystem. The recovery of 15N‐labeled fertilizer in the wheat crop, soil organic matter, and decomposing residues was not statistically different between previous crop treatments or tillage systems. Crop uptake of fertilizer N averaged 52% across treatments. Forty percent of fertilizer N was removed in grains. Immobilization of labeled N on soil organic matter was substantial, averaging 34% of the 15N‐labeled fertilizer retained, but was very small on decomposing residues, averaging 0.2–3.0%. Fertilizer N not accounted for at harvest in the soil–plant system was 12% and was ascribed to losses. Previous crop or tillage system had no impact on wheat yield, but when soybean was the previous crop, N content of grain and straw+roots increased. Discussion is presented on the potential availability of N retained in wheat straw, roots, and soil organic matter for future crops. 相似文献
18.
Increasing organic carbon inputs to agricultural soils through the use of pastures or crop residues has been suggested as a means of restoring soil organic carbon lost via anthropogenic activities, such as land use change. However, the decomposition and retention of different plant residues in soil, and how these processes are affected by soil properties and nitrogen fertiliser application, is not fully understood. We evaluated the rate and extent of decomposition of 13C-pulse labelled plant material in response to nitrogen addition in four pasture soils of varying physico-chemical characteristics. Microbial respiration of buffel grass (Cenchrus ciliaris L.), wheat (Triticum aestivum L.) and lucerne (Medicago sativa L.) residues was monitored over 365-days. A double exponential model fitted to the data suggested that microbial respiration occurred as an early rapid and a late slow stage. A weighted three-compartment mixing model estimated the decomposition of both soluble and insoluble plant 13C (mg C kg−1 soil). Total plant material decomposition followed the alkyl C: O-alkyl C ratio of plant material, as determined by solid-state 13C nuclear magnetic resonance spectroscopy. Urea-N addition increased the decomposition of insoluble plant 13C in some soils (≤0.1% total nitrogen) but not others (0.3% total nitrogen). Principal components regression analysis indicated that 26% of the variability of plant material decomposition was explained by soil physico-chemical characteristics (P = 0.001), which was primarily described by the C:N ratio. We conclude that plant species with increasing alkyl C: O-alkyl C ratio are better retained as soil organic matter, and that the C:N stoichiometry of soils determines whether N addition leads to increases in soil organic carbon stocks. 相似文献
19.
Pierre Bottner Lina Sarmiento Ruben Callisaya-Bautista 《Soil biology & biochemistry》2006,38(8):2162-2177
N-rich (C:N=27) and N-poor (C:N=130) wheat straw, labelled with 14C and 15N, was incubated for 2 yr in two major ecosystems of the upper elevation belt of cultivation in the high Andes: the moist Paramo (precipitation=1329 mm, altitude=3400 m asl, Andes of Merida, Venezuela) and the dry Puna (precipitation=370 mm, altitude=3800 m asl, Central Altiplano, Bolivia). The experiment was installed in young (2 yr) and old (7 yr) fallow plots. The following soil analyses were performed at nine sampling occasions: soil moisture, total-14C and -15N, and Microbial Biomass (MB)-14C and -15N. The measured data were fitted by the MOMOS-6 model (a process based model, with five compartments: labile and stable plant material, MB, and labile (HL) and stable humus (HS)) coupled with the SAHEL model (soil moisture prediction) using daily measured and/or predicted meteorological data. The aim was to understand how (1) the climatic conditions, (2) the quality of plant material, (3) the fallow age and (4) the soil properties affect the cycling of C and N within the soil organic matter system.The fallow age (2 and 7 yr) did not affect the measured data or the model predictions, indicating that in these systems the decomposition potential is not affected by fallow length. During the short initial active decomposition phase, the labile plant material was quickly exhausted, enabling a build up of MB and of HL. During the low activity phase, that covered 4/5 of the time of exposure, the MB size decreased slowly and the HL pool was progressively exhausted as it was reused by the MB as substrate. The HL compartment was directly or indirectly the major source for the inorganic 15N production. If the C:N ratio of the added plant material increased, the model predicted (1) a reduction of the decomposition rates of the plant material (essentially the stable plant material) and (2) an increased mortality of the MB which increased the production of HL (microbial cadavers and metabolites). Thus the essential effect of the slower decomposition due to the N-poor plant material was a higher accumulation of C and N in the HL and its slower recycling by the MB during the low activity phase. The labelling experiment allows to understand the higher soil native organic matter content in Paramo soils compared to Puna. The large sequestration of organic matter generally observed in the Paramo soils can be explained by two abiotic factors: the unfavourable soil microstructure and the accumulation of free aluminium linked to the climatic and acid soil conditions, inhibiting the microbial activity physically and chemically. 相似文献
20.
G. Seneviratne L. H. J. Van Holm S. A. Kulasooriya 《Biology and Fertility of Soils》1997,26(2):136-140
During the dry season in the tropics, agriculture which is solely dependent upon rainfall as its source of water is frequently
affected by soil moisture stress, resulting in crop failures. Farmers therefore depend mainly on other sources of limited
water supply during this period, such as ground water. Soil moisture conservation measures, especially surface mulching with
loppings and, occasionally, leaf litter and crop residues, are practised. Our objective was to study the decomposition and
nitrogen (N) release from these plant materials under continuously wet, low moisture regimes, i.e. comparable to those which
prevail in the mulches used in the agriculture. A greenhouse experiment was conducted with fresh, chopped leaves of six leguminous
trees, wild sunflower and rice, which were spread as a mulch on a layer of soil. They were maintained at eight moisture levels
(a total of between zero and 43l water m–2 applied over 8 weeks) by spraying water. Different optimal moisture requirements for the rapid decomposition of these species
were observed. These were presumably determined by different physical and chemical properties of the leaves. The amount of
water received to the mulches and their soluble polyphenolic and carbon (C) concentrations played an important role in determining
the decomposition and the mode of N release under non-limiting conditions of leaf N. Specifically, the C concentration governed
N release, while the effect of polyphenolics was important when their concentration was low, as a result of leaching under
relatively high moisture regimes. Leaves with a high polyphenolic and C content, which were subjected to high leaching losses
of these fractions, underwent a change in their N dynamics from net immobilization to mineralization. This study indicates
that leaves with a fast rate of decomposition should be mixed with other species, leaves which decompose more slowly in order
to increase the conservation of soil moisture and also improve the synchronization between N release from the mulch and its
demand by crops.
Received: 6 January 1997 相似文献