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1.
Plants often impact the rate of native soil organic matter turnover through root interactions with soil organisms; however the role of root-microbial interactions in mediation of the “priming effect” is not well understood. We examined the effects of living plant roots and N fertilization on belowground C dynamics in a California annual grassland soil (Haploxeralf) during a two-year greenhouse study. The fate of 13C-labeled belowground C (roots and organic matter) was followed under planted (Avena barbata) and unplanted conditions, and with and without supplemental N (20 kg N ha−1 season−1) over two periods of plant growth, each followed by a dry, fallow period of 120 d. Turnover of belowground 13C SOM was followed using 13C-phospholipid fatty acid (PLFA) biomarkers. Living roots increased the turnover and loss of belowground 13C compared with unplanted soils. Planted soils had 20% less belowground 13C present than in unplanted soils after 2 cycles of planting and fallow. After 2 treatment cycles, unlabeled soil C was 4.8% higher in planted soils than unplanted. The addition of N to soils decreased the turnover of enriched belowground 13C during the first treatment season in both planted and unplanted soils, however no effect of N was observed thereafter. Our findings suggest that A. barbata may increase soil C levels over time because root and exudate C inputs are significant, but that increase will be moderated by an overall faster C mineralization rate of belowground C. N addition may slow soil C losses; however, the effect was minor and transient in this system. The labeled root-derived 13C was initially recovered in gram negative (highest enrichment), gram positive, and fungal biomarkers. With successive growing seasons, the labeled C in the gram negative and fungal markers declined, while gram positive markers continued to accumulate labeled belowground C. The rhizosphere of A. barbata shifted the microbial community composition, resulting in greater abundances of gram negative markers and lower abundances of gram positive, actinobacteria and cyclopropyl PLFA markers compared to unplanted soil. However, the longer-term utilization of labeled belowground C by gram positive bacteria was enhanced in the rhizosphere microbial community compared with unplanted soils. We suggest that the activities of gram positive bacteria may be major controllers of multi-year rhizosphere-related priming of SOM decomposition. 相似文献
2.
We examined whether grass species and soil nitrogen (N) availability could enhance Carbon (C) and N turnover during root litter decay in grassland. Three species with increasing competitiveness (Festuca ovina, Dactylis glomerata and Lolium perenne) were grown at two N fertiliser levels in an undisturbed grassland soil, in which soil organic fractions derived for the last 9 years from Lolium root litter which was 13C-depleted. During the subsequent experimental year, the C turnover was calculated using the respective δ13C values of the old and new C in the root phytomass, in two Particulate Organic Matter (POM) fractions above 200 μm and in the lightest part of the aggregated soil fraction between 50 and 200 μm. Soil N availability was monitored during the regrowth periods with ion exchange resins (IER). The C decay rates of each particle size fraction were calculated with a simple mechanistic model of C dynamics. The N mineralisation immobilisation turnover (MIT) was characterised by dilution of 15N-labelled fertiliser in the N harvestThe C:N ratio and the residence time of C in the fractions decreased with particle size. The presence of a grass rhizosphere increased the decay rate of old C. Accumulation of new C in particle size fractions increased with species competitiveness and with N supply. Species competitiveness increased C turnover in the aggregated fraction, as a result of greater accumulation of new C and faster decay of old C. Fertiliser N increased N turnover and C mineralisation in the SOM. Species competitiveness decreased soil -N exchanged with the IER and increased dissolved organic C (DOC) content. The nature of the current rhizosphere is thus an important factor driving C and N transformations of the old root litter, in relation with grass species strategy. Plant competitiveness may stimulate the C and N turnover in the more evolved SOM fractions in a similar way to the mineral N supply. 相似文献
3.
Soil food webs are mainly based on three primary carbon (C) sources: root exudates, litter, and recalcitrant soil organic matter (SOM). These C sources vary in their availability and accessibility to soil organisms, which could lead to different pathways in soil food webs. The presence of three C isotopes (12C, 13C and 14C) offers an unique opportunity to investigate all three C sources simultaneously. In a microcosm experiment we studied the effect of food web complexity on the utilization of the three carbon sources. We choose an incomplete three factorial design with (i) living plants, (ii) litter and (iii) food web complexity. The most complex food web consisted of autochthonous microorganisms, nematodes, collembola, predatory mites, endogeic and anecic earthworms. We traced C from all three sources in soil, in CO2 efflux and in individual organism groups by using maize grown on soil developed under C3 vegetation and application of 14C labelled ryegrass shoots as a litter layer. The presence of living plants had a much greater effect on C pathways than food web complexity. Litter decomposition, measured as 14CO2 efflux, was decreased in the presence of living plants from 71% to 33%. However, living plants increased the incorporation of litter C into microbial biomass and arrested carbon in the litter layer and in the upper soil layer. The only significant effect of food web complexity was on the litter C distribution in the soil layers. In treatments with fungivorous microarthropods (Collembola) the incorporation of litter carbon into mineral soil was reduced. Root exudates as C source were passed through rhizosphere microorganisms to the predator level (at least to the third trophic level). We conclude that living plants strongly affected C flows, directly by being a source of additional C, and indirectly by modifying the existing C flows within the food web including CO2 efflux from the soil and litter decomposition. 相似文献
4.
Understanding soil organic matter (SOM) decomposition and its interaction with rhizosphere processes is a crucial topic in soil biology and ecology. Using a natural 13C tracer method to separately measure SOM-derived CO2 from root-derived CO2, this study aims to connect the level of rhizosphere-dependent SOM decomposition with the C and N balance of the whole plant–soil system, and to mechanistically link the rhizosphere priming effect to soil microbial turnover and evapotranspiration. Results indicated that the magnitude of the rhizosphere priming effect on SOM decomposition varied widely, from zero to more than 380% of the unplanted control, and was largely influenced by plant species and phenology. Balancing the extra soil C loss from the strong rhizosphere priming effect in the planted treatments with C inputs from rhizodeposits and root biomass, the whole plant–soil system remained with a net carbon gain at the end of the experiment. The increased soil microbial biomass turnover rate and the enhanced evapotranspiration rate in the planted treatments had clear positive relationships with the level of the rhizosphere priming effect. The rhizosphere enhancement of soil carbon mineralization in the planted treatments did not result in a proportional increase in net N mineralization, suggesting a possible de-coupling of C cycling with N cycling in the rhizosphere. 相似文献
5.
A theoretical approach to the partitioning of carbon dioxide (CO2) efflux from soil with a C3 vegetation history planted with maize (Zea mays), a C4 plant, into three sources, root respiration (RR), rhizomicrobial respiration (RMR), and microbial soil organic matter (SOM) decomposition (SOMD), was examined. The δ13C values of SOM, roots, microbial biomass, and total CO2 efflux were measured during a 40-day growing period. A three-source isotopic mass balance based on the measured δ13C values and on assumptions made in other studies showed that RR, RMR, and SOMD amounted to 91%, 4%, and 5%, respectively. Two assumptions were thoroughly examined in a sensitivity analysis: the absence of 13C fractionation and the conformity of δ13C of microbial CO2 and that of microbial biomass. This approach strongly overestimated RR and underestimated RMR and microbial SOMD. CO2 efflux from unplanted soil was enriched in 13C by 2.0‰ compared to microbial biomass. The consideration of this 13C fractionation in the mass balance equation changed the proportions of RR and RMR by only 4% and did not affect SOMD. A calculated δ13C value of microbial CO2 by a mass balance equation including active and inactive parts of microbial biomass was used to adjust a hypothetical below-ground CO2 partitioning to the measured and literature data. The active microbial biomass in the rhizosphere amounted to 37% to achieve an appropriate ratio between RR and RMR compared to measured data. Therefore, the three-source partitioning approach failed due to a low active portion of microbial biomass, which is the main microbial CO2 source controlling the δ13C value of total microbial biomass. Since fumigation-extraction reflects total microbial biomass, its δ13C value was unsuitable to predict δ13C of released microbial CO2 after a C3-C4 vegetation change. The second adjustment to the CO2 partitioning results in the literature showed that at least 71% of the active microbial biomass utilizing maize rhizodeposits would be necessary to achieve that proportion between RR and RMR observed by other approaches based on 14C labelling. The method for partitioning total below-ground CO2 efflux into three sources using a natural 13C labelling technique failed due to the small proportion of active microbial biomass in the rhizosphere. This small active fraction led to a discrepancy between δ13C values of microbial biomass and of microbially respired CO2. 相似文献
6.
We used a continuous labeling method of naturally 13C-depleted CO2 in a growth chamber to test for rhizosphere effects on soil organic matter (SOM) decomposition. Two C3 plant species, soybean (Glycine max) and sunflower (Helianthus annus), were grown in two previously differently managed soils, an organically farmed soil and a soil from an annual grassland. We maintained a constant atmospheric CO2 concentration at 400±5 ppm and δ13C signature at −24.4‰ by regulating the flow of naturally 13C-depleted CO2 and CO2-free air into the growth chamber, which allowed us to separate new plant-derived CO2-C from original soil-derived CO2-C in soil respiration. Rhizosphere priming effects on SOM decomposition, i.e., differences in soil-derived CO2-C between planted and non-planted treatments, were significantly different between the two soils, but not between the two plant species. Soil-derived CO2-C efflux in the organically farmed soil increased up to 61% compared to the no-plant control, while the annual grassland soil showed a negligible increase (up to 5% increase), despite an overall larger efflux of soil-derived CO2-C and total soil C content. Differences in rhizosphere priming effects on SOM decomposition between the two soils could be largely explained by differences in plant biomass, and in particular leaf biomass, explaining 49% and 74% of the variation in primed soil C among soils and plant species, respectively. Nitrogen uptake rates by soybean and sunflower was relatively high compared to soil C respiration and associated N mineralization, while inorganic N pools were significantly depleted in the organic farm soil by the end of the experiment. Despite relatively large increases in SOM decomposition caused by rhizosphere effects in the organic farm soil, the fast-growing soybean and sunflower plants gained little extra N from the increase in SOM decomposition caused by rhizosphere effects. We conclude that rhizosphere priming effects of annual plants on SOM decomposition are largely driven by plant biomass, especially in soils of high fertility that can sustain high plant productivity. 相似文献
7.
Initial decomposition rates, changes in organic chemical components (acid-insoluble fraction, holocellulose, polyphenols, soluble carbohydrates) and nutrient dynamics (K, Mg, Ca, P, N) were examined for fine roots and leaves of Japanese cypress (Chamaecyparis obtusa). Litterbag experiments designed to evaluate the relative effects of litter type and position of litter supply in the soil were carried out, considering that root and leaf litter typically occupy different locations and have different substrate qualities. Litterbags of roots and leaves were placed at two positions (on the soil surface and in the humus layer), and collected every 3 months over one year. The mass loss rate and N release were slower during root decomposition in the humus layer than during leaf decomposition on the soil surface. These differences between root and leaf decomposition were mainly caused by the litter type, and the effect of the position on decomposition was relatively small. Root litter was less influenced by position related effects, such as differences in humidity, than leaf litter, and this recalcitrant trait to environmental effects may be responsible for the slower mass loss rate and N release in root decomposition. The results of the present study suggest that fine roots are persistent in the soil and serve an important role in N retention in forest ecosystems because of their litter substrate quality. 相似文献
8.
Carol M. Schwendener Plinio B. de Camargo Erick C.M. Fernandes 《Soil biology & biochemistry》2005,37(4):787-794
It has been proposed that the C/N ratio, or quality, of litter or mulch mixtures affects N release. Although total N release from these mixtures and the effects on soil N are relatively well understood, a mechanistic understanding of the interactions between litter species with respect to their N release is still lacking. This study examines decomposition and N dynamics in mixtures of high-quality leguminous mulch, gliricidia [Gliricidia sepium (Jacq.) Kunth. ex Walp.] with a C/N ratio of 13, and low-quality cupuaçu [Theobroma grandiflorum (Wild. ex Spring) Schumann] litter with a C/N ratio of 42, which occur in combination in agroforestry systems. Ratios of 100:0, 80:20, 50:50, 20:80, 0:100 of fresh 15N-enriched gliricidia leaves and senescent cupuaçu leaves, totaling the same dry weight of 6.64 t ha−1, were applied to an Oxisol and sampled at 6, 14, 38, and 96 days after application. After more than 40% of the N in the gliricidia leaves had been released and the microbial biomass N reached its peak, a significant increase in available soil N occurred at day 14, which was more pronounced with greater amounts of gliricidia in the leaf mixture. However, relative to the N applied in the leaf mixture, there was no significant difference in available soil N with greater proportions of gliricidia. Total N release from the mixtures corresponded to the total N applied by gliricidia. Until day 38, cupuaçu C mineralization was significantly faster in the presence of the highest proportion of gliricidia compared to lower proportions. This faster C mineralization of more than 0.5% per day, however, did not increase total C loss or N release from cupuaçu leaves after 96 days. The use of 15N tracers identified an N transfer from gliricidia leaves and the soil to cupuaçu leaves and consequently, a lower N release from gliricidia to the soil in the presence of cupuaçu leaves. Though we expected that available N in the soil would also decrease with greater amounts of cupuaçu litter in the mixture, our results indicated an additive effect of the two species on N release and soil mineral N, with gross interactions between them canceling net interactive effects. Therefore, N release of leaf mixtures behaved as predicted from a calculated sum of individual release patterns, in spite of a transfer of N from the high- to the low-quality leaves. 相似文献
9.
The rhizosphere priming effect (RPE) is increasingly being considered to be an important regulator of soil organic matter (SOM) decomposition and nutrient turnover, with potential importance for the global CO2 budget. As a result, studies on the RPE have rapidly increased in number over the last few years.Most of these experiments have been performed using unplanted soil as the control, which could potentially lead to incorrect assessment of the RPE. Therefore,we performed a greenhous... 相似文献
10.
Arbuscular mycorrhizal fungi contribute to C and N enrichment of soil organic matter in forest soils
Increasing evidence suggests that accretion of microbial turnover products is an important driver for isotopic carbon (C) and nitrogen (N) enrichment of soil organic matter (SOM). However, the exact contribution of arbuscular mycorrhizal fungi (AMF) to soil isotopic patterns remains unknown. In this study, we compared 13C and 15N patterns of glomalin-related soil protein (GRSP), which includes a main fraction derived from AMF, litter, and bulk soil in four temperate rainforests. GRSP was an abundant C and N pool in these forest soils, showing significant 13C and 15N enrichment relative to litter and bulk soil. Hence, cumulative accumulation of recalcitrant AMF turnover products in the soil profile likely contributes to 13C and 15N enrichment in forest soils. Further research on the relationship between GRSP and AMF should clarify the exact extent of this process. 相似文献
11.
Sat Darshan S. Khalsa Carolina A. Almanza Patrick H. Brown David R. Smart 《Soil Science and Plant Nutrition》2016,62(3):271-276
Our understanding of leaf litter carbon (C) and nitrogen (N) cycling and its effects on N management of deciduous permanent crops is limited. In a 30-day laboratory incubation, we compared soil respiration and changes in mineral N [ammonium (NH4+-N) + nitrate (NO3–-N)], microbial biomass nitrogen (MBN), total organic carbon (TOC) and total non-extractable organic nitrogen (TON) between a control soil at 15N natural abundance (δ15N = 1.08‰) without leaf litter and a treatment with the same soil, but with almond (Prunus dulcis (Mill.) D.A. Webb) leaf litter that was also enriched in 15N (δ15N = 213‰). Furthermore, a two-end member isotope mixing model was used to identify the source of N in mineral N, MBN and TON pools as either soil or leaf litter. Over 30 d, control and treatment TOC pools decreased while the TON pool increased for the treatment and decreased for the control. Greater soil respiration and significantly lower (p < 0.05) mineral N from 3 to 15 d and significantly greater MBN from 10 to 30 d were observed for the treatment compared to the control. After 30 d, soil-sourced mineral N was significantly greater for the treatment compared to the control. Combined mineral N and MBN pools derived from leaf litter followed a positive linear trend (R2 = 0.75) at a rate of 1.39 μg N g?1 soil day?1. These results suggest early-stage decomposition of leaf litter leads to N immobilization followed by greater N mineralization during later stages of decomposition. Direct observations of leaf litter C and N cycling assists with quantifying soil N retention and availability in orchard N budgets. 相似文献
12.
S. Bek 《Biology and Fertility of Soils》1994,17(1):21-26
Soil was amended with 14C-labelled unripe straw only (C:N ratio ca. 20), with 14C-labelled unripe straw plus unlabelled ripe straw (C:N ratio ca. 100) or with 14C-labelled unripe straw plus glucose. Half the samples with 14C-labelled straw and half the samples with 14C-labelled plus unlabelled straw were cropped with rape plants. A decreased rate of mineralization of the 14C-labelled straw was found in the planted soil compared with the unplanted soil. The reduction was most profound in the soil amended with both labelled and unlabelled straw, indicating that at least part of the reduction was due to competition between plants and microorganisms for mineral N. No other explanations for the decrease in mineralization in the presence of plants were found. The soil amended with glucose which simulated the effect of root exudates showed an increased rate of mineralization. Therefore, the reduction in the presence of plants was probably not due to microbial use of the rhizodeposition in favour of the labelled straw. Only a minor part of the reduction was apparently due to uptake of labelled C by the plant, as only small amounts were found in the roots and shoots at harvest. The difference in 14C mineralization between treatments was not reflected in the number of bacteria in the soil at harvest. The number of bacteria, which was determined by plate counts and direct microscopy, was the same in all the soils, rhizosphere soils as well as bulk soils. 相似文献
13.
外源水稻根系和茎叶碳氮在稻田土壤中释放的特征 总被引：2，自引：0，他引：2
东北地区气候寒冷,稻田土壤休耕期长,多处于冻结状态;水稻生长期短,土壤温度高且季节性淹水。外源水稻秸秆碳氮在东北地区稻田土壤休耕期和水稻生长期不同水热条件下的释放特征尚不完全清楚。通过室外培养试验方法,利用双标记(~(13)C和~(15)N)水稻根系和茎叶示踪技术和稳定同位素质谱分析技术,研究水稻根系和茎叶在稻田土壤中的腐解率、有机碳(氮)释放率的动态变化特征。结果表明:水稻茎叶、根系于秋季添加稻田土壤后,经过寒冷漫长的土壤休耕期(11月至次年5月),S1(标记根系+不标记茎叶)和S2(不标记根系+标记茎叶)处理的秸秆腐解率分别达30.2%和34.5%,水稻根系和茎叶碳释放率分别达30.9%和38.2%,氮释放率分别达7.4%和35.0%。添加一年时,S1和S2处理的秸秆腐解率分别达66.5%和66.6%,水稻根系和茎叶碳释放率分别为63.7%和65.8%,氮释放率分别为28.6%和51.1%,水稻根系氮释放率显著低于水稻茎叶氮释放率(P0.05)。本试验条件下,水稻根系和茎叶添加稻田土壤1年,水稻根系和茎叶的腐解率达65%左右,其碳释放与腐解几乎同步,但氮释放相对缓慢,水稻根系氮释放速度显著低于茎叶氮释放速度,温度升高明显促进了水稻根系和茎叶的腐解及其碳氮释放。 相似文献
14.
Christiane Kramer Mats Fröberg Luz Maria Cisneros Dozal Dachun Zhang Guaciara M. Santos 《Soil biology & biochemistry》2010,42(7):1028-56
Microbial communities in soil A horizons derive their carbon from several potential sources: organic carbon (C) transported down from overlying litter and organic horizons, root-derived C, or soil organic matter. We took advantage of a multi-year experiment that manipulated the 14C isotope signature of surface leaf litter inputs in a temperate forest at the Oak Ridge Reservation, Tennessee, USA, to quantify the contribution of recent leaf litter C to microbial respiration and biomarkers in the underlying mineral soil. We observed no measurable difference (<∼40‰ given our current analytical methods) in the radiocarbon signatures of microbial phospholipid fatty acids (PLFA) isolated from the top 10 cm of mineral soil in plots that experienced 3 years of litterfall that differed in each year by ∼750‰ between high-14C and low-14C treatments. Assuming any difference in 14C between the high- and low-14C plots would reflect C derived from these manipulated litter additions, we estimate that <∼6% of the microbial C after 4 years was derived from the added 1-4-year-old surface litter. Large contributions of C from litter < 1 year (or >4 years) old (which fell after (or prior to) the manipulation and therefore did not differ between plots) are not supported because the 14C signatures of the PLFA compounds (averaging 200-220‰) is much higher that of the 2004-5 leaf litter (115‰) or pre-2000 litter. A mesocosm experiment further demonstrated that C leached from 14C-enriched surface litter or the O horizon was not a detectable C source in underlying mineral soil microbes during the first eight months after litter addition. Instead a decline in the 14C of PLFA over the mesocosm experiment likely reflected the loss of a pre-existing substrate not associated with added leaf litter. Measured PLFA Δ14C signatures were higher than those measured in bulk mineral soil organic matter in our experiments, but fell within the range of 14C values measured in mineral soil roots. Together, our experiments suggest that root-derived C is the major (>60%) source of C for microbes in these temperate deciduous forest soils. 相似文献
15.
Substrate quality and decomposition (measured as CO2 release in laboratory microcosms) of fresh leaf litter and fine roots of Cupressus lusitanica, Pinus patula, Eucalyptus grandis and native forest trees were studied. Changes in litter chemistry in each forest stand were analysed by comparing fresh leaf litter (collected from trees) and decomposed litter from the forest floor. Elemental concentrations, proximate fractions including monomeric sugars, and cross polarisation magic-angle spinning (CPMAS) 13C NMR spectra were analysed in leaf litters, decomposed litter and fine roots. Leaf litters and fine roots varied in their initial substrate chemistry with Ca concentration in leaf litters being higher than that in fine roots. In each stand, fine roots had a higher acid unhydrolysable residue (AUR) (except for the Pinus stand), higher holocellulose concentration and lower concentration of water-soluble extractives (WSE) and dichloromethane extractives (NPE) than fresh leaf litter. Likewise, 13C NMR spectra of fine roots showed lower alkyl and carboxyl C, and higher phenolic (except P. patula), aromatic and O-alkyl C proportions than leaf litters. Compared with fresh leaf litter, decomposed litter had lower concentrations of potassium, holocellulose, WSE, NPE, arabinose and galactose, similar or higher concentrations of Mg, Ca, S and P, and higher concentrations of N and AUR. CPMAS 13C NMR spectra of decomposed litter showed a higher relative increase in signal intensity due to methoxyl C, aromatic C, phenolic C and carboxylic C compared with alkyl C. In a microcosm decomposition study, the proportion of initial C remaining in leaf litter and fine roots significantly fitted an exponential regression model. The decomposition constants (k) ranged between 0.0013 and 0.0030 d−1 for leaf litters and 0.0010-0.0017 d−1 for fine roots. In leaf litters there was a positive correlation between the k value and the initial Ca concentration, and in fine roots there was an analogous positive correlation with initial WSE. Leaf litters decomposed in the order Cupressus>native forest>Eucalyptus∼Pinus, and fine roots in the order Pinus>native forest>Cupressus∼Eucalyptus. In each stand the fine root decomposition was significantly lower than the leaf litter decomposition, except for the P. patula stand where the order was reversed. 相似文献
16.
Nicole J. Mathers Rajesh K. Jalota Ram C. Dalal Sue E. Boyd 《Soil biology & biochemistry》2007,39(5):993-1006
Plant litter and fine roots are important carbon (C) inputs to soil and a direct source of CO2 to the atmosphere. Solid-state carbon-13 nuclear magnetic resonance (13C-NMR) spectroscopy was used to investigate the nature of C changes during decomposition of plant litter and fine roots of mulga (Acacia aneura F. Muell. Ex. Benth.), wheat (Triticum aestivum L.), lucerne (Medicago sativa) and buffel grass (Cenchrus ciliaris) over an 18-month period. Alkyl C was closely associated with total N concentrations in all litter materials during decay and as alkyl C increased so did total N, indicating an increase in refractory biomacromolecules. Mulga phyllodes had the greatest alkyl C concentration of all litter and fine root materials, and also exhibited the NMR peaks assigned to tannins that may slow or hinder decomposition rates and nitrification. Mulga litter and fine roots decomposed slower than all other litter materials and the soil under mulga had the highest soil C concentration, indicating slower CO2 release. The alkyl C-to-O-alkyl C ratio is generally used as an index of the extent of decomposition, but is not useful for the decay of woody components. Of all the NMR ratios studied that may indicate the extent of decomposition, the carbohydrate C-to-methoxyl C ratio proved to have the strongest and most consistent relationship with decay time, fraction of mass remaining and total C, even though increases in alkyl C were observed with decreases in carbohydrate C. 相似文献
17.
S.A. Billings 《Soil biology & biochemistry》2006,38(9):2934-2943
In the grassland/forest ecotone of North America, many areas are experiencing afforestation and subsequent shifts in ecosystem carbon (C) stocks. Ecosystem scientists commonly employ a suite of techniques to examine how such land use changes can impact soil organic matter (SOM) forms and dynamics. This study employs four such techniques to compare SOM in grassland (Bromus inermis) and recently forested (∼35 year, Ulmus spp. and Quercus spp.) sites with similar soil types and long-term histories in Kansas, USA. The work examines C and nitrogen (N) parameters in labile and recalcitrant SOM fractions isolated via size and density fractionation, acid hydrolysis, and long-term incubations. Size fractionation highlighted differences between grassland and forested areas. N concentration of forested soils’ 63-212 μm fraction was higher than corresponding grassland soils’ values (3.0±0.3 vs. 2.3±0.3 mg gfraction−1, P<0.05), and N concentration of grassland soils’ 212-2000 μm fraction was higher than forested soils (3.0±0.4 vs. 2.3±0.2 mg gfraction−1, P<0.05). Similar trends were observed for these same fractions for C concentration; forested soils exhibited 1.3 times the C concentration in the 63-212 μm fraction compared to this fraction in grassland soils. Fractions separated via density separation and acid hydrolysis exhibited no differences in [C], [N], δ15N, or δ13C when compared across land use types. Plant litterfall from forested sites possessed significantly greater N concentrations than that from grassland sites (12.41±0.10 vs. 11.62±0.19 mg glitter−1). Long-term incubations revealed no differences in C or N dynamics between grassland and forested soils. δ13C and δ15N values of the smallest size and the heavier density fractions, likely representing older and more recalcitrant SOM, were enriched compared to younger and more labile SOM fractions; δ15N of forested soils’ 212-2000 μm fraction were higher than corresponding grassland soils (1.7±0.3‰ vs. 0.5±0.4‰). δ13C values of acid hydrolysis fractions likely reflect preferential losses of 13C-depleted compounds during hydrolysis. Though C and N data from size fractions were most effective at exhibiting differences between grassland and forested soils, no technique conclusively indicates consistent changes in SOM dynamics with forest growth on these soils. The study also highlights some of the challenges associated with describing SOM parameters, particularly δ13C, in SOM fractions isolated by acid hydrolysis. 相似文献
18.
V. Wolters 《Biology and Fertility of Soils》1991,11(2):151-156
Summary The effects of simulated acid rain on litter decomposition in a calcareous soil (pHH
2
O 5.8) were studied. Litterbags (45 m and 1 mm mesh size) containing freshly fallen beech leaf litter were exposed to different concentrations of acid in a beech forest on limestone (Göttinger Wald. Germany) for 1 year. Loss of C, the ash content, and CO2–C production were measured at the end of the experiment. Further tests measured the ability of the litter-colonizing microflora to metabolize 14C-labelled beech leaf litter and hyphae. The simulated acid rain strongly reduced CO2–C and 14CO2–C production in the litter. This depression in production was very strong when the input of protons was 1.5 times greater than the normal acid deposition, but comparatively low when the input was 32 times greater. acid deposition may thus cause a very strong accumulation of primary and secondary C compounds in the litter layer of base-rich soils, even with a moderate increase in proton input. The presence of mesofauna significantly reduced the ability of the acid rain to inhibit C mineralization. The ash content to the 1-mm litterbags indicated that this was largely due to transport of base-rich mineral soil into the litter. 相似文献
19.
F.A.de Alcântara P Buurman A.E.Furtini Neto E.L Meijer 《Soil biology & biochemistry》2004,36(9):1497-1508
This work is part of a research program with the general objective of evaluating soil sustainability in areas surrounding hydroelectric reservoirs, which have been planted with riparian forest. The specific aims were: (i) to assess if and how the soil organic matter (SOM) chemical composition has changed in such areas, and (ii) to contribute to the knowledge of SOM chemistry in Brazil. To this end, we sampled litter and soil (Anionic Acrustox) in two adjacent areas: one under native vegetation and another forested with riparian species in 1992. The native vegetation was Brazilian savannah orcerrado. In this case, it was a ‘grassy cerrado’, dominated by grasses with few shrubs. Litter was collected and humic substances were extracted from soil by an alkaline solution. Both were characterised by a combination of cross-polarisation-magic angle spinning (CPMAS) solid state 13C nuclear magnetic resonance (NMR) spectroscopy and pyrolysis-gas-chromatography/mass-spectrometry (Py-GC/MS). Eight years after forestation, the addition of the forest litter had changed SOM chemical composition. The C input pattern exerted a key role on the observed alterations. In the grassy cerrado, litter addition is predominantly below-ground and the litter is richer in carbohydrate-derived compounds and poorer in lignin moieties. In the forested area, C input is largely above-ground and grass litter has been partially replaced by a relatively more recalcitrant material. As a result, topsoil under forest was chemically strongly different from that under cerrado. Factor analysis indicated that the largest differences were between topsoil under forest and deepest subsoil under cerrado, where there is influence of remaining cerrado-derived C. Both semi-quantification and factor analysis of pyrolysis data gave further insight on the extent of alterations, but more research on such a quantitative approach should be developed to detail its application in SOM studies. 相似文献
20.
The possible effects of excreta of the Great Cormorant Phalacrocorax carbo on decomposition processes and dynamics of nutrients (N, P, Ca, K, Mg) and organic chemical components (lignin, total carbohydrates) were investigated in a temperate evergreen coniferous forest near Lake Biwa in central Japan. Two-year decomposition processes of needles and twigs of Chamaecyparis obtusa were examined at two sites, control site never colonized by the cormorants (site C) and colonizing site (site 2). Mass loss was faster in needles than in twigs. Mass loss of these litter types was faster at site C than at site 2, which was ascribed to the decreased mass loss rate of acid-insoluble ‘lignin’ at site 2. Net immobilization of N, P, and Ca occurred in needles and twigs at site 2; whereas at site C, mass of these elements decreased without immobilization during decomposition. Duration of immobilization phase of these nutrients at site 2 was estimated to be 1.6 to 2.5 years in needles and 19.6 to 23.5 years in twigs. Immobilization potential (maximum amount of exogenous nutrient immobilized per gram initial material) was similar between needles and twigs for N and Ca but was about 10 times higher in twigs than in needles for P. δ13C in needles was relatively constant during the first year and then increased during the second year, whereas δ13C in twigs was variable during decomposition. Acid-insoluble fraction was depleted in 13C compared to whole needles (1.6-2.1‰) and twigs (2.0-2.5‰). δ15N of needles and twigs and their acid-insoluble fractions approached to δ15N of excreta during decomposition at site 2. This result demonstrated the immobilization of excreta-derived N into litter due to the formation of acid-insoluble lignin-like substances complexed with excreta-derived N. No immobilization occurred in K and Mg and their mass decreased during decomposition at both sites. Based on these results of nutrient immobilization during decomposition and on the data of litter fall and excreta amount at site 2, we tentatively calculated stand-level immobilization potential of litter fall and its contribution to total amount of N and P deposited as excreta. Thus, the potential maximum amount immobilized into litter fall (needles and twigs) was estimated to account for 5-7% of total excreta-derived N and P. 相似文献