Effects of soil mesofauna and farming management on decomposition of clover litter: a microcosm experiment

The effects of soil mesofauna and different farming systems on decomposition of clover (Trifolium repens) litter were investigated in a laboratory experiment. Microcosms were incubated for 16 weeks with fine and coarse litterbags in soils from three types of management systems: fallow, integrated farming and organic farming, the latter two cropped with wheat. The effects were studied by analysing litter mass loss, C and N content, DOC, nitrate and pH in soil leachate, and CO₂ production, as well as mesofauna. Mesofauna significantly accelerated mass loss and C and N release from clover litter in all three soils. With mesofauna access, at the end of the experiment average clover mass loss was almost twice as high and clover C and N content were 60% lower than without mesofauna. Farming systems influenced the decomposition through affecting both element turnover and mesofauna. Although in the first weeks less N was leached from organic farming than from integrated farming soil, cumulative N leaching did not differ between these soils. However, more than 20% less N was leached from the fallow soil than from the field soils. CO₂ production was highest in fallow soil. Here, mesofauna had no effect on this variable. In soil with integrated farming, mesofauna reduced cumulative CO₂ production by 10% whereas in soil from organic farming it increased CO₂ production by 20%. Our data suggest that differences in C and N turnover in different management systems are strongly mediated by soil mesofauna.     

Predicting soil fauna effect on plant litter decomposition by using boosted regression trees

Extensive studies have been conducted to evaluate the effect of soil fauna on plant litter decomposition in terrestrial ecosystems. However, scholars have reported inconsistent results on the direction and magnitude of the soil fauna effect. We present a global synthesis of 75 papers that cover 197 plant species with 543 cases of plant litter decomposition experiments and soil fauna effects on plant litter decomposition. By using a boosted regression tree model (BRT), we aim to provide a synthesis of existing data that comprehensively and quantitatively evaluates how climate, plant litter quality, and study methods interact with soil fauna in affecting plant litter decomposition. Global average effect size (ES) is −0.426, which indicates a 35% lower decomposition rate when soil fauna is excluded by physical or chemical exclusion techniques. The final model explains 32.3% of the variation in ES. The predictors that substantially account for the explained variation include mean annual temperature (MAT, 37.1%), mean annual precipitation (MAP, 9.7%), phosphorus (12.4%), nitrogen (5.6%), and lignin content (5.5%). By contrast, the heterogeneity of the study duration and soil fauna exclusion technique have negligible contributions (each <5%). Log effect size strongly decreases with both MAT and MAP. Plant litters with high quality have stronger soil fauna effect because the log effect size is negatively related to nitrogen and phosphorus content and positively related to lignin content. Our analysis demonstrates the critical role of climate and plant litter quality in determining the soil fauna effect on plant litter decomposition in terrestrial ecosystems. However, the large unexplained variation (67.7%) in ES in the BRT model indicates undiscovered mechanisms underlying the soil fauna effect in our analysis. We call for further studies on this topic in the future.     

Plant litter quality influences the contribution of soil fauna to litter decomposition in humid tropical forests, southwestern China

The aim of this field experiment was to quantify the contribution of soil fauna to plant litter decomposition in three forest sites differing in C/N ratio under natural conditions in Xishuangbanna, southwestern China. We conducted a survey of soil fauna communities, the forest floor litter and investigated mass loss of mixed tree species leaf litter for two years in a tropical secondary forest, an evergreen broad-leaf forest and a tropical rain forest. Exclusion treatments of different sized soil fauna from the leaf litter by using varying mesh size litter bags (2 mm and 0.15 mm) were also performed. Mass loss and C and N concentrations in litter bag leaf materials were determined at monthly intervals. We found that: (1) the three forests differed in floor litter biomass and nutrient contents but not in soil fauna richness and abundance; (2) litter mass loss and decomposition rate were slower when soil macrofauna and most of mesofauna were excluded; and (3) greatest soil fauna contribution to plant litter decomposition occurred in the rain forest, where leaf litter C/N ratio was also highest (41.5% contribution: 54.8 C/N ratio), in comparison to 8.69% in the broad-leaf forest and 19.52% in the secondary forest, both with low leaf litter C/N ratios (<32). Our results suggested that, soil fauna played a more pronounced role in the decomposition of mixed leaf litter in tropical rain forest, and significantly bigger effects from fauna were ascribed to the enhancement of N concentration and decrease of C concentration of the initially high C/N ratio litter in this forest site.     

Connectivity of litter islands remaining after a fire and unburnt forest determines the recovery of soil fauna

Forest wildfires can dramatically affect soil communities and reduce abundance and diversity of soil fauna. The recovery of soil animals after a fire depends both on immigration from the unburnt forest and on local survival in less-burnt spots, but the relative importance of these mechanisms is poorly known. Therefore, these factors were studied with regard to soil macrofauna and soil mites seven years after a wildfire occurring in a pine forest area with shallow soil in 2001 in central Sweden. Three replicate transects, each consisting of four plots were studied. The plots were located in (i) the unburnt forest close to the fire edge; (ii) slightly burnt patches directly attached to the unburnt forest; (iii) slightly burnt patches surrounded by bare rock but connected to the unburnt forest edge by a corridor with mostly unburnt litter and vegetation; and (iv) island patches not connected with a corridor to the unburnt forest edge. The hypothesis was that that soil animals would particularly disperse from the unburnt forest to moderately burnt plots inside a burnt area via the network of less-burnt corridors. Poor dispersers would be especially few in the island patches lacking connection to the “mainland”, whereas good dispersers would be independent of gaps in connectivity. As expected, the highest abundance of both macrofauna and oribatid mites was found in the unburnt forest. Resident soil macro- and mesofauna representatives had half the abundance in the edge and corridor plots as compared to the control, but their abundance was not lower in the island plots than in the corridor plots indicating on-site survival and recovery. Mobile mesostigmatid mites did not show any significant reduction of abundance in any of the plots. The abundance of soil-dwelling oribatid mites did not differ between islands and unburnt forest, but mobile aboveground oribatids had significantly lower abundance on the islands than in the unburnt forest. The opposite was observed for aboveground and belowground oribatid mite species richness. In conclusion, belowground animals showed mainly local survival and seemed to be independent of corridors presence, whereas most aboveground and mobile macro- and mesofauna seemed to be more responsive to isolation induced by forest fires. Soil and litter corridors connecting unburnt patches inside the burnt forests with the unburnt edges were important mainly for less mobile groups of soil macrofauna. This supports the idea that there is a relatively slow process of soil ecosystem recovery and that external colonization of the burnt areas dominates over the local survival and recovery from refuges.     

Impact of litter species diversity on decomposition processes and communities of soil organisms

The effect of plant species diversity and the C/N ratio of litter on soil processes were analysed in mesocosms in a three year field experiment. Plots 0.5 × 0.5 m with a depth of 15 cm containing sand mixed with loam were used to compare five natural and one artificial litter type (polypropylene string). Natural litters were either monospecific (I: Dactylis glomerata; II: Festuca rubra and III: Trifolium pratense) or were species mixtures (IV: mixture of three species I, II and III; V: mixture of twelve species, IV and nine other meadow plants). Differences among treatments in the litter decomposition rate, humic acid content and nematode density depended on the litter quality (C:N ratio) in most cases. By contrast, most of the differences among treatments found in the substratum below the litter cover resulted from litter diversity. The largest increase of carbon and nitrogen amount during growing season was found under litter mixtures (IV, V) and the highest fulvic acid content under the most diverse litter (V). Similarly, the production of algae in the substratum also significantly increased with litter diversity. Higher taxonomic diversity of Nematoda and Collembola and the most mature community of nematodes were observed under the most complex litter. Epigeic macrofauna, both dwelling in and penetrating the litter, did not differ significantly between experimental treatments. However, the highest share of predators was found in the treatment with the richest plant species diversity. In general, the results suggest that the decomposition of diverse plant litter enhances humus acid accumulation in soils. It is likely that algae participate in the process of humus formation.     

易分解有机碳输入量对武夷山不同林型土壤激发效应的影响

凋落物是植物同化碳的重要产物,是土壤有机碳库的主要来源。为系统了解凋落物分解对土壤碳库影响的研究进展,基于中国知网数据库（CNKI）和Web of Science（WOS）核心合集数据源,利用CiteSpace和VOSviewer文献可视化分析工具,从发文趋势、合作关系（团队、机构、国家）和期刊影响力等方面,对1989-2022年的相关文章进行计量分析。结果表明：国内和国际发文量总体呈增长态势。我国在该领域研究中发文量仅次于美国,占全球发文量的27.8％,表明我国研究者对该领域的研究有重要贡献,但整体影响力低于欧美发达国家（地区）,美国和法国综合影响力最高,英国和瑞士论文篇均被引较高。凋落物分解、有机质、气候变化、碳循环和碳储量等关键词是该领域近年来的热点研究主题。未来我国应继续加强国际间合作研究,侧重凋落物分解相关特性对气候变化的响应和对环境污染的研究,提高我国在该领域的研究水平,将研究成果及时转化到碳减排增汇的研究中。     

Positive relationship between herbaceous layer diversity and the performance of soil biota in a temperate forest

The current decline in biodiversity is particularly pronounced in the herbaceous layer of forest ecosystems. We explored the relationship between a naturally occurring plant diversity gradient in the understory vegetation of a deciduous forest and several above-and belowground ecosystem processes. We show that particularly soil microbial parameters and microarthropod densities are positively correlated with plant species richness. These results confirm recent findings in grassland ecosystems and highlight the intimate interconnectance between the diversity and functioning of above-and belowground compartments. We conclude that irrespective of a potential causal relationship between plant species richness and belowground processes, it is essential to consider the performance of soil biota in order to understand the relationship between herbaceous layer composition and ecosystem function.     

Photodegradation effects on CO2 emissions from litter and SOM and photo-facilitation of microbial decomposition in a California grassland

Decomposition of soil organic matter (SOM) and plant litter has been shown to be affected by high solar radiation; this could partly explain why biogeochemical models underestimate decomposition in arid and semi-arid ecosystems. We set out to test the effect of using traditional PVC chambers for measuring soil gas fluxes versus quartz chambers that allowed passage of light during field measurements in a dry-land field in Davis, CA. Results showed that fluxes from quartz-top chambers were on average 29% higher than from opaque chambers. We also studied the effect of solar light exposure on decomposition of native grass litter and SOM in a field experiment where plots were shaded or left exposed for 157 days during summer; litter did not seem to be affected by exposure to light. However, we concluded that SOM decomposition was affected by light exposure since shaded soil had similar respiration to sunlight-exposed soil indicating that microbial respiration occurred under the shade while photo-degradation likely occurred under the sun. Additionally, ¹⁵N-labeled grass was placed in litter bags in the field with either clear filters to allow light or aluminum covers to block light; 3-month exposure caused a change in lignin degradability as indicated by the change in the Ad/Al ratio. Incubation of that litter showed 9.3% more CO₂ produced from litter in clear and aluminum bags than unexposed litter. This showed that photo-facilitation occurred although to a small degree and was a result of light exposure and/or heat degradation. We attributed the similar respiration from clear- and aluminum-exposed litter to heat degradation of the aluminum-exposed litter. In conclusion, our results show that in hot dry ecosystems conventional PVC chambers underestimate measured CO₂ flux rates; sunlight exposure changes litter chemistry and appears to affect the degradation of soil organic matter, but the magnitude of degradation depends on an interaction of factors such as soil temperature and moisture.     

Impact of faunal complexity on microbial biomass and N turnover in field mesocosms from a spruce forest soil

In a field study using soil mesocosms in an acid spruce forest soil we investigated the effects of mesofauna and macrofauna on microbial biomass, dissolved organic matter, and N cycling. Intact soil monoliths were taken from the ground, defaunated by deep-freezing, and wrapped in nets of various mesh-sizes to control re-immigration of different faunal size-classes. The monoliths were then replanted in the field. Three treatments of mesocosms were prepared: (1) with only microbiota, (2) microbiota and mesofauna, and (3) microbiota, mesofauna, and macrofauna (= complex fauna). After 8 months of exposure the mesocosms and the unmanipulated control plots (treatment 4) were destructively sampled. We estimated microbial biomass by substrate-induced respiration and the chloroform fumigation-extraction method. N cycling was measured by monitoring microbial N mineralization, the NH _inf4 ^sup+ content, and selected amino acids and the activities of protease, urease, and deaminase. The results from the L/F layer showed that the pool of the microbial biomass was not changed by the activity of the mesofauna. However, the mesofauna and macrofauna together enhanced SIR. An increase in microbial N mineralization was only observed in treatment 3 (microbiota + complex fauna). Protease activity and NH _inf4 ^sup+ content increased in treatments 2 (microbiota + mesofauna) and 3 (microbiota + complex fauna). The complex fauna induced a soil pH increase in treatment 3 as opposed to treatment 1 and the control. This increase was presumably due to excretory NH _inf4 ^sup+ . Principal component analysis revealed that the complex fauna in treatment 3 caused a significantly higher N turnover per unit of microbial biomass.     

Effect of earthworm addition on soil nitrogen availability,microbial biomass and litter decomposition in mesocosms

The aim of the study was to determine the effect of adding two tropical earthworm species, Rhinodrilus contortus and Pontoscolex corethrurus, to mesocosms on the availability of mineral N (NH₄ ⁺ and NO₃ ^– concentrations), soil microbial biomass (bio-N), and the decomposition rates of three contrasting leaf litter species, in a glasshouse experiment. The mesocosms were filled with forest soil and covered with a layer of leaf litter differing in nutritional quality: (1) Hevea brasiliensis (C/N=27); (2) Carapa guianensis (C/N=32); (3) Vismia sp., the dominant tree species in the second growth forest (control, C/N= 42); and, (4) a mixture of the former three leaf species, in equal proportions (C/N=34). At the end of the 97-day experiment, the soil mineral N concentrations, bio-N, and leaf litter weight loss were determined. Both earthworm species showed significant effects on the concentrations of soil NO₃ ^– (p<0.01) and NH₄ ⁺ (p<0.05). Bio-N was always greater in the mesocosms with earthworms (especially with R. contortus) and in the mesocosms with leaf litter of H. brasiliensis (6 µg N g^–1 soil), the faster decomposing species, than in the other treatments (0.1–1.6 µg N g^–1). Thus, earthworm activity increased soil mineral-N concentrations, possibly due to the consumption of soil microbial biomass, which can speed turnover and mineralization of microbial tissues. No significant differences in decomposition rate were found between the mesocosms with and without earthworms, suggesting that experiments lasting longer are needed to determine the effect of earthworms on litter decomposition rates.     

华北地区有机种植和常规种植模式下土壤重金属含量及污染评价

为探讨有机种植与常规种植两种不同种植方式对土壤重金属含量和污染特性的影响,本文在华北5个地区选取典型的有机蔬菜和有机小麦种植基地及附近相似条件的常规种植地块,比较了土壤中Cu、Zn、Pb、Cr、Cd、As共6种重金属含量的差异,并采用不同评价方法对不同种植方式下土壤中重金属的污染程度进行了评价。结果表明:与常规种植相比,有机种植减轻了土壤酸化和盐渍化,提高了土壤有机质含量和阳离子交换量,在一定程度上有利于降低土壤中重金属的生物有效性。与土壤背景值相比,所有调查地区的土壤重金属均有不同程度的增加和积累。与常规种植相比,有机种植模式能有效降低土壤中Cd、Cr含量,有机小麦种植地块因长期施用大量有机肥导致土壤中Cu、Zn、As大量富集;而常规温室菜田同时施用大量的有机肥、化肥及农药,土壤中Cu、Zn、As富集的风险比有机种植模式高;露天蔬菜有机种植地块土壤中Cu、Zn、As含量与常规地块差异不明显。综合污染指数评价结果显示,调查地区土壤均属于轻污染程度,主要贡献因子为Cd、Cu、Zn,有机种植降低了土壤中重金属的综合污染水平;地累积指数法评价结果表明,调查地区处于无污染到中等污染水平,最明显的污染元素是Cd,有机种植降低了土壤中重金属污染的程度和风险;潜在生态危害指数评价结果表明,所调查地块存在轻微潜在生态风险,其中产生较大生态危害的是Cd,表现出轻微生态危害程度。本研究表明,有机种植减轻了土壤中重金属综合污染水平和污染风险,并减轻了土壤重金属的潜在生态危害。     

有机栽培和常规栽培水稻体系土壤酶及微生物量的比较研究

本研究探讨了有机栽培与常规栽培体系下水稻土微生物量及脲酶、酸性磷酸酶和过氧化氢酶的动态变化过程,以及有机栽培体系不同肥料调控措施对上述指标的影响.结果表明:与常规栽培水稻体系相比,有机栽培水稻有利于土壤微生物的生长和繁衍;水稻生长不同时期有机栽培方式的土壤微生物生物量碳、脲酶、酸性磷酸酶和过氧化氢酶活性均高于常规栽培体系.就水稻全生育期而言,土壤微生物生物量碳高于常规栽培7.3%～9.1%;脲酶、酸性磷酸酶和过氧化氢酶活性分别高于常规栽培7.3%～14.5%、5.2%～6.5%和12.5%～29.2%;有机水稻栽培体系下配施生态肥,在有机肥施用量减半时,土壤微生物生物量碳含量及土壤脲酶、酸性磷酸酶和过氧化氢酶活性较单施有机肥平均分别提高1.6%、6.8%、1.3%和14.8%,在水稻生长前期和中期该增加作用尤为显著.     

Changes in the fauna and its contribution to mass loss and N release during leaf litter decomposition in two deciduous forests

Investigations on the mass loss of leaf litter were carried out between 1992 and 1994 using litter bags of 0.02 mm and 5 mm mesh sizes in a beech and a mixed forest in northern Germany. The two forests on moder humus differed in soil faunal composition, vegetation type, and nutrient supply. Mass loss and N and C concentrations were determined from the litter at bimonthly intervals. From subsamples macrofauna were sorted by hand and mesofauna was extracted by heat. The biomass and N content of the litter bag fauna was estimated. Mass loss, particularly that attributed to the fauna, was different between the two sites with highest rates in the mixed forest and lowest at the beech site. A significantly higher rate of N release was found for the litter extracted from 5 mm mesh size litter bags in the mixed forest but not in the beech forest. Collembola and Cryptostigmata changed in numbers during litter breakdown. Collembola reached high numbers in the beginning, whereas Cryptostigmata dominated later. The diversity of Cryptostigmata increased at both sites during litter breakdown, whereas collembolan diversity only increased in the beech forest and remained at the same level in the mixed forest. Several species of Collembola and Cryptostigmata occurred earlier in the mixed forest than in the beech forest. Mass loss rate attributable to the fauna did not correspond to total faunal biomass. Only Isopoda, Diplopoda and Cryptostigmata appeared to affect the mass loss positively, whereas the biomass of Lumbricidae was negatively correlated with mass loss, particularly in the beech forest. On the other hand, the release of N attributable to the fauna was positively correlated with the total faunal biomass in the beech forest and Lumbricidae in particular were positively correlated with N-release at both sites.     

Effects of soil microarthropods on plant litter decomposition across an elevation gradient in the Wuyi Mountains

Soil microarthropods are considered to be among the strongest determinants of plant litter decomposition in warm, humid sites. Little is known, however, about the regulation of plant litter decomposition dynamics along an elevation gradient in such sites. Our study examined the contributions of soil microarthropods to leaf litter decomposition of a single substrate (Castanopsis carlesii) along an elevation gradient across four types of zonal vegetations in southeastern China: evergreen broadleaf forest (EVB): coniferous forest (COF): dwarf forest (DWF): and alpine meadow (ALM) during April 2007 to March 2008. Leaf litter decomposition of C. carlesii was significantly accelerated by the presence of fauna in all four sites. After 360 days in the field, mass loss rates with the full decomposer assemblage and in the reduction of microarthropods were 62.9% and 41.2% in EVB, 48.1% and 30.6% in COF, 36.4% and 27.8% in DWF, 30.3% and 23.7% in ALM, respectively. The percentage of total decomposition due to the presence of soil fauna was 37% in EVB, 25% in COF, 12% in DWF, and 8% in ALM, thus showing strong systematic variation along the elevational gradient. The mass losses in control plots at the four sites were significantly correlated with the abundances of total Acari, Collembolans, and Mesostigmata mites. Although the proportion of Oribatid mites at EVB was not the highest among the four sites, there were elevated proportions of Mesostigmatid and Prostigmata mites, many of which were microbe-consuming species and induce an indirect influence on litter decomposition. Moreover, Shannon Index (F = 2.455, p = 0.093) and Group Number (F = 5.830, p = 0.005) both decreased along the elevation gradients. Mass losses were also found to be distinctively related to H′ (r² = 0.984, p = 0.016), and GN (r² = 0.952, p = 0.048) across the four sites. Our results suggest that the faunal contribution to plant litter decomposition varies markedly across environmental gradients that differ in litter faunal diversity.     

Long-term organic farming fosters below and aboveground biota: Implications for soil quality, biological control and productivity

Organic farming may contribute substantially to future agricultural production worldwide by improving soil quality and pest control, thereby reducing environmental impacts of conventional farming. We investigated in a comprehensive way soil chemical, as well as below and aboveground biological parameters of two organic and two conventional wheat farming systems that primarily differed in fertilization and weed management strategies. Contrast analyses identified management related differences between “herbicide-free” bioorganic (BIOORG) and biodynamic (BIODYN) systems and conventional systems with (CONFYM) or without manure (CONMIN) and herbicide application within a long-term agricultural experiment (DOK trial, Switzerland). Soil carbon content was significantly higher in systems receiving farmyard manure and concomitantly microbial biomass (fungi and bacteria) was increased. Microbial activity parameters, such as microbial basal respiration and nitrogen mineralization, showed an opposite pattern, suggesting that soil carbon in the conventional system (CONFYM) was more easily accessible to microorganisms than in organic systems. Bacterivorous nematodes and earthworms were most abundant in systems that received farmyard manure, which is in line with the responses of their potential food sources (microbes and organic matter). Mineral fertilizer application detrimentally affected enchytraeids and Diptera larvae, whereas aphids benefited. Spider abundance was favoured by organic management, most likely a response to increased prey availability from the belowground subsystem or increased weed coverage. In contrast to most soil-based, bottom-up controlled interactions, the twofold higher abundance of this generalist predator group in organic systems likely contributed to the significantly lower abundance of aboveground herbivore pests (aphids) in these systems. Long-term organic farming and the application of farmyard manure promoted soil quality, microbial biomass and fostered natural enemies and ecosystem engineers, suggesting enhanced nutrient cycling and pest control. Mineral fertilizers and herbicide application, in contrast, affected the potential for top-down control of aboveground pests negatively and reduced the organic carbon levels. Our study indicates that the use of synthetic fertilizers and herbicide application changes interactions within and between below and aboveground components, ultimately promoting negative environmental impacts of agriculture by reducing internal biological cycles and pest control. On the contrary, organic farming fosters microbial and faunal decomposers and this propagates into the aboveground system via generalist predators thereby increasing conservation biological control. However, grain and straw yields were 23% higher in systems receiving mineral fertilizers and herbicides reflecting the trade-off between productivity and environmental responsibility.     

The role of Armadillidium vulgare (Isopoda: Oniscidea) in litter decomposition and soil organic matter stabilization

We studied the effects of the terrestrial isopod Armadillidium vulgare on organic matter decomposition and stabilization in a long-term (65-week) laboratory experiment. We quantified the microbial activity in leaf litter (Acer pseudoplatanus) which did not come into contact with isopods, in A. vulgare feces produced from the same litter, and in unconsumed leftover of this litter. Freshly fallen leaf litter and up to 3 day old feces and leftover of litter were used. All materials were air dried immediately after collection and rewetted 1 day before use. Simultaneously, we measured how microbial activity in litter and feces are affected by fluctuations in humidity and temperature and by the addition of easily decomposed substances (starch and glucose).Microbial respiration was lower in feces than in litter or unconsumed leaf fragments. At the same time, moisture and temperature fluctuations and addition of glucose or starch increased respiration much more in litter than in feces. The results indicate that the processing of litter by A. vulgare reduces microbial respiration and reduces the sensitivity of microbial respiration to environmental fluctuations. ¹³C NMR spectra from feces indicated preferential loss of polysaccharide-carbon and accumulation of lignin with some modification to the aromatic-carbon. TMAH-Py-GC MS showed that lignin content was higher in feces than in litter and that lignin quality differed between the two substrates. Guaiacyl units were depleted in the feces, which indicated breakdown of guaiacyl associated with gut passage. As a conclusion, the results suggest that this common isopod greatly affects leaf litter decomposition. Decomposition of isopod feces in a long-term experiment is lower than litter decomposition which may support stabilization of organic matter in soil. This is caused mainly due to higher content of aromatic carbon in feces, which may cause its considerable resistance to bacterial degradation.     

中国有机农业发展:贡献与启示

改革开放40年以来,中国农业和农村经济取得了令人瞩目的成就。当前,农业和农村发展正从数量型向质量和数量型并重的模式转变,需要对农业发展模式和措施进一步优化,其中有机农业近年来得到较快发展。到2016年底,中国有机农业耕地面积（180万hm²）约占全国耕地面积的1.5%,有机产值和销售额分别达1 323亿元和450.6亿元。有机农业发展,具有显著的环境、经济和社会效益,特别是在促进物质循环利用、发挥农业生态系统内生能力、加强生产者与消费者互动、振兴乡村经济、创造宜居环境等方面能够发挥重要作用。有机农业也面临着无法充分保障氮素供应以及适度规模化困难等挑战,需要在发展中考虑和关注。政府应制定和实施相应政策,采取生态补偿等具体措施,引导有机农业合理、有序发展。此外,发展有机农业更重要的意义在于对常规农业进行生态化改造,将有机农业理念、原则和技术在常规农业中推广应用,促进中国农业的健康和可持续发展。     

Direct effects of litter decomposition on soil dissolved organic carbon and nitrogen in a tropical rainforest

To clarify how litter decomposition processes affect soil dissolved organic carbon (DOC) and soil dissolved nitrogen (DN) dynamics, we conducted a field experiment on leaf litter and collected DOC and DN from the underlying soil in a tropical rainforest in Xishuangbanna, southwest China. Principal components analysis (PCA) showed the first PCA axis (corresponding to degraded litter quantity and quality) explained 61.3% and 71.2% of variation in DOC and DN concentrations, respectively. Stepwise linear regression analysis indicated that litter carbon mass controlled DOC and hemicellulose mass controlled DN concentrations. Litter decomposition was the predominant factor controlling surface-soil DOC and DN dynamics in this tropical rainforest.     

Effects of sulfuric,nitric, and mixed acid rain on litter decomposition,soil microbial biomass,and enzyme activities in subtropical forests of China

Acid rain pollution is changing gradually from sulfuric acid rain (SAR) to mixed acid rain (MAR) and then to nitric acid rain (NAR) with the rapidly growing number of motor vehicles. The influences of changed acid rain types on ecosystem functions, particularly on litter decomposition, remain unclear. Two dominant litter types from a coniferous forest and a broad-leaved forest were incubated in microcosms with original forest soils and treated by five types of acid rain with different SO₄²⁻ to NO₃⁻ ratios (1:0, 5:1, 1:1, 1:5, and 0:1). During a six-month incubation period, litter mass losses, soil microbial biomass, and enzyme activities were investigated. Results showed that various acid treatments inhibited litter decomposition, soil microbial biomass, and most enzyme activities, and the inhibitory effects of NAR were more significant than those of SAR and MAR. The resistance to external acid of microbial communities in broad-leaved forest was higher than that in coniferous forest. NAR and MAR treatments slowed down soil carbon (C), nitrogen (N), and phosphorus (P) mineralization by attenuating the correlations between litter mass losses and the enzymes involved in C, N, and P cycling. Results reveal that the ratio of SO₄²⁻ to NO₃⁻ in acid rain is an important factor which profoundly influences litter decomposition process. In the future, a decreasing ratio of SO₄²⁻ to NO₃⁻ in acid rain will be observed in subtropical forests. Thus, soil C would accumulate as a consequence of future acid precipitation, and this may seriously affect the balance of ecosystem C, N flux.     

Interactions between litter quality, decomposition and soil fertility: a laboratory study

Leaf litters from beech (Fagus sylvatica L.) and oak (Quercus robur L.) trees were collected from mixed, deciduous woodlands growing on three soil types that varied in mineral nutrient concentrations and N mineralisation potential. Litter quality, including %N, %Mn, %P, acid detergent fibre, cellulose, Klason lignin, phenylpropanoid constituents of lignin, hexose and pentose sugar (mainly from hemicelluloses) varied within species according to soil type. However, oak and beech showed the opposite responses to soil nutrient status for most of these variables. The litters were incubated in the laboratory for 12 months (at 18 °C and constant moisture) on beds of forest floor material from two soils of contrasting high nutrient material (HNM) or low nutrient material (LNM) nutrient status to investigate litter quality and substrate interactions. At 4, 8 and 12 months there were significant differences in mass losses from oak and beech litters from all sites, and for each litter type exposed to the HNM and LMN soils. At 12 months mean mass losses were higher for HNM treatment (38.7% oak, 27.8% beech) than for the LNM treatment (30.6% oak, 25.5% beech). However, the beech and oak litters from the different sites consistently responded in opposite ways on the same soil treatment reflecting site-related effects on litter quality. Initial concentration of Klason lignin was the best predictor for mass losses from litter species and litter types. Intra-specific variation in rates of litter decomposition of beech and oak litters from different sites, and differences in their interactions with the two forest floor materials, illustrate the complexities of proximate controls on decomposition that are often masked in system-level studies.