Collembolans feeding on soil affect carbon and nitrogen mineralization by their influence on microbial and nematode activities

We manipulated Collembola Folsomia candida Willem density and observed the density effect on carbon and nitrogen mineralization and on nematodes in microcosms filled with mineral soil. Collembolan densities were 0 (control), 25 (low), 100 (medium), and 400 (high) individuals per microcosm. The Collembola enhanced soil respiration and nitrogen mineralization rate in a density-dependent manner (P < 0.05). The correlation between collembolan density and the metabolic quotient of microbes, qCO₂, was weakly positive (r = 0.44, P < 0.05). Collembola did not affect microbial biomass. These results suggested that enhanced carbon and nitrogen mineralization was an indirect effect of Collembola mediated by increased microbial activity. Collembola changed the C_nema/C_mic ratio, but only when present at the low density. Thus, Collembola had both positive and negative effects on the nematode population. The positive impact probably depends on the enhancement of microbial activity due to Collembola grazing behavior, while the negative effect appears to result from predation of nematodes.     

Impact of earthworms on the diversity of microarthropods in a vertisol (Martinique)

In a study of a 15-year-old pasture in Martinique (French West Indies), abundance and organization of microarthropod communities were correlated with the spatial distribution of the earthworm Polypheretima elongata (Megascolecidae). In patches of high earthworm density (133 individuals m^–2), microarthropod density was significantly higher (80000 individuals m^–2) than in patches with few earthworms (31 worms m^–2 and 49000 microarthropods m^{– 2}). The diversity of microarthropod communities followed a similar pattern, the Shannon index for Collembola communities being, respectively, 3.12 and 1.82 in and outside earthworm patches. These results suggest that mesofauna abundance and diversity might be at least partly determined by the activity of larger invertebrates, as a result of the dramatic effects that the latter group exerts upon soil structure, pore distribution and food resources. Received: 7 February 1997     

Effect of tillage and farming management on Collembola in marsh soils

The Sanjiang Plain, the second largest marsh in China, has experienced intensive cultivation over the past 50 years. Most of the marshlands were converted to soybean and rice fields. However, little is known about the effects of tillage on the soil fauna. 9 treatments, including original marshland soil, rice and soybean cultivation with and without fertilizer and herbicide applications, were imitated with 135 buckets under greenhouse conditions. The soil characteristics and Collembola in these treatments were investigated for one plant growth season.The soil environment was deteriorated (as indicated by the decreased soil oxidizable organic matter, total nitrogen and soil water content and increased soil compaction) by soybean and rice cultivation treatments. The densities and species richness of Collembola significantly decreased in the rice cultivation treatments but not in the soybean cultivation treatments. For the soybean cultivation treatments, density and species richness of the soil Collembola significantly increased in the fertilizer, herbicide and fertilizer + herbicide application treatments. It probably caused by increasing root and shoot biomass in these treatments.It is concluded that the tillage treatments in a wetland soil had both qualitative and quantitative adverse effects on the soil collembolans, and these effects might further alter the soil ecological processes.     

Vertical distribution of Collembola (Hexapoda) and their food resources in organic horizons of beech forests

 Micro-samples of the surface organic horizons of 13 beech forests in Belgium were fixed immediately after collection in ethanol. Collembola (6255 animals) were sorted directly from micro-samples in the laboratory using a dissecting microscope, while the litter/soil matrix was analysed semi-quantitatively. The vertical distribution of Collembolan species was studied by correspondence analysis. Gut contents of animals were examined under a light microscope and their composition was compared with that of the matrix. A consistent association was found between the vertical distribution of gut contents and that of food resources in the immediate proximity of animals. Species differed in their feeding habits but most of them ingested a wide spectrum of food items. Plasticity in the food regime according to depth could be demonstrated in members of the Onychiuridae family. Received: 11 January 1999     

Effect of plant residue return on the development of surface soil pH gradients

 In the field, surface soil pH gradients were observed under senescing plants over late spring and summer. A soil incubation experiment was conducted (119 days, 20  °C) to provide direct evidence of the influence of plant residue incorporation on soil pH. This was investigated in terms of plant residue type (wheat and subterranean clover) and dry matter addition rate (0, 6.25, 12.5 and 25.0 g kg^–1), as well as the soil layer of incorporation (0–2.5 and 7.5–10 cm) and moisture regime (continuously moist and moist-dry cycles). During incubation, moist unamended soils slowly acidified. In contrast, the addition of plant residue resulted in a rapid (day 0–7) increase of soil pH due to the association, and particularly oxidation, of added organic anions. This was followed by a gradual (day 7–119) pH decline attributed to the mineralization and subsequent nitrification of added organic N. The addition of 12.5–25.0 g kg^–1 of cereal crop residues, and 6.25–25.0 g kg^–1 of legume-based pasture residues, resulted in a net alkalization of the surface 2.5 cm of soil. It was therefore concluded that surface soil pH gradients observed in the field were largely attributable to an increase of pH at the surface 2.5 cm in response to plant residue return. The magnitude of such gradients will be particularly large with the return of large quantities of plant residues of high ash alkalinity in soils of relatively low initial pH and biological activity, and when the surface of the soil is exposed to moist-dry cycles. Received: 11 October 1999     

Impact of coastal wetland cultivation on microbial biomass, ammonia-oxidizing bacteria, gross N transformation and N2O and NO potential production

A ¹⁵N dilution experiment was carried out to investigate effects of cultivation on the gross N transformation rate in coastal wetland zone. Microbial community composition was estimated by phospholipid fatty acid (PLFA) analysis and abundance of soil ammonia-oxidizing bacteria (AOB) was quantified by real-time polymerase chain reaction (PCR). Soil salinity decreased significantly, while total N increased after coastal wetland was cultivated. Microbial biomass (total PLFA), bacterial biomass, fungal biomass, and actinomycete biomass of the native coastal wetland soils were significantly (p < 0.05) lower than those of the cultivated soils whereas AOB population size also significantly increased after coastal wetland cultivation. Multiple regression analysis showed that total PLFA biomass and soil total N (TN) explained 97% of the variation of gross N mineralization rate in the studied soils (gross mineralization rate = 0.179 total PLFA biomass + 5.828TN − 2.505, n = 16, p < 0.01). Gross nitrification rate increased by increasing the soil AOB population size and gross mineralization rate (M) (gross nitrification rate = 3.39AOB + 0.18 M − 0.075, R ² = 0.98, n = 16, p < 0.01). Management of salt discharge and mineral N fertilization during the cultivation of wetland soils might have changed composition of soil microflora and AOB population size, thus influencing mineralization and nitrification. Probably, the cultivation of coastal wetland soils increased the risk of N losses from soil through nitrate leaching and gas emission (e.g., N₂O and NO).     

Responses of soil microarthropods to warming and increased precipitation in a semiarid temperate steppe

Soil microarthropods are an important component in soil food webs and their responses to climate change could have profound impacts on ecosystem functions. As part of a long-term manipulative experiment, with increased temperature and precipitation in a semiarid temperate steppe in the Mongolian Plateau which started in 2005, this study was conducted to examine effects of climate change on the abundance of soil microarthropods. Experimental warming had slightly negative but insignificant effects on the abundance of mites (−14.6%) and Collembola (−11.7%). Increased precipitation greatly enhanced the abundance of mites and Collembola by 117 and 45.3%, respectively. The response direction and magnitude of mites to warming and increased precipitation varied with suborder, leading to shifts in community structure. The positive relationships of mite abundance with plant cover, plant species richness, and soil microbial biomass nitrogen suggest that the responses of soil microarthropods to climate change are largely regulated by food resource availability. The findings of positive dependence of soil respiration upon mite abundance indicate that the potential contribution of soil fauna to soil CO₂ efflux should be considered when assessing carbon cycling of semiarid grassland ecosystems under climate change scenarios.     

Influence of fallow, wheat and subterranean clover on pH within an initially mixed surface soil in the field

 To ascertain the cause of the decrease in pH with depth through the surface 15 cm of moderately acidic soils, pH was monitored in layers of an initially mixed surface soil (to a nominal depth of 10 cm) during two consecutive seasons under fallow, wheat, and subterranean-clover plots. Variation of pH-influencing processes within soil layers to 15 cm depth was measured during the first season. Initially, soil pH was relatively uniform within the surface 7.5 cm, although there was an average 0.53 unit decrease of pH from 0–2.5 cm to 10–15 cm depth. Under all plots, residual lime reaction, net organic anion association and oxidation, net manganese oxidation and reduction, and particularly net N mineralisation and subsequent nitrification, tended to decrease with depth through the surface 15 cm of soil. In wheat and subterranean-clover plots, the alkalinity added with the return of 3.9–4.7 t ha^–1 of plant residue dry matter was predominantly released within the surface 2.5 cm of soil. The dominant pH-influencing processes were net N mineralisation and subsequent nitrification, and the return of alkaline plant residues. In the fallow plots, the surface 10 cm of soil tended to acidify due to nitrification. However in wheat and clover plots, alkalinity added to the surface 2.5 cm of soil from plant residues exceeded acidification resulting from nitrification at this depth. The magnitude of the pH gradient through 0–15 cm depth was therefore maintained under wheat, increased under clover, and decreased under fallow. Received: 11 October 1999     

Effects of the annual invasive plant Impatiens glandulifera on the Collembola and Acari communities in a deciduous forest

Invasive plants can disturb interactions between soil organisms and native plants and thereby alter ecosystem functions and/or reduce local biodiversity. Collembola and Acari are the most abundant microarthropods in the leaf litter and soil playing a key role in the decomposition of organic material and nutrient cycling. We designed a field experiment to examine the potential effects of the annual invasive plant Impatiens glandulifera on species diversity, abundance and community composition of Collembola and Acari in leaf litter and soil in a deciduous forest in Switzerland. Leaf litter and soil samples were obtained from plots invaded by I. glandulifera since 6 years, from plots in which the invasive plant had been removed for 4 years and from plots which were not yet colonized by the invasive plant. The 45 leaf litter and soil samples were equally distributed over three forest areas, which were differently affected by a wind throw 12 years prior to sampling representing a natural gradient of disturbance. Collembola species richness and abundance in the leaf litter and soil samples were not affected by the presence of the invasive plant. However, the species composition of Collembola was altered in plots with I. glandulifera. The abundance of leaf-litter dwelling Acari was increased in invaded plots compared to the two other plot types. Furthermore, the presence of the invasive plant shifted the composition of Acari individuals belonging to different groups. Our field experiment demonstrates that an annual invasive plant can affect microarthropods which are important for nutrient cycling in various ecosystems.     

Soil microarthropods as indicators of exposure to environmental stress in Chihuahuan Desert rangelands

 We studied soil microarthropod communities along livestock grazing disturbance gradients, inside and outside grazing exclosures, and on areas subjected to restoration efforts (herbicide and bulldozing) in order to test the suitability of mites as indicators of rangeland soil quality. We found that mite numbers generally increased with decreased grazing disturbance. Soil microarthropods appeared to respond to a complex of factors including soil compaction, depth to an impervious soil layer, below-ground vegetative biomass, and residual effects of herbicide. All of our study plots, except those that had been herbicide treated, were dominated by microbivorous mites of the family Nanorchestidae. The numerical responses of mites, especially nanorchestids, appeared to provide a sensitive indicator of ecosystem health in a Chihuahuan Desert grassland. Received: 29 December 1997     

Top-down control of soil microarthropods - Evidence from a laboratory experiment

Predator-prey interactions are of eminent importance as structuring forces for animal communities. The present study investigates if and how strongly the density of soil microarthropods is controlled by top-down forces, i.e. predation by mesostigmate mites (Mesostigmata, Acari). We set up a laboratory experiment running for ten weeks with undisturbed soil cores taken from the field using two densities of predatory mesostigmate mites: (1) ambient density (control) and (2) increased density (addition of seven Pergamasus septentrionalis and eight Lysigamasus sp. individuals). Increased predator density resulted in a decrease in the density of Oribatida, Collembola and Protura whereas the density of other taxa including Astigmata, Prostigmata and Uropodina was not significantly affected. Additionally, the species number of Oribatida was also not significantly affected. Taxa of Oribatida and Collembola were differently affected by increased predator density. Among Collembola, densities of Poduridae and Sminthuridae were reduced, whereas Entomobryidae were not affected. Among Oribatida, densities of Oppiidae and Suctobelbidae were reduced whereas Desmonomata, Poronota and Tectocepheus were not affected. Grouping of Oribatida into different size classes and into classes differing in sclerotization suggests that smaller mites (200-300 μm) and mites with less sclerotization were more heavily affected than larger mites and mites with strong sclerotization. The results indicate that predatory mesostigmate mites have the potential to control the density of certain taxa of soil microarthropods. In particular, small and little sclerotized prey is susceptible to predator control indicating that predator defense is an important component of the life history tactics of soil microarthropods, especially of Oribatida.     

Urease activity and its relation to soil organic matter, microbial biomass nitrogen and urea-nitrogen assimilation by maize in a Brazilian Oxisol under no-tillage and tillage systems

 We studied the relationship between urease activity (UA) and soil organic matter (SOM), microbial biomass N (N_biom) content, and urea-N fertilizer assimilation by maize in a Dark Red Latosol (Typic Haplustox) cultivated for 9 years under no-tillage (NT), tillage with a disc plough (DP), and tillage with a moldboard plough (MP). Two soil depths were sampled (0–7.5 cm and 7.5–15 cm) at 4 different times during the crop cycle. Urea was applied at four different rates, ranging from 0 to 240 kg N ha^–1. The levels of fertilizer N did not affect the UA, SOM content, and N_biom content. No significant difference between the treatments (NT, DP, and MP) was observed for SOM during the experiment, probably because the major part of the SOM was in recalcitrant pools, since the area was previously cultivated (conventional tillage) for 20 years. The N_biom content explained 97% and 69% of the variation in UA in the upper and deeper soil layer, respectively. UA and biomass N were significantly higher in the NT system compared to the DP and MP systems. The highest maize productivity and urea-N recovery was also observed for the NT system. We observed that the increase in urea-N losses under NT, possibly as a consequence of a higher UA, was compensated for by the increase in N immobilized in the biomass. Received: 2 July 1999     

Influence of earthworm middens on the distribution of soil microarthropods

Summary Earthworm middens and non-midden soil were sampled for microarthropods in a mowed recreational field and and adjacent woodlot site. Samples were taken in fall 1983 and spring 1984. The earthworm middens of the mowed field supported a higher density of micrarthropods (especially Collembola and prostigmatid mites) than adjacent non-midden soil. This positive midden effect in the mowed field was more pronounced in the fall than in the spring. Woodlot earthworm middens examined in the fall had lower densities of microarthropods (especially oribatid mites) than adjacent non-midden soi, but in the spring woodlot middens supported greater densities of microarthropods (especially Collembola) than adjacent, non-midden soil.     

The short-term cover crops increase soil labile organic carbon in southeastern Australia

Little information is available about the effects of cover crops on soil labile organic carbon (C), especially in Australia. In this study, two cover crop species, i.e., wheat and Saia oat, were broadcast-seeded in May 2009 and then crop biomass was crimp-rolled onto the soil surface at anthesis in October 2009 in southeastern Australia. Soil and crop residue samples were taken in December 2009 to investigate the short-term effects of cover crops on soil pH, moisture, NH₄⁺–N, NO₃⁻–N, soluble organic C and nitrogen (N), total organic C and N, and C mineralization in comparison with a nil-crop control (CK). The soil is a Chromic Luvisol according to the FAO classification with 48.4 ± 2.2% sand, 19.5 ± 2.1% silt, and 32.1 ± 2.1% clay. An exponential model fitting was employed to assess soil potentially labile organic C (C ₀) and easily decomposable organic C for all treatments based on 46-day incubations. The results showed that crop residue biomass significantly decreased over the course of 2-month decomposition. The cover crop treatments had significantly higher soil pH, soluble organic C and N, cumulative CO₂–C, C ₀, and easily decomposable organic C, but significantly lower NO₃⁻–N than the CK. However, no significant differences were found in soil moisture, NH₄⁺–N, and total organic C and N contents among the treatments. Our results indicated that the short-term cover crops increased soil labile organic C pools, which might have implications for local agricultural ecosystem managements in this region.     

百草清除草剂对农田生态系统土壤动物群落结构的影响

用百草清除草剂对农田生态系统土壤动物进行染毒模拟实验,共获得土壤动物967个,隶属3门,6纲,10目。其中弹尾目、甲螨亚目为优势类群,其余为常见类群和稀有类群。实验结果表明,百草清除草剂处理组的动物种类和数量与对照组相比较明显减少,动物种类的减少主要取决于常见种类和稀有种类,动物数量的变化则主要是优势类群的数量消长。并且随着百草清溶液处理浓度的增加,土壤动物的种类和数量显著减少,但上、下层动物随染毒历时递减规律有所不同。     

Effect of differently post-treated dewatered sewage sludge on β-glucosidase activity,microbial biomass carbon,basal respiration and carbohydrates contents of soils from limestone quarries

This work has evaluated the effects of thermally dried (TDS) or composted (CDS) dewatered sewage sludge on β-glucosidase activity, total (TCH) and extractable (ECH) carbohydrate content, microbial biomass carbon and basal respiration of soils from limestone quarries under laboratory conditions. Two doses (low and high) of the dewatered sludge (DS) or of the respective TDS or CDS were applied to a clayey and a sandy soil, both coming from working quarries. The soil mixtures and the controls (soils with no added sludge) were incubated for 9 months at 25°C and 30% of field capacity. The addition of sludge increased all the studied soil parameters, and the increase depended on the amount of sludge. Except in the case of TCH and ECH, the enhancing effect decreased with time, but at the end of incubation, parameters of the treated soils were higher than those of the control. The rank order of the initial stimulating effect was soil–TDS ≥ soil–DS ≥ soil–CDS, and probably, this order depended on the proportion of stable organic matter, which was the lowest in the TDS. Values of metabolic quotient (qCO₂) were higher at the lower dose, and they did not change during incubation in the CDS-treated soils. Both TCH and ECH were the parameters with the greatest significant sludge and dose effects. Basal respiration, microbial biomass carbon and β-glucosidase activity were the best measured parameters in distinguishing the long-term effects of the three sludge types over the soils.     

Temporal dynamics of soil nitrate-N after termination of forage phases in corn-forage rotation

 Efficient N-fertiliser management during the corn (Zea mays L.) phase in corn-forage rotation requires information on temporal dynamics of N release from forage biomass. The influence of forage phase, in corn-forage rotation, and no- versus conventional-till on (1) in situ temporal dynamics of soil nitrate-N (NO₃-N) during corn phase and (2) corn grain yield was investigated in this study. The data used were collected from a crop rotation (corn-forage) experiment, with superimposed tillage treatments, established on a silt loam soil in 1988 and continued until 1994. The cropping treatments were continuous conventionally cultivated (CT) corn, rotations involving corn and forages (alfalfa, Medicago sativa L.; and bromegrass, Bromus inermis L.) and continuous minimally tilled corn with under-seeded red clover (Trifolium pratense L.). The forages were grown for 6 years and corn was re-introduced in these plots under no- and conventional-till systems. Soil NO₃-N in the top 30 cm depth, determined six times during the corn phase, was significantly influenced by previous forage species and tillage system. Regression analysis indicated soil NO₃-N under continuous CT corn did not show significant temporal changes. In the rotations, soil NO₃-N after tillage or herbicide treatment, i.e. in no-till, increased with time until 45 days after tillage (DAT), reached a plateau between 45 and 65 DAT, and then decreased with time. During the plateau, soil NO₃-N in rotation plots ranged from 17 to 33 mg kg^–1 compared to 15.7 mg kg^–1 in the continuous CT corn. Tillage increased soil NO₃-N concentration in alfalfa plots whereas an opposite trend existed in the bromegrass plots. Soil NO₃-N in the rotation plots increased at rates ranging from 0.71 to 1.63 mg kg^–1 day^–1. The interaction involving forage species and the temporal dynamics of soil NO₃-N accounted for 68–77% of variability in corn grain yield. Received: 14 July 1998     

Effects of increasing periods under intensive arable vegetable production on biological, chemical and physical indices of soil quality

 The effects on soil condition of increasing periods under intensive cultivation for vegetable production on a Typic Haplohumult were compared with those of pastoral management using soil biological, physical and chemical indices of soil quality. The majority of the soils studied had reasonably high pH, exchangeable cation and extractable P levels reflecting the high fertilizer rates applied to dairy pasture and more particularly vegetable-producing soils. Soil organic C (C_org) content under long-term pasture (>60 years) was in the range of 55 g C kg^–1 to 65 g C kg^–1. With increasing periods under vegetable production soil organic matter declined until a new equilibrium level was attained at about 15–20 g C kg^–1 after 60–80 years. The loss of soil organic matter resulted in a linear decline in microbial biomass C (C_mic) and basal respiratory rate. The microbial quotient (C_mic/C_org) decreased from 2.3% to 1.1% as soil organic matter content declined from 65 g C kg^–1 to 15 g C kg^–1 but the microbial metabolic quotient (basal respiration/C_mic ratio) remained unaffected. With decreasing soil organic matter content, the decline in arginine ammonification rate, fluorescein diacetate hydrolytic activity, earthworm numbers, soil aggregate stability and total clod porosity was curvilinear and little affected until soil organic C content fell below about 45 g C kg^–1. Soils with an organic C content above 45 g C kg^–1 had been under pasture for at least 30 years. At the same C_org content, soil biological activity and soil physical conditions were markedly improved when soils were under grass rather than vegetables. It was concluded that for soils under continuous vegetable production, practices that add organic residues to the soil should be promoted and that extending routine soil testing procedures to include key physical and biological properties will be an important future step in promoting sustainable management practices in the area. Received: 18 November 1997     

Critical sulphur concentration and sulphur requirement of microbial biomass in a glucose and cellulose-amended regosol

 The critical S concentration and S requirement of the soil microbial biomass of a granitic regosol was examined. S was applied at the rate of 0, 5, 10, 20, 30 and 50 μg S as MgSO₄·7H₂O, together with either 3000 μg glucose-C or 3333 μg cellulose-C, 400 μg N, and 200 μg P g ^–1 soil and 200 μg K g^–1 soil. Microbial biomass, inorganic SO₄ ^2–-S, and CO₂ emission were monitored over 30 days during incubation at 25  °C. Both glucose and cellulose decomposition rates responded positively to the S made available for microbial cell synthesis. The amounts of microbial biomass C and S increased with the level of applied S up to 10 μg S g^–1 soil and 30 μg S g^–1 soil in the glucose- and cellulose-amended soil, respectively, and then declined. Incorporated S was found to be concentrated within the microbial biomass or partially transformed into soil organic matter. The concentration of S in the microbial biomass was higher in the cellulose- (4.8–14.2 mg g^–1) than in the glucose-amended soil (3.7–10.9 mg g^–1). The microbial biomass C:S ratio was higher in the glucose- (46–142 : 1) than in the cellulose-amended soil (36–115 : 1). The critical S concentration in the microbial biomass (defined as that required to achieve 80% of the maximum synthesis of microbial biomass C) was estimated to be 5.1 mg g^–1 in the glucose- and 10.9 mg g^–1 in the cellulose-amended soil. The minimum requirement of SO₄ ^2–-S for microbial biomass formation was estimated to be 11 μg S g^–1 soil and 21 μg S g^–1 soil for glucose- and cellulose-amended soil, respectively. The highest levels of activity of the microbial biomass were observed at the SO₄ ^2–-S concentrations of 14 μg S g^–1 soil and 17 μg S g^–1 soil, for the glucose and cellulose amendments, respectively, and were approximately 31–54% higher during glucose than cellulose decomposition. Received: 20 October 1999     

Significance of litter layer in enhancing mesofaunal abundance and microbial biomass nitrogen in sweet corn-white clover living mulch systems

Living mulch is a type of sustainable farming system that consists of cover crops planted either before or with a main crop; a living mulch is maintained as a living ground cover throughout the growing season of the main crop. Microbial biomass and abundance of mesofauna (microarthropods and enchytraeids) are important soil biological parameters in relation to soil function, plant productivity, and nutrient cycling; however, the effects of living mulch on these parameters are not fully understood. In this study we examined the effects of living mulch treatment with nitrogen fertilizer (0, 40, 160, or 200?kg?ha^?1) on the abundance of soil microarthropods (Oribatida, Mesostigmata, Prostigmata, and Collembola) and the effects of living mulch treatment on the dynamics of the soil biota (mesofauna, microarthropods, enchytraeids, and microbial biomass nitrogen) from spring to autumn. Our results showed that living mulch treatment significantly (p?p?相似文献