Variation in Microbial Activity in Histosols and Its Relationship to Soil Moisture

Microbial biomass, dehydrogenase activity, carbon metabolism, and aerobic bacterial populations were examined in cropped and fallow Pahokee muck (a lithic medisaprist) of the Florida Everglades. Dehydrogenase activity was two- to sevenfold greater in soil cropped to St. Augustinegrass (Stenotaphrum secundatum (Walt) Kuntz) compared with uncropped soil, whereas biomass ranged from equivalence in the two soils to a threefold stimulation in the cropped soil. Biomass in soil cropped to sugarcane (Saccharum spp. L) approximated that from the grass field, whereas dehydrogenase activities of the cane soil were nearly equivalent to those of the fallow soil. Microbial biomass, dehydrogenase activity, aerobic bacterial populations, and salicylate oxidation rates all correlated with soil moisture levels. These data indicate that within the moisture ranges detected in the surface soils, increased moisture stimulated microbial activity, whereas within the soil profile where moisture ranges reached saturation, increased moisture inhibited aerobic activities and stimulated anaerobic processes.     

Soil Microbial Responses to Temporal Variations of Moisture and Temperature in a Chihuahuan Desert Grassland

Global climate change models indicate that storm magnitudes will increase in many areas throughout southwest North America, which could result in up to a 25% increase in seasonal precipitation in the Big Bend region of the Chihuahuan Desert over the next 50 years. Seasonal precipitation is a key limiting factor regulating primary productivity, soil microbial activity, and ecosystem dynamics in arid and semiarid regions. As decomposers, soil microbial communities mediate critical ecosystem processes that ultimately affect the success of all trophic levels, and the activity of these microbial communities is primarily regulated by moisture availability. This research is focused on elucidating soil microbial responses to seasonal and yearly changes in soil moisture, temperature, and selected soil nutrient and edaphic properties in a Sotol Grassland in the Chihuahuan Desert at Big Bend National Park. Soil samples were collected over a 3-year period in March and September (2004-2006) at 0-15 cm soil depth from 12 3 x 3 m community plots. Bacterial and fungal carbon usage (quantified using Biolog 96-well micro-plates) was related to soil moisture patterns (ranging between 3.0 and 14%). In addition to soil moisture, the seasonal and yearly variability of soil bacterial activity was most closely associated with levels of soil organic matter, extractable NH(4)-N, and soil pH. Variability in fungal activity was related to soil temperatures ranging between 13 and 26 degrees C. These findings indicate that changes in soil moisture, coupled with soil temperatures and resource availability, drive the functioning of soil-microbial dynamics in these desert grasslands. Temporal patterns in microbial activity may reflect the differences in the ability of bacteria and fungi to respond to seasonal patterns of moisture and temperature. Bacteria were more able to respond to moisture pulses regardless of temperature, while fungi only responded to moisture pulses during cooler seasons with the exception of substantial increased magnitudes in precipitation occurring during warmer months. Changes in the timing and magnitude of precipitation will alter the proportional contribution of bacteria and fungi to decomposition and nitrogen mineralization in this desert grassland.     

Regulation of Microbial Community Composition and Activity by Soil Nutrient Availability, Soil pH, and Herbivory in the Tundra

Soil nitrogen (N) availability and pH constitute major abiotic controls over microbial community composition and activity in tundra ecosystems. On the other hand, mammalian grazers form an important biotic factor influencing resource coupling between plants and soil microorganisms. To investigate individual effects and interactions among soil nutrients, pH, and grazing on tundra soils, we performed factorial treatments of fertilization, liming, and grazer exclusion in the field for 3 years at 2 contrasting tundra habitats, acidic (N-poor) and non-acidic (N-rich) tundra heaths. The effects of all treatments were small in the non-acidic tundra heaths. In the acidic tundra heaths, fertilization decreased the fungal:bacterial ratio as analyzed by soil PLFAs, but there were no effects of liming. Fertilization increased soil N concentrations more drastically in ungrazed than grazed plots, and in parallel, fertilization decreased the fungal:bacterial ratio to a greater extent in the ungrazed plots. Liming, on the other hand, partly negated the effects of fertilization on both soil N concentrations and PLFAs. Fertilization drastically increased the activity of phenol oxidase, a microbial enzyme synthesized for degradation of soil phenols, in grazed plots, but had no effect in ungrazed plots. Taken together, our results demonstrate that grazers have the potential to regulate the fungal:bacterial ratio in soils through influencing N availability for the soil microorganisms.     

Microbial Responses to Long-Term N Deposition in a Semiarid Grassland

Nitrogen (N) enrichment of the biosphere is an expanding problem to which arid ecosystems may be particularly sensitive. In semiarid grasslands, scarce precipitation uncouples plant and microbial activities, and creates within the soil a spatial mosaic of rhizosphere and cyanobacterial crust communities. We investigated the impact of elevated N deposition on these soil microbial communities at a grama-dominated study site located incentral New Mexico (USA). The study plots were established in 1995 and receive 10 kg ha⁻¹ year⁻¹ of supplemental N in the form of NH₄NO₃. Soil samples were collected in July 2004, following 2 years of severe drought, and again in March 2005 following a winter of record high precipitation. Soils were assayed for potential activities of 20 extracellular enzymes and N₂O production. The rhizosphere and crust-associated soils had peptidase and peroxidase potentials that were extreme in relation to those of temperate soils. N addition enhanced glycosidase and phosphatase activities and depressed peptidase. In contrast to temperate forest soils, oxidative enzyme activity did not respond to N treatment. Across sampling dates, extracellular enzyme activity responses correlated with inorganic N concentrations. N₂O generation did not vary significantly with soil cover or N treatment. Microbial responses to N deposition in this semiarid grassland were distinct from those of forest ecosystems and appear to be modulated by inorganic N accumulation, which is linked to precipitation patterns.     

低能N^＋注入对活性污泥生物活性的影响

在研究不同剂量的N 注入活性污泥细菌存活率与注入剂量的关系的基础上,研究了低能N 注入活性污泥生物活性的变化规律。低能N 注入活性污泥细菌的剂量存活曲线呈典型的“马鞍形”曲线,20 keV,60×1014N /cm2离子注入活性污泥细菌的存活率在0.3左右。20×1014、60×1014和100×1014N /cm2三个剂量的变异均呈现“几乎所有变异为负突变,且突变谱狭窄”的分布特点,这在单一菌株的诱变研究中非常罕见。3种单剂量注入的混合样品的变异特点仍和单剂量注入的相近,没有出现正向突变率提高的现象。     

Behavioural Responses of European Roe Deer to Temporal Variation in Predation Risk

In natural environments, predation risk varies over time. The risk allocation hypothesis predicts that prey is expected to adjust key anti‐predator behaviours such as vigilance to temporal variation in risk. We tested the predictions of the risk allocation hypothesis in a natural environment where both a species‐rich natural predator community and human hunters are abundant and where the differences in seasonal and circadian activity between natural and anthropogenic predators provided a unique opportunity to quantify the contributions of different predator classes to anti‐predator behaviour. Whereas natural predators were expected to show similar levels of activity throughout the seasons, hunter activity was high during the daytime during a clearly defined hunting season. According to the risk allocation hypothesis, vigilance should then be higher during the hunting season and during daytime hours than during the non‐hunting season and night‐time hours. Roe deer (Capreolus capreolus) on the edge of Bia?owie?a Primeval Forest in Eastern Poland displayed vigilance behaviour consistent with these predictions. The behavioural response of roe deer to temporarily varying predation risks emphasises the behavioural plasticity of this species and suggests that future studies of anti‐predator behaviour need to incorporate circadian variation in predation pressure as well as risk gradients of both natural and anthropogenic predators.     

Intraspecific Strategic Responses of African Elephants to Temporal Variation in Forage Quality

ABSTRACT Mammalian herbivores adopt foraging strategies to optimize nutritional trade-offs against restrictions imposed by body size, nutritional requirements, digestive anatomy, physiology, and the forage resource they exploit. Selective or generalist feeding strategies scale with body size across species. However, within species, where constraints should be most similar, responses to limitation have rarely been examined. We used African elephants (Loxodonta Africana) to test for changes in seasonal diet quality of individuals of differing body size and sex through measurement of fecal nitrogen and phosphorus. We measured physiological stress response of these age and sex classes to seasonal change by fecal glucocorticoid metabolite levels (i.e., stress hormones). Large body size increased tolerance to lower-quality forage. Adult males and females exhibited divergent trends; females had higher diet quality than males, irrespective of body size. When limited by forage availability or quality during the dry season, diet quality declined across all body sizes, but weaned calves ingested a higher-quality diet than larger-bodied adults. On release from restriction during the wet season, weaned calf nitrogen concentrations were consistently high and stress hormone levels decreased, whereas adult female phosphorus levels were highest and less variable and stress hormone levels were unchanged. The ability to adjust forage quality is an important strategy used to ensure adequate nutritional intake according to body size limitations. Although body size is a key determining factor of dietary differences between adult elephants, foraging strategies are also driven by specific nutritional requirements, which may override the body size effects driving foraging decisions in some cases. The diversity of intraspecific response highlights ecologically segregated entities within a species and should be a concern for population management planning, particularly for threatened species. Fecal diet quality and stress hormone analysis could provide an early and sensitive indicator for monitoring age and sex class responses to resource restriction in high-density elephant populations.     

Key Edaphic Properties Largely Explain Temporal and Geographic Variation in Soil Microbial Communities across Four Biomes

Soil microbial communities play a critical role in nutrient transformation and storage in all ecosystems. Quantifying the seasonal and long-term temporal extent of genetic and functional variation of soil microorganisms in response to biotic and abiotic changes within and across ecosystems will inform our understanding of the effect of climate change on these processes. We examined spatial and seasonal variation in microbial communities based on 16S rRNA gene sequencing and phospholipid fatty acid (PLFA) composition across four biomes: a tropical broadleaf forest (Hawaii), taiga (Alaska), semiarid grassland-shrubland (Utah), and a subtropical coniferous forest (Florida). In this study, we used a team-based instructional approach leveraging the iPlant Collaborative to examine publicly available National Ecological Observatory Network (NEON) 16S gene and PLFA measurements that quantify microbial diversity, composition, and growth. Both profiling techniques revealed that microbial communities grouped strongly by ecosystem and were predominately influenced by three edaphic factors: pH, soil water content, and cation exchange capacity. Temporal variability of microbial communities differed by profiling technique; 16S-based community measurements showed significant temporal variability only in the subtropical coniferous forest communities, specifically through changes within subgroups of Acidobacteria. Conversely, PLFA-based community measurements showed seasonal shifts in taiga and tropical broadleaf forest systems. These differences may be due to the premise that 16S-based measurements are predominantly influenced by large shifts in the abiotic soil environment, while PLFA-based analyses reflect the metabolically active fraction of the microbial community, which is more sensitive to local disturbances and biotic interactions. To address the technical issue of the response of soil microbial communities to sample storage temperature, we compared 16S-based community structure in soils stored at -80°C and -20°C and found no significant differences in community composition based on storage temperature. Free, open access datasets and data sharing platforms are powerful tools for integrating research and teaching in undergraduate and graduate student classrooms. They are a valuable resource for fostering interdisciplinary collaborations, testing ecological theory, model development and validation, and generating novel hypotheses. Training in data analysis and interpretation of large datasets in university classrooms through project-based learning improves the learning experience for students and enables their use of these significant resources throughout their careers.     

Organic Layer Serves as a Hotspot of Microbial Activity and Abundance in Arctic Tundra Soils

Tundra ecosystem is of importance for its high accumulation of organic carbon and vulnerability to future climate change. Microorganisms play a key role in carbon dynamics of the tundra ecosystem by mineralizing organic carbon. We assessed both ecosystem process rates and community structure of Bacteria, Archaea, and Fungi in different soil layers (surface organic layer and subsurface mineral soil) in an Arctic soil ecosystem located at Spitsbergen, Svalbard during the summer of 2008 by using biochemical and molecular analyses, such as enzymatic assay, terminal restriction fragment length polymorphism (T-RFLP), quantitative polymerase chain reaction (qPCR), and pyrosequencing. Activity of hydrolytic enzymes showed difference according to soil type. For all three microbial communities, the average gene copy number did not significantly differ between soil types. However, archaeal diversities appeared to differ according to soil type, whereas bacterial and fungal diversity indices did not show any variation. Correlation analysis between biogeochemical and microbial parameters exhibited a discriminating pattern according to microbial or soil types. Analysis of the microbial community structure showed that bacterial and archaeal communities have different profiles with unique phylotypes in terms of soil types. Water content and hydrolytic enzymes were found to be related with the structure of bacterial and archaeal communities, whereas soil organic matter (SOM) and total organic carbon (TOC) were related with bacterial communities. The overall results of this study indicate that microbial enzyme activity were generally higher in the organic layer than in mineral soils and that bacterial and archaeal communities differed between the organic layer and mineral soils in the Arctic region. Compared to mineral soil, peat-covered organic layer may represent a hotspot for secondary productivity and nutrient cycling in this ecosystem.     

Natural Selection VS. Random Drift: Evidence from Temporal Variation in Allele Frequencies in Nature

We have obtained monthly samples of two species, Drosophila pseudoobscura and Drosophila persimilis, in a natural population from Napa County, California. In each species, about 300 genes have been assayed by electrophoresis for each of seven enzyme loci in each monthly sample from March 1972 to June 1975. Using statistical methods developed for the purpose, we have examined whether the allele frequencies at different loci vary in a correlated fashion. The methods used do not detect natural selection when it is deterministic (e.g., overdominance or directional selection), but only when alleles at different loci vary simultaneously in response to the same environmental variations. Moreover, only relatively large fitness differences (of the order of 15%) are detectable. We have found strong evidence of correlated allele frequency variation in 13-20% of the cases examined. We interpret this as evidence that natural selection plays a major role in the evolution of protein polymorphisms in nature.     

Useful Carriers for Cyanobacteria: Their Response to Cyanobacterial Growth, Acetylene-Reductase Activity, Cyanobacterial Grazers and Paddy Yield in Calcareous Soil

Summary Snails and nematodes, the potential cyanobacterial grazers, differ in their choice for cyanobacterial diet. Snails prefer non-mucilaginous forms while nematodes prefer mucilaginous forms. Such differences in feeding choice between the cyanobacteria suggests that it may not be possible to select strains of diazotrophic cyanobacteria that are resistant to all grazers. The potential consumption of cyanobacteria at an average field density of 20,000 snails ha⁻¹ was estimated to be about 50 kg (fresh weight) ha⁻¹ day⁻¹. Dorylamus sp. was most dominant nematode associated with cyanobacterial consumption. Phytoextracts of neem (Azadirachta indica), bel (Aegle marmelos) and tobacco (Nicotiana tabacum) were effective in controlling these cyanobacterial grazers. The minimum concentration of neem, bel and tobacco phytoextract in water for 100 % mortality of snails were 0.1, 2.0 and 0.05%, respectively. However, trepellent level was only 0.01% for neem and tobacco phytoextract. Complete mortality of nematode (Dorylamus spp.) required a higher concentration level (2%) even in the most effective tobacco phytoextract. Lower levels of phytoextract (0.1%) were found to stimulate growth and nitrogen fixation of cyanobacteria. Application of these plant biomasses resulted in significant increase in cyanobacterial acetylene-reducing activity (ARA) and rice yield and a significant decrease in snail and nematode population. Augmentation of cyanobacterial acetylene-reducing activity was two to three times higher in comparison to the control in both the years of experimentation. Rice yield also increased between 3.8 and 58.5% over the control, depending on the quantity and nature of plant biomass. Tobacco waste was significantly superior in comparison to neem and bel biomass as carrier of cyanobacterial culture.     

Variation in Soil Methane Release or Uptake Responses to Biochar Amendment: A Separate Meta-analysis

Agricultural soils play an important role in the atmospheric methane (CH₄) budget, where paddy soils can contribute significant CH₄ to atmosphere whereas upland soils may act as a source or sink of atmospheric CH₄, dependent on soil water conditions. Biochar amendments have effects on soil CH₄ production or oxidation processes in individual experiments, but the causative mechanisms are yet to be fully elucidated. To synthesize the response of soil CH₄ release or uptake to biochar amendment, we performed a meta-analysis using data from 61 peer-reviewed papers with 222 updated paired measurements. When averaged across all studies, biochar amendment significantly decreased CH₄ release rates by 12% for paddy soils and 72% for upland soils, and CH₄ uptake rates by 84% for upland soils. Neither soil CH₄ release nor uptake responses to biochar amendment were significant in field soils. Nitrogen (N) fertilizer application would weaken the response of soil CH₄ release or uptake to biochar amendment. Biochar-incurred decreases in soil CH₄ release and uptake rates were the largest in medium-textured soils or neutral-pH soils. Soil CH₄ release or uptake responses to biochar were also significantly altered by biochar characteristics, such as feedstock source, C/N ratio, pH, and pyrolysis temperature. The results of this synthesis suggest that the role of biochar in soil CH₄ mitigation potential might have been exaggerated, particularly in fields when biochar is applied in combination with N fertilizer.     

The Microbial Food Web in the Recently Flooded Sep Reservoir: Diel Fluctuations in Bacterial Biomass and Metabolic Activity in Relation to Phytoplankton and Flagellate Grazers

The spatial distribution of the bacterial biomass and production and of potential heterotrophic activity (PHA) weree measured every 4 h between 23 July (10:00 h) and 25 July (10:00 h) 1997 in a recently flooded oligo-mesotrophic reservoir (the Sep Reservoir, Puy-de-Dôme, France), in relation to temperature, the phytoplankton biomass and production, and the abundance of heterotrophic flagellates. The temperature varied slightly with time during the study, but the well-established thermal stratification agreed well with vertical distribution of the biological variables that were measured. Only the bacterial production and the PHA showed significant diel changes (t-test,p<0.05), with maxima at 18:00 h and minima at 02:00 h. A significant positive relation was found between bacterial abundance and that of heterotrophic flagellates, which, rather than being an association related to the thermal stratification of the water column, was considered to reflect a trophic relation between these two communities. A carbon balance analysis suggested that at least 30% of the C from primary production measured during the sampling period was used by bacteria, and that 42% of this secondary production, or 6% of the primary production, would be used for the development of the heterotrophic flagellates present. We conclude that the bacterioplankton forms, at least occasionally, an important source of carbon for higher trophic levels, and reject the hypothesis that bacterial production in the Sep Reservoir depends exclusively on organic matter of allochthonous origin.     

Temporal Variation of Denitrification Activity in Plant-Covered, Littoral Sediment from Lake Hampen, Denmark

Diel and seasonal variations in denitrification were determined in a littoral lake sediment colonized by the perennial macrophyte Littorella uniflora (L.) Aschers. In the winter, the activity was low (5 μmol of N m⁻² h⁻¹) and was restricted to the uppermost debris layer at a depth of 0 to 1 cm. By midsummer, the activity increased to 50 μmol of N m⁻² h⁻¹ and was found throughout the root zone to a depth of 10 cm. The root zone accounted for as much as 50 to 70% of the annual denitrification. A significant release of organic substrates from the roots seemed to determine the high activities of root zone denitrification in the summer. The denitrification in the surface layer and in the root zone formed two distinct activity zones in the summer, when the root zone also contained nitrification activity, as indicated from the accumulations of NO₃⁻. Light conditions inhibited denitrification in both the surface layer and the upper part of the root zone, suggesting that a release of O₂ by benthic algae and from the roots of L. uniflora controlled a diel variation of denitrification. In midsummer, the rate of denitrification in both the surface layer and the upper part of the root zone was limited by NO₃⁻. In the growth season, there was evidence for a significant population of denitrifiers closely associated with the root surface.     

Responses of Soil Microbial Communities to Experimental Warming in Alpine Grasslands on the Qinghai-Tibet Plateau

Global surface temperature is predicted to increase by at least 1.5°C by the end of this century. However, the response of soil microbial communities to global warming is still poorly understood, especially in high-elevation grasslands. We therefore conducted an experiment on three types of alpine grasslands on the Qinghai-Tibet Plateau to study the effect of experimental warming on abundance and composition of soil microbial communities at 0–10 and 10–20 cm depths. Plots were passively warmed for 3 years using open-top chambers and compared to adjacent control plots at ambient temperature. Soil microbial communities were assessed using phospholipid fatty acid (PLFA) analysis. We found that 3 years of experimental warming consistently and significantly increased microbial biomass at the 0–10 cm soil depth of alpine swamp meadow (ASM) and alpine steppe (AS) grasslands, and at both the 0–10 and 10–20 cm soil depths of alpine meadow (AM) grasslands, due primarily to the changes in soil temperature, moisture, and plant coverage. Soil microbial community composition was also significantly affected by warming at the 0–10 cm soil depth of ASM and AM and at the 10–20 cm soil depth of AM. Warming significantly decreased the ratio of fungi to bacteria and thus induced a community shift towards bacteria at the 0–10 cm soil depth of ASM and AM. While the ratio of arbuscular mycorrhizal fungi to saprotrophic fungi (AMF/SF) was significantly decreased by warming at the 0–10 cm soil depth of ASM, it was increased at the 0–10 cm soil depth of AM. These results indicate that warming had a strong influence on soil microbial communities in the studied high-elevation grasslands and that the effect was dependent on grassland type.     

The Fate of Organic Sources of Carbon in Moss‐rich Tundra Soil Microbial Communities: A Laboratory Experimental Study

Effects of glucose‐carbon supplementation on soil respiration and bacterial and protist biomass were investigated in laboratory studies of three soil samples from Alaskan tundra: spring tussock sample 1 (thin surface moss), spring tussock sample 2 (thick surface moss), and a summer tundra open field sample. Addition of 1% (w/v) glucose solution produced an immediate, pronounced two to three fold increase in respiration above basal rate, which declined over 4 h to baseline levels. Less than 1% (w/w) of glucose‐C supplement was respired during the respiratory spike, relative to the 89 μg/g added. A more substantial amount of the glucose‐C became incorporated in microbial biomass. The total difference in microbial carbon (μg/g) between the experimental treatments and controls without glucose after 1 wk was as follows: spring sample 1 (8), spring sample 2 (31), and summer sample (70). The percent (w/w) of glucose‐C incorporated was: spring sample 1 (5%), spring sample 2 (17%), and summer sample (39%), most attributed to biomass of bacteria and heterotrophic nanoflagellates. Although respiratory response to pulsed glucose‐C was minimal, the overall mean basal rate after 1 wk ranged between 4 and 6 nmol/min/g soil, indicating a significant assimilation and respiration of constituent soil organic carbon.     

Soil Microbial Community Responses to a Decade of Warming as Revealed by Comparative Metagenomics

Soil microbial communities are extremely complex, being composed of thousands of low-abundance species (<0.1% of total). How such complex communities respond to natural or human-induced fluctuations, including major perturbations such as global climate change, remains poorly understood, severely limiting our predictive ability for soil ecosystem functioning and resilience. In this study, we compared 12 whole-community shotgun metagenomic data sets from a grassland soil in the Midwestern United States, half representing soil that had undergone infrared warming by 2°C for 10 years, which simulated the effects of climate change, and the other half representing the adjacent soil that received no warming and thus, served as controls. Our analyses revealed that the heated communities showed significant shifts in composition and predicted metabolism, and these shifts were community wide as opposed to being attributable to a few taxa. Key metabolic pathways related to carbon turnover, such as cellulose degradation (∼13%) and CO₂ production (∼10%), and to nitrogen cycling, including denitrification (∼12%), were enriched under warming, which was consistent with independent physicochemical measurements. These community shifts were interlinked, in part, with higher primary productivity of the aboveground plant communities stimulated by warming, revealing that most of the additional, plant-derived soil carbon was likely respired by microbial activity. Warming also enriched for a higher abundance of sporulation genes and genomes with higher G+C content. Collectively, our results indicate that microbial communities of temperate grassland soils play important roles in mediating feedback responses to climate change and advance the understanding of the molecular mechanisms of community adaptation to environmental perturbations.     

氮沉降对三种林型土壤动物群落生物量的影响

从2003年5月～2004年8月,在华南鼎湖山地区针叶林、混交林和季风林内,采用模拟的方法,构建了对照、低氮[50kg/(hm2.a)]和中氮处理[100kg/(hm2.a)]组。在以后近16个月内,利用线框法收集地表凋落物层,在实验室内用Tullgren干漏斗法采集土壤动物标本,最后根据本地区长期土壤动物研究得出的不同类群动物生物量标准,对土壤动物类群生物量在氮沉降下的响应进行研究。结果表明,整体上氮处理对土壤动物类群生物量并未产生显著影响。然而通过氮处理与取样期和林分的交互作用,土壤动物类群生物量对氮沉降有一定的响应趋势。外界的氮输入明显促进了针叶林土壤动物类群生物量的增长,正效应明显;而季风林在较高氮处理下的负效应明显。经历一周年后,土壤动物类群生物量在各林分中的分布格局发生了显著变化,由实验处理前的季风林>混交林>针叶林,变为针叶林>季风林>混交林。低氮处理在一定程度上显示了对土壤动物类群生物量发展的利好作用,各林分动物类群生物量都有不同幅度的上升,平均季风林为44.33%,混交林9.19%,针叶林60.66%;而中氮处理使季风林和混交林分别下降32.55%和2.81%。提示氮沉降对土壤动物类群生物量的影响可能也存在阈值作用。