Change in soil microbial biomass and regulating factors in an alpine meadow site on the Qinghai-Tibetan Plateau

ABSTRACT

The change in soil microbial biomass (SMB) content and its direct links to soil organic matter (SOM) and environmental factors are not well understood for high-elevation regions. Therefore, this research investigated the temporal variation of SMB and its relationship with SOM and environmental factors in an alpine meadow site on the Qinghai-Tibetan Plateau. The soil organic carbon (SOC) and total nitrogen (TN) contents in alpine meadows showed monthly and seasonal variations and were higher in colder months, and the soil C/N ratio was higher in winter and in autumn than it was in the other seasons (P < 0.05). In addition, the changes in the SMB C and SMB N contents were notable at monthly and seasonal scales, whereas the SMB C and SMB N contents were higher in the winter and spring than they were in the other seasons (P < 0.05); the ratio of SMB C/SOC was higher in spring than it was in the other seasons; the ratio of the SMB N/TN content was higher in cold or cool months than it was in the other months; and the ratio of the SMB C/SMB N was highest in August (P < 0.05). Moreover, the SMB C and SMB N contents were significantly positively correlated to the SOC and TN contents (P < 0.01), and the SMB content was also significantly positively correlated to soil water content and air temperature (P < 0.05), or to soil bulk density and soil pH (P < 0.05). The results suggested that the change in the SMB in the alpine meadows was highly regulated by the SOC and TN and by monthly and seasonal changes in the soil bulk density, the soil pH, soil moisture, and air temperatures.     

Potential applications of soil microbial ecology and next-generation sequencing in criminal investigations

The complex relationships between the changes in microbial community profiles and postmortem interval (PMI) estimates have recently been discussed in the forensic literature. Edaphic, necrobiomic microorganisms at the cadaver-soil interface construct multi-species communities that change in richness and activity when the host body dies and begins to decompose. Characterization of these dynamic changes has been made possible by current advances in high throughput, next-generation platforms. The effectiveness of these metagenomic technologies is that they pride the foundations of a framework for identification of grave sites and the determination of postmortem timelines, or “microbial clocks.” The proposed clocks may help substantiate the estimation of PMI. Studies have demonstrated the differences between soils collected at grave sites and control soils which may be useful in identifying clandestine grave sites. In this review is the discussion of the recent and formative findings involving sequencing applications of soil microbial communities relating the differences in taxon richness and abundance patterns as molecular tools with broad and important applications in forensics.     

土壤微生物生态学在农业中的应用研究综述

土壤微生物生态学是陆地生态系统研究中最重要的组成部分,是土壤学、微生物学和生态学相互渗透、相互结合的一门新兴学科。本文从研究方法、农业施肥、农业种植制度、生态防治及应用展望等方面对土壤微生物生态学的应用研究现状作了综述,加强土壤微生物生态学在农作物生长和调控应用等领域的研究具有巨大的潜在应用前景和重要意义。     

Driving factors of temporal variation in agricultural soil respiration

Investigations of diurnal and seasonal variations in soil respiration support modeling of regional CO₂ budgets and therefore in estimating their potential contribution to greenhouse gases. This study quantifies temporal changes in soil respiration and their driving factors in grassland and arable soils located in Northern Germany. Field measurements at an arable site showed diurnal mean soil respiration rates between 67 and 99 mg CO₂ m^–2 h^–1 with a hysteresis effect following changes in mean soil temperatures. Field soil respiration peaked in April at 5767 mg CO₂ m^–2 day^–1, while values below 300 mg CO₂ m^–2 day^–1 were measured in wintertime. Laboratory incubations were carried out in dark open flow chambers at temperatures from 5°C to 40°C, with 5°C intervals, and soil moisture was controlled at 30%, 50%, and 70% of full water holding capacity. Respiration rates were higher in grassland soils than in arable soils when the incubating temperature exceeded 15°C. The respiration rate difference between them rose with increasing temperature. Monthly median values of incubated soil respiration rates ranged from 0 to 26.12 and 0 to 7.84 µg CO₂ g^–1 dry weight h^–1, respectively, in grassland and arable land. A shortage of available substrate leads to a temporal decline in soil respiration rates, as indicated by a decrease in dissolved organic carbon. Temporal Q₁₀ values decreased from about 4.0 to below 1.5 as temperatures increased in the field. Moreover, the results of our laboratory experiments confirmed that soil temperature is the main controlling factor for the Q₁₀ values. Within the temperature interval between 20°C and 30°C, Q₁₀ values were around 2 while the Q₁₀ values of arable soils were slightly lower compared to that of grassland soils. Thus, laboratory studies may underestimate temperature sensitivity of soil respiration, awareness for transforming laboratory data to field conditions must therefore be taken into account.     

分子生物学与系统生物学技术在土壤污染微生物生态研究中的应用

综述了当前国内外应用于土壤污染生态研究中的各种分子生物学和系统生物学技术,包括核酸杂交和DNA指纹图谱分析技术以及宏基因组学、宏蛋白质组学和代谢组学等“组学”技术.阐述了这些技术方法的原理、应用以及各自的优势和局限性,并对这些新兴生物技术在土壤污染生态学中的应用前景作一展望.     

Soil microbial communities in (sub)alpine grasslands indicate a moderate shift towards new environmental conditions 11 years after soil translocation

A change in environmental conditions may result in altered soil microbial communities in alpine grasslands but the extent and direction of the change is largely unknown. The aim of our study was to investigate (i) differences in soil microbial communities across an elevation gradient of (sub)alpine grassland soils in the Swiss Alps, and (ii) the long-term effect of translocation of soil cores from a higher to a lower elevation site. The translocation of undisturbed soil cores from a high alpine site (2525 m asl) to a subalpine site near the timberline (1895 m asl) induced an effective artificial warming of 3.3 °C. We hypothesized that after longer than a decade, soil microbial community in translocated cores would differ from that at the original site but resemble the community at the new site. Results from soil phospholipid fatty acid (PLFA) analysis confirm significant differences in microbial communities between sites and a shift in total microbial biomass (TMB) and proportional distribution of structural groups in the translocated cores towards the lower elevation community. Patterns related to translocation were also observed as shifts in the fractional biomass of ectomycorrhizal and arbuscular fungi, and in relative contents of several structural groups. Hence, soil microbial community activity and diversity indicate a moderate shift towards new site conditions after 11 years and therefore, our data suggest slow responses of microbial communities to environmental changes in alpine soils.     

Abundance and trophic structure of macro-decomposers on alpine pastureland (Central Alps, Tyrol): effects of abandonment of pasturing

On four differently managed and abandoned alpine meadows and pastures densities, biomasses and ¹⁵N signatures of the macrofauna were assessed to evaluate the structural and functional changes of the decomposer food webs. The composition of the macrofauna decomposer community changes remarkably after the abandonment of alpine meadows and pastures. Lumbricus rubellus functions as key primary decomposer on alpine meadows and pastures whereas on abandoned sites other primary decomposers including Dendrobaena octaedra, Cylindroiulus meinerti, C. fulviceps and diptera larvae become more important. Decomposer species, such as Enantiulus nanus, presumably function as both primary and secondary decomposers and endogeic earthworms, such as Octolasion lacteum and Aporrectodea rosea, uniformly function as secondary decomposers. Abandonment of pasturing causes a shift in the composition of the macrofauna and the newly established fauna is unable to process and translocate the litter materials produced by the plants of the abondoned sites.     

13C标记磷脂脂肪酸分析在土壤微生物生态 研究中的应用

磷脂脂肪酸(PLFA)是微生物细胞膜的重要组成成分,不同微生物群落可通过不同生化途径合成不同的PLFA,因此可选择某些PLFA作为微生物群落结构变化的生物标志物。PLFA与稳定性同位素~(13)C标记(~(13)C-PLFA)技术结合,不仅能够确定原位土壤环境中微生物群落组成,而且能够定向发掘土壤生态系统中参与碳源代谢过程的微生物群落,提供复杂群落中土壤微生物相互作用的信息,具有广阔的应用前景。其基本原理为:将富集~(13)C稳定同位素的基质加入土壤中,土壤中的某些微生物群落利用基质~(13)C合成PLFA,提取并纯化土壤微生物的PLFA,利用气相色谱-燃烧-同位素比例质谱(GC-C-IRMS)测定其~(13)C丰度,通过对比分析,从而获取微生物群落组成与其功能的直接信息。本文在介绍了~(13)C-PLFA原理的基础上,综述了该技术在光合同化碳的根际微生物利用、土壤有机质分解的激发效应、甲烷氧化、有机污染物降解、外源简单碳源和外源复杂碳源的微生物利用等方面的应用,对此项技术的优缺点进行了分析并展望了其未来应用。     

Responses of soil microbial respiration to thermal stress in alpine steppe on the Tibetan plateau

Extensive research has focused on the temperature sensitivity of microbial respiration in tundra and alpine meadows. However, the response of microbial respiration to thermal stress in alpine steppe soils, which have less organic matter and greater aeration, has received less attention. We investigated spatial and temporal variations in microbial respiration using an incubation experiment under different temperature (0, 15 and 30°C) and different percentages of water‐holding capacity (WHC) (50 and 100%) conditions in the alpine steppe, and using a subsequent cooling experiment determined the ‘thermal stress' of soil microorganisms in response to increased temperature in the alpine steppe ecosystem. Microbial respiration rates decreased with increasing temperature at both 50 and 100% WHC for three sampling locations. Thermal stress of soil microorganisms under increased temperatures was found in the alpine steppe because subsequent cooling led to an increase in microbial respiration rates. Soil moisture did not affect microbial respiration, but the temperature sensitivity (Q₁₀) of microbial respiration varied with the interactive effect between soil moisture and sampling location. Our findings suggest that the response of microbial respiration to high temperature may not be always positive as bacteria may experience thermal stress in the alpine steppe. Therefore, it is necessary to include thermal stress responses in alpine steppe models, as they may represent an important negative feedback effect on microbial respiration.     

Throughfall,runoff and soil erosion after prescribed burning in gorse shrubland in Galicia (NW Spain)

The first‐year effect of two different prescribed burning treatments on throughfall, runoff and soil erosion was evaluated in gorse shrubland (Ulex europaeus L.) in Galicia (NW Spain). The treatments compared were: intense burn, light burn and control (no burn). Accumulated annual throughfall represented between the 81 and 87 per cent of total rainfall in intensely burned and lightly burned areas, respectively, whereas in the unburnt areas it was 60 per cent. No significant differences between burning treatments were found for the annual throughfall. However, runoff was significantly greater in intensely burned plots (1·5‐times) than in lightly burned plots. Burning also resulted in a significant increase in runoff (between 2·5 and 1·7‐times, respectively) compared with controls. Total soil losses were small in all treatments, but the intense burn caused significantly greater soil erosion (5·8‐times) compared with the unburned areas. Soil losses after the light burn did not significantly differ from the control although they were higher (2·3‐times). The relationships obtained between erosion and several rainfall parameters were significantly different in burned areas compared to the control. The same response was observed for runoff. Annual erosion losses showed a strong dependence on percentage of bare soil even for small values of this variable. Litter thickness was also a very important variable influencing on erosion rates. This study indicated that by combining ignition techniques and high litter moisture content to maintain the percentage of bare soil below 85 per cent, soil erosion was low. Nevertheless, this result was constrained by the low rainfall that occurred during the study. Copyright © 2005 John Wiley & Sons, Ltd.     

Population dynamics and ecology of ciliates (Protozoa,Ciliophora) in an anoxic rice field soil

Wetland rice fields cover 1.46 million km² globally; the flooded soil of these fields is largely anoxic. While biogeochemistry and microbiology have been studied in detail, the microbial loop and especially the dynamics and function of ciliates are largely unknown. We used anoxic microcosms prepared with soil from an Italian rice field and recorded species composition, abundance and volume of ciliates together with numbers, volume and size distribution of bacteria. Ciliates were the dominating protists observed in the microcosms, but could be outnumbered by flagellates if the soil was amended with rice straw. The number of ciliate taxa was 23. Metopus species were dominant, but 16 of the species recorded in the anoxic soil were facultative anaerobes. Another 29 species were found in accompanying experiments that included the oxic soil surface. Total abundance in the anoxic soil was on average 110 cells g^–1 dry weight and comparable to that of other soils. The population of ciliates declined around 30 days after flooding, but recovered later. The period before the population declined was characterized by a rapid species turnover, many facultative anaerobes and large species. After recovery, the average cell size was much smaller, but even then a facultative anaerobe, Plagiacampa pentadactyla , was common. About 90% of all species were bacteriovores while the others—mainly Gymnostomatidae—were predators. Grazing ciliates may have controlled bacteria during the first 5 days after flooding, as could be shown by a negative correlation between the respective volumes and by the size spectra of the bacteria.     

Conservation of soil moisture by different stone covers on alpine talus slopes (Lassen, California)

This study reports on the influence of stone covers with different clast sizes on the soil moisture of alpine talus slopes in Lassen (California). Fifteen four-plot sets were sampled in the dry season (July 1990) in sandy areas and in talus covered with pebbles, cobbles, or blocks between 2740 and 2775 m. Three depths (0–5, 5–10, 10–15 cm) were sampled. Field moisture content increased gradually with depth in all soil profiles, and also in plots covered by increasingly larger rocks. Surface soils in sand areas were very dry, but under rocks had water contents 6 to 14 times greater. Differences among plots decreased with depth, but subsoil samples in sand were still drier than those beneath any stone cover at similar depths. Blocks were most effective in conserving moisture; water content below them was higher than even in deep (10–15 cm) sand soils. Soil temperatures were recorded in sand and under blocks for an 11-day period. Minima were not significantly different, but average maxima were 5.6°C lower under blocks than in sand, which reached highs 4.4°C lower than the air. Differences in soil moisture among talus types are ascribed to lower evaporation losses under stones, due to both disruption of capillarity by the coarse particles, which prevented water flow to the talus surface, and to their efficient reduction of maximum temperatures. An irrigation experiment was conducted at 2110 m on a steep talus on the Chaos Crags from July 18 to Aug. 2, 1993. Four 100×75 cm plots with the same surface types than at Lassen received 22.5 mm water; moisture content was then periodically sampled. Watering produced similar water distributions among soil depths and talus types to those in Lassen. Evaporation occurred quickly in bare soils due to high air and soil temperatures. The sand surface was already dry 2 days after watering, but stone-covered plots remained moist until day 15, when soils under blocks still retained 77–97% of the water content (percent by weight) at the start of the test.     

Influence of nitrogen fertilization on soil ammonia oxidizer and denitrifier abundance,microbial biomass,and enzyme activities in an alpine meadow

Terrestrial ecosystems are predicted to experience an increasing level of atmospheric nitrogen (N) deposition, which may cause significant shifts in plant community composition and concomitantly stimulate soil acidification. However, little is known concerning the effects of N deposition on belowground microbial communities in alpine grassland ecosystems such as on the Tibetan Plateau. This study examined the responses of soil N-transforming microbes (measured after DNA extraction and quantitative PCR), soil microbial biomass C (SMBC) and N (SMBN), and soil enzyme activities to different forms (NH₄ ⁺-N, NO₃ ^?-N, and NH₄NO₃-N) and rates (1.5 and 7.5 g N m^?2 year^?1, denoted as low and high N, respectively) of N fertilization (addition) in two successive plant growing seasons. The N rate, not N form, influenced the abundance of ammonia-oxidizing archaea (AOA). High N addition significantly increased ammonia-oxidizing bacteria (AOB) abundance which differed across different N form treatments. Nitrogen addition had no significant impact on the abundance of soil denitrifiers. The SMBC and SMBN were significantly decreased by high N additions, but no difference was found among different N forms. Despite higher urease activities being detected in the late plant growing season, the activities of invertase and alkaline phosphomonoesterase stayed unchanged irrespective of the different N amendments and plant growing season. Significant positive correlations were found between potential nitrification rates and AOB abundances. These results highlight that AOB seemed to respond more sensitively to different N fertilization and might have prominent roles in soil N cycling processes in this Tibetan Plateau alpine meadow than AOA.     

长期施肥棕壤有机硫矿化特征及其驱动力

[目的]探究长期不同施肥对土壤有机硫矿化量、动力学特征和酶活性的影响,揭示玉米–大豆轮作体系中棕壤有机硫矿化特征及其主要驱动因子.[方法]沈阳农业大学长期定位试验于1979年建立,为玉米–玉米–大豆(一年一熟)轮作模式.试验设置15个处理,本研究选取了其中7个处理,分别为:CK(不施肥)、N1(低量化学氮肥)、N2(高...     

Annual population dynamics and production ecology of Testacea (Protozoa,Rhizopoda) in an aspen woodland soil

The population studies of Testacea in an aspen woodland soil revealed 28 taxa of living Testacea, 14 of which were considered constant. The 14 species, while comprising 98 and 96% of the mean annual density and total annual production numbers respectively, accounted for only 80% of the mean annual biomass and 86% of the total annual production biomass. All 14 species had a peak in abundance in autumn, immediately or soon after leaf litter fall. While most species maintained small, active and reproducing populations over the winter period, some maintained higher than normal densities, had seasonal peaks in abundance and biomass, or higher than normal rates of production and turnover. All species had an increase in reproduction and usually in abundance also during the late winter-early spring period before spring thaw. The annual mean weekly density and biomass and the annual production totals tor numbers and biomass were highest in the H layer and lowest in the L. The F layer produced the highest numbers of generations per year and the highest annual mean weekly biomass turnover rate for most of the species. The majority of the periods of high intrinsic rate of natural increase, biomass production and turnover occurred during or after an increase, a decrease or a stabilization in soil moisture content. Mean annual biomass and total annual production were estimated as 0.72 and 206 g wet weight m^?2 respectively. The aspen woodland soil Testacea (in a mor humus) had a much higher production and number of generations per year than Testacea from mull and moder humus forms.Total annual ingestion, respiration losses and egestion losses for testate amoebae in an aspen woodland soil were calculated as 1377, 344 and 826 g wet weight of biomass m^?2, respectively. The annual secondary production of Testacea was about 250–300 times the standing crop of Testacea in all the soil layers. The dry weight of carbon respired per year by the Testacea was estimated as 16.2 g m^?2, which amounted to about 6% of the total carbon input.     

Wildfires influence on soil organic matter in an Atlantic mountainous region (NW of Spain)

The principal aim of this research was to determine the influence of wildfires on soil organic matter (SOM) content and composition in soils located on the northern slope of the Cantabrian Cordillera, an Atlantic mountainous region in the North West of Spain, where wildfires are frequent. Samples from soils with similar aspect, slope, elevation and vegetation characteristics, but with different wildfires histories were collected. Total organic carbon and total nitrogen contents were determined as well as the C/N ratio. Furthermore, a qualitative characterization of the soil organic carbon (SOC) was carried out by ¹³C variable amplitude cross polarization magic angle spinning (VACP/MAS) Nuclear Magnetic Resonance (NMR) spectroscopy. Our results show that, on the one hand, all the sampled soils can be considered important pools of carbon in this Atlantic mountainous region, especially in the heath areas. On the other hand, the fire-affected soils present higher SOM contents than their unburnt counterparts. This could be attributed to an important reaccumulation of fresh vegetal material, which is probably a consequence of the decrease of SOM decomposition rates after fire. Moreover, charred organic compounds are not found in all the burnt soils, which could be due to the long time since the last fires events took place, to different fire severities, or to different post-fire erosion processes in the studied soils.     

Incidence of fungus-growing termites (Isoptera, Macrotermitinae) on the structure of soil microbial communities

The aim of this study was to investigate the impact of subterranean fungus-growing termites on the structure of soil microorganism communities. We tested whether termites significantly modify the abundance and structure of microbial communities within their below-ground nests (fungus-comb chambers) and whether these effects are species-specific.The investigations were carried out in a humid savanna reserve with material collected from the fungus-comb chamber walls of two widespread species differing in the mode of nest construction. Ancistrotermes builds diffuse and ephemeral nests while chambers of Odontotermes are mostly concentrated and occupy the same area for a comparatively much longer period of time then creating lenticular mounds. The soil properties (pH, texture and C, N content) and the microbial biomass were analysed and automated rRNA intergenic spacer analysis (ARISA) was used to characterise bacterial (B-ARISA) and fungal (F-ARISA) communities. Our results illustrate that the nest structures created by termites offer a diverse range of physical and chemical environments that differ strongly from those present in the general soil mass. Odontotermes had strong effects on microbial properties at the scale of the fungus-comb chamber and at the scale of the lenticular mound. In the fungus-comb chambers, the microbial biomass is not affected by termites but the structure of microbial community is different from that in the control open savanna soil. In the lenticular mound, the microbial biomass is higher and the structure of bacterial community is distinct than that in the fungus-comb chambers. Ancistrotermes also strongly influenced the structure of soil bacterial and fungal communities in the open savanna. However, we did not find any significant modification of bacterial and fungal community structures in the lenticular mound. The impact of fungus-growing termites is, therefore, species-specific and varies depending on the study site (open savanna vs. lenticular mound).     

Characterization of rhizosphere microbial communities in continuous cropping maca (Lepidium meyenii) red soil,Yunnan, China

ABSTRACT

Continuous cropping maca systems are widespread in Yunan Province, China. However, the relationships between continuous cropping maca systems and microbes are not well understood. The objective of this study was to determine the effects of continuous cropping maca systems (Maca with 0, 1, 2, and 3 years of continuous cultivation) on the soil microbial community. The results showed that the soil organic matter, total N, total P, and total K contents, as well as maca fresh and dry weight, decreased significantly with increased continuous cropping years. Interestingly, qPCR analysis showed that the bacterial and fungal abundance (DNA levels) decreased and active bacterial and fungal abundance (RNA levels) increased with cropping years from the first to the third cropping (p < 0.05). Moreover, the abundance of actinomycetes in the CK soil was significantly higher than that in the other maca soils. In addition, the continuous cropping system resulted in rich diversity in the fungal structure and had little effects on the bacterial and actinomycete communities. Acidobacteria (50%) and Ascomycota (58.3%) were detected in the continuous cropping maca soils. Based on the present results, continuous cropping of maca not exceeding two years could be optimal to maintain soil nutrition and microbial community.     

放牧对小嵩草草甸土壤酶活性及土壤环境因素的影响

观测了放牧对高寒小嵩草草甸土壤酶活性及土壤环境因素的影响,结果表明:①随着放牧压力的增大,植被盖度、地上生物量、土壤有机质、全氮、硝态氮、全磷、有效磷、土壤水分明显下降,而地下生物量、土壤容重、pH及根土比呈现增大趋势,不同放牧处理间植物群落特征及土壤理化特性显示出明显的差异(P0.05);②纤维素分解酶、多酚氧化酶、脲酶、蛋白酶、碱性磷酸酶和蔗糖酶活性均随放牧压力增大而下降,只有过氧化氢酶以轻牧最高,各处理间上述土壤酶活性差异程度不同;③随着土壤深度的增加,土壤水分含量、地下生物量、根土比、土壤有机质及氮、磷养分等明显下降,而土壤容重和pH逐渐增大,且不同层次之间存在显著的差异(P0.05);④除过氧化氢酶和多酚氧化酶外,其它土壤酶活性随土壤深度的加深显著减小。