Amount Of Soil Microbial Biomass Research Articles

Grasshopper herbivory immediately affects element cycling but not export rates in an N‐limited grassland system

AbstractAs a cause of ecosystem disturbances, phytophagous insects are known to directly influence the element and organic matter (OM) cycling in ecosystems by their defoliation and excretion activity. This study focuses on the interplay between short‐term, insect herbivory, plant responses to feeding activity, rhizosphere processes, and belowground nutrient availability under nutrient‐poor soil conditions. To test the effects of insect herbivory on OM and nutrient cycling in an N‐limited pasture system, mesocosm laboratory experiments were conducted using Dactylis glomerata as common grass species and Chorthippus dorsatus, a widespread grasshopper species, to induce strong defoliating herbivory. 13CO2 pulse labeling was used together with labeled 15N feces to trace the fate of C in soil respiration at the beginning of herbivory, and of C and N in above‐ and belowground plant biomass, grasshopper, feces, bulk soil, soil microbial biomass, throughfall solutions, and soil solutions. Within five days, herbivory caused a reduction in aboveground grass biomass by about 34%. A linear mixed‐effects model revealed that herbivory significantly increased total dissolved C and N amounts in throughfall solutions by a factor of 4–10 (P < 0.05) compared with the control. In total, 27.6% of the initially applied feces 15N were translocated from the aboveground to the belowground system. A significant enrichment of 15N in roots led to the assumption that feces‐derived 15N was rapidly taken up to compensate for the frass‐related foliar N losses in light of N shortage. Soil microorganisms incorporated newly available 13C; however, the total amount of soil microbial biomass remained unaffected, while the exploitative grass species rapidly sequestered resources to facilitate its regrowth after herbivory attack. Heavy herbivory by insects infesting D. glomerata‐dominated, N‐deficient grasslands remarkably impacted belowground nutrient cycling by an instant amplification of available nutrients, which led to an intensified nutrient competition between plants and soil microorganisms. Consequently, these competitive plant–soil microbe interactions accelerated N cycling and effectively retained herbivory‐mediated C and N surplus release resulting in diminished N losses from the system. The study highlighted the overarching role of plant adaptations to in situ soil fertility in short‐term ecosystem disturbances.

Drying and rewetting conditions differentially affect the mineralization of fresh plant litter and extant soil organic matter

Drought is becoming more common globally and has the potential to alter patterns of soil carbon (C) storage in terrestrial ecosystems. After an extended dry period, a pulse of soil CO2 release is commonly observed upon rewetting (the so-called ‘Birch effect’), the magnitude of which depends on soil rewetting frequency. But the source and implications of this CO2 efflux are unclear. We used a mesocosm field experiment to subject agricultural topsoil to two distinct drying and rewetting frequencies, measuring Birch effects (as 3-day cumulative CO2 efflux upon rewetting) and the overall CO2 efflux over the entire drying-rewetting cycle. We used 14C-labelled wheat straw to determine the contribution of fresh (recently incorporated) plant litter or extant soil organic matter (SOM) to these fluxes, and assessed the extent to which the amount of soil microbial biomass + K2SO4-extractable organic C (fumigated-extracted C, FEC) before rewetting determined the magnitude of Birch effect CO2 pulses. Our results showed a gradual increase in SOM-derived organic solutes within the FEC fraction, and a decrease in soil microbial biomass, under more extreme drying and rewetting conditions. But, contrary to our hypothesis, pre-wetting levels of FEC were not related to the magnitude of the Birch effects. In the longer term, rewetting frequency and temperature influenced the overall (31-day cumulative) amount of CO2–C released from SOM upon rewetting, but the overall 14CO2–C respired from fresh straw was only influenced by the rewetting frequency, with no effect of seasonal temperature differences of ∼15 °C. We conclude that the mineralization of fresh plant litter in soils is more sensitive to water limitations than extant SOM in soils under drying-rewetting conditions. Moreover, we found little evidence to support the hypothesis that the availability of microbial and soluble organic C before rewetting determined the magnitude of the Birch effects, and suggest that future work should investigate whether these short-term CO2 pulses are predominantly derived from substrate-supply mechanisms resulting from the disruption of the soil organo-mineral matrix.

Are raw materials or composting conditions and time that most influence the maturity and/or quality of composts? Comparison of obtained composts on soil properties

Abstract Waste composting is a process which is spreading worldwide to reduce waste disposal in landfill. The composting technical currents give little attention to the type and chemical composition of biomass that are mixed not considering that these can affect quality and maturity of the compost produced. In addition, during the composting process the amount of oxygen and temperature are generally only monitored but not set up. Our hypothesis is that composts, prepared from different organic wastes, can be chemically different with consequent different fertilizer properties. Stability and quality of composts are dependent on multivariate parameters such as raw material source, proportions used, composting procedure, and maturation time. Starting from this consideration a composting experiment was carried out to evaluate if were the raw materials (chemical composition, mixture and ratio), or the composting conditions and time, to influence the maturity or the quality of composts. We prepared four composts starting from different combinations and ratios of vegetable residues and/or olive pomace. After 120 days, the four composts were physically, chemically and biologically characterized to evaluate maturity degree, stability and quality of the products obtained under the same composting conditions and time. Their ability, as soil improver, was evaluated assessing soil chemical and biochemical properties 90 days after the compost addition. Here we show that the chemical composition of raw materials and the set up parameters of composting processes can have a different weight in influencing compost stability and quality. Our results evidenced that during the composting process all the composts had a similar percentage of C/N ratio reduction and all of them achieved an acceptable maturity degree. The composts produced by olive pomace showed the highest degree of maturity as demonstrated by T value and organic matter loss, both indices of compost stability. Conversely the composts coming from green vegetable residues were richest in nutrients and phenols and had the highest CSC all indices of better quality. In this work we identified two composts able to increase carbon stock, and water holding capacity parameters that positively influence soil structure, and two compost able to increase the amount of soil microbial biomass, their activity and soil biodiversity, improving soil biological fertility. These results highlighted that compost maturity doesn't mean compost quality, suggesting that compost maturity is mainly linked to composting setup parameters, while compost quality is mainly linked to chemical composition. FDA and DHA activities have been identified as markers for assessing the quality of amended soils.

黄土丘陵区小流域侵蚀环境对土壤微生物量及酶活性的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 黄土丘陵区小流域侵蚀环境对土壤微生物量及酶活性的影响 DOI: 10.5846/stxb201310302611 作者: 作者单位: 西北农林科技大学资源环境学院,西北农林科技大学 资源环境学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金重点基金(41030532); 国家自然科学基金面上项目(41171226); 教育部新世纪优秀人才支持计划(NCET-12-0479) Effect of erosion on soil microbial biomass and enzyme activity in the Loess Hills Author: Affiliation: College of Resources and Environment, Northwest A＆F University,College of Resources and Environment, Northwest A＆F University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:土壤侵蚀环境直接影响土壤的特性,对土壤微生物的形成和稳定具有重要的影响。土壤微生物量推动着土壤的物质循环和能量流动,对土壤中各种环境的变化有很强的敏感性。土壤酶活性能表示土壤微生物功能的多样性,与土壤微生物量有着紧密的联系。为了探究不同侵蚀环境对土壤微生物量和酶活性的影响,以黄土丘陵区陈家坬小流域为研究区,选择5种不同侵蚀环境下0-10cm和10-20cm土层的土壤为研究对象,对土壤微生物量及其土壤蔗糖酶、脲酶和碱性磷酸酶活性进行了研究。结果表明:(1)土壤微生物量碳、氮、磷含量均表现为0-10cm大于10-20cm土层;土壤微生物量碳和磷在阴沟坡最大,在阳梁峁坡和峁顶较小,且阴沟坡和峁顶差异显著;土壤微生物量氮在阳沟坡最大,阴阳梁峁坡最小,差异性显著(P < 0.01)。(2)土壤脲酶、蔗糖酶和碱性磷酸酶活性均表现为0-10cm大于10-20cm土层,且在不同侵蚀环境下均表现为阴梁峁坡最大,阳梁峁坡最小。(3)相关性分析表明,土壤微生物量碳、氮、磷与土壤脲酶、蔗糖酶、碱性磷酸酶活性之间均有极显著的正相关。 Abstract:Erosion directly affects soil characteristics and has a significant effect on the formation and stability of the soil microbial community. Soil microbial biomass not only plays a significant role in energy flow and nutrient cycling, but it also shows great sensitivity to changes in soil environment. Soil enzyme activities are indicative of the functional diversity of the soil microbial community, as they are closely associated with soil microbial biomass. To reveal the effect of different erosion environments on soil microbial biomass and soil enzyme activities, soil samples were collected from the Chengjiawa watershed, located in the Yanhe watershed of the hill and gully region of Ansai County, Yan'an, Shaanxi Province, China. Soil samples were collected from five erosion environments in the valley, at depths of 0-10 cm and 10-20 cm. We studied the characteristics of soil microbial biomass including carbon, nitrogen, and phosphorus, soil enzyme activities including soil urease, invertase, and alkaline phosphatase, and correlations between soil microbial biomass and enzyme activities. The results showed that: (1) Soil microbial biomass carbon, nitrogen, and phosphorus were significantly different between the 0-10 cm and 10-20 cm soil layers; soil microbial biomass carbon and phosphorus in the shaded lower slopes were higher than in the other tested environments, whereas in the sunny middle slope and the hill top they were lower than in the other tested soil environments. The difference between the shaded lower slopes and sunny hill top were significant. Soil microbial biomass nitrogen in the sunny lower slope was significantly higher than in the other tested soil environments. Overall, soil microbial biomass of the ditch slope was higher than in the other tested environments. This suggested that the erosion affects the soil microbial properties, and that soil nutrient accumulation and mineralization ability of soils on the downhill slope were higher than in other tested locations. (2) Soil urease, sucrase, and alkaline phosphatase activities were higher in the 0-10 cm layer than in the 10-20 cm layer. In different erosion environments, soil enzyme activities were higher in the shaded middle slope than in any other tested environments, while they were the lowest in the sunny middle slopes. Soil alkaline phosphatase activity did not significantly differ between different soil environments. Soil invertase activity in the shaded middle slopes was significantly different from the other four types of erosion environments. The difference in soil urease activity between the shaded lower slope and other tested environments was significant. Comparisons showed that the environment exposed to erosion affected the properties of soil enzyme activities; the responses of soil invertase and urease were more sensitive to changes in the soil environment. (3) Pearson correlation analysis showed that soil microbial biomass carbon, nitrogen, and phosphorus were significantly positively correlated with each other, as were the soil urease, sucrase, and alkaline phosphatase activities. There was a significant positive correlation between soil microbial biomass and soil enzyme activities, which suggested that these two properties were closely linked and inseparable components of the soil microbial community. Different environments exposed to erosion have diverse levels of soil organic matter content, different physicochemical properties of the soil, diverse forms of soil microbes, and differ in the amount of soil microbial biomass and soil enzyme activities. These differences were reflected in the soil quality, vegetation types, and resistance to soil erosion. 参考文献 相似文献 引证文献

The influence of grazing exclosure on soil C stocks and dynamics, and ecological indicators in upland arid and semi-arid rangelands

Soil carbon (C) storage and quality in rangeland ecosystems may change as a result of long-term heavy grazing, especially in upland arid and semi-arid rangelands characterized by low soil organic C contents. The impact of grazing exclosure on soil C stock and mineralization, microbial biomass C and the activities of invertase and alkaline phosphatase involved in C and P cycling as soil ecological indicators were studied in woody and non-woody rangeland ecosystems of two sites (viz., Sabzkouh with woody cover and Boroujen with non-woody cover) located in Zagros Mountains, Central Iran. At each site, soil samples were taken from 0 to 15cm depth of the two rangelands including heavy grazing (HG) and ungrazed (UG) regimes, and analyzed for their chemical and microbial properties. Results demonstrate that soil organic C and total N contents, and C/N ratios were not affected by grazing regime at Boroujen, while ungrazed rangelands had higher C (17%) and N (19%) contents compared with heavily grazed rangelands at Sabzkouh. Grazing exclosure increased soil C mineralization (44.7–73.6%) and turnover (24–64%) at both study sites, and increased the amount of soil microbial biomass C (5.4-fold) and decreased the metabolic quotient (90%) only at Sabzkouh. Soil invertase activity was significantly higher (1.3–2.1 times) in ungrazed than heavily grazed rangelands at both sites, whereas ungrazed rangelands had significantly greater soil alkaline phosphatase activity (19%) compared with heavily grazed rangelands only at Sabzkouh. The variations in the effect of grazing exclosure on soil organic matter (SOM) dynamics and C sequestration in these upland arid and semi-arid rangelands were due to differences between rangelands in initial SOM contents, and probably could be due to differences in plant productivity and composition, and the amount of rainfall between the study sites. Non-woody rangelands contained less soil C and N contents, and C mineralization but greater microbial biomass C than woody rangelands, reflecting a clear difference in substrate quality and soil C availability. Soil biochemical and microbial indices as ecological indicators can reflect grazing exclosure effects on soil restoration only in woody rangelands.

The combined effects of earthworms and arbuscular mycorrhizal fungi on microbial biomass and enzyme activities in a calcareous soil spiked with cadmium

Earthworms and arbuscular mycorrhizal fungi (AMF) are known to independently affect soil microbial and biochemical properties, in particular soil microbial biomass (SMB) and enzymes. However, less information is available about their interactive effects, particularly in soils contaminated with heavy metals such as cadmium (Cd). The amount of soil microbial biomass C (MBC), the rate of soil respiration (SRR) and the activities of urease and alkaline phosphatase (ALP) were measured in a calcareous soil artificially spiked with Cd (10 and 20mgCdkg−1), inoculated with earthworm (Lumbricus rubellus L.), and AMF (Glomus intraradices and Glomus mosseae species) under maize (Zea mays L.) crop for 60 days. Results showed that the quantity of MBC, SRR and enzyme activities decreased with increasing Cd levels as a result of the elevated exchangeable Cd concentration. Earthworm addition increased soil exchangeable Cd levels, while AMF and their interaction with earthworms had no influence on this fraction of Cd. Earthworm activity resulted in no change in soil MBC, while inoculation with both AMF species significantly enhanced soil MBC contents. However, the presence of earthworms lowered soil MBC when inoculated with G. mosseae fungi, showing an interaction between the two organisms. Soil enzyme activities and SRR values tended to increase considerably with the inoculation of both earthworms and AMF. Nevertheless, earthworm activity did not affect ALP activity when inoculated with G. mosseae fungi, while the presence of earthworm enhanced urease activity only with G. intraradices species. The increases in enzyme activities and SRR were better ascribed to changes in soil organic carbon (OC), MBC and dissolved organic carbon (DOC) contents. In summary, results demonstrated that the influence of earthworms alone on Cd availability is more important than that of AMF in Cd-polluted soils; and that the interaction effects between these organisms on soil microorganism are much more important than on Cd availability. Thus, the presence of both earthworms and AMF could alleviate Cd effects on soil microbial life.

Impact of Fertilization on Microbial Biomass Carbon and Nitrogen from Soil in Vegetable Greenhouse

In this study, columns packed of a greenhouse soil with various soil fertile levels (low, medium and high) were carried out under greenhouse condition. The leaching experiment lasted 51 days. There were four fertilization treatments including no fertilizer [CK], chemical fertilizer [NPK], organic manure [M], organic manure and chemical fertilizer [M+NPK]. Microbial biomass C and N were measured. The results were as follows: organic or inorganic fertilizer increased the contents of soil microbial biomass C and N, and combination of chemical fertilizer and organic fertilizer significantly elevated the amount of soil microbial biomass C and N compared to organic or inorganic fertilizer treatment. There were significant differences in the amount of microbial biomass C and N among different fertile level soil under different fertilization practices in 0-20 and 20-40cm soil layers. Our study showed that application of manure and chemical fertilizer at proper rates according to soil fertile status is beneficial to increase the amount of microbial biomass C and N.

Recent research progress on soil microbial responses to drying–rewetting cycles

Climatic change, such as increases in extreme drought and rainfall events and changes in rainfall intensity and pattern, has been strongly influencing soil moisture. The climatic change impact is particularly common in arid, semi-arid and Mediterranean regions, which is causing dramatic changes in the intensity and frequency of soil drying–rewetting cycles. The soil drying–rewetting cycle is a natural phenomenon that the soil experiences drying, then wetting, and then drying and rewetting again and again. When a dry soil is being rewetted, the amount of soil microbial biomass and its activity can be sharply increasing in a short time period, and then a large amount of gaseous carbon (C) and nitrogen (N) erupts from the soil. The sudden release of gaseous C and N is caused by the stimulation of the soil microbes. Such a phenomenon is called “Birch effect”. The drying–rewetting cycles have direct and indirect effects on soil microbes, and soil microbial responses to the drying and rewetting events play an important role in the feedbacks of terrestrial ecosystems. From aspects of soil microbial biomass, microbial activities and microbial structure, we review recent advances on studies regarding microbial responses to soil drying–rewetting cycles. We interpret the microbial responses using five different types of mechanisms: (1) Microbial stress mechanism: when a soil becomes dry, microorganisms must accumulate compatible solutes such as carbohydrates and aminoacids so that the soil microbes can equilibrate with their environment in order to avoid dehydrating and being killed. When the soil is rewetted, soil microbes must dispose of those osmolytes rapidly by transforming them into carbon dioxide (CO2), dissolved organic carbon (DOC) and nutrients in order to prevent water from being flowing into the cells. (2) Substrate supply mechanism: low soil moisture may result in the physical disruption of soil aggregates which leads to the exposure of new soil surfaces and of previously protected organic matter. When the soil is rewetted, its physical structure is further disrupted by swelling. The increased new soil surfaces and previously protected organic matter will improve the microorganism’s nutrient availability. (3) Soil hydrophobicity mechanism: soil hydrophobicity can cause the reduction of soil moisture and nutrient availability and inhibition of microbial decomposition of soil organic matter. Therefore, soil hydrophobicity is an important factor of explaining the activity of microorganism in drying and rewetting events. (4) Diffusive limitations mechanism: transportation of the soil microbe is limited in a dry soil. When soil moisture is increasing, soil microbial activity is enhanced along with the increased availability of substrate nutrients. (5) Predation mechanism: a moist soil is usually conducive to the increase of bacteria and fungi populations. In response, protozoa and nematodes also increase, leading to the fluctuation of the soil microbial community structure. On the basis of the literature review, we propose five important aspects to be considered in the future: (1) assessing soil microbes’ concrete adapting ways to the drying–rewetting cycles, (2) evaluating the microbial responses to the drying–rewetting cycles based on suitable indicators, (3) interpreting microbial responses to the drying–rewetting cycles by combining field investigation and laboratory controlling experiment, (4) investigating the microbial responses to the drying–rewetting cycles at different temporal and spatial scales.

Assessment of Robinia pseudoacacia cultivations as a restoration strategy for reclaimed mine spoil heaps

Reforestation with black locust (Robinia pseudoacacia) is considered a successful technique that is often used for the reclamation of open-cast mine areas. An alternative reclamation technique could be the natural regeneration of vegetation with spontaneous grass species. In this study, we compared the concentrations of chemical and biochemical variables in soil samples taken under black locust canopy to those from sites covered by spontaneous grass vegetation (control samples) in a time sequence of spoil deposition (0-10years), in order to assess which of the two reclamation techniques yields higher soil quality. Soil quality refers here to the ability of soils to function ecologically. This has a special interest since the main question for the restored soils is their capacity to perform a range of ecological functions under stress or disturbance. Furthermore, we aimed at identifying the effect of vegetation type on soil ecological succession. The effect of vegetation type on primary succession becomes apparent after 2years of reclamation. R. pseudoacacia as a nitrogen-fixing plant enriched soil with organic and inorganic nitrogen and organic matter to a greater extent than the natural grasses. It also increased the amount of soil microbial biomass and the activity of alkaline phosphatase. However, the fact that black locust failed to enhance dehydrogenase activity and actually decreased the activity of urease, activities that represent specialized niche functions and therefore, are more vulnerable to stress or disturbance, suggests that the development of an indigenous grass community in combination with organic supplements might often be more appropriate for the reclamation of similar kinds of mine areas.

干湿交替频率对不同土壤CO2和N2O释放的影响

干旱、半干旱和地中海气候区,乃至一些湿润地区,由干湿交替引起的土壤碳、氮的短暂脉冲式释放很大程度上决定着长时间尺度温室气体释放的总量,是土壤碳、氮温室气体释放的关键过程。选择我国降雨梯度下的森林、农田、草地和荒漠生态系统,采集土样进行实验室统一控制条件下的多重干湿交替循环,对比探讨不同生态系统土壤干湿交替频率对CO₂和N₂O释放的影响模式。结果表明:(1)干湿交替能够显著的激发土壤中CO₂和N₂O的释放,森林、农田、草地和荒漠土壤CO₂和N₂O释放速率对干湿交替的响应模式基本一致,其响应强度与土壤本底中碳和氮的含量有关;(2)在一定培养时间内,随着干湿交替频率的增加,土壤再湿润阶段CO₂释放速率降低,但是,气体释放的总量较之于恒湿对照组有所增加。(3)不同土壤N₂O的释放总量对干湿交替频率的响应模式表现出很大的差异,其中农田和荒漠土壤响应模式类似。;In the context of climate change impacts on the rainfall patterns, understanding the effects of soil drying-rewetting cycles on green-house gas emission has become increasingly important in many ecosystems. Soil carbon and nitrogen releases caused by drying and rewetting cycles largely determine the total amount of greenhouse gases emission for a long time in an ecosystem. Such kind of influence is particularly important in arid, semi-arid and Mediterranean regions. The soil drying-rewetting cycle is a natural phenomenon that the soil experiences drying, then wetting, and then drying and rewetting again and again. When a dry soil is being rewetted, the amount of soil microbial biomass and its activity can be sharply increasing in a short time period, and then a large amount of gaseous carbon (C) and nitrogen (N) erupts from the soil. The sudden release of gaseous C and N is caused by the stimulation of the soil microbes. Such a phenomenon is called Birch effect. The drying-rewetting cycles play an important role in the feedbacks of terrestrial ecosystems. In this study, soil samples were taken from four field sites of forest, agriculture, grassland and desert ecosystems along the precipitation gradient in China. These four sites are Beijing Forest Ecosystem Study, Ansai Agricultural Ecosystem Study, Inner Mongolia Grassland Study and Fukang Desert Ecosystem Study sites of the Chinese Ecosystem Research Network (CERN). Based on the laboratory experiment with 0, 2, 5, 7 and 14 drying-rewetting cycles in the controlling temperature, we examed the patterns of drying-rewetting impacts on soil CO₂ and N₂O emission. Our results showed that: (1) Drying and rewetting cycles significantly stimulated the CO₂ and N₂O releases from soil. For example, in comparison with the control experiment with constant soil moisture in the grassland soil, the average respiration rate of 14-cycle,7-cycle,5-cycle and 2-cycle treatments increased 43%、103%、116% and 192%, respectively. We also found that response patterns in CO₂ and N₂O release rates to drying and rewetting frequencies were similar among different ecosystem soils. The initial rewetting pulses were the highest, and then declined over time. (2) The total amount of CO₂ released from the cycling soil was higher than that from its corresponding control treatment with constant soil moisture. In the forest soil, the 14-cycle soil released a total of 360.11μg C-CO₂/g soil in comparison with the control treatment with constant soil moisture, which released 284.56 μg C-CO₂/g soil. The cycling increased respiration by 27%. In the grassland soil, the 14-cycle soil released a total of 339.88μg C-CO₂/g soil in comparison with the control treatmen, which released 244.01 μg C-CO₂/g soil, increased by 39%. In the agriculture soil, the 14-cycle soil released a total of 299.31μg C-CO₂/g soil in comparison with the control treatment, which released 143.27 μg C-CO₂/g soil, increased respiration by 109%. In the desert soil, the 14-cycle soil released a total of 167.54μg C-CO₂/g soil in comparison with the control treatment, which released 142.79 μg C-CO₂/g soil, increased respiration by 17%. (3) Cumulative N₂O release among different ecosystem soils had different drying-rewetting response patterns, but soils from the agriculture and desert ecosystems have similar response patterns.

Carbon, nitrogen, organic phosphorus, microbial biomass and N mineralization in soils under cacao agroforestry systems in Bahia, Brazil

Large amounts of plant litter deposited in cacao agroforestry systems play a key role in nutrient cycling. Organic matter, nitrogen and phosphorus cycling and microbial biomass were investigated in cacao agroforestry systems on Latosols and Cambisols in Bahia, Brazil. The objective of this study was to characterize the microbial C and N, mineralizable N and organic P in two soil orders under three types of cacao agroforestry systems and an adjacent natural forest in Bahia, Brazil and also to evaluate the relationship between P fractions, microbial biomass and mineralized N with other soil attributes. Overall, the average stocks of organic C, total N and total organic P across all systems for 0–50 cm soil depth were 89,072, 8,838 and 790 kg ha−1, respectively. At this soil depth the average stock of labile organic P was 55.5 kg ha−1. For 0–10 cm soil depth, there were large amounts of microbial biomass C (mean of 286 kg ha−1), microbial biomass N (mean of 168 kg ha−1) and mineralizable N (mean of 79 kg ha−1). Organic P (total and labile) was negatively related to organic C, reflecting that the dynamics of organic P in these cacao agroforestry systems are not directly associated with organic C dynamics in soils, in contrast to the dynamics of N. Furthermore, the amounts of soil microbial biomass, mineralizable N, and organic P could be relevant for cacao nutrition, considering the low amount of N and P exported in cacao seeds.

Effects of Elevated CO2 and O3 and N Fertilization on Amount of Soil Microbial Biomass Carbon in Spring Wheat Growing Season

Experimental platform of Open-top chambers (OTC) was established in 2006 over a spring wheat system, it located at the National Field Observation and Research Station of Shenyang Agro-ecosystems, a member of Chinese Ecosystem Research Network (CERN) established in 1987. We compared the dynamics of soil microbial biomass C with high (225.0kg N hm-2) and low (150kg N hm-2) application rate of chemical fertilizer N exposed to the elevated CO2, O3, CO2 plus O3 and CK after the spring wheat growing season in 2010. The results showed that under elevated CO2 concentration at the jointing stage, high application rate of chemical fertilizer N significantly declined the amount of soil microbial biomass C by 64.97%, compared with the low N application rate of chemical fertilizer N (p<0.01). In treatment with low application rate of chemical fertilizer N, elevated O3 concentration significantly declined the amount of soil microbial biomass C by 52.49% (p<0.05), compared with CK. In treatment with high application rate of chemical fertilizer N, the interaction of CO2 and O3 increased significantly the amount of soil microbial biomass C by 50.03% (p<0.05), compared with CK. At the ripening stage, under elevated CO2 concentration and interaction of CO2 and O3, high application rate of chemical fertilizer N significantly decreased the amount of soil microbial biomass C by 32.92% and 41.45%, compared with low N application rate of chemical fertilizer N, respectively (p<0.05). In treatment with low application rate of chemical fertilizer N, elevated CO2 and interaction of CO2 and O3 significantly increased the amount of soil microbial biomass C by 25.32% and 38.59% (p<0.05), compared with CK, respectively.

Variability of soil N cycling and N2O emission in a mixed deciduous forest with different abundance of beech

The mixture of other broadleaf species into beech forests in Central Europe leads to an increase of tree species diversity, which may alter soil biochemical processes. This study was aimed at 1) assessing differences in gross rates of soil N cycling among deciduous stands of different beech (Fagus sylvatica L.) abundance in a limestone area, 2) analyzing the relationships between gross rates of soil N cycling and forest stand N cycling, and 3) quantifying N2O emission and determining its relationship with gross rates of soil N cycling. We used 15N pool dilution techniques for soil N transformation measurement and chamber method for N2O flux measurement. Gross rates of mineral N production in the 0–5 cm mineral soil increased across stands of decreasing beech abundance and increasing soil clay content. These rates were correlated with microbial biomass which, in turn, was influenced by substrate quantity, quality and soil fertility. Leaf litter-N, C:N ratio and base saturation in the mineral soil increased with decreasing beech abundance. Soil mineral N production and assimilation by microbes were tightly coupled, resulting in low N2O emissions. Annual N2O emissions were largely contributed by the freeze-thaw event emissions, which were correlated with the amount of soil microbial biomass. Our results suggest that soil N availability may increase through the mixture of broadleaf species into beech forests.

Long‐lasting impact of biowaste‐compost application in agriculture on soil‐quality parameters in three different crop‐rotation systems

AbstractSoil‐quality parameters, such as soil organic matter (SOM) and plant‐available nutrient contents, microbial properties, aggregate stability, and the amounts of heavy metals were carried out in arable soils of different rotation schedules applied with a total of 50 Mg dry mass ha–1 biowaste compost relative to an untreated control. This was investigated during a 10 y period from 1994 to 2004. Overall, soil‐quality parameters studied appeared to be promoted by biowaste‐compost application. This was evidenced for example by a remarkable increase of SOM and total N content of ≈ 15%–20% relative to the control. Subsequently, amounts of soil microbial biomass and alkaline phosphatase activity were significantly increased as well. In addition, biowaste‐compost application revealed an increase of plant‐available P and K contents and aggregate stability in soil. There was, however, no treatment effect for net N‐mineralization rates. Moreover, in soils of maize and sugar beet rotation schedule a slight decrease was found. Heavy‐metal contents of Pb and Zn were significantly increased in all compost‐treated soils, whereas no significant increase of Cd and Cu contents was measured. However, the investigated amounts were far below of the limits of the German Biowaste Ordinance. It is finally recommended, that biowaste compost may sustain and improve soil quality in agriculture when N nutrition will be considered.

Changes in the soil microbial community structure with latitude in eastern China, based on phospholipid fatty acid analysis

Phospholipid fatty acid (PLFA) profiles were measured in soils from 14 sites in eastern China representing typical geographic zones of varying latitude from north (47.4°N) to south (21.4°N). Amounts of soil microbial biomass, measured as total amounts of PLFAs, showed no regular trend with latitude, but were positively correlated with soil organic carbon content, the concentration of humic acid and amorphous iron oxide. Soil microbial community structure showed some biogeographical distribution trends and was separated into three groups in a cluster analysis and principal coordinate analysis of log transformed PLFA concentrations (mol%). Soils in the first group came from northern China with medium mean annual temperature (1.2–15.7 °C) and rainfall (550–1021 mm). Soils in the second group originated from southern China with a relatively higher mean annual temperature (15.7–21.2 °C) and rainfall (1021–1690 mm). Soils clustered in the third group originated from the most southerly region. The northern soils contained relatively more bacteria and Gram-negative PLFAs, while the southern soils had more fungi and pressure indexed PLFAs. These differences in soil microbial community structure were largely explained by soil pH, while other site and soil characteristics were less important.

Carbon and Nitrogen Transformations in Surface Soils Under Ermans Birch and Dark Coniferous Forests

Abstract Soil samples were taken from an Ermans birch ( Betula ermanii)-dark coniferous forest ( Picea jezoensis and Abies nephrolepis) ecotone growing on volcanic ejecta in the northern slope of Changbai Mountains of Northeast China, to compare soil carbon (C) and nitrogen (N) transformations in the two forests. The soil type is Umbri-Gelic Cambosols in Chinese Soil Taxonomy. Soil samples were incubated aerobically at 20 °C and field capacity of 700 g kg −1 over a period of 27 weeks. The amount of soil microbial biomass and net N mineralization were higher in the Ermans birch than the dark coniferous forest ( P < 0.05), whereas the cumulative C mineralization (as CO 2 emission) in the dark coniferous forest exceeded that in the Ermans birch ( P < 0.05). Release of the cumulative dissolved organic C and dissolved organic N were greater in the Ermans birch than the dark coniferous forest ( P < 0.05). The results suggested that differences of forest types could result in considerable change in soil C and N transformations.

Formas de fósforo no solo sob leguminosas florestais, floresta secundária e pastagem no Norte Fluminense

Em solos muito intemperizados, a disponibilidade de P para as plantas está estreitamente associada às formas de P orgânico, que tem o seu conteúdo alterado por influência do tipo de cobertura vegetal. O objetivo deste trabalho foi estimar os teores de fósforo de compostos orgânicos (Po-total, Po lábil e P microbiano do solo), em plantios de Acacia auriculiformis (acácia) e Mimosa caesalpiniifolia (sabiá), em floresta secundária e em pastagem. Os teores médios ponderados de Po total e Po lábil, pelo teor de argila, foram de 375 mg kg-1 de P na argila e de 40,2 mg kg-1 de P na argila, respectivamente. Os solos sob acácia e sabiá apresentaram maior teor relativo de Po (total e lábil) do que os solos sob pastagem e capoeira. O Po representou de 22,6 a 39,6 % do P total extraído dos solos das coberturas estudadas. Em relação ao P lábil total, o Po lábil representou, em média, 67,1 %. Para o P microbiano, o maior teor foi encontrado no solo sob sabiá, seguido da floresta secundária, acácia e pastagem. Contudo, foi na capoeira que houve a maior eficiência da biomassa microbiana do solo em imobilizar P. O teor de P disponível por Mehlich-1 correlacionou-se positivamente com o teor de C e o de P da biomassa microbiana. Houve estreita correlação positiva entre o P microbiano e o C microbiano.

Is the soil microbial community related to the basal area of trees in a Scots pine stand?

The main energy sources of soil microorganisms are litter fall, root litter and exudation. The amount on these carbon inputs vary according to basal area of the forest stand. We hypothesized that soil microbes utilizing these soil carbon sources relate to the basal area of trees. We measured the amount of soil microbial biomass, soil respiration and microbial community structure as determined by phospholipid fatty acid (PLFA) profiles in the humus layer (FH) of an even-aged stand of Scots pine ( Pinus sylvestris L.) with four different basal area levels ranging from 19.9 m 2 ha −1 in the study plot Kasper 1 to 35.7 m 2 ha −1 in Kasper 4. Increasing trend in basal respiration, total PLFAs and fungal-to-bacterial ratio was observed from Kasper 1 to Kasper 3 (basal area 29.2 m 2 ha −1). The soil microbial community structure in Kasper 3 differed from that of the other study plots.

Short-term decomposition of 14C-labelled glucose in a fluvo-aquic soil as affected by lanthanum amendment

In this study, we investigated the effects of lanthanum (La), one of the rare earth elements (REEs), on microbial biomass C as well as the decomposition of 14C-labelled glucose in a fluvo-aquic soil in 28 days. The soil was collected from the field plots under maize/wheat rotation in Fengqiu Ecological Experimental Station of Chinese Academy of Sciences, Henan Province, China. Application of La decreased soil microbial biomass C during the experimental period, and there was a negative correlation (P < 0.01) between microbial biomass and application rate of La. La increased microbial biomass 14C after 14C glucose addition, and the increase was significant (P < 0.05) at the rates of more than 160 mg kg−1 soil. La slightly increased 14CO2 evolution at lower rates of application but decreased it at higher rates 1 day after 14C glucose addition, while there was no significant effect from days 2 to 28. For the cumulative 14CO2 evolution during the incubation of 28 days, La slightly increased it at the rates of less than 120 mg kg−1 soil, while significantly decreased (P < 0.05) it at the rate of 200 mg kg−1 soil. The results indicated that agricultural use of REEs such as La in soil could decrease the amount of soil microbial biomass and change the pattern of microbial utilization on glucose C source in a short period.

Elevated Atmospheric CO2 Alters Soil Microbial Communities Associated with Trembling Aspen (Populus tremuloides) Roots

Global atmospheric CO(2) levels are expected to double within the next 50 years. To assess the effects of increased atmospheric CO(2) on soil ecosystems, cloned trembling aspen (Populus tremuloides) seedlings were grown individually in 1 m(3) open bottom root boxes under either elevated (720 ppm, ELEV) or ambient CO(2) (360 ppm, AMB). After 5 years, soil cores (40 cm depth) were collected from the root boxes and divided into 0-20 cm and 20-40 cm fractions. ELEV treatment resulted in significant decreases in both soil nitrate and total soil nitrogen in both the 0-20 cm and 20-40 cm soil fractions, with a 47% decrease in soil nitrate and a 50% decrease in total soil nitrogen occurring in the 0-20 cm fraction. ELEV treatment did not result in a significant change in the amount of soil microbial biomass. However, analysis of indicator phospholipid fatty acids (PLFA) indicated that ELEV treatment did result in significant increases in PLFA indicators for fungi and Gram-negative bacteria in the 0-20 cm fraction. Terminal restriction fragment length polymorphism (T-RFLP) analysis was used to analyze the composition of the soil bacterial communities (using primers targeting the 16SrRNA gene) and the soil fungal communities (using primers targeting the intergenic transcribed spacer region). T-RFLP analysis revealed shifts in both bacterial and fungal community structure, as well as increases in both bacterial and fungal species richness with ELEV treatment. These results indicated that increased atmospheric CO(2) had significant effects on both soil nutrient availability and the community composition of soil microbes associated with aspen roots.