Dwarf mistletoe effects on soil basidiomycete community structure, soil fungal functional diversity, and soil enzyme function: Implications for climate change

We used a combination of molecular, culture and biochemical methods to test the hypothesis that severe infection of pine by dwarf mistletoe (genus Arceuthobium) has significant effects on structure and function of soil fungal communities, and on carbon cycling in soils. PCR and DNA sequencing of the basidiomycete communities in paired blocks of uninfected and infected trees revealed: (1) that the top, organic soil layer in this system is inhabited almost exclusively by ectomycorrhizal fungi; (2) no difference in species richness (6 species core⁻¹ in both) or Shannon-Wiener evenness (0.740 and 0.747 in uninfected and infected blocks respectively), however Shannon-Wiener diversity was significantly greater in infected blocks (1.19 vs 1.94 in uninfected and infected blocks respectively, P < 0.05); (3) significant differences in basidiomycete species composition, with nearly complete absence of two system co-dominant Russula species in infected blocks, and replacement of one co-dominant Piloderma species with another in infected plots, indicating physiological variability within the genus. Soil fungal physiological diversity measured using the Fungilog system was significantly greater in terms of both number of carbon substrates used by culturable soil fungi (both ascomycetes and basidiomycetes) in infected blocks, and the rate at which these substrates were used. Soil enzyme assays revealed greater laccase, peroxidase, and cellulase activities in soils associated with infected trees. Thus, event cascades associated with severe dwarf mistletoe infection not only significantly affected soil fungal species composition and increased species diversity, but also impacted on carbon-related function and functional diversity. Given the geographic range of this pathogen, and forecasts that epidemics of this disease will increase in range in severity with global climate change, these effects have the potential to significantly impact local and global carbon budgets.     

Size Does Matter: Application-driven Approaches for Soil Metagenomics

Metagenomic analyses can provide extensive information on the structure, composition, and predicted gene functions of diverse environmental microbial assemblages. Each environment presents its own unique challenges to metagenomic investigation and requires a specifically designed approach to accommodate physicochemical and biotic factors unique to each environment that can pose technical hurdles and/or bias the metagenomic analyses. In particular, soils harbor an exceptional diversity of prokaryotes that are largely undescribed beyond the level of ribotype and are a potentially vast resource for natural product discovery. The successful application of a soil metagenomic approach depends on selecting the appropriate DNA extraction, purification, and if necessary, cloning methods for the intended downstream analyses. The most important technical considerations in a metagenomic study include obtaining a sufficient yield of high-purity DNA representing the targeted microorganisms within an environmental sample or enrichment and (if required) constructing a metagenomic library in a suitable vector and host. Size does matter in the context of the average insert size within a clone library or the sequence read length for a high-throughput sequencing approach. It is also imperative to select the appropriate metagenomic screening strategy to address the specific question(s) of interest, which should drive the selection of methods used in the earlier stages of a metagenomic project (e.g., DNA size, to clone or not to clone). Here, we present both the promising and problematic nature of soil metagenomics and discuss the factors that should be considered when selecting soil sampling, DNA extraction, purification, and cloning methods to implement based on the ultimate study objectives.     

Loss of low molecular weight dissolved organic carbon (DOC) and nitrogen (DON) in H2O and 0.5 M K2SO4 soil extracts

Soil extracts are routinely used to quantify dissolved organic nutrient concentrations in soil. Here we studied the loss and transformation of low molecular weight (LMW) components of DOC (¹⁴C-glucose, 1 and 100 μM) and DON (¹⁴C-amino acid mixture, 1 and 100 μM) during extraction of soil (0-6 h) with either distilled water or 0.5 M K₂SO₄. The extractions were performed at 20 °C, at 4 °C, or in the presence of an inhibitor of microbial activity (HgCl₂ and Na-azide). We showed that both glucose and amino acids became progressively lost from solution with increasing shaking time. The greatest loss was observed in H₂O extracts at 1 μM for both substances (>90% loss after 15 min). Lower temperature (4 °C) and presence of K₂SO₄ both resulted in reduced loss rates. The presence of microbial inhibitors effectively eliminated the loss of glucose and amino acids. We conclude that microbial transformation of LMW-DOC and DON during H₂O or K₂SO₄ extraction of soil may affect the estimation of their concentrations in soil. This finding has significant implications for methods that rely on chemical extractions to estimate LMW-C components of DOC and DON.     

Quantitative PCR assays to enumerate Rhizobium leguminosarum strains in soil also target non viable cells and overestimate those detected by the plant infection method

The plant infection method is commonly used to estimate the Most Probable Number (MPN) of soil rhizobia. Here, a qPCR method was set-up and validated with newly developed ANU (strain specific) and RHIZ (more general) primers to quantify the specific Rhizobium leguminosarum bv. trifolii ANU843 strain or general R. leguminosarum strains. Detection limits of qPCR protocols in soil were 1.2 × 10⁴ (ANU) and 4.2 × 10³ (RHIZ) cells per g soil. The qPCR assay appears robust and accurate in freshly inoculated soils but overestimated MPN for indigenous soil rhizobia. An incubation experiment showed that qPCR detected added DNA or non viable cells in soils up to 5 months after addition and incubation at 20 °C in moist conditions.     

Reestablishment of ecological functioning by mulching and termite invasion in a degraded soil in an Australian savanna

Soil degradation is a major source of ecological dysfunction in both natural and agricultural landscapes. Termites are key mediators of tropical soil structure and function, but there has been little experimental evaluation of their potential in soil rehabilitation. This study investigated if termite activity can be used as a tool to improve the properties and function of degraded soil in tropical Australia, through mulch addition. A 2 × 2 randomised block design was used, with mulch (bare [B] or mulched [M] plots) and termiticide (termite [T] or non-termite [NT] plots) as factors. Over 4.5 years I tested the hypothesis that the MT plots would show greatest increase in (i) soil macroporosity, (ii) total soil surface carbon and nitrogen, (iii) litter decomposition, (iv) soil water storage and (v) plant cover, and (vi) greatest reduction in soil strength. MT treatment plots showed a 46% and 45% increase in soil macroporosity and plant cover, respectively, and a 25% reduction in soil strength compared with MNT plots. Compared with B treatments (BT, BNT), macroporosity and plant cover were 98% and 60% higher, respectively and soil water storage increased by up to 15%. Termites contributed to 58% of litter loss in MT plots over the transitional/dry season period. Mulching doubled soil carbon and nitrogen levels. This research demonstrates termite-mediated processes can be initiated and maintained in degraded soil, thereby improving soil structure and key ecosystem functions. Termites may represent a valuable biological resource for promoting tropical soil restoration, through incorporating techniques that promote their activity into tropical soil rehabilitation management.     

Influence of leaf litter types on microbial functions and nutrient status of soil: Ecological suitability of forest trees for afforestation in tropical laterite wastelands

The impact of forest tree leaf litters on microbial activity and nutrient status of red laterite soil was tested for the ecological suitability of Cassia siamea, Shorea robusta, Acacia auriculiformes and Dalbergia sissoo, which are typically used for afforestation of wastelands in eastern India. The objectives were to compare seasonal variation in soil enzyme activity in 30-years old afforested sites, and to study nutrient status and microbial biomass and function during short-term in-situ incubation of litter in decomposition pits. In afforested soils, enzyme activities significantly varied between litters and seasons. All enzyme activity except invertase dominated in the soils containing Dalbergia and Cassia litters compared to the others. The seasonal effect was enzyme-dependent, with amylase and cellulase reaching peaks during the rainy season but invertase activity showed a reverse trend with lowest values in rainy season, except in Acacia soil, and protease activity was lowest in the soil containing Cassia and Dalbergia during the rainy season. Dehydrogenase activity was negligible in the soils containing Shorea and Acacia, but remained high with respect to Dalbergia and Cassia during all seasons. The decomposition pit study showed significant increase of soil nutrients with respect to litter types and intervals, except with respect to electrical conductivity. Cassia and Dalbergia litters enabled notable increase of soil nutrients than Shorea and Acacia. The soil enzyme activity, in general, increased with duration of litter decay, but microbial biomass C (MBC) decreased over time except in Shorea. Therefore, the enzyme rates normalized to the MBC indicated inverse relations for all enzymes, except in the soil containing Shorea. A positive relationship existed between MBC and soil respiration in Cassia, Acacia and Dalbergia. Analysis of variance revealed main effects of litter types for increasing protease, MBC and CO₂ output, and a main effect of intervals for enhancing enzymes other than cellulase. Rates of soil respiration were greater in soils contain Cassia and Dalbergia, and showed significant differences between litters and between intervals. All enzymes were significantly correlated with electrical conductivity, organic carbon and available phosphorus contents, and all enzymes except invertase were correlated with nitrate concentrations. The acidic soil pH did not affect enzyme activities, and soil nutrients exerted only weak effect on MBC and respiration. Our study showed that leaf litters of Cassia and Dalbergia trees improved the nutrient status and microbial activity in soil more so than Shorea and Acacia litters, and therefore, afforestation using Cassia and Dalbergia trees may be particularly suitable for soil restoration in tropical laterite wastelands.     

土壤有机污染生物修复技术影响因素的研究进展

土壤有机污染的生物修复技术的论述很多,本文则从对影响这些技术实施的因素进行综合评述,例如污染物的性质、微生物自身特性等。     

基于土地生态要素分区的坝上生态用地生态服务价值分析

坝上地区是京津冀地区的重要生态屏障,也是京津冀的重要水源涵养地和生物多样性保护重要基地,对保障京津冀地区的生态安全和水资源供给有着不可替代的作用。本研究运用软件ARCGIS 10.2,将坝上地区的土壤类型与地貌类型两大主要土地生态要素进行叠加,划分典型类型区,并结合现行的土地利用分类系统和生态系统服务功能,构建生态用地分类体系,在此基础上,以粮食单产进行区位修订,采用当量因子法估算2015年坝上各类型分区内生态用地的生态系统服务价值,以期为坝上地区的生态用地格局规划与区域生态保护管理政策制定提供理论依据。结果表明:1)河北省坝上地区粮食单产大体趋势是自中部向两翼方向逐渐递增,高产区主要是东南部的褐土侵蚀剥蚀低山类型区和褐土侵蚀剥蚀中山类型区,产量高达5 000 kg×hm~(-2)以上;低产区则是主要位于西南的张北县栗钙土玄武岩台地类型区和尚义县粗骨土侵蚀剥蚀中山类型区,产量不足2 500 kg×hm~(-2)。2)河北省坝上生态用地类型以草地和林地为主,两者面积之和占总面积的73.95%。沼泽土侵蚀剥蚀中山类型区、沼泽土冲积风积高原类型区、灰色森林土侵蚀剥蚀中山类型区以及灰色森林土冲积风积高原类型区的生态用地面积占其类型区总面积的95%以上,而盐土湖积高原类型区的生态用地所占比例最小,仅占39.74%。3)2015年坝上生态服务总价值高达634.77亿元,其中坝上地区东部的棕壤侵蚀剥蚀中山类型区生态服务价值最大,主要由林地提供;位于西北部的盐土湖积高原类型区生态服务价值最小,基本为草地所提供。本研究表明,不同的土壤类型和地貌类型均影响着土地生产能力的大小,从而影响着该地区的生态系统服务价值大小。     

吡虫啉对土壤微生物碳转化的影响

[目的]了解吡虫啉对土壤微生物的影响以及可能对土壤生态环境造成的危害.[方法]比较了吡虫啉质量分数为0.27、1.35m(kg对农耕土中微生物碳转化的影响.[结果]试验初期土壤微生物碳转化因农药的加入而产生了波动,施用浓度越高,波动效果越明显,随着时间的推移,碳转化影响逐渐减弱,与对照组趋于一致,对土壤碳转化无长期影响.[结论]试验结果为吡虫啉在其他类型土壤中施用的安全性提供了参考.     

浦城县中稻施肥试验

在浦城县进行中稻氮磷钾3414田间试验,结果表明:在该地试验条件下中稻每667 m2推荐施肥量为N 12.6 kg、P2O54.2 kg、K2O 6.28 kg,可获得较高产量;同时介绍了中稻的施肥技术。