Soil Microbial Abundance Research Articles

Land Use, Landform, and Soil Management as Determinants of Soil Physicochemical Properties and Microbial Abundance of Lower Brahmaputra Valley, India

Due to the shifting course of the Brahmaputra River, the fluvial landforms of the Brahmaputra Valley of Assam, India, are prone to changes in landform and land use. For sustainable soil management under such conditions, it is crucial to have information about soil physicochemical and biological properties for different land uses. Therefore, the present study was conducted to investigate the soil physicochemical properties and soil microbial population across five major land uses under different landforms, such as paddy fields, banana systems, and arecanut cultivations in the alluvial plains; and rubber plantations and sal forests in the uplands, with varying slope gradients and soil depths (0–25 cm and 25–50 cm) in the lower Brahmaputra Valley. The results of the analysis of variance revealed that the effects of different landforms and land uses were found to be statistically significant on very labile soil organic carbon (VLSOC), available K, B, Fe, Mn, Zn, and Cu, and soil moisture content across two different soil depths. Paddy cultivated systems recorded the highest (1.23%) soil organic carbon (SOC), but these levels were statistically at par with other land use scenarios except for banana systems; whereas, forests and rubber plantations showed the highest VLSOC (0.38% and 0.34%, respectively,) and were significantly different from other land use scenarios. All soil microbial populations (bacteria, fungi, and actinomycetes) studied varied significantly in different land uses across varying soil depths. Perennial land uses under arecanut, rubber, and forest cultivations showed significantly higher microbial populations than paddy and banana systems. The principal component analysis (PCA) identified SOC, VLSOC, Cu, K, B, P, and the bacteria count as the major soil quality parameters of the study area. The results showed that landforms, land use, and management practices collectively affect soil properties. Therefore, soil management choices should take into consideration the landforms and land use for maintaining soil health and its sustainability.

Effect of dissolved organic matter (DOM) on greenhouse gas emissions in rice varieties

Rice paddy fields are important sources of atmospheric methane (CH4) and nitrous oxide (N2O). Dissolved organic matter (DOM) is one of the most reactive organic matter fractions in the soil. However, the relationships between greenhouse gas emissions and DOM properties associated with different rice varieties in paddy fields are unclear. Here, a two-year field experiment was conducted to investigate the relationships between DOM characteristics and microbial gene abundance on CH4 and N2O emissions in seven rice varieties. The dissolved organic carbon, dissolved sugar, and NH4-N and NO3-N contents were positively correlated with CH4 and N2O emissions, and dissolved phenol was negatively correlated with CH4 and N2O emissions. Fourier transform infrared (FTIR) and three-dimensional fluorescence (EEM) spectroscopy analysis further indicated that DOM includes more O-H and CO phenol and protein content, of which tryptophan-like and tyrosine-like protein materials were positively correlated with CH4 and N2O emissions. In addition, CH4 and N2O emissions were significantly correlated with microbial functional genes (mcrA, pmoA, AOA, AOB, nirS, and nosZ). The redundancy analysis indicated that dissolved organic carbon, dissolved sugar, NH4-N, NO3-N, and tyrosine-like and tryptophan-like proteins in the DOM were significantly correlated with soil microbial functional gene abundance, suggesting that DOM could regulate CH4 and N2O emissions by influencing microbial abundance. The rice variety with lower greenhouse gas emissions (YY 1540) had the highest yield. These results demonstrated that the differences in greenhouse gas emissions among different rice varieties were dependent on DOM properties and microbial abundance, providing a theoretical basis for mitigating greenhouse gas emissions in rice paddy fields.

Disentangling the impact of contrasting agricultural management practices on soil microbial communities – Importance of rare bacterial community members

Agriculture has a strong effect on soil microbial communities, but it is still unclear how different management practices drive their diversity and composition. To disentangle the effects of temporally contrasting crop management practices on soil microbial abundance and prokaryotic diversity, we analysed samples from a long-term agricultural field experiment, in which plant residues were exported (RE) or returned to soil, i.e., restituted (RR), over a period of 60 years. For 2.5 years, we followed a cropping sequence of maize, winter wheat and barley, in which, as an additional treatment, wheat cultivation was diversified once with pea intercropping. Based on soil-extracted DNA, abundances of bacteria, archaea and fungi were analysed by domain-specific qPCR and the diversity and composition of the prokaryotic community by 16S rRNA gene amplicon sequencing. The abundance of bacteria and fungi, but not for archaea, increased with the long-term restitution, but this effect was only detectable in spring due to their stabilized abundance during winter. The long-term effect of crop restitution on bacterial diversity became tangible when rare and dominant community members were differentiated, with higher sensitivity shown for the rare. In contrast, the cropping sequence equally affected members of both groups. The short-term effect of crop diversification by intercropping was much stronger in the C-depleted RE soils, than in RR soils where the C-loss was compensated, indicating that crop residue restitution increased the environmental resilience of soil microbial communities. Finally, we could confirm that rare bacterial community members, suspected to represent more oligotrophs and synergistic bacteria, formed stronger network structures to each other than the dominant, suspected to be more copiotrophic and competitive. Therefore, our results emphasize the importance to consider the response of rare microbial community members when evaluating long-term effects of agricultural management on the soil microbiome.

The impact of crop diversification, tillage and fertilization type on soil total microbial, fungal and bacterial abundance: A worldwide meta-analysis of agricultural sites

Microorganisms play a key role in nutrient cycling in agriculture and can contribute to improve soil quality and enhance crop production. Thus, there is a need to identify the most suitable management practices which foster increases in soil microbial biomass and diversity. A meta-analysis was performed to assess changes in microbial abundance in agricultural soils affected by: (i) management practices (tillage, fertilization and crop diversification); and (ii) environmental factors, including climate characteristics and soil properties. The scope of the meta-analysis was to evaluate whether microbial abundances are affected or not by organic fertilization or no fertilization, crop diversification (intercropping and crop rotations) and conservation tillage (reduced tillage/no-tillage) as an alternative to intensive conventional monocultures in agriculture. Only papers showing data on phospholipid fatty acids (PLFAs), providing indicators about soil microbial (total PLFA), fungal and bacterial biomass reached a critical mass to perform the meta-analysis. Therefore, soil microbial diversity could not be analyzed considering different management practices. Results showed that intercropping and crop rotations only significantly increased the abundance of fungi, with the corresponding increase in the fungal-to-bacterial ratio. Organic fertilization contributed to significant increases in bacterial and fungal abundance and total PLFA compared to mineral fertilization. Contrarily, the lack of fertilization negatively affected total PLFA, with no significant effect on bacterial and fungal abundances. Reduced tillage significantly increased total PLFA, fungal and bacterial abundances compared to conventional tillage, while no tillage had only a positive effect on fungi. Thus, as a general pattern, the adoption of sustainable management practices, mostly organic fertilization and reduced tillage, has overall positive effects on soil total microbial, fungal and bacterial abundance. These variables were not related to soil physicochemical properties and climatic factors, suggesting a positive global effect of sustainable management practices on soil microbial abundances. Thus, this study shows new insights by a meta-analysis of global studies about the effect of sustainable management practices on soil microbial abundances, needed for land-managers, policy-makers and farmers to select sustainable cropping systems that enhance microbial abundance.

Tillage and residue management affect growing-season soil respiration in paddy fields

Farmland soil respiration (SR) plays a pivotal role in affecting global carbon (C) cycling. To examine impacts of paddy management (including tillage and residue management) on growing-season SR, four long-term treatments were established: conventional tillage with residue mulching (CTM), conventional tillage with residue removal (CT), reduced tillage with residue mulching (RTM), and reduced tillage with residue removal (RT). All treatments lasted for six years starting on October 19th, 2014. Since the growing season is May to October, the measurements were performed from May 8th to September 30th, 2020. In-situ measurements were made of SR, and corresponding soil samples were collected and analyzed for soil texture, soil nutrient, soil organic carbon (SOC), C composition, and soil microbial abundance. Results showed that four treatments had a significant difference in terms of growing-season SR. The cumulative SRs of CT, CTM, RT, and RTM were 2.066, 2.502, 2.396, and 2.649 kg m-2, respectively. The observation was contrary to the conventional perspective that no-tillage with residue mulching leads to lower CO2 emissions. For soil microbial abundance, compared with CTM, RT, and RTM, CT had the lowest contents of total PLFA, bacteria, and fungi. In addition, CT had the lowest unstable C compositions, and the highest stable C compositions among all treatments. Redundancy analyses (RDA) indicated that cumulative SR increased with the increase of soil microbial abundance. Further, Pearson correlation analyses showed that cumulative SR had a positive correlation with unstable C characteristics and a negative correlation with stable C characteristics. The results suggested that CT is more conducive than the other three treatments in slowing the growing-season SR. This study provides novel insights regarding the impact of agricultural management on growing-season SR, which has practical significance for the management of agricultural lands in the context of carbon cycling.

The Impact of Drought Stress on Soil Microbial Community, Enzyme Activities and Plants

Nowadays, the most significant consequence of climate change is drought stress. Drought is one of the important, alarming, and hazardous abiotic stresses responsible for the alterations in soil environment affecting soil organisms, including microorganisms and plants. It alters the activity and functional composition of soil microorganisms that are responsible for crucial ecosystem functions and services. These stress conditions decrease microbial abundance, disturb microbial structure, decline microbial activity, including enzyme production (e.g., such as oxidoreductases, hydrolases, dehydrogenase, catalase, urease, phosphatases, β-glucosidase) and nutrient cycling, leading to a decrease in soil fertility followed by lower plant productivity and loss in economy. Interestingly, the negative effects of drought on soil can be minimized by adding organic substances such as compost, sewage slugs, or municipal solid waste that increases the activity of soil enzymes. Drought directly affects plant morphology, anatomy, physiology, and biochemistry. Its effect on plants can also be observed by changes at the transcriptomic and metabolomic levels. However, in plants, it can be mitigated by rhizosphere microbial communities, especially by plant growth-promoting bacteria (PGPB) and fungi (PGPF) that adapt their structural and functional compositions to water scarcity. This review was undertaken to discuss the impacts of drought stress on soil microbial community abundance, structure and activity, and plant growth and development, including the role of soil microorganisms in this process. Microbial activity in the soil environment was considered in terms of soil enzyme activities, pools, fluxes, and processes of terrestrial carbon (C) and nitrogen (N) cycles. A deep understanding of many aspects is necessary to explore the impacts of these extreme climate change events. We also focus on addressing the possible ways such as genome editing, molecular analysis (metagenomics, transcriptomics, and metabolomics) towards finding better solutions for mitigating drought effects and managing agricultural practices under harsh condition in a profitable manner.

Effects of multiple global change factors on soil microbial richness, diversity and functional gene abundances: A meta-analysis

Soil microbial richness, diversity, and functional gene abundance are crucial factors affecting belowground ecosystem functions; however, there is still a lack of systematic understanding of their responses to global change. Here, we conducted a worldwide meta-analysis using 1071 observation data concerning the effects of global change factors (GCFs), including warming (W), increased precipitation (PPT+), decreased precipitation (PPT-), elevated CO2 concentration (eCO2), and nitrogen deposition (N), to evaluate their individual, combined, and interactive effects on soil microbial properties across different groups and ecosystems. Across the dataset, eCO2 increased microbial richness and diversity by 40.5% and 4.6%, respectively; warming and N addition decreased the abundance of denitrification functional genes (nirS, nirK, and nozS); N addition had a greater impact on soil C-cycling functional genes than on N-cycling ones. Long-term precipitation change was conducive to the increase in soil microbial richness, and fungal richness change was more sensitive than bacterial richness, but the sensitivity of bacteria richness to N addition was positively correlated with experimental duration. Soil microbial richness, diversity, and functional gene abundances could be significantly affected by individual or multiple GCF changes, and their interactions are mainly additive. W×eCO2 on microbial diversity, and N×PPT+ and W×N on N-cycling functional gene abundance showed synergistic interactions. Based on the limitations of the collected data and the findings, we suggest designing experiments with multiple GCFs and long experimental durations and incorporating the effects and interactions of multiple drivers into ecosystem models to accurately predict future soil microbial properties and functions under future global changes.

自然增温对南亚热带森林土壤微生物群落与有机碳代谢功能基因的影响

基于海拔高度下降气温上升的关系，将模拟的生态系统（含植物和土壤）从高海拔整体移位至低海拔地区，实现自然增温的效果。通过对自然增温条件下土壤环境因子及其相关理化性质的动态监测，结合磷脂脂肪酸分析与宏基因组学方法，测定土壤微生物群落结构以及与土壤有机碳分解相关基因丰度，探究自然增温对鼎湖山南亚热带山地常绿阔叶林土壤有机碳代谢的影响及其微生物学机制。结果表明：（1）增温处理显著改变了0-10 cm土壤温度与湿度：2016-2018年间土壤温度显著上升2.48℃，湿度显著下降23.93%。（2）增温处理下，干季土壤有机碳含量与湿季土壤硝态氮含量显著降低，其他土壤理化因子无显著变化。（3）增温处理下，干季和湿季土壤微生物群落结构发生改变，且湿季变化显著。土壤湿度是影响干季和湿季土壤微生物群落结构变化的主要因子，解释了干季50.2%的变异度与湿季79.2%的变异度。（4）宏基因组结果表示：增温抑制了干季山地常绿阔叶林土壤有机碳代谢基因丰度，增强了湿季山地常绿阔叶林土壤有机碳代谢基因丰度。以上结果表明，增温通过改变土壤微生物生物量和群落结构以及有机碳代谢相关功能基因的丰度，最终影响南亚热带山地常绿阔叶林土壤有机碳代谢过程。;Global warming is one of the environmental problems that cannot be ignored in the world today, which has significant impacts on soil carbon dynamics and soil microorganisms. Soil microorganisms affect the soil nutrient cycling process and play a leading role in the net carbon balance of terrestrial ecosystems. Further exploration of microbial responses to climate warming is important for predicting the feedback and carbon budget of terrestrial ecosystems in warmer climates. In this study, soil organic carbon content and microorganisms were investigated in a natural warming experiment using a whole ecosystem transplanting approach. Plots of plants and soil in a subtropical mountain evergreen broadleaf forest at high altitude (600 m asl) were moved to low altitude (30 m asl) in Dinghu Mountain to experience natural warming treatment. Plots with similar plants and soil at the high altitude were used as the control. To explore the effect of natural warming on soil organic carbon metabolism and its microbiological mechanism, soil physical and chemical properties, soil organic carbon, and soil microbial community structure were measured for the control and warmed plots. Meta-genomic method was used for soil microbial community structure and abundance of genes involved in soil organic carbon decomposition. Results showed that:(1) warming treatment significantly changed soil temperature and moisture of the 0-10 cm soil layer. From 2016 to 2018, the soil temperature was significantly increased by 2.48℃, and the soil moisture was significantly decreased by 23.93% (relative change). (2) Warming treatment significantly reduced soil organic carbon content in the dry season and the soil nitrate nitrogen content in the wet season, while other soil physical and chemical factors had no significant changes under warming treatment. (3) Warming treatment changed the soil microbial community structure in both dry and wet seasons, and the change was significant in wet season. The results of principal component analysis showed that soil moisture was the main factor affecting the variation of soil microbial community structure in dry season and wet season, which explained the variation degree of 50.2% in dry season and 79.2% in wet season. (4) The metagenomic analysis showed that increasing temperature inhibited the abundance of soil organic carbon metabolism genes of mountain evergreen broadleaf forest in the dry season, and enhanced them in the wet season. Our results showed that although warming treatment did not significantly change soil microbial biomass in the subtropical mountain evergreen broadleaf forest, it reduced soil organic carbon by changing soil microbial community structure and abundance, and significantly affected soil organic carbon metabolic processes and ecosystem carbon cycling.

Impacts of increasing maize stalk retention amount on soil respiration and temperature sensitivity

Conservation tillage with maize stalk retention is an effective method to replenish soil nutrients. Nutrient availability plays a major role in the control of soil respiration (SR). However, it is not known how different degrees of maize stalk retention control SR and its temperature sensitivity (Q10). To investigate the effect of maize stalk retention amount on SR and Q10, four maize (Zea mays L.) stalk retention treatments, including (i) control treatment (CT) without maize stalk retention, (ii) standing maize stalk retention (SCR), (iii) partial maize stalk retention with ‘three-year cycle’ (TYR) and (iv) chopped maize stalk retention (CCR) was set up. In order to investigate the differences in soil nutrient, soil organic carbon (SOC) quality and soil microbial biomass among four treatments, soil analysis with 6 replicates was conducted. The experimental results showed that SR rates were 1.07, 0.88, 0.59 and 0.37 g/kg of dry soil, and the average Q10 was 1.535, 1.585, 1.62 and 1.725 for CT, SCR, TYR and CCR, respectively. Increasing maize stalk retention led to the reduction of soil microbial abundance and labile carbon compositions. Pearson correlation analysis showed that soil microbial abundance had a positive correlation with SR, while labile carbon fraction had a negative correlation with Q10. In short, increasing the amount of maize stalk retention decreases SR while increasing Q10 in northeast China. This research could provide a reference value for balancing carbon sequestration and carbon decomposition in farming practice. Keywords: stalk management, soil nutrient, carbon composition, microbial biomass, laboratory incubation DOI: 10.25165/j.ijabe.20221502.6411 Citation: Yuan H F, Wang G, Huang D Y, Glatzel S, Zhuang J, Jia H L. Impacts of increasing maize stalk retention amount on soil respiration and temperature sensitivity. Int J Agric & Biol Eng, 2022; 15(2): 135–141.

Microbial community diversity and enzyme activity varies in response to long-term fertilisation in a continuous potato (Solanum tuberosum L.) cropping system

Context The misuse of chemical fertilisers is still prevalent in potato cultivation. However, the large-scale application of manure is increasingly being accepted by growers to improve soil health. Aim To clarify what effect manure and chemical fertilisers have on the development of soil microbes in potato fields. Methods The status of soil microbial community abundance and structure were determined by analysing soil metagenomes, which were assessed by applying high through-put sequencing technology. The potato field received one of the following treatments for 9 years: manure (M); manure plus nitrogenous (N), phosphatic (P), and potassic (K) fertiliser (MNPK); NPK fertiliser; NP fertiliser; NK fertiliser; PK fertiliser; and no fertiliser. Key results The application of manure significantly increased soil organic matter, and this increase was one of the main factors in reducing bacterial Shannon and Heip indices and increasing the Simpson index. The MNPK treatment significantly reduced the relative abundance of α-Proteobacteria and β-Proteobacteria in the soil, which are essential microorganisms involved in nitrogen cycling. The M treatment significantly increased the abundance of Actinobacteria. Conclusions In summary, applying manure increases Actinobacteria’s abundance, and using MNPK fertilisers decreases the abundance of Proteobacteria, whereas chemical fertilisers are detrimental to soil fungal diversity. Implications Applying MNPK fertilisers has a complex effect on soil microorganisms. It is not simply a combination of the effects of manure and chemical fertilisers on microbes; the interaction mechanism of microbial succession needs to be further explored.

Understanding Arbuscular Mycorrhizal Colonization in Walnut Plantations: The Contribution of Cover Crops and Soil Microbial Communities

Soil microorganisms play a central role in biological soil functioning. One of the beneficial microbiota that has a symbiotic association with most of the plants is arbuscular mycorrhizal fungi (AMF). Nevertheless, little is known about the impact of cover crops—widely used in conservation agriculture or organic farming—on native mycorrhizal fungi. This study was conducted in Southern France, in 20-year-old walnut orchards, where faba bean (Vicia faba Roth) was intercropped. To find whether the native AM fungal community associated with walnut trees was influenced by cover crops and soil microbial communities, analyses of soil physicochemical and microbiological indicators were carried out with roots and soil samples collected from four modalities (walnut in conventional farming with and without cover crops, and walnut in organic farming with and without cover crops). Our results showed that the presence of cover crops mainly influenced the soil microbial abundance and activities in conventional plots. In contrast, cover crops stimulated AM fungal colonization of walnut roots in organic plots, reaching 35% and 54% for arbuscule abundance and mycorrhizal intensity, respectively. In conventional plots, ergosterol and mineral nitrogen contents were mainly correlated with mycorrhizal colonization, while only acid phosphatase activity in soil was positively correlated with mycorrhizal colonization in organic plots. The use of the faba bean showed the great role played by cover crops in the enhancement of walnut trees’ mycorrhizal colonization. Identification of the functional traits of AM fungi sensitive to walnut trees is required to inform decisions in specific agricultural practices.

Rhizosphere effects on soil extracellular enzymatic activity and microbial abundance during the low-temperature dormant season in a northern hardwood forest

Plant roots alter nutrient cycling, including nitrogen (N) and phosphorus (P) cycling, within the soil surrounding them (rhizosphere) by affecting microbes and enzyme activities. Recent studies have focused on nutrient uptake by plants in low-temperature seasons. This study aimed to reveal the nutrient dynamics in the rhizosphere during low-temperature seasons in a northern hardwood forest in Japan. For this purpose, the potential extracellular enzymatic activity, bacterial, fungal, and archaeal abundances, and soil chemical properties in the rhizosphere of canopy trees and understory vegetation and non-rhizosphere bulk soil were measured at the beginning of the dormant season (November), end of the dormant season (April and May), and middle of the growing season (August) in a northern hardwood forest in Japan. The abundance of fungi was 1.1–1.7 times higher in the rhizosphere than in non-rhizosphere bulk soil regardless of the season. The activity of enzymes involved in N- and P- cycles in the rhizospheres was also 1.4 to 4.0 and 1.3 to 1.9 times higher than that in bulk soil, respectively. The concentration of extractable organic N was 1.5–2.0 times higher in the rhizosphere than in the non-rhizosphere bulk soil at the beginning and end of the dormant season, respectively, but this trend was not observed in the middle of the growing season for organic N. Since the concentration of nutrients in the rhizosphere is determined by the balance between nutrient uptake by fine roots and root-induced acceleration of decomposition, our results suggest that plant roots would accelerate N and P cycles during the dormant season, even though the amount of nutrient uptake by plants was lower during the season.

Effect of Nitrogen Addition on Soil Microbial Functional Gene Abundance and Community Diversity in Permafrost Peatland.

Nitrogen is the limiting nutrient for plant growth in peatland ecosystems. Nitrogen addition significantly affects the plant biomass, diversity and community structure in peatlands. However, the response of belowground microbe to nitrogen addition in peatland ecosystems remains largely unknown. In this study, we performed long-term nitrogen addition experiments in a permafrost peatland in the northwest slope of the Great Xing’an Mountains. The four nitrogen addition treatments applied in this study were 0 g N·m−2·year−1 (CK), 6 g N·m−2·year−1 (N1), 12 g N·m−2·year−1 (N2), and 24 g N·m−2·year−1 (N3). Effects of nitrogen addition over a period of nine growing seasons on the soil microbial abundance and community diversity in permafrost peatland were analyzed. The results showed that the abundances of soil bacteria, fungi, archaea, nitrogen-cycling genes (nifH and b-amoA), and mcrA increased in N1, N2, and N3 treatments compared to CK. This indicated that nitrogen addition promoted microbial decomposition of soil organic matter, nitrogen fixation, ammonia oxidation, nitrification, and methane production. Moreover, nitrogen addition altered the microbial community composition. At the phylum level, the relative abundance of Proteobacteria increased significantly in the N2 treatment. However, the relative abundances of Actinobacteria and Verrucifera in the N2 treatment and Patescibacteria in the N1 treatment decreased significantly. The heatmap showed that the dominant order composition of soil bacteria in N1, N2, and N3 treatments and the CK treatment were different, and the dominant order composition of soil fungi in CK and N3 treatments were different. The N1 treatment showed a significant increase in the Ace and Chao indices of bacteria and Simpson index of fungi. The outcomes of this study suggest that nitrogen addition altered the soil microbial abundance, community structure, and diversity, affecting the soil microbial carbon and nitrogen cycling in permafrost peatland. The results are helpful to understand the microbial mediation on ecological processes in response to N addition.

Fire and post-fire management alters soil microbial abundance and activity: A case study in semi-arid shrubland soils

Soil microbial communities play a key role in ecological processes; however, the effects of fire, and post-fire management practices such as hydroseeding, on microbial abundance and activity are still poorly known. We sampled surface soil (0–10 cm) from unburned (UNB), burned and naturally regenerating (NAT), and burned but hydroseeded (HYD) chaparral stands on the campus of California State University San Marcos five years after fire. Soil was analyzed for microbial biomass carbon (C), bacterial taxonomic composition at the phylum level, and microbial activity (enzyme activity and nitrification) to test the hypothesis that fire and hydroseeding would significantly alter microbial abundance and activity. Total soil nitrogen (N) and C, microbial C, enzyme activity, and nitrification rate were significantly lower in burned stands than in the UNB stand; however, some of these patterns were affected by hydroseeding. Carbon inputs from hydroseeding, and associated changes in the composition of colonizing plant species, caused soil C and N and microbial C to be similar in the HYD and UNB stands. Relative abundances of bacterial taxa were similar for the UNB, HYD, and NAT stands, and there were no significant differences in taxonomic diversity between the stands. Activities of key C (β-glucosidase, peroxidase) and nutrient (N-acetylglucosaminidase (NAGase), phosphatase) cycling enzymes were significantly lower in burned stands, but hydroseeding did not affect their activities, and the declines in enzyme activity were due in part to declines in microbial biomass, soil C and N pools, and increases in pH. Our data suggest that fire and post-fire treatments alter soil microbial biomass and activity for years after fire, which will affect ecosystem C and N cycling and management of fire-prone semi-arid shrublands like chaparral.

Continuous monocropping highly affect the composition and diversity of microbial communities in peanut (Arachis hypogaea L.)

Continuous cropping systems are the leading cause of decreased soil biological environments in terms of unstable microbial population and diversity index. Nonetheless, their responses to consecutive peanut monocropping cycles have not been thoroughly investigated. In this study, the structure and abundance of microbial communities were characterized using pyrosequencing-based approach in peanut monocropping cycles for three consecutive years. The results showed that continuous peanut cultivation led to a substantial decrease in soil microbial abundance and diversity from initial cropping cycle (T1) to later cropping cycle (T3). Peanut rhizosphere soil had Actinobacteria, Protobacteria, and Gemmatimonadetes as the major bacterial phyla. Ascomycota, Basidiomycota were the major fungal phylum, while Crenarchaeota and Euryarchaeota were the most dominant phyla of archaea. Several bacterial, fungal and archaeal taxa were significantly changed in abundance under continuous peanut cultivation. Bacterial orders, Actinomycetales, Rhodospirillales and Sphingomonadales showed decreasing trends from T1>T2>T3. While, pathogenic fungi Phoma was increased and beneficial fungal taxa Glomeraceae decreased under continuous monocropping. Moreover, Archaeal order Nitrososphaerales observed less abundant in first two cycles (T1&T2), however, it increased in third cycle (T3), whereas, Thermoplasmata exhibit decreased trends throughout consecutive monocropping. Taken together, we have shown the taxonomic profiles of peanut rhizosphere communities that were affected by continuous peanut monocropping. The results obtained from this study pave ways towards a better understanding of the peanut rhizosphere soil microbial communities in response to continuous cropping cycles, which could be used as bioindicator to monitor soil quality, plant health and land management practices.

Dynamics of insects, microorganisms and muscle mRNA on pig carcasses and their significances in estimating PMI

The accurate estimate of the postmortem interval (PMI) is of vital significance in the investigation of homicide cases. In this study, three pig carcasses were placed in the field to study the pattern of insect succession, the change of microorganisms and the degradation of muscle tissue RNA during the decomposition process. The results showed that insects could quickly colonize the carcasses and still exist on them until the end of the experiment (41 days). Their development and succession patterns are useful indicators for PMI estimation. The diversity of rectal microorganisms decreased with the decomposition time. In different decomposition periods, significant differences in the rectal and soil microbial composition and relative abundance were found, which could be used to estimate the PMI with an accuracy of 3–4 days. The RNA of muscle tissue was found to have a time-dependent relationship with the PMI. Ppia and Gapdh showed a linear upward trend within 10 h after the death, followed by a gradual downward trend from 10 to 240 h. The expression of β-actin gene showed a gradual downward trend during 0–240 h. This is the first study in China to analyze the changes of insects, muscle RNA and microorganisms on pig carcasses in the same natural environment, which provide basic data for the PMI estimation.

Plant-microbe Interactions in Rhizospheric soil Treated with Different Quality Organic Residues

The objective of this research was to study plant-microbe interactions in rhizospheric soil treated with different quality organic residues in short-term incubation of the soil and subsequent planting of maize crop. The treatments combinations were, 1) untreated soil (control; CT), 2) groundnut stover (GN) with high nitrogen (N) but low lignin (L) and polyphenol (PP), 3) tamarind leaf and petiole litter (TM) with medium N, L and PP, 4) rice straw (RS) with low N, L and PP but high cellulose, 5) GN+TM, 6) GN+RS and 7) TM+RS. Single and mixed residue additions of GN and TM, both high and intermediate quality, resulted in higher soil microbial properties and nutrients than the application of RS as a low quality. Accordingly, the application of the former group increased microbial abundances (i.e., bacteria, archaea, and fungi), elevated the enzymes related to the decomposition of organic residue (i.e., invertase, protease, phenoloxidase and peroxidase activity), and enhanced soil nutrients and plant growth. The results indicated that the chemical compositions (N, L, and PP) of the organic residues amendment are key factors regulating soil microbial abundance and enzyme activity both in after incorporation and after planting. Moreover, bacterial and archaeal abundance, and microbial activities including soil respiration, invertase, protease, and peroxidase activity in the soil after planting higher than those in the soil before planting.

Organic amendments, deficit irrigation, and microbial communities impact extracellular polysaccharide content in agricultural soils

Soil extracellular polysaccharides (EPSac) can improve irrigation water productivity in agriculture by increasing soil aggregate stability and retaining water on and around plant roots. However, limited studies assay soil EPSac directly from field trials and to date no studies have examined the long-term confounding impacts of organic amendments and deficit irrigation on soil EPSac and the underlying microbial communities. We quantified soil aggregate stability, EPSac content, chemical properties, and microbial community compositions and abundances in separate field studies in turfgrass and tomato. Soil samples were collected 4–5 years after soil amendment with compost, biochar, their combination, or biosolids from plots that had received full and deficit irrigation regimens for 4 years. Amending the soil with compost, with or without biochar co-application, enhanced soil total carbon, aggregate stability, EPSac, and total soil microbial biomass and shifted microbial community structures, trends which were more pronounced under turfgrass than for tomato. In both sites deficit irrigation treatments had higher quantities of soil EPSac per unit of microbial biomass. Indicators of microbial physiological stress and ubiquitous classes of soil bacteria were associated with soil EPSac production. These results provide mechanistic understanding of organic amendment benefits in drought-impacted and deficit-irrigated agriculture.

SOIL CHARACTERISTICS AND MICROBIAL RESPONSES IN POST-MINE RECLAMATION AREAS IN A TYPICAL RESOURCE-BASED CITY, CHINA

Mining activities worldwide have resulted in soil nutrient loss, which pose risks to crop and environmental health. We investigated the effects of post-mine reclamation activities on soil physicochemical properties and microbial communities based on 16S rRNA sequencing and the further statistical analysis in the coal base in Peixian city, China. The results revealed significant differences in soil microbial relative abundance between reclamation and reference soils. Proteobacteria was the most abundant phyla in all seven mine sites regardless of reclamation age while considerable differences were found in microbial community structure at other levels among different sites. Notebly, Gammaproteobacteria, member of the phylum Proteobacteria, had relatively high abundance in most sites. Furthermore, Kendall’s tau-b correlation heatmap revealed that potentially toxic elements and other physicochemical properties play vital roles in microbial community composition.

Responses of soil microbial community composition and enzyme activities to long-term organic amendments in a continuous tobacco cropping system

Organic amendment may be an effective management practice for alleviating soil degradation in continuous cropping systems. However, few studies focus on the effects of long-term organic amendments on soil microbial community and microbial nutrient status in continuous tobacco fields. Here, an 11-year field experiment was conducted to investigate the effects of organic amendments on plant and soil physiochemical properties, microbial communities, ecoenzymatic stoichiometry, and glomalin-related soil protein (GRSP) accumulation in a continuous tobacco field. Five treatments were applied: CK (no fertilizer); CF (chemical fertilizer only); CFS (chemical fertilizer plus corn straw); CFO (chemical fertilizer plus oilseed residues); CFM (chemical fertilizer plus composted pig manure). Organic amendments increased soil microbial abundances. Application of organic fertilizers significantly reduced gram-positive to gram-negative bacterial ratios, but significantly increased fungi/bacteria ratios, probably because gram-negative bacteria and fungi are the dominant decomposers of increased available nutrients and recalcitrant materials, respectively. Organic amendments significantly enhanced soil enzyme activities, except for the difference in β-1,4-N-acetylglucosaminidase, Leucine aminopeptidase, and polyphenol oxidase (PPO) activities between the CF and CFO. The lowest soil organic carbon (SOC) content in CFS among organic amendments treatments was probably because the positive priming effects of straw and the highest peroxidase and PPO activities increased stable SOC mineralization rates due to the high C:N:P ratio of nutrients input. Microbial activities were limited by carbon, nitrogen, and phosphorus in CFS, while carbon and phosphorus were the limiting factors in CK, CF, CFO, and CFM. Relative to CF, CFO significantly enhanced microbial carbon and phosphorus limitation, whereas CFM significantly decreased microbial carbon limitation. CFM had the highest GRSP content among treatments. Our results demonstrated that combined application of composted pig manure and chemical fertilizers is a consistently effective measure for alleviating soil degradation in continuous tobacco fields.