Size Of Soil Microbial Community Research Articles

How Pharmaceutical Residues Occur, Behave, and Affect the Soil Environment.

Many pharmaceuticals (PhMs), compounds for the treatment or prevention of diseases in humans and animals, have been identified as pollutants of emerging concern (PECs) due to their wide environmental distribution and potential adverse impact on nontarget organisms and populations. They are often found at significant levels in soils due to the continuous release of effluent and sludge from wastewater treatment plants (WWTPs), the release of which occurs much faster than the removal of PhMs. Although they are generally present at low environmental concentrations, conventional wastewater treatment cannot successfully remove PhMs from influent streams or biosolids. In addition, the soil application of animal manure can result in the pollution of soil, surface water, and groundwater with PhMs through surface runoff and leaching. In arid and semiarid regions, irrigation with reclaimed wastewater and the soil application of biosolids are usual agricultural practices, resulting in the distribution of a wide number of PhMs in agricultural soils. The ability to accurately study the fate of PhMs in soils is critical for careful risk evaluation associated with wastewater reuse or biosolid return to the environment. The behavior and fate of PhMs in soils are determined by a number of processes, including adsorption/desorption (accumulation) to soil colloids, biotic (biodegradation) and abiotic (chemical and photochemical degradation) degradation, and transfer (movement) through the soil profile. The sorption/desorption of PhMs in soils is the main determinant of the amount of organic chemicals taken up by plant roots. The magnitude of this process depends on several factors, such as crop type, the physicochemical properties of the compound, environmental properties, and soil-plant characteristics. PhMs are assumed to be readily bioavailable in soil solutions for uptake by plants, and such solutions act as carriers to transport PhMs into plants. Determining microbial responses under exposure conditions can assist in elucidating the impact of PhMs on soil microbial activity and community size. For all of the above reasons, soil remediation is critical when soil pollutants threaten the environment.

Soil microbial activity profiles associated with organic compost fertilizers in an urban garden

AbstractBiological soil health is recognized as an important component of sustainable agriculture due to microbial biomineralization of nutrients. However, soil health can be difficult to assess consistently across urban agricultural systems due to diverse land use histories, soil heterogeneity, and lack of mechanistic links to agricultural management practices (e.g., recycled compost addition) and crop outcomes. In this study, we characterized soil microbial activity profiles in an urban agriculture system in Minnesota, USA, including microbial abundance, soil respiration, extracellular enzyme activity, and crop yield. Garden plots were fertilized with recycled organic compost (either manure or municipal) at high or low rates (ranging from 2.6 to 39 tons ha−1) targeted to crop N and P demands. Control plots received inorganic fertilizer or no fertilizer. We found that a high application rate of manure compost supported 6–10x higher basal respiration than municipal compost or inorganic fertilizer. Enzyme activity data demonstrated that soil microbial communities exhibited unique profiles of biochemical function that varied among fertilizers of different compositions. Microbial biochemical function predicted 50% of the variability in bell pepper (Capsicum annuum) yield, while soil microbial community size alone was a poor predictor of yield. Yield was highest in plots fertilized with municipal compost, outperforming inorganic fertilizer by threefold. High‐yield plots exhibited higher ratios of N to P enzyme activity compared to those with lower yield. Our findings demonstrate that “more is better” may not necessarily be true regarding soil microorganisms in biological soil health, and that measures of soil microbial biochemical function may be more important.

Elevated [CO2] enhances soil respiration and AMF abundance in a semiarid peanut agroecosystem

Rising atmospheric carbon dioxide [CO2] is a main climate change driver, and soil respiration is the most relevant contributor to ecosystem respiration. However, the soil microbiome and respiration responses of semiarid agroecosystems under elevated [CO2] (eCO2) conditions must be better understood. In particular, peanut agroecosystems host rhizobia and arbuscular mycorrhizal fungi (AMF) associations. Here, we sought to address the following questions: a) Does eCO2 conditions (650 µmol CO2 m−2 s−1, +250 µmol CO2 m−2 s−1, aCO2, control) alter soil chemical properties, soil microbial community size and composition, soil respiration, and β-Glucosidase activity? b) Are these responses influenced by transient water deficit periods? We conducted this study in a typical West Texas semiarid region (no well-watered treatment and drought was not an experimental factor) during two consecutive growing seasons (May-Oct). We induced the atmospheric CO2 enrichment using field-installed Canopy Evapotranspiration and Assimilation (CETA) systems. Our results showed no consistent significant changes in soil moisture, C: N ratio, total soil microbial EL-FAME abundance, or β-Glucosidase activity. However, we found that eCO2 increased soil temperature (+1 °C), AMF abundance (EL-FAME marker, +49%), and soil respiration (+82%). Our findings suggest that in future semiarid climates, peanut agroecosystems may experience: 1) increased soil metabolic activity as a result of increased autotrophic respiration; 2) increased AMF, which could further facilitate plant nutrient and water uptake; and 3) minimal change in the total size of the microbial community and C cycling enzyme activity during the growing season. In this manuscript, we demonstrated that soil respiration and temperature could be indicators of ecosystem productivity and climate feedback. Furthermore, soil organic carbon and AMF were good indicators of poor nutrient soil ecosystem transitional health across well-watered and water-deficit cycles. This study will increase our understanding of how these changes will affect soil ecology and climate feedback and will provide new insight into the peanut agroecosystem carbon source/sink functioning and productivity in future climates.

Impact of Downed Logs of Masson Pine (Pinus massoniana Lamb.) on Soil Microbial Community in a Climate Transitional Forest of Central China

Downed woody debris (DWD) can alter the chemical and biological properties of forest soils, and this process is affected by the degree of DWD decay. Our aim was to assess the effects of the entire decay process of DWD on the associated soil microbial communities. Here, we examined the differences in soil microbial community size and composition among five decay stages (DC Ⅰ–Ⅴ) of Masson pine (Pinus massoniana Lamb.) at two soil depths in a climate transitional forest and then linked these differences to soil chemical properties. The decay of DWD increased soil total PLFAs, and the complexity of soil microbial networks was highest in stage Ⅱ and then decreased with the decay stage. The relative abundance of fungi increased with the decay stage, while the relative abundance of gram-positive bacteria decreased with the decay stage. The microbial community composition at a soil depth of 0–10 cm was mainly driven by soil pH and organic C (SOC), and at a depth of 10–20 cm, soil pH was the primary determinant of microbial community composition. Our findings suggest that DWD decomposition reduces microbial physiological stress, promotes fungal growth, and stimulates microbial biomass, highlighting the positive impact of DWD on forest soils. Future research is needed to elucidate the universal effects of DWD decomposition on soil properties, especially focusing on the response of soil microbial processes to the decomposition time of DWD.

Responses of Soil Microbial Community Size, Respiration Rate and Functional Diversity to Invasive Plant Species Richness

Responses of Soil Microbial Community Size, Respiration Rate and Functional Diversity to Invasive Plant Species Richness

Plant-microbial linkages underpin carbon sequestration in contrasting mountain tundra vegetation types

Tundra ecosystems hold large stocks of soil organic matter (SOM), likely due to low temperatures limiting rates of microbial SOM decomposition more than those of SOM accumulation from plant primary productivity and microbial necromass inputs. Here we test the hypotheses that distinct tundra vegetation types and their carbon supply to characteristic rhizosphere microbes determine SOM cycling independent of temperature. In the subarctic Scandes, we used a three-way factorial design with paired heath and meadow vegetation at each of two elevations, and with each combination of vegetation type and elevation subjected during one growing season to either ambient light (i.e., ambient plant productivity), or 95% shading (i.e., reduced plant productivity). We assessed potential above- and belowground ecosystem linkages by uni- and multivariate analyses of variance, and structural equation modelling. We observed direct coupling between tundra vegetation type and microbial community composition and function, which underpinned the ecosystem's potential for SOM storage. Greater primary productivity at low elevation and ambient light supported higher microbial biomass and nitrogen immobilisation, with lower microbial mass-specific enzymatic activity and SOM humification. Congruently, larger SOM at lower elevation and in heath sustained fungal-dominated microbial communities, which were less substrate-limited, and invested less into enzymatic SOM mineralisation, owing to a greater carbon-use efficiency (CUE). Our results highlight the importance of tundra plant community characteristics (i.e., productivity and vegetation type), via their effects on soil microbial community size, structure and physiology, as essential drivers of SOM turnover. The here documented concerted patterns in above- and belowground ecosystem functioning is strongly supportive of using plant community characteristics as surrogates for assessing tundra carbon storage potential and its evolution under climate and vegetation changes.

Field application of pure polyethylene microplastic has no significant short-term effect on soil biological quality and function

Plastics are now widespread in the natural environment. Due to their size, microplastics (MPs; defined as particles <5 mm) in particular, have the potential to cause damage and harm to organisms and may lead to a potential loss of ecosystem services. Research has demonstrated the significant impact of MPs on aquatic systems; however, little is known about their effects on the terrestrial environment, particularly within agroecosystems, the cornerstone of global food production. Soil biology is highly responsive to environmental perturbation and change. Hereby, we investigated the effect of pure low-density polyethylene (LDPE) MP loading (0, 100, 1000, or 10000 kg ha−1) on soil and plant biological health in a field environment over a cropping season. Our results showed that MP loading had no significant effect (p > 0.05) on the soil bacterial community diversity (as measured by amplicon sequencing of bacterial 16S rRNA gene), the size and structure of the PLFA-derived soil microbial community, or the abundance and biomass of earthworms. In addition, metabolomic profiling revealed no dose-dependent effect of MP loading on soil biogenic amine concentrations. The growth and yield of wheat plants (Triticum aestivum L., cv. Mulika) were also unaffected by MP dose, even at extremely high (≥1000 kg ha−1) loading levels. Nitrogen (N) cycling gene abundance before and after N fertiliser application on the MP loaded experimental plots showed relatively little change, although further experimentation is suggested, with similar trends evident for soil nitrous oxide (N2O) flux. Overall, we illustrate that MPs themselves may not pose a significant problem in the short term (days to months), due to their recalcitrant nature. We also emphasise that most MPs in the environment are not pure or uncontaminated, containing additives (e.g. plasticisers, pigments and stabilisers) that are generally not chemically bound to the plastic polymer and may be prone to leaching into the soil matrix. Understanding the effect of additives on soil biology as well as the longer-term (years to decades) impact of MPs on soil biological and ecological health in the field environment is recommended.

Compost and legume management differently alter soil microbial abundance and soil carbon in semiarid pastures

AbstractEstablishment of improved perennial pasture systems for livestock production has been demonstrated to improve soil health in the semiarid Texas Southern High Plains (SHP). Use of waste products from other components of the animal production chain, such as applying composted manure from feedlot operations to grazed pastures, may provide an additional means of improving soil health and sustainability of these systems. However, few studies have examined the impact of composted animal manure on the changes in soil microbial communities, although they are important indicators of soil health. We investigated the effects of a one‐time composted cattle manure application at 3.36 Mg ha−1 on soil microbial community size and structure, soil organic C (SOC), total N (TN), and soil organic matter (SOM) up to 1.5 yr after application. We compared pastures consisting of either WW‐B. Dahl Old World bluestem grass [Bothriochloa bladhii (Retz.) S.T. Blake] alone or in mix with alfalfa (Medicago sativa L.). Results showed that compost application significantly increased SOC by about 4.4 g kg−1 soil within 1.5 yr after application. In N‐fertilized grass‐only pastures, compost addition increased microbial phospholipid fatty acid abundance, SOC, TN, and SOM, but no significant differences were observed between compost treatments in unfertilized pastures containing legumes. Our results show that even a one‐time compost addition at a relatively low rate can augment SOC in this semiarid pasture system after 1.5 yr, and that stimulation of soil microbial abundance and soil C and N from compost is more pronounced in fertilized grass‐only pastures compared with those with legume establishment.

Data on soil physicochemical properties and biodiversity from conventional, organic and organic mulch-based cropping systems.

The data presented here are related to the article entitled “Soil functions are affected by transition from conventional to organic mulch-based cropping system”[1]. Data were collected in 2016 in a processing tomato field located near Perugia, Italy. In details, data were collected in three differently managed processing tomato cropping systems: conventional integrated (INT); traditional organic with cover crops and conventional tillage (ORG); and organic coupled with conservation agriculture, with mulch-based cover crop and no-tillage (ORG+). We report data on the impact of each cropping system on crop biomass and yield, soil physicochemical properties, size and structure of soil microbial community, soil invertebrate biodiversity and habitat provision (predator-prey trophic interactions).

Soil functions are affected by transition from conventional to organic mulch-based cropping system

Soil ecosystem services depend on soil properties and their interactions, which are mostly influenced by soil use and management. The main objective of the present study was to evaluate, through a multidisciplinary approach, the effect of different cropping systems on food provisioning, soil chemical features, size and structure of soil microbial community, soil invertebrate biodiversity and habitat provision (trophic interactions). The systems were: conventional integrated (INT); traditional organic with cover crops and conventional tillage (ORG); and organic coupled with conservation agriculture (cover crop mulching and no-tillage, ORG+). During 2016, we conducted soil and field samplings and collected data relative to the crop yield, C and N content in the agroecosystem, chemical and microbial soil properties and soil invertebrate abundance and trophic interactions. The INT system showed the highest crop yield (similar to ORG and three-fold higher than ORG+). Nevertheless, the INT system showed the greatest amount of N lost with drainage water (six-fold higher than the other systems), the lowest soil total PLFA abundance (around two-fold lower than ORG and ORG+ in the Ap1 horizon of soil). Additionally, INT system was characterized by the lowest invertebrate biodiversity (e.g., two-fold and ten-fold lower than ORG and ORG+ respectively for ground-dwelling predator abundance). By contrast, the ORG+ system had the lowest crop yield, but it showed the highest soil total organic C concentration and microbial biomass in the Ap1 horizon, supported higher invertebrate biodiversity and a slightly wider prey-spectrum for ground beetle predators. The ORG system had an intermediate behaviour between INT and ORG+. The results of this study demonstrate that, despite the reduction of crop yield, the conversion from INT to ORG or ORG+ possibly enhances important soil functions like nutrient cycling and storage, biodiversity and habitat provisioning. However, management optimization for improving crop yield would be required to make ORG+ a viable system.

The microbial community size, structure, and process rates along natural gradients of soil salinity

Over 840 M ha of arable land is affected by salinization, and the area is predicted to increase due to global change. Assessments of the status of the microbial community in saline soils have frequently been based on microbial biomass estimates, which might not accurately reflect microbial process rates in soil. Moreover, assessments of how the relative importance of major decomposer groups bacteria and fungi are affected by salinity remain inconclusive. In this study we set out to assess the soil microbial community size, structure and process rates along two salinity gradients. To distinguish between the direct effects of high salinity and indirect effects resulting from reduced soil organic matter (OM) concentrations in saline soils we also assessed the gradients following plant litter amendments to compensate for differences in OM content between soils and isolate the effect of salinity. The research aims were to (i) investigate the microbial biomass responses to salinity as estimated based on both PLFA concentrations and qPCR measurements and to compare these responses to those of respiration and microbial growth, (ii) compare the responses of bacteria and fungi to increased salinity and (iii) assess the responses of these microbial variables to the alleviation of OM scarcity expected in saline soils. Microbial biomass estimates generally were less negatively affected by salinity than bacterial growth and respiration, and were not correlated to rates of microbial growth or respiration rates. While bacterial growth was strongly inhibited by salinity, fungal growth was similar in soils of all salinities, indicating a higher fungal tolerance to salinity. OM additions increased process rates in saline soils and alleviated some of the negative impact of salinity on respiration and growth. In conclusion, this study demonstrates differential responses of saprotrophic fungi and bacteria to increasing salinity and that bacteria are directly impacted by soil salinity while fungi are responding to the indirect effect by salinity related to reduced plant C input.

Access mats partially mitigate direct traffic impacts on soil microbial communities in temperate grasslands

Significant areas of the mixedgrass prairie (MGP) in Alberta have experienced heavy equipment traffic due to industrial infrastructure development, which may change edaphic conditions that influence soil microbial communities. Direct wheeled traffic effects may be alleviated by using access mats that spread traffic impacts over a larger area; however, no scientific assessments of access mat efficacy have been conducted on soil microbial responses. Our objectives were to assess soil properties and the diversity, community structure, and size of soil microbial communities, as impacted by wheeled traffic occurring with and without access mat use on grassland. Two representative sites with differing soil texture (sandy versus loamy) were selected from a set of MGP sites established at the University of Alberta Mattheis Research Ranch in SE Alberta, Canada. Treatments at each site included non-disturbed vegetation controls, areas affected by direct traffic, and grassland with access mats placed for 12 weeks with traffic applied. Soil was sampled in July 2015 (immediately after access mat/traffic treatments ended) and in 2016 (12 months after access mat/traffic treatments) from both sites. Soil DNA was extracted and used to target N-cycling genes via qPCR and for next-generation sequencing (Illumina Miseq) of bacterial, archaeal, and fungal communities. Direct wheeled traffic without access matting increased the size of the N2O-reducing community in the sandy soil and conversely deceased the size of this community in the loamy soil. Non-metric multidimensional scaling, perMANOVA, and indicator species analyses indicated a large effect of traffic without access mat use on fungal community structure, as well as distinct bacterial and fungal indicator OTUs associated with disturbed soils compared to control soils. Fungal community structure remained affected by traffic impacts 12 months later, highlighting the extended impacts of traffic on fungal communities. Access matting mitigated some of the impacts direct traffic had on fungal community structure, but in the loamy site increased soil N and decreased the size of the N2O-reducing bacterial community. The latter indicates that ecosystem functioning of these grasslands may not only be impacted by direct wheeled traffic but also by using matting as a mitigation technique.

Soil organic matter and microbial community responses to semiarid croplands and grasslands management

Livestock integration in cropping systems and conversion of croplands into grazing lands has been increasingly considered to improve agricultural sustainability, yet their roles in soil health and resilience are not clear due to the complex interactions of soil, climate, and agricultural systems. A study was conducted to evaluate the effects of cropland and grassland management systems on soil organic carbon (SOC) and total nitrogen (N) across the soil profile (0–20, 20–40, 40–60, and 60–80 cm) and microbial community size, structure, and activity in the soil surface (0–20 cm) as indicators of soil health. Cropland systems compared included conventional-tilled winter-grazed cropland (CTGC) and no-tilled and strip-tilled croplands (NTC and STC) without livestock grazing. Grassland systems included grazed grassland (GGL) and ungrazed grassland (UGL). Grassland soils accumulated 18% greater SOC and 13% greater total N than cropland soils in the 0–80 cm profile. Microbial community size (sum of ester-linked fatty acid methyl esters [El-FAME]) in the surface 0–20 cm was 90% greater, and enzyme activities were 131–155% greater in the grasslands than in the croplands. Within grasslands, cattle (Bos taurus) grazing increased microbial community size by approximately 42%, which was mainly due to greater fatty acid methyl esters (FAME) markers for gram-positive bacteria (51%) and Actinobacteria (73%). Grazed cropland had 95% more β‑glucosaminidase activity than ungrazed croplands. This study suggests light grazing and grassland restoration has potential to improve soil health and resilience through an increase in SOC and microbial community responses related to nutrient cycling.

Warming but Not Nitrogen Addition Alters the Linear Relationship Between Microbial Respiration and Biomass.

Soil contains a large amount of organic matter, which constitutes the largest terrestrial carbon pool. Heterotrophic or microbial respiration (Rh) that results from microbial decomposition of soil organic carbon (SOC) constitutes a substantial proportion of soil C efflux. Whether soil microbial biomass is of primary importance in controlling Rh remains under debate, and the question of whether the microbial biomass-decomposition relationship changes with warming and nitrogen (N) deposition has rarely been assessed. We conducted an incubation experiment to test the relationship between Rh and the size of soil microbial communities in two layers of soil collected from a natural subtropical forest and to examine whether the relationship was affected by changes in temperature and by added N in different forms. The results showed that regardless of the added N species, the N load did not significantly affect Rh or the size of the soil microbial communities. These results could be due to a long-term N-rich soil condition that acclimates soil microbial communities to resist N inputs into the studied forest; however, warming may significantly stimulate SOC decomposition, reducing soil microbial biomass under high temperatures. A significant linear soil microbial biomass-decomposition relationship was observed in our study, with the coefficients of determination ranging from 54 to 70%. Temperature rather than N additions significantly modified the linear relationship between soil microbial biomass and respiration. These results suggest that warming could impose a more substantial impact than N addition on the relationship between soil microbial biomass and SOC decomposition.

Bacterial community composition under long-term reduced tillage and no till management.

The purpose of this study was to assess impacts of long-term reduced tillage and no till management on bacterial communities in agricultural field soils. Samples from surface soils were collected from field plots maintained under reduced tillage and no till conditions for 14years. No till soils had significantly higher microbial biomass, as well as β-glucosidase activity, which is linked to organic matter breakdown. Sequencing of the 16S rRNA gene revealed most variability in bacterial community composition was observed in low abundance community members. Diversity estimates (Chao 1, ACE, and Shannon indices) were lower in no till soils, and several bacterial taxa linked to organic matter breakdown were significantly higher in no till compared to tilled soils. Long-term no till management can significantly enhance the size of soil microbial communities while negatively impacting bacterial diversity, through the lack of soil disturbance and breakdown of crop residues left on soil surfaces. This study provides insights into how no till management can influence the microbial community's contribution to soil health and suggests that long-term no till field plots may benefit from occasional tillage.

Soil microbial community size and composition changes along a tanglehead (Heteropogon contortus) gradient in a semiarid region

Invasive plants are a serious concern throughout many rangelands in North America because of their detrimental effects on vegetation community composition, diversity and wildlife habitat. Growing evidence shows that invasive plants affect ecosystem processes such as energy and nutrient cycling and soil microbial associations. Tanglehead (Heteropogon contortus [L.] P. Beauv. ex Roem and Schult.) is a C4, perennial caespitose grass that is rapidly increasing throughout the Coastal Sand Plain in southern Texas. In a field study, we examined the response of soil microbial community size and structure over a 3-year period (2013–2015) along a tanglehead invasion gradient represented by the natives-without-tanglehead plant communities (<15% tanglehead), natives-with-tanglehead mixtures (15–70% tanglehead), and tanglehead-dominated (>70% tanglehead) plant communities. Soil microbial size [microbial biomass carbon (MBC), nitrogen (MBN), and total fatty acid methyl esters (FAME)] differed between natives-without-tanglehead and tanglehead-dominated sites in 2013 and 2015 (dry years). MBC averaged ~200 mg kg−1 soil in natives-without-tanglehead sites but <70 mg kg−1 soil in invaded sites, and total FAME averaged 36 and 41 nmol g−1 soil in native-without-tanglehead and invaded sites, respectively, in 2013 and 44 and 55 nmol g−1 in 2015. Invaded sites had higher saprophytic fungi:bacteria ratios than sites with <15% tanglehead (0.64 vs. 0.53) over all 3 years. We conducted a separate inoculation experiment where tanglehead was planted in native soils that lacked tanglehead to investigate effects of tanglehead inoculation on soil microbial community dynamics; introduction of tanglehead to native soils did not change microbial community structure, size, or relative abundance of key microbial FAME indicators over the course of 18 months. Field study results revealed different soil microbial communities associated with tanglehead, but at what point these communities change during invasion is not clear, and how these effects are related to overall habitat degradation associated with this invasive plant requires further study.

Soil Health and Yields on Non‐Sodic Soils Amended with Flue Gas Desulfurization Gypsum

Core Ideas Flue gas desulfurization gypsum did not affect crop yield or grain. Flue gas desulfurization gypsum did not improve soil physical properties. Soil sulfate levels increased at both sites, electrical conductivity increased at one site. There were no effects on soil microbial community size or structure. Flue gas desulfurization gypsum (FGDG) is approved for use in Kansas as a fertilizer and as a soil amendment. Gypsum is an effective product used in remediation of sodic soils. Marketing has promoted the general use of FGDG as a means of improving soil health, and this has prompted extension questions regarding whether or not FGDG would be beneficial for soil health when applied to non‐sodic soils. Two 3‐year studies were conducted in Kansas from 2013 to 2015 on long‐term no‐tilled fields; one was done with small research plots, and the other site was an on‐farm collaboration with a producer and an agricultural retailer. No crop yield effects were observed for any of the site years. Soil SO4–S consistently increased with increasing FGDG at both sites. Electrical conductivity (EC) and Mehlich‐3 P values were affected by the treatments on the small‐plot study location, but not at the larger field study. The small‐plot study location received less‐than‐average precipitation every year of the project, while the larger on‐farm study location received above‐average precipitation two out of 3 years, likely explaining the differences in EC at the two sites. There were no treatment differences at either site for the selected soil physical and biological indicators of soil health. Based on the results of this project, FGDG did not improve the health of two no‐tilled, non‐irrigated, non‐sodic soils during a 3‐year period, other than to supply SO4–S.

Intensive Tillage Converting Grassland to Cropland Immediately Reduces Soil Microbial Community Size and Organic Carbon

Core Ideas Decreased CRP funding is resulting in US grassland being tilled. Intensive tillage of grassland rapidly decreases soil health indicators. One month after tilling grassland surface microbial biomass (0–10 cm) decreased 52%. Soil organic C decreased by 20% in the top 30 cm after one growing season. Alternative grassland conversion methods are needed to sustain soil health. Intensive tillage of grassland has negative long‐term effects on soil health, but little data exist to understand how quickly this decline occurs. We sampled a commercial field in the semiarid Southern Plains of the United States before and after tilling grassland and compared the results to adjacent row crop and perennial grass fields. Within the first month of tillage, we detected losses of 52% of microbial biomass C (505 to 241 mg kg−1 soil), 33% of organic C (11.6 to 7.78 g kg−1 soil), 30% of total N (1.09 to 0.760 g kg−1 soil) and 64 to 70% of β‐glucosidase and phosphodiesterase activities. The rapid decreases in these soil health indicators demonstrate that tillage management decisions are crucial for maintaining soil health if perennial grasses are converted to row cropping.

Grazing intensity influence soil microbial communities and their implications for soil respiration

Abstract Soil microorganisms regulate carbon (C) transfer from terrestrial sources to the atmosphere, therefore playing a pivotal role in soil C dynamics. Worldwide, grazing is one of the most prevalent grassland management strategies, yet the effects of grazing on soil microbial community size and soil respiration (SR) are still active areas of debate. We conducted a meta-analysis of 71 publications to synthesize the responses of soil microbial community size and SR to grazing. Our results showed that grazing significantly decreased soil total microbial, bacterial and fungal community size by 11.74, 8.85 and 11.45%, respectively. However, this effect were differed when the studies were grouped by the grazing intensity. Briefly, light and moderate grazing intensity had no effect on soil microbial, bacterial and fungal community size, but heavy grazing intensity significantly reduced soil’s total microbial, bacterial and fungal community size by 14.79, 16.48 and 28.12%, respectively. The responses of microbial community size to grazing were positively correlated with those of SR both under moderate and heavy grazing intensity. Our findings indicate that soil microbial community size could be an important underlying mechanism involved in determining soil C dynamics under grazing. Hence better understanding of the responses of soil microbial community size would greatly contribute to our understanding of soil C dynamics. Lastly, our results underscore the importance of factoring grazing intensity into consideration to further improve the model’s projection of soil C dynamics.

Changes in Soil Microbial Community and Its Effect on Carbon Sequestration Following Afforestation on the Loess Plateau, China.

Afforestation plays an important role in soil protection and ecological restoration. The objective of this study is to understand the effect of afforestation on soil carbon and soil microbial communities in the Loess Plateau of China. We measured two chemically-separated carbon fractions (i.e., humic acid, HA, and fulvic acid, FA) and soil microbial communities within shrublands (18-year-old Caragana korshinskii Kom (shrubland I) and 28-year-old Caragana korshinskii Kom (shrubland II)) and cropland. The size and structure of the soil microbial community was measured by phospholipid fatty acid (PLFA) analysis. The analysis of C-fractions indicated that at a depth of 0–20 cm, FA-C concentration in shrubland I and shrubland II were 1.7 times that of cropland, while HA-C had similar values across all three sites. Total PLFAs, G+ (Gram positive) bacterial, G− (Gram negative) bacterial, and actinobacterial PLFAs were highest in shrubland II, followed by shrubland I and finally cropland. Fungal PLFAs were significantly higher in shrubland II compared to the other sites. Additionally, we found a high degree of synergy between main microbial groups (apart from fungi) with FA-C. We concluded that planting C. korshinskii in abandoned cropland could alter the size and structure of soil microbial community, with these changes being closely related to carbon sequestration and humus formation.