Microbial Community Size Research Articles

Winter cover crops and no till management enhance enzyme activities in soybean field soils

Elimination of tillage and planting winter cover crops are two conservation practices employed in agricultural row crop production to promote the accumulation of plant residues on the soil surface, improve soil structure, reduce erosion, and decrease losses of excess nutrients in runoff. The purpose of the current study was to assess the effects of no till management and two different cover crop species, Elbon rye (Secale cereal L.) and Crimson clover (Trifolium incarnatum L.), on microbial aspects of soil health, namely microbial biomass and enzyme activities (phosphatase, β-glucosidase, N-acetylglucosaminidase, and fluorescein diacetate [FDA] hydrolysis) in order to determine potential impacts on the size and nutrient cycling capabilities of microbial communities in lower Mississippi Delta soybean (Glycine max L.) field soils over a three-year period. Microbial biomass in surface soil was elevated under no till and both cover crop treatments. Soil enzyme activities associated with organic matter breakdown were increased by cover crop more than tillage, while phosphatase and FDA hydrolysis were increased by both. The higher activities due to cover crop input appear to be the result of an enlarged microbial community as well as increased substrate availability. While these enhanced soil biological traits did not translate into higher soybean yields, longer evaluation periods may be necessary to fully appreciate the benefits of improved soil health in crop production systems.

Microbial community size is a potential predictor of nematode functional group in limed grasslands

Agronomic management practices can impose structural change within soil biotic communities that may negatively impact soil processes including function and biodiversity. Thus, optimizing sustainable crop production that confers minimal impacts on the structure and function of soil biota is an imperative to deliver healthy, functional and resilient production systems. Liming is a management intervention to mitigate soil acidification with a generally positive effect on crop biomass. The application of lime changes soil pH, a known driver of microbial community composition, but it is unknown whether pH derived shifts in bacterial communities result in altered nematode communities. In this study we used qPCR, next generation sequencing and nematode directed T-RFLP to characterise microbial and nematode communities in a liming field trial with a control and three liming applications to incrementally increase pH by 0.5, 0.75 and 1 pH unit. We demonstrate over a 14-month experimental period an interaction between microbial and nematode communities in managed grasslands. Liming had a limited effect on nematode and microbial community structures. However bacterial and archaeal abundance as measured by 16S rRNA gene copy number was found to be a potential predictor of nematode functional group, based on recognized trophic strategies, with increased abundance of omnivorous and predatory nematodes, that are known to prey upon bacterivorous nematodes, with a concomitant increase of 16S rRNA gene copy number. Thus, indirectly suggesting suppression of the bacterial and archaeal community in the presence of bacterivorous nematodes. Where populations of bacterivorous nematodes were highest the relative abundance of both predatory and omnivorous nematodes was lowest. Thus, this study demonstrates clear connectivity between soil microbial and nematode communities in grassland soil.

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.

Liming reduces N2O emissions from Mediterranean soil after-rewetting and affects the size, structure and transcription of microbial communities

In Mediterranean regions, the accumulation of nitrogenous substrates in soil during summer fallow period has been linked to pulses of N2O emissions upon soil rewetting. Although the mechanisms of N2O emission after soil rewetting have been previously studied, potential mitigation of agronomic practices on N2O pulses is still poorly understood. We studied the N2O emissions after rewetting of degraded soils managed by no-tillage (NT) and conventional tillage (CT), both with or without lime application under laboratory conditions. The soil was rewetted to 50 and 100% of field capacity (FC) and the N2O fluxes, size, structure and gene transcription of the microbial communities involved in the N2O emissions were evaluated. Liming reduced the cumulative N2O emission by more than 70 and 65% respect to the unamended soil after soil rewetting to 50% and 100% of FC, respectively, whereas no significant effect of tillage on N2O emission was observed. Liming strongly influenced the size and structure of ammonia oxidizing bacteria (AOB) and denitrifier communities, increased the transcription of the nirK after soil rewetting, while transcription of genes encoding nitrification enzymes was undetectable. Tillage slightly affected the nitrifier and denitrifier communities, with CT increasing the size of nosZ community. The results indicated that the N2O pulse after soil rewetting was caused by denitrification rather than nitrification. In addition, the increase of nirK transcription suggested that the mitigation of N2O emissions observed in limed soils was due to changes in the denitrification process, possibly with a higher or more efficient reduction of N2O to N2. This study showed the potentials of NT and liming management to mitigate the N2O emission from degraded Mediterranean soils after soil rewetting due to changes in the efficiency of the denitrification process. Our results also showed the usefulness of coupling determinations of gas emission, microbial community structure and gene transcription to clarify the underlying mechanisms of N2O emissions from soil.

Soil biochemical properties and bacteria community in a repeatedly fumigated-incubated soil

The regulatory gate hypothesis considers that soil organic C mineralization is a two-step process, where stable C is firstly transformed abiotically and is only then a microbially available substrate. The mechanisms involved in the abiotic conversion of non-microbially available to available soil organic C remain largely unknown. We conducted a perfusion experiment using a repeated fumigated-incubated soil and the corresponding fresh soil. We found that repeated fumigation-incubation significantly decreased soil microbial ATP to 0.22 nmol g−1 soil, 10% of that in the fresh soil, and significantly destroyed microbial composition and diversity. However, it had little influence on the soil CO2-C evolution rate after the flush of fumigant-killed dead biomass (8 μg CO2-C g−1 soil day−1) or dissolved organic C (DOC) concentration (about 7 μg C g−1 soil) and composition during long-term perfusion. We conclude that soil CO2 evolution rate and DOC generation were not regulated by the size or composition of the soil microbial communities. This is in support of the regulatory gate hypothesis. We suggest that abiotic processes in soil organic C mineralization need to be considered more and studied further.

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.

Metagenomic and chemical characterization of soil cobalamin production

Cobalamin (vitamin B12) is an essential enzyme cofactor for most branches of life. Despite the potential importance of this cofactor for soil microbial communities, the producers and consumers of cobalamin in terrestrial environments are still unknown. Here we provide the first metagenome-based assessment of soil cobalamin-producing bacteria and archaea, quantifying and classifying genes encoding proteins for cobalamin biosynthesis, transport, remodeling, and dependency in 155 soil metagenomes with profile hidden Markov models. We also measured several forms of cobalamin (CN-, Me-, OH-, Ado-B12) and the cobalamin lower ligand (5,6-dimethylbenzimidazole; DMB) in 40 diverse soil samples. Metagenomic analysis revealed that less than 10% of soil bacteria and archaea encode the genetic potential for de novo synthesis of this important enzyme cofactor. Predominant soil cobalamin producers were associated with the Proteobacteria, Actinobacteria, Firmicutes, Nitrospirae, and Thaumarchaeota. In contrast, a much larger proportion of abundant soil genera lacked cobalamin synthesis genes and instead were associated with gene sequences encoding cobalamin transport and cobalamin-dependent enzymes. The enrichment of DMB and corresponding DMB synthesis genes, relative to corrin ring synthesis genes, suggests an important role for cobalamin remodelers in terrestrial habitats. Together, our results indicate that microbial cobalamin production and repair serve as keystone functions that are significantly correlated with microbial community size, diversity, and biogeochemistry of terrestrial ecosystems.

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.

Sources and selection of snow-specific microbial communities in a Greenlandic sea ice snow cover

Sea ice and its snow cover are critical for global processes including climate regulation and biogeochemical cycles. Despite an increase in studies focused on snow microorganisms, the ecology of snow inhabitants remains unclear. In this study, we investigated sources and selection of a snowpack-specific microbial community by comparing metagenomes from samples collected in a Greenlandic fjord within a vertical profile including atmosphere, snowpack with four distinct layers of snow, sea ice brine and seawater. Microbial communities in all snow layers derived from mixed sources, both marine and terrestrial, and were more similar to atmospheric communities than to sea ice or seawater communities. The surface snow metagenomes were characterized by the occurrence of genes involved in photochemical stress resistance, primary production and metabolism of diverse carbon sources. The basal saline snow layer that was in direct contact with the sea ice surface harbored a higher abundance of cells than the overlying snow layers, with a predominance of Alteromonadales and a higher relative abundance of marine representatives. However, the overall taxonomic structure of the saline layer was more similar to that of other snow layers and the atmosphere than to underlying sea ice and seawater. The expulsion of relatively nutrient-rich sea ice brine into basal snow might have stimulated the growth of copiotrophic psychro- and halotolerant snow members. Our study indicates that the size, composition and function of snowpack microbial communities over sea ice were influenced primarily by atmospheric deposition and inflow of sea ice brine and that they form a snow-specific assemblage reflecting the particular environmental conditions of the snowpack habitat.

Forest organic matter removal leads to long-term reductions in bacterial and fungal abundance

Intensive organic matter removal (OMR) associated with forest harvest has been shown to significantly affect soil physical, chemical, and biological properties; however, the influence on microbial abundance has been neglected, especially at depth and over time. We used quantitative PCR to assess the long-term impact of two different intensities of OMR, soil depth, seasonality, and their interactions on bacterial and fungal abundances 18 years post-harvest, relative to an unharvested control. Both bacterial and fungal community sizes were significantly reduced by intensive OMR, and these effects were largest in surface soil (0–10 and 10–30 cm), and largest in summer and spring. The response ratios for bacteria and fungi were not statistically different, indicating that both taxonomic groups were susceptible to long-term changes in soil properties induced by intensive OMR. Furthermore, we found that root biomass was significantly correlated to bacterial and fungal abundance in unharvested, low-intensity harvest, and high-intensity harvest stands throughout time and across soil depths, suggesting that the input of organic matter through root exudation and turnover are key to controlling microbial community size. These reductions in bacterial and fungal community sizes suggest that microbial community functions related to biogeochemical processes may be altered for decades post-harvest, with potential implications for forest productivity and ecosystem function during subsequent rotations.

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.

Quantitative responses of potential nitrification and denitrification rates to the size of microbial communities in rice paddy soils

Nitrification and denitrification are important to nitrogen balance in agricultural ecosystems. However, the molecular drivers and limiting steps for these microbial processes in rice paddy soils are not well understood. Here, we assessed soil properties and abundances of functional genes affiliated with nitrification (amoA and nxrA), denitrification (nirS, nirK and nosZ), nitrate reduction (narG and napA) processes, and measured potential nitrification and denitrification rates (PNRs and PDRs) at 15 sites in Xiamen, China. The soil properties imposed indirect impacts on the potential rates by mediating the relative abundances of microbial communities. No significant relationships between the size of microbial communities and the potential rates were observed. Instead, we found the variables that best explained the variations in the PNRs and PDRs were AOB/nirS and (nirK + nirS)/nosZ, respectively. The PNRs were mainly limited by the relative strength of two steps, namely bacterial ammonium oxidation and nitrite into nitric oxide reduction, whereas the PDRs were mainly limited by the relative strength of the second and last denitrification steps. These results indicated that the dynamics of microbial communities based on the relative gene abundances are valuable in integrating fluctuations in soil physicochemical properties and are indictive of potential rates in paddy soils. Results of this study contribute to our quantitative understanding of the relative importance of soil physicochemical and biological factors in driving microbial potential in paddy soils.

Responses of microbial tolerance to heavy metals along a century-old metal ore pollution gradient in a subarctic birch forest

Heavy metals are some of the most persistent and potent anthropogenic environmental contaminants. Although heavy metals may compromise microbial communities and soil fertility, it is challenging to causally link microbial responses to heavy metals due to various confounding factors, including correlated soil physicochemistry or nutrient availability. A solution is to investigate whether tolerance to the pollutant has been induced, called Pollution Induced Community Tolerance (PICT). In this study, we investigated soil microbial responses to a century-old gradient of metal ore pollution in an otherwise pristine subarctic birch forest generated by a railway source of iron ore transportation. To do this, we determined microbial biomass, growth, and respiration rates, and bacterial tolerance to Zn and Cu in replicated distance transects (1 m–4 km) perpendicular to the railway. Microbial biomass, growth and respiration rates were stable across the pollution gradient. The microbial community structure could be distinguished between sampled distances, but most of the variation was explained by soil pH differences, and it did not align with distance from the railroad pollution source. Bacterial tolerance to Zn and Cu started from background levels at 4 km distance from the pollution source, and remained at background levels for Cu throughout the gradient. Yet, bacterial tolerance to Zn increased 10-fold 100 m from the railway source. Our results show that the microbial community structure, size and performance remained unaffected by the metal ore exposure, suggesting no impact on ecosystem functioning.

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.

How Well Do Restored Intertidal Oyster Reefs Support Key Biogeochemical Properties in a Coastal Lagoon?

The restoration of dead/degraded oyster reefs is increasingly pursued worldwide to reestablish harvestable populations or renew ecosystem services. Evidence suggests that oysters can improve water quality, but less is known about the role of associated benthic sediments in promoting biogeochemical processes, such as nutrient cycling and burial. There is also limited understanding of if, or how long postrestoration, a site functions like a natural reef. This study investigated key biogeochemical properties (e.g., physiochemical properties, nutrient pools, microbial community size and activity) in the sediments of dead reefs; 1-, 4-, and 7-year-old restored reefs; and natural reference reefs of the eastern oyster, Crassostrea virginica, in Mosquito Lagoon (FL, USA). Results indicated that most of the measured biogeochemical properties (dissolved organic carbon (C), NH4 +, total C, total nitrogen (N), and the activity of major extracellular enzymes involved in C, N, and phosphorus (P) cycling) increased significantly by 1-year postrestoration, relative to dead reefs, and then remained fairly constant as the reefs continued to age. Few differences were observed in biogeochemical properties between restored reefs of any age (1 to 7 years) and natural reference reefs. Variability among reefs of the same treatment category was often correlated with differences in the number of live oysters, reef thickness, and/or the availability of C and N in the sediments. Overall, this study demonstrates the role of live intertidal oyster reefs as biogeochemical hot spots for nutrient cycling and burial and the rapidity (within 1 year) with which biogeochemical properties can be reestablished following successful restoration.