Differences In Soil Microbial Communities Research Articles

Reduced moisture caused by short-term grazing prohibition results in a significant decrease of fungi abundance

The grassland ecosystem is an integral component of the global ecosystem. However, the changes in soil and soil microbial communities during the transition from natural grazing to grazing prohibition period in the Stipa Krylovii steppe, along with the driving factors behind the differences in soil microbial communities, remain unclear. In this study, soil characteristics and the fungal community diversity were measured and assessed. The results indicated that during the initial period of grazing prohibition, the dominant fungal species remained consistent, yet there were notable changes in their abundance and the physicochemical properties of the soil. Under natural grazing, a significant inverse relationship was observed between fungal abundance and pH. Conversely, a positive association was found between fungal diversity and volumetric water content (VWC), along with a highly significant positive correlation between fungal abundance, fungal diversity, and soil organic matter (SOM). In the initial period of grazing prohibition, fungal abundance exhibited a noteworthy positive association with SOM, VWC, and soil temperature (ST). Similarly, fungal diversity displayed a significant positive correlation with SOM and ST. Fungal abundance appeared to be more influenced by soil factors compared to fungal diversity, with VWC identified as the most crucial element impacting factor on fungal abundance.

Seedling performance in a dioecious tree species is similar near female and male conspecific adults despite differences in colonization by arbuscular mycorrhizal fungi

Plant–soil feedbacks (PSFs) are a key driver of species diversity and composition in plant communities worldwide; however, the factors that may cause feedbacks to vary within species are rarely examined. In dioecious species, the strength of feedbacks may differ near female plants that produce seed versus near male plants (which do not) because repeated inputs of seeds and high seedling densities near females may cause accumulation of host‐specific soil microbes that influence seedling performance. To test whether conspecific seedling performance is reduced near seed‐producing female trees relative to male or heterospecific trees, we conducted shadehouse and field experiments with a dioecious tropical tree species, Virola surinamensis (Myristicaceae), on Barro Colorado Island, Panama. The shadehouse experiment isolated the effect of soil microbial communities on seedling growth and allowed us to quantify colonization by mutualistic arbuscular mycorrhizal (AM) fungi, while the field experiment allowed us to assess seedling survival and growth in the presence of nearby conspecific adults and seedlings. In both experiments, seedling performance was similar between seedlings grown in the soil microbial communities and field environments underneath female conspecific, male conspecific, and heterospecific trees. However, contrary to expectation, seedling colonization by AM fungi was higher in male conspecific soil microbial communities than in female or heterospecific soil microbial communities at the end of the shadehouse experiment. Together, our experiments show that while differences among female and male plants in dioecious species may influence the association of conspecific seedlings with AM fungi in their soils, this variation does not necessarily translate directly to differences in seedling performance, at least over the time frame of our experiments. Studies of additional dioecious species are needed to help determine differences in soil microbial communities beneath male and female plants and to assess the role of seed input versus adult root systems in driving PSFs.

Enhanced soil function and health by soybean root microbial communities during in situ remediation of Cd-contaminated soil with the application of soil amendments.

The interactions between soil microbiomes at various trophic levels are essential for restoring soil functions. Legumes are considered as "pioneer crops" in degraded or contaminated soils because they can fix nitrogen through symbiotic relationships with rhizobacteria, which promotes soil fertility. However, little is known about the abilities of legumes to contribute to the health of soil contaminated with cadmium (Cd). In this research, we applied a soil amendment (commercial Mg-Ca-Si conditioner, CMC) at two rates (1,500 and 3,000 kg/ha) in a Cd-contaminated soybean field. Bulk and rhizosphere soil samples were collected to assess the amendment-induced effects on four microbial lineages (bacteria, fungi, arbuscular mycorrhizal fungi [AMF], and nematodes) and their functions including Cd stabilization, nutrient cycling, and pathogen control. Compared with the control, both CMC application rates increased the pH and reduced labile Cd fraction in the bulk and rhizosphere soils. Although the total Cd concentrations in the soil were similar, the Cd accumulation in the grains was significantly reduced in treatments of soil amendments. It was observed that the application of CMC can significantly reduce the AMF diversity but increased the diversity of the other three communities. Moreover, the biodiversity within keystone modules (identified by co-occurrence network analysis) played key roles in driving soil multifunctionality. Specifically, key beneficial groups in module 2 such as Aggregicoccus (bacteria), Sordariomycetes (fungi), Glomus (AMF), and Bursaphelenchus (nematode) were strongly associated with soil multifunctionality. By co-culturing bacterial suspensions with the soybean root rot pathogen Fusarium solani in the in vitro assays, we experimentally validated that the application of CMC promoted the suppression of soil bacterial community on pathogens by inhibiting the mycelium growth and spore germination. Also, the bacterial community was more resistant to Cd stress in soils receiving CMC amendment. Our findings provide valuable theoretical references for enhancing soil functions and health via applying a soil amendment (CMC) during Cd-contaminated soil remediation. IMPORTANCE Restoration of microbiome-driven soil functions and health is of great importance during Cd-contaminated soil remediation via soil amendment. Soybean and its symbiotic mutualism can provide abundant nitrogen and phosphorus to relieve the nutrient deficiency of Cd-contaminated soil. This study provides a novel perspective on the potential role of applying a soil amendment (CMC) in enhancing the functions and health of Cd-contaminated soils. Our results showed the distinct differences in soil microbial community responding to amendment-induced changes in edaphic properties. The biodiversity within keystone modules had major contributions to the maintenance of the soil's multifunctionality and health. Additionally, a higher CMC application rate showed more beneficial effects. Collectively, our results enhance our understanding about the effects of applying CMC, together with soybean rotation, to enhance and maintain soil functions and health during the field Cd stabilization process.

Differences in Soil Microbial Communities between Healthy and Diseased Lycium barbarum cv. Ningqi-5 Plants with Root Rot.

For a long time, the development of the Lycium barbarum industry has been seriously restricted by root rot disease. In general, the occurrence of plant root rot is considered to be closely related to the composition and diversity of the soil microbial community. It is critical to understand the relationship between the occurrence of root rot in L. barbarum and the soil microbial composition. In this study, samples of the rhizosphere, rhizoplane, and root zone were collected from diseased and healthy plants. The V3-V4 region of bacterial 16S rDNA and the fungal ITS1 fragment of the collected samples were sequenced using Illumina MiSeq high-throughput sequencing technology. The sequencing results were first quality controlled and then aligned with the relevant databases for annotation and analysis. The richness of fungal communities in the rhizoplane and root zone of the healthy plants was significantly higher than that of the diseased plants (p < 0.05), and the community evenness and diversity of all the rhizoplane samples were significantly different from those of the rhizosphere and root zone. The richness of the bacterial communities in the rhizosphere and root zone of healthy plants was significantly greater than those of diseased plants (p < 0.05). The community composition of the rhizoplane was quite different from the other parts. The abundance of Fusarium in the rhizoplane and rhizosphere soil of diseased plants was higher than that in the corresponding parts of healthy plants. The abundances of Mortierella and Ilyonectria in the three parts of the healthy plants were correspondingly higher than those in the three parts of the diseased plants, and Plectosphaerella was the most abundant in the rhizoplane of diseased plants. There was little difference in the composition of the dominant bacteria at the phylum and genus levels between healthy plants and diseased plants, but the abundances of these dominant bacteria were different between healthy and diseased plants. Functional prediction showed that the bacterial community had the largest proportion of functional abundance belonging to metabolism. The functional abundances of the diseased plants, such as metabolism and genetic information processing, were lower than those of the healthy plants. The fungal community function prediction showed that the Animal Pathogen-Endophyte-Lichen Parasite-Plant Pathogen-Soil Saprotroph-Wood Saprotroph group had the largest functional abundance, and the corresponding fungi were Fusarium. In this study, we mainly discussed the differences in the soil microbial communities and their functions between the healthy and diseased L. barbarum cv. Ningqi-5, and predicted the functional composition of the microbial community, which is of great significance to understanding the root rot of L. barbarum.

Differences in soil microbial communities with successional stage depend on vegetation coverage and soil substrates in alpine desert shrublands

In semiarid ecosystems, changes in plant communities are promoted under shrub canopies during restoration, but the link between shrub community restoration dynamics and changes in soil microbe communities is still unclear. We characterized the community structure and plant interactions of soil microbes by combining different methodological approaches (including high-throughput sequencing of the 16S rRNA gene and ITS gene, analysis of phospholipid fatty acids (PLFAs) and chloroform fumigation) and the key driving factors along a successional gradient of Sophora moorcroftiana shrub community in the middle reaches of the Yarlung Zangbo River. Soil microbial biomass carbon (MBC) and nitrogen (MBN), total PLFAs, and alpha diversity increased significantly as the successional stage advanced, and MBC and MBN were positively correlated with the carbon and nitrogen contents in the soil. Mantel test showed that successional stage-induced changes in soil microbial beta diversity were mainly associated with shrub coverage and soil physicochemical properties. The relative abundances of bacterial PLFAs, particularly those of gram-negative bacteria, such as Bacteroidetes, Alphaproteobacteria and Betaproteobacteria, significantly decreased with succession; the opposite was true for Acidobacteria, Planctomycetes, Gemmatimonadetes Deltaproteobacteria and Gammaproteobacteria. However, the proportion of fungi did not significantly differ among the four successional stages; the dominant phyla were Ascomycota and Basidiomycota. We suggest that shrubs directly shape soil microbial communities or indirectly affect such communities by altering soil substrates. Our findings advance the current understanding of sand-stabilizing plant–soil interactions during natural restoration and the reversal of desertification in stressful desert ecosystems.

Morel Production Associated with Soil Nitrogen-Fixing and Nitrifying Microorganisms.

True morels (Morchella, Pezizales) cultivated in soil are subject to complex influences from soil microbial communities. To explore the characteristics of soil microbial communities on morel cultivation, and evaluate whether these microbes are related to morel production, we collected 23 soil samples from four counties in Sichuan and Yunnan Provinces, China. Based on ITS and 16S rDNA amplicon sequencing, the alpha diversity analysis indicated that the biodiversity of morel cultivation soil showed a downward trend compared with the bare soil. The results also showed that there were no significant differences in soil microbial communities between OC (bare soil) and OO (after one-year suspension of sowing). This means that, after about one year of stopping sowing, the component and structure of soil that once cultivated morel would be restored. In co-occurrence networks, some noteworthy bacterial microbes involved in nitrogen fixation and nitrification have been identified in soils with high morel yields, such as Arthrobacter, Bradyhizobium, Devosia, Pseudarthrobacter, Pseudolabrys, and Nitrospira. In contrast, in soils with low or no morel yield, some pathogenic fungi accounted for a high proportion, including Gibberella, Microidium, Penicillium, Sarocladium, Streptomyces, and Trichoderma. This study provided valuable information for the isolation and culturing of some beneficial microbes for morel cultivation in further study and, potentially, to harness the power of the microbiome to improve morel production and health.

Salt tolerance of halotolerant bacteria from coastal soils and sediments near saltern field of Hainan Island, China.

Understanding the salt tolerance of microbial communities may help to elucidate the effects of salt concentration and other environmental factors on soil biodiversity. Here, high-throughput sequencing of 16S rDNA and ITS was combined to investigate the distribution and salt tolerance of microbial communities in coastal soils and sediments near the Yinggehai saltern field of Hainan Island, China. The microbial communities in the soils and sediments of the land zone (YGHLS), the intertidal zone (YGHIS), and the inshore zone (YGHWS) were compared. PCoA of weighted and unweighted UniFrac distance revealed obvious differences in soil microbial community among different samples. ANOSIM analysis could clearly separate the three samples from each other. Three halotolerant bacteria, including Halomonas, Halobacillus and Wallemia, were found in the samples, which accounted for 0.0335 ± 0.0586%, 0.0241 ± 0.0304%, and 0.0308 ± 0.0445% of the total microbial community, respectively. The relative abundance of Trk system potassium uptake protein, Kdp operon response regulator, and Na+/H+ antiporter in the samples exceeded 0.09%, 0.06%, and 0.02%, respectively, indicating that the Trk system plays a major role in the salt tolerance of halotolerant bacteria in Yinggehai coastal soils and sediments.

Plant legacies and soil microbial community dynamics control soil respiration

Through litter and root inputs, plants modulate soil properties and the soil microbial communities around them. In turn, these changes in soil properties and microbial community composition can impact plant performance (i.e., plant-soil feedbacks). Many studies have focused on how plant-soil feedbacks affect plant performance and successional patterns, but studies on the impact of plant-soil feedbacks on ecosystem processes are rare. Our research focused on the potential of species-specific plant-soil feedbacks to affect rates of soil organic matter (SOM) decomposition. We conducted a “home vs. away” plant-soil feedback greenhouse experiment using two C3 grass species (Bromus inermis and Pascopyrum smithii) grown in C4 tallgrass prairie soil. We used a closed-circuit CO2 trapping method and isotopic analysis to differentiate between root-derived and SOM-derived CO2 production. Contrary to our predictions, plant-soil feedbacks on plant biomass were independent of the effects of plant-soil interactions on SOM-derived CO2 production, but we did detect a significant legacy of conditioning by B. inermis on subsequent total belowground respiration (i.e., total belowground respiration was higher in soils originally conditioned by B. inermis regardless of which plant species was currently growing in those soils). We attribute these results to the differential effects of these plant species on soil chemistry and soil microbes during the original conditioning phase. This is supported by the observation that differences in soil chemistry and bacterial community composition persisted in soils conditioned by different plant species throughout the entire experiment. Together these results suggest that plant-soil history is important for soil respiration and that differences in soil microbial communities induced by conditioning with different plant species may have lasting effects on ecosystem processes.

Plantations of Cinnamomum camphora (Linn) Presl with Distinct Soil Bacterial Communities Mitigate Soil Acidity within Polluted Locations in Southwest China

Although the underlying mechanisms remain unknown, soils from different forest types exhibit distinct acidification-buffering capacities. We investigated soil properties and bacterial communities across five plantation types and different soil horizons in a severely acid-polluted site in Southwest China and evaluated the potential mechanisms driving differences in community structure. Soils collected from pure stands of Pinus massoniana Lamb.or Schima superba Gardn. et Champ. or mixed stands of these species showed the lowest soil pH and greater abundances of acid-producing and acidophilic taxa (Halanaerobiales and Rhodospirillales). Soils from pure stands of Cinnamomum camphora (Linn) Presl, or a mixture of C. camphora and P. massoniana, yielded the greatest concentrations of exchangeable calcium (Ca) and magnesium (Mg) and greater soil pH. Increased relative abundances of beneficial taxa may have contributed to soil aggregate formation (e.g., Bradyrhizobium canariense and Terracidiphilus sp.) and heightened environmental stress resistance (e.g., Gaiellales). Fewer acid-producing and acidophilic taxa found in soils associated with C. camphora suggest that planting C. camphora may help soils recover from acidification, while planting S. superba may not be as beneficial. Our findings illustrate how differences in soil microbial communities may impact soil-acidification-buffering capacity across different forest types, which have important implications for understanding environmental functions within the context of microbial diversity.

Soil aggregate–associated mercury (Hg) and organic carbon distribution and microbial community characteristics under typical farmland–use types

In order to get insight into the distribution characteristics of mercury (Hg) and organic carbon in soil aggregates, and the diversity and composition of soil microbial community under different farmland–use types (soil form three adjacent cultivation systems, i.e., corn, vegetable, and rice fields, named as CFS, VFS, and RFS), a field investigation close to Wanshan Hg mining area was conducted. Results indicated that soil total Hg (0–20 cm) presented in decreasing order of RFS (5.27 mg kg−1) > VFS (4.32 mg kg−1) > CFS (2.21 mg kg−1), implying soils from rice field with higher ability of Hg accumulation. Soil aggregate–associated Hg and organic carbon enriched with the decrease of particle size under all farmland–use types, with the maximum at microaggregates (<0.053 mm). Due to the mass ratio of soil aggregates fraction, soil aggregate–associated Hg and organic carbon mainly distributed in >2 mm particles for RFS, whereas 0.25–2 mm particles for CFS and VFS. Furthermore, 16S rRNA results revealed the obvious differences in RFS and dry land soils (CFS and VFS), such as the observed species and unique OUTs, Shannon index, relative abundance at phylum and genus, which implied the diversity and composition of soil microbial community were greatly affected by farmland–use types. Spearman correlation and RDA results suggested farmland–use types, pH and total Hg were main drives for differences in soil microbial community. These findings provide evidence that farmland–use type is an important factor that affects soil total Hg accumulation, soil aggregate–associated Hg and organic carbon distribution, as well as the indigenous microbial community profiles.

Biogeographic Changes in Forest Soil Microbial Communities of Offshore Islands—A Case Study of Remote Islands in Taiwan

Biogeographic separation has been an important cause of faunal and floral distribution; however, little is known about the differences in soil microbial communities across islands. In this study, we determined the structure of soil microbial communities by analyzing phospholipid fatty acid (PLFA) profiles and comparing enzymatic activities as well as soil physio-chemical properties across five subtropical granite-derived and two tropical volcanic (andesite-derived) islands in Taiwan. Among these islands, soil organic matter, pH, urease, and PLFA biomass were higher in the tropical andesite-derived than subtropical granite-derived islands. Principal component analysis of PLFAs separated these islands into three groups. The activities of soil enzymes such as phosphatase, β-glucosidase, and β-glucosaminidase were positively correlated with soil organic matter and total nitrogen. Redundancy analysis of microbial communities and environmental factors showed that soil parent materials and the climatic difference are critical factors affecting soil organic matter and pH, and consequently the microbial community structure.

Differences in soil microbial communities and enzyme activity due to the application of bioslurry under cultivation

Soil micro-organisms influence soil ecosystem processes and properties. Their influence can be modified by cultivation practices, which affect their interaction with cultivated plants as well as soil physical and chemical properties. The study investigated differences in soil microbial activities between cultivated maize fields with a bioslurry application and non-cultivated land. Bioslurry crust and soil samples were collected from two farms located in the Free State province of South Africa. For soil microbial analysis, which included functional diversity and soil microbial enzymatic activity, soil samples were collected from the maize fields where bioslurry was applied and outside where no bioslurry was applied, as a reference. Liquid bioslurry and bioslurry sediment were scooped separately from digesters on the same farms for nutrient analysis. Community substrate utilisation profiles were assessed using Biolog EcoPlatesTM to determine functional diversity. Soil microbial enzymatic activities were assayed by measuring β-glucosidase, alkaline phosphatase, acid phosphatase and urease activities in the soil. The bioslurry crust had the highest nutrient content in comparison to bioslurry and bioslurry sediment. Principal component analysis showed differences in carbon source utilisation profiles between the different samples. Soil microbial populations present in the bioslurry crust and soil supplied with bioslurry were more similar, compared to those present in the untreated soil. The bioslurry crust sample demonstrated the highest overall enzyme activities. The study showed that the bioslurry and bioslurry crust could be used as organic soil amendments, with positive effects on soil health and fertility, contributing towards sustainability of the environment and ultimately to food security.

Highly connected taxa located in the microbial network are prevalent in the rhizosphere soil of healthy plant

The microbial community in the rhizosphere soil highly affects plant health and vice versa. However, the differences in soil microbial communities associated with different pathogenic statuses in the same field and their causes have not been comprehensively investigated. Here, we deciphered the dissimilarities in the rhizosphere soils of lisianthus (Eustoma grandiflorum) with different pathogenic statuses in a field under uniform management strategies at multiple scales. The rhizosphere soils of diseased plants harbored higher bacterial abundances and diversities compared to that of healthy plants. The relative abundances of three keystone operational taxonomic units (OTUs) and cumulative relative abundance of members in the central module (the largest module) of microbial network significantly decreased by 51.1%, 49.4%, 47.6%, and 42.0% in the rhizosphere soil of infected plants and by 64.3%, 58.8%, 63.4%, and 61.8% in that of dying plants, while the relative abundances of Flavobacteriales, Sphingobacteriales, and Xanthomonadales significantly increased to 4.89-, 1.88-, and 1.44-fold in the rhizosphere soil of infected plants and to 2.89-, 1.55-, and 1.66-fold in that of dying plants, respectively compared with that of healthy plants. Some human disease-related pathways and fluorescein diacetate hydrolysis were more prevalent in the rhizosphere soils of diseased plants. Stochastic processes contributed more than 50.6% and 86.4% to the assembly of different bacterial and fungal communities in these soils, and plants further shaped the bacterial communities, compared to fungal communities, probably by actively recruiting some potential suppressive agents in their rhizosphere when attacked by the pathogen. Overall, here, we firstly reported that the keystone taxa and members in the central module were enriched in the rhizosphere soil of healthy plants, which might be a potential indicator for the soil supporting plant health.

Microbial community analysis of apple rhizosphere around Bohai Gulf

Bohai Gulf is the main area for apple tree cultivation in China. Consecutive replanting significantly affects the yield and quality of apple trees in this area. Microecological imbalance in apple trees’ rhizospheres caused by variation in the soil microbial community is considered the primary cause of apple replant disease (ARD). This study analysed the microbial communities of the rhizospheres of perennial apple trees (PAT) and apple tree saplings under replanting (ATS) around Bohai Gulf using high-throughput sequencing. The results revealed increased populations of typical pathogenic fungi Verticillium and bacteria Xanthomonadaceae, and decreased populations of beneficial bacterial populations Pseudomonas and Bacillus with replanting, suggesting that competition between pathogens and beneficial microbes varies according to the ratio of pathogens to beneficial microbes in rhizosphere soil under the replanting system. Meanwhile, replanting was accompanied by an increase in the antagonistic bacteria Arthrobacter and fungus Chaetomium, suggesting that increased numbers of pathogens can lead to more instances of antagonism. Redundancy analysis (RDA) revealed site position and the main soil properties (pH, organic matter, available N, available K, available P, and moisture) affected the microbial community composition. It found clear differences in soil microbial communities and demonstrated a better understanding of the causes for ARD.

Soil microbial community composition and its driving factors in alpine grasslands along a mountain elevational gradient

Understanding the vertical distribution patterns of soil microbial community and its driving factors in alpine grasslands in the humid regions of the Tibet Plateau might be of great significance for predicting the soil microbial community of this type of vegetation in response to environmental change. Using phospholipid fatty acids (PLFA), we investigated soil microbial community composition along an elevational gradient (3094 similar to 4131 m above sea level) on Mount Yajiageng, and we explored the impact of plant functional groups and soil chemistry on the soil microbial community. Except for Arbuscular Mycorrhizal fungi (AM fungi) biomarker 18:2 omega 6,9 increasing significantly, other biomarkers did not show a consistent trend with the elevational gradient. Microbial biomass quantified by total PLFAs did not show the elevational trend and had mean values ranging from 1.64 to 4.09 mu mol per g organic carbon (OC), which had the maximum value at the highest site. Bacterial PLFAs exhibited a similar trend with total PLFAs, and its mean values ranged from 0.82 to 1.81 mu mol (g OC)(-1). The bacterial to fungal biomass ratios had the minimum value at the highest site, which might be related to temperature and soil total nitrogen (TN). The ratios of Gram-negative to Gram-positive bacteria had a significantly negative correlation with soil TN and had the maximum value at the highest site. Leguminous plant coverage and soil TN explained 58% of the total variation in the soil microbial community and could achieve the same interpretation as the whole model. Other factors may influence the soil microbial community through interaction with leguminous plant coverage and soil TN. Soil chemistry and plant functional group composition in substantial amounts explained different parts of the variation within the soil microbial community, and the interaction between them had no impact on the soil microbial community maybe because long-term grazing greatly reduces litter. In sum, although there were obvious differences in soil microbial communities along the elevation gradient, there were no clear elevational trends found in general. Plant functional groups and soil chemistry respectively affect the different aspects of soil microbial community. Leguminous plant coverage and soil TN had important effects in shaping soil microbial community.

Litter decomposition, residue chemistry and microbial community structure under two subtropical forest plantations: A reciprocal litter transplant study

Litter decomposition is a key process for ecosystem fertility and carbon (C) balance, key uncertainties remain about how this fundamental process is affected by microbial community composition. Evidence is growing that plant litter generally decays fastest at the site from which it was derived, owing to the presence of specialized microbial communities that can decompose specific types of litter. The objectives were to determine the impact of sites on litter decomposition and to examine the relationships among microbial community composition, litter chemistry, and decomposition rates of coniferous Cunninghamia lanceolata litter of higher lignin content and broadleaved Mytilaria laosensis litter of lower lignin content at different stages of decomposition under plantations of the respective species. The study was conducted for 16 months using a randomized split-plot design experiment with four replications of all combinations of treatments, the treatments being litter type and site (plantation species). The results showed that decomposition rates were the same for all combinations of amendments and sites, meaning that both sites had microbial communities equally capable or adapted to decompose plant substrates it had not previously encountered, despite marked differences in soil microbial communities between sites and the chemistry of the two litter types. Initial M. laosensis litter was of lower lignin content and C:N ratio and decomposed faster in the first 8 months than C. lanceolata litter under either M. laosensis or C. lanceolata forest. Litter decomposition was significantly slower in the environment from which it was derived between month 8 and month 16. This could be attributed to the exceptionally poor decomposition of M. laosensis litter which was significantly higher lingnin content at month 8 under M. laosensis than under C. lanceolata due to the impact of site on preferential degradation of litter C. Decomposers under C. lanceolata forest were more efficient in degrading alkyl C and/or less efficient in degrading O-alkyl C than those under M. laosensis forest during the experimental period, which might be related to the microbial community composition in the decomposing litter. Our study clearly showed interactions between changing litter chemistry and litter microbial communities and their impacts on litter decomposition. Site was not important in impacting decomposition rates, but played an important role in the preferential degradation of C components. However, further studies are needed to examine the conditions in forests where more rapid litter decomposition beneath the parent species than another species is considered to be common, in order to improve our ability to model decomposition globally.

The core root microbiome of sugarcanes cultivated under varying nitrogen fertilizer application.

Diazotrophic bacteria potentially supply substantial amounts of biologically fixed nitrogen to crops, but their occurrence may be suppressed by high nitrogen fertilizer application. Here, we explored the impact of high nitrogen fertilizer rates on the presence of diazotrophs in field-grown sugarcane with industry-standard or reduced nitrogen fertilizer application. Despite large differences in soil microbial communities between test sites, a core sugarcane root microbiome was identified. The sugarcane root-enriched core taxa overlap with those of Arabidopsis thaliana raising the possibility that certain bacterial families have had long association with plants. Reduced nitrogen fertilizer application had remarkably little effect on the core root microbiome and did not increase the relative abundance of root-associated diazotrophs or nif gene counts. Correspondingly, low nitrogen fertilizer crops had lower biomass and nitrogen content, reflecting a lack of major input of biologically fixed nitrogen, indicating that manipulating nitrogen fertilizer rates does not improve sugarcane yields by enriching diazotrophic populations under the test conditions. Standard nitrogen fertilizer crops had improved biomass and nitrogen content, and corresponding soils had higher abundances of nitrification and denitrification genes. These findings highlight that achieving a balance in maximizing crop yields and minimizing nutrient pollution associated with nitrogen fertilizer application requires understanding of how microbial communities respond to fertilizer use.

The Effect of Restoration Treatment Soils and Parent Tree on Tropical Forest Tree Seedling Growth

Restoration treatments can impact the growth and development of tree seedlings; however, it is often difficult to discern whether responses are driven by changes in microclimate, biotic interactions, or soil properties. To isolate for the latter, we quantified the growth response of four species [Ocotea puberula (Lauraceae); Otoba novogranatensis (Myristicaceae); Pseudolmedia mollis (Moraceae); Senna papillosa (Fabaceae)] grown under similar shade-house conditions in soils collected from 6 - 7 year old active (four species plantation) and passive restoration plots (natural recovery), and nearby reference forest sites in Costa Rica. We also evaluated the role of parent tree by collecting individuals from five mother trees. We measured height, above- and below-ground biomass, and determined root: shoot ratios (RSR). Species differed markedly in their responses. Ocotea, and to a lesser extent Pseudolmedia, were largely driven by parent tree. In contrast, Senna showed a strong soil response for all variables with more growth in active than passive restoration soils; reference forest seedlings were typically intermediate. An interaction suggested that some genotypes are more responsive to different soil properties than others. Otoba had higher soil-driven RSR in both restoration treatments. Surprisingly most soil nutrients, including %N, were similar or significantly lower in active restoration soils, suggesting that seedlings are responding to differences in soil microbial communities or more labile nutrients (e.g., NH4+ and NO3-). Active restoration appears to facilitate the growth of other species by improving certain soil properties. Additionally, genotypes are an important driver of seedling vigor and some species may be more responsive to subtle differences in soil properties than others.

Eupatorium adenophorum invasion alters soil bacterial community and diversity

The invasion of alien species can affect biological community structure and ecosystem functioning, but the relationships between invasive plants and soil microbial composition and diversity are still unclear. In order to examine the effect of the invasion of an exotic plant Eupatorium adenophorum on soil chemical properties and microbial community structure and diversity, we compared the differences in soil microbial community of three communities with different densities of E. adenophorum (native plant community, E. adenophorum and native plant mixed community, and E. adenophorum dominated community) by high-throughput sequencing. Analysis of soil chemical properties showed that soil pH, organic matter, total nitrogen and total potassium decreased with increasing invasion of E. adenophorum. However, total phosphorus was highest in the most heavily invaded soil. The high-throughput sequencing results showed that there were 7,755 soil microbial OTUs (operational taxonomic unit) in total. The invasion of E. adenophorum 666 生 物 多 样 性 Biodiversity Science 第 23卷 did not exert heavy impacts on soil microbial diversity. ACE index and Chao index showed no significant differences among the three different communities. However, soil microbial diversity of the mixed community of E. adenophorum and native plant species showed the lowest Shanonn index. The relative abundances of Acidobacteria and Verrucomicrobia in the medium invaded community were the highest. In sum, the invasion of E. adenophorum altered the diversity and structure of soil microbial communities, and changed the soil chemical properties.

Salinity-induced differences in soil microbial communities around the hypersaline Lake Urmia

Lake Urmia in north-western Iran is one of the largest hypersaline lakes in the world, and agricultural production in the surrounding area is limited by soil salinity. We investigated the effects of salinity on belowground microbial communities in soils collected from fields of cultivated onions (Allium cepa L.) and lucerne (Medicago sativa L.), and sites with the native halophyte samphire (Salicornia europaea L.). We tested the hypotheses that salinity reduces microbial biomass and changes the structure of the microbial community. The physical and chemical properties of soil samples were analysed, and phospholipid fatty acids were identified as signatures for various microbial groups. We found that the organic carbon (OC) content was the dominant determinant of microbial biomass. We also found linear relationships between OC and the biomass of various groups of organisms across the wide salinity gradient studied. Salinity, on the other hand, caused changes in the microbial fatty acid composition that indicated adaptation to stress and favoured saprotrophic fungi over bacteria, and Gram-negative bacteria over Gram-positive. Principal component analysis showed that salinity variables and microbial stress indices formed one group, and OC and microbial biomass another. The importance of OC for high microbial biomass in severely stressed soils indicates that OC amendment may be used to mitigate salt stress and as a method of managing saline soils.