A meta‐analysis of soil salinization effects on nitrogen pools,cycles and fluxes in coastal ecosystems

Salinity intrusion caused by land subsidence resulting from increasing groundwater abstraction, decreasing river sediment loads and increasing sea level because of climate change has caused widespread soil salinization in coastal ecosystems. Soil salinization may greatly alter nitrogen (N) cycling in coastal ecosystems. However, a comprehensive understanding of the effects of soil salinization on ecosystem N pools, cycling processes and fluxes is not available for coastal ecosystems. Therefore, we compiled data from 551 observations from 21 peer‐reviewed papers and conducted a meta‐analysis of experimental soil salinization effects on 19 variables related to N pools, cycling processes and fluxes in coastal ecosystems. Our results showed that the effects of soil salinization varied across different ecosystem types and salinity levels. Soil salinization increased plant N content (18%), soil NH₄⁺ (12%) and soil total N (210%), although it decreased soil NO₃^? (2%) and soil microbial biomass N (74%). Increasing soil salinity stimulated soil N₂O fluxes as well as hydrological NH₄⁺ and NO₂^? fluxes more than threefold, although it decreased the hydrological dissolved organic nitrogen (DON) flux (59%). Soil salinization also increased the net N mineralization by 70%, although salinization effects were not observed on the net nitrification, denitrification and dissimilatory nitrate reduction to ammonium in this meta‐analysis. Overall, this meta‐analysis improves our understanding of the responses of ecosystem N cycling to soil salinization, identifies knowledge gaps and highlights the urgent need for studies on the effects of soil salinization on coastal agro‐ecosystem and microbial N immobilization. Additional increases in knowledge are critical for designing sustainable adaptation measures to the predicted intrusion of salinity intrusion so that the productivity of coastal agro‐ecosystems can be maintained or improved and the N losses and pollution of the natural environment can be minimized.     

Microbial resistance and resilience in response to environmental changes under the higher intensity of human activities than global average level

With the increasing intensity of global human activities, the ecosystem function, which is supported by the microbial community, will be dramatically changed and impaired. To investigate microbial resistance and resilience of microbial communities to human activities, we chose two typical types of human disturbances, urbanization, and reclamation under the higher intensity of human activities than the global average level. We examined microbial traits, including the abundance, diversity, phylogeny, and co‐occurrence interactions in soil microbial communities, together with the nitrification activities observed in the subtropical coastal ecosystem of the Pearl River Estuary and in soil microcosm experiments. Microbial communities were less resistant to the environmental changes caused by urbanization than to those caused by reclamation, which was significantly reflected in the nitrogen and/or carbon‐related patterns. However, most of the microbial traits could be recovered almost to the original level without significant differences in the microcosm after 40 days of incubation. The co‐occurrence interactions between nitrifiers and other microbial communities were dramatically changed and could not be completely recovered, but this change did not affect their nitrification activities for balancing the ammonium in the soil to the original level during the recovery stage, suggesting that the interactions between microbial communities might have fewer effects on their activities than previously thought. This study quantitatively demonstrated that microbial communities as a whole can recover to a status similar to the original state in a short time after the removal of stress at a large ecosystem scale even under the higher intensity of human activities than global average level in coastal ecosystems, which implied a strong recovery capacity of soil microbial community even after intense human disturbance.     

Salinity controls soil microbial community structure and function in coastal estuarine wetlands

Soil salinity acts as a critical environmental filter on microbial communities, but the consequences for microbial diversity and biogeochemical processes are poorly understood. Here, we characterized soil bacterial communities and microbial functional genes in a coastal estuarine wetland ecosystem across a gradient (~5 km) ranging from oligohaline to hypersaline habitats by applying the PCR-amplified 16S rRNA (rRNA) genes sequencing and microarray-based GeoChip 5.0 respectively. Results showed that saline soils in marine intertidal and supratidal zone exhibited higher bacterial richness and Faith's phylogenetic diversity than that in the freshwater-affected habitats. The relative abundance of taxa assigned to Gammaproteobacteria, Bacteroidetes and Firmicutes was higher with increasing salinity, while those affiliated with Acidobacteria, Chloroflexi and Cyanobacteria were more prevalent in wetland soils with low salinity. The phylogenetic inferences demonstrated the deterministic role of salinity filtering on the bacterial community assembly processes. The abundance of most functional genes involved in carbon degradation and nitrogen cycling correlated negatively with salinity, except for the hzo gene, suggesting a critical role of the anammox process in tidal affected zones. Overall, the salinity filtering effect shapes the soil bacterial community composition, and soil salinity act as a critical inhibitor in the soil biogeochemical processes in estuary ecosystems.     

Biodiversity dynamics of freshwater wetland ecosystems affected by secondary salinisation and seasonal hydrology variation: a model-based study

Freshwater wetlands worldwide are under threat from secondary salinisation and climate change. Given that many freshwater wetlands naturally have highly variable hydrology, it is important to understand the combined effects of salinity and water regime on wetland biodiversity. Here a mathematical model has been developed to explore the biodiversity dynamics of freshwater wetland ecosystems affected by secondary salinisation and seasonal hydrology variation. The model shows that seasonal hydrological change can drive the wetland ecosystem into a stable oscillatory state of biodiversity, with the same period as the wetting and drying cycle. The initial condition of a wetland mediates the ecological response of the wetland ecosystem to salinity and seasonal variability. There are two manifestations of stability that occur in relation to wetland biodiversity: monostability and bistability. In model simulations, some wetland ecosystems may respond to the effects of seasonal change quickly, while others may do so more slowly. In ‘slow response’ wetlands, seasonal variability has a weak impact on the ecosystem properties of stability, resilience, sensitivity and the species richness–mean salinity relationship. In contrast, ‘fast response’ wetlands are seasonally controlled heavily. Seasonal variability can play a critical role in determining ecosystem properties. Changes in the strength of seasonality can induce the transition between monostability and bistability. Seasonal variability may also reduce wetland resilience, exacerbating the risk of secondary salinisation. On the other hand, seasonal variability may provide opportunities for the restoration of salinised wetlands by increasing their sensitivity to management actions and facilitating recovery processes. Model simulations show that the response of the stable biodiversity oscillation to changing mean salinity is dependent on seasonality strength (primarily for fast response wetlands) and other wetland conditions. Generally, there are two types of wetland responses to changes in mean salinity: type 1 wetlands exhibit a graded response of species richness (a surrogate for biodiversity), whereas a hysteretic response occurs in type 2 wetlands. Species diversity displays critical behaviour: regime shifts in diversity occur at the thresholds of mean salinity, strength of seasonality or initial species diversity. The predictions are consistent with previously-published field observations in salinised freshwater wetlands. Handling editor: D. Hamilton     

Microbial and macroinvertebrate communities,but not leaf decomposition,change along a mining‐induced salinity gradient

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盐度对滨海土壤细菌多样性和群落构建过程的影响

滨海盐土是重要的农业土地后备资源。微生物是土壤中物质循环的关键动力,然而盐度对土壤微生物群落特征影响的研究还很缺乏。本研究采集滨海地区的土壤样品,研究非盐、轻盐和高盐3组不同盐度对土壤细菌数量、多样性和群落构建的影响。结果表明: 与非盐和轻盐土壤相比,高盐土壤的脱氢酶活性和细菌数量显著降低,而细菌α多样性没有变化,细菌群落结构发生分异。利用零模型反演群落构建过程,发现盐度是细菌群落构建过程的主控因子,盐度主导的高确定性过程控制了滨海盐土细菌的群落结构。说明在现有的盐度范围内,高盐土壤中同样含有丰富的微生物种质资源,具有盐土改良的生物学基础,然而由于高确定性的群落构建机制,外源物种很难定殖于滨海盐土。因此,在利用微生物技术改良滨海盐土时,应尽可能筛选耐盐的土著菌种,提高定殖效率。     

Effect of salinisation of soil on growth and macro- and micro-nutrient accumulation in seedlings of Acacia catechu (Mimosaceae)

The effects of salinisation of soil on Acacia catechu (Mimosaceae) were studied by means of emergence and growth of seedlings and pattern of mineral accumulation. A mixture of chlorides and sulphates of Na, K, Ca and Mg was added to the soil and salinity was maintained at 4.1, 6.3, 8.2,10.1 and 12.2 dSm⁻¹. A negative relationship between proportion of seed germination and salt concentration was obtained. Seedlings did not emerge when soil salinity exceeded 10.1 dSm⁻¹. Results suggested that this tree species is salt tolerant at the seed germination stage. Seedlings survived and grew up to soil salinity of 10.1 dSm⁻¹, which suggests that this species is salt tolerant at the seedling stage too. Elongation of stem and root was retarded by increasing salt stress. Among the tissues, young roots and stem were most tolerant to salt stress and were followed by old roots and leaves, successively. Leaf tissue exhibited maximum reduction in dry mass production in response to increasing salt stress. However, production of young roots and death of old roots were found to be continuous and plants apparently use this process as an avoidance mechanism to remove excess ions and delay onset of ion accumulation in this tissue. This phenomenon, designated “fine root turnover”, is of importance to the mechanisms of salt tolerance. Plants accumulated Na in roots and were able to regulate transfer of Na ions to leaves. Stem tissues were a barrier for translocation of Na from root to leaf. Moreover, K was affected in response to salinity; it rapidly decreased in root tissues with increased salinisation. Nitrogen content decreased in all tissues (leaf, stem and root) in response to low water treatment and salinisation of soil. Phosphorus content significantly decreased, while Ca increased in leaves as soil salinity increased. Changes in tissue and whole plant accumulation patterns of the other elements tested, as well as possible mechanisms for avoidance of Na toxicity in this tree species during salinisation, are discussed.     

Combined impacts of warming and salinisation on trophic interactions and mortality of a specialist ephemeral wetland predator

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Extensive Management Promotes Plant and Microbial Nitrogen Retention in Temperate Grassland

Leaching losses of nitrogen (N) from soil and atmospheric N deposition have led to widespread changes in plant community and microbial community composition, but our knowledge of the factors that determine ecosystem N retention is limited. A common feature of extensively managed, species-rich grasslands is that they have fungal-dominated microbial communities, which might reduce soil N losses and increase ecosystem N retention, which is pivotal for pollution mitigation and sustainable food production. However, the mechanisms that underpin improved N retention in extensively managed, species-rich grasslands are unclear. We combined a landscape-scale field study and glasshouse experiment to test how grassland management affects plant and soil N retention. Specifically, we hypothesised that extensively managed, species-rich grasslands of high conservation value would have lower N loss and greater N retention than intensively managed, species-poor grasslands, and that this would be due to a greater immobilisation of N by a more fungal-dominated microbial community. In the field study, we found that extensively managed, species-rich grasslands had lower N leaching losses. Soil inorganic N availability decreased with increasing abundance of fungi relative to bacteria, although the best predictor of soil N leaching was the C/N ratio of aboveground plant biomass. In the associated glasshouse experiment we found that retention of added ¹⁵N was greater in extensively than in intensively managed grasslands, which was attributed to a combination of greater root uptake and microbial immobilisation of ¹⁵N in the former, and that microbial immobilisation increased with increasing biomass and abundance of fungi. These findings show that grassland management affects mechanisms of N retention in soil through changes in root and microbial uptake of N. Moreover, they support the notion that microbial communities might be the key to improved N retention through tightening linkages between plants and microbes and reducing N availability.     

Effect of salinisation of soil on growth, water status and general nutrient accumulation in seedlings .of Delonix regia (Fabaceae)

Greenhouse experiments were conducted to assess the effect of salinisation of soil on emergence, growth, water content, proline content and mineral accumulation of seedlings of Delonix regia (Hook.) Raf. (Fabaceae). Sodium chloride (NaCl) was added to the soil and salinity was maintained at 0.3, 1.9, 3.9, 6.0 and 7.9 dS m^?1. A negative relationship between seedling emergence and salt concentration was obtained. Salinity caused reduction in water content and water potential of tissues (leaves, stems, tap roots and lateral roots) that resulted in internal water deficit to plants. Consequently, shoot and root elongation, leaf expansion and dry matter accumulation in leaves, stems, tap roots and lateral root tissues of seedlings significantly decreased in response to increasing concentration of salt. Proline content in tissues was very low. There were no effective mechanisms to control net uptake of Na on root plasma membrane and subsequently its transport to shoot tissues. Potassium content significantly decreased in tissues in response to salinisation of soil. This tree species is a moderate salt-tolerant glycophytic plant. Nitrogen and calcium content in tissues significantly decreased as soil salinity increased. Phosphors content in tissues exhibited a declining trend with increase in soil salinity. Changes in tissues and whole-plant accumulation pattern of other elements tested, as well as possible mechanisms for avoidance of Na toxicity in this tree species in response to salinisation, are discussed.     

Effect of salinisation of soil on growth, water status and general nutrient accumulation in seedlings of Delonix regia (Fabaceae)

Greenhouse experiments were conducted to assess the effect of salinisation of soil on emergence, growth, water content, proline content and mineral accumulation of seedlings of Delonix regia (Hook.) Raf. (Fabaceae). Sodium chloride (NaCl) was added to the soil and salinity was maintained at 0.3, 1.9, 3.9, 6.0 and 7.9 dS m⁻¹. A negative relationship between seedling emergence and salt concentration was obtained. Salinity caused reduction in water content and water potential of tissues (leaves, stems, tap roots and lateral roots) that resulted in internal water deficit to plants. Consequently, shoot and root elongation, leaf expansion and dry matter accumulation in leaves, stems, tap roots and lateral root tissues of seedlings significantly decreased in response to increasing concentration of salt. Proline content in tissues was very low. There were no effective mechanisms to control net uptake of Na on root plasma membrane and subsequently its transport to shoot tissues. Potassium content significantly decreased in tissues in response to salinisation of soil. This tree species is a moderate salt-tolerant glycophytic plant. Nitrogen and calcium content in tissues significantly decreased as soil salinity increased. Phosphors content in tissues exhibited a declining trend with increase in soil salinity. Changes in tissues and whole-plant accumulation pattern of other elements tested, as well as possible mechanisms for avoidance of Na toxicity in this tree species in response to salinisation, are discussed.     

Changes of Soil Particle Size Distribution in Tidal Flats in the Yellow River Delta

Background

The tidal flat is one of the important components of coastal wetland systems in the Yellow River Delta (YRD). It can stabilize shorelines and protect coastal biodiversity. The erosion risk in tidal flats in coastal wetlands was seldom been studied. Characterizing changes of soil particle size distribution (PSD) is an important way to quantity soil erosion in tidal flats.

Method/Principal findings

Based on the fractal scale theory and network analysis, we determined the fractal characterizations (singular fractal dimension and multifractal dimension) soil PSD in a successional series of tidal flats in a coastal wetland in the YRD in eastern China. The results showed that the major soil texture was from silt loam to sandy loam. The values of fractal dimensions, ranging from 2.35 to 2.55, decreased from the low tidal flat to the high tidal flat. We also found that the percent of particles with size ranging between 0.4 and 126 μm was related with fractal dimensions. Tide played a great effort on soil PSD than vegetation by increasing soil organic matter (SOM) content and salinity in the coastal wetland in the YRD.

Conclusions/Significance

Tidal flats in coastal wetlands in the YRD, especially low tidal flats, are facing the risk of soil erosion. This study will be essential to provide a firm basis for the coast erosion control and assessment, as well as wetland ecosystem restoration.     

Environmental effects on CO2 efflux from riparian tundra in the northern foothills of the Brooks Range,Alaska, USA

Summary Carbon dioxide efflux and soil microenvironmental factors were measured diurnally in Carex aquatilus-and Eriophorum angustifolium-dominated riparian tundra communities to determine the relative importance of soil environmental factors controlling ecosystem carbon dioxide exchange with the atmosphere. Measurements were made weekly between 18 June and 24 July 1990. Diurnal patterns in carbon dioxide efflux were best explained by changes in soil temperature, while seasonal changes in efflux were correlated with changes in depth to water table, depth to frozen soil and soil moisture. Carbon dioxide efflux rates were lowest early in the growing season when high water tables and low soil temperatures limited microbial and root activity. Individual rainfall events that raised the water table were found to strongly reduce carbon dioxide efflux. As the growing season progressed, rainfall was low and depth to water table and soil temperatures increased. In response, carbon dioxide efflux increased strongly, attaining rates late in the season of approximately 10 g CO₂ m^–2 day^–1. These rates are as high as maxima recorded for other arctic sites. A mathematical model is developed which demonstrates that soil temperature and depth to water table may be used as efficient predictors of ecosystem CO₂ efflux in this habitat. In parallel with the field measurements of CO₂ efflux, microbial respiration was studied in the laboratory as a function of temperature and water content. Estimates of microbial respiration per square meter under field conditions were made by adjusting for potential respiring soil volume as water table changed and using measured soil temperatures. The results indicate that the effect of these factors on microbial respiration may explain a large part of the diurnal and seasonal variation observed in CO₂ efflux. As in coastal tundra sites, environmental changes that alter water table depth in riparian tundra communities will have large effects on ecosystem CO₂ efflux and carbon balance.     

Cloud shading and fog drip influence the metabolism of a coastal pine ecosystem

Assessing the ecological importance of clouds has substantial implications for our basic understanding of ecosystems and for predicting how they will respond to a changing climate. This study was conducted in a coastal Bishop pine forest ecosystem that experiences regular cycles of stratus cloud cover and inundation in summer. Our objective was to understand how these clouds impact ecosystem metabolism by contrasting two sites along a gradient of summer stratus cover. The site that was under cloud cover ~15% more of the summer daytime hours had lower air temperatures and evaporation rates, higher soil moisture content, and received more frequent fog drip inputs than the site with less cloud cover. These cloud‐driven differences in environmental conditions translated into large differences in plant and microbial activity. Pine trees at the site with greater cloud cover exhibited less water stress in summer, larger basal area growth, and greater rates of sap velocity. The difference in basal area growth between the two sites was largely due to summer growth. Microbial metabolism was highly responsive to fog drip, illustrated by an observed ~3‐fold increase in microbial biomass C with increasing summer fog drip. In addition, the site with more cloud cover had greater total soil respiration and a larger fractional contribution from heterotrophic sources. We conclude that clouds are important to the ecological functioning of these coastal forests, providing summer shading and cooling that relieve pine and microbial drought stress as well as regular moisture inputs that elevate plant and microbial metabolism. These findings are important for understanding how these and other seasonally dry coastal ecosystems will respond to predicted changes in stratus cover, rainfall, and temperature.     

Human-induced salinity changes impact marine organisms and ecosystems

Climate change is fundamentally altering marine and coastal ecosystems on a global scale. While the effects of ocean warming and acidification on ecology and ecosystem functions and services are being comprehensively researched, less attention is directed toward understanding the impacts of human-driven ocean salinity changes. The global water cycle operates through water fluxes expressed as precipitation, evaporation, and freshwater runoff from land. Changes to these in turn modulate ocean salinity and shape the marine and coastal environment by affecting ocean currents, stratification, oxygen saturation, and sea level rise. Besides the direct impact on ocean physical processes, salinity changes impact ocean biological functions with the ecophysiological consequences are being poorly understood. This is surprising as salinity changes may impact diversity, ecosystem and habitat structure loss, and community shifts including trophic cascades. Climate model future projections (of end of the century salinity changes) indicate magnitudes that lead to modification of open ocean plankton community structure and habitat suitability of coral reef communities. Such salinity changes are also capable of affecting the diversity and metabolic capacity of coastal microorganisms and impairing the photosynthetic capacity of (coastal and open ocean) phytoplankton, macroalgae, and seagrass, with downstream ramifications on global biogeochemical cycling. The scarcity of comprehensive salinity data in dynamic coastal regions warrants additional attention. Such datasets are crucial to quantify salinity-based ecosystem function relationships and project such changes that ultimately link into carbon sequestration and freshwater as well as food availability to human populations around the globe. It is critical to integrate vigorous high-quality salinity data with interacting key environmental parameters (e.g., temperature, nutrients, oxygen) for a comprehensive understanding of anthropogenically induced marine changes and its impact on human health and the global economy.     

Priming effect and microbial diversity in ecosystem functioning and response to global change: a modeling approach using the SYMPHONY model

Integration of the priming effect (PE) in ecosystem models is crucial to better predict the consequences of global change on ecosystem carbon (C) dynamics and its feedbacks on climate. Over the last decade, many attempts have been made to model PE in soil. However, PE has not yet been incorporated into any ecosystem models. Here, we build plant/soil models to explore how PE and microbial diversity influence soil/plant interactions and ecosystem C and nitrogen (N) dynamics in response to global change (elevated CO₂ and atmospheric N depositions). Our results show that plant persistence, soil organic matter (SOM) accumulation, and low N leaching in undisturbed ecosystems relies on a fine adjustment of microbial N mineralization to plant N uptake. This adjustment can be modeled in the SYMPHONY model by considering the destruction of SOM through PE, and the interactions between two microbial functional groups: SOM decomposers and SOM builders. After estimation of parameters, SYMPHONY provided realistic predictions on forage production, soil C storage and N leaching for a permanent grassland. Consistent with recent observations, SYMPHONY predicted a CO₂‐induced modification of soil microbial communities leading to an intensification of SOM mineralization and a decrease in the soil C stock. SYMPHONY also indicated that atmospheric N deposition may promote SOM accumulation via changes in the structure and metabolic activities of microbial communities. Collectively, these results suggest that the PE and functional role of microbial diversity may be incorporated in ecosystem models with a few additional parameters, improving accuracy of predictions.     

Plant invasion alters nitrogen cycling by modifying the soil nitrifying community

Plant invasions have dramatic aboveground effects on plant community composition, but their belowground effects remain largely uncharacterized. Soil microorganisms directly interact with plants and mediate many nutrient transformations in soil. We hypothesized that belowground changes to the soil microbial community provide a mechanistic link between exotic plant invasion and changes to ecosystem nutrient cycling. To examine this possible link, monocultures and mixtures of exotic and native species were maintained for 4 years in a California grassland. Gross rates of nitrogen (N) mineralization and nitrification were quantified with ¹⁵N pool dilution and soil microbial communities were characterized with DNA‐based methods. Exotic grasses doubled gross nitrification rates, in part by increasing the abundance and changing the composition of ammonia‐oxidizing bacteria in soil. These changes may translate into altered ecosystem N budgets after invasion. Altered soil microbial communities and their resulting effects on ecosystem processes may be an invisible legacy of exotic plant invasions.     

森林次生演替和土壤层次对微生物群落结构的影响

森林次生演替与生态系统结构和功能的动态变化密切相关。大多数研究主要关注植物群落以及土壤有机碳(SOC)的变化,然而土壤微生物群落如何响应森林次生演替还需要进一步探究。本研究以长白山森林次生演替序列(20、80、120、200和≥300年)和两个土壤层次为对象,采用磷脂脂肪酸微生物标志物,探究温带森林次生演替过程中地下微生物群落结构变化。森林次生演替改变了土壤微生物群落结构,主要归因于某些特定微生物类群的变化,演替前期革兰氏阴性菌和腐生真菌占主导,而在演替后期革兰氏阳性菌和丛枝菌根真菌占主导。另外,土壤有机质数量和质量差异是影响微生物群落结构和生物量的主要环境因素。森林演替前期和中期增加的SOC含量促进了微生物生物量,而演替后期增加的难分解芳香族有机组分抑制了微生物生物量合成。土壤层次间理化性质的差异导致微生物群落变化,有机质层高的SOC以及氮含量导致更多微生物生物量的合成。微生物群落在时间和空间尺度的变化及其驱动因素反映了生态系统结构和功能对环境变化的响应。     

Fish and crustaceans in northeast Greenland lakes with special emphasis on interactions between Arctic charr (Salvelinus alpinus), Lepidurus arcticus and benthic chydorids

Many inland waters are becoming more saline from human activities, particularly in semi-arid and arid regions. The causes and distribution of anthropogenic salinisation, the salinisation of freshwater lakes, rivers and streams, and increases in the salinity of large, permanent saline lakes are discussed. The impacts of anthropogenic salinisation are far-reaching, increasing, deleterious and largely irreparable. Environmental, social and environmental costs are high. Attention is drawn to the importance of anthropogenic salinisation and its impacts. The need for better recognition of the costs of salinisation and for more effective management is stressed.     

种植盐地碱蓬改良滨海盐渍土对土壤微生物区系的影响

利用盐生植物盐地碱蓬对天津河口滨海盐碱地进行生物修复,研究了其对土壤微生物区系的影响.结果表明,种植区碱蓬根系土壤的可溶性盐分与对照土壤相比下降了41%（重量法）和37%（电导法）;根系土壤的微生物数量明显增加,其中细菌、放线菌和真菌分别较对照增加了2.3倍、4.3倍和71倍,与对照相比均为显著性差异.根系微生物的耐盐性结果显示,随着土壤盐分的降低,根系微生物生长的最适盐度也随之降低,耐盐性较低的微生物种群已逐渐成为优势种群.系统发育分析表明,枯草杆菌属成为植物修复后土壤中的优势种群.