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Managed and natural vegetation restorations are two vital measures of land restoration; however, their effects on soil microbial communities at a large scale are not clearly understood. Hence, changes in the microbial community composition after 15 years of vegetation restoration along a climatic gradient in the subtropical karst region of Southwest China were assessed based on phospholipid fatty acids (PLFAs) profiles. Managed (plantation forest) and natural (naturally recovered to shrubbery) vegetation restoration types were compared, with cropland and mature forest serving as controls. Soil microbial community abundance was significantly higher under the two vegetation restoration types than in the cropland; however, it was lower than in the mature forest. The abundance, composition, and structure of soil microbial communities did not differ significantly between plantation forest and shrubbery. Soil organic carbon or total nitrogen was the primary factor positively affecting soil microbial abundance, whereas the mean annual temperature (MAT) was recognized as the primary factor contributing to the variation in the soil microbial community structure. Moreover, temperature had opposite effects on different indicators of microbial community structure. That is, it positively and negatively affected the ratios of gram-positive to gram-negative bacterial PLFAs (GP:GN) and fungal to bacterial PLFAs (F:B), respectively. Our results show that both vegetation restoration types have the ability to improve soil productivity in karst areas. Furthermore, shifts in soil microbial community structure (GP:GN and F:B ratios) induced by warming are likely to lead to a higher proportion of labile carbon, which is sensitive to soil tillage. Hence, more attention should be paid to ecological restoration in warmer karst areas to alleviate the severe loss of soil carbon in croplands. [ABSTRACT FROM AUTHOR]

Bacteria, fungi, and protist are important in driving nutrient cycling. The microbiological mechanism underlying vegetation restoration during different temperature and precipitation gradients remains unclear. To determine the relationship between microbes and nutrients, we examined the changes in soil bacterial, fungal, and protist diversity and community composition under two different temperatures in a plantation forest and shrubland as well as reference cropland in a karst region. Bacterial and protist diversity in the warm and low‐altitude region of Guangxi (average temperature 20.9°C) was higher in cropland than in shrubland or plantation forest. By contrast, fungal richness was lower in cropland than in shrubland. A co‐occurrence network revealed higher numbers of correlated links among the bacterial, fungal, and protist taxa in the cool and high‐altitude region of Guizhou (average temperature 14.6°C) than in the warm and low‐altitude region of Guangxi. Stronger interactions were observed among microbial taxa under cropland than in vegetation restoration. The protist groups Cercozoa and Lobosa showed the highest numbers of links with the bacterial phyla Acidobacteria and Proteobacteria and with the fungal phylum Ascomycota. The numbers of Proteobacteria, Ascomycota, and Cercozoa were most correlated with soil nutrient levels of carbon, nitrogen, and phosphorus. Overall, microbial interactions were higher at low temperatures than at high temperatures, consequently intensifying the predation of bacteria and fungi by protists at a low‐temperature level. Furthermore, Proteobacteria, Ascomycota, and Cercozoa were the keystone taxa linked to nutrient availability; hence, effective monitoring of these dominant groups may be beneficial for increasing nutrient accumulation during vegetation restoration. [ABSTRACT FROM AUTHOR]

Vegetation restoration often promotes the development of biological soil crusts (biocrusts), which have a significant role in the terrestrial nitrogen (N) cycle. However, biocrusts are not always considered when assessing soil N responses to restoration efforts, especially in subtropical regions. We assessed the effect of various restoration strategies on moss-dominated biocrust properties and soil N variables (0–5 cm topsoil and 5–10 cm sub-topsoil) in the subtropical karst region of southwestern China. Four restoration strategies were included: restoration with plantation forest, forage grass, and a combination of forest and grass, and spontaneous regeneration to natural grassland. Cropland under maize-soybean rotation (CR) was used as reference. The biocrust under combination restoration strategy had significantly higher biomass, saturated water adsorption ratio, and carbon content than did the other strategies; and the soil generally had the highest total N, ammonium, and microbial biomass carbon and N content but the lowest nitrate content. Redundancy analysis, variation partitioning, and stepwise multiple linear regression all indicated that biocrust properties play an important role in affecting soil N variables, especially in the topsoil. Vegetation restoration strategies that use various plant functional group assemblages, such as forest and grass, are preferable in enhancing the development of biocrusts and thus improving soil N properties. • Vegetation restoration is beneficial in promoting biocrust development. • Biocrust properties were the main factors affecting soil N variations. • Combination of plantation trees and forage grasses had higher soil N and biocrusts. • Combination restoration strategy should be favored in vegetation restoration efforts. [ABSTRACT FROM AUTHOR]

Vegetation restoration affects belowground microbial diversity and trait-based life strategies, as well as soil organic matter (SOM) accumulation. Despite the growing focus on microbial diversity, the relationship between SOM accrual and life strategies following vegetation restoration remains unclear. We used three independent but complementary approaches to relate six soil parameters to SOM accrual and further connected them with microbial diversity and life strategies. Sites with two vegetation restoration strategies (after 15 years of vegetation recovery): i) actively planted forests and ii) passive naturally regenerating forests, were compared with croplands and established 60-year-old secondary forests. Data from seven sites along a large climatic gradient (Δ temperature >9 °C) in subtropical karst regions showed that the average index of SOM accrual increased by 47% in plantations and by 60% in natural regeneration forests compared to that in croplands, but remained lower than that of secondary forests. Related soil parameters (water holding capacity, organic carbon and total nitrogen contents, and bacterial and fungal biomasses) were comparable. Compared to croplands, vegetation restoration decreased the sensitivity of the soil parameters to climate warming. Vegetation restoration reduced bacterial diversity and shifted the community towards K-strategy, as evidenced by i) lower 16S rRNA operon copy number and ii) higher ratios of phyla classified a priori as oligotrophic versus copiotrophic bacteria. These changes were mainly attributed to the decline in labile nutrient content and increase in carbon stability in calcium-rich karst soils after vegetation restoration. Bacterial diversity was negatively associated with SOM accrual at low levels of functioning, whereas the prevalence of K-strategists showed a strong positive association with it, especially at near-peak capacity. Consequently, i) bacterial rather than fungal diversity and life strategies are associated with SOM accrual, and ii) linking bacterial life strategies with SOM accrual is important to deepen the understanding of soil-microbial interactions. • Both active and passive vegetation restoration promote SOM accrual. • Vegetation restoration shifts microbial community towards K-strategy. • Bacterial rather than fungal traits are associated with SOM accrual. • Bacterial K/r ratios show strong positive association with SOM accrual. [ABSTRACT FROM AUTHOR]

Vegetation restoration has been proposed as an effective strategy for increasing soil organic carbon (SOC) sequestration. However, the responses of SOC to managed and natural vegetation restoration strategies at a large scale are poorly understood due to the varying SOC components and changing climatic conditions. Here, we measured bulk SOC, particulate organic carbon (POC), and mineral-associated organic carbon (MOC) after 15 years of vegetation restoration along an elevation gradient with a corresponding temperature gradient in the calcareous soils of karst region, Southwest China. We compared managed plantation forest and naturally recovered shrubland vegetation restoration strategies, using cropland and mature forest as references. Overall, we found that the SOC and POC densities in both plantation forest and shrubland were significantly higher than in the cropland but lower than in the mature forest. There were no significant differences in the SOC pool between the plantation forest and shrubland. Furthermore, the relative changes in the SOC and POC densities increased with increasing mean annual temperature in the plantation forest and shrubland. Our results showed that both vegetation restoration strategies, characterized by higher soil microbial abundance and exchangeable Ca concentration, were beneficial to POC but not MOC accumulation, and sufficiently compensated SOC decomposition at lower elevation with higher MAT. Our results highlight the potential of both vegetation restoration strategies for promoting SOC accumulation in warmer karst regions and emphasize the necessity to understand soil carbon stabilization mechanisms in calcareous soils. Unlabelled Image • Managed and natural vegetation restoration were compared along a climatic gradient. • Both vegetation restoration strategies increased soil carbon stocks in warmer regions. • Higher temperature shifted soil microbial community structure. • Restored vegetation had higher microbial abundance and calcium than cropland. • Microbial abundance and calcium negated effect of temperature on SOC decomposition. [ABSTRACT FROM AUTHOR]

Mosses are multifunctional communities that are increasingly recognized as potential and sustainable resources to restore degraded ecosystems. However, available information is limited on the influence of mosses on soil multifunctionality during vegetation restoration in subtropical ecosystems. We investigated the effects of mosses on soil multifunctionality and four single functions in three vegetation restoration approaches (monoculture plantations, monoculture forage grasses and intercropping of trees and forage grasses) by conducting a moss removal and retention experiment. Moss removal decreased soil multifunctionality and the single functions of nutrient provisioning, water retention and plant–microbe symbiosis, particularly in monoculture plantations, in the 0–5 cm soil layer. Moss removal decreased the phospholipid fatty acid abundance of soil microbes (e.g., bacteria, Gram-negative bacteria and general fungi) in the 2–5 cm soil layer but had nonsignificant effects on the nematode community. Random forest analysis showed that moss properties were more important factors than the soil physicochemical, microbial and nematode properties linked to soil multifunctionality. Moss properties (diversity, thickness, biomass, carbon and nitrogen concentrations, carbon to nitrogen ratio, biological nitrogen fixation rate and saturated water absorption content) were positively associated with soil multifunctionality, nutrient provisioning, water retention and plant–microbe symbiosis. These findings highlight the importance of preserving mosses to maintain soil multifunctionality during vegetation restoration in degraded subtropical ecosystems, especially in monoculture plantations. • Moss removal decreased the functions of nutrient provisioning, water retention and plant–microbe symbiosis. • Soil microbial community was more responsive than nematode community to moss removal. • Moss properties were positively associated with soil multifunctionality. [ABSTRACT FROM AUTHOR]

[Display omitted] • High habitat heterogeneity in a karst area increased AMF and plant biodiversity. • Rocky soil surface areas rich in plant diversity have the highest AMF abundance. • Interactions among AMF taxa were stronger in rocky soil than in other habitats. • Shrub diversity affects AMF abundance and communities via soil nutrient accumulation. • Species–area relationships show that plants have a larger-scale habitat size than AMF. Arbuscular mycorrhizal fungi (AMF) constitute one of the factors that regulate the success of vegetation restoration. Karst ecosystems are heterogenous in nutrient content and plant communities because of preferential water fluxes within cracks and gullies in the soil parent material. The effects of habitat on soil nutrients, shrub, and AMF diversity in karst ecosystems are yet to be established. Thus, we investigated the diversity of shrubs and AMF within three habitats: i) rocky soil surface (Rock), ii) soil surface (Soil), and iii) rocky gully (Gully) in a typical karst shrub ecosystem. We observed that AMF diversity was independent of the sampling location, whereas AMF abundance and the shrub Shannon index increased with sampling distance, reaching a plateau in a sampling area of 1000 m2. The AMF community composition was driven by dominating shrubs (Vitex negundo , Tirpitzia ovoidea). Higher shrub diversity and AMF abundance occurred in Rock than in Soil and Gully areas, suggesting higher habitat heterogeneity in Rock areas. Based on co-occurrence network analysis, interactions with a high link number among the AMF taxa were stronger in Rock than in Gully because the network complexity in the Rock areas strongly depended on symbiosis with AMF taxa to cope with high habitat heterogeneity. The Random forest model revealed that AMF abundance was mainly affected by available phosphorous, total potassium, and shrub diversity. Available phosphorous, soil pH, and exchangeable Ca2+, rather than plant diversity, were the main factor controlling AMF community composition. Overall, the results suggest that the increase in shrub diversity raised AMF abundance and richness, and strengthened the interactions among AMF taxa because of nutrient exchange. Thus, increasing habitat heterogeneity with abundant shrub diversity, but soil nutrient limitation, enriches AMF abundance and diversity. [ABSTRACT FROM AUTHOR]

Diazotrophs and arbuscular mycorrhizal fungi (AMF) are important functional microbes that provide and transport nutrients to plants. Diazotroph and AMF diversity and community composition were investigated in karst mature forests (MFs) and non-karst forests, as well as in croplands (CRs) as a reference. Diazotroph diversity and community composition significantly shifted in MFs between karst and non-karst soils, with a higher diazotroph richness and Shannon index in karst MFs than in non-karst soils. Similar levels of AMF diversity and community composition were observed between karst and non-karst CRs and MFs. According to the co-occurrence network analysis results, the pairs of correlation links within the diazotroph and AMF groups were higher in karst MFs than in non-karst MFs, whereas this interaction was lower in karst CRs than in non-karst CRs. The diazotroph genera Bradyrhizobium and Anabaena and the AMF genera Glomus and Rhizophagus were mostly correlated with other species in both karst and non-karst soils. Diazotrophs and AMF communities were mainly affected available nutrients (e.g., nitrogen and phosphorus) and environmental factors (e.g., temperature and precipitation), respectively. Soil calcium content was an important factor that affected the distributions of diazotrophs and AMF between karst and non-karst soils. Overall, our study suggested that the increased interactions between diazotrophs and AMF in karst forests, as compared with those in non-karst soil, led to the stability of the diazotrophs and AMF co-occurrence patterns for maintaining nutrients that are effectively absorbed and utilized. Thus, strengthening the cooperative relationships between diazotrophs and AMF are important and necessary in calcareous soils during natural vegetation restoration. [Display omitted] • Diazotroph diversity increased in karst mature forest compared with that in non-karst soil. • Arbuscular mycorrhizal fungal (AMF) diversity was similar in karst and non-karst soil. • Karst mature forest strengthened interactions among diazotroph and AMF. • AMF were more sensitive to climate; diazotrophs were more sensitive to nutrients. [ABSTRACT FROM AUTHOR]