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Background: China is a country with a burden of high rates of both TB and multidrug-resistant TB (MDR-TB). However, published data on pyrazinamide (PZA) resistance are still limited in Hunan province, China. This study investigated the prevalence, transmission, and genetic diversity of PZA resistance among multidrug-resistant Mycobacterium tuberculosis isolates in Hunan province. Methods: Drug susceptibility testing (DST) with the Bactec MGIT 960 PZA kit and pyrazinamidase (PZase) testing were conducted on all 298 MDR clinical isolates. Moreover, 24-locus MIRU-VNTR and DNA sequencing of pncA, rpsA, and panD genes were conducted on 180 PZA-resistant (PZA-R) isolates. Results: The prevalence of PZA resistance among MDR-TB strains reached 60.4%. Newly diagnosed PZA-R TB patients and clustered isolates with identical pncA, rpsA, and panD mutations showed that transmission of PZA-R isolates played a significant role in the formation of PZA-R TB. Ninety-eight mutation patterns were observed in the pncA among 180 PZA-R isolates, and seventy-one (72.4%) were point mutations. Twenty-four of these mutations are new, including 2 base substitutions (V93G and T153S) and 22 nucleotide deletions or insertions. The W119C was found in PZA-S isolates, on the other hand, F94L and V155A mutations were found in both PZA resistant and susceptible isolates with positive PZase activity, indicating that they were not associated with PZA resistance. This is not entirely in line with the WHO catalogue. Ten novel rpsA mutations were found in 10 PZA-R isolates, which all combined with mutations in pncA. Thus, it is unpredictable whether these mutations in rpsA can impact PZA resistance. No panD mutation was found in all PZA-R isolates. Conclusion: DNA sequencing of pncA and PZase activity testing have great potential in predicting PZA resistance. [ABSTRACT FROM AUTHOR]

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]

In biodiverse forest ecosystems, plant diversity has been reported to increase plant-derived lignin accumulation and soil organic carbon (SOC) storage. However, little is known about the fate of lignin and its degradation dynamics from plant to soil. This process is critical for the formation of SOC, especially in natural forest ecosystems with diverse plant species. This study presents the lignin biomarker characteristics of several common plant species and in mixed litter. The study was conducted in 45 plots along a plant species diversity gradient in a subtropical forest located in southwest China. Our results demonstrate that lignin content and its biochemical characteristics in plant leaves vary among species, while different plant species also alter the content of lignin and its monomeric compounds in the litter. Lignin compounds are gradually disintegrated from plant leaf to litter and then to soil, further indicating that plant-derived lignin from plant sources contributes to the formation and accumulation of forest SOC. These findings provide novel information on the linkage between tree species diversity and lignin accumulation while indicating the role of plant-derived lignin on SOC storage. These results may be useful in predicting forest soil C dynamics in Earth system models. [ABSTRACT FROM AUTHOR]

The stability of soil organic matter (SOM) plays a critical role in soil carbon (C) dynamics under global warming. However, the factors influencing SOM stability, particularly the significance of bedrock geochemistry and its hierarchical relationship with climate and soil properties, remain poorly understood. To address this gap, we conducted a study along a large climatic gradient (Δtemperature > 9 °C) in the subtropical karst forests of southwest China, quantifying SOM stability using thermal analysis and investigating the contributions of bedrock geochemistry, climate, and soil properties. Our results showed that SOM stability was positively correlated with mineral-associated organic C (MAOC) rather than particulate organic C. Hierarchical partitioning analysis further demonstrated that bedrock geochemistry was the predominant contributor to SOM stability variance, accounting for 23.7%. Following this, soil minerals contributed to 21.1%–22.6% of the variance, the mean annual temperature to 20.3%, and microbial biomass C to 17.2%. In particular, bedrock geochemistry—specifically the presence of calcium-rich bedrock—was found to enhance SOM stability by promoting the accumulation of exchangeable calcium and calcium carbonate in soils. Additionally, high temperature improved SOM stability by increasing the content and proportion of MAOC and soil pH. These results highlight the fundamental role of bedrock geochemistry in controlling SOM stability and emphasize the importance of considering hierarchical relationships among bedrock–soil–climate interactions for evaluating soil C dynamics. [ABSTRACT FROM AUTHOR]

Lithology has such an important effect on the sustainability of soil carbon (C) pools. Forests are an important part of terrestrial C sinks; yet, it is unclear whether their soil carbon sensitivity to temperature changes is regulated by lithology, especially in karst ecosystems, which are widely distributed globally. Along a climate gradient in the subtropical region of southwest China, we compared the contents of soil organic C (SOC) and total N (TN) in karst and non-karst forests. The data were analyzed and processed using ANOVA, regression analysis, and random forest. The results showed that the karst forests had significantly higher SOC and TN contents but lower ratio of SOC to TN (C:N) than non-karst forests, mainly because of the higher soil calcium (Ca) content and microbial biomass. With rising mean annual temperature (MAT), SOC and TN contents in non-karst forests significantly decreased, whereas in karst forests they were not correlated with MAT; while, the opposite was true for C:N. In karst forests, soil Ca constrain warming induced decomposition of SOC and TN by forming stable complexes with SOM through exchangeable Ca, and by promoting aggregate stability through the role of calcium carbonate. The correlation between δ13C and the logarithm of SOC concentration also supported that conclusion. In karst forests compared to non-karst forests, soil C pools are larger and less sensitive to regional temperature change. Nevertheless, climate warming may still accelerate soil C loss in karst forests by increasing microbial C limitation. Thus, soil C sequestration potential and loss risk coexist in karst areas. The ratio of SOC to TN (C:N) is regulated through appropriate management measures in the process of karst vegetation restoration, thus promoting long-term stable sequestration of soil carbon pools. [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]

Background: Tuberculosis (TB) seriously threatens individual and public health. Recently, TB outbreaks in schools have been reported more frequently in China and have attracted widespread attention. We reported three TB outbreaks in high schools in Hunan Province, China. Methods: When a tuberculosis patient was reported in a school, we carried out field epidemiological investigations, including tuberculin skin testing (TST), chest X-ray (CXR) and laboratory test for all close contacts, and whole-genome sequencing (WGS) analyses to understand the transmission patterns, the causes and the risk factors for the outbreaks, thereby providing a foundation for the control of TB epidemics in schools. Results: A total of 49 students with TB patients were identified in the three schools where TB outbreaks occurred, including nine patients in School A, 14 patients in School B, and 26 patients in School C. In Schools A, B and C, the putative attack rates in the classes of the index case were 13.8% (8/58), 7.6% (5/66), and 40.4% (21/52), while the putative attack rates of expanding screening in the school were 0.3% (1/361), 0.2% (9/3955), and 0.2% (5/2080), respectively. Thirteen patients had patient delay, with a median delay interval of 69 days (IQR 30.5– 113 days). Twelve patients had a healthcare diagnostic delay with a median delay interval of 32 days (IQR 24– 82 days). Phylogenetic analysis of culture-positive patients revealed that most of them shared a small genetic distance (≤ 12 SNPs), with three separate genetic clusters (including one MDR-TB genomic cluster), indicating the recent transmission of Mycobacterium tuberculosis strains. Conclusion: This combination of field investigation and WGS analysis revealed the transmission of three TB outbreaks in schools. Reinforced implementation is needed to improve timely case finding and reduce diagnosis delay in routine TB control in the school population. [ABSTRACT FROM AUTHOR]

Highlights • SOC recovers to levels of primary forest within a shorter period than soil N. • Recuperation time of SOC and soil N had opposite patterns in topsoil and subsoil. • Soil N is capable of sustaining SOC accumulation in the long term in karst regions. Abstract Vegetation restoration following agricultural abandonment is an effective method for soil organic carbon (SOC) sequestration. However, SOC dynamics during post-agriculture succession in different soil layers, and its regulation by soil nitrogen (N), are not well understood. We investigated SOC and soil N dynamics during post-agriculture succession at soil depths of 0–10, 10–20, 20–30, and 30–50 cm in a subtropical karst area in southwest China. The succession sequence included grassland (∼9 years), shrubland (∼25 years), secondary forest (∼52 years), and primary forest, with cropland as a reference. In the 0–50 cm soil profile, the SOC and soil N stocks will recover to the primary forest level in ∼74 years at a rate of 112.35 g C m−2 yr−1 and in ∼100 years at a rate of 12.07 g N m−2 yr−1, respectively. The accumulation rate of SOC and soil N was higher in the topsoil (0–20 cm) than in the subsoil (20–50 cm). The estimated time for SOC stock to recover to the primary forest level in topsoil and subsoil was similar (72 and 76 years, respectively), whereas that for soil N stock require more time in topsoil than in subsoil (106 and 89 years, respectively). The higher rate of relative N stock change than that of SOC suggests that progressive N limitation does not occur in the long term following agricultural abandonment. Our results highlight the importance of soil depth and soil N in determining SOC change for secondary succession. Furthermore, the results suggest that, compared to that of previous studies, which considered only surface soil in the karst regions of southwest China, the recovery period of C and N in soil profile may be longer than that assumed previously. [ABSTRACT FROM AUTHOR]

• AMF richness increased at high temperature levels in shrubland and mature forest. • AMF community was more sensitive to climatic levels than that of diazotrophs. • High temperature and precipitation strengthened AMF-diazotroph interactions. • Glomus and Bradyrhizobium contributed to the most correlation links in co-occurrence patterns. Arbuscular mycorrhizal fungi (AMF) and diazotrophs have the potential for nutrient transfer and biological nitrogen fixation in ecosystems, respectively. However, their response to vegetation restoration remains unclear, especially under varying temperature and precipitation levels in karst ecosystems. This study aimed to understand the effects of three climatic levels within four natural and managed vegetation restoration types on the diversity and community composition of AMF and diazotrophs. The interactive effects of temperature, precipitation, and vegetation types affected AMF diversity, while diazotroph diversity was not affected. Under conditions of natural vegetation restoration, there was an increase in AMF diversity in response to increasing temperature and precipitation. AMF richness was higher in shrubland and mature forest than in cropland when temperatures were over 20 ℃ and precipitation was high. Thus, in terms of diversity, AMF were more responsive to changes in climatic conditions and vegetation recovery than diazotrophs. Both AMF and diazotroph community compositions were affected by temperature and vegetation type. The relative abundances of AMF groups (e.g., Gigaspora , Glomus , and Septoglomus) and diazotroph taxa (e.g., Frankia) increased at temperatures above 18 ℃. The relative abundances of the AMF genus Glomus and the diazotroph genus Bradyrhizobium in shrubland and mature forest were higher than those in cropland, while abundances of the AMF genus Septoglomus and diazotroph genus Anabaena increased in cropland. Network complexity increased with increasing temperature and precipitation between AMF and diazotroph taxa. Glomus and Bradyrhizobium showed the most links with other groups, confirming that the dominant genera perform well in the co-occurrence network. These results suggested high hydrothermal regions resist rapid nutrient decomposition by strengthening the interactions between AMF and diazotrophs, especially between the abundant groups Glomus and Bradyrhizobium. Management to increase AMF and diazotroph abundance during vegetation recovery in high climate level may stimulate nutrient absorption and transport. [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]

• Natural and managed vegetation restoration were compared in a karst region in China. • PLFAs in topsoil were higher after 15 years of restoration than in cropland. • AMF was significantly higher in natural than in managed restored vegetation. • SOC and the SOC:N ratio affected the abundance of soil microbial communities. • Natural vegetation restoration has more potential to improve soil fertility. The soil microbial community is a key indicator to evaluate the effectiveness of vegetation restoration in degraded ecosystems. However, few studies have simultaneously compared the effects of managed and natural vegetation restoration strategies on the soil microbial community in the ecologically fragile karst region using signature lipid biomarker analysis to provide information on a variety of microbial properties. Here, phospholipid fatty acids (PLFAs) in the soil microbial community were measured following different restoration strategies in a karst region of southwest China. Managed vegetation restoration (including restoration with plantation forest, forage grass, and a combination of plantation forest and forage grass) and natural vegetation restoration (spontaneous regeneration to natural grassland) were compared, using cropland as a reference. The abundance of total PLFAs and the PLFAs of four microbial functional groups (bacteria, fungi, actinomycetes, and arbuscular mycorrhizal fungi [AMF]) significantly increased in the topsoil (0–5 cm soil depth) following vegetation restoration. In the sub-topsoil layer (5–10 cm soil depth), the abundance of PLFAs was not significantly higher than that in the cropland, except in AMF in natural vegetation restoration. Principal component analysis indicated that the microbial PLFA composition differed between the restoration strategies, and the abundance of AMF PLFAs was significantly higher in natural than in managed vegetation restoration for both soil depths. The ratio of soil organic carbon to total nitrogen and dissolved organic carbon content were the primary factors affecting the abundance of soil microbial communities in the topsoil and sub-topsoil, respectively. In addition, soil pH served as another explanatory variable for the topsoil. Our findings suggest that vegetation restoration over a relatively short period (15 years) mainly improved topsoil fertility. Moreover, natural vegetation restoration may be superior to managed vegetation restoration for the maintenance of multiple ecosystem functions in the short term in the karst regions, owing to the potentially significant role of AMF. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) have been found to help plants adapt to water deficit conditions. However, it still lacks filed evidence on how AMF affect plant physiology and soil microbial communities under natural extreme drought events. Here, we conducted an AMF-inoculation and legume-intercropping (Medicago sativa) field experiment in a forage (Broussonetia papyrifera) monoculture ecosystem, and assessed the effects of AMF on plants and soil microbes during a severe drought event lasting for 40 d. The results showed that the mycorrhizal colonization rate was significantly higher for M. sativa than B. papyrifera. In plots with both B. papyrifera and M. sativa , the physiological properties (e.g., diurnal range of water potential and malondialdehyde concentration) of M. sativa were better in the AMF-inoculation plots than in non-inoculation plots; the trend was opposite for B. papyrifera. AMF-inoculation significantly increased the aboveground productivity of M. sativa by increasing diurnal range of water potential and stem water content during the drought event, resulting in more severe soil water deficits. AMF-inoculation or/and legume-intercropping weakened taxonomic interactions (i.e., edges) and increased the modularity of co-occurrence networks compared with the control. The structural equation model analysis indicated that soil nutrients had a direct positive correlation with soil microbial community composition, whereas soil nutrients and moisture had an indirect negative correlation with soil microbial community diversity by inducing changes in aboveground biomass of B. papyrifera. Overall, AMF-inoculation helps M. sativa acquire water during the drought event, which exacerbates soil water deficits and thereby may increase interspecific water competition between B. papyrifera and M. sativa. AMF-inoculation or/and legume - intercropping maintain the stability of microbial networks by weakening taxonomic interactions and increasing the modularity under the extreme drought event. Our findings improve the understanding of AMF effects on plant-plant and plant-soil interactions under climate extremes. [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]