Arbuscular mycorrhiza (AM) is one of the oldest symbionts between plants and soil microorganisms, and about 80% terrestrial plant species can associate with AM fungi on earth. Because of the stable climate and poor soil phosphorus content in tropical and subtropical forests, this mutualistic symbiosis is much more common there. Previous studies have extensively investigated the diversity of AM fungi in tropical and subtropical forests, and have shown that AM fungi can promote plant recruitment and growth. However, this positive effect of AM fungi on plants (i.e., the positive plant-soil feedback) can weaken the contribution of the negative plant-soil feedback (caused by soil-borne pathogens) to maintaining tree species diversity, which appears to contradict with the surprisingly high tree diversity and high proportion of rare tree species in tropical and subtropical forests. Recently, a mounting number of empirical studies have found that the diversity of AM fungi varies significantly in different habitats and AM colonization depends on the identity of host species, thereby affecting the fitness of plants and further shaping the plant community structure. Through synthesizing the current research about the diversity of AM fungi in promoting plant coexistence and maintaining community diversity, we expect to put forward a promising study direction for testing the “rare species advantage” hypothesis, therefore improving the conservation of rare plant species.

Selenium is an essential micronutrient element for humans. The range between “beneficial” and “harmful” levels of selenium is very narrow, so biofortification through plants is a safe and effective way to supplement selenium. This article reviewed the processes of selenium uptake, transport, and metabolism in plants. Plants mainly absorb selenate, selenite, and organic selenium from soil. The root system has different absorption mechanisms for different forms of selenium, and the absorption process is participated by different transporters. The absorbed selenium is mainly transported in plants in the form of selenate ion, transported to the aboveground through the xylem and the phloem, and metabolized under the action of various enzymes. Finally, part of the selenium absorbed by the roots is stored in the plant as organic selenium, and the other part is released into the atmosphere in the form of selenide. This article also focuses on the effects of different types of rhizosphere microorganisms on plant selenium biofortification. Arbuscular mycorrhizal fungi, ectomycorrhizal fungi, and rhizosphere promoting bacteria can promote the absorption of selenium in plants to a certain extent, but their internal mechanisms are still unclear. Based on the current research status, the future research focuses are put forward: 1) the process of selenium absorption by plants and its gene regulation; 2) the underlying mechanism and application potential of microorganisms on selenium biofortification in plants.

Aims Understanding the effects of shrub encroachment on plant and soil microorganisms in the forest-grassland ecotone will help improve the understanding and management of shrub encroachment in the forest-grassland ecotone.

Methods In this study, different levels (light, moderate and heavy) of shrub encroachment were selected in the forest-grassland ecotone of Dongling Mountain Nature Reserve in Beijing, to explore the effects of shrub encroachment on plant diversity, soil microbial diversity, plant individual trait and soil nutrients by plot method and high-throughput sequencing technology. The correlation between plant diversity, soil microbial diversity, plant individual trait and soil nutrients were also developed in order to further explore the effects of shrub encroachment on plants and soil microorganisms and associated mechanisms.

Important findings Our results showed that: 1) Shrub encroachment significantly reduced the diversity of plants with the different responses of arbor, shrub and herb, among which the diversity index of herb plants decreased in the largest level. 2) Shrub encroachment significantly increased the diversity of soil fungal microorganisms. 3) Shrub encroachment significantly increased the height and crown width of shrubs, while soil total nitrogen and organic carbon contents increased significantly with the increasing shrub encroachment level. 4) The partial least squares path model (PLS-PM) revealed that shrub encroachment had a direct impact on plant and soil microorganisms, whereas plant individual trait and soil nutrients did not have a direct impact on them. The redundancy analysis (RDA) further showed that shrub height made great contribution to the interpretation of changes in plant diversity, and soil total nitrogen content was the main factor in affecting soil microbial diversity. There was a stronger correlation of soil fungal microbial diversity with plant diversity than its relationship with soil bacterial microbial.

Aims The aim of this research was to clarify the effects of intercropping and inoculation with arbuscular mycorrhizal fungi (AMF) on carbon transport and phosphorus uptake in black locust (Robinia pseudoacacia) and konjac (Amorphophallus konjac). The results could provide empirical evidence to reveal the mechanisms of black locust intercropping for disease control and plant growth promotion of konjac, and popularize the green and high-yielding cultivation technique of konjac under black locust.

Methods The experiment was carried out in two-compartment rhizoboxes separated by a 25-μm nylon net, each of which comprised compartment A (non-inoculated or AMF-inoculated black locust) and compartment B (monocropped black locust or intercropped konjac). A ¹³C stable isotope labeling technique was used to label the leaves of black locust in compartment A with ¹³CO₂. Carbon transport from black locust to konjac and the effects of AMF colonization on agronomic traits, ¹³C abundance, and phosphorus content in both crops were investigated.

Important findings The result showed that: (1) After inoculation, the AMF infection rate of black locust and konjac plants by hyphal links in compartment B reached 47.1% and 60.4%, respectively. For black locust, this AMF infection rate was 14.1% lower than that of directly inoculated plants under monocropping. In the case of intercropping, the biomass (dry mass) of AMF-inoculated konjac plants was 9.7% (aboveground parts) and 36.2% (belowground roots) higher than that of non-inoculated plants. (2) Compared with the non-inoculated plants under monocropping, the carbon fixed by photosynthesis of black locust plants in other treatments (non-inoculated + intercropping, inoculated + monocropping, and inoculated + intercropping) was mainly allocated to the plant roots and rhizosphere soil in compartment A, and more carbon passed through the nylon net in the form of root exudates to reach the rhizosphere of neighboring crop plants. (3) Compared with the respective non-inoculated controls, AMF inoculation in the monocropping and intercropping systems prominently improved phosphorus contents in the leaves, stems/petioles, roots, and total plants of black locust and konjac in compartment B. The findings suggest that AMF colonization could facilitate carbon transport from black locust to the rhizosphere soil and plant tissues of konjac. Intercropping konjac with black locust is an effective practice to promote AMF colonization and phosphorus uptake by both host plants.

Aims Fire is an important disturbance factor in the northern forest ecosystem, and black carbon, a product of fire, widely exists in most forest soils. Many studies have shown the positive impact of black carbon on plant yield, but little is known about the synergy between black carbon and microorganisms (such as mycorrhizal fungi) which can promote plant growth. Ectomycorrhiza (ECM) fungi is like a bridge between coniferous trees and soil in the northern forest ecosystem. Exploring the changes of ECM fungal community after fire can provide a theoretical basis for the carbon pool restoration and help with scientific management of the northern forest ecosystem after fire.

Methods In this study, Larix gmelinii forest in the Da Hinggan Mountains was taken as the research object. Samples were taken at the beginning of the growing season (June) and at the end of the growing season (September) after fire disturbance. ECM fungi were identified by high-throughput sequencing method to explore the changes and key influencing factors of ECM fungal community under the treatment of fire and black carbon addition.

Important findings The results showed that: (1) During the growing season, compared with CK, the α-diversity of ECM fungal community treated by fire decreased significantly by 31.52%, while it increased significantly by 49.02% under black carbon addition treatment. There were significant differences in the β-diversity of of ECM fungal community under fire and black carbon addition treatments during the growing season. (2) During the growing season, the abundance of ECM fungi treated by fire decreased significantly by 46.35%, but the fire treatment significantly increased Basidiomycetes species abundance, while black carbon addition treatment increased Ascomycetes and Basidiomycetes species abundance. (3) During the growing season, the composition of ECM fungal community in Larix gmelini forest was significantly affected by soil pH, water content and total nitrogen content under the fire and black carbon addition treatments, but it was positively correlated with soil pH and total nitrogen content and negatively correlated with soil water content in the black carbon addition treatment. The results of this study showed that fire reduced the diversity of ECM fungi in Larix gmelinii forest during the growing season, and significantly reduced the abundance of ECM fungi. However, the addition of black carbon after fire may change this negative effect. By affecting the changes of soil pH and soil nitrogen content, black carbon promoted the recovery of ECM fungi and increased its diversity. Therefore, the long-term impact of black carbon on ECM fungal community should be continuously monitored in the future.

Aims Endophyte is a new microbial resource, which has a complex micro-ecological relationship with plants. In this paper, the antagonistic effect of endophytic fungi on the growth of salt-tolerant plants was confirmed by adding endophytic fungi to the plants and testing the physiological characteristics and biomass of the seedlings.

Methods Two salt-tolerant endophytic fungi Botryosphaeria sp. Z1 (T3), Hypoxylon sp. Y6 (T4), and their mixture (T2) were cultured in solid fermentation and added to potted soil planted with seedlings of Casuarina equisetifolia at different salinity (mass fraction: 0, 3‰, 6‰ and 9‰), which were treated with an added fungi of seedlings. The addition of microbiological medium (T1) and no added microbiological medium (CK) were treated as two experimental controls, which was to confirm the effect of the fungi, but not the microbiological medium. Samples were taken at 15 day intervals, four times, for a total of 60 days, and the relative electronic conductivity (REC), malondialdehyde (MDA) content, soluble sugar (SS) content, soluble protein (SP) content, proline (PRO) content, superoxide dismutase (SOD) activity, peroxidase (POD) activity, catalase (CAT) activity, reactive oxygen (H₂O₂) content of leaves and the biomass of seedling were determined each time.

Important findings We found that the biomass of seedlings treated by fungal strain was significantly increased under salt stress, and the physiological characteristics were significantly affected by soil salinity, time and fungal species. At 3‰ salinity, the contents of SS and SP, and the activity of SOD and CAT were higher in T2 treatment than in CK and T1 after 15 days of treatment, but the REC was significantly lower in T2, T3 and T4 treatments during the stress period. At 9‰ salinity, T2 treatment significantly reduced the REC and the contents of H₂O₂ and MDA, but significantly increased the content of SS and the activity of SOD and CAT. Especially, SP content and POD activity were also significantly increased in T2 treatment after 60 days. A stepwise regression was used to model the relationship between physiological characteristics and biomass of seedlings treated with the strains, and the path analysis showed that REC, POD activity and SS content were the main physiological factors affecting biomass. In conclusion, the effects of different fungi on the content of osmoregulatory substances, oxidase activity and biomass of seedlings were different, and the antagonistic effect of the mixed fungi was the most obviously. Thus, the relationship between osmotic regulatory substances, antioxidant enzymes, biomass and endophytic fungi of C. equisetifolia under salt stress was clarified, which provided a basic for the further study on the stress resistant engineering fungi for C. equisetifolia.

Aims The relationship between biodiversity and ecosystem function is one of the hotspots in ecological research. In the past, the research on the relationship between biodiversity and ecosystem function only focused on the experimental or observational investigation of single ecosystem function (SEF), ignoring the most essential value that ecosystem can provide multiple functions and services at the same time. Identifying the relationship between plant functional diversity and ecosystem multifunctionality (EMF) can provide a clear understanding of changes in ecosystem function.

Methods In this study, Bayanbulak alpine meadow was taken as the study area, and five altitude sites were set at an interval of 200 m from 2 194 to 3 062 m above sea level. Soil total nitrogen content, nitrate nitrogen content, ammonium nitrogen content, total phosphorus content, available phosphorus content, total potassium content, available potassium content, soil density, aboveground and underground biomass of plant community were selected to characterize EMF, which were closely related to nutrient cycling, soil organic carbon accumulation and plant growth.

Important findings (1) The species composition of the plant community varied greatly along the altitude gradient, and the species richness at the altitude of 2 600 m was significantly higher than that at the other altitudes. Functional evenness index (FEve), functional richness index (FRic) and functional dispersion index (FDis) all showed a “single peak” trend with the rise of altitude, and the highest values were found at 2 600, 2 800 and 2 800 m, respectively. Rao’ quadratic entropy (Rao’Q) showed a monotonically decreasing trend. (2) FRic and FDis at each altitude were positively correlated with soil EMF, which accounted for 47% and 43% of the variation in EMF, respectively. FEve was significantly correlated with nutrient cycling index and soil organic carbon storage index at the altitude of 2 600 m. Rao’Q at 3 000 m was significantly correlated with soil nutrient cycling index, organic carbon storage and EMF. The relationship between plant functional diversity and EMF along the altitude gradient was analyzed by constructing a structural equation model, which showed that altitude could exert impacts on EMF through changing functional diversity, with the greatest effect of functional richness on EMF. In conclusion, with the alteration of altitude, the functional diversity may result in changes, thereby affect the SEF and EMF, and the functional diversity is important to maintain the EMF.

Aims Investigating the needle phenotypic variation and its geographical distribution pattern of related species complexes will aid in understanding conifer geographic variation, population dynamics, and physiological and ecological responses to geographical climates. Here we focus on the Pinus kesiya, P. yunnanensis, and the hybrid species P. kesiyavar. langbianensis, which are primarily distributed across tropical and subtropical Southeast Asia, exhibiting abundant climate and genetic variation.

Methods We selected thirty-one representative populations covering the distribution areas of three pine species, and sampled ten individuals from each population. Eight traits were measured, including needle length, stomatal density, stomatal guard cell length, stomatal guard cell width, woody thickening layer length, woody thickening layer width, stomatal cavity length, and stomatal cavity width. Variation between species and populations was assessed using a nested variance analysis. Principal components analysis was applied to evaluate the underlying dimensionality of the needle variation. Clustering analysis among populations was performed using the Ward method to infer the population structure. Pearson’s correlation coefficient between latitude and needle characters was assessed. Finally, a multiple linear regression model was used to identify the main environmental factors influencing needle trait variation.

Important findings The variation coefficients of the eight needle traits ranged from 12.01% to 34.08% across populations. The phenotypic differentiation coefficient was higher for stomata guard cell length, woody thickening layer length and width, needle length, and stomatal density. Most morphological needle characteristics were significantly different between P. yunnanensis and P. kesiya,while P. kesiyavar. langbianensis showed intermediate values between the two parental pines. Hierarchical clustering analysis showed that the variation pattern of needle traits was related to geographical region. Needle length and stomatal density were positively correlated with latitude, while the stomatal cavity length and width were negatively correlated with latitude. The key environmental factors affecting the needle traits of the three pine species were mean temperature during the driest quarter, precipitation seasonality, mean diurnal range, precipitation during wettest month, and precipitation during the driest month. The needle traits of the three pine species displayed high interspecific and interpopulation variation. The significant latitudinal gradient trend in needle trait variation indicates long-term evolutionary adaptation to the environment. The response of needle character variation to environmental factors can provide essential insights for geographical provenance selection in afforestation breeding

Aims Nutrient reabsorption is one of the important strategies for plants to adapt to the environment. In this study, we investigated the nutrient content of green and senescent leaves and soil in the Carex muliensis herb swamp in August and October, in order to examine soil nutrient content and nutrient reabsorption efficiency, as well as the relationship between them under the water level drop and natural water level based on the simulation experiment.

Methods Single factor analysis of variance was used to compare the differences of leaf nitrogen (N) content, phosphorus (P) content, soil available N content, soil available P content, leaf N:P and nutrient reabsorption efficiency among different treatments, and the relationship between soil available N, P contents and nutrient reabsorption efficiency was also fitted by univariate linear regression. Pearson correlation analysis was used to analyze the relationship of N, P contents, N:P with nutrient reabsorption efficiency in leaves of C. muliensis.

Important findings The results showed that the soil available N content increased and the available P content decreased after the water level drop, which further led to an increase in the N content and a decrease in the P content of the green leaves, a decrease in the N content and P content of the senescent leaves, and an increase in the N and P reabsorption efficiency of the leaves of C. muliensis. These results indicated that the decreased water level affected the nutrient content of the green leaves of C. muliensis by changing the contents of soil available nutrients, and thus affected the nutrient contents of the senescent leaves by changing the plant nutrient acquisition ability (i.e. root number and root length), and consequently affected the nutrient reabsorption efficiency.

Aims The objective of this study was to reveal the effects of climate warming on fine root dynamics of a plantation in subtropical China.

Methods An in situ soil warming experiment in a mature Cunninghamia lanceolataplantation was conducted at the Fujian Sanming Forest Ecosystem National Observation and Research Station. The effects of soil warming on the growth, morphology and physiological metabolism characteristics of fine roots in this mature plantation in different seasons were investigated by using the in-growth core method.

Important findings In the rainy season, warming significantly increased the growth of 0-1 mm fine roots and total fine roots (0-2 mm) by 109.9 % and 78.2% respectively, and also increased the specific root length (SRL) and soluble sugar content of 0-1 mm fine roots by 28.8% and 41.5% respectively, compared with the control. However, warming significantly decreased the root specific respiration rate (SRR) and starch content of total fine roots by 64.1% and 15.9% respectively. In the dry season, there were no significant changes in the growth and morphological indices of 0-1 mm and 1-2 mm fine roots after warming, while the SRR of 0-1 mm fine roots and the contents of starch and non-structural carbohydrates (NSC) of 1-2 mm fine roots were significantly reduced by 60.7%, 43.9% and 14.2% respectively. Therefore, under future climate warming, the mature C. lanceolata plantation may have strong adaptability in the subtropical region. During the rainy season, the mature C. lanceolata plantation maintains normal physiological activities by increasing fine root SRL to absorb more resources and promoting the transformation of starch to soluble sugar, so as to promote the growth of fine roots in response to warming. In the dry season, the mature C. lanceolata plantation responds to the warming by reducing the SRR of fine roots to reduce internal nutrient depletion and increasing the NSC utilization to improve water transport efficiency to maintain normal fine root growth; adjusting the SRL, specific root surface area and root tissue density of fine roots may not be the main strategies for the mature C. lanceolata plantation in response to warming.

Aims This study aimed to reveal the impacts of long-term vegetation restorations on soil total organic carbon content, active organic carbon fractions content and enzyme activities in karst rocky desertification ecosystems, which provided scientific bases for the management of degraded karst ecosystem and the carbon regulation by land use in southwest China.

Methods In the typical karst area of southwest China, seven representative vegetation restoration measures, that were, Cupressus funebris planting, Tectona grandisplanting, Zanthoxylum bungeanum planting, Hylocereus undatus planting, Lonicera japonica planting, Pennisetum sinese planting and Amomum villosum planting, were selected. Responses of contents of soil total organic carbon (TSOC), microbial biomass carbon (MBC), dissolved organic carbon (DOC) and easy oxidation organic carbon (EOC) and enzyme activities of urease (URE), sucrase (SUC), amylase (AMY) and alkaline phosphatase (ALP) to these vegetation restorations were investigated.

Important findings (1) The vegetation restorations significantly improved TSOC distribution and accumulation, and remarkably changed soil active organic carbon fraction contents and their proportions to TSOC in the karst rocky desertification ecosystem. But the impacts of different vegetation restorations on contents of TSOC and its active fractions were obviously different. The TSOC contents and stocks under C. funebris and L. japonicasoils were higher, while those of the two measures under artificial grassland soils (P. sinese and A. villosum planting) were the lowest among the seven vegetation restorations. The EOC and MBC contents under C. funebrisand L. japonica soils were higher, while DOC content under Z. bungeanum soil were higher compared to other vegetation restorations. (2) The four soil enzymes activities were all significantly increased in various levels by the long-term vegetation restorations. However, response mechanisms of different soil enzyme activities to the vegetation restorations were also different. The URE activities of the other six restoration measures were significantly higher compared to the control plot (CK) except Z. bungeanum planting. The SUC and ALP activities of the remaining six restoration measures were significantly higher than those of CK except P. sinese planting. Among the seven restorations, only AMY activity under C. funebris soil was significantly higher than that of CK. (3) There were significant correlations between soil enzyme activities and contents of TSOC and its active fractions. But correlations of different enzyme activities with TSOC and its active fraction contents were obviously different. Correlations of AMY and ALP activities with TSOC and its active fraction contents were stronger than that of URE and SUC. While the ALP and AMY activities were closely related to soil organic carbon accumulation, and mineralization rate and active organic carbon fractions in the karst rocky desertification ecosystem.

Aims The subalpine forests of southwest China belongs to a typical seasonal frozen soil area. This study aimed to explore the effects of freeze-thaw changes on the soil physicochemical properties and enzyme activities under forest soils in response to climate warming.

Methods Infrared radiation heaters were applied to simulate climate warming. Soils in the root zone of Picea asperata and Fargesia nitida were collected to explore the effects of warming on soil freeze-thaw cycles, soil physicochemical properties and enzyme activities. Meanwhile, soil incubation experiments were conducted to further analyze the effects of different freeze-thaw cycles on soil properties.

Important findings Our results showed that (1) Experimental warming increased the soil temperatures by 2.85 and 2.13 °C, decreased freezing days by 60 and 32 days, and also declined freeze-thaw cycles from 1-3 times to 0 time at the 5 cm and 15 cm soil depths, respectively. (2) Warming increased the contents of soil total nitrogen (TN), dissolved organic nitrogen (DON) and microbial biomass nitrogen (MBN), but significantly reduced the content of ammonium nitrogen (NH₄⁺-N) under both P. asperata and F. nitida plots. The soil freezing days and number of freeze-thaw cycles were significantly negatively correlated with TN and DON contents, and significantly positively correlated with NH₄⁺-N content. (3) Warming significantly promoted the activity of β-N-acetylglucosaminidase (NAG), but significantly inhibited the activity of urease (Ure) under the root zone soil of the two species. The activities of NAG and Ure were significantly correlated with freezing days and the number of freeze-thaw cycles. (4) Similar to results of the field study, the simulated freeze-thaw cycles significantly increased NH₄⁺-N content and 4-methylumbelliferyl-β-D-glucoside (BG) activity, but decreased NAG activity under the root zone soil of P. asperata. On the other hand, freeze-thaw cycles increased NH₄⁺-N content and reduced the activities of NAG and BG under the root zone soil of F. nitida. However, the effects of freeze-thaw cycles on the contents of nitrate nitrogen (NO₃^--N) and DON as well as the activities of Ure and protease (Pro) were different based on the results of field experiment. Redundancy analysis showed that soil enzyme activities under the root zone of F. nitida were mainly affected by DON content, whereas those parameters under the root zone of P. asperatawere significantly correlated with pH, NH₄⁺-N and DON contents. These results suggested that the disappearance of freeze-thaw cycles caused by future climate warming would significantly affect the soil physicochemical properties (especially soil nitrogen pool) and enzyme activities during non-growing season under subalpine forests of southwest China. But the underlying mechanism needs further study.