Haoqiang Zhang

Communities of arbuscular mycorrhizal fungi and bacteria in the rhizosphere of Caragana korshinkii and Hippophae rhamnoides in Zhifanggou watershed

The process of ecological restoration and reconstruction in Zhifanggou watershed forms a special ecosystem on the Loess Plateau. Little is known about the communities of arbuscular mycorrhizal fungi (AMF) and bacteria in this ecosystem. The aim of this study was to analyze the communities of AMF and bacteria, and their relationship in the rhizosphere of Caragana korshinkii and Hippophae rhamnoides in Zhifanggou watershed. Soil samples were collected from Zhifanggou watershed. The communities of AMF and bacteria were analyzed by using nested PCR of rDNA fragments and denaturing gradient gel electrophoresis (DGGE). Diversity analysis revealed that the bacterial Shannon diversity index was higher than that of AMF, and the AMF and bacterial Shannon diversity index in the rhizosphere of H. rhamnoides was higher than that of C. korshinkii. Principal component analysis (PCA) revealed that host plant had a significant influence on the bacterial community structure, but no strict specificity with AMF. Correlation analysis showed that the AMF communities had a significant positive correlation with the bacterial communities, and that indicated a significant effect of AMF on bacteria.

Symbiosis of Arbuscular Mycorrhizal Fungi and Robinia pseudoacacia L. Improves Root Tensile Strength and Soil Aggregate Stability.

Robinia pseudoacacia L. (black locust) is a widely planted tree species on Loess Plateau for revegetation. Due to its symbiosis forming capability with arbuscular mycorrhizal (AM) fungi, we explored the influence of arbuscular mycorrhizal fungi on plant biomass, root morphology, root tensile strength and soil aggregate stability in a pot experiment. We inoculated R. pseudoacacia with/without AM fungus (Rhizophagus irregularis or Glomus versiforme), and measured root colonization, plant growth, root morphological characters, root tensile force and tensile strength, and parameters for soil aggregate stability at twelve weeks after inoculation. AM fungi colonized more than 70% plant root, significantly improved plant growth. Meanwhile, AM fungi elevated root morphological parameters, root tensile force, root tensile strength, Glomalin-related soil protein (GRSP) content in soil, and parameters for soil aggregate stability such as water stable aggregate (WSA), mean weight diameter (MWD) and geometric mean diameter (GMD). Root length was highly correlated with WSA, MWD and GMD, while hyphae length was highly correlated with GRSP content. The improved R. pseudoacacia growth, root tensile strength and soil aggregate stability indicated that AM fungi could accelerate soil fixation and stabilization with R. pseudoacacia, and its function in revegetation on Loess Plateau deserves more attention.

Arbuscular mycorrhizas influence Lycium barbarum tolerance of water stress in a hot environment

Arbuscular mycorrhizal (AM) fungi can assist their hosts to cope with water stress and other abiotic stresses in different ways. In order to test whether AM plants have a greater capacity than control plants to cope with water stress, we investigated the water status and photosynthetic capacity of Lycium barbarum colonized or not by the AM fungus Rhizophagus irregularis under three water conditions during a hot summer. Sugar levels and transcriptional responses of both plant and AM fungus aquaporin genes in roots were analyzed. Compared with control plants, AM plants increased transpiration rate and stomatal conductance but decreased leaf relative water content under moderate water stress. Severe water stress, however, did not inhibit the quantum yield of PSII photochemistry in AM plants versus control plants. AM plants had higher expression levels of plasma membrane intrinsic proteins or tonoplast intrinsic proteins and Rir-AQP2 and lower leaf temperature than control plants under dry-hot stress. Additionally, AM plant sugar levels under normal water conditions were similar to those of control plants under moderate water stress, but sugar levels of AM plants especially increased with severe water stress. When these aspects of performance of AM and control plants under different water conditions are compared overall, AM plants displayed an obvious superiority over control plants at coping with moderate water stress in the hot environment; AM plants maintained normal photochemical processes under severe water stress, while sugar levels were affected strongly.

Effects of Nitrogen and Exogenous Rhizophagus irregularis on the Nutrient Status, Photosynthesis and Leaf Anatomy of Populus × canadensis ‘Neva’

The productivity of poplar is associated with large nitrogen (N) requirements. Exogenous arbuscular mycorrhizal fungi (AMF) show potential for use as bio-fertilizers. Understanding the interaction between N and exogenous AMF has theoretical and practical significance for poplar plantation. A pot experiment was conducted to assess the effects of N and exogenous Rhizophagus irregularis on plant growth, nutrient uptake, photosynthesis, water status, and leaf anatomical properties of Populus × canadensis ‘Neva’ in natural soil. The results showed that N fertilization increased plant growth, net photosynthesis, water status and the conduit diameter of midribs. The concentrations of carbon (C) and N in leaves were increased, but the phosphorus (P) concentration was decreased by N fertilization. The effectiveness of exogenous R. irregularis varied under different N levels. Under low N levels, exogenous R. irregularis-inoculated plants grew faster and exhibited superior photosynthetic capacity, water status and leaf conduit diameters than non-inoculated plants. Under high N levels, C, N and P concentrations were enhanced by exogenous R. irregularis inoculation. Furthermore, the average conduit diameter of midribs presented a significant positive correlation with plant growth parameters, photosynthesis, relative water content (RWC) and leaf C and N concentrations. It was concluded that exogenous R. irregularis exerted the strongest positive effects under low N levels by promoting plant growth and photosynthesis, and the fungus promoted plant nutrition decoupled from the level of N fertilization. Moreover, the improvement of plant physiological traits due to N fertilization or exogenous R. irregularis inoculation was accompanied by changes in internal anatomical properties.

Arbuscular Mycorrhizal Fungus Rhizophagus irregularis Increased Potassium Content and Expression of Genes Encoding Potassium Channels in Lycium barbarum

Potassium in plants accounts for up to 10% dry weight, and participates in different physiological processes. Under drought stress, plant requires more potassium but potassium availability in soil solutes is lowered by decreased soil water content. Forming symbiosis with arbuscular mycorrhizal (AM) fungi not only enlarges exploration range of plant for mineral nutrients and water in soil, but also improves plant drought tolerance. However, the regulation of AM fungi on plant root potassium uptake and translocation from root to shoot was less reported. In current study, the effect of an AM fungus (Rhizophagus irregularis), potassium application (0, 2, and 8 mM), and drought stress (30% field capacity) on Lycium barbarum growth and potassium status was analyzed. Ten weeks after inoculation, R. irregularis colonized more than 58% roots of L. barbarum seedlings, and increased plant growth as well as potassium content. Potassium application increased colonization rate of R. irregularis, plant growth, potassium content, and decreased root/shoot ratio. Drought stress increased colonization rate of R. irregularis and potassium content. Expression of two putative potassium channel genes in root, LbKT1 and LbSKOR, was positively correlated with potassium content in root and leaves, as well as the colonization rate of R. irregularis. The increased L. barbarum growth, potassium content and genes expression, especially under drought stress, suggested that R. irregularis could improve potassium uptake of L. barbarum root and translocation from root to shoot. Whether AM fungi could form a specific mycorrhizal pathway for plant potassium uptake deserves further studies.

Subcellular Compartmentalization and Chemical Forms of Lead Participate in Lead Tolerance of Robinia pseudoacacia L. with Funneliformis mosseae

The effect of arbuscular mycorrhizal fungus on the subcellular compartmentalization and chemical forms of lead (Pb) in Pb tolerance plants was assessed in a pot experiment in greenhouse conditions. We measured root colonization, plant growth, photosynthesis, subcellular compartmentalization and chemical forms of Pb in black locust (Robinia pseudoacacia L.) seedlings inoculated with Funneliformis mosseae isolate (BGC XJ01A) under a range of Pb treatments (0, 90, 900, and 3000 mg Pb kg-1 soil). The majority of Pb was retained in the roots of R. pseudoacacia under Pb stress, with a significantly higher retention in the inoculated seedlings. F. mosseae inoculation significantly increased the proportion of Pb in the cell wall and soluble fractions and decreased the proportion of Pb in the organelle fraction of roots, stems, and leaves, with the largest proportion of Pb segregated in the cell wall fraction. F. mosseae inoculation increased the proportion of inactive Pb (especially pectate- and protein-integrated Pb and Pb phosphate) and reduced the proportion of water-soluble Pb in the roots, stems, and leaves. The subcellular compartmentalization of Pb in different chemical forms was highly correlated with improved plant biomass, height, and photosynthesis in the inoculated seedlings. This study indicates that F. mosseae could improve Pb tolerance in R. pseudoacacia seedlings growing in Pb polluted soils.

Community diversity of bacteria and arbuscular mycorrhizal fungi in the rhizosphere of Amorpha fruticosa L., Hippophae rhamnoides L. and Robinia pseudoacacia L. in different ecological regions of Loess Plateau in Shaanxi Province of China

The research of rhizosphere microorganism community structure in degraded areas has been a focus recently. The aim of this study is to analyze the community diversity of bacteria and arbuscular mycorrhizal fungi (AMF) in the rhizosphere of Amorpha fruticosa L., Hippophae rhamnoides L. and Robinia pseudoacacia L. in three different ecological regions of Loess Plateau in Shaanxi Province of China by terminal restriction fragment length polymorphisms (T-RFLP). Results obtained that the AMF and bacterial diversity differed greatly between regions and native plants species. Species richness and the Shannon diversity index of bacteria and AMF in rhizosphere of R. pseudoacacia were higher than that of H. rhamnoides and A. fruticosa in the three regions. The results of principal component analysis and redundancy analysis (RDA) indicated that host plants had no strict specificity with both AMF and bacterial community diversity while environmental condition did great influence on AMF community diversity and organic matter content, and pH were primary influencing factor. The community diversity of AMF was significant correlative to that of bacteria (p<0.01). These results suggest that the environmental conditions exhibit greater influence on the community diversity of AMF than the host plants. And organic matter and pH are more indicative of the change of community diversity of bacteria and AMF.

Characterization of six PHT1 members in Lycium barbarum and their response to arbuscular mycorrhiza and water stress

Phosphorus (P) is vitally important for most plant processes. However, the P available to plants is present in the soil in the form of inorganic phosphate (Pi), and is often present in only limited amounts. Water stress further reduces Pi availability. Previous studies have highlighted the important roles of members of the PHOSPHATE TRANSPORTER 1 (PHT1) family and arbuscular mycorrhizal (AM) associations for Pi acquisition by plants growing in various environments. In order to understand the Pi uptake of Lycium barbarumL., a drought-tolerant ligneous species belonging to the Solanaceae family, we cloned and characterized six L. barbarum genes encoding transporter proteins belonging to the PHT1 family, and investigated their transcriptional response to AM associations and water stress. The six cloned PHT1 genes of L. barbarum had a similar evolutionary history to that of PHT1 genes found in other Solanaceae species. Three of these genes (LbPT3, LbPT4 and LbPT5) were AM-induced; the other three genes (LbPT1, LbPT2 and LbPT7) played distinct roles in Pi acquisition, translocation and remobilization in roots and leaves. AM-induced PHT1 genes maintained their function under water stress, while moderate and severe water stress upregulated non-AM-induced PHT1 genes in roots and leaves, respectively. Moreover, although LbPT1 was upregulated in AM roots under water stress, LbPT2 and LbPT7 were inhibited in AM roots, which suggested that an AM association satisfied the demand for Pi in roots under water stress and that LbPT1 may play a role in translocating Pi from roots to shoots in this situation.

Arbuscular mycorrhizal fungi alter nitrogen allocation in the leaves of Populus × canadensis ‘Neva’

Background and aimsIntra-leaf nitrogen allocation plays a pivotal role in plant growth performance; however, the effects of arbuscular mycorrhizal (AM) fungi on the allocation of nitrogen within a leaf remain poorly understood.MethodsA pot experiment was conducted with different nitrogen levels and Populus × canadensis ‘Neva’ with or without Rhizophagus irregularis inoculation. The fractions of leaf nitrogen allocated to water-soluble protein, membrane-bound protein, cell wall protein and photosynthetic apparatus were used to estimate nitrogen allocation strategy.ResultsAM fungi increased the light-saturated photosynthetic rate (Pmax) and photosynthetic nitrogen use efficiency (PNUE) under low nitrogen levels, whereas the nitrogen content per unit area (Narea) and nitrogen content per unit mass (Nmass) were unaffected. AM inoculation decreased leaf mass per area (LMA) and the fraction of leaf nitrogen allocated to cell walls but increased the fraction of nitrogen allocated to photosynthesis under low nitrogen levels. The increased fraction of photosynthetic nitrogen allocated to carboxylation (PC) and bioenergetics (PB) in response to AM inoculation under low nitrogen levels contributed to the higher Pmax and PNUE values.ConclusionThe improved photosynthesis and PNUE resulting from AM inoculation were mostly determined by the relative allocation of nitrogen to photosynthesis and not by the leaf nitrogen concentration. AM fungi may enhance nitrogen allocation to photosynthesis at the expense of cell walls.