Potassium (K) in plants participates in a variety of physiological processes and is kept at a higher concentration than its soluble form in soil. Potassium solubilizing bacteria (KSB) release K from minerals. Arbuscular mycorrhizal (AM) fungi facilitate bacterial movement along their extraradical hyphae and improve plant K status. However, the interaction of KSB and AM fungi is rarely reported. This study aimed to isolate KSB and evaluate their interaction with AM fungi in promoting plant K uptake and growth. Soil was sampled from the rhizosphere of Robinia pseudoacacia in the southern area of the Loess Plateau, where soil available K is lower than plant demand. KSB from soil was isolated using a select medium in which K-feldspar is the only K source. KSB that showed an obvious dissolving circle and relatively high K solubilizing efficiency (over 20%) were isolated and identified. A pot experiment was conducted in a randomized design to evaluate the effect of KSB and AM fungi and their interaction. Four out of 12 isolated strains that showed high potassium solubilizing efficiency were from the genus Pseudomonas. Inoculation of KSB promoted the growth and K content of R. pseudoacacia. KSB showed a variety of (increase, decrease, and not-obvious) influences on the colonization status of R. irregularis. Co-inoculation of R. irregularis and KSB promoted plant growth, K content of the plant, and the available K in the growth substrate. This study provided a basis for the utilization of KSB and AM fungi as biofertilizers in the Loess Plateau.

Acer truncatum Bunge, an economically significant species, is often growth-limited by phosphorus availability. Phosphate transporters, especially the PHT1 family, are crucial for plant phosphorus absorption, transport, and redistribution. This study aimed to elucidate the role of Acer truncatum PHT1 genes in phosphorus transport. We cloned five PHT1 family genes (AtPT1, AtPT2, AtPT4, AtPT9, and AtPT11) and investigated their expression and function under varying phosphorus regimes in the context of arbuscular mycorrhizal (AM) symbiosis with Rhizophagus irregularis. Real-time quantitative PCR revealed differential gene expression patterns in response to AM colonization and phosphorus levels. Functional characterization through yeast complementation, tobacco overexpression, subcellular localization, and GUS reporter gene assays confirmed the plasma membrane localization and typical PHT1 family traits of these transporters. AM colonization upregulated AtPT4 and AtPT11, with AtPT11 having a specific induction pattern for mycorrhizal phosphorus acquisition. AtPT4 was linked to phosphorus uptake via mycorrhizal symbiosis, AtPT1 is involved in phosphorus remobilization within plant tissues, AtPT2 in phosphorus transport and remobilization (suppressed by AM colonization), and AtPT9 in phosphorus uptake and transport efficiency under high-phosphorus conditions. These findings provide insights into the molecular mechanisms underlying phosphorus homeostasis in Acer truncatum and its mycorrhizal interactions.

Potassium participates in a variety of plant physiological processes and has great impact on plant growth and stress adaptation. The absorption of potassium by Plant is mediated by potassium channels and transporters, and the Shaker potassium channel gene family plays an important role in potassium uptake. Arbuscular mycorrhizal (AM) fungi form ubiquitous symbioses with plants and increase plants' potassium uptake. However, few studies have focused on the interaction of plant potassium channels from the Shaker gene family with AM fungi. In this study, the potassium uptake function of LbKT1 and LbSKOR (homologs of AKT1 and SKOR in Arabidopsis) from the Shaker gene family in Lycium barbarum was verified by the complementary assay using a yeast potassium uptake mutant. LbKT1 and LbSKOR were also overexpressed in tobacco to assess their influence on AM fungi under low and normal potassium conditions in a pot experiment. LbKT1 could rescue the phenotype of the yeast mutant, while LbSKOR could not. Overexpression of LbKT1 increased tobacco plant growth and potassium uptake and promoted the colonization of AM fungi. Meanwhile, overexpression of LbSKOR promoted potassium translocation from root to shoot and showed no obvious influence on the colonization of AM fungi. Our results suggested that the AM fungi could promote tobacco growth and potassium uptake, while the plant potassium status and the AM fungal colonization may form positive feedback in promoting tobacco potassium uptake and growth.

Previous studies have proved that arbuscular mycorrhizal fungi infection and phosphate transporters are particularly important for phosphorus uptake by plants. Early laboratory studies found that LbPT7 played a role in Pi uptake and it was affected by arbuscular mycorrhizal fungi. In order to verify the phosphorus uptake function of LbPT7 gene and the effect of interaction with arbuscular mycorrhiza on plants, we constructed LbPT7 overexpression vector with Nicotiana tabacum and obtained T1 generation overexpression positive plants as test material. Under the condition of pot experiment, we designed three factors: Arbuscular Mycorrhizal Fungi treatment, genotype treatment, phosphorus concentration treatment. After 4 weeks of treatment, we measured the biomass and phosphorus content of tobacco, and determined the colonization. The results showed that overexpression of LbPT7 can promote plant phosphorus uptake and inoculation of AM fungi further promote plant phosphorus uptake in phosphorus deficiency condition, but this effect of them can’t superpose in phosphorus adequate conditions. Overexpression of LbPT7 promoted the absorption of phosphorus, but impeded the utilization of phosphorus of N. tabacum in phosphorus deficiency condition. Overexpression of LbPT7 had little effect on the colonization of AM fungi in N. tabacum.

KEY MESSAGE:Overexpressing the copper transporter LbCOPT1 leads to a notable increase in the abundance of mycorrhizal arbuscules that suggests the potential application of LbCOPT1 in breeding programs aimed at enhancing symbiotic nutrient uptake in Lycium barbarum L.

Lead (Pb) is a hazardous heavy metal that accumulates in many environments. Phytoremediation of Pb polluted soil is an environmentally friendly method, and a better understanding of mycorrhizal symbiosis under Pb stress can promote its efficiency and application. This study aims to evaluate the impact of two ectomycorrhizal fungi (Suillus grevillei and Suillus luteus) on the performance of Pinus tabulaeformis under Pb stress, and the biomineralization of metallic Pb in vitro. A pot experiment using substrate with 0 and 1,000 mg/kg Pb2+ was conducted to evaluate the growth, photosynthetic pigments, oxidative damage, and Pb accumulation of P. tabulaeformis with or without ectomycorrhizal fungi. In vitro co-cultivation of ectomycorrhizal fungi and Pb shots was used to evaluate Pb biomineralization. The results showed that colonization by the two ectomycorrhizal fungi promoted plant growth, increased the content of photosynthetic pigments, reduced oxidative damage, and caused massive accumulation of Pb in plant roots. The structural characteristics of the Pb secondary minerals formed in the presence of fungi demonstrated significant differences from the minerals formed in the control plates and these minerals were identified as pyromorphite (Pb5(PO4)3Cl). Ectomycorrhizal fungi promoted the performance of P. tabulaeformis under Pb stress and suggested a potential role of mycorrhizal symbiosis in Pb phytoremediation. This observation also represents the first discovery of such Pb biomineralization induced by ectomycorrhizal fungi. Ectomycorrhizal fungi induced Pb biomineralization is also relevant to the phytostabilization and new approaches in the bioremediation of polluted environments.

The Loess Plateau is one of the key areas for soil and water erosion control in China. Planting vegetation, such as Robinia pseudoacacia, is one of the mainstream methods to prevent soil and water erosion. However, the combination of abundant calcium ions and phosphate in the soil of the Loess Plateau limits the phosphorus nutrition of plants. In the present study, soil samples were collected under the R. pseudoacacia forest, from which two PSB strains with efficient phosphate solubilization capacities, named PSB2 and PSB7, were isolated and screened. The dissolved phosphate concentrations of their culture media were 9.68-fold and 11.61-fold higher, respectively, than that of the control group. After identification, PSB2 was classified as Pseudomonas and PSB7 as Inquilinus. This is the first time that Inquilinus has been isolated as a PSB from calcareous soil in the Loess Plateau. We then investigated the effects of different growth conditions on their phosphate solubilization capacities. Both strains effectively utilized glucose and ammonium nitrogen while maintaining high phosphate solubilization efficiency. In addition, PSB2 preferred to survive under neutral conditions and PSB7 under acidic conditions. Pot experiments indicated that the inoculation with PSB7 significantly increased the phosphorus content in the roots of R. pseudoacacia. These results imply the potential of this PSB as a phosphorus biofertilizer for R. pseudoacacia, which may be beneficial for soil and water management on the Loess Plateau.

Arbuscular mycorrhizal (AM) fungi can establish a mutualistic relationship with the roots of most terrestrial plants to increase plant nutrient uptake. The effects of potassium uptake and transport by AM symbiosis are much less reported compared to other nutrients. In this research, a heterologous yeast system was used to verify that the LbHAK has capacity for potassium uptake. The split-roots system implemented using seedlings of Lycium barbarum confirmed that R. irregularis locally induced LbHAK expression, which means that LbHAK is only expressed in mycorrhizal roots. Furthermore, the impacts of overexpression of LbHAK on the growth, nutrients and water uptake, and transport of mycorrhizal tobacco (inoculation with Rhizophagus irregularis) at 0.2 mM and 2 mM K conditions were assessed. The mycorrhizal tobacco growth and potassium accumulation were significantly enhanced through LbHAK overexpression in tobacco. In addition, overexpression of LbHAK substantially enhanced phosphorus content, while stimulating the expression of NtPT4, Rir-AQP1, and Rir-AQP2 in mycorrhizal tobacco. Moreover, LbHAK overexpression greatly promoted AM colonization. LbHAK has a potential role in facilitating potassium absorption through the mycorrhizal pathway, and overexpression of LbHAK in tobacco may promote the transport of potassium, phosphorus, and water from AM fungi to tobacco. These data imply the important roles played by the LbHAK in AM-fungi-induced potassium uptake in L. barbarum and in improving plant nutrients and AM colonization.

Potassium plays important roles in most plant physiological processes. Arbuscular mycorrhizal (AM) fungi promote plant water and mineral nutrient acquisition to promote plant growth. However, few studies have focused on the effect of AM colonization on potassium uptake by the host plant. In this study, the effects of an AM fungus (Rhizophagus irregularis) and potassium concentration (0, 3, or 10 mM K+) on Lycium barbarum were evaluated. A split-root test with L. barbarum seedlings was conducted, and the potassium uptake capacity of LbKAT3 was verified in yeast. A tobacco line overexpressing LbKAT3 was generated and mycorrhizal functions under two potassium concentrations (0.2 and 2 mM K+) were studied. Inoculation of R. irregularis and application of potassium increased the dry weight, and potassium and phosphorus contents of L. barbarum, and increased the colonization rate and arbuscule abundance of R. irregularis. In addition, the expression of LbKAT3 and AQP genes in L. barbarum was upregulated. Inoculation of R. irregularis induced LbPT4, Rir-AQP1, and Rir-AQP2 expression, and application of potassium upregulated the expression of these genes. Inoculation with the AM fungus locally regulated the expression of LbKAT3. Inoculation of R. irregularis improved the growth, and potassium and phosphorus contents, and induced NtPT4, Rir-AQP1, and Rir-AQP2 expression in tobacco overexpressing LbKAT3 under both potassium concentrations. Overexpression of LbKAT3 in tobacco improved the growth, potassium accumulation, and AM colonization, and upregulated the expression of NtPT4 and Rir-AQP1 in mycorrhizal tobacco. The results suggest that LbKAT3 may assist in mycorrhizal potassium uptake, and overexpression of LbKAT3 may promote potassium, phosphorus, and water transport from the AM fungus to tobacco.

Platycladus orientalis is a significant woody plant for phytoremediation in heavy metals contaminated soils. The growth and tolerance of host plants under the lead (Pb) stress were enhanced by arbuscular mycorrhizal fungi (AMF). To evaluate the adjustment by AMF on growth and activity of antioxidant system of P. orientalis under Pb stress. The two-factor pot experiment was conducted with three AM fungal treatments (noninoculated, Rhizophagus irregularis, and Funneliformis mosseae) and four Pb levels (0, 500, 1000, and 2000 mg kg-1). AMF increased dry weight, phosphorus uptake, root vitality, and total chlorophyll content of P. orientalis in spite of Pb stress. Compared with nonmycorrhizal treatments, mycorrhizal P. orientalis had lower H2O2 and malondialdehyde (MDA) contents under Pb stress. AMF increased Pb uptake in roots and decreased the Pb translating to the shoots yet under Pb stress. Total glutathione and ascorbate in roots of P. orientalis were decreased by AMF inoculation. Mycorrhizal P. orientalis had higher superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and glutathione S-transferase (GST) activities in shoots and roots than nonmycorrhizal counterparts. Mycorrhizal P. orientalis under Pb stress showed higher expression of PoGST1 and PoGST2 in roots than that in CK treatments. Future studies will explore the function of induced tolerance genes by AMF of P. orientalis under Pb stress.

Drought stress, one of the major abiotic stresses, affects plants growth by changing root morphology, impacting leaf water status and photosynthesis, and interrupting the reactive oxygen species (ROS) balance in plants. Arbuscular mycorrhizal (AM) fungi and extra potassium can promote plants growth under drought stress. However, it is not clear whether AM fungi and extra potassium application would affect the photosynthesis and antioxidant system, which help Lycium barbarum to alleviate drought stress. In this study, the synergistic effects of AM fungus (Rhizophagus irregularis) and extra potassium (0 mM, 3 mM, and 10 mM K+) on growth, photosynthesis, leaf water status, root morphology, activities of antioxidant enzymes, concentrations of antioxidant substances, and expression of genes of L. barbarum under drought stress (30% field capacity) were evaluated. Under drought stress, inoculation of R. irregularis and application of potassium significantly increased the photosynthesis of L. barbarum and the expression of LbrbcL and LbrbcS, which might be due to the significant increase of the root growth and leaf relative water content. Moreover, the activities of antioxidant enzymes, concentrations of antioxidant substances, and the expression of three genes encoding superoxide dismutase (SOD) were increased. The concentration of proline and expression of LbP5CS were significantly up-regulated by potassium application and down-regulated by R. irregularis inoculation. The concentrations of malondialdehyde (MDA) and hydrogen peroxide (H2O2) were significantly decreased. The results suggested that R. irregularis and extra potassium have a synergistic effect on the enhancement of L. barbarum against drought tolerance through reduction of ROS accumulation and oxidative damage by improving photosynthetic and antioxidant capacity.

Nitrogen (N) is an essential nutrient that plants require and is, most of the time, limited in different terrestrial ecosystems. Forming symbioses with plants, arbuscular mycorrhizal (AM) fungi improve mineral element uptake and the net primary production of plants. Recent reports have suggested that AM fungi mediate N uptake in plants. However, there are fewer studies on the influence of AM fungi on the response of Lycium barbarum, a medicinal plant in northwest China, under different N-addition conditions. In this study, the effect of Rhizophagus irregularis, N forms (NO3− and NH4+), and N levels (1.5, 7.5, 15, 30 mM) on the performance of L. barbarum was evaluated through a pot experiment. The application of R. irregularis significantly improved L. barbarum biomass, net photosynthetic rate, and root tissue viability under adequate NO3− and NH4+ supplies, and mycorrhizal plants showed better performance under NO3− supply. AM colonization enhanced N acquisition under adequate NO3− supply and strongly induced the expression of LbAMT3-1 in L. barbarum roots. Based on these results, we propose that NO3−-dominated N supply favors mycorrhizal symbiosis to a greater extent than NH4+; this study provides a basis for maintaining beneficial AM symbiosis during nitrogen fertilizer use in arable land.

Arbuscular mycorrhizal (AM) fungi form ubiquitous symbioses with terrestrial plants in different ecosystems and provide a variety of benefits including improved drought tolerance of host plants. However, the difference and contribution of colonized and un-colonized root-system parts within mycorrhizal plants against drought stress is uncertain. A split-root system was used and the root compartments were either non-inoculated or inoculated with Rhizophagus irregularis, and were subjected to either well-watered or drought-stressed conditions. The growth, photosynthesis, reactive oxygen species (ROS) scavenging, and relative gene expression of aquaporins and phosphate transporters of hybrid poplar (Populus × canadensis ‘Neva’) were evaluated. Our results indicated that the inoculation by R. irregularis in either one or both compartments of split-root systems increased poplar biomass accumulation, photosynthesis, and ROS regulation under well-watered and drought-stressed conditions. When inoculum was applied in both compartments of split-root systems, the beneficial effect of R. irregularis was greater than that in treatment where only one compartment received inoculum. The effect of R. irregularis may attribute to improved phosphorus uptake via upregulation of relative expressions of PcPT3, PcPT4, PcPT5, and a possible improvement of water uptake via modulation of aquaporins (PcPIP2-3, PcPIP2-5, PcTIP1-1, and PcTIP1-2) in colonized root-system parts. Our results demonstrated that the benefits of the AM symbiosis depend on the extent of root colonization through which AM fungus may modulate plant phosphate and water uptake to improve tolerance of poplar against drought stress.

An ammonium transporter LbAMT3-1 overexpression increases the arbuscular abundance of mycorrhizal that opens the possibility of using LbAMT3-1 in breeding programs to improve symbiotic nutrient uptake in Lycium barbarum. Nitrogen (N) is one of the most essential nutrients required by plants and limits net primary production much of the time in most terrestrial ecosystems. Arbuscular mycorrhizal (AM) fungi can enhance plant nutrient uptake and improve plant productivity in nutrient limit ecosystems. Here, we identified an ammonia transporter, LbAMT3-1, specifically induced by AM fungi in Lycium barbarum. To understand the expression characteristics and biological functions, LbAMT3-1 was cloned, characterized, and overexpressed in Nicotiana tabacum (tobacco). A BLAST search identified the coding sequence for LbAMT3-1 with an open-reading frame of 1473 bp. Reverse transcription polymerase chain reaction (RT-PCR) analysis indicated that, besides mycorrhizal roots, LbAMT3-1 were barely detectable in other tissues, including stems and leaves. Promoter-GUS assay showed that GUS staining was detected in mycorrhizal roots, and GUS activity driven by the LbAMT3-1 promoter was exclusively confined to root cells containing arbuscules. LbAMT3-1 functionally complemented the yeast mutant efficiently, and yeast expressing LbAMT3-1 showed well growth on the agar medium with 0.02, 0.2, and 2 mM NH4+ supply. Moreover, overexpression of LbAMT3-1 in N. tabacum resulted a significant increase in arbuscular abundance and enhanced the nutrient acquisition capacity of mycorrhizal plants. Based on the results of our study, we propose that overexpression of LbAMT3-1 can promote P and N uptake of host plants through the mycorrhizal pathway, and increase the colonization intensity and arbuscular abundance, which opens the possibility of using LbAMT3-1 in breeding programs.

Arbuscular mycorrhizal (AM) fungi promote plant mineral nutrient acquisition, and AM fungal hyphae can transport water and nutrients. Potassium has significant effects on plant photosynthesis, stomatal conductance, and other physiological processes. However, it is little known whether foliar-applied potassium in one plant could affect the nearby plant that connected by the AM fungal hyphae network. We analyzed the effects of foliar-applied potassium (2% K2SO4) in the potassium additional compartment (potassium was foliar-sprayed on plant in this compartment) on growth, photosynthesis, chlorophyll fluorescence parameters, potassium content, and the relative expression of potassium channel/transporter genes (LbHAK, LbKAT3, LbAKT2, LbKT1, and LbSKOR) of mycorrhizal Lycium barbarum in the potassium-free compartment (potassium was not foliar-sprayed on plant in this compartment) via AM fungal hyphae network of a three compartments culture system (the system contains three compartments, namely two root compartments on the left and right and a hyphal compartment in the middle). Compared with inoculation of Rhizophagus irregularis, foliar-applied potassium improved growth, photosynthesis, and potassium content of mycorrhizal L. barbarum in the potassium-free compartment, but had no effect on mycorrhizal L. barbarum chlorophyll fluorescence parameters. Additionally, foliar-applied potassium increased the relative expressions of LbHAK, LbKAT3 LbKT1 and LbSKOR in roots of mycorrhizal plants in the potassium-free compartment, while the relative expression of LbAKT2 in shoots of mycorrhizal plant was increased in the potassium-free compartment. This study suggests that AM fungal hyphae network transports potassium to the potassium-free compartment, then potassium regulates the expression of potassium channel/transporter genes to promote potassium uptake and transport, thus improves photosynthesis, and ultimately, promotes the growth of mycorrhizal L. barbarum in the potassium-free compartment.

[目的]探讨丛枝菌根真菌(arbuscular mycorrhiza fungi,AMF)异形根孢囊霉(Rhiizophagus irregu-laris,Ri)和摩西斗管囊霉(Funneliformis mosseae,Fm)根外菌丝对重金属铅的吸收及转运能力,为明确AMF根外菌丝的铅转运能力提供依据.[方法]以菌根植物蒺藜苜蓿(Medicago truncatula,寄主)和非菌根植物油菜(Brassica napus)为试验材料,采用三室培养系统(菌根室-施铅室-非菌根室)进行研究,其中菌根室种植蒺藜苜蓿并进行AMF处理,包括接种Ri、Fm和未接种对照(CK)3个处理;施铅室(中间隔室)设置0和800 mg/kg 2个铅处理;非菌根室种植油菜,试验共设CK、Ri、Fm、Pb、Ri×Pb、Fm×Pb 6个处理,研究铅胁迫下2种AMF根外菌丝对植物生长及铅离子富集的影响.[结果](1)与CK处理比,Ri和Fm处理蒺藜苜蓿总生物量分别提高了43.55％和256.98％,铅胁迫对Ri和Fm处理蒺藜苜蓿的生物量无显著影响.(2)0 mg/kg铅胁迫下,2种AMF均能够与蒺藜苜蓿形成良好共生关系,Fm和Ri处理菌根侵染率达到90％以上.Fm和Fm×Pb处理侵染根段丛枝丰度分别是Ri和Ri×Pb处理的8.75和2.51倍.(3)与Ri处理比,Ri×Pb处理菌根室培养基质中菌丝密度显著提高231.57％,施铅室培养基质中菌丝密度显著降低49.56％;与Fm处理比,Fm×Pb处理菌根室培养基质中菌丝密度提高314.09％,施铅室培养基质中菌丝密度降低21.09％.(4)Ri×Pb、Fm×Pb处理蒺藜苜蓿地上部铅含量分别是CK处理的3.60和8.45倍,根系铅含量分别是CK处理的7.45和217.87倍;Fm×Pb处理油菜根系铅含量是CK处理的62.15倍.[结论]AMF根外菌丝能够直接吸收并转运铅至寄主植物根部,并可能借由"外排"效应将铅运输至非菌根植物根系,且Fm促进植物生长及根外菌丝吸收转运铅的能力显著高于Ri.

Potassium plays important roles in most plant physiological processes, and its availability in soil would be reduced by drought stress. Arbuscular mycorrhizal (AM) fungi promote plant water and mineral nutrient acquisition to against drought stress. Potassium uptake is linked to phosphorus uptake, and AM fungal aquaporins are involved in phosphorus transport from AM fungi to the host plant. However, little is known about whether or how potassium, phosphorus and water co-transport from AM fungi to the host plant. In current study, the effect of an AM fungi (Rhizophagus irregularis), potassium condition (0, 3, 10 mM K+), and drought stress (30% field capacity) on the growth, potassium and phosphorus concentrations were evaluated. Inoculation of R. irregularis colonized over 60% roots and significantly increased dry weight of Lycium barbarum by promoting potassium and phosphorus uptake. Potassium application improved plant growth, potassium and phosphorus concentrations, and colonization rate and arbuscule abundance of R. irregularis. Drought stress reduced plant growth, potassium and phosphorus concentrations. The putative genes encoding potassium transporter and potassium channel, LbHAK and LbKAT3, could uptake potassium, and the relative expressions of LbHAK and LbKAT3 were highly induced in AM plant. The relative expression of phosphorus transporter (LbPT4), and AM fungal aquaporins (Rir-AQP1 and Rir-AQP2) were regulated by potassium level. Positive correlations were observed among the relative expressions of LbHAK, LbKAT3, LbPT4, Rir-AQP1, and Rir-AQP2. The results suggested that LbKAT3 and LbHAK may be involved in potassium transport from AM fungi to plant, and the phosphorus and water may co-transport in the transport process.

丛枝菌根真菌(AMF)在促进植物生长和矿质营养吸收方面发挥重要作用.采用盆栽试验,探索了不同浓度氮处理(0、1、15 mmol NH4NO3)下丛枝菌根真菌对宁夏枸杞生长、光合作用和氮代谢的影响.结果 表明,AMF对宁夏枸杞的侵染率随施氮量增加而增加,3种浓度氮处理下AMF侵染率分别为29.32％、43.93％和62.81％.施氮和接种AMF均提高宁夏枸杞叶片叶绿素含量和光合速率,提高根系和叶片全氮含量,提高根系硝酸还原酶活性(NR)及叶片谷氨酰胺合成酶(GS)活性;1 mmol NH4NO3处理能够促进宁夏枸杞生物量累积,提高叶片总叶绿素含量和NR活性;15 mmol NH4NO3处理能够提高宁夏枸杞叶片和根系NH4+含量,提高根系NH4+百分比,降低叶片NO3-百分比.表明AMF能够通过改善氮代谢及提高光合能力,促进宁夏枸杞生长.

The soil fungal community is an important factor in the forest ecosystems, and a better understanding of its composition and dynamic changes will contribute to the maintenance, preservation, and sustainable development of the forest ecosystems. Pinus tabuliformis has been widely planted for local ecological restoration on the Loess Plateau in China in recent decades. However, these plantations have been degraded to different degrees with increasing stand age. Hence, we tried to find the possible causes for the plantation degradation by analyzing soil environmental changes and soil fungal community composition at different stand ages. We collected rhizosphere soil samples from young (10-year-old), middle-aged (20-year-old), and near-mature (30-year-old) P. tabuliformis plantations in this region and characterized their soil properties and soil fungal community diversity and composition. Our results showed that with increasing stand age, the contents of organic carbon, ammonium nitrogen (AN) and nitrate nitrogen (NN) in the soil increased significantly, while the content of available phosphorus (AP) decreased significantly. The main factors affecting the composition of the soil fungal community were the contents of AP, AN, and NN in the soil. In addition, the genus Suillus was the dominant ectomycorrhizal (ECM) fungus in all periods of P. tabuliformis plantations in this region. The results of structural equation modeling showed that the community composition of ECM fungi was significantly correlated with stand age, soil NN, and AP contents, and that of pathogenic (PAG) fungi was significantly correlated with soil AN and AP contents. The decrease in the relative abundance of ECM fungi and the increase in the relative abundance of PAG fungi would exacerbate the degradation of P. tabulaeformis plantation. Our results illustrated that the content of soil AP is not only an important factor limiting the development of plantations, but it also significantly affects the community composition of soil fungi in the rhizosphere of the P. tabuliformis plantation. This study provides a novel insight into the degradation of P. tabuliformis plantations and builds a solid foundation for their subsequent management, restoration, and sustainable development on the Loess Plateau of China.

[目的]探讨侧柏[Platycladus orientalis(L.)Franco]与丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)的共生情况,为合理应用AMF进行侧柏育苗造林提供参考依据.[方法]以侧柏为试材,在盆栽试验条件下,设置不接种(CK)、接种根内根孢囊霉(Rhizophagus intraradices,Ri)和接种摩西斗管囊霉(Funneliformis mosseae,Fm)3个处理,研究了接种AMF在2周、4周和6周后对侧柏侵染、生长、养分吸收及叶绿素含量的影响.[结果]2种AMF均能够与侧柏形成共生,接种2周后形成A-型丛枝结构,菌根侵染率超过80％;Ri处理和Fm处理的菌根侵染强度、丛枝丰度由相对较低水平持续增长,接种4周后趋于稳定,分别约为20％和40％.接种2周、4周和6周后,侧柏地上、地下部分生物量变化均不显著;接种2周、4周、6周后与对照相比,Ri处理和Fm处理均显著提高侧柏磷含量,分别提高57.99％和90.14％,67.44％和121.98％,64.06％和145.51％;2种AMF均可提高侧柏叶绿素含量,其中Fm处理效果优于Ri处理.[结论]2种AMF与侧柏存在共生关系,可在短时间(6周)内改善侧柏的磷营养状况,促进光合作用;摩西斗管囊霉(Fm)与侧柏的选择适应性更佳,具有开发为侧柏菌根菌剂的潜力.