Species Diversity Of AMF And Its Effects On Eco-physiology Of Dominant Plant Species In Limestone Soil

The distribution of Karst landscape is very general in the world, especially in the southwest of China. In limestone districts, ecological restoration is very difficult due to low water retention capacity, low fertility and growing rocky desertification. Several eco-physiological studies have demonstrated that the arbuscular mycorrhizal (AM) symbiosis often results in altered rates of water movement into, through and out of the host plants, with consequent effects on tissue hydration and plant physiology. Although the real mechanisms were not clear, some researchers conclude that AM symbiosis probably affected the water relations of host plants indirectly improved nutrition, especially P. So AMF might be useful in ecological restoration in limestone districts.The goal of this paper is to investigate the effects of AMF on eco-physiology of dominant plant species in limestone soil. And species diversity of AMF in limestone soil is the other goal of this paper. Following 5 experiments were conducted:Experiment 1:Effects of soil moisture and AM inoculation on root morphology and fractal character in Broussonetia papyrifera (L.) VentEffects of Glomus mosseae and water stress on morphology and fractal characteristic of root system in Broussonetia papyrifera (L.) Vent were studied in this experiment based on scanner-based image analysis. The results showed that drought and AM inoculation had a large, significant effect on plant development. Biomass, total length, surface area, volume, number of root nodes, average diameter and fractal dimension of root system in Broussonetia papyrifera (L.) Vent decreased with the reduction of soil moisture, while they were increased by AM inoculation. Special root length in non-AM plants increased when soil moisture was reducing, but it was decreased by AM inoculation. It was concluded that Glomus mosseae inoculation improved the drought resistance of Broussonetia papyrifera (L.) Vent, especially in moderate stressed conditions. And the contribution of AM symbiosis to plant to avoid the stress or to increase its tolerance might be the result of modification of root morphology and fractal character. The same conclusion was proved by Glomus etunicatum.Experiment 2:Influence of arbuscular mycorrhizae on activities of protective enzyme in Bidens pilosa L. under water stressThe effects of vesicular-arbuscular mycorrhizal fungus (AMF) Glomus mosseae on activities of protective enzyme in Bidens pilosa L. were investigated in pot culture under three water treatments: well watered (A) , middle drought treatment (B) and serious drought treatment (C) .The contents of malondialdehyde (MDA) and soluble sugar, superoxide dismutase (SOD), catalase (CAT), peroxide dismutase (POD), polyphone oxidase (PPO) and ascorbic acid peroxidase (AsP) activities were compared between plants infected with Glomus mosseae (AM plants) and those not infected (Non-AM plants) at different water-treatments. The results showed that water stress significantly increased the activities of SOD, CAT, ASP, POD and PPO; the contents of MDA and soluble sugar were also increased by draught. There were no significant differences between AM plants and non-AM plants when they were well watered. But this was not the case in drought treatment. Soluble sugar content, SOD and CAT activities in non-AM plants were significantly higher than that in AM plants in middle drought treatment. And MDA content was not significantly different before 28d, but it was significant at 35d. POD activity in non-AM plants was markedly higher than in AM plants only at 28d and 35d in middle drought treatment, but AsP and PPO activities in leaves of Bidens pilosa L. were not affected significantly by AM infection. The content of MDA and soluble sugar, CAT activity were higher in non-AM plants than that in AM plants in serious drought treatment, but there were no significant differences in POD and PPO activity between AM and non-AM plants. And AsP activity was higher in non-AM plants than that in AM plants at 28d and 35d. It was concluded that draught stress did affect the protective enzyme system of Bidens pilosa L., and AM weakened the injury caused by draught. But this protection effect was limited by the heavier and longer draught.Experiment 3:Photosynthetic responses of AMF-infection and AMF-free Bidens pilosa L.to drought stress conditionsTo reveal the effects of vesicular-arbuscular mycorrhiza(AM) on the photosynthesis of Bidens pilosa L., three draught treatments were set: well watered (A) , middle drought treatment (B) and serious drought treatment (C) . Total chlorophyll content, net photosynthetic rate(Pn), Stomatal conductance(Gs), transpiration rate(Tr), intercellular CO₂ concentration(Ci), apparent quantum yield(AQY), carboxylation efficiency(CE) and water use efficiency (WUE) were compared between plants infected with Glomus mosseae (AM plants) and those not infected (Non-AM plants) at different water-treatments The results showed that the Pn, Gs, Tr, AQY, CE of plants decreased significantly under draught stress, but total chlorophyll content increased under draught stress, while Ci decreased at the early stage of draught stress (7d), and raised with the soil-water-content decreasing at the late stage of draught stress. The WUE of middle draught stress plants was higher than control, but the WUE of serious stressed plants was lower than control. The photosynthetic parameters of well watered plants were not significantly effected by Glomus mosseae infection. Especially before 28d of treatment, AM plants had higher Pn, Gs, Tr, AQY and CE than non-AM plants under middle draught stress, but they had not significant difference under serious draught stress. It was concluded that draught stress did effect the photosynthesis of Bidens pilosa L. because of Stomatal resistances at the early stage of treatment and nonstomatal limitation at later stage of treatment. The photosynthesis of well watered plants were not effected by Glomus mosseae infection. Under draught stress, AM improved the Gs and CE of plants to weaken the injury caused by draught, but this protection effect was limited by the heavier and longer draught treatment.Experiment 4:Effects of AM fungi on number and flowering time in Bidens pilosa (Compositae) under water stressThe effects of vesicular-arbuscular fungi Glomus etunicatum and Glomus mosseae on number and flowering time in Bidens pilosa L. under water stress were studied in potted culture. The results showed that contents of water in soil played a great role in the processes of flowering in Bidens pilosa L. and water stress brought flowering time forward, although it was not significant, while the number of flowers per plant was increased significantly by water stress. The process of blooming in Bidens pilosa L. was also influenced by vesicular-arbuscular fungi inoculation. The times of first blooming were significantly brought forward by vesicular-arbuscular fungi in different water status and plants infected by vesicular-arbuscular fungi had the same numeric dynamics of flowers. It was concluded that plant growing in water stress habitat had more flowers was its ecological adaptation of the explosive population in Bidens pilosa L.. And plants infected by vesicular-arbuscular fungi growing in different water stress habitats having the same numeric dynamics of flowers was the result of vesicular-arbuscular fungi improving drought tolerance in Bidens pilosa L..Experiment 5:Species diversity of AMF community colonized in roots of herbages in limestone and purple soilThe species diversity of arbuscular mycorrhizal fungi (AMF) in roots of various herbages were studied in this paper. Seventeen common herbages were selected as host plants of AMF colonization in this research and they were grown in limestone soil and purple soil, respectively. The plants were sampled at 120^th day after seedling and DNA of AMF in plant roots was extracted by CTAB method. The partial rDNA sequence encoding ribosomal 28S big unit was amplified with special primers U1/U2 for fungi, and PCR products were analyzed with PAGE silver staining method. Twenty-nine AMF species were found in roots of 17 host plant species in limestone soil and each host plant was colonized by 8.29 AMF species, while only twenty-four AMF species in purple soil and 9.47 AMF species in each host plant in purple soil. All the AMF species in roots were divided into two different groups, unique species group and common species group. Results of cluster analysis showed that colonization of AMF to host plants was family-specific, and the specificity was also affected by soil factors. The possibility of AMF used in ecological restoration of limestone area was also discussed in this paper.In general, AMF may be used in ecological restoration in limestone districts because AM symbiosis weakened the injury caused by draught, though this protection effect was limited by the heavier and longer draught treatment. The species of AMF in limestone soil in this study were not less than that in purple soil, which means more research work should be done in future.