Drought Resistance Of Arbuscular Mycorrhizal Fungi Seedlings In Rocky Desertification Area

By pot experiment, the growth, physiological and biochemical index, chlorophyll fluorescence characteristics and content of nitrogen and phosphorus in Toona sinensis and Bischofia javaica seedlings colonized by arbuscular mycorrhizal fungi under drought stress were investigated using arbuscular mycorrhiza inoculation. Results are showed as the folio wings:1. Zenia insignis was taken as a reference species. Zenia insignis, Toona sinensis and Bischofia javaica had weak or no dependence on AM fungi. Seedling height, diameter and biomass of the three species were improved after AM fungi was inoculated on the seedlings. The biomass of Bischofia javaica, with the highest above-ground accumulation, was maximum, followed by Zenia insignis and Toona sinensis. Zenia insignis and Bischofia javaica had better root system when comparing with Toona sinensis. For the ratio of seedling diameter to height (D/H ratio), Toona sinensis and Bischofia javaica had bigger D/H ratio and better quality of seedlings than those of Zenia insignis. The D/H ratio of Zenia insignis was minimum, and the growth relationship between seedlings height and diameter were imbalance, which affected the quality of seedlings.2. As the inoculation methods were different in species, the height, diameter, biomass, and specific leaf area of seedlings exhibited different responses with the increase of drought stress and stress time. AM fungi inoculation promoted the seedling height, diameter and biomass accumulation, and also increased the leaf biomass per unit area and capture ability of light energy, reduced the specific leaf area in Toona sinensis. Bischofia javaica showed no significant response to the AM fungi inoculation in the seedling height, diameter, biomass accumulation or leaf area.3. With the increase of drought stress and stress time, the change of contents of chlorophyll a, chlorophyll b and total chlorophyll were basically consistent. The chlorophyll content of Toona sinensis had a decreasing trend, while chlorophyll a/b showed an increasing trend; the chlorophyll content of Bischofia javaica decreased firstly and then increased. Under drought stress, effects of AM fungi inoculation on contents of chlorophyll a, b and total chlorophyll of Toona sinensis seedlings were not significant. With an increase of drought stress, the chlorophyll content of Bischofia javaica was higher. This could be related to the characteristics of species.4. With the extension of drought stress time, leaf relative water content of Toona sinensis decreased firstly, then increased and finally decreased again, while that of Bischofla javaica showed a decreased trend. Leaf relative water deficit was inversely proportional with the relative water content. With the drought stress increasing, the changing trend of the leaf relative water deficit contrary to that of the relative water content. Under drought stress, AM fungi inoculation reduced leaf water content of Toona sinensis and Bischofia javaica. The drought stress was more serious, the decline rate of relative water content of mycorrhizal seedlings was the greater.5. With increasing intensity of drought stress and stress time, leaf slice of cytoplasm membrane permeability of Toona sinensis and Bischofia javaica had different amplitudely increase, and both were higher than those under normal water conditions; SOD activity content of Toona sinensis showed a first decline after a sharply rising, and then gently rising trend again; SOD activity content of Bischofia javaica showed a first increased and later decreased trend; the proline content of Toona sinensis was in greater changes, while the proline content of Bischofia javaica was in small scope changes. Under drought stress, changes of cytoplasm membrane permeability of mycorrhizal seedlings of Toona sinensis and Bischofia javaica were slightly smaller than that of control, while leaf cytoplasmic membrane permeability of mycorrhizal seedlings of Bischofia javaica was larger than that of control. But the changing magnitude of leaf cytoplasm membrane permeability of mycorrhizal seedlings was smaller than that of control. These indicated that AM fungi inoculation on Bischofia javaica seedlings could protect cytoplasm membrane under water stress. AM fungi inoculation decreased SOD activity content of two species, but SOD activity content under drought stress was still higher than that in a normal water condition, AM fungi inoculation promoted the accumulation of proline content of two species, but in the whole process of drought stress, proline content of mycorrhizal seedlings of Toona sinensis affected by drought stress was slightly larger than that of Bischofia javaica. Mycorrhizal seedlings showed a weaker adaptability under drought stress when comparing with non-mycorrhizal seedlings. SOD activity content and proline content of Toona sinensis were significantly higher than those of Bischofia javaica, which might be related to the characteristics of the species themselves.6. With the intensification of stress time and stress level, Fv/Fm, Fv/Fo, Fm/Fo, qP, phi PSII, ETR value of Toona sinensis and Bischofia javaica decreased significantly, but the chlorophyll fluorescence parameters showed different changing ranges among species with different inoculation methods. AM fungi inoculation reduced the damage degree of PSII reaction center, improved the efficiency of PSII light energy conversion efficiency, captured the excitation energy and electron transfer efficiency, and enhanced the utilization rate of light energy, so as to improving the drought resistance of Toona sinensis and Bischofla javaica seedlings.7. Under drought stress, the effect of AM fungi inoculation on N content of Toona sinensis seedling was small, while the effect on P content of the seedling was obviouse, with an increasing P content. Among drought stress treatments, the P contents of roots, stem, leaf and the whole plant of seedlings colonized by arbuscular mycorrhizal fungi under the severe drought stress was the highest. The N content of Bischofia javaica seedlings inoculated with AM fungi was not significantly higher than that of control. AM fungi inoculation reduced the accumulation of N content in each organ. But under drought stress, the seedlings inoculated with AM fungi promoted leaves and stems to absorb more N elements. AM fungi inoculation could promote the absorption of P in Bischofia javaica seedlings with the intensification of drought stress; But in the same moisture conditions, AM fungi inoculation reduced the P content. These indicated that nutrients absorption of seedlings would be able to be effectively improved by arbuscular mycorrhiza inoculation, and the improvements would be better under more serious drought stress.8.19drought-resistant indices were classified into three principal components using principal component analysis (pea), the cumulative percentage of the first two principal components reached93.55%, which basically represented most information of18original indexes. The first principal components included12indices, namely total chlorophyll content, PSII photochemical maximum quantum yield (Fv/Fm), specific leaf area, PSII capture excitation energy efficiency (Fm/Fo), electron transport efficiency (ETR), potential activity of PSII (Fv/Fo), relative water deficit, SOD activity content, total biomass, cytoplasmic membrane permeability and proline contentand relative water content. The second principal components included6indices, namely P content, root-shoot ratio, diameter, height, coefficient of photochemical quenching (qP) and quantum efficiency of PSII (O PSII). The third principal component consisted of the N content index.The drought resistances of Toona sinensis and Bischofia javaica seedlings were comprehensively evaluated using subordinative function method.Their drought-resistant capabilities were in the following deseeding order:Bischofia javaica mycorrhizal seedlings> Bischofia javaica non-mycorrhizal seedlings> Toona sinensis mycorrhizal seedlings> Toona sinensis non-mycorrhizal seedlings. Results showed that AM fungi inoculation improved significantly the drought-resistance of seedlings for the both species, and Bischofia javaica exhibited stronger drought-resistant ability when comparing with Toona sinensis.