Effects On Photosynthetic Characteristics Of Rhododendron Annae Seedlings Inoculated With ERM Fungi Under Drought Stress

Rhododendron is a famous traditional flower in China,it is known as the “Beauty of Flowers”. In the Ericaceae Rhododendron Subgen Hymenanthes, Rhododendron annae Franch is a kind of late flowering Rhododendron with high ornamental value,its growth is often affected by the dry environment. Ericoid mycorrhizal(ERM) is one of the key reasons for the widespread existence of such plants in harsh environment.In this study, we used one-year-old Rhododendron annae Franch seedlings as test material, and it was inoculated with TY02, TY21,TY29,TY35 fungi isolated from the root of Rhododendron annae Franch, to study its growth and photosynthetic rates under the drought, and how the ERM fungi effect on Rhododendron annae. It would provide theoretical basis for its introduction and urban landscape application. The study has taken 2 different measures( gradually watering and watering after continuous drought), to analyze 8 indexes such as the seedling height, ratio,ramet,weight,chlorophyll contents, diurnal variation of photosynthesis and light response curve etc. The findings are as follows:1.It apparently improved the seedlings’ height, ramet, weight and enlarges their root-shoot ratio by inoculating ERM; The seedlings with ERM fungi obviously grew faster than the reference, but different fungus had different affects. Although the young seedlings had different dependance on different fungus, they all had a higher rate than 100%,the colonization rates were up to 38.4%~57.8%.2.Under drought situation, the fungi significantly helped the growth of the seedlings. The deeper the drought, the more obvious the distinctions. With the increase of the drought level, each index of the reference was lower than those with ERM. Under the condition of continuous drought,the ERM fungi encouraged roots development better than the other parts of the plants, it enlarged the root-shoot ratioand improved their biomass;with the extension of the duration of drought,the growth was first increased and then decreased, it reached a max on the 10 th day. After watering, the fungi gave obvious stimulation effect on the seedlings, each growth index has recovered and even higher than the level of the drought days, the recovery ability of TY29 was the strongest among them.3.Under the drought,the chlorophyll content, net photosynthetic rate(Pn),transpiration rate(Tr), stomatal conductance and their water use efficiency(WUE) of the seedlings with ERM were all higher than the control. With the increase of drought stress, the chlorophyⅡ content of seedlings has decreased, but seedlings with TY29 and TY35 increased under mild drought condition(soil water content was 65%~75%). The plants’ photosynthetic indexes(except for CO2 concentration between cells) such as net photosynthetic rate and transpiration rate showed a downward trend, and the decline range was lower than the control. The decline was the narrowest of the TY29 and TY35 and which became obvious when the soil moisture content was between 35% to 45%. When CK, TY02, TY21 was under mild stress, stomatal restriction was the dominant leading to the decline of photosynthetic efficiency of the seedling,and it was mainly caused by non-stomatal restriction under moderate and severe stress, only under severe drought condition, the decline of photosynthetic efficiency of TY29 and TY35 strain treated seedling was considered as a result of non-stomatal restriction.4.Under the condition of continuous drought, the chlorophyll content of Rhododendron annae seedlings has increased on the 5th day, then declined gradually.The net photosynthetic rate, transpiration rate and stomatal conductance decreased with the extension of drought time.However, the ERM fungi could significantly slow down the decline of Pn parameters, to maintain the Photosynthetic capacity of the seedlings. The WUE of TY02, TY29 and TY35 were the highest on the 5th drought day, TY29 and TY35 were still higher on the 10 th day than on the 1st day. After re-watering, the ERM fungi enhanced the photosynthetic capacity of seedlings, which reduced the damage to the seedlings.5.The curve of diurnal variation of Rhododendron annae seedlings’ photosynthesisshowed two single peak.When the PAR was less than 200μmol?m-2?s-1, the utilization efficiency of light of the Rhododendron annae seedling was higher, at this time, the net photosynthetic rate and transpiration rate increased rapidly; When the PAR was larger than 800μmol?m-2?s-1,each index changed gently, and the light suppression happened. Inoculation of ERM fungi under drought stress could significantly improve the utilization efficiency of light energy and delayed the occurrence of light suppression.6. Under drought stress, the chlorophyll fluorescence parameters of Rhododendron annae inoculated seedling was higher than those of the none-inoculated seedlings.Along with the increase of the degree of stress and the extension of the duration of drought, the chlorophyll fluorescence parameters Fm、Fv/Fo、ΦPSⅡ、ETR and qP of the seedling decreased, while Fo, Fv/Fm and NPQ increased gradually, and the deeper the stress degree, the greater the variation range of the parameters.But the variation range of mycorrhizal seedling was lower than that of the control group under the same stress condition, among them, the decrease of TY35 was the smallest, followed by TY29; After rewatering, the chlorophyll fluorescence parameters of the seedling without inoculation failed to recover, while the other mycorrhizal seedling was able to recover, and TY35 and TY29 returned to the normal level basically.