Study On The Drought Resistance And Shade Tolerance Of The Plant With Extremely Small Population Viburnum Japonicum

Viburnum japonicum is an evergreen plant species belongs to caprifoliaceae,only found in the islands of Taizhou and Zhoushan,Zhejiang Province in China.This species was listed in the Directory of Plant Species with Extremely Small Populations in Zhejiang Province,because the wild individuals were extremely rare.And the plant has high ornamental value and great potential for development and utilization in landscaping.The paper studied the photosynthetic characteristics and physiological and biochemical characteristics of V.japonicum unter drought,shading treatments,evaluated the abilities of resistance.Based on the experiments,it provided the theoretical references for the in conservation and popularization and application of the species.The results as follows:?1?2-year-old seedlings of V.japonicum were potted and grown under four soil water conditions:normal water supply?CK,80%of the field moisture capacity?,mild water stress?LS,60%of the field moisture capacity?,moderate water stress?MS,40%of the field moisture capacity?,and severe water stress?SS,20%of the field moisture capacity?.Determinations were implemented on photosynthetic and physiological characteristics in the 15,30,45,60,and 75 d of treated seedlings.The result demonstrated that V.japonicum seedlings could grow normally under CK,LS,and MS,but they died at75 d under SS.The net photosynthetic rate?P_n?,SPAD value,maximum net photosynthetic rate(P_nmax),apparent quantum yield?AQY?,and dark respiration rate?R_d?of different treated seedling leaves decreased with the decrease of soil water content,while the light saturation point?LSP?and light compensation point?LCP?increased.The AQY increased gradually over time under all moisture gradients,and P_n was below 0?mol m^-2 s^-1 from 45 d under SS.The changes in the maximum quantum yield of photosystem II?PSII??F_v/F_m?was small during any stress;the actual photochemical efficiency of PSII(?_PSII),electron transport rate?ETR?and photochemical quenching coefficient?qP?of seedlings decreased with increasing water stress,but the non-photochemical quenching coefficient?NPQ?showed the opposite trend.The differences in the chlorophyll fluorescence parameters changed slightly among LS,MS,and CK,while the gaps between SS and CK increased.RWC was decreased and MDA was increased with the increasing intensity and duration stress,cytoplasmic membrane of seedlings were damaged seriously under SS.The soluble protein content,the soluble sugar content,SOD,POD were increased as the water content decreased under CK,LS,MS,while dereased significantly under SS in60 d.The results also showed that total biomass production was rised with soil drought stress,however the root to shoot ratio and root mass ratio was the opposite trend.Leaf mass ratio than to had a significant increase under LS.The experiment resulted that V.japonicum seedlings under LS and MS showed some degree of adaptability and resistance to drought,but be seriously influenced under SS with long duration.?2?Effect of different shading treatments?the full light,30%,60%,85%shade?on the photosynthetic and physiological characteristics of V.japonicum was studied to understand the light requirement and adaptability.The results showed that at lower light levels,specific leaf weight?SLW?and R_d declined.Relative growth rate?RGR?at shading of 30%and 60%was significantly higher,while had no shape increase at the full light.Shading resulted in decreases in the LCP.The LSP increased with the increasing of shading levels under the shading condition,however was the lowest under the full light.The AQY,P_nmax was significantly lower at the full light,and they reached the top point under the shading of 60%.The P_n of V.japonicum varied as a bimodal curve with a‘midday depression'phenomenon at the shading of 30%,and as unimodal curves under other treatments.The P_n at the full light was much lower than the shading condition,and the principal cause of the reduction in photosynthesis at 8:00—10:00 was attributed to stomatal limitation and non-stomatal limitation at later.With the increase of shading ratio,the chlorophyll content,F_v/F_m,?_PSII,qP decreased in turn,while NPQ was contrary.Under the full light,the MDA,the soluble sugar content,SOD,anthocyanin content were hightest,however the soluble protein content,POD decreased.The MDA,the protective enzyme activity and the amount of osmotic regulation substances was markedly reduced in the shading of 60%.In conclusion,V.japonicum suffered serious photoinhibition under the full light,while possessed a strong flexibility to shading treatments even under the shading of 85%.V.japonicum was best to grow in the habitat with 60%shading.