Physiological Response Of Nenjiang Spruce And Korean Spruce To Drought And SO₂ Stress

Nenjiang spruce (Picea koraiensis Nakai var.nenjiangensis S. Q. Nie et X. Y. Yuan) is the variety of Korean spruce(Picea koraiensis Nakai). It has a relatively longer life cycle and stronger stress-resistance. In this paper, the heredity difference in the genome level between these two species were identified using modem molecular marker technology RAPD and ISSR. The physiological characteristics of Nenjiang spruce and Korean spruce seedlings were studied under different water conditions and SO₂ stress in order to explore their adaptation mechanism to water stress and SO₂ stress, and the adaptability of two spruces were compared. The main contents and results are as follows:The optimal reaction system and program of molecular marker were found through the orthogonal experimental design. Three RAPD primers OPN-07, OPA-17, S25 and one ISSR primer ISSR-67 were screened out to differentiate the two spruce species, in which the species- specific bands were amplified in the genomic DNA of Nenjiang spruce at 1000bp, 950 bp, 1500bp and 2000bp in molecular size, but not in Korean spruce. The study indicated that RAPD and ISSR could be used to differentiate the two species.Changing regularity of some physiological indexes under water stress were studied systematically. The results showed that the maximum photosynthetic rate(P max) of two spruces seedlings(3-year-old) under different light intensities reduced with the reduction of soil moisture content, and the reduction of Nenjiang spruce was smaller; apparent quantum yield (AQY), transpiration rate(T_r), stomatal conductance (G_s), carboxylation efficiency (CE) also decreased. Dark respiration rate(R_d )and water use efficiency (WUE) rised firstly and then descended as drought became intensified, however, intercellular CO₂ (C_i)descended firstly then rised. These results showed that photosynthesis was limited by non-stomatal factor under serious drought. CO₂ compensation point (Γ) of Nengjiang spruce was lower than that of Korean spruce, it indicated that the ability to use low CO₂ concentration of Nenjiang spruce was higher than that of Korean spruce under water stress.Photochemical quantum efficiency (Φ_Psll), maximum efficiency of photosystemâ…¡(F_v/F_m), F_v/F_o and photochemical quenching of chlorophyll fluorescence (q_p) decreased with the reduction of soil moisture content. Analysis indicated that photosystemâ…¡damaged, and primary light chemistry conversion of PSII (q_p), activities of PSII (F_v/F_o) decreased; photosynthetic electron transport, photosythetic primary reaction inhibited. Non-photochemical quenching (NPQ) in Nenjiang spruce increased under slight drought, it indicated that heat disseminates which possess photoprotective effect increased, and this function of Korean spruce was not obvious. Chlorophyll contents decreased with the reduction of soil moisture content and the declining degrees of chlorophyll a and total chlorophyll of Korean was higher. The value of Chla/Chlb increased under slight drought, and decreased under serious drought. It indicated that light-harvesting complexâ…¡content decreased under drought stress incunabulum. It is beneficial for protecting photosystern and decreasing the damage of photooxidation whith increasing the value of carotenoid /chlorophyll under drought stress.ABA content in roots, stems and leaves increased with the reduction of soil moisture content, and the increasing degrees of Nenjiang spruce were higher. IAA increased under slight or even medium drought stress and decreased under serious drought. GA also decreased during water stress, but the reduction was not very apparent, it indicated that the effect of drought on GA was insignificant. ZR content decreased significantly with the reduction of soil moisture content. It indicated that ABA, ZR and ABA/ZR play the important role in stomatal regulation by analysising the correlation between the stomatal conductance and the endogenous.Generating rate of O₂ , maionadialdehyde (MDA) content, membrane permeability increased with the reduction of soil moisture content, it indicated that a large amount of free radicals produced and the lipid peroxidation appeared. Supperoxide dismutase (SOD) activity increased under slight drought, and achieved maximum value at 4d after drought, then decreased. Catalase (CAT) activity increased slightly under slight drought, and also achieved its maximum vaiue at 4d after drought, then decreased. Peroxidase (POD) activity in Nenjiang spruce increased rapidly under medium degree drought, but that in Korean spruce decreased. They all decreased under serious drought. Ascorbic acid (AsA) content changed significantly with the reduction of soil moisture content, it increased under slight drought and decreased under serious drought. Carotenoid (Car) content also declined, and the declining degree in Nenjiang spruce was lower. The free radicals in spruces could be cleared away by enzymes system and antioxidant when drought was not serious.Water content, relative water content (RWC) in leaves of two spruces decreased with the reduction of soil moisture content, and water saturation deficit (WSD) increased. The results showed that the reduction of Nenjiang spruce was smaller. Spruces can adapt the water changing by osmotic adjustment. Soluble protein content, soluble sugar and proline contents increased under water stress, and the changing degree of Nenjiang spruce was higher.Ψ_w,Ψ_s andΨ_s¹⁰⁰ decreased with the reduction of soil moisture content, especially Nenjiang spruce. It showed that the osmotic adjustment ability of Nenjiang spruce was stronger.Photosynthesis parameters and water parameters of Nenjiang spruce and Korean spruce spalings(8-year-old) were studied under the same different water conditions, and the results concluded compared with the results of using 3-year-old spruce seedlings as experimental material, it is indicated that the results were similer. Using mixed liquid of Na₂SO₃ and NaHSO₃ to simulate the damages of SO₂ to plants. Nenjiang spruce and Korean spruce spalings were sprayed with 20, 50 and 100 mmol.L^-1 mixed liquid, and some physiological indexes were determined at 3, 11 and 20 d after treatment. The results showed that photosynthesis rate (P_n), F_v/F_m,Φ_psll, contents of Chl a, Chl b and carotenoid decreased at the 3d after treatment, but the electrical conductivity rised.The degree of injury increased with the stress increasing. The physiological indexes resumed at the 8～20 d after treatment. There were no significant changes of stomatal conductance and intercellular CO₂. The sensitivity to stress of Korean spruce was higher than that of Nenjiang spruce, and the self-recovering capability of Korean spruce was better than Nenjiang spruce under serious stress of mixed Liquid of Na₂SO₃ and NaHSO₃.The results displayed that there were heredity difference in the genome level between these two species, and the difference could be identified by using modern molecular marker technology RAPD and ISSR. The determined results of some physiological indexes under drought stress showed that the adaptability to drought stress of Nenjiang spruce is stronger than that of Korean spruce. The sensitivity to SO₂ stress of Korean spruce was greater than that of Nenjiang spruce, and the self-recovering capability of Korean spruce was better than Nenjiang spruce under serious stress of mixed Liquid of Na₂SO₃ and NaHSO₃. We think that these results have not only theoretical but also realistic significance in spruces systematical evolution, species identification and tree species selection of forestation and landscaping.