Physiological Responses Of Red Pine Seedlings To Soil PH Variations

Red pine(Pinus resinosa Ait.) is one of the most important tree species for plantation forests in North America,and tentative success has been achieved with the introduction of the species to mountainous area of Northeast China since 2004.In order to grow red pine in other parts,the adaptability of this species to soil conditions,especially soil acidity,has to be studied. Red pine seedlings were grown in soils with different acidity(pH=4.5,5.5,6.5,7.5,8.0) to study their physiological responses to soil pH,and by which the feasible soil pH was evaluated. The main results were as follows:(1) At the time that soil pH increased,dramatic physiological responses of red pine seedlings needles' membrane stability were detected(p＜0.05).When soil pH value was up from 5.5 to 8.0,membrane lipid peroxide level increased in sequence.Under soil pH 5.5,the seedling foliages grew best,with the lowest malondialdehyde(MDA) content and relative conductivities.Compared with the soil pH 5.5,under the higher soil pH(7.5 and 8.0),in the needles contents of MDA were 10%and 11%higher respectively,relative conductivities were 15%and 18%higher.(2) When soil pH increased,dramatic physiological responses of red pine seedlings needles' antioxidant system were detected(p＜0.05).The seedling foliages was with the highest activity of superoxide dismutase(SOD) and catalase(CAT) under soil pH 5.5,secondly for seedlings grown in soil pH 4.5 and 6.5,and under soil pH 7.5 and 8.0,The SOD and CAT activity of seedling foliages was lowest.Compared with the soil pH 7.5 and 8.0,under the soil pH 5.5,in the needles activity of SOD were 42%and 51%higher respectively,and activity of CAT were 15%and 18%higher respectively.Compared with SOD and CAT,there was a reverse trend in the change of peroxidase(POD).The SOD and CAT activity could serve as an effective index for adaptability of plants to soil acidity;unsuitable soil pH will cause decrease of SOD and CAT activity.(3) When soil pH increased,enormous changes of red pine seedlings needles' osmotic adjustment substances content were detected(p＜0.05).The lowest proline and soluble sugar content found in seedling foliages under soil pH 5.5,secondly for seedlings grown in soil pH 4.5 and 6.5,and under soil pH 7.5 and 8.0,The proline and soluble sugar content of seedling foliages was highest..Compared with the soil pH 5.5,under the higher soil pH 7.5 and 8.0,in the needles contents of proline were 7%and 57%higher respectively and contents of soluble sugar were 5%and 16%higher respectively.(4) When soil pH increased,huge changes of red pine seedlings needles' Chlorophyll a and b content,photosynthetic rate(Pn),chlorophyll fluorescence parameters fluorescence origin(Fo),fluorescence maximum(Fm),fluorescence variety(Fv),photochemical efficiency of (Fv/Fm)and quantum yield of PSII electron transport(Φ)PSII) were detected(p＜0.05).Under soil pH 5.5,the seedling foliages had the highest chlorophyll content and Pn.Compared with the soil pH 7.5 and 8.0 in which foliages had the lowest chlorophyll content and Pn,under soil pH 5.5,in the needles chlorophyll content were 41%and 50%higher respectively,and Pn, were 61%and 88%higher respectively.Research on fluorescence parameters showed that under soil pH 7.5 and 8.0,the seedling foliages had a significant photo inhibition,under the soil pH 5.5;foliages had the highest Fv/Fm andΦPSII.Compared with the soil pH 7.5 and 8.0, under the soil pH 5.5,Fv/Fm was 8%and 12%higher respectively,andΦPSII.was 22%and 35%higher respectively.Ratio of Chlorophyll a and b,stomatal conductance,transpiration rate, intercellular CO₂ concentration,photochemical quenching and non-photochemical quenching, these could not serve as an effective index for adaptability of plants to soil acidity.(5) When soil pH increased,both growth and biomass accumulation of red pine declined. Compared with the soil pH 4.5,6.5,7.5 and 8.5,under soil pH 5.5,seedling height were 13%, 18%,27%and 50%higher respectively,and seedling ground diameter were 10%,16%,22% and 33%higher respectively.Likewise,under soil pH 5.5,conifer needles biomass,stem biomass and total biomass were significantly greater than others(p＜0.05).Total biomasses were 10%,24%,40%and 77%higher respectively.To sum up,under soil pH 5.5,growth and physiological index of red pine needles had the best comprehensive performance;the indexes of red pine needles were in moderate levels under soil pH 4.5 and 6.5;and the index of red pine needles had the worst comprehensive performance under soil pH 7.5 and 8.0.Results suggested that red pine could grow best in the soil of which pH was 5.5,following by in the soil of which pH was 4.5 and 6.5,and could not suit the soil of which pH was above7.5.