Water Stress And Winter Injury Mechanism Of Red Pine Seedlings

Red pine (Pinus resinosa Ait.) is one of the major tree species for afforestation in the northeast areas of the United States of America with good material quality and wide usage. In 2004, preliminary success was achieved in the introduction of red pines in the eastern mountainous regions of Northeast China. It was found in the process of cultivation that etiolation of needles and even withering to death of the whole plant occurred in red pine saplings at parts of microsites after overwintering, which was thought to be linked with factors such as soil moisture, temperature fluctuation, photooxidation and so on by the preliminary analysis. The pot cultivation method was adopted to study physiological response of seedlings under different treatments of soil moisture(flooding treatment,100%,80%,60%,40% and 20% of field capacity were respectively marked by FC, FC80, FC60, FC40 and FC20) and to evaluate the adaptability mechanism and tolerance of red pine seedlings under different conditions of soil moisture. Meanwhile the experiment of natural overwintering was conducted on seedlings under different treatments (including autumn waterlogging, autumn temperature fluctuation and winter shading); by means of variation of physiological indicators, the cause of winter injury was analysed in combination of the situation of winter injury and recovery. The main research conclusions were as follows:(1)The different soil moisture treatments had significant influence on growth and biomass of red pine seedlings(p<0.05).Under the treatment of FC60, seedling height, caliper and biomass were all significantly higher than those under the other treatments. Under the low soil moisture treatments, growth and biomass of seedlings both decreased, and root shoot ratio increased significantly(p<0.05).Under the treatments of FC40 and FC20, biomass of seedlings dropped respectively by 17% and 26% over that under the treatment of FC60. Under the high soil moisture treatments of FC80, FC and FL, growth and biomass of seedlings decreased to some extent, and root shoot ratio decreased significantly(p<0.05). Thereinto, biomass under the treatment of FL dropped by 41% over that under the treatment of FC60.(2)The different soil moisture treatments had obvious influence on the plasma membrane stability of red pine seedling needlings, and had significant influence on the content of MDA(p<0.05). Under the treatment of FC60, the content of MDA and relative electrical conductivity in needlings were both the lowest. The content of MDA under the treatment of FC40 was lower than that under the treatment of FC20. The contents of MDA under the treatments of FC80, FC and FL increased successively. The content of MDA under the treatment of FL rose obviously, which was respectively 92.2%,46.1% and 70.0% higher than that under the treatment of FC60 on the 7th,14th and 21th day.(3)The different soil moisture treatments had obvious influence on the antioxidation system of red pine seedling needlings, thereinto, they had significant influence on POD and CAT(p<0.05). Under the treatment of FC60, the activity of CAT was the highest, while the activity of POD was lower. Under the treatment of FC40, the activity of CAT in needlings was higher than that under the treatment of FC20, and the activity of POD was lower than that under the treatment of FC20. Under the treatments of FC80, FC and FL, the activities of CAT in seedling needlings decreased successively and the activities of POD increased successively. Soil water stress caused regular variation of the activities of CAT and POD in needlings.(4)The different soil moisture treatments had significant influence on the contents of osmoregulation substances in red pine seedling needlings (p<0.05). Under the treatment of FC60, the contents of proline and soluble sugar in seedling needlings were the lowest. The contents of proline and soluble sugar in seedling needlings under the treatment of FC20 were higher than those under the treatment of FC40. The contents of proline and soluble sugar in seedling needlings under the treatments of FC80, FC and FL increased successively. Thereinto, the contents of proline and soluble sugar under the two treatments of FC20 and FL were the highest. On the 21st day of treatment, the content of proline was respectively 4.9 times and 5.8 times higher than that under the treatment of FC60, and the content of soluble sugar was respectively 1.4 times and 1.9 times higher than that under the treatment of FC60.(5)The different soil moisture treatments had obvious influence on the photosynthetic metabolism of red pine seedling needlings, and had significant influence on photosynthetic pigments(Chla, Chlb and total content of chlorophyll), photosynthetic parameters(Pn, Tr and Gs) and fluorescence parameters(Fo,Fm,Fv,Fv/Fm,ΦPSII) (p<0.05). Under the treatment of FC60, the total content of chlorophyll, Pn, Fv/Fm andΦPSII in seedling needlings were all the highest. The total content of chlorophyll, Pn, Chla, Chlb and Car under the treatment of FC40 were all higher than those under the treatment of FC20. Above-mentioned indicators for the treatments of FC80, FC and FL decreased successively. The total contents of chlorophyll under the treatments of FC20 and FL decreased respectively by 44.7% and 49.2% over that under the treatment of FC60. Drought and waterlogging treatment both posed stronger light restrain to seedling needlings.(6)After stress relief, there was recovery of different extents in all physiological indicators for the treatments of FC40 and FC20, and the treatments of FC80, FC and FL, among which the indicators for the treatments of FC80, FC and FC40 got recovered faster. However, some index value under the treatments of FC20 and FL at the second week after stress relief didn't achieve full-recovery yet. (7)The winter shading treatment was able to improve cold resistance of red pine seedling and reduce winter injury and mortality rates. In the process of temperature drop of early overwintering, compared with the check, the permeability of plasma membrane of needlings under the shading treatment decreased; the content of MDA reduced; and variation which was favorable to improving cold resistance capacity occurred in both the antioxidant enzyme system and the contents of osmoregulation substances such as proline, soluble sugar and so on. Seedlings which suffered winter injury were 4% lower than those under check. With the rising again of air temperature of late overwintering, all physiological indicators for seedling needlings under the shading treatment got recovered to some extent, and the mortality rate decreased by 4% over that under check after overwintering.(8)The treatments of autumn waterlogging or temperature fluctuation both obviously reduced cold resistance of red pine seedlings, and caused winter injury and mortality of seedlings. Compared with the check, the permeability of plasma membrane of seedling needlings under the treatments of autumn waterlogging and temperature fluctuation increased; variation which was not favorable to cold resistance occurred in the permeability of plasma membrane, the antioxidant enzyme system and the contents of osmoregulation substances such as proline and soluble sugar of seedlings in the early overwintering. With the rising again of air temperature of late overwintering, all physiological indicators for seedling needlings under the two treatments got recovered to some extent, but the degrees of winter injury and mortality rates were both higher than those under check. In March, the discoloration rates of seedling needlings under the treatments of autumn waterlogging and temperature fluctuation reached 44% and 100% respectively,30% and 86% higher than those under check. In May, the mortality rates of seedlings were respectively 4% and 10% higher than those under check.In summary, red pines displayed different adaptability when they were subjected to adversity of drought, waterlogging and low temperature. Red pines resisted drought rather than waterlogging. The seedlings under the condition of 60% of field capacity presented the optimum comprehensive performance. Red pines were suitable to be cultivated under the condition of moderately inclined arid soil. Red pines had stronger cold resistance and were able to response quickly to low temperature adversity of various kinds. Winter shading was favorable to safe overwintering of red pine seedlings. Either autumn waterlogging or autumn temperature fluctuation would cause decrease of cold resistance of red pine seedlings so as to increase the degree of winter injury of seedlings.