The Comparison Of Physiological Characteristic Of Resistance Against Abiotic Stress Between Pinus Densiflora Var. Zhangwuensis And Pinus Sylvestris Var. Mongolica In Sandy Soil At Different Growth Stages

For an objective evaluation of stress resistance and a better understanding of its mechanisms in Pinus densiflora var. zhangwuensis, four-year-old P. densiflora var. zhangwuensis and P. sylvestris var. mongolica was adopted as test materials, and experimental researches on adversity resistance were carried out. With a potting experiment, morphological parameters and five physiological indicators including malondialdehyde(MDA), catalase(CAT), chlorophyll(Chl), proline(Pro), and leaf water content(LWC) of P. densiflora var. zhangwuensis and P. sylvestris var. mongolica were measured in different soil moisture gradients. The results showed that: P. densiflora var. zhangwuensis had significantly heavier total dry weight, dry weight of root, dry weight of stem and greater ratio of root and stem, had significantly smaller single needle area, and had slightly more thick needle than P. sylvestris var. mongolica. In different water gradients, P. densiflora var. zhangwuensis had lower MDA contents, and higher CAT and Pro contents than P. sylvestris var. mongolica. In mild drought area(40%FMC, SWP=-4.82bar), MDA, CAT and Pro contents of P. sylvestris var. mongolica had a ascending trend in comparison with those in control area(100%FMC, SWP=-2.81bar), and the three physiological indicators had a further increase in moderate drought area(30%FMC, SWP=-10.35bar) and reached to the maximum in serious drought area(20%FMC, SWP=-20.14bar). By contrast in mild drought area these three physiological indicators in leaves of P. densiflora var. zhangwuensis were lower than those in control area, and began to increase in moderate drought area, especially the CAT content was significantly higher than that in control area, and they also reached to the maximum in serious drought area. The above results determinated that P. densiflora var. zhangwuensis showed stress symptoms at a lower soil moisture, and it could endure and adapt to drought stress by improving protective enzyme activity(CAT) and increasing osmotic substance(Pro). At different moisture gradients, both Chl and LWC of P. densiflora var. zhangwuensis were more than those of P. sylvestris var. mongolica, and these two indicators in the same species had the same changing trend,which was : CK > mild drought area > moderate drought area > serious drought area.For an objective evaluation of salinity-alkalinity tolerance and a better understanding of its mechanisms in Pinus densiflora var. zhangwuensis, 4-year-old P. densiflora var. zhangwuensis and P. sylvestris var. mongolica were studied. Pot experiments were used to examine the effects of three types of salt (NaCl, Na2CO3, and NaHCO3) and alkali stress (NaOH) on seedling growth and physiological and biochemical indices. The substrate was fine sand taken from Zhanggutai sandy land, Liaoning Province, China. In the salt stress treatments, the matrix salt content was 4 g salt kg-1, and in NaOH stress treatments, the matrix pH value was 9.0. In P. densiflora var. zhangwuensis, the injury level was smaller, and the root tolerance index was bigger under salt-alkali stress. Malondialdehyde (MDA) content did not significantly increase under salt-alkali stress, while catalase (CAT) activity was significantly induced by stress, by as much as 22.6 times that of the control. Finally, chlorophyll (Chl) content did not significantly decline, and leaf water content (LWC) increased slightly. Pinus sylvestris var. mongolica responded differently to salt-alkali stress; its MDA content increased (NaCl treatment) or significantly increased (remaining three treatments), but its CAT activity did not increase significantly. Leaf Chl content declined significantly under salt-alkali stress, with Chl contents in the Na2CO3, NaHCO3, NaCl treatments 36.2%, 21.7%, and 62.3% lower than in the control. In addition, LWC decreased in leaves under stress. The results suggest that P. densiflora var. zhangwuensis has greater salt-alkali tolerance than P. sylvestris var. mongolica and that it ensures this tolerance by increasing CAT activity and maintaining high contents of Chl and leaf water. Higher levels of iron in needles of P. densiflora var. zhangwuensis enhanced CAT activity and Chl content, while higher levels of elemental zinc and copper were also associated with stronger resistance. In P. densiflora var. zhangwuensis, salinity stress did not cause drought stress, so growth was not inhibited by drought stress, but by ion toxicity and nutrient imbalance due to salinity stress.Freezer method was used to carry out cold-stress test at different temperature gradients. With the combination between conductivity method and physiological method, relative conductivity as well as physiological and biochemical indicators such as MDA, CAT, Pro and SS in leaves of seedlings before and after stress were measured in order to identify cold resistance of the two species and to clarify their mechanism of cold hardiness. The results showed that: After cold resistance exercise, half-lethal temperature of P. densiflora var. zhangwuensis and P. sylvestris var. mongolica was -54.23℃and -50.34℃, respectively, which indicated that both species were strong cold hardiness, but a little cold hardiness in P. densiflora var. zhangwuensis higher than P. sylvestris var. mongolica due to cold acclimation. With the deepening of stress, Pro and SS changes model of two species was basically the same, while CAT activity in different patterns. In lower than -20℃, the CAT activity in leaves of P. densiflora var. zhangwuensis seedlings gradually increased, while that of P. sylvestris var. mongolica remained constant. In every temperature gradient, Pro and SS content was lower in leaves of P. densiflora var. zhangwuensis than P. sylvestris var. mongolica, while CAT activity of the former higher than the latter. The two species had slightly different cold-resistance mechanisms: From the point of view of content of indicators, P. densiflora var. zhangwuensis focused on using higher antioxidant enzyme activities to resist stress injury, and P. sylvestris var. mongolica focused on using higher ability of osmotic adjustment to enhance cold tolerance. From the point of view of variation trend in the indicators with the stress deepening, in mild cold stress, the two species could increase cold hardiness by increasing osmolyte (Pro and SS) content. But in severe cold stress (-40℃~-60℃) that caused stress injuries, P. densiflora var. zhangwuensis had a smaller increase of MDA by increasing CAT activity and maintaining the SS increments, while P. sylvestris var. mongolica had no such mechanism.In order to photosynthesize, land plants must open their stomata to exchange small amounts of CO2 at the cost of losing a lot of water vapor through transpiration. This gas exchange is unequal in that more water is lost than CO2 is taken in. In general, fast growing species are characterized by their high photosynthetic capacity, most of which is achieved at the expense of consuming large amounts of water. This trade-off poses a serious challenge to forestry in the selection of fast-growing tree species in arid and semiarid areas. The ideal forestry species for drier climates should maintain a high photosynthetic capacity as well as low water consumption for transpiration, but such species are very rare. In this study, the LI-6400 (LICOR, Inc. Lincoln, NE, USA) portable photosynthesis system was employed to measure diurnal changes in photosynthetic and transpiration indices in sexually mature P. densiflora var. zhangwuensis and P. sylvestris var. mongolica (18 years old). In addition, the cut-branch transpiration method was used to compare stomatal and cuticular transpiration in order to evaluate the sensitivity of stomatal opening and closing and to characterize the photosynthetic productivity and water consumption for transpiration in these two species in different growing seasons. P. densiflora var. zhangwuensis had a higher photosynthesis rate (Pn) and a lower transpiration rate (Tr) than P. sylvestris var. mongolica under the same conditions. In May and July, the diurnal changes of Pn and Tr in P. densiflora var. zhangwuensis formed double-peaked curve as a result of mid-day stomatal limitation, while it formed single-peaked curve in October. The daily variation of Pn and Tr in P. sylvestris var. mongolica exhibited a monopeak curve throughout the growing season. The net photosynthesis per day in P. densiflora var. zhangwuensis was higher than in P. sylvestris var. mongolica; values for the former were 163.4 (May), 211.1 (July), and 183.6 (October) percent of the latter. The photoresponse parameter measurements showed that, in different months, the maximum rate of photosynthesis of P. densiflora var. zhangwuensis was greater than that of P. sylvestris var. mongolica, and the former also had a higher light saturation point and a lower light compensation point. The stomatal conductivity (Gs) and Tr of P. densiflora var. zhangwuensis were lower than those of P. sylvestris var. mongolica when measured at random times. The stomatal and cuticular Tr of P. densiflora var. zhangwuensis were lower, and in the same drought conditions, its stomata were deeper and had a higher sensitivity for opening and closing. Water use efficiency (WUE) of P. densiflora var. zhangwuensis was 2.29 times that of P. sylvestris var. mongolica. Analysis of the correlation between Gs and WUE showed that P. densiflora var. zhangwuensis could maintain high WUE when Gs levels were high. In May and July, when P. densiflora var. zhangwuensis exhibited midday photosynthetic depression, its Gs level was low, usually in the 90~200 mmol ? m-2 ? s-1 range. At the same time, its WUE was higher than that of P. sylvestris var. mongolica, indicating that P. densiflora var. zhangwuensis could effectively conserve water by closing its stomata rapidly at midday, so as to maintain its high WUE. Nitrogen content per unit leaf area(Narea) and photosynthetic nitrogen use efficiency (PNUE) was higher, and gaseous conductance through intercellular air space(gias) was also larger in P. densiflora var. zhangwuensis. The stomata diameter and density was small, which was also able to maintain a smaller Gs and Tr, and thus a reason to maintain a larger WUE in P. densiflora var. zhangwuensis. These results implied that P. densiflora var. zhangwuensis can improve its WUE, yielding its higher Pn and lower Tr, and achieves its fast growth in arid and semiarid regions through its sensitive stomatal response and leaf xeromorphism.