Effect Of Increased Temperature And Water Stress On Pinus Koraiensis Seed Germination And Seedling Growth

Seed germination and seedling establishment are considered major bottlenecks in the life history in many ecosystems, often limiting population dynamics and expansion more than seed production per se. The distribution of many plant species will change with global climate change, depending on their ability to disperse into, and establish in, new communities. The importance of emergence time is not surprising as it has been demonstrated to strongly determine the fate of seedlings. Global temperatures are rising gradually, and increase soil drought. However, their combined effect on the pinus seed germination and seedling growth has received less attention in China because of long dormancy of seed. So, our research conclusions provide basal information and theoretical evidences for subject on the response of pinus population to climate change in its early growth days. Increased temperature treatments were conducted on the basis of average temperature of two months in which a lot of seed germination occurred and subsequent seedling growth (a mean June and July temperature of19℃and21℃, respectively) in the environment of the Pinus koraiensis. The experiment consisted of3temperature levels (+0℃,+4℃,+6℃), in which seed was exposed to control (85-90%), mild water stress (60%～65%), serve water stress (35～40%). Thus, the experiment was a factorial3×3design with3replicate plot of each temperature×soil water stress combination. Seed germination and seedling emergence were monitored from June2012until July2012, and seeding growth indexes were determined at the end of experiment. In addition, we also conducted an individual experiment to determine the effect of increased temperature on seed characteristics of physiology, growth and germination rate.Increased temperature and soil water stress had significantly effect on seed germination, only soil water stress significantly influenced on seedling emergence percentage, but no significant effect was found among their combinations. Main root length and the numbers of lateral root were significantly by their combination. Soil water stress only had significantly effect on height and lateral root length; however, specific leaf area was only significantly affected by increased temperature. Leaf length was not affected by increased temperature, soil water stress and their interaction. Main root biomass, lateral biomass, total biomass and root/shoot were all significantly affected by their combination. Leaf and shoot biomass were only significantly affected by increased temperature.A4℃or6℃increased in temperature promoted seed germination, and slightly shortened seed coat rupture and hypocotyl crook disappear time, but had little effect on seedling emergence. Biomass of the various parts of seedling had increased slightly with temperature increased4℃, and tend to decrease as temperature increased6℃. Seedling growth may be more sensitive to increased temperature compared with seed germination. Serve soil water stress (SD) significantly inhibited seed germination, delayed seed coat rupture and hypocotyl crook disappear time, and reduced seedling emergence. Although seeding emergence time was delayed by SD, seeding growth was not reduced, in contrary, seeding growth tended to increase. Seed germination was more sensitive than seedling growth to severe soil water stress. The delay in seed coat rupture and hypocotyl crook disappear time and the decrease of seedling emergence percentage resulted from SD, had a major influence on the dynamics of Pinus koraiensis communities and subsequent interspecific competition.Our results indicated that a increased4℃or6℃in June temperature significantly increased final germination percentage and germination rate index (GRI), and decreased the time necessary to reach50%of the final germination percentage (T50) and mean germination time compared, in addition, the initial period of downward seedling growth following germination was also be inhibited. The activity of catalase on the9th day and glutathione reductase on the25th day of germination test significantly increased when temperature increased4℃or6℃, but ascorbate peroxidase showed no pronounced change. A4℃or6℃warming might improve Pinus koraiensis seed germination behavior, if moisture is not limited, and the best germination effect was found at+4℃. The activity of CAT and GR may contribute to improvement in germination behavior, however, APX showed little help. Germination rate displayed greater sensitivity than final germination percentage to elevated temperature, and physiological parameters prior to morphology indexes.