Effects of open-field warming and precipitation manipulation on abnormal shoot growth of Pinus densiflora seedlings
The objective of this study was to investigate the effects of open-field warming and precipitation manipulation on the abnormal shoot growth of three-year-old Pinus densiflora seedlings under experimental climate change. Using infrared lamps, the temperature in warming plots has been increased to be 3°C higher than control plots. Precipitation manipulation consisted of decreased (-30%), increased (+30%) precipitation treatments and the control. About sixty of two-year-old P. densiflora seedlings were planted for each treatments in April, 2013. P. densiflora normally produce new shoots once a year in spring, therefore additional new shoot growth was categorized as abnormal shoot. The abnormal shoots of individual seedlings were monitored from July 1 to December 11 in 2014, in 5-7day intervals. The process of abnormal shoot growth was assessed as 1 of 5 stages: 0 = closed bud; 1 = slight swelling; 2 = bud elongated over 2 cm; 3 = at least one needle observed; 4 = needle grew to terminal end of new shoot; and 5 = needle at the terminal end of new shoot elongated over 2 cm.
Abnormal shoots were first observed in August, elongated in September and October, and generally maintained the last observed stage after November with all treatments. From September to December, the effect of warming treatment was always significant, meanwhile the effect of precipitation manipulation treatments was rarely significant (p<0.05). When stages of the seedlings were averaged for each treatment, the time to reach stage 1 was advanced in warming plots by 23, 36 and 19 days for precipitation control, decrease and increase treatments, respectively. In addition, only in warming plots, stage 2 was reached with all precipitation manipulation. On the other hand, about 14% of the seedlings in warming plots was in stage 3 or higher, however, such stages were not observable in control plots. As these observation suggest, the occurrence of abnormal shoots was higher in warming plots than in control plots. Meanwhile, a constant tendency was not found with all precipitation manipulation treatments. As a result, we conclude that warming might stimulate the abnormal shoot growth and change the shoot growth pattern. Therefore, further studies should consider the change in growth pattern to examine and estimate the effects of climate changes on trees with fixed growth pattern including P. densiflora.