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Pinus thunbergii is one of the main tree species of the coastal forest in Shandong peninsula,China,and plays important roles in resisting natural perturbation and maintaining its ecological functions.Adapted to the sandy ocean coast habitats and the windy conditions,the species has developed shrubby crown due to compensatory response,an important mechanism to adapt the stress environments,induced by the insect boring wounds through still unknown mechanisms.For the purpose of sustainable management of P.thunbergii forests,this study elucidated the mechanism of compensatory response and its role in the formation process of crown architecture by comparing growth characteristics of the pre-and post-boring treatments.We randomly sampled 20 trees from the coastal pine forests for monitoring the morphological changes of buds and the crown dimension during March 2009 and May 2010,and identified the shoots into three age categories according to the morphological responses to the stressing perturbation.The results showed that 1) the current and next year shoots clearly increased by 1.56 and 1.4 times after the boring,while the treatment effect on the current shoots was higher than that of the next year.It indicated that the compensatory response was persistent but gradually decreased.The compensatory response of leaf module showed similar trend but was statistically insignificant among shoots of different ages.2) A close relationship between the compensatory growth and the position of one year shoots was found,and the branch length and leaf module near the top was increased 1.75 and 1.43 times in average,respectively,after the boring,but the compensatory growth near the bottom was not tested significant.3) The process of adapted architecture begun with the change of bud module quantity and forms.The mortality of bud increased by 5.4 times which could be explained by density effect,and the number of vegetative bud increase after boring.The production of vegetative bud increased by 1.55 times on average,but the production of generative bud had no significant difference.These results suggested that the boring induced compensatory response stimulates invest in vegetative growth.4) The shoot leaders stopped growing after the boring and the number of bifurcation was increased resulting in a 25% improvement in the box-counting dimension(Db) of shoot.There was a post-peak functional relationship between the crown dimension and damage rate of shoot: the crown dimension reached the maximum while the damage rate was also increased to about 70%.This compensatory response might enhance the competitive ability of the species for space.5) The total shoot and leaf biomass did not have significant differences between pre-and post treatment indicating an equal-compensatory growth.This study revealed that apical dominance removal and the consequent compensatory responses to the boring wounds resulted in some drastic changes in crown architecture of Pinus thunbergii in the stressed coastal environments.The morphological changes of bud and their deviating normal development,as well as the crown dimension could be used as the indicators of this compensatory growth.Further studies should focus on the physiological mechanisms of the stress responses of the species. |
