| Larch (Larix spp.) and poplar(Populus spp.) are the main plantation tree species in Northeast China. Both play an important role in the increase of forest carbon sequestration sinks in the process, but pests and diseases do threat to the forestry continued production, stability, development and emission reduction targets in recent years. In order to ascertain the influences of the extent of damage and means of forest insect resistance induced on enhancing forest carbon sequestration.2-year-old larch(Larix gmelinii) and poplar {Populus simonii×P. nigra) were chosen as the research object, larch and poplar seedling leaf were cut to mimic the defoliator damages. Comparing biomass and chlorophyll content with the control, the impact of the loss of broad-leaved trees leaf level on carbon sequestration was analyzed. And methyl jasmonate was applied to induce resistance of plants. The impact of the inducer on both plant(growth, development, chlorophyll content) and its pest(growth, development) were analyzed to explore the relationship between pest control effect and tree defense costs so that a reasonable solution can be provided. In coniferous trees, the differences of defense responses induced were compared to provide optimal solutions. The results were as follows:1. Potential effects of artificial defoliations at25%,50%and75%levels to mimic the defoliator damages on biomass and chlorophyll contents of the larch and poplar seedlings were investigated in the current study. Our results showed that there were no significant differences among the treatments in the plant height and root length (P>0.05) for both tree species, except that50%larch seedling needle removal resulted in a significant increase of root length (P＜0.05). Fresh and dry weights of the poplar seedling roots and whole seedling biomass in the three defoliation treatments were significantly lower than those of the untreated control, whereas the fresh and dry weights of the poplar seedling stems were not different among the treatments and the control. Fresh and dry weights of the larch seedling root, stem and whole seedling biomass in either defoliation group were significantly lower than those in the control group. Defoliations of poplar leaves resulted in different levels of increase in chlorophyll content; significant increase of chlorophyll contents for three defoliation levels occurred5and10days after the defoliation (P＜0.05). The chlorophyll contents of larch seedlings at25%and75%defoliation levels showed a pattern of increase-decrease-increase; i.e. increased after the fifth day, decreased after the10th day, and further decreased to a level similar to the control on the15th day; its content levels increased again after the20th day. The larch seedling chlorophyll contents in the50%defoliation group were significantly lower than that of the control within25days of the defoliations, but were significantly higher after the25days of defoliations.2. We studied the effect of plant exogenous hormones on the gypsy moth control and the plant carbon sequestration capacity. After the methyl jasmonate was sprayed, the biomass and chlorophyll content of the larch and the poplar, were monitored; the growth and development of the gypsy moth larvae feeding on the leaves of the sprayed plants were also measured. The results showed that:root dry and fresh weights of the larch were significantly higher than those of un-sprayed control (P＜0.05); stem dry and fresh weights were significantly lower than those of the control P＜0.05), but there were no significant differences in the whole plant biomass between the sprayed treatments and un-sprayed controls (P>0.05). Both fresh and dry weights of roots, stems and the whole plant biomass of the poplar were all significantly lower than those of the controls P＜0.05). The chlorophyll b and the total chlorophyll contents in larch needles were significantly higher than those of the control (P＜0.05) at the fifth and tenth day after the spray; whereas, no significant differences (P>0.05) in chlorophyll a, b and total chlorophyll content were detected the10th day after the sprays. Contents of the three types of chlorophylls in the sprayed the poplar leaves were all higher than those of un-sprayed controls10days after the treatment, and then started decreasing rapidly. They were all significantly lower than those in the un-sprayed controls the15th day and the20th day after the spray treatments(P＜0.05). The body weights of the3rd to6th instar gypsy moth larvae feeding on the sprayed the larch needles were lower than those on the un-sprayed control needles (P<0.05). The larval relative growth rates were also lower in the treatment group than were the control group. The body weights of the third, fourth and sixth instar larvae feeding on the sprayed the poplar leaves were significantly lower than those on the un-sprayed control needles (P＜0.05). The larval relative growth rates were also lower than those of the control group. but the significant difference was only detected among3rd instar larvae.These result indicated that defoliations has effects on carbon sequestration and photosynthetic physiological responses of poplar and larch seedling. Increasing the chlorophyll contents and improving the photosynthesis efficacy (per unit area) should compensate the decreases of carbon sequestration and biomass loss caused by the defoliations to some degrees, and polar seedlings seemed to show a stronger compensation ability than do the larch seedlings. Methyl jasmonate as an inducer can enhance defensive responses (resistance) of both poplar and larch trees against defoliators, however, it might also weakened the carbon sequestration capacity to poplar, but not to larch. |
PDF Full Text Request