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Scientia Silvae Sinicae ›› 2015, Vol. 51 ›› Issue (3): 93-101.doi: 10.11707/j.1001-7488.20150312

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Effects of Defoliations on the Chlorophyll Contents and Biomass of the Poplar (Populus simonii×P. nigra) and Larix gmelinii Seedlings

Li Yuanyuan, Zhang Kai, Li Shuangwen, Yan Shanchun   

  1. College of Forestry, Northeast Forestry University Harbin 150040
  • Received:2013-11-13 Revised:2014-05-27 Published:2015-04-10

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Abstract:

Defoliations by leaf/needle-feeding insects can cause significant losses of tree growth, biomass, and carbon storage. Potential effects of artificial defoliations at 0%, 25%, 50% and 75% levels to mimic the defoliator damages on biomass and chlorophyll contents of the poplar (Populus simonii×P. nigra) and larch (Larix gmelinii) seedlings at 5, 10, 15, 20 and 25 days after each treatment 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 that 50% 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 contents ("a" > "b"). Significant increase of chlorophyll contents already occurred at 5th day after the defoliation, with the 75% level being significantly higher than the control and the two lower levels (25% and 50%) for both chlorophyll "a" and "a"+"b" (P<0.05). At 10th day after the defoliation, chlorophyll "a" and "a"+"b" contents of 25% and 75% defoliations were significantly higher than that of the control, and were not different among the treatments. At 15th days after the defoliation, there were no differences in chlorophyll contents among the treatments and the control (P>0.05). At 20th day after the defoliation, chlorophyll "a", "b" and "a"+"b" contents of 50% defoliation were significantly lower than those of 25% defoliation and control; and slightly lower (but not significantly) than those of the 75% level. At 25th day after the defoliation, there were no differences in chlorophyll contents between each treatment and the control (P>0.05). Chlorophyll contents of the 50% defoliation level were significantly higher than those of 25% defoliation treatment, and slightly higher (but not significantly) than those of the 75% level.. In contrast to the poplar leaves, the chlorophyll "b" content was higher than chlorophyll "a" in the larch needles. The chlorophyll contents of larch needles at 25% and 75% defoliation levels showed a pattern of increase-decrease-increase; i.e. increased after the fifth day, decreased after the 10th day, and further decreased to a level similar to the control on the 15th day; its content levels increased again after the 20th day, and reached back to control level at 25th day after the treatments. The larch needle chlorophyll contents in the 50% defoliation group were lower than that of the control at 5th, 15th, and 20th days of the defoliations; the contents at 5th and 20th days were even lower than those in 25% and 75% defoliation groups; the contents at 10th day were not different significantly from the control and 25% and 75% defoliation groups. At 25th day after the 50% defoliation, chlorophyll contents in the larch needles were significantly higher than those of control and 25% and 75% defoliation groups. Our results showed that defoliations have significant impacts on carbon sequestration and photosynthetic physiological responses of both poplar and larch seedlings. 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.

Key words: Larix gmelinii, Populus simonii×, P. nigra, defoliation, biomass, chlorophyll

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