| Fraxinus mandshurica and Quercus mongolica, two of the most important broadleaved commercial tree species, are the main associated tree species of broad-leaved korean pine forest in the eastern mountainous area of Northeast China. The history of silviculture for plantation forest established with F. mandshurica and Q. mongolica are short, with extremely limited plantation area. Less effort has been invested in the study of physiological and ecological features of this tree species, especially shade-tolerance. We grew2-year-old F. mandshurica and Q. mongolica seedings in pots under four shading treatments (100%,75%,50%and25%of full light, FL, LS, MS and HS for short, respectively), and observed the growth, leaf characteristics and photosynthetic characteristics during the growth season in two consecutive years.The results showed that:(1)Shading promoted the height growth of two tree species, in2010and2011, the height growth of F. mandshurica under LS, MS and HS treatments respectively was1.22,1.22,1.09and1.76,2.21,2.49times as great as FL; the height growth of Q. mongolica under LS, MS and HS treatments respectively was1.20,1.17,1.15and1.33,1.89,0.91times as great as FL Moderate shading was make for the accumulation of biomass, in2010and2011, the whole plant biomass of F. mandshurica under MS treatment were the largest, respectively was46.00g and121.70g; the whole plant biomass of Q. mongolica under LS treatment were the largest, respectively was16.73g and31.05g, suggesting that:F. mandshurica was adapt to the LS light environment, Q. mongolica was adapt to the MS light environment. With the increase of shading degree, the order of root shoot ratio was FL>LS>MS>HS, suggesting that strong light promoted more biomass to root, the more part of biomass allocated to the part of ground under low light.(2)Shading promoted the increase of chlorophyll content (Chl), leaf area and the relative water content of leaves, leaded the decrease of the leaf dry mass per unit leaf area (LMA), with the increase of shading degree, the order of chlorophyll content (Chl), the leaf area and relative water content of two tree species respectively was FL<LS<MS<HS, the order of LMA was FL>LS>MS>HS, suggesting that two tree species could ability to meet certain low light environment.(3)The maximum net photosynthetic rate (Pmax) of two tree species under shading treatments were smaller than FL, in2011, the Pmax of F. mandshurica and Q. mongolica under LS, MS and HS treatments respectively was reduced by5.57%,24.23%,28.27%and11.76%,0.76%,21.87%than FL. The apparent quantum efficiency (AQY) were bigger than FL, in201lyear, the order of AQY of two tree species were FL<LS<MS<HS. Dark respiration rate (Rd) decreased with the increase of shading degree, the order were FL<LS<MS<HS in two consecutive years. In2011, the light compensation point(LCP) of two tree species decreased along with increasing of shading degree. Suggesting that two tree species were moderately shade tolerant at the seedling stage, through a series of photosynthetic response to adapt to the light environment. In2011, the LCP of F. mandshurica was smaller than Q. mongolica under HS treatment, reapectively was19.13μmol·m-2·s-1a nd26.61μmol·m-2·s-1, suggesting that F. mandshurica has stronger shade-tolerance than Q. mongolica.(4)Under low light intensity (PPFD<200μmol·m-2·s-1), light use efficiency(LUE) of two tree species in shading treaments were higher than FL, suggesting that two tree species had strong ability of useing weak light. Plasticity index of Q. mongolica was higher than F. mandshurica, the average plasticity index of Q. mongolica in two years was1.09times as great as F. mandshurica, suggesting that Q. mongolica could adapt to the wider range of light than F. mandshurica. |
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