关键词: 白桦, 油松, 华北落叶松, 白杄, 发育阶段, 光响应, 形态可塑性

Abstract:

In the mountainous area of Northern China, Betula platyphylla-Larix principis-rupprechtii mixed stands, L. principis-rupprechtii-Picea meyeri mixed stands and B. platyphylla-Pinus tabulaeformis mixed stands are dominant forest types in secondary forests. The understory regeneration in these stands is essential to their long term existence after disturbances at canopy level. To interpret and predict the development and succession of these stands, 1-year-old seedlings and 4-year-old saplings of B. platyphylla, P. tabulaeformis, L. principis-rupprechtii and P. meyeri were grown at three transmittance levels of 100%, 18.7% and 7.2% of full natural light in field environment with artificially controlled light regimes for one growing season. Morphology and survival rates of these seedlings and saplings were measured to investigate their shade acclimation mechanisms at different development stages of these four woody species. The results showed that 1-year-old seedlings of B. platyphylla and P. tabulaeformis did not respond to shading in biomass accumulation, allocation and survival, while stem mass, A/B ratio and survival rate of 4-year-old saplings of B. platyphylla were reduced and A/B ratio of P. tabulaeformis saplings was increased. The survival rates of L. principis-rupprechtii and P. meyeri seedlings were increased by shading, while stem mass of L. principis-rupprechtii seedlings as well as LMR and A/B ratio of P. meyeri seedlings were increased. In contrary, at sapling stage, root and total mass of L. principis-rupprechtii and P. meyeri were both increased by shading but no responses in biomass allocation and survival were detected. At 7.2% transmittance level, seedling survival of these 4 woody species was only significantly and negatively correlated with the stem mass, but the sapling survival was positively correlated with LMR and SMR and negatively correlated with RMR. Furthermore, the morphological plasticity indices of B. platyphylla and P. tabulaeformis were smaller than that of L. principis-rupprechtii and P. meyeri at the seedling stage, but a reverse trend was observed at the sapling stage. Therefore, there were significant differences in morphological responses, survival rates and morphological plasticity indices to shading between seedlings and saplings of these 4 woody species, indicating that there were species-specific characteristics and ontogenetic changes in light acclimation mechanisms of woody species. Additionally, L. principis-rupprechtii seedlings had similar morphological responses to shading to the two intolerant species, B. platyphylla and P. tabulaeformis, however their responses in survival and morphological plasticity were similar to tolerant species of P. meyeri. L. principis-rupprechtii saplings also had similar responses in survival, morphology and morphological plasticity to P. meyeri, suggesting that the shade tolerance of L. principis-rupprechtii at its early developmental stage could be intrinsic to facilitate its wide distribution in L. principis-rupprechtii-spruce mixed forests in mountainous area of Northern China.

Key words: Betula platyphylla, Pinus tabulaeformis, Larix principis-rupprechtii, Picea meyeri, development stage, light response, morphological plasticity