| Pinus koraiensis is a precious timber tree species in northern China,which has high economic value.Pinus koraiensis has become one of the three major coniferous afforestation species in the construction of artificial forests in the northeastern mountainous areas.With the implementation of the"planting needles to maintain width"approach,more and more Pinus koraiensis are planted or naturally regenerated under the canopy in the Northeast temperate forest region,making it particularly important to promote the rapid growth and development of Pinus koraiensis under the forest.This study took Pinus koraiensis under different light intensities as the object,and selected the appropriate light intensities for the growth of Pinus koraiensis under the canopy by measuring and analyzing the morphological,physiological,and biochemical indicators of the development of branches and needles of Pinus koraiensis.This study provided a scientific basis for solving the technical bottlenecks in promoting the growth and development of Pinus koraiensis under the canopy,and also judged whether the response of Pinus koraiensis to the shade environment was shade avoidance or shade tolerance.Main findings:(1)The response of branch angle and N content in branches and needles of Pinus koraiensis to light intensity is the most obvious.The change trend of branching angle with light intensity showed that it first increased,and under the forest,the light intensity was high(PPFD:>50μmol/m~2/s),the maximum value is 74.0°;After that,the minimum value is 31.9°in full light environment,with a difference of 42.1°.Small branching angles and narrow crown types increase the proportion of photosynthetic products allocated to the trunk;Large branch angles,sparse branches,and few leaves are not conducive to growth.The N content of the branches and needles of Pinus koraiensis was determined by the light intensity under the forest(PPFD:25μmol/m~2/s-50μMol/m~2/s)treatment was the highest,38.2%and 17.1%higher than the total light treatment with the lowest N content,respectively,and showed the most significant correlation with other indicators in the correlation analysis.At the same time,plant photosynthesis was also affected by the N element content.Under forest low light intensity(PPFD:<25μmol/m~2/s)and full light,stress on Pinus koraiensis significantly reduced the content of N element.(2)Under the forest,Pinus koraiensis grows best under high light intensity.At this time,Pinus koraiensis has better branch traits and higher IAA,and the branching rate is the highest under high light intensity,which is 0.46;Minimum 0.23 in full light environment;IAA has the highest value under high light intensity,which is 49.6%higher than the lowest medium light intensity.At the same time,the analysis of the starch content,soluble sugar content,non structural carbohydrates,C content,N content,P content,C:N,and plant hormones in the branches and leaves of smaple Pinus koraiensis trees found that low light intensity and full light environment had a stress effect on the growth of Pinus koraiensis.(3)Under different light intensities,Pinus koraiensis has different responses to shade,and branch morphology,N content of branches and needles,C:N,and NSC content all undergo transitions under medium and high light intensities.At this time,the response strategy of Pinus koraiensis to shade changes from shading to shading tolerance,and there is a certain light intensity threshold between medium and high light intensities to control the shading tolerance and shading response of Pinus koraiensis.In summary,the response of morphological and physiological and biochemical characteristics of branches and leaves of Pinus koraiensis under canopy to different light intensities is represented by branch angle and N content of branches and leaves.Under high light intensity,Pinus koraiensis under forest has better morphological and physiological and biochemical indicators,which is suitable for rapid growth of Pinus koraiensis under forest.At the same time,there was a change in the response strategy of Pinus koraiensis to shading between medium and high light intensities,from shading avoidance to shading tolerance. |
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