Gao Yuan, Zhang Zhidong, Lu Deliang, Zhou Ying, Liu Qiang
Hebei Agricultural University, College of Forestry, Baoding, China.
Qingyuan Forest CERN, National Observation and Research Station, Shenyang, Liaoning, China.
Front Plant Sci. 2024 Mar 14;15:1340058. doi: 10.3389/fpls.2024.1340058. eCollection 2024.
Under-canopy afforestation using different tree species is a key approach in close-to-nature management to improve the structural and functional stability of plantation forests. However, current research on understory afforestation mainly focuses on the seedling stage, with limited attention to saplings or young trees. In this study, we evaluated the growth characteristics and leaf traits of 14-year-old var. trees under four different upper forest density (UFD) treatments: 0 trees/hm (canopy openness 100%, CK), 150 trees/hm (canopy openness 51.9%, T1), 225 trees/hm (canopy openness 43.2%, T2), and 300 trees/hm (canopy openness 28.4%, T3). We found that the survival rate of in the T3 was significantly lower than in the other treatments, with a decrease of 30.2%, 18.3%, and 19.5% compared to CK, T1, and T2, respectively. The growth of in the T1 treatment exhibited superior performance. Specifically, T1 showed a significant increase of 18.8%, 5.5%, and 24.1% in tree height, diameter at breast height, and crown width, respectively, compared to the CK. The mean trunk biomass ratio in the understory was significantly higher than that in full light by 15.4%, whereas the mean leaf biomass ratio was significantly lower by 12.3%. Understory trees tended to allocate more biomass to the trunk at the expense of decreasing leaf biomass, which would facilitate height growth to escape the shading environment, although the promotion was relatively limited. Leaf length, leaf width, leaf area, leaf thickness, mesophyll tissue thickness, epidermis thickness, and leaf carbon content were the highest in the CK and tended to decrease with increasing UFD, indicating that a high-light environment favored leaf growth and enhanced carbon accumulation. In summary, young trees adapted to moderate shading conditions created by the upper canopy, and the T1 treatment was optimal for the growth of understory . This study provides insights into different adaptive strategies of young trees to changes in light environment, providing practical evidence for under-canopy afforestation using light-demanding trees during pure plantation transformation.
利用不同树种进行林下造林是近自然经营中提高人工林结构和功能稳定性的关键途径。然而，目前关于林下造林的研究主要集中在幼苗阶段，对幼树或小树的关注有限。在本研究中，我们评估了在四种不同上层林分密度（UFD）处理下14年生[树种名称]树的生长特性和叶片性状：0株/公顷（林冠开阔度100%，CK）、150株/公顷（林冠开阔度51.9%，T1）、225株/公顷（林冠开阔度43.2%，T2）和300株/公顷（林冠开阔度28.4%，T3）。我们发现，T3处理下[树种名称]的成活率显著低于其他处理，分别比CK、T1和T2降低了30.2%、18.3%和19.5%。T1处理下[树种名称]的生长表现出优势。具体而言，与CK相比，T1处理下树高、胸径和冠幅分别显著增加了18.8%、5.5%和24.1%。林下平均树干生物量比显著高于全光照下15.4%，而平均叶片生物量比显著低12.3%。林下[树种名称]树倾向于将更多生物量分配到树干上，以减少叶片生物量为代价，这将有助于高度生长以逃离遮荫环境，尽管促进作用相对有限。叶片长度、叶片宽度、叶面积、叶片厚度、叶肉组织厚度、表皮厚度和叶片碳含量在CK中最高，并随着UFD的增加而趋于降低，表明高光环境有利于叶片生长并增强碳积累。总之，幼龄[树种名称]树适应上层林冠创造的适度遮荫条件，T1处理对林下[树种名称]树的生长最为适宜。本研究揭示了幼龄[树种名称]树对光照环境变化的不同适应策略，为纯林改造过程中利用喜光树种进行林下造林提供了实践依据。
