竹林扩张对濒危植物华木莲开花结实的影响机制

Sinomanglietia glauca, a species of state key protected plant (Class I), was found only in Yichun City of Jiangxi Province and Yongshun County of Hunan Province, China. Our previous studies have found that the quantity of flowering and fruiting of S. glauca sharply decreased because of the encroachment of bamboo forests in Yichun areas. We suspected that the changes of community microclimate and soil nutrient ingredients due to the encroachment of bamboo might be the main reason. To fully understand the influence mechanisms of bamboo encroachment on S. glauca flowering and fruiting, we plan to perform an experiment on adjusting the community structure and controlling the soil nutrient ingredients in Mingyueshan Mountain, Yichun City of Jiangxi Province, in order to explore the influence of these factors on the following indicators: (i) reproductive indicators by using bud differentiation and flowering abilities, fruit quantity, seed vigor level, (ii) growth indicators by using diameter at breast height (DBH), tree height, branch length, (iii) physiological indicators by using photosynthesis rate, nutrient absorbability, concentration of nutrients, endogenous hormone levels, (iv) climatic indicators by using sunlight, temperature, relative humidity, etc. Finally, we will analyze the influence of encroachment by bamboo on flowering and fruiting of S. glauca, and we try to find the main impact factors that substantially impeded flowering and fruiting. In addition, the correlation between stoichiometry homeostasis and reproduction status would be expected to be elucidated, and the influence mechanism of encroachment of bamboo on blossoming of S. glauca is expected to be also revealed from the perspective of ecological stoichiometry. Research findings would not only be helpful for S. glauca conservation, but also provide an insight to the endangering mechanism for the rare and endangered plant species.

华木莲（Sinomanglietia glauca）是国家一级重点保护植物，迄今仅发现于江西宜春市与湖南永顺县。前期研究发现，宜春华木莲种群正遭受竹林扩张的干扰，开花结实量锐减,濒危程度加剧，并推测竹林扩张引起群落小气候与土壤养分变化可能是主要原因，然而其作用机制尚不清楚。本项目拟在华木莲集中分布区江西宜春明月山开展群落结构调整与土壤养分调节控制实验，观测华木莲花芽分化、花蕾开放、坐果数量、种子活力等生殖指标和胸径、树高、枝长等营养生长指标；同时测定光合作用、养分吸收、养分浓度、内源激素等生理指标和光照、温度、相对温度等气候指标。最后分析林竹扩张对华木莲开花结实的影响并确定关键影响因子，阐明扩张强度-化学计量内平衡-开花结实的作用过程，并试从化学计量学的角度揭示毛竹扩张对华木莲开花结果的影响机制。研究成果不仅有利于华木莲这一珍稀种质资源保护，也为探索珍稀植物濒危机制提供新的思路。

华木莲（Sinomanglietia glauca）是国家一级重点保护植物，迄今仅发现于江西宜春市与湖南永顺县。前期调查发现，宜春华木莲种群正遭受竹林扩张的干扰，开花结实量锐减，濒危程度加剧，并推测竹林扩张引起群落小气候与土壤养分变化可能是主要原因。. 为了验证这一推测并解析主要因子的作用机制，2014-2018年，在江西玉京峰落叶木莲自然保护区（江西宜春市）、温汤林场(江西宜春市)和江西农业大学校园，以样株为研究单元，观测华木莲花芽分化、花蕾开放、坐果数量、种子活力等生殖指标和胸径、树高、枝长等营养生长指标；同时测定光合作用、养分吸收、养分浓度等生理指标和光照、温度、相对温度等气候指标。分析竹子扩张导致华木莲开花结实减少的外部环境因子（气象、土壤）和内部因子（光合作用、养分分配）的作用关系。研究结果发现：. （1）竹子在向华木莲群落扩张，可以遮挡和部分遮挡阳光，华木莲受光强度减少、空气相对湿度增加，同时土壤有效N含量下降、P含量有增加。. （2）华木莲是一种阳性植物，有较高的光合作用饱和点与补偿点，而被竹子遮荫的枝叶来不及适应低光照环境，净光合速率下降，而整枝系数增加。华木莲树体结构改变，树冠伸展度下降、冠幅缩减、有效树冠体积和叶面积减少。. （3）有效树冠减小、光合作用减弱，非结构性碳（可溶性糖、淀粉）积累不足，氮含量增加，C/N比较低，花芽分化率降低、坐果率下降，而且种子质量不高，种子较小、萌发率降低。另外，树冠减少还直接减少了花果的承载空间。导致华木莲开花结实数量不足，质量不高，严重影响.这些结果表明，竹子扩张影响华木莲开花结实的主要原因是，遮荫减弱了光合作用，导致枝叶C储不足，养分化学计量失衡，导致开花结实率下降。为了保护华木莲这一珍稀种质资源，建议加强竹子扩张管控和调整群落结构。