不同生境下木棉树形结构特征及其影响因子

The characteristics of tree shape structure and the influencing factors of Bombax ceiba L.in different habitats

明确树形结构对异质生境的响应特征,不仅能了解树木对生境的适应性,还能研判其生长策略。通过对元江和勐腊地区气象、地形及土壤的分析,耦合该区域木棉枝下高、树高、胸径、冠幅、树冠比和一级分枝数等,探明不同生境下(干热河谷、热带雨林)木棉树形结构的变化及其对环境因子的响应。结果表明:元江和勐腊地区木棉树形结构有较大差异,勐腊地区各径级木棉的枝下高、树高、胸径和冠幅大于元江地区,而一级分枝数、树冠比较小。另外,主导两地木棉树形结构变异的主要环境因子各不相同,元江地区木棉树形结构主要受年均最高气温(37.8%)、坡向(7.2%)、平均水汽压(5.2%)、日照时数(6.8%)、年均降水量(7.0%)、全磷含量(3.6%)、硝态氮含量(2.6%)影响,勐腊地区主要受平均气温(63.5%)、硝态氮含量(8.9%)、全磷含量(3.1%)、全氮含量(2.4%)、铵态氮含量(2.2%)、年均最低气温(1.8%)、有效磷含量(1.7%)、平均相对湿度(1.8%)影响。气候、地形及土壤因素是影响木棉生长的重要环境因子,但影响程度不同,元江及勐腊地区环境因子因素解释木棉树形结构的变异分别为81.9%与87.2%,但勐腊地区木棉树形结构受土壤养分的影响程度更大。总体而言,木棉树形结构能够通过功能性状的可塑性来适应两种极端生境,研究结果可为探索树形结构对异质生境的适应关系提供科学借鉴。

Identifying the response characteristics of tree shape structure to heterogeneous habitats can help understand the adaptability of trees to their habitats and the factors determining their growth strategies.Based on the analy-sis of meteorological,topographic and edaphic factors in Yuanjiang and Mengla,together with under-branch height,tree height,diameter at the breast height,crown diameter,crown ratio and primary branch number of Bombax ceiba L.,we quantified the changes of Bombax ceiba tree shape structure in response to environmental factors in different habitats(hot dry valley vs.tropical rain forest).The results showed that tree shape structure of Bombax ceiba was different between Yuanjiang and Mengla.The under-branch height,tree height,diameter at breast height,and crown diameter of Bombax ceiba were greater,while the primary branch number and crown ratio were smaller in Mengla than those in Yuanjiang.The main environmental factors influencing tree shape structure at the two sites were different.Tree shape structure of Bombax ceiba in the Yuanjiang was mainly affected by annual mean maximum temperature(37.8%),slope direction(7.2%),mean vapor pressure(5.2%),average sunshine hours(6.8%),mean annual precipitation(7.0%),total phosphorus content(3.6%),and nitrate-nitrogen content(2.6%).By contrast,tree shape structure of Bombax ceiba in the Mengla was mainly affected by average annual temperature(63.5%),nitrate-nitrogen content(8.9%),total phosphorus content(3.1%),total nitrogen content(2.4%),ammonium-nitrogen content(2.2%),annual mean minimum temperature(1.8%),available phosphorus content(1.7%),and average relative humidity(1.8%).Meteorological,topographical and edaphic factors were the important environmental factors affecting the growth of Bombax ceiba,although their relative importance can vary.Environmental factors explained 81.9% and 87.2% of the variation of Bombax ceiba tree shape structure in Yuanjiang and Mengla,respectively.Tree shape structure of Bombax ceiba in Mengla was more affected by soil nutrients.Collectively,tree shape structure of Bombax ceiba can adapt to the two extreme habitats by the plasticity of functional traits.Our results can provide scientific reference for exploring the relationship between tree shape structure and heterogeneous habitats.