Estimate of coarse root biomass and nutrient contents of trees in a subtropical broadleaf forest in Taiwan

We studied the biomass and estimated the nutrient content of coarse roots (≥ 5 mm) of trees (dbh ≥ 10 cm) in a subtropical broadleaf forest at Fushan, northeastern Taiwan. The results from excavating 8 trees of 7 species indicated that the biomass of coarse roots accounted for 13.4~30.2% of the total tree biomass. This percentage was not correlated to the diameter at breast height (dbh). Based on the natural logarithmic regression established by sample trees, the biomass of each category and the total biomass of coarse roots were highly significantly related to dbh. In the coarse roots, the stump and ≥ 100-mm roots had the highest percentage of biomass, each accounting for approximately 30.0% of the coarse root biomass. Comparatively, the biomass of coarse roots accounted for 21.9% of the total tree biomass and 28.0% of aboveground biomass. The biomass of coarse roots of trees was 65.1 Mg ha-1, which is higher than the average root biomass of tropical evergreen forests reported in the literature. The root/shoot ratio calculated from coarse roots was 0.28, higher than those for both tropical forests and the global average. The higher root/shoot ratio of the Fushan forest is likely a result of severe branch and leaf damage caused by frequent typhoons, leaving the forest with lower aboveground biomass. The nutrient allocation of coarse roots in trees of the Fushan forest is similar to that of temperate broadleaf forests.本研究针对中国台湾东北部福山亚热带阔叶林中胸径（diameter at breast height, dbh）≥10 cm的林木，测定其粗根（直径≥5 mm）的生物量并估算养分含量。通过挖掘7个物种共8株样木的结果显示，粗根生物量占林木总生物量的13.4%~30.2%，且该占比与胸径无显著相关性。基于样木构建的自然对数回归模型可知，各粗根类别生物量及粗根总生物量均与胸径呈极显著相关关系。在粗根组分中，根桩与直径≥100 mm的粗根生物量占比最高，二者分别约占粗根总生物量的30.0%。相较而言，粗根生物量占林木总生物量的21.9%，占地上生物量的28.0%。该区域林木粗根生物量为65.1 Mg·ha⁻¹（兆克每公顷），高于文献报道的热带常绿林平均根系生物量水平。基于粗根计算得到的根冠比为0.28，高于热带森林及全球平均根冠比水平。福山阔叶林较高的根冠比，可能源于频繁台风引发的枝叶重度损伤，导致该林分地上生物量偏低。福山阔叶林林木粗根的养分分配模式与温带阔叶林较为相似。