Unearthing the hidden world of roots: Root biomass and architecture differ among species within the same guild

The potential benefits of planting trees have generated significant interest with respect to sequestering carbon and restoring other forest based ecosystem services. Reliable estimates of carbon stocks are pivotal for understanding the global carbon balance and for promoting initiatives to mitigate CO2 emissions through forest management. There are numerous studies employing allometric regression models that convert inventory into aboveground biomass (AGB) and carbon (C). Yet the majority of allometric regression models do not consider the root system nor do these equations provide detail on the architecture and shape of different species. The root system is a vital piece toward understanding the hidden form and function roots play in carbon accumulation, nutrient and plant water uptake, and groundwater infiltration. Work that estimates C in forests as well as models that are used to better understand the hydrologic function of trees need better characterization of tree roots. We harvested 40 trees of six different species, including their roots down to 2 mm in diameter and created species-specific and multi-species models to calculate aboveground (AGB), coarse root belowground biomass (BGB), and total biomass (TB). We also explore the relationship between crown structure and root structure. We found that BGB contributes ~27.6% of a tree’s TB, lateral roots extend over 1.25 times the distance of crown extent, root allocation patterns varied among species, and that AGB is a strong predictor of TB. These findings highlight the potential importance of including the root system in C estimates and lend important insights into the function roots play in water cycling.

植树造林的潜在效益在固碳及修复其他森林生态系统服务功能领域引发了广泛关注。可靠的碳储量估算对于理解全球碳平衡、推动通过森林管理减缓二氧化碳排放的相关举措均至关重要。已有众多研究采用异速生长回归模型，将林木清查数据转换为地上生物量（aboveground biomass, AGB）与碳储量（C）。然而，绝大多数异速生长回归模型未考虑根系系统，且此类方程亦未详细阐明不同树种的根系构型与形态特征。根系系统是揭示根系在碳积累、养分与植物水分吸收以及地下水入渗过程中所发挥的地下形态与功能的关键环节。无论是森林碳储量估算相关研究，还是用于深入解析树木水文功能的模型，均需对树木根系开展更完善的特征描述。本研究伐倒采集了6个不同树种共40株树木，采集范围涵盖直径不小于2毫米的所有根系，并构建了树种专属模型与多树种混合模型，用于计算地上生物量（AGB）、粗根地下生物量（coarse root belowground biomass, BGB）以及总生物量（total biomass, TB）。同时，本研究还探究了冠层结构与根系结构之间的关联。研究结果显示，粗根地下生物量（BGB）约占树木总生物量（TB）的27.6%，侧根延伸范围可达冠层幅宽的1.25倍以上，不同树种的根系分配模式存在显著差异，且地上生物量（AGB）可有效预测总生物量（TB）。上述发现凸显了在碳储量估算中纳入根系系统的潜在重要性，并为解析根系在水分循环中所发挥的功能提供了关键见解。