The role of fine‐root mass, specific root length and lifespan in tree performance: a whole‐tree exploration,Functional Ecology

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The role of fine‐root mass, specific root length and lifespan in tree performance: a whole‐tree exploration
Functional Ecology ( IF 4.6 ) Pub Date : 2020-02-05 , DOI: 10.1111/1365-2435.13520
Monique Weemstra _{1,

2} , Natasa Kiorapostolou _{1,

3} , Jasper Ruijven ₂ , Liesje Mommer ₂ , Jorad Vries ₄ , Frank Sterck ₁

Affiliation

The root economics spectrum (RES) hypothesis predicts that fast‐growing tree species have short‐lived roots with high specific root length (SRL) to allow rapid resource uptake, and opposite trait expressions for slow‐growing species. Yet, the mixed support for this hypothesis suggests that trees can adopt alternative strategies to increase resource uptake, besides an increase in SRL. We combined a novel mechanistic whole‐tree model and empirical fine‐root data of ten tree species to test the effects of one of these alternative strategies, notably increasing fine‐root mass, on the tree's net C gain (used here as a proxy for tree performance), and to assess how fine‐root lifespan influences the relative importance of SRL and fine‐root mass for the C balance of trees. Our results indicate that accounting for the short lifespan of high‐SRL roots has important implications for explaining tree performance and the role of roots herein. Without considering their faster turnover, high‐SRL roots and low fine‐root mass resulted in the highest performance as predicted from the RES. Yet, when their higher turnover rates were accounted for, a high fine‐root mass and low SRL lead to the highest performance. Both our model outcomes and field data further show a negative relationship between SRL and fine‐root mass through which species aim to realise a similar root length density. This trade‐off further indicates how high a SRL and low fine‐root mass as well as opposite trait values can both lead to a positive C balance in a similar environment. Our study may explain why high‐SRL roots do not necessarily lead to the fastest tree growth as often hypothesised and demonstrates the importance of fine‐root mass in combination with fine‐root lifespan for explaining interspecific differences in tree performance. More generally, our work demonstrates the value of identifying and investigating different belowground strategies across species from a whole‐plant modelling perspective, and identifies the relationship between SRL, fine‐root biomass and lifespan as an important functional dimension to variation in species’ performance.

中文翻译：

细根质量、比根长度和寿命在树木性能中的作用：全树探索

根经济谱（RES）假设预测，快速生长的树种具有短寿命的根，具有高比根长（SRL）以允许快速吸收资源，而生长缓慢的树种则具有相反的性状表达。然而，对该假设的不同支持表明，除了增加 SRL 外，树木还可以采用替代策略来增加资源吸收。我们结合了一种新的机械全树模型和十种树种的经验细根数据来测试这些替代策略之一的影响，特别是增加细根质量，对树的净 C 增益（此处用作树性能），并评估细根寿命如何影响 SRL 和细根质量对树木 C 平衡的相对重要性。我们的结果表明，高 SRL 根的寿命短对于解释树木性能和根在此处的作用具有重要意义。不考虑它们更快的周转率，高 SRL 根和低细根质量导致了 RES 预测的最高性能。然而，当考虑到它们较高的周转率时，高细根质量和低 SRL 导致最高性能。我们的模型结果和现场数据都进一步显示了 SRL 与细根质量之间的负相关关系，物种旨在通过该关系实现相似的根长密度。这种权衡进一步表明，在类似环境中，SRL 高、细根质量低以及相反的特性值可以导致正 C 平衡。我们的研究可以解释为什么高 SRL 根并不一定会像通常假设的那样导致最快的树木生长，并证明细根质量与细根寿命相结合对于解释树木性能的种间差异的重要性。更一般地说，我们的工作证明了从整株植物建模的角度识别和研究不同物种地下策略的价值，并将 SRL、细根生物量和寿命之间的关系确定为物种性能变化的重要功能维度。

更新日期：2020-02-05

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