1. Fine roots and above‐ground litterfall play a pivotal role in carbon dynamics in forests. Nonetheless, direct estimation of stocks of fine roots remains methodologically challenging. Models are thus widely used to estimate these stocks and help elucidate drivers of fine root growth and turnover, at a range of scales.
2. We updated a database of fine root biomass, necromass and production derived from 454 plots across European forests. We then compared fine root biomass and production to estimates obtained from 19 different models. Typical input variables used for the models included climate, net primary production, foliage and above‐ground biomass, leaf area index (LAI), latitude and/or land cover type. We tested whether performance could be improved by fitting new multiple regression models, and explored effects of species composition and sampling method on estimated fine root biomass.
3. Average fine root biomass was 332 g/m², and necromass 379 g/m², for European forests where the average fine root production was 250 g m⁻² year⁻¹. Carbon fraction in fine roots averaged 48.4%, and was 1.5% greater in broadleaved species than conifers.
4. Available models were poor predictors of fine root biomass and production. The best performing models assumed proportionality between above‐ and below‐ground compartments, and used remotely sensed LAI or foliage biomass as key inputs. Model performance was improved by use of multiple regressions, which revealed consistently greater biomass and production in stands dominated by broadleaved species as well as in mixed stands even after accounting for climatic differences.
5. Synthesis. We assessed the potential of existing models to estimate fine root biomass and production in European forests. We show that recalibration reduces by about 40% errors in estimates currently produced by the best available models, and increases three‐fold explained variation. Our results underline the quantitative significance of fine roots (live and dead) to the global carbon cycle.

中文翻译：

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欧洲森林细根碳储量和通量的改进模型

1. 细根和地上凋落物在森林碳动态中起关键作用。尽管如此，直接估算细根存量在方法上仍然具有挑战性。因此，模型被广泛用于估算这些种群，并在各种规模上帮助阐明细根生长和周转的驱动力。
2. 我们更新了来自欧洲森林454个样地的细根生物量，坏死生物和产量的数据库。然后，我们将细根生物量和产量与从19种不同模型获得的估计值进行了比较。用于模型的典型输入变量包括气候，净初级生产，树叶和地上生物量，叶面积指数（LAI），纬度和/或土地覆盖类型。我们测试了是否可以通过拟合新的多元回归模型来改善性能，并探讨了物种组成和采样方法对估计的细根生物量的影响。
3. 对于欧洲森林，平均细根生物量为332 g / m ²，而死灵为379 g / m ²，欧洲森林的平均细根生物量为250 g m - ² 年^-1。细根中的碳含量平均为48.4％，阔叶树种中的碳含量比针叶树高1.5％。
4. 可用的模型不能很好预测细根生物量和产量。表现最好的模型假设地上和地下地层之间是成比例的，并使用遥感的LAI或树叶生物量作为关键输入。通过使用多元回归改善了模型的性能，这表明即使考虑了气候差异，在阔叶树种为主的林分和混交林中，生物量和产量始终保持较高水平。
5. 合成。我们评估了现有模型估计欧洲森林细根生物量和产量的潜力。我们显示，重新校准可将目前最好的可用模型产生的估计值减少约40％的误差，并增加三倍的解释偏差。我们的研究结果强调了细根（活的和死的）对全球碳循环的定量意义。