Data from: Root functional parameters predict fine root decomposability at the community level

1. Root quality is one of the main drivers of fine root decomposition, an important process controlling soil carbon (C) and nutrient cycling in most terrestrial ecosystems. Root quality is defined by chemical and morphological traits, which differ across species and thus communities. This trait variation is assumed to follow a trade-off between resource acquisition and conservation (i.e. the root economics spectrum). To what extent root quality or the economics spectrum influence fine root decomposition rates at the community level remains poorly understood, particularly within the context of land use change. 2. Changes in land use induce shifts in plant community composition, which also affect root distribution within the soil profile, resulting in changes in root quality. We hypothesize that at the community level, i) root decomposability is driven by community root functional parameters (i.e. root traits measured at the community level), ii) changes in root functional parameters among land use types and with soil depth translate into changes in root decomposability. 3. We collected shallow and deep fine roots (< 2 mm) from 20 plant communities across contrasting land use types in 7 sites worldwide, ranging from agricultural crops to natural forests and determined their decomposition rate in standard conditions. Fine root quality was related to known values of functional parameters for these communities, including carbon (C), nitrogen (N) and lignin concentrations. 4. A combination of chemical functional parameters (lignin, C and N concentrations) best explained root decomposition rates at the community level, whereas root economics remained a poorer predictor of decomposability rates. Among land use gradients, roots from agricultural and agroforestry communities decomposed faster than roots from forest sites. Across and within plant communities, a consistently greater decomposability in shallow roots was observed. Both land use and depth effects were explained by changes in root chemical traits at the community level. 5. Synthesis. Our results suggest that the conversion of plant communities from forests to agricultural lands leads to changes in root functional parameters, that drastically increase root decomposition rates and may lead to major soil C losses, especially in shallow soil layers.

1. 根品质（root quality）是细根分解（fine root decomposition）的核心驱动因子之一，而细根分解是调控多数陆地生态系统（terrestrial ecosystems）土壤碳（C）与养分循环（nutrient cycling）的关键过程。根品质由化学性状与形态学性状（morphological traits）共同决定，不同物种乃至不同植物群落间的性状差异显著。学界普遍认为，这类性状变异遵循资源获取与资源保守之间的权衡策略，即根经济学谱（root economics spectrum）。但目前对于群落层面上，根品质或根经济学谱对细根分解速率（decomposition rate）的影响程度仍不甚明确，在土地利用变化（land use change）的研究背景下这一问题尤为突出。
2. 土地利用变化会引发植物群落组成（plant community composition）的转变，同时也会改变根系在土壤剖面（soil profile）中的分布格局，进而导致根品质发生改变。我们提出如下群落层面的假说：其一，根分解可降解性由群落根系功能参数（functional parameters）驱动，即通过群落水平测定的根系性状来决定；其二，不同土地利用类型间以及随土壤深度变化的根系功能参数差异，会转化为根分解可降解性的变化。
3. 我们在全球7个研究点位的20个不同土地利用类型的植物群落中，采集了直径<2 mm的浅层与深层细根，涵盖从农作物（agricultural crops）到天然林（natural forests）的多种土地利用场景，并在标准培养条件下测定了它们的分解速率。我们将细根品质与这些群落已知的功能参数进行了关联分析，包括碳（C）、氮（N）与木质素（lignin）浓度。
4. 化学功能参数（木质素、碳与氮浓度）的组合能够最佳解释群落层面的细根分解速率，而根经济学谱对分解可降解性的预测能力则相对较弱。在土地利用梯度上，农业与农林业（agroforestry）群落的细根分解速率快于森林群落。在植物群落间以及群落内部，浅层细根的分解可降解性始终更高。土地利用类型与土壤深度对分解速率的影响，均可通过群落水平的根系化学性状变化得到解释。
5. 综合分析。我们的研究结果表明，将植物群落从森林转为农用地会改变根系功能参数，进而大幅提升细根分解速率，可能引发严重的土壤碳损失，在浅层土壤层这一效应尤为显著。