Divergent contributions of living roots to turnover of different soil organic carbon pools and their links to plant traits

1. Rhizodeposits and root litter contribute critically to soil organic
carbon (SOC) formation and decomposition. This root-induced SOC turnover
shows great interspecific variations. Bulk SOC consists of diverse
functional pools differing in formation and stabilization. Yet, it remains
unclear which plant traits regulate the effects of living roots on the
turnover of different SOC pools across species. 2. By performing 13CO2
continuous labelling of six grassland species for a growing season in a
climate-controlled chamber, we quantified the contributions of living
roots to the dynamics of the fast-cycling particulate organic C and the
slow-cycling mineral-associated organic C, and explored their relations to
plant traits. 3. The results showed that new root-derived SOC varied more
than threefold among the six species. The variation in new root-derived
SOC was best explained by the ratio of shoot to root biomass. Plant
species with higher shoot:root ratio formed more new root-derived SOC.
Most of the root-derived C (72%) was incorporated into the particulate
organic C pool. All species caused positive rhizosphere priming effects
(RPE), which varied sevenfold across species. Among plant traits, specific
root length was the best predictor of interspecific variations in the RPE,
with greater RPE associated with higher specific root length. Most of the
RPE (70%) occurred in the mineral-associated organic C pool. Our results
also showed that most plant species caused more old SOC decomposition via
the RPE than new SOC formation, leading to net SOC losses, especially for
the mineral-associated organic C pool. 4. Overall, we provide novel
insights into the effects of plant traits on root-induced turnover of
particulate and mineral-associated organic C. Our findings should be
valuable for understanding how specific plant traits regulate SOC
accumulation and stabilization.

1. 根际沉积（Rhizodeposits）和根系凋落物对土壤有机碳（SOC）的形成与分解具有关键作用。这种由根系诱导的SOC周转存在显著的种间差异。整体SOC由形成与稳定机制各异的多种功能库组成。然而，目前尚不清楚哪些植物性状调控着活体根系对不同物种间不同SOC库周转的影响。
2. 通过在气候控制舱内对六种草原物种进行一个生长季的13CO₂连续标记，我们量化了活体根系对快速循环的颗粒有机碳和缓慢循环的矿物结合有机碳动态变化的贡献，并探究了这些贡献与植物性状的关系。
3. 结果显示，六种物种间新根系来源的SOC差异超过三倍。新根系来源SOC的变异可通过地上部与根系生物量比得到最佳解释：地上部/根系比值较高的物种形成更多新根系来源的SOC。大部分根系来源碳（72%）被整合到颗粒有机碳库中。所有物种均产生正根际激发效应（RPE），且种间差异达七倍。在植物性状中，比根长是RPE种间变异的最佳预测因子——RPE越大，比根长越高。大部分RPE（70%）发生在矿物结合有机碳库中。我们的结果还表明，多数植物物种通过RPE导致的旧SOC分解量大于新SOC形成量，从而造成SOC净损失，尤其在矿物结合有机碳库中。
4. 综上，我们为植物性状对根系诱导的颗粒有机碳和矿物结合有机碳周转的影响提供了新见解。我们的发现对理解特定植物性状如何调控SOC积累与稳定具有重要价值。