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

Abstract

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. 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. 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. 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. A free Plain Language Summary can be found within the Supporting Information of this article.

Cover crops affect pool specific soil organic carbon in cropland – A meta‐analysis

“…In an experiment by Jilling et al (2021), the authors observed that common root exudates (i.e., glucose and oxalic acid) caused a significant increase in turnover and potential release of C from MAOM through direct (e.g., mobilization of metal oxides) and indirect (e.g., enzyme induction) mechanisms. Similar effects were found in another field experiment by Huang et al (2021), who showed that about 70% of rhizosphere priming occurred in MAOC, which differed between species. The interspecific variations in the priming effects were explained by the differences in specific root length and root N concentration.…”

“…Despite the acknowledged significance of roots in SOC accrual, their measurement is often neglected in experimental studies due to labour‐intensive efforts. Nevertheless, it is evident that both the rhizodeposits of living roots and the decomposition of dead roots contribute substantially to both MAOC and POC (Huang et al, 2021; Sokol, Kuebbing, et al, 2019; Yang et al, 2023). The predominant impact of living root inputs on the net formation of MAOC aligns with expectations from the ‘dissolved organic C (DOC)‐microbial pathway’ theory (Cotrufo et al, 2015).…”

“…In contrast, structural litter inputs are believed to preferentially contribute to POC (Cotrufo et al, 2015). These underlying processes are species-dependent, influenced by factors such as the root-to-shoot ratio (Huang et al, 2021) and root morphology, which exerts a stronger impact on the accrual of root carbon into the MAOC and POC pools than root quality (C:N ratio) (Engedal et al, 2023). This influence extends beyond the described C allocated in the form of rhizodeposition to include the provision of root surface area for in vivo and ex vivo transformation of fresh C. Additionally, CC functional groups exhibit varying qualitative traits, such as root length, that significantly impact SOC pool accrual (Engedal et al, 2023).…”

The grassland carbon cycle: Mechanisms, responses to global changes, and potential contribution to carbon neutrality

“…In addition, different grassland species have distinct responses to precipitation changes and levels of resistance or resilience to drought stress [ 20 , 161 ] and consequently, plant community composition could determine ecosystem resistance or resilience to climate changes [162] . Diversity can also contribute greatly to soil C storage because species differ in the quantity and quality of plant litter and mycorrhizal C inputs, which collectively determine soil C storage [ 48 , 163 ]. Screening for species with suitable leaf and root traits, strong resistance to climate fluctuations, and complementary functions within the plant community could therefore accelerate C sequestration during grassland restoration [ 9 , 164 ].…”

Soil recalcitrant but not labile organic nitrogen mineralization contributes to microbial nitrogen immobilization and plant nitrogen uptake

“…Previous investigators reported that POM is typically considered a more temperature-sensitive indicator (Benbi et al, 2014;Georgiou et al, 2024), but such studies do not consider the rhizosphere. The rhizosphere priming effects can cause MAOM to be active (Huang et al, 2021), which poses a new challenge for us to accurately estimate M Nrec and M Nlab . Thus, there is still a need for a holistic, quantitative understanding of the patterns and controlling factors of the M Nrec and M Nlab and their effects on ecosystem N cycle.…”