Trade‐off in carbon allocation between roots and rhizodeposition underpins plant adaptation to acidification in a meadow steppe
Yu Shang, Ruzhen Wang, Bin Wang, Ying Zhang, Tianpeng Li, Xue Feng, Heyong Liu, Michael Bahn, Osbert Jianxin Sun, Xingguo Han, Hui Li, Yong Jiang
Abstract
Abstract Soil acidification caused by atmospheric sulphur (S) deposition may have a significant impact on plant carbon (C) assimilation and allocation, thereby altering soil organic C (SOC) dynamics. However, it remains largely unknown how plants allocate photosynthetic C among below‐ground C sinks and whether they can leverage these limited C resources to adapt to abiotic stresses. We conducted a 13 CO 2 pulse labelling experiment in a meadow to investigate the effects of soil acidification, induced by S addition, on photosynthetic C allocation and to explore the trade‐offs among plant below‐ground sinks as well as the contribution of below‐ground C allocation to SOC formation. We found that soil acidification decreased rhizodeposit C (13%–60%) and the absolute amount of 13 C allocated to soil (0.8%–51%), due to a 30%–36% reduction in shoot photosynthetic 13 C assimilation. Conversely, S addition increased the proportion of 13 C allocated to roots by 3%–52%. The root biomass, non‐structural carbohydrates (NSC) and respiration increased with S addition rates, and a threshold point appeared around 20 g S m −2 year −1 , after which they began to decline. Root 13 C was negatively correlated with soil 13 C but positively associated with both root biomass and NSC. Soil acidification led to an increase in below‐ground biomass, while SOC stocks remained unchanged, possibly due to reduced rhizodeposit C input accompanied by suppressed SOC decomposition. Synthesis . These results confirm that under soil acidification, less photosynthetic C in roots was converted into rhizodeposit C entering the soil, while proportionally more was invested in root growth, respiration and storage to cope with acidification stress. Overall, the trade‐off in C allocation between root biomass and rhizodeposition may underlie plant adaptation to soil acidification and is a key indicator for predicting SOC dynamics.