Fine root litter quality regulates soil carbon storage efficiency in subtropical forest soils

Highlights

● High-quality and low-quality root litter had contrasting patterns of mass loss.

● Greater litter-derived C was incorporated into soils under high-quality root litter.

● Root litter decay rate or litter-derived C were related to soil microbial diversity.

● Root litter quality had little effect on soil physicochemical properties.

● High root litter quality was the main driver of enhanced soil C storage efficiency.

Abstract

Decomposing root litter is a major contributor to soil carbon (C) storage in forest soils. During decomposition, the quality of root litter could play a critical role in soil C storage. However, it is unclear whether root litter quality influences soil C storage efficiency. We conducted a two-year greenhouse decomposition experiment using ¹³C-labeled fine root litter of two tree species to investigate how root litter quality, represented by C to nitrogen (C/N) ratios, regulates decomposition and C storage efficiency in subtropical forest soils in China. ‘High-quality’ root litter (C/N ratio = 26) decayed faster during the first year (0−410 days), whereas ‘low-quality’ root litter (C/N ratio = 46) decomposed faster toward the end of the two-year period (598−767 days). However, over the two years of the study, mass loss from high-quality root litter (29.14 ± 1.42%) was lower than ‘low-quality’ root litter (33.01 ± 0.54%). Nonetheless, root litter C storage efficiency (i.e., the ratio of new root litter-derived soil C to total mineralized root litter C) was significantly greater for high-quality root litter, with twice as much litter-derived C stored in soils compared to low-quality root litter at the end of the experiment. Root litter quality likely influenced soil C storage via changes in microbial diversity, as the decomposition of high-quality litter declined with increasing bacterial diversity, whereas the amount of litter-derived soil C from low-quality litter increased with fungal diversity. Our results thus reveal that root litter quality mediates decomposition and C storage in subtropical forest soils in China and future work should consider the links between root litter quality and soil microbial diversity.

Graphical abstract

Keywords

fine root litter quality / root litter decomposition / litter carbon storage efficiency / soil organic carbon accumulation / subtropical forest

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Competing interests

The authors declare that they have no conflict of interest.

Author contributions

SX designed this study. SX and FLS did the experiments. SX analyzed the data and depicted the figures. SX and EJS wrote the paper. All authors contributed to interpretation and comment on the details of the manuscript drafts.

Data availability statement

The data set underpinning the results will be made available after acceptance.

Acknowledgments

We acknowledged Profs. Guoyi Zhou, Deqiang Zhang and Dr. Xin Xiong for the ¹³C-labeled fine root materials. We also acknowledged Prof. Xiaoli Cheng for her suggestions on the litter decomposition experiment design. This study was financially supported by the National Natural Science Foundation of China (Grant No. 31901135), the Guangdong Natural Science Foundation (Grant No. 2020A1515011257), the Research Grants Council of the Hong Kong Special Administrative Region, China (Grant Nos. CUHK14302014, CUHK14305515 and CUHK14122521), the Chinese University of Hong Kong (Grant No. 4052228).

Electronic supplementary material

Supplementary material is available in the online version of this article at https://doi.org/10.1007/s42832-023-0182-6 and is accessible for authorized users.

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