Bedrock geochemical properties govern soil mineral composition and nutrient availability, thereby regulating microbial community structure and function will ultimately influence soil carbon (C) and nitrogen (N) accumulation. To address this knowledge gap, a research team led by Prof. WANG Kelin from the Institute of Subtropical Agriculture of the Chinese Academy of Sciences conducted regional-scale field sampling in southwest China.

Their latest findings provide new insights into ecosystem sustainable in karst regions and were published in Global Change Biology and Communications Earth & Environment, respectively.

From the perspectives of lithological differences, researchers compared forest ecosystems developed on limestone and clastic rocks to systematically investigate free-living nitrogen fixation rates in soil and litter, as well as their relationships with microbial interaction networks. Furthermore, under warming conditions, They elucidated the microbial regulatory pathways through which vegetation restoration promotes C and N accumulation in karst ecosystems, thereby highlighting the critical role of multi-trophic biological interactions in soil C and N cycling and climate change adaptation in calcium-rich environments.

Compared with clastic rock soils, limestone soils exhibited higher pH and exchangeable calcium, which significantly increased the abundance of diazotrophs and phoD-harboring bacteria. These changes enhanced the cooperative interactions among diazotrophs, phoD-harboring bacteria, and arbuscular mycorrhizal fungi, leading to more stable and complex microbial networks and ultimately higher nitrogen fixation rates (Fig.1). In phosphorus-limited karst soils, phoD-harboring bacteria play a key role by forming tight associations with diazotrophs and arbuscular mycorrhizal fungi, highlighting that lithology promotes soil N inputs by regulating key functional microbial groups and their interactions.

Furthermore, regarding soil C and N accumulation, plantation forests showed significantly higher mineral-associated organic carbon, total organic carbon, and total nitrogen than croplands, with stronger C and N coupling. Warming increased C and N stocks in plantation forests, whereas soil organic carbon declined in croplands under elevated temperature (Fig.2).

Moreover, these differences were closely linked to higher exchangeable calcium levels, greater microbial necromass accumulation, and stronger calcium–microbial and multi-trophic interactions in plantation soils. The mechanisms by which calcium-rich soils enhance C and N accumulation can be summarized in two aspects: first, elevated soil exchangeable calcium promotes microbial growth and metabolism, enhancing the formation and stabilization of microbial residues; second, calcium strengthens both microbial and cross-trophic interactions, leading to more stable and tightly connected micro-food webs that facilitate coupled C and N accumulation under warming conditions.

This study advances the understanding of how calcium regulates soil C and N accumulation through microbial growth and interspecific interactions. It further proposes a conceptual framework of “calcium–microbe–micro-food web” regulation, providing new insights for enhancing C sequestration and ecosystem sustainability in karst regions under global climate change.

Contact: WANG Kelin

E-mail: kelin@isa.ac.cn

Fig.1 Microbial mechanisms driving free-living nitrogen fixation rates in soil and litter of karst and non-karst forests.(Imaged by XIAO Dan)

Fig.2 Mechanistic responses of soil carbon and nitrogen accumulation to warming in karst plantation forests and croplands.(Imaged by XIAO Dan)