Enhancing soil carbon sequestration in jasmine gardens: Differential effects of straw and biochar on mineral-associated and particulate organic carbon.

Reducing chemical fertilizer use while enhancing soil organic carbon (SOC) stability, through straw return and biochar amendment presents an integrated strategy for climate change mitigation and sustainable agriculture. However, the effectiveness of their carbon (C) sequestration potential and organic C pool stability is influenced by varing environmental conditions. This study investigated the effects of straw and biochar on C sequestration potential and SOC pool stability in jasmine garden soil in Fuzhou, China. Six treatments were compared: No Fertilizer (Control), Fertilizer (F) (NPK fertilizer), No Fertilizer + Straw (NF + S), Fertilizer + Straw (F + S), No Fertilizer + Biochar (NF + B), and Fertilizer + Biochar (F + B). Fertilizer (compound NPK 16:16:16) was applied at a total rate of 260 kg·ha-1, split into two applications of 130 kg·ha-1 each. Straw and biochar were both applied at a rate of 8000 kg·ha-1 each. We measured mineral-associated organic C (MAOC), particulate organic C (POC), their binding mechanisms, and key physicochemical properties. The results showed that, compared to the control, NF + B significantly increased MAOC (13.29 %; p < 0.05). Biochar application (F + B and NF + B) significantly increased POC (150.57 %-211.34 %) and calcium-bound organic C (Ca-SOC) (22.22 %-31.94 %; p < 0.05), with more pronounced effects in the absence of fertilizer. Both straw and biochar applications significantly improved soil pH (2.74 %-15.40 %) and decreased soil bulk density (BD) (10.08 %-26.36 %; p < 0.05), while straw significantly increased electrical conductivity (EC) (17.91 %-35.82 %; p < 0.05). Furthermore, both straw and biochar amendments significantly increased SOC (34.66 %-57.18 %), easily oxidizable organic C (EOC) (23.35 %-48.58 %), and dissolved organic C (DOC) (15.98 %-93.00 %; p < 0.05). Redundancy analysis (RDA) showed that pH (70.4 % variance explained) and SOC (7.5 % variance explained) were the dominant drivers of SOC pool stability. These findings suggest that biochar amendment, particularly without chemical fertilizers, represents a promising strategy for enhancing soil C sequestration and stability in jasmine gardens. This approach holds significant potential for sustainable agricultural practices and climate change mitigation in subtropical regions.