Fruit tree-based agroforestry as a nature-based solution for carbon sequestration in the vulnerable Eastern Himalayan ecosystem: plant–soil microbe feedbacks in the context of global change

Fruit tree–based agroforestry systems (FBS) represent a promising nature-based solution for enhancing carbon storage and sequestration, restoring soil health, and supporting livelihood security in the fragile Eastern Himalayan ecosystems. We evaluated six fully grown, uniform, 20-year-old FBS: guava, peach, Assam lemon, pear, plum and Khasi mandarin against adjacent cropland at the ICAR Research Complex for the North Eastern Hill Region, India. A total of 126 composite soil samples were collected across six depth intervals (0–1.0 m) to assess total carbon (TC), total organic carbon (TOC), total inorganic carbon (TIC), soil microbial biomass carbon (SMBC), total nitrogen (TN), carbon fractions (C VL , C L , C LL , C NL ) and carbon stocks, while above- and belowground biomass, seasonal litter fall and leaf carbon inputs were quantified using allometric and field-based measurements. Aboveground biomass ranged from 22.68 to 31.98 Mg ha −1 and belowground biomass from 5.9 to 8.31 Mg ha −1 . Compared with cropland, FBS soils exhibited significantly ( p < 0.05) greater TC (+5–28%), TOC (+2–29%), SMBC (+13.5–35%), and TN (+16–38%). Peach-based systems recorded the highest SMBC (551.1 μg g −1 ), indicating enhanced microbial biomass and activity. The very labile carbon (C VL ) fraction was 8.5–33.7% higher under FBS than cropland, reflecting increased substrate availability for microbial metabolism and patterns consistent with positive plant–soil–microbe feedbacks. Perennial fruit trees sustained microbial activity at greater soil depths, a pattern consistent with deeper rhizosphere influence from fine-root networks. Total carbon stocks were highest under Khasi mandarin (279.0 Mg ha −1 ) and peach (274.3 Mg ha −1 ) at 0–1.0 m depth. The study provides integrated empirical evidence that FBS enhances both labile and stable soil carbon storage through patterns consistent with positive plant–soil–microbe interactions and litter-derived carbon inputs, functioning as an effective climate-smart land-use strategy for carbon storage in mountain ecosystems of Eastern Himalaya.