Contrasting processes of microbial anabolism and necromass formation between upland and paddy soils across regional scales

Abstract

Well-drained upland soils generally have stronger microbial catabolism during organic C transformation than water-logged paddy soils. However, the intensity of microbial anabolism and necromass formation processes in these contrasting agricultural soils is unclear. To quantify these processes, 40 pairs of adjacent upland and paddy soils collected from four climates (mid-temperate, warm temperate, subtropics, and tropics) across eastern China were incubated with 13C-labeled root exudates under simulated field water conditions for 50 days. Upland soil collected from warm temperate exhibited a higher 13C incorporation into living microbial biomass than other climates. In contrast, the lowest newly formed necromass was detected due to the inhibition of fungal anabolism under the high pH condition. Paddy soils collected from cooler climates (mid-temperate and warm temperate) exhibited faster microbial biomass growth than those from warmer climates (subtropics and tropics). Still an opposite trend was observed for microbial necromass accumulation, possibly because of the faster turnover rate of microbial biomass induced by the high N availability in warmer climates. Regardless of climates, 13C incorporated into living microbial biomass (phospholipid fatty acids) was 1.4–2.6 times higher in upland than paddy soils, resulting in 1.8–3.9 times greater accumulation of newly-formed microbial necromass in the former. This was mainly caused by the stronger fungal anabolism (2.5–5.6 times higher) due to the oxygen-sufficient condition of upland soil. Our findings highlighted the weaker accumulation but stronger stability of organic C stored in upland soils because of the greater microbial catabolism and anabolism during organic C transformation.