[Dynamic Variation Characteristics of Hydrolases and Oxidases in Black Soils Under Increasing Hydrothermal Gradients...

Hydrolases and oxidases regulate the decomposition of labile and recalcitrant soil organic matter， respectively， with their activities being highly sensitive to hydrothermal variations. Utilizing a cross-climatic zone soil translocation platform along China's North-South Transect， we transplanted in situ black soils from a cold temperate region （Hailun） to warm temperate （Fengqiu） and subtropical （Yingtan） zones， analyzing enzyme activity dynamics over a decade （from 2006 to 2015） through time-series analysis and structural equation modeling. Hydrolase activities exhibited a U-shaped temporal dynamic across three sites， most prominently in black soils from the warm temperate zone （Fengqiu） with an initial 25.71% decline （from 2006 to 2010） followed by a 151.32% surge by 2015. In contrast， oxidase activities experienced sustained suppression in black soils from the warm temperate zone， decreasing by 16.4% before stabilizing. These shifts drove a 125% elevation in the hydrolase-to-oxidase （H/O） ratio by 2015， indicating accelerated labile carbon turnover. The structural equation model revealed that hydrothermal variations indirectly regulated the H/O ratio through soil physicochemical factors： Black soils from the cold temperate zone were influenced by soil organic matter （β = -0.57） and total phosphorus （β = 0.32）， while black soils from the warm temperate zone were primarily constrained by pH reduction （β = 0.38） and amorphous aluminum oxides （β = 0.07）. Black soils from the subtropical zone displayed inhibition from organo-aluminum complexes （β = -0.42）. Under climate warming， rising H/O ratios may enhance labile carbon cycling， while mineral protection stabilizes recalcitrant carbon， collectively shaping the long-term carbon persistence of black soils.