Depth-dependent temperature sensitivity of soil heterotrophic respiration in restored lands of the Atlantic Forest, Brazil

Land restoration has the potential to increase deep soil carbon stocks; yet, the biodegradability of deep soil carbon and thus its response to climate change is unknown. Here, we assessed both potential heterotrophic soil respiration rate and its temperature sensitivity in the topsoil (0–20 cm), subsoil (40–100 cm) and deep soil (150–200 cm) in arable soil, in lands restored with different approaches, and secondary forests in the Atlantic Rainforest, Brazil. We found that respiration rates were higher in deep soil than in the topsoil, but the temperature sensitivity in deep soil was lower. Respiration rates of the subsoils were intermediate. As the restoration process advanced from arable land to secondary forest, deep soil respiration rate decreased, but temperature sensitivity increased. Soil fertility governed this temperature sensitivity below topsoil, with phosphorus being the main controlling factor in the subsoil, and nitrogen in the deep soil. We conclude that with restoration of degraded land to forests, the sequestered C is stable in the subsoil of restored lands. The reduced biodegradability of soil C is due to nutrient limitations that inhibit sub- and deep soil carbon respiration rate with warming, particularly in agroforestry systems and natural regeneration sites, though less with reforestation measures. • Deep soil carbon biodegradability decreased with the progress of land restoration. • Restoration strategy matters - agroforestry and natural regeneration minimize carbon biodegradability. • Deep soil temperature sensitivity is decoupled from topsoil. • Nitrogen and phosphorus contents were the main controlling factors of temperature sensitivity below topsoil.