Growing season drives the temperature sensitivity of extracellular enzymes in Tibetan forest soils

Abstract:

Asymmetric effects of spring and autumn warming on the terrestrial carbon cycle in the northern Hemisphere has been generally documented, but the mechanisms behind this phenomenon remain highly uncertain. Soil organic matter (SOM) decomposition is controlled by microbe-derived extracellular enzymes (EEs), however, the environmental factors driving EE temperature sensitivity remains largely uncertain. This study is the first to explore whether early versus late growing seasons or soil factors play a bigger role in driving EEs temperature sensitivity in forest soils. We found that EEs temperature sensitivity was highly dependent of growing season and late growing (LG) season exhibited higher sensitivity than early growing (EG) season. The higher temperature sensitivity was consistent with the higher activation energy, which reflects low substrate availability in LG season. Growing season played a bigger role in changing soil physicochemical factors than elevation, but NH₄⁺-N failed to show seasonal difference with a clear elevational pattern in the two seasons. LG season exhibited lower soil moisture and hot water extractable carbon than EG season, but was much higher in NO₃-N and soil temperature. Our findings highlight next generation of earth system models should incorporate the seasonal discrepancy in temperature sensitivity of SOM enzymatic degradation to more accurately project future climate and carbon cycle feedbacks.