An experimentally tested theory based on enzyme inactivation and microbial energy limitation predicts lower SOM mineralization with warming

Dr Tanvir Shahzad1

1Department Of Environmental Sciences & Engineering, Government College University Faisalabad, Faisalabad, Pakistan

The kinetic theory predicts higher mineralization rates of soil organic matter (SOM) with increasing temperature. Number lab incubation studies have supported this theory. However, long term soil-warming field experiments indicate that temperature do not accelerate SOM mineralization. Similarly, soil respiration under warm ecosystems is relatively lower than cold ones (except artic ecosystems where soil processes come to halt due to frost) when gas exchange measurements are generalized. We propose a simple model that includes two key processes that can reconcile these differences in theory, lab incubations and long term field warming experiments. First process: microbial decomposers are limited by fresh energy-rich C which controls their enzyme production capability to mineralize recalcitrant C in soil. Second, enzyme inactivation, occurring due to loss of three dimensional structures of enzymes induced by the Brownian movement, accelerates with warming. The analysis of the model emphasizes on the need of separating non steady-state-system like incubated bare soil wherein there is a continuous decrease in enzymatic pool, from a steady-state-system where the enzymatic pool is maintained by microbes which are supplied with fresh C like in soil-plant system. The model predicts that soil C mineralization should increase with temperature till an optimum in bare soil whereas it should continuously decrease with temperature in planted soil. These predictions were confirmed by an experiment on planted soil and bare soil systems submitted to seasonal temperature variation for 479 days. A distinction was made between plant derived and soil C derived CO2 to account for production of new enzymes decomposing recalcitrant soil C.


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