Temperature and soil moisture change microbial allocation of pesticide-derived carbon

Temperature and soil moisture are known to control pesticide mineralization. Half-life times (DT50$$ {DT}_{50} $$) derived from pesticide mineralization curves generally indicate longer residence times at low soil temperature and moisture but do not consider potential changes in the microbial allocation of pesticide-derived carbon (C). We aimed to determine carbon use efficiency (CUE$$ CUE $$, formation of new biomass relative to total C uptake) to better understand microbial utilization of pesticide-derived C under different environmental conditions and to support the conventional description of degradation dynamics based on mineralization. We performed a microcosm experiment at two MCPA (2-methyl-4-chlorophenoxyacetic acid) concentrations (1 and 20 mg kg-1) and defined 20 & DEG;C/pF 1.8 as optimal and 10 & DEG;C/pF 3.5 as limiting environmental conditions. After 4 weeks, 70% of the initially applied MCPA was mineralized under optimal conditions but MCPA mineralization reached less than 25% under limiting conditions. However, under limiting conditions, an increase in CUE$$ CUE $$ was observed, indicating a shift towards anabolic utilization of MCPA-derived C. In this case, increased C assimilation implied C storage or the formation of precursor compounds to support resistance mechanisms, rather than actual growth since we did not find an increase in the tfdA gene relevant to MCPA degradation. We were able to confirm the assumption that under limiting conditions, C assimilation increases relative to mineralization and that C redistribution, may serve as an explanation for the difference between mineralization and MCPA dissipation-derived degradation dynamics. In addition, by introducing CUE$$ CUE $$ to the temperature- and moisture-dependent degradation of pesticides, we can capture the underlying microbial constraints and adaptive mechanisms to changing environmental conditions. Changing environmental conditions alter the MCPA degradation dynamics and the allocation of pesticide-derived carbon to anabolic or catabolic metabolism.image