Organic fertilization reduces litter retention in SOM
Organic fertilization reduced litter C and N remaining in the soil relative to control treatments, but there were no significant differences between control and high N fertilization treatments.
Organic fertilization reduced the litter C remaining in total SOM by 14% (Fig. 5a , p<0.01) relative to the unfertilized control treatment. Within the SOM fractions, the loss of litter C was driven by an 18% reduction in litter C incorporation into MAOM (Fig.5a , brown, p=0.018). Organic fertilization reduced litter N remaining in total SOM by 12% (Fig. 5b , p=0.020) relative to unfertilized control treatments. Within the SOM fractions, the loss of litter N was primarily driven by a 16% reduction in litter N incorporation into MAOM (Fig. 5b , brown, p<0.001).
Organic fertilization treatments had 25% greater microbial biomass (SI Fig. 3 , p=0.09) relative to unfertilized treatments. Microbial decomposition in organic fertilization treatments was more effective with less litter C remaining in each SOM pool per gram microbial biomass compared to control fertilization (SI Fig. 4 a-c ). However, this decomposition was less effective for litter N than litter C, with no significant difference in litter N in POM pools per gram of microbial biomass across nutrient treatments (SI Fig. 4, d-e ). Litter C and N incorporation into MAOM was lower per gram of microbial biomass with organic fertilization compared to control fertilization (SI Fig.4c, 4f ).