Root hair-deficient mutant of maize promoted an increase in C and N in loamy soil after 5 years of monoculture

Abstract Soil fertility is strongly determined by soil organic matter content, which is modulated by the interplay between soil properties, roots, and microbial activity. However, it is unclear how root morphology in interaction with soil texture affects microbial traits and the storage of organic matter in soil. To address this gap, two maize genotypes differing in the presence of root hairs (the root hair deficient mutant rth3 and its corresponding wild type) were grown in monoculture for five consecutive years in excavated plots filled with two homogenised substrates (loam and sand). In the fifth year of maize monoculture, soil was sampled during plant growth in summer and after six months of winter fallow after harvest. We found slower microbial growth and lower microbial C accumulation in summer with rth3 grown in loam compared to wild-type plants. We also observed increased soil organic C and total N contents in loam after winter fallow of rth3 compared to the wild type. This was accompanied by a higher relative abundance of carboxylic acids, lignin, primary amides and ester groups in the former. In sand, retarded microbial growth and lower microbial C content were observed compared to the loam. In conclusion, heterotrophic microorganisms appear to play a crucial role in the accumulation of soil organic matter during winter, when there is no input of fresh labile molecules from active roots. It is therefore essential to implement agricultural practices that facilitate these processes.