Ms Leanne Peixoto1, Jørgen Eivind Olesen1, Dr Jim Rasmussen1, Dr Lars Elsgaard1
1Aarhus University, Department of Agroecology, Tjele, Denmark
The growth of deep-rooted crops within agricultural soils has the potential to increase carbon deposition within deep subsoil layers potentially mitigating climate change. The growth of these deep-rooted crops and subsequent availability of both labile C substrates and nutrients such as nitrogen (N), phosphorus (P), and/or sulfur (S) have the potential to influence both C turnover and stability within deep subsoil layers. The present study utilized intact soil samples obtained from 5-6 m to study the effects of nutrient limitations for microbial C turnover when glucose or an artificial root exudate (ARE) mixture, and supplementary nutrients (N-P-S) were introduced as different treatments to deep subsoil samples during a 10-week incubation study. Our results document that C substrates alone are not the only drivers in C turnover, although significant differences between the addition of only C substrates were documented with the addition of only glucose compared to the addition of the ARE mixture. Such differences were interpreted as a partial alleviation of the N limitation due to the N-containing amino acid, L-arginine within the ARE mixture, but differences are also a likely a response to the diversity of compounds within the ARE mixture. Furthermore, we found potential effects of a co-limitation of N and P on C turnover in these deep subsoil samples to depths of 5-6 m, far exceeding depths from previous studies. As such, based on the co-limitation of N and P as observed within this study, it is important to know the N and P status of subsoils to predict the fate of organic C in deep soils as the production of microbial residues is based on the coupling of these nutrients to meet the stoichiometric microbial demand. Hence, managements removing such limitations could facilitate the stability and long-term storage of C in deep subsoil.