Combined influence of external nitrogen and soil contact on plant residue decomposition and indications from stable isotope signatures
2019
Jiang, Chunming | Yu, Wantai
External nitrogen (N) supply has been testified to exert important impacts on plant residue decomposition. The influence of N may be interactive with soil contact in terrestrial ecosystems. However, the joint mechanisms of decomposition of plant residues driven by soil contact and N addition remain incomplete. Using contrasting residues, including needles of Chinese fir (Cuninghamia lanceolata) (Cl) (relatively hard to degrade) vs. leaves of eucalyptus (Eucalyptus urophylla) (Eu) (relatively easy to degrade), a full factorial experiment was conducted by 360-day experiment to investigate the combined effect of N addition and soil contact on residue decay. As the microbe-manipulated decomposition could leave an imprint on the residue carbon (C) and N stable isotope, variations of the two signatures (δ¹³C and δ¹⁵N) were synchronously monitored. Our results firstly showed that added N sped up initial decomposition, while it played an opposite role in subsequent stage, and soil contact always stimulated decay. Under soil contact condition, we found a markedly more accelerating effect of N addition on decay of Cl than without soil contact. Linking with residue N dynamics, we thought that although N immobilized from soil could not completely meet microbial needs for decay of Cl, this N limitation was just relieved by added N, leading to this synergistic effect. At late decay stage, the N inhibiting influence was partly offset under soil contact condition, and this phenomenon was more dramatic for Eu. Our results lastly revealed that the ¹³C and ¹⁵N signatures mirrored and explained the underlying mechanisms of the above interactions. Overall, we concluded that external N and soil contact could interactively affect decay, depending on plant residue decomposability. These results would be used to accurately predict C sequestration for terrestrial ecosystems under heightened N scenario in the future.
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