Résumé
Litter nitrogen (N) release during decomposition crucially influences
ecosystem N cycling and the amount of N available to plants and other soil
organisms. However, the role of initial litter traits in affecting
patterns of temporal N release from litters and determining the fate of N
in the soil is still poorly understood. Here, we measured litter N release
during the 12-month decomposition of 15N-labelled leaf and root litters of
12 common Mediterranean herbaceous species. We further traced the fate of
N during decomposition of the litters into the soil and measured the
inorganic N content in the soil solution as well as total N in the
particulate (POM) and mineral-associated organic matter (MAOM) fractions
at the end of the incubation. While most litters exhibited a very rapid
initial N release, they were also quite variable in their N dynamics. As
such they differed in the quantity and temporal patterns of N release, the
accumulation of inorganic N in the soil solution, as well as in the
incorporation of N in stable soil organic matter (SOM) fractions during
decomposition. This variability was driven by differences in initial
litter chemistry, particularly N, but also P and Mn, and litter C leachate
concentrations. These and other traits (including water soluble compounds
and lignin concentrations) explained up to 81% of the variance in N
release rate, 48% for N accumulation in the soil solution, 57% for N
entering the soil POM and 55% for MAOM fraction. Synthesis: We identified
litter traits and litter types (root versus leaf) with afterlife effects
on N cycling in soils and important implications for ecosystem
functioning. Highly decomposable litters (typically high-N; including most
leaf litters) generally support a fast N release through mineralisation,
thereby the immediate supply of N to plants, but also potentially higher
losses from the system, and long-term storage as MAOM-N, likely within
microbial resynthesis products. In contrast, poorly decomposable litters
(typically low-N; including most root litters) promote longer and weaker N
release and foster N retention via lower N losses and increased POM-N
formation.