Long-term retention of post-fire soil mineral nitrogen pools in Mediterranean shrubland and grassland
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Background and Aims
The post-fire mineral N pool is relevant for plant regrowth. Depending on the plant regeneration strategies, this pool can be readily used or lost from the plant–soil system. Here we studied the retention of the post-fire mineral N pool in the system over a period of 12 years in three contrasted Mediterranean plant communities.
Three types of vegetation (grassland, mixed shrub-grassland and shrubland) were subjected to experimental fires. We then monitored the fate of 15 N-tracer applied to the mineral N pool in soils and in plants over 12 years.
The plant community with legumes (mixed shrub-grasslands) showed the lowest soil retention of 15 N-tracer during the first 9 months after fire. Between years 6 and 12 post-fire, a drought promoted plant and litter deposition. Coinciding with this period, 15 N-recovery in the first 15 cm of the soil increased in all cases, except in mixed shrub-grassland. This lack of increase may be attributable to the input of impoverished 15 N plant residues and enhanced leaching and denitrification, possibly by N2-fixing shrubs. After the drought, the deepest soil layer showed large decreases in total N and 15 N-recovery, which were possibly caused by N mineralization.
Twelve years after the fires, plant communities without N2-fixing shrubs recycled a significant part of the N derived from the post-fire mineral N and this pool continued to interact in the plant–soil system.
Keywords15N-recovery Drought Soil organic C Soil N Legume N2-fixing plant
We thank Maximilian Fuetterer and Dr. Núria Gómez-Casanovas for comments on the manuscript. This research was supported by the projects Lindeco (CGL2009-13497-CO2-02), GRACCIE (CSD2007-00067), from the Spanish Ministry of Science and Technology, and the GHG-Europe project (FP7-ENV-2009-1, project no. 244122), from the European Commission. Pere Casals is supported by a Ramón y Cajal Contract (Ministerio de Economía y Competitividad, Spain).
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