High-frequency fire alters soil and plant chemistry but does not lead to nitrogen-limited growth of Eucalyptus pilularis seedlings
Background and aims
Vegetation fire often raises levels of soil phosphorus (P) relative to those of nitrogen (N), while long-term fire exclusion is associated with accumulation of soil N and depletion of soil available P. Thus, high-frequency fire regimes might trigger N-limited plant growth in otherwise P-limited plant communities.
We used soils from a long-term prescribed burning trial to grow Eucalyptus pilularis under several nutrient amendment conditions. We measured seedling growth, soil and plant chemistry, and root enzyme activities to assess nutrient status.
Biennially-burned (2yB) soils had higher labile P concentrations than long-unburned (NB) soils, and lower total and labile N:P ratios. This did not correspond to N-limited growth or stimulate seedling N demand. Seedlings grown with addition of N, P and micro-nutrients in combination (μMax treatment) attained 68% more biomass than unfertilised seedlings. Addition of P resulted in higher total biomass than addition of N, and similar biomass to the μMax treatment, suggesting partially P-limited growth. Plants grown in 2yB soils tended to be enriched with P, K, Ca and Mg compared to those grown in NB or 4yB soils.
High-frequency prescribed burning depletes soil N relative to P, but this does not trigger a shift toward N-limited growth of E. pilularis seedlings. Instead, E. pilularis seedlings appear to grow under partial P-limitation which persists regardless of their soil’s fire history.
KeywordsPrescribed burning Stoichiometry Phosphatase Chitinase Ash deposition
The authors wish to thank the members of Griffith Environmental Biogeochemistry Laboratory for their assistance in the field and laboratory. We would also like to acknowledge support of Professor Brendan Mackey. Orpheus Butler is a recipient of the South-East Queensland Fire & Biodiversity Consortium scholarship. This work was supported by a grant of Australian Research Council Future Fellowship project (FT0990547).
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