『Abstract
In the prolonged absence of major disturbances, ecosystems may
enter a stage of retrogression, which is characterized by decreased
ecosystem process rates both above and belowground, and often
reduced availability of phosphorus (P). Disturbance through wildfire
can increase soil P losses through leaching or erosion, but in
the long-term absence of fire, soil P could potentially become
increasingly bound in more stable forms that are less available
to microbes. We studied forms of P and microbial respiration kinetics
in the humus layer of a group of islands that vary considerably
in wildfire frequency (40-5,300 years since last fire), and which
are known to enter retrogression in the prolonged absence of fire.
We found a decrease in labile P with decreasing fire frequency
but no change in total P. Soil microorganisms responded more strongly
to N than to P addition, and microbial biomass N:P ratios remained
unchanged across the gradient. However, the concentration of labile
P was the best predictor of microbial respiration responses across
the islands, and this provides some evidence that declining access
to P could contribute to the decline in soil microbial activity
during retrogression. Our results show that even though N is arguably
the main limiting nutrient during retrogression in this chronosequence,
long term absence of fire also causes a decline in P availability
which negatively affects microbial activity. This in turn could
potentially impair microbially driven processes such as decomposition
and mineralization and further contribute to the reduced availability
of soil nutrients during retrogression.
Keywords: Boreal forest; Microbial respiration; Phosphorus; Retrogression;
Succession; Wild fire』
Introduction
Materials and methods
Study site and soil sampling
Micrbial respiration
Soil and microbial C, N and P determinations
Data analyses
Results
Microbial respiratory responses to N and P additions
Soil and microbial C, N and P
Relations between microbial and chemical measurements
Discussion
Effects of fire history on P forms and availability
Microbial nutrient limitation
Ecosystem loss of P during absence of fire
Conclusions
Acknowledgments
References