『Abstract
Soil nutrient environments are changing in forests of the northeastern
United States due to decades of anthropogenic nitrogen (N) emissions
and acidic deposition, causing N enrichment and cation depletion,
and possibly alleviating N limitation to forest growth. We asked
whether biotic demand for phosphorus (P) or calcium (Ca) exceeded
that for N and used an ingrowth core approach to test belowground
responses to different nutrients. We tested fine root foraging
for nutrients (N, P, or Ca) in three mid-age (26-30 years) and
mature (≧100 years) northern hardwood forest stands in the Bartlett
Experimental Forest (BEF), NH, and in one mature forest stand
in the Hubbard Brook Experimental Forest (HBEF), NH, USA. Fine
root colonization of cores responded clearly to Ca in mature forest
at HBEF, responded to P in mid-age forests at BEF, and responded
primarily to N in mature forests at BEF. Net N mineralization
potential was higher in soils of mid-age than mature forests at
BEF, with roots responding to N where N availability was low and
to P or Ca where N availability was high. Nutrients elicited no
responses from either fungi or phosphatase activity in mid-age
forests, but in mature forests at BEF, N enhanced phosphatase
activity. While no straightforward pattern emerged among the different
mechanisms of nutrient acquisition that we tested, our results
do suggest that P and Ca can be important limiting nutrients in
these northern hardwood forests when N availability is relatively
high. We hypothesize that the interacting effects of disturbance
by forest harvest and N deposition can cause a transient P limitation
to forest growth, and that other nutrients become more limiting
as forests age.
Keywords: Fine roots; Root foraging; Fungal hyphae; Phosphatase;
Nutrient acquisition; Nutrient limitation; Northern hardwoods;
Ingrowth』
Introduction
Methods
Study sites and design
Ingrowth cores
Soil properties
Statistical analysis
Results
Discussion
Fine roots
Fungal hyphae and phosphatase activity
Conclusions
Acknowledgments
References