Nitrogen Limits an Invasive Perennial Shrub in Forest Understory |
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Authors: | Timothy M Cassidy James H Fownes Robin A Harrington |
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Institution: | (1) Department of Natural Resources Conservation, University of Massachusetts at Amherst, Amherst, MA 01003, USA |
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Abstract: | Plant invasions can harm communities by domination of one or more vegetation layers. We studied whether Japanese barberry
(Berberis thunbergii DC.) is limited by soil acidity or nitrogen availability in its domination of relatively undisturbed forest understories.
In two sites, one more acid than the other, we applied lime, urea, or a sawdust–sugar mix to replicate plots in established
barberry populations. We predicted that the acid site would be pH or cation limited, while the less acid site was N limited,
unless N availability was inherently higher before treatment. Barberry above-ground net primary production (NPP) was estimated
by a combination of harvest and allometric analysis. Foliar N increased in the urea treatment and was proportional to incubation
estimates of net N mineralization and nitrification. Foliar Ca and P were unaffected by the treatments. Foliar K was proportional
to foliar N. The more acid site had higher foliar Mn, but otherwise the sites differed little. Barberry NPP was proportional
to pre-treatment biomass. The ratio of net production to pre-treatment woody biomass (relative production rate) increased
with foliar N and soil N availability and decreased when soil N was immobilized by sawdust and sugar. There was no effect
of soil pH or cation status on barberry growth, although a correlation with foliar K was reflected by the maintenance of a
constant K : N ratio. Although more severely acid sites may be less invasible than those studied here, N availability is the
primary limitation to invasive dominance in this landscape.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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Keywords: | Berberis thunbergii foliar N net primary production nitrification nitrogen mineralization plant invasion soil acidity |
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