Kosola, K.R., D. Parry, C.A. Russell, D.I. Dickmann, D.A. Herms, J.M. Scriber, S. Gage, D. Harris, G.P. Robertson, E.A. Paul
Presented at the ASM at Snowbird (2000-08-02 to 2017-12-05 )
The effects of defoliation on tree physiology are expected to cascade through the entire forest ecosystem, altering carbon, nitrogen, and water fluxes, and subsequently affecting nitrogen cycling and plant-herbivore interactions. We examined these phenomena for three years in a hybrid poplar plantation where we regulated defoliation by gypsy moths and nitrogen availability. We expected to see large losses of N from the system following defoliation, due to leaching losses of frass N. Even with intense defoliation, N leaching and soil N pools (inorganic N, microbial N) were unchanged. There was a small increase in ammonium volatilization from defoliated plots (about 1 kg N ha-1 year-1 above controls). Although defoliation led to increased levels of leaf phenolics, bioassays showed that decreased gypsy moth caterpillar growth on leaves produced after defoliation was primarily due to lower foliar N. Defoliation decreased tree capacity for NO3- and NH4+ uptake, although it had little affect on root production and mortality. Defoliation decreased tree growth and increased the rate of top dieback in the stand. Defoliation led to transient declines in allocation to starch. Although N fertilization increased tree growth, it did not alter defoliation effects on starch accumulation or top dieback.
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