Feeding of leaf beetle to two species of alder grown under two different soils in a free-air CO2 enrichment

Abstract

ABSTRACT The effects of elevated CO2 concentration on the defensive ability of two Alnus species (A. maximowiczii, A. hirsuta) against herbivory attacks (alder leaf beetle; Agelastica coerulea) were investigated using a free-air CO2 enrichment. Elevated CO2 significantly affected consumed leaf area index (CLI) of A. maximowiczii but soil fertility did not, while more significant effects on CLI of A. hirsuta were found in both CO2 and soil fertility. As found in natural conditions, A. hirsuta was grazed five times more than A. maximowiczii in both CO2 levels, which was explained with the low condensed tannin (CT) concentration of the leaves. The value of leaf mass per area in fertile soil was 10 g m−2 lower than that in infertile soil under ambient CO2 in July. Leaf C/N ratio was not affected by elevated CO2 for both species but that of A. hirsuta was little higher in infertile soil when compared to fertile soil in July. CT of A. maximowiczii tended to increase in September under elevated CO2. CT of A. hirsuta was higher in infertile soil than in fertile soil in July and showed an overall decrease in September compared to July. Nitrogen-fixing activity by a nodule of Frankia sp. on A. maximowiczii was higher in elevated CO2 treatments than in ambient CO2 independent of soil fertility. As a result of changes in these parameters, except for fertile soil, the peak of the herbivorous damage was later in elevated CO2 for the Alnus species than in the control.