The Effect of Successive Years of Defoliation by the Larch Sawfly (pristiphora Erichsonii (hartig)) on the Foliage Properties of the Japanese Larch (larix Kaempferi (lamb.) Carr.), with Particular Reference to the Cn Balance Hypothesis

The carbon/nutrient balance hypothesis (CNBH) attempts to explain the mechanism of induced changes in plant properties. The responses of the Japanese larch (Larix kaempferi) to defoliation by the larch sawfly (Pristiphora erichsonii) were examined from the perspective of the CNBH. This study was conducted in seven Japanese larch plantations in central Hokkaido, Japan. The defoliation intensity was determined from canopy photos taken from 2009 to 2012. The chemical and physical properties of the foliage were determined from 2010 to 2012. Severe insect defoliation was found at two sites in 2009 and at all seven sites in 2010 and 2011. A decrease in foliar nitrogen and increases in phenolics, tannins, and the CN ratio were found in the years following severe defoliation and were significantly influenced by the 2009 defoliation intensity. The influence of defoliation in 2010 and 2011 was weaker. These results indicated that the past defoliation history additively affected the foliage properties in the 2 years following insect defoliation. In addition to the 2009 defoliation effects, site effects were found on phenolics, sugars, and the CN ratio. Relative to the other sites, the CN ratio was high at both sites where severe defoliation was found in 2009. Phenolics and sugars did not increase linearly with the CN ratio, indicating that limitations affected their synthesis. These results suggest that the induced changes in L. kaempferi properties are partially up-regulated under nitrogen limitation, but that secondary compound synthesis was, most likely, influenced by external site-dependent factors other than nitrogen limitation.