Delayed Inducible Resistance in Mountain Birch in Response to Fertilization and Shade

Abstract

Delayed inducible resistance (DIR) is triggered by artificial or herbivorecaused foliar damage and is manifested as decreased performance of herbivore generation(s) feeding on the trees subsequent to the generation during which the damage took place. DIR is associated with increase in concentrations of foliage phenolics and decrease in nitrogen. The growth-differentiation balance hypothesis, and the carbon-nutrient balance (CNB) hypothesis contained in it, claim that DIR is caused by nutritional stress after defoliation of trees growing on nutrient-poor soils. In these environments, nutrient uptake limits plant growth more strongly than does photosynthesis; that is, carbon-based secondary metabolites (e.g., phenolics) are prone to accumulate. According to the CNB hypothesis, an excess of limiting nutrient(s) or reduced photosynthetic rate should lead to elimination of DIR. We tested this using same-aged Betula pubescens ssp. tortuosa trees of five open-pollinated families growing in a common arboretum in northernmost Finland. In addition to unmanipulated control trees, we had three nutritional treatments during three successive growth seasons: N-fertilization, PK-fertilization adding all nutrients except N, and shading to decrease carbon assimilation. Half of the trees in each treatment were artificially defoliated (50% leaf area) in the second study year, one year before the growth trial with geometrid (Epirrita autumnata) larvae.Tree growth measurements showed that N is the growth-limiting nutrient in our study area. N-fertilization and shading of the trees affected foliage chemistry generally as proposed by the CNB hypothesis. For example, they reduced foliar concentrations of total phenolics and condensed tannins. The birch families differed significantly in foliage chemistry, suggesting genetic differences, but the differences were not associated with fertilizations, shading, or defoliation of the trees. Contrary to fertilizing-shade treatments, changes in leaf chemistry and E. autumnata performance caused by defoliation were not consistent with the CNB hypothesis. For example, defoliation caused significant DIR irrespective of N-fertilization or shading. There were no significant differences among the birch families in performance of the moth larvae or in effects of fertilization, shade, or defoliation on larval performance. These responses to defoliation contrast with those of some other studies, especially those on the Betula resinifera-Rheumaptera hastata system in Alaska, which provide clear support for the CNB as an explanation of DIR. We find methodological differences to be an unlikely explanation for the different results but are unable to propose any single mechanism that will explain the diverse plant responses.

Influence of Nitrogen Fertilization on Wheat, and Soil Carbon, Nitrogen and Phosphorus Stoichiometry Characteristics

“…N fertilization significantly increased N concentrations in wheat (Fig. 1 c, d), which was observed in other studies (Ruohomaki et al, 1996;Tomassen et al, 2003;Esmeijer-Liu et al, 2009). At harvest, the grain N and P contents were higher, indicated that N and P in other parts of wheat transferred to the grain.…”

Dynamics of Ni‐based defence and organic defences in the Ni hyperaccumulator, Streptanthus polygaloides (Brassicaceae)

“…This hypothesis is supported by our data as the congeneric non-hyperaccumulator (S. insignus) had higher glucosinolate concentrations than the Ni hyperaccumulator (S. polygaloides). Levels of many plant defences are not static and are subject to edaphic, climatic, and biotic influences (Coley et al, 1985 ;Bryant et al, 1987 ;Ruohoma$ ki et al, 1996 ;Karban & Baldwin, 1997). Here, the presence of Ni within the hyperaccumulator, S. polygaloides, was dependent on Ni availability in the soil, whereas Ni concentrations in S. insignus were unaffected by soil Ni concentrations.…”

The effect of nutrient supply and light intensity on tannins and mycorrhizal colonisation in Dutch heathland ecosystems

“…Whereas, Hansen et al (2006) even found a positive response of shading on the concentration of condensed tannins in V. vitis-idaea and C. tetragona. In non-ericaceous plants, shading usually reduces the levels of carbon-based secondary chemicals (Hartley et al 1997;Henriksson et al 2003, Ruohomäki et al 1996Iason et al 1996). In plants with ectomycorrhizal fungal symbionts, shade effects on the amount of colonisation or amounts of structures are ranging from no effect (Brearly et al 2007;Dehlin et al 2004) to decreased colonisation rates (Becker 1983;Ingleby et al 1998) or even increased colonisation rates (Prajadinata and Santoso 1993;Be'reau et al 2000).…”