Fertilization Changes Chemical Defense in Needles of Mature Norway Spruce (Picea abies)

Abstract

Nitrogen availability limits growth in most boreal forests. However, parts of the boreal zone receive significant levels of nitrogen deposition. At the same time, forests are fertilized to increase volume growth and carbon sequestration. No matter the source, increasing nitrogen in the boreal forest ecosystem will influence the resource situation for its primary producers, the plants, with possible implications for their defensive chemistry. In general, fertilization reduces phenolic compound concentrations in trees, but existing evidence mainly comes from studies on young plants. Given the role of the phenolic compounds in protection against herbivores and other forest pests, it is important to know if phenolics are reduced with fertilization also in mature trees. The evergreen Norway spruce is long-lived, and it is reasonable that defensive strategies could change from the juvenile to the reproductive and mature phases. In addition, as the needles are kept for several years, defense could also change with needle age. We sampled current and previous year needles from an N fertilization experiment in a Norway spruce forest landscape in south-central Norway to which N had been added annually for 13 years. We analyzed total nitrogen (N) and carbon (C), as well as low-molecular phenolics and condensed tannins. Needles from fertilized trees had higher N than those from controls plots, and fertilization decreased concentrations of many flavonoids, as well as condensed tannins in current year needles. In previous year needles, some stilbenes and condensed tannins were higher in fertilized trees. In control trees, the total phenolic concentration was almost five times as high in previous year needles compared with those from the current year, and there were great compositional differences. Previous year needles contained highest concentrations of acetophenone and stilbenes, while in the current year needles the flavonoids, and especially coumaroyl-astragalins dominated. Condensed tannins did not differ between current and previous year needles from control trees. In conclusion, the phenolic defense of current year needles of mature P.abies trees was strongly changed upon fertilization. This may imply that nitrogen deposition and forest fertilization leave forests less robust in a time when pests may take advantages of a changing climate.

Fertilization of Norway spruce forest with wood ash and nitrogen affected both tree growth and composition of chemical defence

“…The explanation for the big differences between the cohorts may be the timepoint of sampling, just after the current-year needles were fully grown, which is probably when the use of N is at its highest and the needle N concentrations at their lowest. We earlier found corresponding results in needles from mature spruce sampled at the same time of the year (Nybakken et al, 2018).…”

“…After fertilization, more C is used for growth, and production of phenolic compounds is usually reduced (Koricheva et al, 1998). In our previous study of chronically fertilized spruce on a low fertility site, we found large reductions in low-molecular weight phenolics in current-year needles, while there was no effect on those from the previous year (Nybakken et al, 2018).…”

“…In a recent experiment with chronic N-fertilization (i.e. repeated additions over several years) of mature Norway spruce, we found that levels of phenolics were strongly reduced in current year needles, while one-year-old needles were not much affected (Nybakken et al, 2018).…”

Influence of Continuous Spectrum Light on Morphological Traits and Leaf Anatomy of Hazelnut Plantlets

“…Flavonoids are also considered indicators of nitrogen availability in a plant (Nybakken et al, 2018). Nitrogen, as a component of the major macromolecules, is a fundamental macronutrient in plant nutrition.…”

The Effect of Supplementary LED Lighting on the Morphological and Physiological Traits of Miniature Rosa × Hybrida ‘Aga’ and the Development of Powdery Mildew (Podosphaera pannosa) under Greenhouse Conditions

“…Significantly lower nitrogen balance indexes and higher flavonol indexes were recorded for irradiated plants than for the control plants, however the influence of different LED light spectra on the nitrogen balance index (NBI) was not demonstrated. Flavonoids, as non-nitrogenous secondary metabolites, are considered indicators of nitrogen availability in a plant [ 50 , 51 ]. The flavonoid content increases under low N availability [ 36 , 51 , 52 ].…”