Does timing of boron application affect needle and bud structure in Scots pine and Norway spruce seedlings?

Abstract

Loss of apical dominance is a well-known boron (B) deficiency symptom in trees. Recent field studies indicate that B deficiency may cause irreversible damage in emerging leader buds leading to bushy growth, and changes in developing needles in mature Norway spruce trees. We experimentally studied if timing of B application affects needles and buds of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) seedlings with low initial B levels. The treatments were: no B (B0); B supply from the beginning of the simulated summer (B1); starting soon after bud burst (B2) and starting at the occurrence of first needle primordia in new spruce buds (B3). At the end of the experiment, B concentration in B1 was 23 mg kg À1 (pine) or 17 mg kg À1 (spruce) and lower in the later applications. In B0 it was at deficiency limit. In B0, B2 and B3, there were fewer sclerenchyma cells, and cavities occurred in vascular cylinders in pine needles, and in spruce buds there were more tanniferous cells in the primordial shoots compared to B1. Furthermore, in all but B1 there was cell collapse in the bud apex of some spruce seedlings. The experimentally induced changes were the same as earlier reported in B deficient conifers in the field, and indicate, similarly as in the field that adequate B is necessary throughout the growing season for healthy growth, particularly for spruce. The differences between spruce and pines are due, at least partly, to the differences in time frame of needle development and in the differences in development of conducting tissues in the buds.

Microscopic structure of Scots pine (Pinus sylvestris (L.)) needles during ageing and autumnal senescence

“…Hypertrophy of the parenchyma cells in the phloem was reported earlier in yellow 2-year old needles of Mg deficient spruce (Fink 1991). Accumulation of tannin in the phloem parenchyma and cavity formation in the vascular cylinder has been reported in young needles of B deficient Scots pines (Raitio 1983;Sutinen et al 2007). However, any visible signs of B deficiency, i.e.…”

Boron in forest trees and forest ecosystems

“…This can also explain to some extent why B deficiency is apparently an on/off phenomenon in conifers, rather than causing a gradual decline in growth such as N deficiency. Malformation at the cellular level can be found in Scots pine and Norway spruce needles in low-B trees before any visible symptoms appear (Raitio and Rantala, 1977;Sutinen et al, 2006Sutinen et al, , 2007. In these species, the development of the bud for the following year's new vegetative shoots starts directly after bud burst in the spring, and continues until the autumn, when the bud starts to harden (Sutinen et al, 2006).…”

“…During bud development, the primary cell walls form, and therefore B supply is critical for the whole of this time. Application of B later in the growing season did not prevent bud damage in Norway spruce, manifesting as increased numbers of collapsed cells in the bud apex (Sutinen et al, 2007).…”

“…Rapid fluctuations in B concentrations (e.g. Sutinen et al, 2006) and the fact that B deficiency at a particular point in time during the growing season can cause irreversible damage (Bell, 2000;Sutinen et al, 2007), cause uncertainties in the prediction of B deficiency.…”

Decomposition and element concentrations of Norway spruce needle litter with differing B, N, or P status

“…In earlier studies on Norway spruce seedlings, tannins have increased slightly in low-B treatments. Seedlings with low B status had higher concentrations of condensed tannins and their precursor, (+)-catechin, in fully developed needles (Rummukainen et al 2007), as well as more tanniferous cells in primordial shoots (Sutinen et al 2007). These effects were not very large, and probably would not make a difference for the health of the trees, as the increase was less than the change in tannin concentration due to seasonal variation (Rummukainen et al 2007).…”