Excess nitrogen fertilization and the structure of Scots‐pine needles

Abstract

The effects of excess nitrogen fertilization on tbe structure of Scots-pine needles {Pinus sylvestris) were examined in Finnish Lapland. Tbe trees were fertilized witb calcium ammonium-nitrate, and tbe levels of nitrogen applied were 0, 75, 150, 250, 500 and 1000 kg N/ba, respectively. Tbe thickness and widtb of the needle and thicknesses of tbe tissues were measured, and the conditions of various celltypes were classified at the light-microscopy level. In addition, tbe areas of the cell organdies were measured and tbe conditions of tbe cbloroplasts and otber cell compartments observed at tbe ultrastructural level. Larger needles and a thicker adaxial mcsopbyll were observed following excess N application (250-1000 kg N/ha). Tbe natural xcromorphic structure of tbe conifer needles became more mesomorphic, possibly influencing tbe protection afforded against environmental stresses. A bigli level of nitrogen fertilization caused changes in tbe central cylinder, especially in tbe vascular bundle and tbe sclerencbyma. Tbe needle nitrogen concentration was bigh in the highly fertilized trees and tbe boron concentration was simultaneously extremely low. As a consequence of tbe cbanges in tbe central cylinder, pbotoassimilate transport from tbe mesopbyll to tbe pbloem may be disturbed at bigb fertilization levels. Tbe cbanges at the ultrastructural level, i.e. injuries to the cbloioplast tbylakoids and tbe plasma membrane, and tbe formation of lipid accumulations, were indicators of tbe adverse effects of excess nitrogen. Witb an increasing atmospheric-nitrogen load, lower nitrogen fertilization levels in pine forests naturally adapted to low soil N sbould be considered in forest management.U. S.

Phenotypic Plasticity Explains Response Patterns of European Beech (Fagus sylvatica L.) Saplings to Nitrogen Fertilization and Drought Events

“…An indication of drought stress based on the plants' leaf δ 13 C signatures in the ND treatment was particularly pronounced for one-year-old plants (see paragraph on "effects of sapling age"). We cannot rule out the possibility that other factors, such as nutrient imbalances or a failure of photoassimilate transport, may have also contributed to the dieback of branches of two-year-old plants, because these factors are impaired by N fertilization [41].…”

Seasonal dynamics of histological parameters of the needles of Scots pine (Pinus sylvestris L.) growing in conditions of excess ammonia

“…Xeromorphic features play protection role against environmental stresses (drought, freeze, pathogenic organisms) (Huttunen, 1973;Jokela, 1998). On the contrary, mesomorphic needle features are related to thicker and longer needles and also larger width of adaxial mesophyll (Jokela et al, 1995;Jimenez, 2000).…”

“…Application of calcium, ammonium and nitrate containing fertilizers with total nitrogen concentrations corresponding to 0, 75, 150, 250, 500 and 1 000 kg ha -1 to the stands of Scots pine resulted in changes of nitrogen concentration in the needles and also natural structure transformation to the mesomorphic one (Jokela et al, 1995). Fertilization with high level nitrogen (250, 500, and 1 000 kg N ha -1 ) caused changes in the current-year needle thickness and width.…”

“…In the case of N excess, the cell walls of sclerenchyma might become thinner due to deficiency of certain nutrients, for example, boron (Jokela et al, 1995;Jokela, 1998).…”

“…Ammonia deposits to the soil turn into ammonia ions and nitrates and might be absorbed by plants through the roots (Jokela et al, 1995). Nutrition through the roots is essential, because rhizosphere of plants has a large surface area.…”