E. Dreyer et al., NUTRIENT CONTENT AND PHOTOSYNTHESIS OF YOUNG YELLOWING NORWAY SPRUCE TREES (PICEA-ABIES L KARST) FOLLOWING CALCIUM AND MAGNESIUM FERTILIZATION, Plant and soil, 160(1), 1994, pp. 67-78
Severely yellowed ten-year-old spruce trees growing in the Vosges Moun
tains on an acidic soil were fertilised with Magnesium lime during the
spring of 1990. The effects of this treatment were assessed 18 months
later. A very significant improvement of the mineral status of the tr
ees was detected, with increasing Mg contents in the needles, and as a
consequence, reduced yellowing and improved chlorophyll content. Only
slight differences with control trees were observed for height increa
se. Effects of this improved nutrition on photosynthesis were tested m
easuring net CO, assimilation rates and chlorophyll a fluorescence. Li
ght-saturated net assimilation rates of current-year needles were high
, reaching 5.3 mumol m-2 s-1 on a total needle area basis. The improve
ment in chlorophyll and Mg content had no significant effect on net as
similation rates or on any parameter describing photochemical function
s of both current-and previous-year needles. Despite the strong inter-
individual variability in needle chlorophyll and Mg contents (ranging
from 0.2 to 0.8 mg g-1 fresh weight, and 0.05 to 0.5 mg g-1 dry weight
respectively), photochemical efficiency of PS II under limiting irrad
iance only decreased significantly on older needles displaying Mg cont
ents below 0.1 mg g-1. It is concluded from these results that spruce
trees exhibit a high degree of plasticity with regard to Mg deficiency
on acidic soils, and that improved Mg nutrition and increased chlorop
hyll content do not necessarily improve photosynthesis and height grow
th.