Comparison of the bud morphology and shoot growth dynamics of four species of Mediterranean subshrub growing along an altitudinal gradient

Abstract

Bud morphology, bud activity, and shoot growth dynamics were studied over 13 months in four species of Mediterranean subshrubs growing along an altitudinal gradient in north-east Spain. The species selected were representative of the main functional types of subshrubs that grow naturally along altitudinal gradients on Mediterranean mountains. All species bore naked buds as their renewal structures, but the degree of protection of the buds varied between species, increasing with altitude. The period of morphogenesis and the level of shoot pre-formation also varied along the gradient. The species growing at low altitude had partially neoformed shoots, longer shoot growth periods, and started morphogenesis earlier than those growing at high altitude. These differences may indicate different morphological and phenological adaptations of Mediterranean subshrubs in response to increased winter cold along the gradient. At low altitudes, brachyblast-bearing species with partially neoformed shoots may be favoured because of the plastic shoot growth these structures confer. However, as the climate becomes colder and more predictable, brachyblast-bearing species may be replaced by species without brachyblasts, with tightly protected buds and more constrained patterns of shoot development.