The influence of low light, drought and fertilization on transpiration andgrowth in young seedlings of Quercus robur L.

The aim was to identify the influence of light, water, nutrients and seedli ng age on the relation between water consumption and growth in young seedli ngs of oak Quercus robur, in order to achieve optimized water use in forest regeneration and plant nurseries. Newly emerged oak seedlings were grown i n a controlled environment chamber for two growing seasons at various photo synthetic photon flux densities (PPFD) ranging from 0.7 to 23.1 mol m(-2) d ay(-1). The transpiration rate increased with PPFD during the first 11 week s after seedling emergence. At short-term variation in irradiance, transpir ation rate increased with increased PPFD, and decreased with increase in se edling age. At 15 weeks, transpiration rate decreased with increased previo us long-term PPFD level, A set of seedlings grown at 1.5 mol m(-2) day(-1) irradiance were supplied with nutrients of various strengths containing 2.7 , 8 or 15.9 mM of nitrogen, and a second set grown at 23.1 mol m(-2) day(-1 ) irradiance were supplied with 8, 15.9 or 31.9 mM of nitrogen. Another set of seedlings, given 15.9 mM of nitrogen, were grown at 14.5 mol m(-2) day( -1) and subjected to two periods of drought. Transpiration rate decreased w ith nutrient strength and with soil water content. Seedlings grown at 0.7 o r 14.5 mol m-2 day(-1) in Year 1 were transferred to 0.7, 7.3 and 14.5 mol m(-2) day(-1) in Year 2. In the two-year-old seedlings transpiration rate i ncreased with increases in current and previous-year PPFD. The increase in dry mass over a certain period was compared with the integrated transpirati on, i.e. the calculated total amount of water transpired during the same pe riod. Dry mass and integrated transpiration were closely correlated during the first and second year of growth in seedlings, in relation to PPFD. The correlation between growth and total water consumption became weaker when n utrient strength or water availability changed. The influence of PPFD on wa ter-use efficiency (WUE), changed with seedling age. WUE became highest at the highest nutrient strength and increased with decrease in soil water con tent. The results of this study indicate that young seedlings of oak may in crease their water-use efficiency when nutrient availability is increased b y removal of competing ground vegetation. (C) 2000 Elsevier Science B.V. Al l rights reserved.