The effects that competing vegetation and nitrogen limitation have on the current annual increment (CAI), leaf biomass, and growth efficiency (GE) of different aged loblolly pine (Pinus taeda L.) stands planted on a Piedmont and lower Coastal Plain location in Georgia, U.S.A. were determined by measuring stands receiving a factorial combination of complete interspecific competition control and annual nitrogen fertilization. At the Piedmont location, CAI increased with age (5, 10, and 12 years) as well as fertilization (7.3-9.2 Mg·ha -1 ) and competition control (6.8-9.6 Mg·ha -1
To determine the importance of competition control and annual fertilization on leaf gas exchange, lightsaturated net photosynthesis (A sat ), stomatal conductance (g s ), and internal CO 2 concentration (C i ) were measured multiple times in different-aged loblolly pine (Pinus taeda L.) stands growing at a Piedmont (BF Grant) and Coastal Plain (Waycross) location in Georgia, U.S.A. At both locations, competition control decreased A sat and g s (A sat from 4.53 to 4.12 µmol·m -2 ·s -1 , g s from 0.058 to 0.050 mol·m -2 ·s -1 at BF Grant; A sat from 4.22 to 4.01 µmol·m -2 ·s -1 , g s from 0.054 to 0.049 mol·m -2 ·s -1 at Waycross). Overall, fertilization did not have a positive impact on A sat , even though fertilization significantly increased foliar nitrogen concentration. At BF Grant, fertilization significantly decreased g s from 0.057 to 0.051 mol·m -2 ·s -1 and C i from 217 to 205 µmol·mol -1 . In addition, the decrease in C i associated with fertilization became larger with stand age. At Waycross, fertilization decreased C i from 211 to 203 µmol·mol -1 and the interaction between fertilization and stand age was significant for g s and C i . These results indicate that silivcultural practices that increase resource availability and stand growth did not enhance leaf gas exchange. Résumé :Pour déterminer l'importance du contrôle de la compétition et de la fertilisation annuelle sur les échanges gazeux du feuillage, la photosynthèse nette en condition de lumière saturée (A sat ), la conductance stomatale (g s ) et la concentration interne en CO 2 (C i ) ont été mesurées plusieurs fois dans des peuplements de pin à encens (Pinus taeda L.) d'âges différents croissant dans le Piedmont (BF Grant) et la Plaine côtière (Waycross) en Géorgie, aux États-Unis. Aux deux endroits, le contrôle de la compétition a diminué A sat et g s (A sat de 4,53 à 4,12 µmol·m -2 ·s -1 , g s de 0,058 à 0,050 µmol·m -2 ·s -1 à BF Grant; A sat de 4,22 à 4,01 µmol·m -2 ·s -1 , g s de 0,054 à 0,049 µmol·m -2 ·s -1 à Waycross). Dans l'ensemble, la fertilisation n'a pas eu d'impact positif sur A sat , même si elle a significativement accrue la concentration en azote du feuillage. À BF Grant, la fertilisation a significativement réduit g s de 0,057 à 0,051 µmol·m -2 ·s -1 et C i de 217 à 205 µmol·mol -1 . De plus, la diminution de C i associée à la fertilisation a augmenté avec l'âge du peuplement. À Waycross, la fertilisation a diminué C i de 211 à 203 µmol·mol -1 et l'interaction entre la fertilisation et l'âge du peuplement était significative pour g s et C i . Ces résultats indiquent que les pratiques sylvicoles qui accroissent la disponibilité de la ressource et la croissance du peuplement n'améliorent pas les échanges gazeux du feuillage.[Traduit par la Rédaction] 1083Munger et al.
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