The role of morphological versus physiological foliar plasticity in the capacity for, and mechanisms of, photosynthetic acclimation was assessed in Picea abies (L.) Karst. and Abies alba Mill. saplings in a forest gap-understory light gradient (relative irradiance, RI, ranging from 0.02 to 0.32). The species investigated showed a similar foliar morphological plasticity along the light gradient, at both the needle level (through alteration in leaf dry mass per area) and the shoot level (through alteration in the silhouette area ratio, e.g., shoot silhouette to projected needle area ratio). In both species chlorophyll (Chl) concentration on a mass basis decreased at increasing RI, but was independent of RI when expressed on an area basis. In contrast, leaf N concentration on a mass basis was independent of RI, but was positively influenced by RI when expressed on an area basis. The parameters describing photosynthetic performance at low light (dark respiration rate, apparent quantum yield and light compensation point) suggest that Abies alba was better suited to maintain a positive carbon balance in shaded conditions. By contrast, parameters describing biochemical capacity at high light (maximum electron transport rate, Jmax and maximum ribulose-1,5-biphosphate carboxylation capacity, Vcmax) indicate that only Picea abies was capable of acclimating physiologically to high photosynthetic photon flux densities (PPFDs) by increasing nitrogen partitioning to Rubisco and Vcmax/mass by increasing RI. These results support the hypothesis that interspecific differences in nitrogen partitioning within the photosynthetic apparatus may provide a mechanistic basis for species separation along a light gradient. The differences in photosynthetic plasticity observed are likely to influence regeneration patterns and habitat breadth of the species investigated. The limited ability of Abies alba saplings to exploit high-light conditions may be a competitive disadvantage in large canopy gaps and thus limit recruitment of this species to small gaps.
In a 0.75-ha plot in a Norway spruce (Picea abies Karst.) -silver fir (Abies alba Miller) stand in Comelico (Italian eastern Alps), we analysed (i) the distribution and growth of natural regeneration of Norway spruce and silver fir as affected by stand structure and (ii) the age structure of all saplings between 0.2 and 10 m in height in a 30-yearold gap. In both species, most natural regeneration was clumped and located at the margin of the gaps; however, fir saplings were more represented in understorey environments and less represented in gaps as compared with spruce. Age structure of natural regeneration in the selected gap revealed that the majority (75%) of saplings appeared after the formation of the gap; however, for regeneration taller than 2 m (which has a better chance of reaching the uppermost canopy layer), saplings already present at gap formation predominated. We conclude that (i) gap edges represent a preferential regeneration niche in this forest and (ii) saplings established before gap formation can play an important role in gap refilling. These results provide useful information to ensure, through silvicultural practices, favourable conditions for the temporal and spatial continuity of the regeneration process.Résumé : Nous avons analysé dans une placette de 0,75 ha située dans un peuplement d'épinette de Norvège (Picea abies Karst.) -sapin argenté (Abies alba (Miller)) de Comelico (dans la partie est des Alpes italiennes) : (i) la distribution et la croissance de la régénération naturelle de l'épinette de Norvège et du sapin argenté telles qu'affectées par la structure du peuplement et (ii) la structure d'âge de toutes les gaules de 0,2 à 10 m de hauteur dans une trouée vieille de 30 ans. Chez les deux espèces, la régénération naturelle était regroupée et localisée à la marge des trouées; toutefois et en comparaison avec l'épinette, les gaules du sapin étaient plus représentées dans des environnements sous couvert et moins représentées dans les trouées. La structure d'âge de la régénération naturelle dans la trouée échantil-lonnée montre que la majorité (75 %) des gaules sont apparues après la formation de la trouée; toutefois, quant à la ré-génération plus haute que 2 m (qui a de meilleures chances de rejoindre la couche la plus haute du couvert), les gaules déjà présentes au moment de la formation de la trouée prédominaient. Nous concluons que : (i) la bordure des trouées représente une niche préférentielle pour la régénération dans cette forêt et que (ii) les gaules établies avant la formation de la trouée peuvent jouer un rôle important dans sa fermeture. Ces résultats fournissent une information utile pour assurer, par le biais de pratiques sylvicoles, des conditions favorables à la continuité spatio-temporelle de la régénération.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.