Coping with branch excision when measuring leaf net photosynthetic rates in a lowland tropical forest

Type Article
Date 2020-07
Language English
Author(s) Verryckt Lore T.1, Van Langenhove Leandro1, Ciais Philippe2, Courtois Elodie A.3, Vicca Sara1, Peñuelas Josep4, Stahl Clément5, Coste Sabrina5, Ellsworth David S.6, Posada Juan M.7, Obersteiner Michael8, Chave Jérôme9, Janssens Ivan A.1
Affiliation(s) 1 : Department of Biology University of Antwerp Wilrijk ,Belgium
2 : Laboratoire des Sciences du Climat et de l’Environnement CEA‐CNRS‐UVSQ Gif‐sur‐Yvette ,France
3 : Laboratoire Ecologie, Évolution, Interactions des Systèmes Amazoniens (LEEISA) Université de Guyane CNRS IFREMER Cayenne, French Guiana
4 : CSIC Global Ecology CREAF‐CEAB‐CSIC‐UAB Cerdanyola del Valles Barcelona, Spain
5 : UMR Ecofog, AgroParisTech, CNRS, Cirad INRA Université des Antilles Université de Guyane Kourou ,France
6 : Hawkesbury Institute for the Environment Western Sydney University Penrith NSW ,Australia
7 : Biology Department Faculty of Natural Sciences Universidad del Rosario Bogotá ,Colombia
8 : International Institute for Applied Systems Analysis (IIASA) Laxenburg, Austria
9 : UMR 5174 Laboratoire Evolution et Diversité Biologique Université Paul Sabatier CNRS Toulouse ,France
Source Biotropica (0006-3606) (Wiley), 2020-07 , Vol. 52 , N. 4 , P. 608-615
DOI 10.1111/btp.12774
WOS© Times Cited 13
Keyword(s) branch cutting, canopy physiology, French Guiana, gas exchange, photosynthesis, rainforest, stomatal conductance

Measuring leaf gas exchange from canopy leaves is fundamental for our understanding of photosynthesis and for a realistic representation of carbon uptake in vegetation models. Since canopy leaves are often difficult to reach, especially in tropical forests with emergent trees up to 60 m at remote places, canopy access techniques such as canopy cranes or towers have facilitated photosynthetic measurements. These structures are expensive and therefore not very common. As an alternative, branches are often cut to enable leaf gas exchange measurements. The effect of branch excision on leaf gas exchange rates should be minimized and quantified to evaluate possible bias. We compared light‐saturated leaf net photosynthetic rates measured on excised and intact branches. We selected branches positioned at three canopy positions, estimated relative to the top of the canopy: upper sunlit foliage, middle canopy foliage, and lower canopy foliage. We studied the variation of the effects of branch excision and transport among branches at these different heights in the canopy. After excision and transport, light‐saturated leaf net photosynthetic rates were close to zero for most leaves due to stomatal closure. However, when the branch had acclimated to its new environmental conditions—which took on average 20 min—light‐saturated leaf net photosynthetic rates did not significantly differ between the excised and intact branches. We therefore conclude that branch excision does not affect the measurement of light‐saturated leaf net photosynthesis, provided that the branch is recut under water and is allowed sufficient time to acclimate to its new environmental conditions.

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Verryckt Lore T., Van Langenhove Leandro, Ciais Philippe, Courtois Elodie A., Vicca Sara, Peñuelas Josep, Stahl Clément, Coste Sabrina, Ellsworth David S., Posada Juan M., Obersteiner Michael, Chave Jérôme, Janssens Ivan A. (2020). Coping with branch excision when measuring leaf net photosynthetic rates in a lowland tropical forest. Biotropica, 52(4), 608-615. Publisher's official version : , Open Access version :