PHOTOSYNTHETICA

Photosynthetica 2021, 59(1):61-73 | DOI: 10.32615/ps.2020.079

Performing gas-exchange measurements on excised branches - evaluation and recommendations

J.E.C. MISSIK^{1, 2}, A.C. OISHI³, M.C. BENSON¹, V.J. MERETSKY¹, R.P. PHILLIPS⁴, K.A. NOVICK¹

¹ O'Neill School of Public and Environmental Affairs, Indiana University - Bloomington, 702 N Walnut Grove Avenue, Bloomington, IN 47408, USA

² Department of Civil and Environmental Engineering, Washington State University, PO Box 642910, Washington State University, Pullman, WA 99164, USA

³ Coweeta Hydrologic Lab, USDA Forest Service - Southern Research Station, 3160 Coweeta Lab Road, Otto, NC 28763, USA

⁴ Department of Biology, Indiana University - Bloomington, 1001 E. 3rd St., Bloomington, IN 47405, USA

In forest canopies, it is common to perform leaf-level gas-exchange measurements on recently excised branches, often without testing for excision-related biases. We conducted a formal test of excision effects using gas-exchange measurements from cut and uncut canopy branches of three deciduous hardwoods - sugar maple (Acer saccharum Marsh.), tulip poplar (Liriodendron tulipifera L.), and white oak (Quercus alba L.). Across all species, excision immediately reduced photosynthesis and stomatal conductance by 27-62% relative to pre-excision rates. In white oak, which had particularly long (> 100 cm) vessels, gas exchange was more impaired for shorter (~ 30 cm) as compared to longer (~ 100 cm) branches. Additional hypotheses linking branch height and species water-use strategy to excision bias were tested but not confirmed. A survey of 23 previously published studies confirms that our results are not without precedent. Excision-related biases should be considered when interpreting measurements performed on excised branches.

Additional key words: canopy physiology; cut branch; hydraulics; isohydricity; measurement bias; methodology.

Received: August 14, 2020; Revised: November 6, 2020; Accepted: November 19, 2020; Prepublished online: January 20, 2021; Published: March 18, 2021  Show citation