A Test of Gas Exchange Measurements on Excised Canopy Branches of Ten Tropical Tree Species

Abstract

We studied gas exchange of leaves on branches that had been cut and then re-cut under water to assess the utility of measuring gas exchange on leaves of excised canopy branches. There was large variation between species in their ability to photosynthesize following excision. Some species maintained up to 86.5 % of intact photosynthetic rate 60 min after excision, whereas other species dropped below 40 % of intact photosynthetic rates within 3 min. Three species showed significant reductions in maximum rates of gross photosynthetic rate (P G ) on leaves of excised branches relative to intact branches. Excision significantly reduced carboxylation rates (Vc max ) in four species and electron transport (J max ) in two species. There were also significant increases in compensation irradiance and reductions of day rates of respiration relative to intact measurements. While gas exchange on excised branches can provide useful measures for canopy species, responses of individual species to branch excision need to be taken into account. Measurements on pre-screened species allow a greater understanding of canopy photosynthesis of large trees when canopy access is not an option.

Are measurements from excised leaves suitable for modeling diurnal patterns of gas exchange of intact leaves?

“…In some species, however, a decrease in gas exchange rates and stomatal closure were observed soon after excision. Therefore, pre‐screening of the focal species is required to determine whether the obtained excised leaf data are reliable (Santiago and Mulkey, 2003).…”

“…This study invoked the importance of the new protocol: comparison of the modelled gas exchange rates using excised leaf data with the measured ones, rather than the comparison of each ecophysiological parameter (Santiago and Mulkey, 2003). Because model ouputs are very sensitive to V cmax and m , even non‐significant differences in these parameters between excised leaf data and intact leaf data may confound efforts to model g s with excised leaf data.…”

“…Instantaneous light‐saturated photosynthetic rates of excised leaves have been found to be reliable (Reich et al , 1995; Cai et al , 2009; Joesting et al , 2009) after pre‐screening the effects of excision. On the other hand, stomatal control and resulting modelled gas exchange are believed to be altered by excision and subsequent change in water conditions (Sala and Tenhunen, 1996; Santiago and Mulkey, 2003; Ewers et al , 2007; Domingues et al , 2010). Therefore, until now, excised leaf data have not been recognized as an alternative to intact leaf data in the meteorological model simulation.…”

Measurement of Leaf Hydraulic Conductance and Stomatal Conductance and Their Responses to Irradiance and Dehydration Using the Evaporative Flux Method (EFM)

“…First, this g s measurement is made on an excised leaf, rather than on an intact plant, and second, the determination of stomatal conductance is based on climate measurement some distance from the leaf, rather than close to the leaf as in a porometer chamber, though the ventilation of leaf with the fan equilibrates the leaf surface with surrounding air. For some species, excised leaves may show different stomatal responses than for leaves on an intact plant 16,32 . However, for several species g s estimated using the EFM was similar to values measured on intact plants with a porometer for leaves at mid-day Ψ leaf 16 ( Fig. …”

Características funcionais de folhas de sol e sombra de espécies arbóreas em uma mata de galeria no Distrito Federal, Brasil

“…Esta porção de cada folha/folíolo foi aclimatada à densidade de fl uxo de fótons fotossintéticos (DFFF) de 1600 μmol m ). Apesar do procedimento utilizado (corte dos ramos) poder interferir nos resultados, nenhuma das espécies estudadas em questão apresentava pronunciada exsudação de resina ou goma na região do corte, fatores estes frequentemente responsáveis por alterações nos padrões de trocas gasosas (Santiago & Mulkey 2003). Em 21 e 22 de Fevereiro de 2009 foram realizados testes para se verifi car um possível efeito do destacamento de ramos nas variáveis fotossintéticas estudadas (A area e gs).…”