Shape of leaf photosynthetic electron transport versus temperature response curve is not constant along canopy light gradients in temperate deciduous trees

Abstract

energy for mitochondrial respiration rate were also observed, indicating that acclimation to temperature of mitochondrial and chloroplastic electron transport proceeds in a co-ordinated manner, and possibly involves longterm changes in membrane fluidity properties. We conclude that, because of correlations between temperature and light, the shapes of J max versus T, and R d versus T response curves vary within tree canopies, and this needs to be taken account in modelling whole canopy photosynthesis.Key-words: Populus tremula; Tilia cordata; chlorophyll fluorescence; feedback limitations; light gradients; photosynthetic electron transport; temperature acclimation. INTRODUCTIONIn temperate trees, foliar maximum photosynthesis rates (A max ) increase with long-term integrated quantum flux density (e.g. Walters & Field 1987;Ellsworth & Reich 1993;Pearcy & Sims 1994;Niinemets & Tenhunen 1997;, and the light acclimation of leaf photosynthetic characters is the major factor optimizing whole canopy carbon gain (Gutschick 1988;Gutschick & Wiegel 1988;. Although the positive scaling of A max with irradiance improves canopy carbon gain under moderate environmental stresses that always occur in natural ecosystems, in long-term, canopy carbon accumulation is also dependent on the ability of leaves to maintain this increased capacity over periods of more severe and long-lasting stresses that may frequently accompany light gradients in tree canopies. For example, daily average integrated quantum flux density incident on the leaves (Q int ) correlates positively with daily average air temperature and vapour pressure deficit (Chiariello 1984;Shuttleworth et al. 1985;Margolis & Ryan 1997) within the canopy. Because of these correlations, the leaves exposed to higher irradiance frequently also suffer from greater water ( ABSTRACTResponses of foliar light-saturated net assimilation rate (A max ), capacity for photosynthetic electron transport (J max ) and mitochondrial respiration rate (R d ) to long-term canopy light and temperature environment were investigated in a temperate deciduous canopy composed of Populus tremula L. in the upper (17-28 m) and of Tilia cordata Mill. in the lower canopy layer (4-17 m). Climatic measurements indicated that seasonal average daily maximum air temperature (T max ) was 5·5°C (range 0·7-10·5°C) higher in the top than in the bottom of the canopy, and strong positive correlations were observed between T max and seasonal average integrated quantum flux density (Q int ), as well as between seasonal average daily mean temperature and Q int . Because of changes in leaf dry mass and nitrogen per unit area, A max , J max , and R d scaled positively with Q int in both species at a common leaf temperature (T). According to J max versus T response curves and dark chlorophyll fluorescence transients, photosynthetic electron transport was less heat resistant in P. tremula with optimum temperature of J max , T opt , of 33·5 ± 0·6°C than in T. cordata with T opt of 40·7 ± 0·6°C. This difference was suggested t...

Foliar photochemical processes and carbon metabolism under favourable and adverse winter conditions in a Mediterranean mixed forest, Catalonia (Spain)

“…The method of cutting twigs rehydrated stressed leaves at optimum conditions and allowed us to analyse their longterm acclimation to the environmental conditions from which they were derived. This method has been used in other studies (Epron and Dreyer, 1992;Haldimann and Feller, 2004;Laisk et al, 2002;Niinemets et al, 1999Niinemets et al, , 2005, and we confirmed that the leaves remained fresh and functional for several days controlled by g s and fluorescent signals (data not shown). Our ambient values of the GE-and CF-derived parameters accordingly represented the "ambient capacity" of pre-conditioned leaves under near-optimal ambient environmental conditions of CO 2 concentrations and saturating light and at a room temperature of 20-25 • C (Reich et al, 1998).…”

“…Five replicates of each species were collected for the analysis of GE. The twigs were pre-conditioned in the laboratory at a room temperature of 24-28 • C in dim light for 1-3 d and freshly cut the following morning before the measurement of GE (Niinemets et al, 1999(Niinemets et al, , 2005. We intended to avoid the problems we had faced in the field, such as the limited ability of the instruments to reach the standard operating temperature of 25 • C, which was hampered by low ambient temperatures or unpredictable plant responses such as closed stomata or patchy stomatal conductance Buckley, 1998, 2000).…”

Process-based simulation of seasonality and drought stress in monoterpene emission models

“…It links the emission rates to synthase enzyme activity (S S ) to predict the capacity of isoprenoid synthesis as well as to foliar photosynthetic metabolism via the photosynthetic electron transport rate, J , to predict substrate (Niinemets et al, 1999;Niinemets et al, 2002a). The supply of dimethylallyl-pyrophosphate (DMAP) and nicotinamiddinucleotid-phosphate (NADPH), which both depend on the rate of photosynthetic electron transport, are considered to be the main controlling factors.…”

“…Thus, emissions are closely linked to photosynthetic activity of leaves using only one single leaf dependent parameter ε, the fractional allocation of electron transport to synthase activity. Emission rates are given by the equation (Niinemets et al, 1999;Niinemets et al, 2002a):…”

“…F d (g m −2 mol electrons mol isoprenoid −1 ) is the scaling constant that depends on isoprenoid synthase content (g m −2 ) and also converts from isoprenoid units to electron transport units (mol isoprenoids mol electrons −1 ) (Niinemets et al, 1999(Niinemets et al, , 2002a. Thus, light dependence of isoprenoid emission entirely results from the light effects on photosynthetic electron transport, while temperature dependence is a combined temperature response of isoprenoid synthase and electron transport activities.…”