Construction costs, chemical composition and payback time of high- and low-irradiance leaves

Abstract

The effect of irradiance on leaf construction costs, chemical composition, and on the payback time of leaves was investigated. To enable more generalized conclusions, three different systems were studied: top and the most-shaded leaves of 10 adult tree species in a European mixed forest, top leaves of sub-dominant trees of two evergreen species growing in small gaps or below the canopy in an Amazonian rainforest, and plants of six herbaceous and four woody species grown hydroponically at low or high irradiance in growth cabinets. Daily photon irradiance varied 3-6-fold between low- and high-light leaves. Specific leaf area (SLA) was 30-130% higher at low light. Construction costs, on the other hand, were 1-5% lower for low-irradiance leaves, mainly because low-irradiance leaves had lower concentrations of soluble phenolics. Photosynthetic capacity and respiration, expressed per unit leaf mass, were hardly different for the low- and high-light leaves. Estimates of payback times of the high-irradiance leaves ranged from 2-4 d in the growth cabinets, to 15-20 d for the adult tree species in the European forest. Low-irradiance leaves had payback times that were 2-3 times larger, ranging from 4 d in the growth cabinets to 20-80 d at the most shaded part of the canopy of the mixed forest. In all cases, estimated payback times were less than half the life span of the leaves, suggesting that even at time-integrated irradiances lower than 5% of the total seasonal value, investment in leaves is still fruitful from a carbon-economy point of view. A sensitivity analysis showed that increased SLA of low-irradiance leaves was the main factor constraining payback times. Acclimation in the other five factors determining payback time, namely construction costs, photosynthetic capacity per unit leaf mass, respiration per unit leaf mass, apparent quantum yield, and curvature of the photosynthetic light-response-curve, were unimportant when the observed variation in each factor was examined.

Leaf size and leaf display of thirty-eight tropical tree species

“…Poorter et al (2006aPoorter et al ( , 2006b) provided an independent, objective, and continuous measure of the regeneration light requirements of the species (i.e., the inverse of shade tolerance) by analyzing the crown exposure (CE) for each species in relation to the height of individual trees. This allows one to go beyond the subjective classiWcation into pioneers and shade tolerants, and to show how species traits change gradually and continuously with the light requirements of the species.…”

“…The CE can be measured repeatedly (average diVerence between two independent observers is 0.1 § 0.01 SE), and there is a good relation between CE and both canopy openness and incident radiation (Davies et al 1998;Clark et al 1993;Keeling and Phillips 2007). For each species the CE was related to tree height, using a multinomial regression analysis (Poorter et al , 2006a(Poorter et al , 2006b). Using the regression equation, the average population-level CE at a standardized height of 2 m (juvenile CE) was calculated.…”

“…Selected trees were not included in the study to describe the regeneration light requirements (Poorter et al 2006a(Poorter et al , 2006b, and were between 10-20 cm DBH and 8-15 m height. Erythrochiton fallax and Picramnia sellowii attain a maximum height of only 5-6 m and for these species the tallest individual trees were sampled.…”

“…Metamer traits are related to a quantitative and continuous measure of the regeneration light requirements of the species (i.e., the inverse of shade tolerance, Poorter et al 2006aPoorter et al , 2006b). This is, to our knowledge, the Wrst study to comprehensively analyze dimensions, biomass, and construction costs of internodes, petioles, and leaves and determine the relative strengths of intra-and interspeciWc variation.…”

Canopy conundrums: building on the Biosphere 2 experience to scale measurements of inner and outer canopy photoprotection from the leaf to the landscape

“…Two recent studies encourage our growing sense that sometimes the retention of leaves in deep shade may involve more than repayment of the mortgage. First, measurements and modelling in European forests by Poorter et al (2006) showed that in spite of 5-to 20-fold larger payback times than outer canopy leaves, investment in inner canopy leaves exposed to as little as 5% of seasonal irradiance paid a dividend. Second, Reich et al (2009) reported that, in the dry sclerophyll woodland of eastern Australia, leaves of most species retained positive carbon balance (remained productive) throughout their typical life-span.…”