Leaf paraheliotropism in Styrax camporum confers increased light use efficiency and advantageous photosynthetic responses rather than photoprotection

Abstract

Styrax caporum is a native shrub from the Brazilian savanna. Most of its leaves are diaheliotropic, whereas some are paraheliotropic, mainly at noon. A previous study of this species revealed higher stomatal conductance (gs) and transpiration rates (E) in para-compared to diaheliotropic leaves, and a rise in CO 2 assimilation rates (A) with an increase of irradiance for paraheliotropic leaves. We hypothesized that this species exploits the paraheliotropism to enhance the light use efficiency, and that it is detected only if gas exchange is measured with light interception by both leaf surfaces. Gas exchange was measured with devices that enabled light interception on only one of the leaf surfaces and with devices that enabled light interception by both leaf surfaces. Water relations, relative reflected light intensity, leaf temperature (T l), and leaf anatomical analyses were also performed. When both leaf surfaces were illuminated, a higher A, E, and gs were observed in para-compared to diaheliotropic leaves; however, A did not depend on gs, which did not influence CO 2 accumulation in the stomatal cavity (Ci). When only the adaxial leaf surface was illuminated, a greater A was detected for para-than for diaheliotropic leaves only at 11:00 h; no differences in T l were observed between leaf types. Light curves revealed that under non-saturating light the adaxial side of paraheliotropic leaves had higher A than the abaxial side, but they showed similar values under saturating light. Although the abaxial leaf side was highly reflective, both surfaces presented the same response pattern for green light reflection, which can be explained by the compact spongy parenchyma observed in the leaves, increasing light use efficiency in terms of CO 2 consumption for paraheliotropic leaves. We propose that paraheliotropism in S. camporum is not related to leaf heat avoidance or photoprotection.

Daily heliotropic movements assist gas exchange and productive responses in DREB1A soybean plants under drought stress in the greenhouse

“…In V7–V10 g s was lower in P58 than in BR 16, while in the reproductive stages the situation was reversed. Normally, paraheliotropic leaves have greater A and g s , leading to greater daily transpiration (Habermann et al ., ), as was expressed in our experiment, especially in BR 16 in V7–V10. Under water‐limiting conditions, E at midday was lower in P58 than in BR 16, giving a lower relative reduction in E in P58 than in BR 16 in the vegetative stages.…”

“…The adaptive significance of paraheliotropism is mostly related to the promotion of carbon assimilation by increasing light-use efficiency rather than enhancing photoprotection (Habermann et al, 2011). Heliotropic movements of leaflets in soybean suggest that improvement of photosynthesis, g s , dissipation of excess light energy as a photoprotective mechanism and better WUE are strategies to improve soybean performance.…”

Bicolored display of Miconia albicans fruits: Evaluating visual and physiological functions of fruit colors

“…The mean temperature in the chamber was 30°C (± 2.15). Light curves ( A /PPFD) were obtained by varying the PPFD from 1200 µmol·m −2 ·s −1 to zero (Habermann et al, 2011). After measurements, we estimated the area (cm 2 ) of fruits that comprised the sample within the chamber and recalculated A based on the corrected fruit surface.…”

Towards a New Ecophysiological Approach to Understand Citrus Crop Yield Under Abiotic Stresses Mirroring in the Brazilian Savanna Genetic Resources

“…Cerrado plant architectures, on the other hand, exhibit diverse strategies when it comes to sunlight penetration into the canopy. Despite the limited data concerning plant architecture in cerrado woody plants, their strategies range from vertical leaf orientation, which may not be related to leaf heat avoidance (Habermann et al, 2011b) to evergreen/deciduousness behaviors (Franco et al, 2005). Although citrus and cerrado woody plants may show similar photochemical parameters, their overall ecophysiological strategies are quite distinct, which might represent hidden consequences for land use, which has not been studied so far.…”