Diurnal Change of the Photosynthetic Light-Response Curve of Buckbean (Menyanthes trifoliata), an Emergent Aquatic Plant

Abstract

Understanding plant physiological responses to high temperature is an important concern pertaining to climate change. However, compared with terrestrial plants, information about aquatic plants remains limited. Since the degree of midday depression of photosynthesis under high temperature depends on soil water conditions, it is expected that emergent aquatic plants, for which soil water conditions are always saturated, will show different patterns compared with terrestrial plants. We investigated the diurnal course of the photosynthetic light-response curve and incident light intensity for a freshwater emergent plant, buckbean (Menyanthes trifoliata L.; Menyanthaceae) in a cool temperate region. The effect of midday depression was observed only on a very hot day, but not on a moderately hot day, in summer. The diurnal course of photosynthetic light-response curves on this hot day showed that latent morning reduction of photosynthetic capacity started at dawn, preceding the apparent depression around the midday, in agreement with results reported in terrestrial plants. We concluded that (1) midday depression of emergent plants occurs when the stress intensity exceeds the species’ tolerance, and (2) measurements of not only photosynthetic rate under field conditions but also diurnal course of photosynthetic light-response curve are necessary to quantify the effect of midday depression.

Plant phenology and species‐specific traits control plant CH4 emissions in a northern boreal fen

“…3°C in high summer). Light availability and temperature can affect stomatal conductance (Roelfsema & Hedrich, 2005; Okamoto et al ., 2022), which has been reported to impact fCH 4p of Carex (Morrissey et al ., 1993), while other studies observed no such effect in Carex ‐dominated surfaces (Günther et al ., 2014; Luan & Wu, 2014) or with M. trifoliata (MacDonald et al ., 1998). Over most of the growing season, our site had light throughout the night and the maximum recorded air temperature was 31.4°C (Fig.…”

“…Over most of the growing season, our site had light throughout the night and the maximum recorded air temperature was 31.4°C (Fig. S10), much lower than the value that can significantly decrease stomatal conductance (Okamoto et al, 2022), both factors indicating low potential impact of diurnal variability on fCH 4p on our site.…”

Terrestrial and Floating Aquatic Plants Differ in Acclimation to Light Environment

“…This contrasts with a limited inability to provide evaporative cooling upon sudden transfer to high PFD seen in shade-grown leaves of terrestrial plants with their limiting water-transport infrastructure ( Section 5 below). Furthermore, the direct contact with water of the whole surface of duckweed fronds should allow more efficient heat buffering than is the case for emergent aquatic plants growing in standing water (but without direct contact of much of their leaf surface with water) that are known to be vulnerable to heat stress [ 38 , 39 ].…”