Characteristics of sun- and shade-adapted populations of an endangered plant Primulina tabacum Hance

Abstract

Primulina tabacum Hance is an endangered perennial herb distributed in calcium-rich and nitrogen-limited soil of the karst limestone areas in southern China. The morphological, ultrastructural, and physiological traits were determined for P. tabacum populations growing in three different environment conditions: twilight zone of a cave (site TZ, extremely low light intensity), at a cave entrance (site EZ, low light intensity), and in an open area (site OA, high light intensity). At site OA, P. tabacum plants were exposed to high light (635 μmol m -2 s -1 of mean daily photosynthetically active radiation) with drought stress, and expressed traits to minimize light capture and water loss. Compared to plants at sites EZ and TZ, those at site OA had thicker leaves with higher densities of stomata and pubescence, higher palisade/spongy ratio, higher light-saturated rate of net photosynthetic rate (P max ), higher biomass, higher non-photochemical quenching coefficient (NPQ), and higher light saturation point (LSP) but fewer grana per chloroplast and less thylakoid stacking per granum. In contrast, P. tabacum growing at the cave vicinities: EZ (mean daily irradiance 59 μmol m -2 s -1 ) and TZ (mean daily irradiance 11 μmol m -2 s -1 ) showed typical shade-adapted characteristics for optimum light capture. The presence of sun-and shade-adapted characteristics indicates that P. tabacum has different strategies to cope with different environments but whether these strategies reflect genetic selection or phenological plasticity is yet to be determined. Such variability in physiological and morphological traits is important for the survival of P. tabacum in heterogeneous light conditions.

Common-garden studies on adaptive radiation of photosynthetic physiology among Hawaiian lobeliads

“…These findings are consistent with the rich literature on adaptations of equilibrium (or static) photosynthetic light responses to contrasting light regimes [5,8,10,11,[15][16][17][18][19][20][21][22][23][24][25][26]. Such adaptations have only rarely been studied in large numbers of closely related taxa (Euphorbia and Scaevola [27][28][29]; Acer [30][31][32]; Psychotria [33]; Sonchus alliance [34]), and, outside the Hawaiian lobeliads, never for plants whose distributions along natural light gradients have been quantified and whose phylogenetic relationships with each other are well characterized.…”

Phylogenetic analyses of Begonia sect. Coelocentrum and allied limestone species of China shed light on the evolution of Sino-Vietnamese karst flora

“…60 species (see Taxonomic Treatment) mainly distributed in Guangxi, inhabit the ‘twilight zone’ (Poulson and White1969) of limestone caves and cave-like microhabitats such as shaded fissures and crevices abundantly occurring throughout the Sino-Vietnamese limestone karst region (Sweeting1978; Schindler1982; Xu1995; Zhu2007). Such cave-like microhabitats, characterized by constant temperature, high humidity, and indirect and low light (Liang et al2010), function as shelters on the limestone bedrock characterized by highly alkaline conditions, thin soil layers, and severe desiccation due to high porosity (Clements et al2006). In addition to Begonia , these cave-like microhabitats are also inhabited by several species-rich, calciphilous herbaceous plant groups such as Aspidistra Ker Gawl.…”

Do thick leaves avoid thermal damage in critically low wind speeds?

“…, 2001; Panditharathna et al. , 2008; Liang et al. , 2010), may also play a role in thermal tolerance.…”

“…An example is the large cladodes of American desert cacti, which can have time constants of several hours because of their great thermal mass (Nobel, 1988). More subtle changes in the thermal mass of much smaller plant parts, for example through increases in leaf thickness towards the outer canopy (Terashima et al, 2001;Panditharathna et al, 2008;Liang et al, 2010), may also play a role in thermal tolerance. In one of the few studies investigating this concept, Ball et al (1988) showed that the large heat capacities of thick mangrove leaves at the top of a plant crown damp fluctuations in leaf temperature relative to thinner leaves, thereby reducing excursions into the temperature range unfavourable for photosynthesis.…”