Background: Rhododendron is one of the most well-known alpine flowers. In order to identify performances relating to Rhododendron’s natural habitats we investigated the leaf anatomical structures and photosynthetic characteristics of R. yunnanense, R. irroratum and R. delavayi, which showed different responses after being transplanted into a common environment. Results: When compared with R. irroratum and R. delavayi, R. yunnanense had lower leaf dry mass per unit area (LMA) and larger stomata, but smaller stomatal density (SD) and total stomata apparatus area percent (At), lower stomatal conductance (Gs), transpiration rate (Tr), light compensation point (LCP), light saturation point (LSP), light-saturated photosynthetic rate (Amax) and leaf nitrogen content per unit area (Na). LMA was positively correlated with Amax and maximum rates of carboxylation (Vcmax). However, leaf N content was not significantly correlated with Amax. Thus, the variation in leaf photosynthesis among species was regulated largely by changes in LMA, rather than the concent of nitrogen in leaf tissue. Conclusions: R. yunnanense plants are vulnerable to moisture and light stress, while R. irroratum and R. delavayi are better suited to dry and high radiation environments. The present results contribute to our understanding physiological trait divergence in Rhododendron, as well benefit introduction and domestication efforts for the three species of Rhododendron studied in this work.

Plants of the genus Camellia are widely cultivated throughout the world as ornamentals because of their bright and large flowers. The widely cultivated varieties are mainly derived from the mutant lines and hybrid progenies of Camellia japonica Linn. and Camellia reticulata Lindl. While their geographical distributions and environmental adaptabilities are significantly different, no systematic comparison has been conducted between these two species. To investigate differences in how these plants have adapted to their environments, we measured photosynthesis and 20 leaf functional traits of C. japonica and C. reticulata grown under the same conditions. Compared with C. japonica, C. reticulata showed higher values for light saturation point, light-saturated photosynthetic rate, leaf dry mass per unit area and stomatal area, but lower values for apparent quantum efficiency, leaf size, stomatal density and leaf nitrogen content per unit mass. Stomatal area was positively correlated with light-saturated photosynthetic rate and light saturation point, but negatively correlated with stomatal density. The differences between C. reticulata and C. japonica were mainly reflected in their adaptations to light intensity and leaf morphological traits. C. reticulata is better adapted to high light intensity than C. japonica. This difference is related to the two species’ differing life forms. Thus, leaf morphological traits have played an important role in the light adaptation of C. reticulata and C. japonica, and might be first noticed and selected during the breeding process. These findings will contribute to the cultivation of camellia plants.

Knowledge about how species richness varies along spatial and environmental gradients is important for the conservation and use of biodiversity. The Ericaceae is a major component of alpine and subalpine vegetation globally. However, little is known about the spatial pattern of species richness and the factors that drive that richness in Ericaceae. We investigated variation in species richness of Ericaceae along an elevational gradient in Yunnan, China, and used a variation partitioning analysis based on redundancy analysis ordination to examine how those changes might be influenced by the mid-domain effect, the species-area relationship, and climatic variables. Species richness varied significantly with elevation, peaking in the upper third of the elevational gradient. Of the factors examined, climate explained a larger proportion of the variance in species richness along the elevational gradient than either land area or geometric constraints. Species richness showed a unimodal relationship with mean annual temperature and mean annual precipitation. The elevational pattern of species richness for Ericaceae was shaped by the combined effects of climate and competition. Our findings contribute to a better understanding of the potential effects of climate change on species richness for Ericaceae.

Rhododendron delavayi Franch. is a famous ornamental plant. However, seasonal drought caused by a monsoon climate seriously limits its growth and flowering performance in urban gardens. Our previous study has found that brassinosteroids (BRs) can improve the tolerance of R. delavayi to drought stress. Here, we employed a data-independent acquisition (DIA) approach to compare the protein expression profiles under drought treatment (D) and pre-treatment with BR before drought treatment (BR). With an increase in drought stress, the net photosynthetic rate, stomatal conductance, and transpiration rate in the BR treatment showed more stable changes that were significantly higher than those in the D treatment. However, the contents of malondialdehyde, soluble sugar, soluble protein, and the activity of superoxide dismutase (SOD), peroxidase, and catalase showed opposite trends. The pre-treatment with BR alleviated the negative effect of drought stress on the photosynthetic performance of R. delavayi. A total of 3453 differentially expressed proteins (DEPs) were identified, and 683 DEPs were significantly expressed in the D and BR treatments. The DEPs uniquely expressed in the BR treatment participated in the pathways of “ribosome”, “ether lipid metabolism”, “photosynthesis”, and “oxidative phosphorylation”. The improvement effect of the BR treatment on the drought tolerance of R. delavayi was mainly attributed to improved photosynthesis by alleviating stomatal closure and oxidative stress, maintaining the integrity and stability of the ribosomal complex to mediate protein synthesis and the balance between energy metabolism and carbon metabolism. Our study presents a comprehensive understanding of the key proteins and metabolic pathways related to the response of R. delavayi to drought and will contribute to the breeding of drought-tolerant rhododendrons.