# Rhododendron minus seedlings achieve similar performance across light environments with anthocyanin accumulation and architectural adjustments under light stress

## TL;DR

This study explores how Rhododendron minus seedlings adapt to different light conditions using anthocyanins and architectural changes, which help maintain performance despite environmental shifts.

## Contribution

The study reveals novel insights into how anthocyanin accumulation and architectural adjustments enable Rhododendron minus seedlings to maintain performance across varying light environments.

## Key findings

- Supplemental light seedlings had higher anthocyanin levels but no significant differences in chlorophyll or biomass.
- Northern provenance plants showed higher anthocyanin levels compared to southern ones, suggesting climate-driven variation.
- Architectural adjustments like leaf movements help balance light interception and metabolic needs.

## Abstract

Influences of climate change on light availability are often overlooked; yet, understory species may experience shifts in irradiance as rising temperatures influence phenology and community composition. Light management is crucial for seedling success, and a whole-plant approach can help elucidate consequences of light on plant performance. Rhododendron minus is an evergreen shrub native to the Southeast United States that grows from rock outcrops to the understory. We conducted two experiments to unravel influences of light on plant function: (i) a manipulative greenhouse experiment on seedlings from a sun-exposed provenance examining pigments, plant architecture, and biomass patterns under shade, ambient, and supplemental light and (ii) a common garden experiment comparing pigments of mature plants from six provenances differing in latitude, elevation, climate, and solar radiation. We used multispectral imaging to estimate anthocyanin through the normalized difference anthocyanin index (NDAI) and chlorophyll through the normalized difference vegetation index (NDVI). Supplemental light seedlings had significantly higher NDAI than shade and ambient seedlings, but there was no significant treatment effect on NDVI or total biomass. Supplemental light seedlings also exhibited leaf movements that reduced projected surface area over time. This work highlights the importance of anthocyanins and plant architecture in allowing seedlings to maintain similar performance across light environments. In our common garden experiment, plants from northern, colder provenances had higher NDAI compared to warmer, southern provenances. We suggest that interactions between temperature and irradiance likely drive intraspecific variation in NDAI across the range, indicating that climate change could influence future pigment evolution.

Rhododendron minus plants growing in exposed, cold habitats of the Appalachian Mountains may benefit from higher anthocyanin due to combined pressures of high light and low temperature during winter months. In addition to anthocyanins, architectural adjustments may help plants balance light interception with metabolic capacity. Plants from the southern region of the species range had less anthocyanin and may instead use carotenoids as a photoprotection mechanism.