Sustained carbohydrate formation and growth concur with drought-limited photosynthesis in an alpine plant species.

Abstract

This study aimed to understand the drivers of non-structural carbohydrate (NSC) formation in the alpine plant Phacelia secunda in habitats with drought and low temperatures. It was hypothesized that NSCs may accumulate passively due to growth limitations, or actively through storage prioritization. Additionally, it was explored how local adaptation affects growth and photosynthesis sensitivity to environmental constraints, influencing NSC formation. The study investigated NSC formation in plants at three elevations (1600 m to 3600 m a.s.l.) under three watering regimes (control, mild drought, severe drought), and two temperature regimes (5/2°C and 15/7°C) for 1 month. Growth, photosynthesis, NSC concentrations, and survival were measured. In low-elevation plants exposed to 5/2°C, growth decreased more than photosynthesis, and NSC increased, suggesting passive NSC accumulation. In low- and mid-elevation plants exposed to 15/7°C under mild or severe drought, and in mid-elevation plants exposed to 5/2°C with mild drought, NSC concentrations increased despite photosynthesis being reduced more than growth, suggesting active NSC formation. Local adaptation influences growth and photosynthetic sensitivity to environmental stress, affecting NSC regulation. In plants from lower elevations, locally adapted to drier conditions, NSC increased when growth was less reduced than photosynthesis, indicating that NSC formation was not passive. This study demonstrates that in drought-adapted plants, growth and NSC formation can occur simultaneously, even with limited carbon gain.