Photosynthetic temperature responses of montane species across elevational experiments in Colombia and Rwanda, 2024-2025

Measurements were conducted in common garden plantations established to evaluate the physiological performance of native tropical tree species under contrasting temperature conditions. Experimental sites were established along elevation gradients in the Colombian Andes in January 2019 and in the Albertine Rift in Rwanda in January 2018.

In Colombia, the experimental sites are characterized as follows: a 14 °C mean annual temperature (MAT) site (99th percentile temperature, T99 = 21 °C; annual precipitation = 2774 mm; elevation = 2452 m a.s.l.) and a 22 °C MAT site (T99 = 33 °C; annual precipitation = 2045 mm; elevation = 1326 m a.s.l.). The experimental design comprised 360 saplings of 15 species planted at each of two sites in four plots, with six replicates per species per plot. All trees were planted in soils originating from the high-elevation site and were irrigated when no rainfall occurred.

In Rwanda, the experimental sites include a 15 °C MAT site (T99 = 23 °C; annual precipitation = 2144 mm; elevation = 2400 m a.s.l.) and a 20 °C MAT site (T99 = 28 °C; annual precipitation = 1672 mm; elevation = 1600 m a.s.l.). The experimental design includes 1,800 planted trees at each experimental site across 18 plots arranged in six treatment combinations with three replicates per treatment. The experiment included 20 native tropical Afromontane and highland tree species, with five individuals per species planted in each plot. Treatments consisted of three water levels (low, medium, and high) replicating the natural precipitation level at each experimental location, mixed with two nutrient levels (unfertilised natural soils and fertilised natural soils+ limed).
The dataset includes 193 photosynthetic temperature response curves collected from 162 individual trees representing 29 species across the two countries using a LI-6800 Portable Photosynthesis System. Measurements were conducted in situ on attached leaves of trees growing in the experimental plantations under saturating light conditions (1600 mol/m2 s-1), CO2 set to 420 ppm, with leaf temperature and VPD under controlled conditions.

Each temperature response curve (~17 ºC- 46ºC) consisted of a series of physiological variables as measured by a LI-6800 after leaves had reached physiological steady state. Initial stabilization point required 25-60 minutes, whereas subsequent temperature points required 15-25 minutes. Temperature and vapour pressure deficit (VPD) were standardized across all response curves, and each measurement represents the average of 30 seconds under stable photosynthesis and stomatal conductance.
Quality control procedures included daily instrument calibration following the manufacturer's recommendations, verification of chamber stability before each measurement, and regular inspection of gas analysers and environmental controls. Measurements were accepted only after photosynthesis and stomatal conductance had reached physiological steady state. All response curves were visually inspected, and anomalous measurements or instrument errors were identified and excluded before model fitting and statistical analyses.

Detailed descriptions of sampling locations, field protocols, data processing procedures, model fitting, and dataset-specific methodological information are provided in the supporting documentation.