<![CDATA[Altitude-associated changes in microclimate may influence leaf gas exchange and water relations in rice. This study evaluated transpiration rate and stomatal conductance of rice (Oryza sativa L. cv. Inpari Sembilan) along an altitudinal gradient in South Tapanuli Regency and Padangsidimpuan City, North Sumatra, Indonesia. Measurements were conducted at six locations ranging from 316 to 647 m above sea level, with 20 plants sampled at each location. Microclimatic variables, including air and leaf temperatures, relative humidity, photosynthetically active radiation (PAR), and leaf-to-air vapor pressure deficit (VPD), together with transpiration rate (E) and stomatal conductance (gs), were measured on fully expanded flag leaves using a portable photosynthesis system. Transpiration rate and stomatal conductance showed a non-linear pattern along the elevation gradient, with the highest values observed at intermediate elevations. The highest E (0.886 mmol H₂O m⁻² s⁻¹) and gs (0.055 mol m⁻² s⁻¹) were recorded at Sibong-bong (393 m asl), whereas lower values occurred at both lower and higher elevations. Mean VPD decreased from 2.37 kPa at 316 m to 1.45 kPa at 647 m asl. Quadratic regression indicated a relatively weak relationship between elevation and transpiration rate (R² = 0.218), suggesting that elevation alone explained only a limited proportion of the observed variation. Overall, rice leaf gas exchange varied considerably along the altitudinal gradient, with intermediate-elevation sites showing more favorable conditions for transpiration and stomatal conductance. These findings indicate that local microclimatic factors, particularly temperature, humidity, radiation, and VPD, should be considered together with elevation when evaluating physiological responses of rice across different agroecological environments.]]>
