How is the rate of transpiration affected by decreasing humidity and by decreasing light intensity? Decreasing humidity : Decreasing light intensity

Transpiration is the loss of water vapor from plant leaves [2]. The rate of transpiration is significantly influenced by environmental factors including humidity and light intensity. Decreasing humidity increases the vapor pressure gradient between the leaf's internal air spaces and the surrounding atmosphere, thereby increasing the rate of evaporation and transpiration. Conversely, light intensity directly affects stomatal behavior; as light intensity decreases, stomatal conductance typically decreases as well [1]. Since stomata are the primary exit points for water vapor, their partial or full closure under low light conditions leads to a decrease in the transpiration rate [3]. Therefore, decreasing humidity increases transpiration by enhancing the driving force for evaporation, while decreasing light intensity decreases transpiration by reducing stomatal opening [2].

Sources

1. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 24: Hydrological Cycle (Water Cycle) > Relative Humidity > p. 326
2. [1] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Activity 5.8 > p. 95
3. [3] https://pmc.ncbi.nlm.nih.gov/articles/PMC11324428/