Water Affecting Photosynthesis of Seedlings Growing in the Oopen

An assessment of the decrease in the photosynthesis intensity due to the lack of moisture were carried out on 6-year-old oak, pine and spruce seedlings grown in containers in the open air within the Serebryanoborsky forestry district by the Institute of Forest Science of the RAS (Moscow region). We determined at which values of pre-dawn water potential (PWP) seedlings growing in the open are resistant to the lack of moisture. Almost all seedlings of these species with insufficient water supply have a depression of photosynthesis, which occurs more rapidly as the moisture deficit increases and at lower solar radiation. In case of an oak, when the PWP reaches –1.1 MPa, the intensity of photosynthesis decreases by half, and in case of pine and spruce — at a PVP equal to –0.8 MPa. For the oak, the intensity of photosynthesis drops to zero at –3.0 MPa, in pine — at –1.6 ÷ –1.8 MPa, in spruce — at –1.5 MPa. Thus, the most resistant to the lack of moisture is oak, then pine, and the most demanding in terms of water supply is spruce.