Gas exchange parameters of 8-year-old Abies fraseri (Pursh) Poir. seedlings under different irrigation regimes

Abstract

Eight-year-old Abies fraseri seedlings were grown under different irrigation regimes to determine how drought stress might affect the seedlings in terms of gas exchange parameters. In this study, net photosynthesis (Anet), transpiration rate (E), stomatal conductance (gs), intercellular CO2 (Ci), Ci to ambient CO2 (Ca) concentration ratio (Ci/Ca), intrinsic water use efficiency (iWUE), and water use efficiency (WUE) were measured on August 11 and 27. Irrigation and measurement time were statistically significant on all gas exchange parameters except WUE for irrigation and measurement time and Anet for measurement time. E and gs were significant under the irrigation and measurement time interactions. In this study, increasing irrigation generally decreased Anet, and gs, while increased E, iWUE, and Ci/Ca. On August 27, A. fraseri had higher Anet, gs, E, Ci, Ci/Ca, and lower iWUE values than August 11. However, there was a robust positive correlation between gs and Anet, while a negative correlation between gs and iWUE in A. fraseri seedlings. In general, prolonged water deficiency leads plants to decrease Anet, gs, and E while iWUE increases, contrary to the current study. A well-developed and deeper root system, especially in plants under less or no-irrigation regimes, may alleviate drought stress effects in the long run and provide an advantage in leaf gas exchange parameters. In addition, the fact that soil moisture did not differ much between treatments, although irrigation levels were different, may explain the similar behavior among individuals measured in terms of gas exchange parameters.