Relationships between diurnal and seasonal variation of photosynthetic characteristics of Eucalyptus plantation and environmental factors under dry-season irrigation with fertilization

Abstract

Eucalyptus is widely planted in South China and has high economic and ecological values. However, the seasonal drought in southern China severely limits the productivity of Eucalyptus plantation. In this study, the dry-season irrigation was carried out after the conventional production and planting of Eucalyptus. The diurnal changes of photosynthetic characteristics of Eucalyptus plantations were measured in July, October 2017 and January, May 2018 to explore the diurnal and seasonal variations and their responses to both dry-season irrigation and environmental factors. The results showed that during the first-year growth of Eucalyptus urophylla × E. grandis plantation, (1) the diurnal changes of the trees under different treatments showed single-peak curves with the varied occurrence time of the highest photosynthetic characteristics in different months; the E. urophylla × E. grandis without dry-season irrigation (CK and F) had transpiration midday depression in January and that with the only dry-season irrigation (W) exhibited both photosynthetic and transpiration midday depression in May. (2) The trees of CK and F were subjected to mild drought stress in the dry season and their maximum photosynthetic and transpiration rate were lower than those of W and WF treatment respectively, but they had higher maximum WUE. The trees of W had significantly higher daily net CO2 assimilation and daily water transpiration in dry season. (3) The diurnal changes of photosynthetic characteristics were mainly influenced by water vapor pressure deficit (VPD) at the corresponding time of the month. (4) In the short-term treatments, dry-season irrigation and fertilization significantly increased the biomass of E. urophylla × E. grandis. Dry-season irrigation alleviated the mild drought stress for gas exchange in the dry season and further promote the biomass of E. urophylla × E. grandis. This study provided an important practical exploration for improving the productivity of E. urophylla × E. grandis plantation in seasonal arid areas.