Dry-season irrigation further promotes the growth of Eucalyptus urophylla × E. grandis plantations under the conventional fertilization

Seasonal drought limits the growth of plantations. Functional traits are effective indicators to clarify the controlling factors of plantation productivity. In this study, four treatments were carried out for the juvenile Eucalyptus urophylla × E.grandis plantations as (1) no dry-season irrigation or conventional fertilization (C); (2) only dry-season irrigation (W); (3) only conventional fertilization (F); (4) dry-season irrigation and conventional fertilization (WF). During the two years of treatment, growth traits, gas exchange characteristics, and structural properties were measured. The results showed that both dry-season irrigation and conventional fertilization could promote the growth of E. urophylla × E. grandis plantations. The effect of fertilization on increasing biomass of E. urophylla × E. grandis (3 times that of C) was greater than that of dry-season irrigation (only 1.5 times that of C). The biomass of WF was significantly higher than that of F. Dry-season irrigation could play the greatest role in promoting growth only when soil nutrients were sufficient. E. urophylla × E. grandis increased the total leaf area per tree but not the single leaf photosynthetic capacity, indicating the increased growth reflected greater canopy light interception. Fertilization increased the growth of E. urophylla × E. grandis plantations more than irrigation alone, but combining fertilization and dry-season irrigation further improved biomass yields of the juvenile plantations. Therefore, suitable dry-season irrigation management should be considered in seasonally arid areas to further improve the productivity of conventional plantations with only fertilization. This study elucidated the mechanism of dry-season irrigation to enhance the productivity of Eucalyptus plantations by functional traits, which provided strong data support for enhancing the productivity of plantation forests in seasonal arid areas.