A simulated drier climate reduces growth and alters functional traits of Eucalyptus trees: A three-year experiment in South China

Abstract

Global climate change is triggering more occurrences of drought events, which is continuously enlarging a worldwide area of arid and semi-arid regions. South China is a typical area that suffers seasonal drought events, which reduce plantation productivity and increase tree mortality. Eucalyptus is widely cultivated in South China due to its fast growing speed and high dry mass yield, but its response to severe drought stress is still not assessed. In this study, we analyzed how a 50 % throughfall reduction (TR) and season affected stand growth, foliar gas exchange parameters, leaf stomatal morphological traits, and hydraulic conductance. Three-year observations showed that TR intensified drought stress in the dry season by decreasing soil relative water content, resulting in the diameter at breast height growth, tree height growth, and stand volume growth of TR were 12.6 %, 19.0 %, and 23.7 % lower than those of the control treatment (CK), respectively. With the continuous drought, TR decreased the net photosynthetic rate, while having little effect on the transpiration rate and water use efficiency. Photosynthetic pigment analysis revealed a significant interaction between throughfall reduction and season, TR markedly decreased photosynthetic pigments during the wet season. Hydraulic conductivity declined by TR, which primarily existed during the dry season. To limit water loss, Eucalyptus adapted to drought stress by altering these functional traits, which were not entirely consistent with the drought resistance mechanisms of other tree species. Overall, our study indicated that the simulated drier climate included growth decline and variation in functional traits of Eucalyptus trees in South China. This study is important for understanding the drought resistance mechanisms of Eucalyptus, as well as predicting the risk of declining Eucalyptus timber production owing to global climate change.