Daily trunk radial growth patterns in relation to precipitation in orange trees in the dry-hot valley region of Southwest China

The dry-hot valley regions of Southwest China suffer droughts and high temperatures coexist environment. The efficient use of rainfall makes it possible for plants to safely cope with the environmental stress in the region. To reveal the driving mechanism of rainfall on typical tree secondary growth, orange tree (Citrus sinensis L. Osbeck), the commonly grown economic tree in the region was selected. Trunk diameter, sap flow, leaf humidity, meteorological conditions and soil water content were simultaneously monitored for the 2020-2022 period. Based on frequency distribution of trunk diameter changes data, trunk diameter changes were classified into positive growth (dramatic expansion, and common expansion), and negative growth (dramatic shrinkage, and common shrinkage) types. Furthermore, the relationships among the different growth patterns and rainfall or drought events were analyzed. The results showed: i) Trunk diameter maintained positive growth on rainy days, whereas both positive and negative growth occurred on rainless days. Although rainy period was not frequent, a high proportion of the total growth occurred during that time. ii) The common expansion type with a high frequency contributed to approximately 30% of the total growth, whereas the dramatic expansion type with a low frequency contributed to approximately 70% of the total growth. iii) There was a highly significant correlation between dramatic tree diameter expansion and rainfall. iv) Cumulative growth in tree diameter during rainy period was significantly driven by the duration of rainfall, the wetting time of leaf and the amount of rainfall. v) Compared with rainfall amount, the time rainfall related indexes were more closely related with tree dramatic diameter expansion. vi) While increasing soil water content and dry air mitigation due to rainfall enhanced average growth, it concurrently suppressed negative growth of tree trunk diameter after rainfall. The study confirmed that rainfall was critical for tree diameter growth in dry-hot valley regions of Southwest China. Relevant results are beneficial for improving understanding of plant precipitation utilization mechanism and could provide useful information on extreme meteorological hazards assessment in the context of climate change.