Environmental drivers of stem radius change and heterogeneity of stem radial water storage in the mangrove Avicennia marina (Forssk.) Vierh.

The dynamics of stem water storage can provide insight on a tree's capacity to face imbalances between water supply and demand, and thus maintain hydraulic function and growth under fluctuating environmental conditions. Recent work on the mangrove Avicennia marina (Forssk.) Vierh showed that stem radius change (SRC) is highly heterogeneous due to the structure of A. marina wood, composed of multiple reticulate cambia. The heterogeneity of short and long-term SRC in trees with reticulate cambia, common in dry environments, complicates the study of environmental drivers of stem water storage. In order to find the environmental drivers of stem water storage and understand the nature of this heterogeneity we analysed high-resolution SRC of A. marina for one and a half years. Nine point dendrometers measured SRC in upper, lower and mid stem of three A. marina trees in northern New Zealand. Stem radius change was detrended for growth to obtain water-related shrinking and swelling only (Delta W). Despite heterogeneity in SRC measurements, Delta W changes in A. marina still had seasonal trends of high winter and low summer diel amplitudes and strong responses to mean diel environmental conditions. Environmental drivers of Delta W were more apparent once the data was standardized to show relative changes, and segregated by upper and lower stem tiers. Moving window correlations showed stem contraction was correlated with atmospheric water demand and precipitation, whilst stem swelling was correlated with light sums more often than with measures of water availability. The correlation of stem water storage with light seen in our work provides backing for the hypothesized role of carbohydrates in the mechanism behind daytime stem swelling of A. marina water storage tissues. Our work highlights the importance of sensor locations and data analysis approaches if we are to use established SRC technologies in a larger diversity of environments and species.