Long-term versus daily stem diameter variation in co-occurring mangrove species: Environmental versus ecophysiological drivers

• High temporal resolution physiological measurements were conducted on co-occurring mangrove species.
• Similar long-term growth indicated a similar response to environmental drivers.
• Opposite daily stem diameter variations indicated different physiological processes among species.
• Interactions between physiology and environment determine stem diameter variations.

High temporal resolution stem diameter variation (SDV) patterns have been widely recognized as a tool to study fundamental plant physiological mechanisms underlying whole-plant functioning and growth. As an integrative response to hydraulic and carbon related processes, SDV research has greatly improved insights in plant functioning of several herbaceous and woody species. Nevertheless, to date little detailed information on SDV and related physiological processes is available for mangrove species. By measuring continuous tree physiological variables such as stem diameter variations, sap flow and stem water potential in relation to the microclimatic conditions, the water use strategies of two co-occurring mangrove species, Avicennia marina (Forssk.) Vierh. and Rhizophora stylosa Griff. were investigated. Even though both species showed a similar long-term growth trend, closely linked to the environmental conditions, their daily SDV pattern was markedly different. While for Avicennia marina the SDV showed the standard daily pattern of morning decline and evening rise, the opposite daily SDV pattern was observed for Rhizophora stylosa. The contrasting patterns of SDV in both species thriving in the same environment indicates the importance and complexity of physiological endogenous mechanisms in addition to environmental conditions in controlling SDV and radial stem growth.