Dynamics of non-structural carbohydrates following a full masting event reveal a role for stored starch in relation to reproduction in Fagus crenata.

Abstract

Although mature trees have substantial non-structural carbohydrate (NSC) storage that is well documented with respect to its capacity to buffer the asynchrony of supply and demand at the whole-plant level, its role in reproduction remains poorly understood, especially in mast seeding species. In order to elucidate whether masting depletes the whole-tree NSC storage pool, seasonal and inter-annual variations in starch and soluble sugar (SS) concentrations in branchlets, stems and coarse roots of Fagus crenata were measured in two stands over 5 years after a full masting event. Full masting reduced individual storage pools to 72% and 49% of the maxima in the two stands; this was observed 2-3 years after full masting. In addition, temporary reduction in starch concentration in summer due to moderate fruiting was found in roots and deep sapwood cores of stems, representing tree rings formed 20 years ago, but not in branchlets. Together with a higher starch storage pool in roots than in branchlets, these results indicate that starch stored in roots and stems is available and supports life-history traits, such as masting events, that occur irregularly. Moreover, limited rainfall in the late growing season caused a reduction in both organ NSC concentration and individual storage irrespective of masting, which further complicated the masting-NSC relationship. These findings have important implications for interpreting the role of carbon resources in masting events.