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Intra-annual wood density fluctuations and tree-ring width patterns are sex- and site-dependent in the dioecious conifer Juniperus thurifera L.

Abstract:

Key message: Sex and site conditions modulate intra- and inter-annual secondary growth and its climatic sensitivity in a dioecious Mediterranean conifer. Abstract: Divergent evolutionary pressures associated with differential reproductive costs in dioecious trees may lead to sex-related variation in non-reproductive functions. Sex-related differences may be site-dependent, with different outcomes depending on environmental conditions. We explored the effects of sex and environmental conditions on the climatic control of annual secondary growth and intra-annual wood density fluctuations (IADF) of a dioecious conifer (Juniperus thurifera L.) growing in two sites with contrasting hydrological conditions under a continental Mediterranean climate. Different sex-related strategies had variable effects on relative secondary growth, with females outperforming males under more favorable hydrological conditions, and males outperforming females under water-limited conditions. Ring width and IADF formation were driven by climatic factors occurring at different temporal scales. Tree-ring growth depended on factors acting prior to the initiation of the xylogenesis and to conditions directly affecting the duration and pace of cambial activity, and ring width, therefore, integrated a complex signal of factors occurring over a relatively long period, and on an annual cycle. In contrast, IADFs responded to singular short-term events that alleviated drought and promoted cambial reactivation during the summer arrest. Female trees showed a more opportunistic water use, displayed in the stronger ring-width response to June–July conditions. Enhanced cambial sensitivity in females set a lower threshold for IADF occurrence, leading to a higher frequency of IADFs irrespective of site. Intra-annual and inter-annual female growth patterns reflect an opportunistic strategy to benefit from favorable climatic windows.