Multi-centennial phase-locking between reproduction of a South American conifer and large-scale drivers of climate

• Published in: Nature plants Vol. 7; no. 12; pp. 1560 - 1570
• Main Authors: Mundo, Ignacio A., Sanguinetti, Javier, Kitzberger, Thomas
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-12-2021; Nature Publishing Group
• Subjects: 631/158/2454; 704/158/2165/2457; Anomalies; Biomedical and Life Sciences; Climate; Climate effects; Cold; Cold Temperature; Conifers; Dendrochronology; Drought; Droughts; El Nino; El Nino-Southern Oscillation; Females; Frequency dependence; Influence; La Nina; Life Sciences; Locking; Males; Plant reproduction; Plant Sciences; Reproduction; Reproductive cycle; Reproductive effort; Reproductive status; Seeds; Sexes; South America; Southern Oscillation; Synchronism; Tracheophyta - physiology; Trees; South America
• ISSN: 2055-0278; 2055-0278
• DOI: 10.1038/s41477-021-01038-1

Climate forcings determine the episodic occurrence of local climate anomalies that trigger the occurrence of masting events (massive, synchronized and intermittent seed production by perennial plants). This suggests some kind of phase-locking of the reproductive cycles of individual plants to the climatological cycle, thus further reinforcing reproductive synchrony and the Moran effect. We propose a dendrochronological approach to filter out the long-term direct effects of climate on tree radial growth and temporal reproductive effort by sex by using actual trees as climatic controls to reconstruct masting events in
Araucaria araucana
, a long-lived dioecious masting conifer. In this way, we developed a multi-century-long tree masting reconstruction for South America using female–male radial growth determined by differences in timing and magnitude of the reproductive effort between sexes. We provide evidence for a regional synchronizing mechanism of masting which is drought induced by strong cold La Niña phases of El Niño/Southern Oscillation (ENSO) amplified by the positive phases of the Southern Annular Mode (SAM) that activate both female and male cone bud formation during year −2 before seed fall; that is, a long-term phase-locking between the ENSO cycle and the reproductive cycle modulated by the strength of SAM. In addition, our regional index of masting frequency showed its maximum during the late twentieth century relative to the previous centuries, suggesting that the species is currently at its maximum masting frequency concurrent with a period of enhanced temperature and drought conditions in Patagonia, probably driven by the positive phase of the SAM.
This study establishes the effect of ENSO cycles modulated by SAM in South America on a native conifer over multiple centuries and the reproductive cycle of individual plants on a regional scale in line with climate events.