Extended xylogenesis and stem biomass production in Juniperus przewalskii Kom. during extreme late-season climatic events

Abstract

Key message: Late-season extreme climatic events induced variations in wood density and extended growth for more than a month in 2016 inJuniperus przewalskiiKom. growing on the Northeastern Tibetan Plateau, suggesting extraordinary growth resilience of the species in response to short extreme events over the cold and arid region. Context: Monitoring xylem formation (xylogenesis) during extreme meteorological events helps assessing climate change impacts on tree growth. Aims: For better insight into tree-growth responses, here we compare the intra-annual formation of annual ring with and without intra-annual density fluctuation in J. przewalskii in a cold and arid environment on the Northeastern Tibetan Plateau. Methods: Cambial phenology and xylogenesis observations of five mature trees during the 2016 intra-annual density fluctuation growth ring and the five-preceding year (2011–2015) were used for comparison. The frequency of population level occurrence of intra-annual density fluctuation in 2016 was examined on additional 50 randomly selected trees. Results: The return of precipitation in conjunction with warm temperatures after summer drought promoted the growth resumption in 64% of our study trees, resulting in the observed intra-annual density fluctuation. These trees experienced a growing season 1 month longer than trees without intra-annual density fluctuation. The extended growth period resulted in a 17% increase in stem biomass in trees that experienced intra-annual density fluctuation. Conclusion: Our results highlight the extraordinary resilience of J. przewalskii trees in response to extreme climatic events in the cold and dry conditions of the Tibetan Plateau.