Drought limits wood production of Juniperus przewalskii even as growing seasons lengthens in a cold and arid environment

Studies of xylogenesis can provide mechanistic understandings of the influence of climate on wood production and carbon sequestration at the cellular level. It is not yet clear how trees will respond to increasing temperature and precipitation variability and other extreme meteorological events that are expected to occur as climate continues to change. Here, we analyzed cambial phenology and xylogenesis of Juniperus przewalskii Kom. weekly (2011-2014) or biweekly (2015-2016) over six years on the northeastern Tibetan Plateau. We found that temperature plays a decisive role in the onset of xylogenesis and a daily mean temperature of 6.1 degrees C appears to be the threshold that determines growth onset. Additionally, we observed the end of xylogenesis is related to summer drought conditions. During the course of our observations, the onset of xylogenesis advanced nearly twice as much as the end of xylogenesis (3.1 vs 1.8 days decade(-1), respectively), indicating a slight lengthening of the growing season. However, an increase in the duration of the growing season did not necessarily result in a greater level of wood production. In fact, we found that water availability affects the growth rate and early summer precipitation appears to be a key factor of wood production over the northeastern Tibetan Plateau. Our study provides new evidence of the malleable nature of tree growth and reveals potential mechanisms of how tree growth adjusts to climatic variations in cold and arid region.