Response of xylem formation of Larix sibirica to climate change along the southern Altai Mountains, Central Asia

Under the ongoing warmer and wetter climate in the arid and semi-arid Altai Mountains, the key to under-standing and predicting how forest growth responds to the changing climate in this area is to explore the dy-namics of xylem formation and its climate drivers. However, such precise and high-time resolution knowledge is currently scarce. Here, we investigated the cambium activity and xylem formation of Siberian larch (Larix sibirica Ledeb.) in four sites along the southern Altai Mountains during the two consecutive growing seasons of 2018 and 2019. We found that the onset of xylem formation along the southern Altai Mountains started from mid-May to early June and ceased from late August to early September. The linear mixed model results showed that the onset of xylogenesis happened earlier when April was warmer and with lower precipitation. The cessation of xylem differentiation was closely related to the total number of xylem cells, regardless of temperature and precipitation. Therefore, a greater number of xylem cells resulted in delayed completion of cell enlargement and wall thick-ening. In addition, xylem cell production (total number of xylem cells) was negatively affected by May-July temperature and positively affected by May-July total precipitation. Our findings provide key data at the cellular level and high time resolution (weekly) and new insights into how forest ecosystems in the southern Altai Mountains respond to a warmer and wetter climate in the context of global warming.