Wood formation consumes around 15% of the anthropogenic CO2 emissions per year and plays a critical role in long-term sequestration of carbon on Earth. However, the exogenous factors driving wood formation onset and the underlying cellular mechanisms are still poorly understood and quantified, and this hampers an effective assessment of terrestrial forest productivity and carbon budget under global warming. Here, we used an extensive collection of unique datasets of weekly xylem tissue formation (wood formation) from 21 coniferous species across the Northern Hemisphere (latitudes 23 to 67°N) to present a quantitative demonstration that the onset of wood formation in Northern Hemisphere conifers is primarily driven by photoperiod and mean annual temperature (MAT), and only secondarily by spring forcing, winter chilling, and moisture availability. Photoperiod interacts with MAT and plays the dominant role in regulating the onset of secondary meristem growth, contrary to its as-yet-unquantified role in affecting the springtime phenology of primary meristems. The unique relationships between exogenous factors and wood formation could help to predict how forest ecosystems respond and adapt to climate warming and could provide a better understanding of the feedback occurring between vegetation and climate that is mediated by phenology. Our study quantifies the role of major environmental drivers for incorporation into state-of-the-art Earth system models (ESMs), thereby providing an improved assessment of long-term and high-resolution observations of biogeochemical cycles across terrestrial biomes.

• Keywords
• Northern Hemisphere conifer, photoperiod, temperature, wood formation, xylogenesis,
• MeSH
• Models, Biological MeSH
• Tracheophyta genetics   growth & development   MeSH
• Wood growth & development   MeSH
• Ecosystem MeSH
• Photoperiod MeSH
• Global Warming MeSH
• Climate Change MeSH
• Forests MeSH
• Climate MeSH
• Seasons MeSH
• Trees growth & development   MeSH
• Temperature MeSH
• Xylem growth & development   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH

Cytokinin is a multifaceted plant hormone that plays major roles not only in diverse plant growth and development processes, but also stress responses. We summarize knowledge of the roles of its metabolism, transport, and signalling in responses to changes in levels of both macronutrients (nitrogen, phosphorus, potassium, sulphur) and micronutrients (boron, iron, silicon, selenium). We comment on cytokinin's effects on plants' xenobiotic resistance, and its interactions with light, temperature, drought, and salinity signals. Further, we have compiled a list of abiotic stress-related genes and demonstrate that their expression patterns overlap with those of cytokinin metabolism and signalling genes.

• Keywords
• abiotic stress, cytokinin, drought, nutrient, stress tolerance, temperature,
• MeSH
• Acclimatization MeSH
• Circadian Clocks MeSH
• Cytokinins metabolism   MeSH
• Stress, Physiological * MeSH
• Plant Physiological Phenomena * MeSH
• Droughts MeSH
• Gene Expression Regulation, Plant MeSH
• Plants genetics   metabolism   MeSH
• Salinity MeSH
• Signal Transduction * MeSH
• Light MeSH
• Temperature MeSH
• Plant Development MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Cytokinins MeSH