Critical minimum temperature limits xylogenesis and maintains treelines on the southeastern Tibetan Plateau

Xiaoxia Li; Eryuan Liang; Jozica Gričar; Sergio Rossi; Katarina Čufar; Aaron M Ellison

doi:10.1016/j.scib.2017.04.025

Critical minimum temperature limits xylogenesis and maintains treelines on the southeastern Tibetan Plateau

Sci Bull (Beijing). 2017 Jun 15;62(11):804-812. doi: 10.1016/j.scib.2017.04.025. Epub 2017 May 3.

Authors

Xiaoxia Li¹, Eryuan Liang², Jozica Gričar³, Sergio Rossi⁴, Katarina Čufar⁵, Aaron M Ellison⁶

Affiliations

¹ Key Laboratory of Alpine Ecology and Biodiversity, Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China.
² Key Laboratory of Alpine Ecology and Biodiversity, Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China; CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China. Electronic address: liangey@itpcas.ac.cn.
³ Slovenian Forestry Institute, Department of Yield and Silviculture, Vecna pot 2, SI-1000 Ljubljana, Slovenia.
⁴ University of Quebec in Chicoutimi, Département des Sciences Fondamentales, 555, Boulevard de l'Université, Chicoutimi (QC) G7H2B1, Canada; Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, Guangdong Provincial Key Laboratory of Applied Botany, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China.
⁵ University of Ljubljana, Biotechnical Faculty, Department of Wood Science and Technology, Jamnikarjeva 101, SI-1000 Ljubljana, Slovenia.
⁶ Harvard Forest, Harvard University, 324 North Main St., Petersham, MA 01366, USA.

PMID: 36659277
DOI: 10.1016/j.scib.2017.04.025

Abstract

Physiological and ecological mechanisms that define treelines are still debated. It has been suggested that the absence of trees above the treeline is caused by low temperatures that limit growth. Thus, we hypothesized that there is a critical minimum temperature (CT_min) preventing xylogenesis at treeline. We tested this hypothesis by examining weekly xylogenesis across three and four growing seasons in two natural Smith fir (Abies georgei var. smithii) treeline sites on the southeastern Tibetan Plateau. Despite differences in the timing of cell differentiation among years, minimum air temperature was the dominant climatic variable associated with xylem growth; the critical minimum temperature (CT_min) for the onset and end of xylogenesis occurred at 0.7±0.4°C. A process-based modelling chronology of tree-ring formation using this CT_min was consistent with actual tree-ring data. This extremely low CT_min permits Smith fir growing at treeline to complete annual xylem production and maturation and provides both support and a mechanism for treeline formation.

Keywords: Cambial activity; Critical minimum temperature; Timberline; Vaganov-Shashkin model; Xylem.