Critical temperature and precipitation thresholds for the onset of xylogenesis of Juniperus przewalskii in a semi-arid area of the northeastern Tibetan Plateau
Ren, Ping (Chinese Academy of Sciences. Institute of Tibetan Plateau Research)
Rossi, Sergio (Rossi Heras) (Université du Québec à Chicoutimi. Département des Sciences Fondamentales)
Camarero, Jesús Julio (Instituto Pirenaico de Ecología)
Ellison, Aaron M. (Harvard University)
Liang, Eryuan (Chinese Academy of Sciences. Institute of Tibetan Plateau Research)
Peñuelas, Josep (Centre de Recerca Ecològica i d'Aplicacions Forestals)

Data:	2018
Resum:	Background and Aims. The onset of xylogenesis plays an important role in tree growth and carbon sequestration, and it is thus a key variable in modelling the responses of forest ecosystems to climate change. Temperature regulates the resumption of cambial activity, but little is known about the effect of water availability on the onset of xylogenesis in cold but semi-arid regions. Methods. The onset of xylogenesis during 2009-2014 was monitored by weekly microcoring Juniperus przewalskii trees at upper and lower treelines on the north-eastern Tibetan Plateau. A logistic regression was used to calculate the probability of xylogenic activity at a given temperature and a two-dimensional reverse Gaussian model to fit the differences between the observed and estimated days of xylogenesis onset at given temperatures and precipitation within a certain time window. Key Results. The thermal thresholds at the beginning of the growing season were highly variable, suggesting that temperature was not the only factor initiating xylem growth under cold and dry climatic conditions. The onset of xylogenesis was well predicted for climatic thresholds characterized by a cumulative precipitation of 17. 0 ± 5. 6 mm and an average minimum temperature of 1. 5 ± 1. 4 °C for a period of 12 d. Conclusions. Xylogenesis in semi-arid regions with dry winters and springs can start when both critical temperature and precipitation thresholds are reached. Such findings contribute to our knowledge of the environmental drivers of growth resumption that previously had been investigated largely in cold regions without water shortages during early growing seasons. Models of the onset of xylogenesis should include water availability to improve predictions of xylem phenology in dry areas. A mismatch between the thresholds of temperature and moisture for the onset of xylogenesis may increase forest vulnerability in semi-arid areas under forecasted warmer and drier conditions.
Ajuts:	European Commission 610028
Drets:	Tots els drets reservats.
Llengua:	Anglès
Document:	Article ; recerca ; Versió acceptada per publicar
Matèria:	Tree growth ; Temperature ; Precipitation ; Critical thresholds ; Xylogenesis ; Juniperus przewalskii ; Xylem formation ; Drought ; Two-dimensional reverse Gaussian model ; Semi-arid area ; Tibetan Plateau
Publicat a:	Annals of Botany, Vol. 121, Issue 4 (March 2018) , p. 617-624, ISSN 0305-7364

DOI: 10.1093/aob/mcx188
PMID: 29300821

Postprint 31 p, 1.5 MB

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