Is precipitation a trigger for the onset of xylogenesis in Juniperus przewalskii on the north-eastern Tibetan Plateau?
OBJECTIVE
A series of studies have shown that temperature triggers the onset of xylogenesis of trees after winter dormancy. However, little is known about whether and how moisture availability influences xylogenesis in spring in drought-prone areas.


METHODS
Xylogenesis was monitored in five mature Qilian junipers (Juniperus przewalskii) by microcore sampling from 2009 to 2011 in a semi-arid area of the north-eastern Tibetan Plateau. A simple physical model of xylem cell production was developed and its sensitivity was analysed. The relationship between climate and growth was then evaluated, using weekly wood production data and climatic data from the study site.


RESULTS
Delayed onset of xylogenesis in 2010 corresponded to a negative standardized precipitation evapotranspiration index (SPEI) value and a continuous period without rainfall in early May. The main period of wood formation was in June and July, and drier conditions from May to July led to a smaller number of xylem cells. Dry conditions in July could cause early cessation of xylem differentiation. The final number of xylem cells was mainly determined by the average production rate rather than the duration of new cell production. Xylem growth showed a positive and significant response to precipitation, but not to temperature.


CONCLUSIONS
Precipitation in late spring and summer can play a critical role in the onset of xylogenesis and xylem cell production. The delay in the initiation of xylogenesis under extremely dry conditions seems to be a stress-avoidance strategy against hydraulic failure. These findings could thus demonstrate an evolutionary adaptation of Qilian juniper to the extremely dry conditions of the north-eastern Tibetan Plateau.
Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Key Laboratory of Alpine Ecology and Biodiversity, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China, CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China, University of Chinese Academy of Sciences, Beijing 100049, China, Département des Sciences Fondamentales, University of Quebec in Chicoutimi, 555, Boulevard de l'Université, Chicoutimi (QC) G7H2B1, Canada, Department of Yield and Silviculture, Slovenian Forestry Institute, Vecna pot 2, 1000 Ljubljana, Slovenia and Biotechnical Faculty, Department of Wood Science and Technology, University of Ljubljana, Jamnikarjeva 101, 1000 Ljubljana, Slovenia Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Key Laboratory of Alpine Ecology and Biodiversity, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China, CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China, University of Chinese Academy of Sciences, Beijing 100049, China, Département des Sciences Fondamentales, University of Quebec in Chicoutimi, 555, Boulevard de l'Université, Chicoutimi (QC) G7H2B1, Canada, Department of Yield and Silviculture, Slovenian Forestry Institute, Vecna pot 2, 1000 Ljubljana, Slovenia and Biotechnical Faculty, Department of Wood Science and Technology, University of Ljubljana, Jamnikarjeva 101, 1000 Ljubljana, Slovenia Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Key Laboratory of Alpine Ecology and Biodiversity, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China, CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China, University of Chinese Academy of Sciences, Beijing 100049, China, Département des Sciences Fondamentales, University of Quebec in Chicoutimi, 555, Boulevard de l'Université, Chicoutimi (QC) G7H2B1
Ping
P
Ren
Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Key Laboratory of Alpine Ecology and Biodiversity, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China, CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China, University of Chinese Academy of Sciences, Beijing 100049, China, Département des Sciences Fondamentales, University of Quebec in Chicoutimi, 555, Boulevard de l'Université, Chicoutimi (QC) G7H2B1, Canada, Department of Yield and Silviculture, Slovenian Forestry Institute, Vecna pot 2, 1000 Ljubljana, Slovenia and Biotechnical Faculty, Department of Wood Science and Technology, University of Ljubljana, Jamnikarjeva 101, 1000 Ljubljana, Slovenia.
Sergio
S
Rossi
Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Key Laboratory of Alpine Ecology and Biodiversity, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China, CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China, University of Chinese Academy of Sciences, Beijing 100049, China, Département des Sciences Fondamentales, University of Quebec in Chicoutimi, 555, Boulevard de l'Université, Chicoutimi (QC) G7H2B1, Canada, Department of Yield and Silviculture, Slovenian Forestry Institute, Vecna pot 2, 1000 Ljubljana, Slovenia and Biotechnical Faculty, Department of Wood Science and Technology, University of Ljubljana, Jamnikarjeva 101, 1000 Ljubljana, Slovenia.
Jozica
J
Gricar
Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Key Laboratory of Alpine Ecology and Biodiversity, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China, CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China, University of Chinese Academy of Sciences, Beijing 100049, China, Département des Sciences Fondamentales, University of Quebec in Chicoutimi, 555, Boulevard de l'Université, Chicoutimi (QC) G7H2B1, Canada, Department of Yield and Silviculture, Slovenian Forestry Institute, Vecna pot 2, 1000 Ljubljana, Slovenia and Biotechnical Faculty, Department of Wood Science and Technology, University of Ljubljana, Jamnikarjeva 101, 1000 Ljubljana, Slovenia Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Key Laboratory of Alpine Ecology and Biodiversity, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China, CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China, University of Chinese Academy of Sciences, Beijing 100049, China, Département des Sciences Fondamentales, University of Quebec in Chicoutimi, 555, Boulevard de l'Université, Chicoutimi (QC) G7H2B1, Canada, Department of Yield and Silviculture, Slovenian Forestry Institute, Vecna pot 2, 1000 Ljubljana, Slovenia and Biotechnical Faculty, Department of Wood Science and Technology, University of Ljubljana, Jamnikarjeva 101, 1000 Ljubljana, Slovenia liangey@itpcas.ac.cn.
Eryuan
E
Liang
Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Key Laboratory of Alpine Ecology and Biodiversity, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China, CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China, University of Chinese Academy of Sciences, Beijing 100049, China, Département des Sciences Fondamentales, University of Quebec in Chicoutimi, 555, Boulevard de l'Université, Chicoutimi (QC) G7H2B1, Canada, Department of Yield and Silviculture, Slovenian Forestry Institute, Vecna pot 2, 1000 Ljubljana, Slovenia and Biotechnical Faculty, Department of Wood Science and Technology, University of Ljubljana, Jamnikarjeva 101, 1000 Ljubljana, Slovenia.
Katarina
K
Cufar
D002980:Climate; D055864:Droughts; D018653:Juniperus / Q000254:growth & development*; D011891:Rain; D012621:Seasons; D012914:Snow; D018609:Tibet; D014934:Wood / Q000254:growth & development*
Juniperus przewalskii; SPEI; Semi-arid forest; drought; juniper; onset of xylogenesis; standardized precipitation evapotranspiration index; wood formation; xylem differentiation; xylem production rate