Spring precipitation effects on formation of first row of earlywood vessels in Quercus variabilis at Qinling Mountain (China)
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Under drier spring conditions, Q. variabilis might slow the FEV growth rate but will not produce narrower FEVs. FEV size might be a trade-off between hydraulic efficiency and hydraulic safety.
Wood anatomical features can encode tree reactions to fluctuating environmental conditions. The first row of earlywood vessels (FEV) has proven to be very promising with respect to the inter-annual climate variability. However, knowledge of how intra-annual FEV formation reflects climate is still limited. We observed wood formation of Quercus variabilis in a warm temperate–subtropical climate transition at Qinling Mountain, China. Using micro-cores, growth of six trees was monitored at weekly/biweekly intervals February–December in 2015 and 2016, of which 2016 had a drier spring. Cambial activity and xylem cell differentiation were documented by microscopic observation. The FEV diameter and ring width were measured. The onset of xylem growth, which significantly differed between the years, occurred 8 days earlier in 2016, in mid-March. However, the completion of FEV was synchronized in mid-April over the 2 years. This delayed completion of FEV in 2016, when precipitation increased and Standardized Precipitation Evapotranspiration Index changed from a negative to positive value. The cessation of xylem formation was 3 weeks earlier during the drought year (September 5, 2016) compared to the moist year (September 29, 2015) because of the drought conditions in late summer. This finding was supported by evidence that a positive and significant correlation between precipitation and xylem growth was found only in 2016. The ring width differed significantly between the years, but the FEV diameter did not. Our results suggest that the drought-induced delayed formation of FEV and earlier cessation could be a strategy for oak trees to adapt to water stress.
KeywordsChinese cork oak Earlywood vessels of first row Drought Xylogenesis SPEI
We thank Shoudong Zhao for data analysis and Yan Wen for image editing. Special thanks to the anonymous referees for their valuable comments and suggestions.
This work was supported by the National Natural Science Foundation of China (Grant no. 41401063, 41801026), the Starting Foundation for Doctors of Henan University of Science and Technology (No. 4026-13480057), and the Laboratory Technology Development Foundation of Henan University of Science and Technology (No. SY1718059).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no competing interests.
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