Morphological mechanism of growth response in treeline species Minjiang fir to elevated CO2 and temperature

To test whether and how morphological traits are linked with growth responses of plants to temperature and CO is important for understanding the mechanism underlying how plant growth will respond to global warming. In this study, using closed-top chambers to mimic future elevated CO and temperature, the growth response, morphological traits of Minjiang fir (Abies faxoniana Rehd.et Wils.) and the relationship of the two were investigated after two years of exposure to the single and combined elevation of CO and temperature. The results showed that biomass of Minjiang fir was 21%, 31%, and 35% greater than the control in elevated CO, elevated temperature and the combination of elevated CO and temperature treatments, respectively. Elevated CO and temperature significantly affected the morphology of Minjiang fir, and a few morphological traits were highly correlated with growth responses. Larger branch angles at the upper layer, crown volume, and relative crown length contributed to positive growth responses to elevated CO, while decreased specific leaf area (SLA) constricted any further growth response. Leaf morphological traits were more closely correlated with the response ratio than crown did in the elevated temperature, while in the combination of elevated CO and temperature, crown was more correlated with the response ratio than the leaf morphological traits. Thus, our results indicate that morphological traits may contribute differently to growth responses under different experimental conditions. 2 2 2 2 2 2 2 2