Abstract: [Objective] Carpinus tientaiensis is a plant with extremely small population and poor acclimatization, it is only distributed in Tiantai County and Pan'an County of Zhenjiang Province. The leaf is sensitive to light conditions and with a strong plasticity. The relationship between leaf shape variability and environmental factors of C. tientaiensis was analyzed by geometric morphometrics, and the differential growth mode of the leaf of C. tientaiensis under different light environment was explored, providing a theoretical basis for cultivation of C. tientaiensis.[Method] The response of leaf shape of C. tientaiensis to irradiance intensity in varied simulated growth environment (low irradiance LI, moderate irradiance MI and full irradiance FI) was studied. In mid-March, different shading treatments were carried out on C. tientaiensis before leaf expansion, and mature leaves were collected in late July. To investigate the differences of leaf shape among 3 groups of irradiance gradients, geometric morphometrics was used, while the 17 landmark points of leaf profile were digitalized to be standard images on the basis of Tpsdig 2 program. The Coordgen software in IMP series software was used to calculate the standard contour coordinates data of each gradient population, and the thin plate spline graph was used to indicate the relative morphological changes. The application of PAST 3.14 showed differences in leaf shape and vein. The effect of environmental factors on leaf morphology was analyzed by SPSS 11.5 software.[Result] The geometric morphometrics analysis of C. tientaiensis leaf indicated that the leaf was oval, and the base was slightly heart-shaped with a gradual pointy tip. In different light conditions, the leaf shapes were similar, but the allometry of leaf shape was more obvious. Principal component analysis and multivariate analysis of variance showed three significant leaf shape variables, and the principal component of the total variance was 77.48%. Correlation analysis showed that the morphological difference of C. tientaiensis leaf was significantly correlated with photosynthetic active radiation (PAR), surface temperature (T_s), atmospheric temperature (T_a) and relative humidity (RH) (P<0.05). When the leaf shape changes had significant positive correlations with PAR, T_s and T_a, and significant negative correlation with RH, the leaves appeared to expand or shrink in the middle, and the variation focuses on the alternating expansion of the leaf blade and leaf apex. Growing in weak light environment, the middle of the leaf was expanded and the leaf apex was compressed. In strong light environment, there was extrusion of the middle of the leaves and enlargement of the leaf apex. When the leaf shape change had significant negative correlations with PAR, T_s and T_a, and significant positive correlation with RH, the petiole length and leaf apex stretch ratio were involved in the leaf shape changes. In strong light and weak light environments, the petiole was elongated and the leaf apex contracted. The petiole contracted and the leaf apex enlarged in the moderate irradiance. Only when the leaf shape changes had significant positive correlations with PAR, T_s and T_a, it involved with the leaf expansion rate. Under the moderate irradiance, the petiole shrank, the lower half of the blade was extruded, and the leaf apex was dilated. By using principal component data to make the relative distortion of leaf shape, it showed under the influence of light environment the petiole and leaf apex appeared twisted up and down.[Conclusion] In different light environments, C. tientaiensis leaves grow at allometry. With the enhancement of light, C. tientaiensis changes the shape of the leaves, it regulates the position of petioles, in order to increase its photosynthetic capacity. The correlation analysis between leaf variation of C. tientaiensis and light environment showed that due to the adaptation to the moderate irradiance in forest gap, C. tientaiensis oval leaves become more full. The basal and the lower half of the blade were extruded, while the leaf apex was dilated. Shorter petioles were more effective in conducting water and nutrients. In nature, C. tientaiensis relies on special growing environment. The introduction and cultivation of the C. tientaiensis should choose forest gaps where the light is stronger, in favor to restore and expand the C. tientaiensis population effectively.

Key words: Carpinus tientaiensis, leaf shape, geometric morphometrics, light environment