Morphological and physiological responses of Opisthopappus species to shading

• Genus Opisthopappus is an ideal model for studies of Asteraceae adaptation to light • The Opisthopappus two species showed common and divergent shade responses • Morphological and physiological traits in Opisthopappus peaked under 60% shading • Key photosynthetic traits (e.g., Pn) and chlorophyll content increased under shade The responses of cliffs plants in the Taihang Mountains, such as Opisthopappus species ( Opisthopappus taihangensis and O. longilobu s) to the heterogeneous light exposure of diverse habitats remains unexplored. For this study, we assessed the morphological, photosynthetic, and physiological parameters of Opisthopappus seedlings under different shading conditions (CK: full light, S1: 20% shading, S2: 40% shading, S3: 60% shading, S4: 80% shading). Under S2 and S3 treatments, the leaves of both species remained smooth and green. In response to shading, several morphological parameters (e.g., leaf length (LL), leaf width (LW), specific leaf area (SLA)), and antioxidant enzyme activities (POD) in both species exhibited enhanced trends. Conversely, other morphological traits (e.g., leaf thickness (LH), stomatal opening (SO)) and enzymatic activities (SOD, CAT, APX) displayed opposite trends. Soluble sugar (SS) and soluble protein (SP) tended to initially increase and then decrease, while the concentration of proline presented an opposite trend with increased shading. Among photosynthetic parameters, the net photosynthetic rate (Pn), transpiration rate (Tr), and intercellular CO 2 concentration (Ci) increased under different shading treatments. Chlorophyll (Chl) a, Chl b, carotenoid, and total chlorophyll generally tended to first increase and then decrease. Overall, the estimated parameters mostly peaked under S3 shading, with stronger effects on O. longilobu s than O. taihangensis. This indicated that 60% shading was more beneficial for Opisthopappus growth. The two species exhibited a number of common and differential responses to shade stress. When both species were compared, O. longilobu s showed greater tolerance to shade stress.