Abstract:

Eupatorium adenophorum is a typical alien invasive species in China, however, limited message on the relations between gas exchange characteristics and invasive ability was reported. We measured the photosynthetic capacities of the adult leaves of E. adenophorum in Dechang, Liangshan Autonomous prefecture of Sichuan Province (27°28′36″N, 102°12′28″E), and comparison with other 8 local accompanying species and 12 species grown in different regions of China and Japan was also done. For finding the possible implication for its invasive ability, the stomatal regulation on gas exchange in diurnal changing microenvironment and long term acclimation to xeric and hygric habitats as well as water use efficiency were examined. Generally, net photosynthetic rate at noon was only about one third of that in the morning and with time onward in the afternoon, photosynthetic capacities partially recovered but cannot reach that in the morning. Stomatal and non stomatal regulations ware responsible for this diurnal pattern, I.e. Stomata regulated the photosynthesis by decreasing the intercellular CO₂ concentration and increasing the value of stomatal limitation, whereas biochemical regulation adjusted the photosynthetic capacity by decreasing the carboxylation efficiency and apparent quantum yield.With considering the relative importance of stomatal and non stomatal regulation, stomatal regulation control more on this diurnal pattern. This type of strategy was similar to other common species, showing limited implication on its rampancy. However, after long term acclimation in xeric and hygric habitats, stomatal regulation functioned with plasticity. Different from a wide range of 20 species, net photosynthetic rate and transpiration rate were dramatically higher in hygric habitats than those in xeric habitats. Moreover, leaf nitrogen in hygric habitats was significant higher than that in xeric habitats although soil organic matter, soil pH value and soil available nitrogen were slightly different. Furthermore, water use efficiency increased with stomatal conductance decrease when stomatal conductance was low for the wide range of species. E. adenophorum grown in xeric habitats also showed this type strategy on water utilization. However, it increased the water use efficiency with stomatal conductance increase in hygric habitats, indicating that the water use strategy of this weed included both conservative traits and prodigal traits. This flexibility in water utilization and stomatal function with plasticity facilitates its survival even in xeric habitats and rampancy in hygric habitats, which is of importance for its colonization in new habitats.

Key words: Eupatorium adenophorum, stomatal regulation, non stomatal regulation, water use efficiency, invasive ability