Morpho-anatomical and photosynthetic responses of Taxodium hybrid 'Zhongshanshan' 406 to prolonged flooding

Abstract

Taxodium hybrid ‘Zhongshanshan 406’ (T. mucronatum Tenore ♀×T. distichum (L.) Rich ♂; Taxodium 406) has been selected as a species for reforestation in flooding areas, China. To elucidate its adaptive strategies to prolonged flooding environments, morpho-anatomical, photosynthetic and growth responses of Taxodium 406 were investigated during three months of flooding stress, i.e. half-flooding (HF) and total-submergence (TS). Taxodium 406 showed 100% survival rate under both flooding treatments. Compared to control (CK), root biomass and root/shoot ratio of HF plants were reduced, while height and shoot biomass were increased by 40% and 58% respectively, and thus total biomass was unchanged. For TS plants, their root biomass, total biomass and root/shoot ratio were 69, 48 and 58% lower respectively, than those of CK plants. Compared to initial values, however, non-elongating height and increased basal diameter of TS plants were observed. Besides, TS plants had greater chlorophyll contents than the other two treatments at the end of the experiment. Well-developed aerenchyma, hypertrophied lenticels, large intercellular spaces and adventitious roots of Taxodium 406 plants were formed under HF flooding treatment. Additionally, tested root morphological parameters, i.e. total length, surface area, volume, tips and length in diameter of four classes were lower for HF and TS plants than for CK plants, and no significant difference was found between HF and TS plants. Compared to CK plants, net photosynthetic rate of HF plants was unchanged, while stomatal conductance, transpiration rate and intercellular carbon dioxide concentration were enhanced across the experiment. Therefore, morpho-anatomical adaption and maintenance of photosynthesis of HF plants and the growth retardation of TS plants are responsible for the survival and growth of Taxodium 406 plants under extreme flooding environments.