Comparative study on growth and photosynthetic characteristics of different Eucommia ulmoides cultivars

Eucommia ulmoides Oliver is an important ecological and economic tree species in China. With expansion of its cultivation area, the growth adaptability of different cultivars in various regions has attracted extensive attention. In this study, the cultivars of ‘Huazhong’ series: ‘Huazhong No. 16’ (H16), ‘Huazhong No. 17’ (H17), ‘Huazhong No. 18’ (H18), and ‘Huazhong No. 21’ (H21) were introduced in Huai'an City, Jiangsu Province, and seasonal dynamic monitoring was conducted to investigate their growth and photosynthetic characteristics. The results showed that H16 exhibited the optimal tree height and diameter at breast height among different cultivars; while its leaf biomass and photosynthetic performance also maintained a relatively high level. The decrease and subsequent recovery of photosynthetic pigment content in H18 between August and October indicated its susceptibility to the local high-temperature conditions. Interestingly, the photochemical quenching coefficient (qP) of different cultivars increased in October, with an opposite pattern to their effective quantum efficiency of PSII photochemistry (Fᵥ'/Fₘ'), ensuring a stable actual quantum efficiency (φPSII). Based on JIP-test, photoinhibition of PSII reaction centers led to varying degrees of obstruction of photosynthetic electron transport and decreased activity of terminal electron acceptors in different cultivars. H21 maintained a high level of energy dissipation in the experiment corresponding to its low photosynthetic performance. The performance index (PI abs and PI total ) further reflected the overall coordination of photosynthetic apparatus.