Abstract:

Objective: This study aims to investigate dynamic features of root phenotypes and photosynthetic characteristics of Corylus heterophylla × C. avellana cuttings at different growth stages. A model representing the relationship between root growth and photosynthetic indices was established and used to simulate root growth conditions of cuttings, so as to lay the foundation for future exploration of the response of mature root growth indicators to photosynthetic indicators. Method: Photosynthetic indices (net photosynthetic rate, transpiration rate, intercellular CO₂ concentration and stomatal conductance) of one-year-old C. heterophylla × C. avellana cuttings were measured at different growth periods (rooting, early growth, intermediate growth, and vigorous growth periods). A root scanner was used to scan the complete root system and determine root growth indicators such as total root length, total surface area, average root diameter, total root volume, and number of root tips. A quadratic polynomial stepwise regression method was used to construct a root growth and development evaluation model based on photosynthetic indices to clarify the relationship between photosynthetic indicators and root growth indicators. Result: 1) There were significant differences in various root growth indicators at the different growth stages. The total root length, total surface area, and total root volume during the vigorous root period were effective indices of root growth conditions and exceeded those during the rooting period by factors of 3.6, 2.8, and 2.0, respectively. 2) The maximum number of root tips occurred during the intermediate growth period and exceeded those during the rooting and vigorous growth periods by factors of 8.9 and 2, respectively. These results suggest that number of root tips is an effective index of root activity. 3) There were significant differences in photosynthetic indicators such as net photosynthetic rate, transpiration rate among the different root growth periods of the cuttings. The net photosynthetic rate and transpiration rate during rooting period exceeded those during the vigorous growth period by factors of 1.8 and 4.3, respectively. The intercellular CO₂ concentration increased with growth, and that during the vigorous growth exceeded that during the rooting period by a factor of 1.3. The stomatal conductance increased and then decreased with progressive growth periods, reaching a peak in the intermediate growth period when it exceeded that during the rooting period by a factor of 2.4, following which it decreased sharply by 75% in the vigorous growth period. 4) The total root volume, total root length, and total surface area of cuttings were positively correlated with intercellular CO₂ concentration and stomatal conductance. The net photosynthetic rate and transpiration rate were positively correlated with average root diameter, and the number of root tips was positively correlated with stomatal conductance. 5) The performance indices (R²=0.75; mean squared error MSE=0.12) confirmed the excellent performance of the proposed photosynthetic indices-based model for evaluating root growth and development. Conclusion: Root system growth indicators and photosynthetic indicators show significant differences at different growth periods. Overall, the proposed model based on photosynthetic indicators serves as a feasible and effective approach for non-destructive evaluation of root growth and development of cuttings of C. heterophylla × C. avellana. It can also lay the foundation for exploring the response of root growth indicators of mature trees to photosynthetic indicators.

Key words: Corylus heterophylla × C. avellana, root development, root growth period, photosynthetic characteristics, root growth model