Photosynthetic and physiological responses of seedlings from 10 Carya illinoinensis cultivars to drought-rewatering

To explore the changes of growth, photosynthesis, and other physiological indices of Carya illinoinensis under drought stress and rewatering, and to provide a reference for the study of drought resistance mechanisms and breeding of drought-tolerant cultivars in C. illinoinensis.

Two-year-old grafted seedlings of 10 C. illinoinensis cultivars from southern provinces were used as test materials, with rootstocks being ‘Shaoxing’ seedlings. Drought stress and rewatering treatments were conducted through potted water control. Growth status of each cultivar was investigated on day 0 (D0), day 5 (D5), day 10 (D10) of drought stress, and day 10 after rewatering (R10). Leaf photosynthetic parameters, leaf anatomical structures, and related physiological indicators were measured. Principal component analysis and membership function analysis were used to comprehensively evaluate the drought resistance of the 10 cultivars.

1) Under drought stress, all cultivars showed wilting symptoms such as leaf curling and branch drooping. Leaf thickness (LT), lower epidermal thickness (LET), palisade tissue (PT), and spongy tissue thickness (ST) decreased to varying degrees. Among them, ‘TJS’ showed the largest decline, with LT, LET, PT, and ST significantly decreasing by 27.42%, 29.96%, 32.67%, and 40.19%, respectively, compared with D0. ‘C28’ had the smallest decline, with decreases ranging from 4.73% to 13.22% for the four indicators compared with D0; 2). Compared with D0, ‘KD’ exhibited the highest net photosynthetic rate (Pn) and transpiration rate (Tr) at D10 [4.53 μmol/(m²·s) and 1.2 mmol/(m²·s), respectively], with the smallest decreases (68.01% and 83.72%, respectively). ‘MD’ showed the smallest decrease in stomatal conductance (G_s) (75.86%) ‘WQT’ exhibited relatively low P_n, G_s, and T_r values with the largest decreases, reaching 91.30%, 94.44%, and 95.35%, respectively; 3) Root activity of different pecan varieties initially increased and then decreased. At D10, although root activity decreased for all varieties, it remained significantly higher than that at D0 for all except ‘XN’ and ‘FKT’. Among these, ‘NKL’ exhibited the greatest difference, with root activity increasing by 1-fold compared with D0. Leaf relative electrical conductivity (REC) gradually increased over time, with significant differences between D10 and D0; 4) At R10, the leaf anatomical structures and photosynthetic characteristics of the 10 seedlings basically recovered to normal levels, while root activity remained at a high level. However, the recovery degrees of various indices also differed among cultivars; 5) The comprehensive evaluation scores of the cultivars were ranked as: ‘KD’, ‘C28’, ‘NKL’, ‘MD’, ‘XN’, ‘FKT’, ‘WQT’, ‘TJS’, ‘BN’, and ‘GX 5’.

Timely rewatering can alleviate the drought damage of C. illinoinensis and make the root vitality overcompensate. Therefore, when the drought time in summer and autumn is longer than 10 days, the plants should be watered in time; In addition, when planting C. illinoinensis in southern provinces with seasonal drought, it is advisable to consider drought-resistant varieties such as ‘KD’, ‘C28’ and ‘NKL’.