Fig. 4

Correlations among ETR and Pn, NPQ of tea plants grown under conventional agriculture (panels A, C) and sod culture (panels B, D) in four seasons (●=spring, ▼=summer, ■=fall, ◆=winter, The solid ones are CA and the hollow ones are SC.) monitored from June 2019 to May 2020. Plants were subjected to light irradiances at 1,200, 1,500, 1,800, and 2,000 μmol m^− 2 s^− 1 PPFD for 20 min. Each symbol represents the average of five mature leaves on one plant, and five plants were randomly selected from tillage and season treatments. Each line represents the time point of 16 values (four seasons multiplied by 4 PPFD) from model validation datasets. Correlation coefficients (r) are calculated and significance (p) is at the 0.0001 probability (*****) level