Fig. 2: Effects of frosts on ecosystem carbon fluxes across from 2017 to 2023.

The linear mixed-effect models illustrated the frosts effects on carbon fluxes, included net ecosystem productivity (NEP, a–c), ecosystem respiration (ER, d–f), and gross ecosystem productivity (GEP, g–i). Spring/autumn frost periods (left and right panels) extended for a total of 21 days that include 7 days before, 7 days during, and 7 days after the frost treatments, with 2-3 times repeated measurements within 7 days. The growing seasons (middle panel) in this study had 2-3 times measurements for each month and did not include the 21-days measurement periods. Parameter significance was assessed by t tests (two-tailed). Asterisks (*) indicated significant differences between treatments in pairwise comparisons at the P < 0.05 level without adjustment. The asterisks in Fig. 2a: t ratio = 2.78, P = 0.05; the asterisks in Fig. 2b: t ratio = 3.916, P = 0.004. Data were presented as mean ± standard error across all sampling date (biological replicates n = 6, colored point). Sample size n = 2400 for spring/autumn frost measurement periods, and n = 1320 for the growing seasons that exclude the 21-days measurement period. C: the plots without frost, S: plots experiencing spring frosts, A: plots experiencing autumn frosts, SA: plots experiencing spring plus autumn frosts. Source data are provided as a Source Data file.