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The leaf maximum rate of carboxylation (Vcmax) is a key parameter of plant photosynthetic capacity. The accurate estimation of Vcmax is crucial for correctly predicting the carbon flux in the terrestrial carbon cycle. Vcmax is correlated with plant traits including leaf nitrogen (Narea) and leaf photosynthetic pigments. Proxies for leaf chlorophyll (Chlarea) and carotenoid contents (Cararea) need to be explored in different ecosystems. In this study, we evaluated the relationship between leaf maximum rate of carboxylation (scaled to 25°C; Vcmax25) and both leaf Narea and photosynthetic pigments (Chlarea and Cararea) in winter wheat in a farmland ecosystem. Our results showed that Vcmax25 followed the same trends as leaf Chlarea. However, leaf Narea showed smaller dynamic changes before the flowering stage, and there were smaller seasonal variations in leaf Cararea. The correlation between leaf Vcmax25 and leaf Chlarea was the strongest, followed by leaf Cararea and leaf Narea (R2 = 0.69, R2 = 0.47 and R2 = 0.36, respectively). The random forest regression analysis also showed that leaf Chlarea and leaf Cararea were more important than leaf Narea for Vcmax25. The correlation between leaf Vcmax25 and Narea can be weaker since nitrogen allocation is dynamic. The estimation accuracy of the Vcmax25 model based on Narea, Chlarea, and Cararea (R2 = 0.75) was only 0.05 higher than that of the Vcmax25 model based on Chlarea and Cararea (R2 = 0.70). However, the estimation accuracy of the Vcmax25 model based on Chlarea and Cararea (R2 = 0.70) was 0.34 higher than that of the Vcmax25 model based on Narea (R2 = 0.36). These results highlight that leaf photosynthetic pigments can be a predictor for estimating Vcmax25, expanding a new way to estimate spatially continuous Vcmax25 on a regional scale, and to improve model simulation accuracy.

The effect of NaCl on seedling emergence, plant growth and ion accumulation for two sugar beet cultivars was evaluated. The result showed that seedling emergence in Tianyan309 was much lower than that in KWS3418 in the initial 6 days. High salinity markedly decreased final seedling emergence in both cultivars, especially in Tianyan309, while salinity had no adverse effect on total seedling emergence after the recovery experiment in both cultivars. Low salinity (86 mM NaCl) had no significant effect on shoot and root dry weights, while 171 and 257 mM NaCl inhibited shoot and root dry weights of two cultivars, especially for KWS3418. Concentrations of Na+ and Cl- in leaves were increased with increasing NaCl in both cultivars. There was no significant difference between two cultivars in concentrations of Na+ and Cl- in the leaves at different concentrations of NaCl, except that Cl- concentration in leaves of Tianyan309 was lower than that in KWS3418 at 257 mM NaCl. The characteristic of Cl- uptake and/or accumulation may relate to different salt tolerance of KWS3418 and Tianyan309.