On the aforementioned dates, the photosynthetic rate and N content of the upmost fully-expanded leaves were measured. Three gas exchange analyzers (Li-Cor 6400 portable photosyn the - sis measurement system, Li-Cor, Lincoin, NE, USA) were used tomeasure leaf photosynthetic rate. The measurement was made dur-ing 0900–1100 h when photosynthetic active radiation above the canopy was 1300–1500 mol m−2s−1. Each gas exchange analyzer was used in one treatment replicate, and six leaves were measuredfor each treatment. N content in leaves was determined according