Relationship Between Leaf Nitrogen and Photosynthetic Characteristics in Brassica juncea and B. campestris

The relationship between leaf nitrogen content (N) versus photosynthetic rate (PN) and other associated parameters was examined in Brassica juncea, cv. Pusa Bold and B. campestris, cv. Pusa Kalyani. Leaf N, specific leaf weight (SLW), leaf area and PN were significantly higher in B. juncea, while the chlorophyll content was significantly lower compared to Brassica campestris. A significant positive correlation was obtained between leaf N content and photosynthetic rate in both species. Similarly, SLW was also positively related with leaf N content. Brassica jitncea showed higher photosynthetic nitrogen use efficiency (PNUE) than B. campestris. Leaf N and PNUE were negatively associated. This was attributed to a low investment of N in photosynthesis related reactions and/or partitioning of N towards coumpounds functionally unrelated to photosynthesis. This attribution is further supported by the negative relationship obtained between SLW and PNUE.