Partitioning of carbon and nitrogen during growth and development of pigeonpea (Cajanus cajan L.)

Abstract

Budgets for C and N were computed for pigeonpea (Cajanus cajan L.) at 15 d intervals, for the entire life cycle. Maximum C and N in dry matter was observed at 90 d after sowing. Of the plants total respiratory loss during the vegetative phase, shoots, roots and nodules accounted for 65%, 23% and 12%, respectively. During the reproductive phases, the respiratory burden of the roots increased, while that of shoots and nodules decreased. Total respiratory loss as a proportion of net photosynthate remained more or less constant until 'flowering and pod-setting' but increased heavily during seed filling, losing nearly 75% of the photosynthate in respiration. The efficiency of nitrogen fixation, in relation to respiratory output of the whole plant and nodulated roots, decreased during the period 60-90 d after sowing, while that of nodules decreased from day 45 onwards. Photosynthate supply to nodules and nodulated roots increased up to 75 d and 90 d after sowing, respectively. During 45-90 d, nodules were fixing a constant proportion of N per unit of C translocated (0.2 mg N mg^-1 C). Nodulated roots, on an average, fixed 0.07 mg N mg^-1 C translocated in the vegetative phase and this value decreased considerably during the subsequent phases. The crop produced during its life cycle 50.4 g of glucose equivalents and yielded 3.8 g seed dry matter and 0.8 g seed protein giving an average of 13.2 g g^-1 seed dry matter and 62.8 g g^-1 seed protein. Selection criteria for the improvement of C, N economy in pigeonpea have been suggested.