Energy flow, carbon and nitrogen cycling in Populus deltoides clones in north India

Three clones of Populus deltoides were planted on a degraded alluvium from the river Ganges at Lucknow, India (80° 53′E, 26° 42′N). These were studied for biomass production, energy conservation and nitrogen (N) cycling efficiency at 6–7 years of growth stage. The clones did not differ from each other in energy and carbon (C) concentration, however, N concentration decreased significantly in the order G3>D121>G48. The average N concentration of the aerial plant components increased about 21% from lower to upper portions of the trees. Energy values in the root were less than the shoot. The C concentration was greater in woody components in comparison to leaf tissues, whereas the inverse pattern was recorded for N concentration. Energy, C and N contents in the standing crop were greatest in clone G3 followed by G48 and D121 clones. Though the fluxes of energy, C and N were greatest for clone G3 at community levels (tree and grass), at tree populations G48 was found to be more efficient in energy flow as well as C and N cycling. Trees having high N concentration in their foliage (G3) had greater N resorption prior to senescence. Clone G48 was found to be superior to others in N use efficiency based on wood or net production per unit of net N uptake. Integration of N uptake with energy fixation and C intake through a mathematical model estimated about 20 kg ha−1 year−1 of N demand for the sustained production of P. deltoides under the present set of conditions.