Effect of leaf nitrogen and water regime on the photosynthetic capacity of kenaf (Hibiscus cannabinus L.) under field conditions

Abstract

To understand the influence of nitrogen (N) supply on the productivity of kenaf (Hibiscus cannabinus L.), the dependence of photosynthetic capacity, measured as light-saturated leaf CO2 assimilation rate (CA) and crop radiation use efficiency (RUE), on specific leaf nitrogen (SLN) was examined under well-watered conditions in the field. Photosynthetic capacity increased hyperbolically with SLN and was most responsive at SLN values less than c. 1.5 g m-2. The relationship reached a plateau at a maximum CA of 37 8mol m-2 s-1 and a maximum RUE of 1.5 g MJ-1 Increasing N application from 0 to 24 g N m-2 increased both RUE and SLN. Where ample N was applied, RUE and SLN were higher in those plots which previously experienced water deficit than in those that were always fully irrigated. The stimulation in growth following alleviation of water deficit was directly associated with the increase in SLN during water deficit. SLN varied according to differences in N uptake, the proportion of N allocated to leaves and the leaf area index. In particular, N application had much less effect on SLN and consequently RUE, than on N uptake, due to lower N partitioning to leaves and higher LAI where a high rate of N was applied. The importance of quantitative information on the relationship between photosynthetic capacity and SLN, in order to predict crop performance under varying environmental conditions, is discussed.