Carbon assimilation, nitrogen, and photochemical efficiency of different Himalayan tree species along an altitudinal gradient

In the area of Jumla region in Western Nepal, measurements of saturated leaf net photosynthetic rate (P-sat), nitrogen content, leaf fluorescence, carbon isotopic composition, and water status were performed on woody coniferous (Pinus wallichiana, Picea smithiana, Abies spectabilis, Jumperus wallichiana, Taxus baccata), evergreen (Quercus semecarpifolia, Rhododendron campanulatum), and deciduous broadleaved species (Betula utilis, Populus ciliata, Sorbus cuspidata) spreading from 2 400 m up to the treeline at 4 200 m a.s.l. With the exception of J wallichiana, P-sat values were lower in coniferous than broadleaved species. Q. semecarpifolia, that in this area grows above the coniferous belt between 3 000 and 4 000 m, showed the highest P-sat at saturating irradiance and the highest leaf N content. This N content was higher and P-sat lower than those of evergreen oak species of temperate forests at middle and low altitudes. For all species, P-sat and N content were linearly correlated, but instantaneous nitrogen use efficiency was lower than values measured in lowland and temperate plant communities. The values of carbon isotopic composition, estimated by delta(13)C, showed the same range reported for temperate tree species. The ranking of delta(13)C values for the different tree types was conifers< evergreen broadleaved