Effects of nitrogen and phosphorus supply on growth and physiological traits of two Larix species

• The effects of N and P fertilization on Larix olgensis and L. kaempferi were studied.
• N and combined N and P fertilization promoted growth in the two Larix species.
• P fertilization increased growth of L. olgensis but decreased that of L. kaempferi.
• The N and P balance is more important in L. kaempferi than in L. olgensis.
• L. kaempferi partitions more biomass to aboveground parts than does L. olgensis.

To investigate how nitrogen (N) and phosphorus (P) fertilization affect plant growth, biomass accumulation and allocation, leaf N and P concentration, and also eco-physiological responses of Larix species with contrasting growth characteristics, slow growing (L. olgensis) and fast growing (L. kaempferi) saplings grown in larch plantation soil were exposed to different N and P regimes. The results showed that N and combined N and P (NP) fertilization promoted growth with a higher biomass accumulation, height growth rate (GRH), net photosynthesis rated (Pn), and photosynthetic P-use efficiency (PPUE) in both species, while P fertilization alone had a positive effect on the growth of L. olgensis but a negative effect on that of L. kaempferi. Moreover, N and NP fertilization increased the photosynthetic N-use efficiency (PNUE) of L. olgensis, while all fertilization treatments decreased that of L. kaempferi. Furthermore, P fertilization increased the N concentration of L. olgensis leaves but had no influence on that of L. kaempferi leaves, while it decreased the NSC concentration of L. olgensis leaves but stimulated the accumulation of starch, fructose and NSC in L. kaempferi leaves. In addition, L. kaempferi with higher GRH showed a greater biomass accumulation, growth, Pn, PNUE, and PPUE when compared to L. olgensis, except for biomass and PPUE under P fertilization and PNUE under N fertilization. These results indicated that the N and P balance rather than the absolute amount of them enhances the growth of L. kaempferi effectively, and P fertilization affects the morphological and physiological traits of the two larch species differently. We propose that the distinct effects of P fertilization on the two larch species were related to different regulation effects of P fertilization on the N concentration, and on the accumulation and transportation of photosynthetic products.