[Effects of short-term combined application of ammonium nitrogen and nitrate nitrogen on the growth and leaf traits of seedlings].

Trees are characterized with selective absorption of different forms of nitrogen. Ammonium nitrogen (NH-N) and nitrate nitrogen (NO-N) are the main forms of nitrogen for plant absorption. We examined the differences of absorption between NH-N and NO-N for 1-year-old seedlings planted in local hilly red soil in a pot experiment. A controlled experiment with 7 different NH-N/NO-N treatments was conducted, to study the effects of nitrogen forms and different NH-N/NO-N ratios on the growth and leaf traits of seedlings. The results showed that there were no significant differences in the relative growth rate of ground diameter (GD), plant height (TH), and biomass (RGR) of seedlings with different NH-N/NO-N ratios for four months, but these parameters were relatively high under the treatment of NH-N:NO-N=5:5. The seedlings of didn't show obvious preference for NH-N and NO-N in short term. The extremely low NH-N/NO-N ratio application was unsuitable for their growth. Different NH-N/NO-N application had significant effects on leaf area (LA), specific leaf area (SLA), leaf dry matter content (LDMC), leaf relative water content (LRWC), net photosynthetic rate (), intercellular CO concentration (), water use efficiency (WUE), and photosynthetic nitrogen use efficiency (PNUE). seedlings under the treatment of NH-N:NO-N=1:9 had the highest LA, SLA, , WUE and PNUE. However, the seedlings under the treatment of NH-N:NO-N=9:1 had the lowest LDMC, leaf tissue density (LTD), LRWC and . Different NH-N/NO-N combined application did not affect leaf nitrogen content (LN) and leaf phosphorus content (LP), which were highest under the treatment of NH-N:NO-N=5:5. Across different NH-N/NO-N combined treatments, GD, TH, and RGR were significantly negatively correlated with SLA, while both GD and RGR were significantly negatively correlated with PNUE. Our results could provide theoretical basis for precise nutrient management and high-efficiency cultivation techniques during the seedling stage of the .