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

Trees are characterized with selective absorption of different forms of nitrogen. Ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3--N) are the main forms of nitrogen for plant absorption. We examined the differences of absorption between NH4+-N and NO3--N for 1-year-old Machilus pauhoi seedlings planted in local hilly red soil in a pot experiment. A controlled experiment with 7 different NH4+-N/NO3--N treatments was conducted, to study the effects of nitrogen forms and different NH4+-N/NO3--N ratios on the growth and leaf traits of M. pauhoi 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 M. pauhoi seedlings with different NH4+-N/NO3--N ratios for four months, but these parameters were relatively high under the treatment of NH4+-N:NO3--N=5:5. The seedlings of M. pauhoi didn't show obvious preference for NH4+-N and NO3--N in short term. The extremely low NH4+-N/NO3--N ratio application was unsuitable for their growth. Different NH4+-N/NO3--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 (Pn), intercellular CO2 concentration (Ci), water use efficiency (WUE), and photosynthetic nitrogen use efficiency (PNUE). M. pauhoi seedlings under the treatment of NH4+-N:NO3--N=1:9 had the highest LA, SLA, Pn, WUE and PNUE. However, the seedlings under the treatment of NH4+-N:NO3--N=9:1 had the lowest LDMC, leaf tissue density (LTD), LRWC and Ci. Different NH4+-N/NO3--N combined application did not affect leaf nitrogen content (LN) and leaf phosphorus content (LP), which were highest under the treatment of NH4+-N:NO3--N=5:5. Across different NH4+-N/NO3--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 M. pauhoi.林木对不同形态氮素具有选择性吸收特征,铵态氮和硝态氮是植物吸收的主要氮素形态。为了明确刨花楠对铵态氮和硝态氮的吸收差异,采用盆栽试验方法,以铵态氮和硝态氮为氮源,以1年生刨花楠实生苗为研究对象,以当地山地红壤为基质,设置了7种不同的铵硝比配施添加试验,研究氮素形态和配比对刨花楠幼苗生长和叶片性状的影响。结果表明: 不同铵态氮∶硝态氮(简称铵硝比)配施4个月后刨花楠幼苗的地径相对生长速率(GD)、株高相对生长速率(TH)和生物量相对生长速率(RGR)均相差不明显,但以铵硝比为5∶5处理相对较高;短期内刨花楠幼苗并没有对铵态氮和硝态氮的吸收存在明显的偏好性,但铵硝比过低时极不利于其生长。不同铵硝比配施对刨花楠幼苗叶片的叶面积(LA)、比叶面积(SLA)、叶干物质含量(LDMC)、叶相对含水率(LRWC)、净光合速率(Pn)、胞间CO2浓度(Ci)、水分利用效率(WUE)和光合氮利用效率(PNUE)均具有显著影响,其中LA、SLA、Pn、WUE和PNUE以铵硝比为1∶9处理最高,铵硝比为9∶1处理最低;叶片的LDMC、叶组织密度(LTD)、LRWC和Ci则相反,以铵硝比为1∶9处理最低。不同铵硝比配施对刨花楠叶片的氮(LN)和磷含量(LP)的影响虽不明显,但均以铵硝比5∶5处理较高。经不同铵硝比配施处理后的刨花楠幼苗GD、TH和RGR与SLA呈显著负相关,GD和RGR与PNUE呈显著负相关。研究结果可为刨花楠苗期精准养分管理与高效培育技术制定等提供理论依据。.