马尾松组培苗对氮素形态的生长响应

马尾松属高氮需求树种,然而在苗木培育中马尾松对氮素,尤其是不同形态氮素的需求尚不明确。该文以马尾松组培苗为试验材料,采用基质培养方法,针对硝态氮、铵态氮两种氮素形态均分别设置了2、4、8、16 mmol·L~(-1)4个处理,以不添加氮素为对照,对苗木的高径生长、根构型参数(总根长、总表面积、总体积、平均直径和根尖数)以及生物量的变化进行了分析。结果表明:(1)在2～8 mmol·L~(-1)硝态氮处理下,除根冠比外,苗高、地径、根构型参数、生物量均不低于对照,其中以2 mmol·L~(-1)水平下苗木生长效果最好,苗高、地径、根构型参数、生物量均高于对照;在16 mmol·L~(-1)硝态氮处理下,苗高、总根长与根尖数低于对照。(2)在2～16 mmol·L~(-1)供试范围内,铵态氮处理下的苗木根冠比小于对照,但其苗高、地径、根构型参数、生物量均不低于对照,整体上以4 mmol·L~(-1)处理下的苗木生长表现最佳。(3)在任一供氮水平,除根冠比和2mmol·L~(-1)处理下的根总表面积与根尖数在两种氮素形态间无明显差异外,铵态氮处理下的苗木生长情况显著优于硝态氮处理,这说明马尾松组培苗偏好于吸收和利用铵态氮。综上结果表明,外施硝态氮、铵态氮均能促进马尾松组培苗生长,但需控制在适宜浓度范围内,其中以2 mmol·L~(-1)硝态氮和4 mmol·L~(-1)铵态氮处理效果较佳。高浓度硝态氮会抑制苗木高度及根系发育,且在相同施肥水平下,对苗木生长的促进效果大多弱于铵态氮。因此,今后为达到培育优质壮苗和提高肥效、减少肥害的目的,可考虑使用铵态氮肥。

Growth responses of tissue cultured seedlings in Pinus massoniana to nitrogen forms

Nitrogen(N)directly affects Pinus massoniana seedling growth, but the nitrogen demand, especially different nitrgen forms of nitrogen demand are not clear until now. In this study, four N levels, i.e. 2, 4, 8 and 16 mmol·L^-1 were respectively set for each of two N forms(nitrate N, NO₃^--N; ammonium N, NH₄⁺-N), and no N supply was used as the control using the matrix culture method. Variations for growth of plant height and basal diameter, root configuration parameters(RC), including total root length, total surface area, total volume, average diameter and the total number of root tip), and biomass of tissue cultured seedlings of P. massoniana were investigated exposed to N treatments. The results were as follows:(1)Under the treatment of 2 to 8 mmol·L^-1 NO₃^--N, plant height(H), basal diameter(D), RC and biomass(B)were not lower than that under the control except for ratios of root to shoot biomass(RRS), and the best growth performance of seedlings was observed at the 2 mmol·L^-1, where H, D, RC and B were higher than that at the control. However, H, total root length(RL)and number of root tips(NR)were lower under the treatment of 16 mmol·L^-1 NO₃^--N compared with the control.(2)In the range of 2 to 16 mmol·L^-1 tested levels, NH₄⁺-N supply caused the reduced RRS, while H, D, RC and B were not decreased in comparison to the control without NH₄⁺-N addition. In general, the optimal growth results were investigated at the 4 mmol·L^-1 of NH₄⁺-N.(3)There was no significant differences in RRS between NO₃^--N and NH₄⁺-N within a N supply level, while the growth of seedlings was better under NH₄⁺-N treatment than that under NO₃^--N treatment, except for the observed similar values of total root surface area(RS)and NR between NO₃^--N and NH₄⁺-N treatments at 2 mmol·L^-1 level. This indicated that P. massoniana preferred to absorb and utilize NH₄⁺-N. In summary, it was initially concluded that the application of exogenous NO₃^-N and NH₄⁺-N were all able to promote growth of tissue cultured seedlings in P. massoniana on the assumption of controlling the applied concentration of N at optimal level. The best promotive effects of N on seedling growth were found at 2 mmol·L^-1 level of NO₃^--N and 4 mmol·L^-1 level of NH₄⁺-N, respectively. High supply level of NO₃^--N was prohibitive to the development of shoot and root. Furthermore, the promotive effect of NO₃^--N to seedling growth was weaker in contrast with that of NH₄⁺-N in the case of equal fertilization level. Hence, the application of NH₄⁺-N fertilizer should be considered in the future cultivation of P. massoniana seedlings.