供磷水平对平邑甜茶幼苗NO3-吸收、利用特性的影响

运用~(15)N示踪及非损伤微测技术,研究了不同供磷水平(0 mmol×L~(-1)、1.0 mmol×L~(-1)、2.0 mmol×L~(-1)、3.0 mmol×L~(-1)、4.0 mmol×L~(-1)、6.0 mmol×L~(-1)、8.0 mmol×L~(-1)、12.0 mmol×L~(-1)和16.0 mmol×L~(-1) H_2PO_4~-)对平邑甜茶幼苗NO_3~--N吸收及利用特性的影响,为提高果园氮肥利用效率提供理论依据。结果表明,在低磷水平(0~1.0 mmol×L~(-1))时,平邑甜茶根系长度、根系总表面积较小,且根尖数较少。随着供磷水平的增加,在2.0~4.0 mmol×L~(-1)磷浓度处理时,平邑甜茶幼苗生物量、根系长度、根系总表面积及根尖数显著高于其他处理。而在6.0~16.0 mmol×L~(-1)时,过量供磷抑制了根系的生长,使平邑甜茶幼苗根系长度、表面积均大幅降低,根尖数量骤降。非损伤扫描离子选择电极测试表明,当生长介质磷浓度在3.0~6.0 mmol×L~(-1)时,平邑甜茶对NO_3~-有吸收作用,并在3.0 mmol×L~(-1)磷浓度时其吸收速率最高。而在0~2 mmol×L~(-1)及8.0~16.0 mmol×L~(-1)磷浓度处理下,平邑甜茶对NO_3~-有外排作用。随供磷水平的增加,各器官从肥料中吸收分配到的~(15)N量对该器官全氮量的贡献率(Ndff)及植株氮素利用率呈现先升高后降低的趋势,4.0 mmol×L~(-1)磷浓度时植株氮素利用率最大,为42.24%,超过4.0 mmol×L~(-1)植株氮素利用率显著降低。适当充足的供磷刺激了幼苗根系生长,从而促进平邑甜茶对氮素的获取,过量的NO_3~-抑制了平邑甜茶根系的生长,同时叶片硝酸还原酶的活性受到抑制,因此其氮素吸收和利用效率较低。因此,磷浓度在3.0~4.0 mmol×L~(-1)时最有利于平邑甜茶幼苗的生长及氮素的吸收利用。

Characteristics of NO3- absorption and utilization in Malus hupehensis Rehd. seedlings under different phosphorus levels

In recent years, excessive application of nitrogen and phosphate fertilizers has not only wasted fertilizer, but also brought a high potential risk of environmental pollution. In addition, an unreasonable fertilization over the long-term has damaged the physical and chemical properties of soil, including soil porosity and nutrients contents. Therefore, it is crucial for sustainable fruit tree production to promote scientific utilization of nutrient, increase fertilizer utilization rate, reduce eluviation, volatilization and loss of nitrogen. In order to determine the key factors influencing nitrogen utilization ratio under different phosphorus levels, ¹⁵N-labeled tracer and non-invasive micro-test techniques were used to investigate NO₃^- absorption and utilization in Malus hupehensis Rehd. seedlings under different phosphorus levels (0 mmol·L^-1, 1.0 mmol·L^-1, 2.0 mmol·L^-1, 3.0 mmol·L^-1, 4.0 mmol·L^-1, 6.0 mmol·L^-1, 8.0 mmol·L^-1, 12.0 mmol·L^-1, 16.0 mmol·L^-1 H₂PO₄^-). The study aimed to increase nitrogen fertilizer utilization and reduce nitrogen fertilizer loss, which could provide theoretical basis for scientific and efficient utilization of phosphate fertilizer in apple orchard. The results showed that root length, root surface area and root tip quantity were lower in seedlings under phosphorus deficiency (0-1.0 mmol·L^-1). With the addition of 2.0-4.0 mmol·L^-1 of phosphorus, the biomass of single plant, root length, root surface area and root tip quantity increased over seedlings under other treatments. Also root growth was restrained in seedlings under excess phosphorus (6.0-16.0 mmol·L^-1). The absorption of NO₃^- in M. hupehensis seedlings was significantly different under different phosphorus levels. The non-invasive micro-test technique showed significant absorption of NO₃^- by M. hupehensis seedlings under 3.0-6.0 mmol·L^-1 phosphorus with the highest rate of absorption under 3.0 mmol·L^-1 treatment. While 0-2 mmol·L^-1 and 8.0-16.0 mmol·L^-1 phosphorus applications showed efflux effect of NO₃^- by M. hupehensis seedlings. With the addition of phosphorus, Ndff (percent of nitrogen derived from fertilizer) and nitrogen utilization efficiency initially increased and then decreased. The highest nitrogen use efficiency (42.24%) was observed under the phosphorus treatment of 4.0 mmol·L^-1. Then there was a significant reduction under phosphorus application in excess of 4.0 mmol·L^-1 treatments. Leaf nitrate reductase activity was very low under phosphorus deficiency, but it had significantly higher levels under 1.0-3.0 mmol·L^-1 phosphorus application. There was a marked decrease in leaf nitrate reductase activity when the phosphorus concentration exceeded 4.0 mmol·L^-1. In conclusion, phosphorus level had significant effect on NO₃^- absorption and utilization by M. hupehensis seedlings. Root growth and nitrogen absorption increased with appropriate phosphorus application. With phosphorus overdose, root growth and nitrate reductase activity decreased significantly. This resulted in a decrease in the absorption and utilization of nitrogen. The analysis showed that 3.0-4.0 mmol·L^-1 of phosphorus was beneficial to the efficient growth of M. hupehensis seedlings, nitrogen absorption and utilization.