不同氮处理下速生柳对水体氮的吸收、分配及生理响应

采用水培法,研究了旱柳苗在外源添加不同氮水平(贫氮、中氮、富氮、过氮)的铵态氮(NH+4-N)和硝态氮(NO-3-N)的生长、氮吸收、分配和生理响应。结果表明:一定范围氮浓度的增加能够促进旱柳苗的生长,但过量氮会抑制其生长,且NH+4-N的抑制作用大于NO-3-N;两种氮处理下,旱柳表现出对NH+4-N的吸收偏好,在同一氮水平时,旱柳各部位氮原子百分含量Atom%15N(AT%)、15N吸收量和来自氮源的N%(Ndff%)均为NH+4-N处理大于NO-3-N处理,且随着氮浓度的增加,差异增大,且在旱柳各部位的分布为根﹥茎﹥叶;2种氮素过量和不足均会对旱柳根和叶生理指标产生不同的影响,其中在过氮水平时,NH+4-N和NO-3-N处理下根系活力比对照减少了50.61%和增加了19.53%;在过氮水平时,NH+4-N处理柳树苗根总长、根表面积、根平均直径、根体积和侧根数分别对照下降了30.92%、29.48%、19.44%、27.01%和36.41%,NO-3-N处理柳树苗相应的根系形态指标分别对对照下降了1.66%、5.65%、1.49%、5.06%和25.72%。可见,高浓度NH+4-N对旱柳苗的胁迫影响大于NO-3-N,在应用于水体氮污染修复时可通过改变水体无机氮的比例,削弱其对旱柳的影响,从而提高旱柳对水体氮污染的修复效果。

Nitrogen absorption/distribution and physiological characteristics of Salix matsudana seedlings grown in hydroponic solution

In recent years, due to global climate change and unpredictable human activities, the problem of water resource shortage and environmental water pollution has become widespread. Particularly, nitrogen pollution of water in China is a problem, owing to atmospheric nitrogen deposition and excess of nitrate, which results in a significant increase in water soluble nitrogen and eutrophication. To address the issue, an important multipurpose tree species, willow (Salix sp.), which has large biomass production and high resistance to environmental stress, has been studied, and as proved effective in the uptake and accumulation of pollutants from contaminated waters and soils. Hence, it was employed in the present experiment. In the current study, the seeding of Salix matsudana was selected to probe the characteristics of growth, nitrogen absorption/distribution, and physiological responses under different nitrogen treatments. These included poor nitrogen (1.4 mg/L), medium nitrogen (2.8 mg/L), high nitrogen (7.0 mg/L), and excessive nitrogen (28.0 mg/L), which are levels related to the water eutrophication classification standard. Nitrogen was added as ammonium nitrogen (NH₄⁺-N) and nitrate nitrogen (NO₃^--N) through water culture experiments. The results showed that the biomass of Salix matsudana increased with increasing nitrogen to some extent, but the growth was inhibited under excessive nitrogen concentrations, and NH₄⁺-N showed a higher inhibition than NO₃^--N. Meanwhile, Salix matsudana had a preference for NH₄⁺-N absorption over NO₃^--N when provided with the same concentration of nitrogen. The order of AT% contents, ¹⁵N absorption and Ndff% in different organs of Salix matsudana was, root > stem > leaf, and the content of NH₄⁺-N was higher than that of NO₃^--N. Furthermore, the difference showed an increasing trend with rising nitrogen concentration. Moreover, with increasing nitrogen concentration, the rate of ¹⁵N allocation was significantly different in different organs for the two kinds of nitrogen. Specifically, for NH₄⁺-N treatment, the ¹⁵N allocation rate showed a trend of increasing after first decreasing, and nitrogen levels peaked in the root of Salix matsudana. The maximum value appeared under medium nitrogen concentrations; while the ¹⁵N allocation rate in leaves showed a trend of gradually falling, and the maximum value appeared in the case of poor nitrogen concentration. Both inadequate and excessive nitrogen in solution showed significant effects on the physiological traits of willow seedlings. The chemical form of nitrogen also showed significantly different effects on physiological characterizations of willow. The root activity decreased by 50.61% and increased by 19.53% under excessive nitrogen when compared with the control. Furthermore, indicators such as root length, root surface area, root volume, root diameter and root tips of Salix matsudana, decreased by 30.92%, 29.48%, 19.44%, 27.01%, and 36.41% respectively, under NH₄⁺-N treatment. The root length, root surface area, root volume, root diameter, and root tips of Salix matsudana were decreased by 1.66%, 5.56%, 1.49%, 5.06%, and 25.72% respectively, under NO₃^--N treatment. Thus, it could be concluded that the influence of NH₄⁺-N stress on Salix matsudana was higher than that of NO₃^--N when seedlings were exposed to high concentration of nitrogen. Therefore NO₃^--N certain concentrations could be added to alleviate the damage caused by NH₄⁺-N on Salix matsudana.