氮水平对桤木属幼苗根系形态及氮累积利用影响

采用温室沙培试验,通过不同浓度氮处理,研究红桤木、喜马拉雅灰桤木、欧洲桤木和灰桤木4种国外引种的桤木属幼苗对不同氮水平的响应差异,分析了氮胁迫对桤木属幼苗根系形态和氮累积利用的影响.结果表明:随着氮水平(N0、N1/2、N1(标准E.G.Bollard营养液)、N2)的增加,各桤木属植物的生物量、氮累积量和根长、根体积、根表面积、须根数等生长参数均呈先增后降的趋势,且在N1/2水平中各参数值最大；细根比例及氮利用效率、氮利用率均呈持续下降趋势.参试的4种桤木中欧洲桤木、红桤木的生物量、氮累积量、根系形态参数均较高,且在N1/2时氮利用率较高,分别为44.57％、40.14％,具有在我国长江中下游地区作为生态防护和短周期工业用材树种推广应用潜力；灰桤木和喜马拉雅灰桤木各生长参数均较低,不宜推广.试验结果也表明尽管桤木属植物具有一定的固氮能力,但在低地力河滩沙地、丘陵等地区集约化经营中仍需采取一定施肥措施.

Effects of Supplied Nitrogen Levels on Root Morphology, Accumulation and Utilization Efficiency of Nitrogen of Four Exotic Alder Seedlings

By sand culture in greenhouse, the experiment of growing process on four exotic alders including Alnus glutinos, Alnus rubra, Alnus nitada and Alnus incana were conducted under four different concentrations of nitrogen (N0, N1/2, N1, N2) in order to discover the growing responses to nitrogen and to analyze root morphology of seedling, accumulation and utilization efficiency of nitrogen. The results showed that the growth parameters of 4 exotic alders, such as the total biomass, accumulation of nitrogen, length of root, surface area of root, volume of root and number of rootlets increased when the concentration of nitrogen varied from no nitrogen (N0) to low nitrogen (N1/2), yet decreased at normal nitrogen (N1) and high nitrogen (N2). However the rootlet ratio and utilization efficiency of nitrogen decreased significantly with increasing nitrogen supplied. Among 4 experimental materials, Alnus glutinos and Alnus rubra had higher total biomass, accumulation of nitrogen, root morphological parameters and nitrogen utilization efficiency than Alnus nitada and Alnus incana, and they could be potentially used in ecological protection and plantations for short rotation trees in the plain of middle and lower Yangtze River. Although the alders had certain nitrogen fixation ability, certain amount of nitrogen fertilization is still needed in the low fertility sandy soil and hilly region in the intensive management of plantations of alders.