施用磷对王桉 (Eucalyptus regnans F. Muell.)幼苗生长及其氨基酸组

王桉 (Eucalyptus regnans F. Muell.) 是澳大利亚桉树中最重要的商业用材和人工造林树种之一.研究王桉的施肥与其体内氨基酸的积累和转化及与食叶虫害之间的相关性具有重要的经济和生态意义.在温室内利用2种不同来源的土壤对王桉幼苗进行了不同磷施用量(100 kg hm~(-2)和 200 kg hm~(-2))处理.结果显示,不同土壤和不同磷施用量对苗木生长影响显著,但均未显著影响苗木各部分的氮和磷含量水平.苗木木质部渗出液中的氨基酸含量以谷氨酰胺为主,并与苗木生长和磷施用量呈反相关.不同土壤和磷施用量对苗木组织中游离氨基酸组分和含量的影响不显著,但游离氨基酸的组分和相对水平随叶龄变化明显,尤其是精氨酸在嫩叶氨基酸总量中只占2%～3%,但在老叶中占到20%多;精氨酸在老叶中的积累极有可能是某些蛋白质降解而精氨酸即时合成所致,因为精氨酸一般不在韧皮部转运.谷氨酰胺在树液中含量最高并与苗木生长呈反相关或许可以作为预测桉树发生食叶昆虫危害的一个有用指标.

Impact of phosphorus supply on growth and amino acid composition and concentration of Eucalyptus regnans F. Muell. seedlings

Eucalyptus regnans F. Muell. is one of the most commercially important timber trees in Australia. Study on the relationship between fertilizer application, amino acid accumulation and transformation and insect herbivory for eucalypts is both economically and ecologically necessary. E. regnans seedlings were grown with two rates of phosphorus (100 and 200 kg hm-2) in two soils with different P fixation capacity. The seedlings were grown in a glasshouse with 4 replicates. Experiment results showed: 1) seedling growth was significantly affected by the different soils and P treatment; 2) N and P concentrations in plant components were not significantly different with the soil and P treatments, while N and P concentrations in leaves decreased with leaf age; 3) amino acid concentration of xylem sap was dominated by glutamine and significantly affected by P application (concentration in xylem sap of seedlings grown with 100 kg hm-2 was 2 times more than that with 200 kg hm-2); 4) amino acid composition and concentration in leaves significantly changed with leaf age, particularly for arginine which was several-fold greater in old leaves than in young leaves. The change of arginine concentration in leaves is most likely due to some protein degradation and in situ arginine synthesis because arginine is not generally phloem sap mobile. The fact that glutamine concentration in xylem sap was dominant and inversely related to seedling growth suggests that specific nitrogenous solutes may be useful indices of the nitrogen status of E. regnans for insect herbivory.