叶片性状和根系特性对氮贮存与内转移的作用机制研究

Nitrogen storage and remobilization is a key mechanism to support plant primary functions and maintain matter circulation of terrestrial ecosystems. A substantial body of studies have thoroughly quantified plant growth and remobilized nitrogen in deciduous broadleaf, evergreen coniferous, and evergreen broadleaf trees. In contrast, little attention has been paid on deciduous coniferous trees, resulting in that the relationship between leaf habit and nutrient remobilization is not fully understood. Furthermore, more information is needed on how root characteristic in combination with leaf habit affects the process of nitrogen storage and remobilization. In the current study, five distinct tree species native to North China were used in full consideration of their leaf habit and main root type. Seedlings were fertilized with contrasting fertilization rates to build deficient and luxury nutrient reserves and transplanted in the following spring into sand-filled pots fertilized with labelled isotope nitrogen fertilizer simulating poor and rich fertility soils. Seedlings were sampled at the conclusion of the establishment and rapid growth phases, respectively. We investigated whether these tree species differed in: (1) nitrogen storage and allocation pattern in main root, lateral root, stem and foliage; (2) remobilized nitrogen amounts from perennial tissues and their nitrogen remobilization rates during two differentiated developmental phases; (3) partitioned patterns of remobilized nitrogen in new root, stem and foliage and the relative contribution of remobilized nitrogen to the growth of these current tissues during developmental phases; (4) distributed patterns of soil nitrogen uptake in current tissues and the relative contribution of nitrogen availability to the growth of these current tissues during developmental phases. The study would distinguish the roles of leaf habit and root characteristic to determine the nitrogen storage and remobilization and thereby would be beneficial to unravel the mechanism of nutrient internal cycling of woody plants.

阐明氮贮存与内转移规律对于认识树木养分利用策略以及生态系统物质循环具有重要意义，因此受到普遍关注。以往研究主要集中在落叶阔叶、常绿阔叶和常绿针叶树种，落叶针叶树种涉及甚少，叶片性状对氮内转移的作用机制尚不十分清楚，树种其它生物学和生态学特性如何影响养分内转移知之更为匮乏。依据叶片性状和根系特征，项目选择华北地区五个乡土树种，实施氮肥处理使苗木形成亏缺和富足两种养分状态，翌年春季将苗木移栽至用氮同位素肥料构建的不同肥力土壤上，在苗木生长初期和速生期等阶段，研究氮贮存量以及在主根、侧根、茎和叶等组织分配规律，多年生组织养分转移的时空规律，转移养分在当年生根茎叶等组织的分配规律以及与苗木生长的数量关系，土壤供给养分在当年生组织分配规律以及对苗木养分积累的贡献率。项目在叶片性状分类的基础上利用根系特征进一步区分树种特性，预期成果将完善树种特性对养分贮存与内转移的作用机制。

阐明氮贮存与内转移规律对于认识树木养分利用策略以及生态系统物质循环具有重要意义，因此受到普遍关注。以往研究主要集中在落叶阔叶、常绿阔叶和常绿针叶树种，落叶针叶树种涉及甚少，叶片性状对氮内转移的作用机制尚不十分清楚，树种其它生物学和生态学特性如何影响养分内转移知之更为匮乏。依据叶片性状和根系特征，项目选择华北地区四个乡土树种，实施氮肥处理使苗木形成亏缺和富足两种养分状态，翌年春季将苗木移栽至用氮同位素肥料构建的不同肥力土壤上，在苗木生长初期和速生期等阶段，研究氮贮存量以及在主根、侧根、茎和叶等组织分配规律，多年生组织养分转移的时空规律，转移养分在当年生根茎叶等组织的分配规律以及与苗木生长的数量关系，土壤供给养分在当年生组织分配规律以及对苗木养分积累的贡献率。项目的主要发现总结如下：①苗木氮贮存规律：生长季末，常绿针叶（油松，白扦）苗木主要氮贮存部位为针叶；栓皮栎主要将氮贮存在主根。而华北落叶松苗木的氮贮存部位会随氮肥供应改变。 ②苗木养分转移的空间规律：四个树种第二年初春至夏初的生长季中，新叶是主要的库器官，而主要的源器官与其各自主要氮贮藏部位一致 ③苗木养分转移的时间规律：翌年生长初期，四个树种对氮的利用主要依赖养分内转移，但速生期在土壤肥力较高的条件下，华北落叶松对氮的利用主要依赖外界养分获取。 ④苗木利用土壤养分的规律：四个树种翌年春季利用土壤养分时间规律不同，生长初期白扦对土壤养分依赖性更高，速生期相对生长速度快的树种对土壤养分的依赖性更高。以上关于四个树种第二年春季的对于内部贮存养分和土壤养分利用策略的差异研究，有助于理解自然分布下树种的养分利用策略，对于森林经营及植被恢复工作等有指导意义。此外，项目在叶片性状分类的基础上利用根系特征进一步区分树种特性，完善了树种特性对养分贮存与内转移的作用机制。