Abstract

Robinia pseudoacacia L. is a legume species that is widely used in afforestation, which has high N₂ fixation capacity and rapid growth rate. Both nitrogen (N) supply and phenology affect plant growth, photosynthesis and leaf senescence. The aim of this study was to determine how N supply affects N₂ fixation, leaf photosynthesis and senescence of R. pseudoacacia at different phenological stages. Seedlings of R. pseudoacacia were supplied with different levels of ¹⁵N-labelled NH₄NO₃ solution, with seedlings of Sophora japonica Linn. as reference plants to calculate the percentage of N derived from the atmospheric N₂ (%Ndfa). Compared with plants supplied with a high N level, those with a low N supply had a higher %Ndfa at an early developmental stage. Nitrogen fixation compensated the effect of a low N supply on plant growth in R. pseudoacacia. A high N supply decreased biomass allocation to lateral roots and nodules, and increased the relative growth rate of plant height as well as specific leaf area. The eighth mature compound leaf of R. pseudoacacia tended to have a higher net photosynthetic rate than the fourth leaf, and the leaves still maintained a moderate photosynthetic rate in early autumn. Plants tended to allocate more biomass to leaves at an early developmental stage and to stems and roots at a later developmental stage (3 months old). The N level did not affect leaf photosynthesis at different phenological stages, primarily due to (i) a high %Ndfa under low N supply at early growing stage, and a similar high %Ndfa under all N supplies at a late growing stage, and (ii) the delayed greening phenotype of expanding leaves to save nutrients for mature leaves.

中文翻译：

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快速固氮有助于提供不同水平氮素的刺槐的相似生长和光合速率

摘要

刺槐（Robinia pseudoacacia L.）是一种广泛用于造林的豆科植物，具有较高的N ₂固定能力和快速的生长速度。氮（N）的供应和物候都影响植物的生长，光合作用和叶片衰老。本研究的目的是确定N的供电是如何影响Ñ ₂固定，光合作用及衰老刺槐在不同的物候阶段。幼苗刺槐具有不同水平的被供给的¹⁵ N-标记的NH ₄ NO ₃溶液中，用的苗槐属。作为参考植物来计算来自大气氮的氮的百分比₂（％Ndfa）。与供应高氮水平的植物相比，供应低氮的植物在发育早期具有更高的％Ndfa。固氮补偿了低氮供应对假木兰植物生长的影响。高氮供应减少了生物量分配到侧根和根瘤，并增加了植物高度和特定叶面积的相对增长率。拟金合欢的第八个成熟复合叶趋于具有比第四片叶子更高的净光合速率，并且在初秋时叶仍然保持中等的光合速率。植物倾向于在发育的早期向叶片分配更多的生物量，而在发育的后期（3个月大）则向茎和根分配更多的生物量。氮水平在不同的物候阶段均未影响叶片的光合作用，这主要是由于（i）生长初期处于低氮供应下的％Ndfa较高，而生长后期处于所有氮供应下的％Ndfa相似，并且（ ii）延展叶片的延迟绿化表型，以节省成熟叶片的养分。