Abstract Sandy soils presenting low organic matter levels do not provide enough N to meet Eucalyptus sp. demands. Nitrogen fertilizers can be applied to soil surface, although N losses tend to happen and to decrease the amounts of this component used by plants. Alternatively, N can be applied to planting pits at seedling transplantation time or to small holes dug close to the plants. However, aspects such as the impact of different N supply modes applied to the soil on the growth parameters of root systems and the way these supply modes can affect morphological and physiological parameters of the shoot remain poorly known. The aim of the current study is to assess shoot and root growth in Eucalyptus grandis trees grown in soil subjected to different N supply modes. Eucalyptus grandis clones (GPC 23) were subjected to three N supply modes, namely: control (without N application) (C), N application to soil surface (SN) and N application to the pit (PN). Plant height, stem diameter, N concentration and chlorophyll a fluorescence in leaves, morphological parameters of the root system (total root surface area and mean root diameter), total length of active roots and total number of living and dead roots were analyzed. The PN supply mode has led to the highest mineral N levels (NH4+ and NO3−) in the soil, as well as increased the total length of active roots, the number of living roots and the root surface area in soil layers 20–40 cm and 40–60 cm. This process has enabled greater N uptake by plants, which, in its turn, has increased N concentrations in leaves, favored photosynthetic processes and resulted in taller plants presenting greater stem diameter. The SN supply method did not increase the mineral N in the soil, and it restricted the total length of active roots in soil layer (0–20 cm) and resulted in higher mean root diameter.

中文翻译：

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施氮方式对巨桉根系生长动态的影响

摘要 有机质含量低的沙质土壤不能提供足够的氮来满足桉树的生长。需要。可以将氮肥施用于土壤表面，尽管 N 损失往往会发生并减少植物使用的这种成分的数量。或者，可以在幼苗移植时将氮施用于种植坑或在靠近植物的地方挖小孔。然而，诸如应用于土壤的不同 N 供应模式对根系生长参数的影响以及这些供应模式如何影响芽的形态和生理参数等方面仍然知之甚少。当前研究的目的是评估生长在土壤中的桉树在不同 N 供应模式下的芽和根生长。Eucalyptus grandis 克隆 (GPC 23) 经历了三种 N 供应模式，即：控制（不施氮）（C），施氮到土壤表面（SN）和施氮到坑（PN）。分析了植物高度、茎直径、氮浓度和叶中叶绿素 a 荧光、根系形态参数（总根表面积和平均根直径）、活根总长度和活根和死根总数。PN 供应模式导致土壤中矿物质 N 水平（NH4+ 和 NO3−）最高，并增加了土壤层中活跃根的总长度、活根数和根表面积 20-40 cm和 40-60 厘米。这个过程使植物能够吸收更多的氮，这反过来又增加了叶子中的氮浓度，有利于光合作用过程，并导致更高的植物呈现更大的茎直径。