Nitrogen (N) is considered as a major factor that limits plant growth and metabolism, and absorptive roots play a critical role in plant resource acquisition. However, little is known about the roles of mycorrhizal colonization, and morphological and architectural traits of absorptive roots in N uptake rates. We examined the uptake rates for ammonium ( $${\text{NH}}_{4}^{ + }$$ NH 4 + ), nitrate ( $${\text{NO}}_{3}^{ - }$$ NO 3 - ) and glycine using a 15 N isotope tracer technique and measured mycorrhizal colonization rates and functional traits (morphology, architecture and chemistry) of absorptive roots in a subtropical plantation during the growing season. Results showed that trees, shrubs and herbs all preferred to take up $${\text{NH}}_{4}^{ + }$$ NH 4 + over $${\text{NO}}_{3}^{ - }$$ NO 3 - and glycine, likely due to the dominant available N form in native soils. Species coexisting in the subtropical plantation did not show chemical niche differentiation, but there was a temporal niche separation in N acquisition across plant species. Absorptive roots with higher mycorrhizal colonization rates exhibited higher N uptake rates than those with lower colonization. In May, morphological traits (diameter and root tissue density) seemed playing important roles in N acquisition on that the absorptive roots with larger diameter and shorter specific root length (SRL) showed higher uptake rates for $${\text{NH}}_{4}^{ + }$$ NH 4 + , $${\text{NO}}_{3}^{ - }$$ NO 3 - , and glycine than those with smaller diameter and longer SRL. While in August, the architectural traits of root branching might be essential to enhance nutrient absorption on that the absorptive roots with intensive branching exhibited higher N uptake rates than those with less branching. Our findings suggested that plant species may evolve effective N acquisition strategies integrated mycorrhizal symbiosis, and root morphological and architectural traits over a temporal scale to acclimate to the changing environments.

中文翻译：

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华南亚热带松林乔木和林下树种根系氮获取策略

氮（N）被认为是限制植物生长和代谢的主要因素，吸收根在植物资源获取中起着关键作用。然而，人们对菌根定植的作用以及吸收根的形态和结构特征在 N 吸收率中的作用知之甚少。我们检查了铵 ( $${\text{NH}}_{4}^{ + }$$ NH 4 + )、硝酸盐 ( $${\text{NO}}_{3}^{ - }$$ NO 3 - ) 和甘氨酸使用 15 N 同位素示踪技术，并测量了生长季节亚热带种植园中吸收性根的菌根定植率和功能特征（形态、结构和化学）。结果表明，乔木、灌木和草本植物都喜欢吸收$${\text{NH}}_{4}^{ + }$$ NH 4 + 超过$${\text{NO}}_{3}^ { - }$$ NO 3 - 和甘氨酸，可能是由于原生土壤中占主导地位的有效氮形式。亚热带人工林共存的物种没有表现出化学生态位分化，但在不同植物物种的 N 获取中存在时间生态位分离。具有较高菌根定植率的吸收性根比具有较低定植率的吸收性根表现出更高的氮吸收率。5 月，形态特征（直径和根组织密度）似乎在 N 获取中起重要作用，因为具有较大直径和较短比根长度 (SRL) 的吸收性根对 $${\text{NH}}_ 的吸收率更高{4}^{ + }$$ NH 4 + 、$${\text{NO}}_{3}^{ - }$$ NO 3 - 和甘氨酸比直径更小、SRL更长的那些。而在八月，根分枝的结构特征可能是增强养分吸收的必要条件，因为分枝密集的吸收根比分枝少的吸收根表现出更高的氮吸收率。我们的研究结果表明，植物物种可能会在时间尺度上进化出有效的氮获取策略，整合菌根共生、根形态和结构特征，以适应不断变化的环境。