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Background <p>This study aimed to elucidate in greater detail the relationship between the chemical forms of applied nitrogen and root system development in alfalfa (<i>Medicago sativa</i> L.) by applying fractal dimension (D) and lacunarity (Lf) as analytical indicators.</p> Results <p>Total root length increased exponentially with plant growth under both ammonium nitrogen (NH₄-N) and nitrate nitrogen (NO₃-N) treatments. After 40 days after sowing (40 DAS), the total root length under NH₄-N treatment became significantly greater than that under NO₃-N treatment. A similar tendency was observed for the number of lateral roots, which was also significantly higher under the NH₄-N treatment than under the NO₃-N treatment after 40 DAS. D increased approximately lineary with plant growth under both nitrogen treatments and was higher under the NH₄-N treatment than under the NO₃-N treatment only at 30 and 40 DAS. Lf increased until 20 DAS under both treatments, then decreased as growth continued. A significantly higher Lf was detected under the NH₄-N treatment than under the NO₃-N treatment at 20 DAS only. Both treatments showed an increasing trend in D in the upper root region as growth progressed. In contrast, in the lower region, D decreased until 20 DAS and then began to increase thereafter. Lf in the upper region reached its highest value at 20 DAS for both nitrogen forms, whereas in the lower region it peaked at 30 DAS. Over the entire growth period, no overall correlation was observed between Lf and D, total root length, or lateral root number; however, stage-specific correlations were evident when analyzed by growth phase.</p> Conclusions <p>The application of D and Lf made it possible to identify differences in root system development caused by the chemical forms of applied nitrogen that could not be detected through root length or root number alone. The findings further suggest that the effects of distinct nitrogen forms on root development first emerge in the spatial distribution of roots, then in root system complexity, and ultimately in total root length and lateral root number.</p>

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Analysis of root morphology in alfalfa (Medicago sativa L.) seedlings cultivated with ammonium or nitrate nitrogen using fractal dimension and lacunarity

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  • 发表日期：

    2025年12月22日

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  • Daisuke Hirose

摘要

Background

This study aimed to elucidate in greater detail the relationship between the chemical forms of applied nitrogen and root system development in alfalfa (Medicago sativa L.) by applying fractal dimension (D) and lacunarity (Lf) as analytical indicators.

Results

Total root length increased exponentially with plant growth under both ammonium nitrogen (NH₄-N) and nitrate nitrogen (NO₃-N) treatments. After 40 days after sowing (40 DAS), the total root length under NH₄-N treatment became significantly greater than that under NO₃-N treatment. A similar tendency was observed for the number of lateral roots, which was also significantly higher under the NH₄-N treatment than under the NO₃-N treatment after 40 DAS. D increased approximately lineary with plant growth under both nitrogen treatments and was higher under the NH₄-N treatment than under the NO₃-N treatment only at 30 and 40 DAS. Lf increased until 20 DAS under both treatments, then decreased as growth continued. A significantly higher Lf was detected under the NH₄-N treatment than under the NO₃-N treatment at 20 DAS only. Both treatments showed an increasing trend in D in the upper root region as growth progressed. In contrast, in the lower region, D decreased until 20 DAS and then began to increase thereafter. Lf in the upper region reached its highest value at 20 DAS for both nitrogen forms, whereas in the lower region it peaked at 30 DAS. Over the entire growth period, no overall correlation was observed between Lf and D, total root length, or lateral root number; however, stage-specific correlations were evident when analyzed by growth phase.

Conclusions

The application of D and Lf made it possible to identify differences in root system development caused by the chemical forms of applied nitrogen that could not be detected through root length or root number alone. The findings further suggest that the effects of distinct nitrogen forms on root development first emerge in the spatial distribution of roots, then in root system complexity, and ultimately in total root length and lateral root number.