Aims

Deep-rooted crops have been widely used in agricultural systems to access deep resources such as water and nitrogen (N). However, the potential of deep roots to take water and N at various depths have not been well studied. Here we used chicory (Cichorium intybus L.) to study the potential and dynamics of water and nitrogen uptake in deep soil layers (below 1 m).

Methods

Chicory plants grown in outdoor rhizotrons were labelled by injecting a ²H₂O and Ca(¹⁵NO₃)₂ mixture into the soil column at 1.1, 2.3 and 3.5 m depth. Five, ten and twenty days after injection, ²H and ¹⁵N were traced in transpiration water and leaves.

Results

We found enriched ²H and ¹⁵N in water and plant samples, and both water and N uptake were observed down to 3.5 m. The ²H enrichment after injection at 1.1 m depth was 1552‰, almost 10 times higher than after injection at 2.3 m depth, which was 156‰. In contrast, injection at 1.1 and 2.3 m depth resulted in similar ¹⁵N enrichment of leaf samples.

Conclusion

Deep water uptake was found to be more sensitive to increased depth and reduced root intensity than N uptake, and labelled N was used more rapidly than labelled water. We propose several possible explanations for the discrepancies between deep water and N uptake, and further discuss the challenges of using isotopes and models in deep root studies.

中文翻译：

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² H和¹⁵ N双重标记显示菊苣深根在吸收潜力上的差异

目的

根深蒂固的农作物已广泛用于农业系统，以获取深层资源，例如水和氮（N）。但是，尚未深入研究深根在不同深度吸收水和氮的潜力。在这里，我们使用菊苣（Cichorium intybus L.）研究了深层土壤（低于1 m）中水和氮的吸收潜力和动态。

方法

通过将² H ₂ O和Ca（¹⁵ NO ₃）₂混合物注入深度分别为1.1、2.3和3.5 m的土壤柱中，对生长在室外根际的菊苣植物进行标记。注射后五天，十天和二十天，在蒸腾水和叶片中追踪到² H和^15N。

结果

我们发现水和植物样品中富含² H和¹⁵ N，在低至3.5 m时都观察到了水和N的吸收。在1.1 m深度注入后的² H富集量为1552‰，几乎是在2.3 m深度注入后的² H富集量156‰。相比之下，在1.1和2.3 m深度处注入会导致相似的¹⁵ N的叶片样品富集。

结论

发现深水吸收比N吸收对增加深度和降低根系强度更敏感，标记N的使用比标记N的吸收要快。我们为深水和氮的吸收量之间的差异提出了几种可能的解释，并进一步讨论了在深根研究中使用同位素和模型的挑战。