PREMISE While root-order approaches to fine-root classification have shown wide utility among wild plants, they have seen limited use for perennial crop plants. Moreover, inadequate characterization of fine roots across species of domesticated perennial crops has led to a knowledge gap in the understanding of evolutionary and functional patterns associated with different fine-root orders. METHODS We examined fine-root traits of common horticultural fruit and nut crops: Malus ×domestica, Prunus persica, Vitus vinifera, Prunus dulcis, and Citrus ×clementina. Additional roots were sampled from 33 common perennial horticultural crops, native to tropical, subtropical, and temperate regions, to examine variation in 1st- and 2nd-order absorptive roots. RESULTS First-order roots of grape and 1st- and 2nd-order roots of apple and peach were consistently thin, nonwoody, mycorrhizal, and had high N:C ratios. In contrast, 4th- and 5th-order roots of grape and 5th-order roots of apple and peach were woody, nonmycorrhizal, had low N:C ratios, and were thicker than lower-order roots. Among the 33 horticultural species, diameter of 1st- and 2nd-order roots varied about 15-fold, ranging from 0.04 to 0.60 mm and 0.05 to 0.89 mm respectively. This variation generally was phylogenetically conserved across plant lineages. CONCLUSIONS Collectively, our research shows that root-order characterization has considerably more utility than an arbitrary diameter cutoff for identifying roots of different functions in perennial horticultural crops. In addition, much of the variation in root diameter among species can be predicted by evolutionary relationships.

中文翻译：

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多年生园艺作物根系功能的表征

前提虽然细根分类的根序方法在野生植物中显示出广泛的实用性，但它们在多年生作物中的应用有限。此外，对驯化多年生作物物种细根的不充分表征导致对与不同细根目相关的进化和功能模式的理解存在知识差距。方法我们检查了常见园艺水果和坚果作物的细根性状：Malus ×domestica、Prunus persica、Vitus vinifera、Prunus dulcis 和 Citrus ×clementina。从原产于热带、亚热带和温带地区的 33 种常见多年生园艺作物中取样其他根，以检查一阶和二阶吸收性根的变化。结果葡萄的一级根和苹果和桃的一级和二级根一致地纤细、非木本、菌根，并且具有高N:C比。相比之下，葡萄的 4 级和 5 级根以及苹果和桃的 5 级根是木质的、非菌根的，N:C 比低，并且比低级根粗。在33个园艺品种中，一阶和二阶根的直径相差约15倍，分别为0.04～0.60mm和0.05～0.89mm。这种变异通常在植物谱系中在系统发育上是保守的。结论 总的来说，我们的研究表明，在识别多年生园艺作物中具有不同功能的根时，根序特征比任意直径截断值具有更大的实用性。此外，