Key message

Juveniles and canopy trees may not exhibit similar nitrogen acquisition responses to soil temperature change caused by variation in snow cover over winter.

Abstract

The use of ¹⁵N tracer is a powerful tool for tracking the effects of variation in soil frost on plant nitrogen acquisition. While the responses of juvenile trees to environmental change are often used to infer the responses of canopy trees, the ¹⁵N enrichment responses of juveniles and mature canopy trees may not be comparable. We conducted a winter soil temperature manipulation study (snow exclusion, ambient snow or soil insulation) in a lowland Fagus sylvatica forest. ¹⁵N tracer was applied the following spring and the ¹⁵N enrichments of soil, juvenile and mature canopy trees were examined in late fall. Within canopy trees and juveniles, the relative treatment effects on ¹⁵N enrichment were consistent among all sampled tissues (roots, stem cores, leaves, buds and the current year’s shoot growth). For juveniles, ¹⁵N enrichment was highest under snow exclusion (coldest soil) and lowest under soil insulation (warmest soil), and lower ¹⁵N enrichment occurred under ambient conditions than under snow exclusion. For canopy trees, ¹⁵N enrichment also was highest under snow exclusion and lowest under soil insulation, but there was no difference in ¹⁵N enrichment between ambient conditions and the snow exclusion treatment. Therefore, our results indicate that sampling of juveniles may overestimate the nitrogen acquisition responses of mature trees to winter temperature variation.

中文翻译：

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冠层乔木和幼树对冬季土壤温度操纵的15 N示踪剂富集有所不同

关键信息

幼树和冠层树对冬季因积雪变化引起的土壤温度变化可能不会表现出相似的氮素吸收响应。

抽象

¹⁵ N示踪剂的使用是一种强大的工具，可用于跟踪土壤霜冻变化对植物氮素吸收的影响。虽然通常使用幼树对环境变化的响应来推断冠层树的响应，但幼树和成熟冠层树的¹⁵ N富集响应可能不具有可比性。我们在低地的Fagus sylvatica森林中进行了冬季土壤温度控制研究（除雪，环境降雪或土壤隔热）。次年春季施用¹⁵ N示踪剂，并在深秋检查¹⁵ N富集的土壤，幼树和成熟冠层树。在树冠和少年中，对¹⁵种树的相对治疗效果在所有采样的组织（根，茎核，叶，芽和当年的枝条生长）中，氮的富集是一致的。对于未成年人，在积雪排除（最冷的土壤）下¹⁵ N富集最高，在土壤隔绝物质（最温暖的土壤）下最低¹⁵ N富集，并且在环境条件下发生的¹⁵ N富集低于积雪。对于冠层树木，除雪条件下的¹⁵ N富集也最高，而土壤保温条件下的最低¹⁵ N富集，但是环境条件与除雪处理之间的¹⁵ N富集没有差异。因此，我们的结果表明，对幼体进行采样可能会高估成熟树木对冬季温度变化的氮素吸收响应。