Purpose

Stable isotope tracer experiments provide a powerful tool for understanding plant root distributions, resource uptake, niche partitioning and water cycling. Plant water is typically collected from pre-transpiring tissues to avoid the effects of evaporative isotope enrichment at the leaf surface, but extracting water from these plant samples is difficult and expensive. The purpose of this study was to test a simple transpiration bagging approach for measuring hydrologic tracer uptake.

Methods

Sampling was performed as part of a depth-specific tracer experiment in which ²H₂O was injected to target depths (5, 15, 30, 60, or 150 cm) in different replicated plots. One day following injections, leaves from three species were sealed in bags for 16 h and transpired water was collected. Water from pre-transpiring stem tissue was then collected in a separate set of samples and extracted using cryogenic distillation.

Results

Deuterium concentrations from the two techniques were correlated (R² = 0.84) and both approaches produced similar descriptions of vertical root distributions for three dominant plant species. ¹⁸O concentrations from the two techniques were not correlated.

Conclusion

Bagging transpired water produced similar estimates of ²H tracer uptake as the standard sampling technique. Bagging requires no destructive sampling, specialized laboratory equipment, training or consumables and is expected to halve sampling costs. While effective in this tracer experiment, bagging may be not be effective in natural abundance experiments, or tracer experiments with very small plants or small transpiration rates (i.e., early-season or arid sites).

中文翻译：

---

套袋：一种用于示踪剂研究的便宜，快速，无损的蒸腾水取样方法

目的

稳定的同位素示踪剂实验为了解植物根系分布，资源吸收，生态位分配和水循环提供了强大的工具。通常从蒸腾前的组织中收集植物水，以避免叶表面蒸发同位素富集的影响，但是从这些植物样品中提取水既困难又昂贵。这项研究的目的是测试一种简单的蒸腾套袋方法，以测量水文示踪剂的吸收。

方法

作为深度特定示踪剂实验的一部分进行采样，其中在不同的重复样图中将² H ₂ O注入目标深度（5、15、30、60或150 cm）。注射后一天，将三种物种的叶子密封在袋中16小时，并收集蒸发的水。然后，将出汗前的干组织中的水收集在单独的一组样品中，并使用低温蒸馏进行萃取。

结果

两种技术的氘浓度相关（R ²  = 0.84），两种方法都对三种优势植物物种的垂直根分布产生了相似的描述。两种技术的¹⁸ O浓度无关。

结论

套袋蒸发的水产生的² H示踪剂吸收量与标准采样技术相似。套袋不需要破坏性采样，专用实验室设备，培训或消耗品，并且有望将采样成本减半。尽管套袋法在该示踪剂实验中很有效，但在自然丰度实验或具有很小植物或很小蒸腾速率（即早期或干旱地点）的示踪剂实验中可能无效。