Field 13C Pulse Labeling of Pea, Wheat, and Vetch Plants for Subsequent Root and Shoot Decomposition Studies

ABSTRACT Isotopic labeling of plants is useful in tracking the fate of carbon (C) from different plant parts in a soil-plant system when these parts decompose simultaneously. Pulse labeling is a relatively simple technique and is amenable for use in the field. Therefore, we evaluated a 13CO2 pulse-labeling method to label crop plants under subtropical field conditions for simultaneous root and shoot decomposition studies. Wheat (Triticum aestivum L.), pea (Pisum sativum L.), and vetch (Vicia sativa L.) plants were grown inside polyvinyl chloride (PVC) cylinders and pulse labeled once a week for a total of 11 times. After harvest, “paired” treatments were designed by combining 13C-labeled shoots with unlabeled roots and unlabeled shoots with 13C-labeled roots, resulting in six treatments (2 combinations × 3 species), plus an unamended control treatment. The 13C enrichment of plant parts, chemical fractions, 13C recovery, and distribution in roots, shoots, and soil were determined. Soil CO2 emissions were measured continuously by the alkaline trap method for 180 days. Plant dry matter production and chemical composition were not modified by 13C labeling. The maximum level of 13C enrichment (δ13C) in plants was +495 %o in wheat, +426 %o in pea, and +378 ‰ in vetch plants. All three crops showed similar patterns of 13C distribution in the following order: shoots > roots > soil. On average, 81 to 89 % of the recovered 13C was in the shoots, 7 to 14 % was in the roots, and 2.7 to 4.3 % was in the soil. The rate of C mineralization and cumulative C mineralization were not different between “paired” treatments of the three crops, showing that the paired treatments were equally degradable. The pulse-labeling technique used under field conditions allowed for production of sufficiently labeled wheat, pea, and vetch plants. Therefore, it is a practical approach with respect to resource demand (tracer and labor costs), and it is suitable for in situ labeling.

摘要：对植物进行同位素标记（isotopic labeling），可在植物不同部位同时分解时，追踪其碳（C）在土壤-植物系统中的归趋。脉冲标记（pulse labeling）技术相对简便且适用于田间场景，因此本研究针对亚热带田间条件，评估了一种13CO2脉冲标记法，用于标记作物植株以开展根系与地上部同时分解的相关研究。本研究将普通小麦（Triticum aestivum L.）、豌豆（Pisum sativum L.）和野豌豆（Vicia sativa L.）种植于聚氯乙烯（polyvinyl chloride, PVC）柱中，每周开展1次脉冲标记，总计标记11次。收获后设置“配对”处理组：将13C标记的地上部与未标记根系组合，以及未标记地上部与13C标记根系组合，共得到6个处理（2种组合×3个物种），另设1组未改良对照处理。随后测定了植株各部位、化学组分的13C富集度，以及13C的回收率及其在根系、地上部和土壤中的分布情况；采用碱液捕集法连续180天测定土壤CO2排放通量。研究表明，13C标记并未改变植株的干物质产量与化学组成。三种作物的植株最大13C富集度（δ13C）分别为小麦+495‰、豌豆+426‰、野豌豆+378‰。三种作物的13C分布模式均一致，遵循地上部＞根系＞土壤的顺序。平均而言，回收的13C中有81%~89%分布于地上部，7%~14%分布于根系，2.7%~4.3%分布于土壤。三种作物的“配对”处理组间，碳矿化速率与累积碳矿化量均无显著差异，表明各配对处理组的降解性相当。本研究采用的田间脉冲标记技术可获得足够标记量的小麦、豌豆和野豌豆植株，因此该方法在示踪剂与人力成本等资源需求层面切实可行，适用于原位标记（in situ labeling）。