Hirte Juliane, Leifeld Jens, Abiven Samuel, Oberholzer Hans-Rudolf, Hammelehle Andreas, Mayer Jochen
Department of Natural Resources and Agriculture, Institute for Sustainability Sciences, AgroscopeZurich, Switzerland; Department of Geography, University of ZurichZurich, Switzerland.
Department of Natural Resources and Agriculture, Institute for Sustainability Sciences, Agroscope Zurich, Switzerland.
Front Plant Sci. 2017 Mar 1;8:284. doi: 10.3389/fpls.2017.00284. eCollection 2017.
Root biomass is one of the most relevant root parameters for studies of plant response to environmental change, soil carbon modeling or estimations of soil carbon sequestration. A major source of error in root biomass quantification of agricultural crops in the field is the presence of extraneous organic matter in soil: dead roots from previous crops, weed roots, incorporated above ground plant residues and organic soil amendments, or remnants of soil fauna. Using the isotopic difference between recent maize root biomass and predominantly C3-derived extraneous organic matter, we determined the proportions of maize root biomass carbon of total carbon in root samples from the Swiss long-term field trial "DOK." We additionally evaluated the effects of agricultural management (bio-organic and conventional), sampling depth (0-0.25, 0.25-0.5, 0.5-0.75 m) and position (within and between maize rows), and root size class (coarse and fine roots) as defined by sieve mesh size (2 and 0.5 mm) on those proportions, and quantified the success rate of manual exclusion of extraneous organic matter from root samples. Only 60% of the root mass that we retrieved from field soil cores was actual maize root biomass from the current season. While the proportions of maize root biomass carbon were not affected by agricultural management, they increased consistently with soil depth, were higher within than between maize rows, and were higher in coarse (>2 mm) than in fine (≤2 and >0.5) root samples. The success rate of manual exclusion of extraneous organic matter from root samples was related to agricultural management and, at best, about 60%. We assume that the composition of extraneous organic matter is strongly influenced by agricultural management and soil depth and governs the effect size of the investigated factors. Extraneous organic matter may result in severe overestimation of recovered root biomass and has, therefore, large implications for soil carbon modeling and estimations of the climate change mitigation potential of soils.
根生物量是研究植物对环境变化的响应、土壤碳建模或土壤碳固存估算中最相关的根参数之一。田间农作物根生物量量化的一个主要误差来源是土壤中存在外来有机物质：前茬作物的死根、杂草根、地上植物残体和有机土壤改良剂，或土壤动物的残骸。利用近期玉米根生物量与主要源自C3的外来有机物质之间的同位素差异，我们确定了来自瑞士长期田间试验“DOK”的根样本中玉米根生物量碳占总碳的比例。我们还评估了农业管理方式（生物有机和传统）、采样深度（0 - 0.25、0.25 - 0.5、0.5 - 0.75米）和位置（玉米行内和行间）以及由筛网尺寸（2毫米和0.5毫米）定义的根大小类别（粗根和细根）对这些比例的影响，并量化了从根样本中手动排除外来有机物质的成功率。我们从田间土壤芯中获取的根质量中只有60%是当季实际的玉米根生物量。虽然玉米根生物量碳的比例不受农业管理方式的影响，但它们随土壤深度持续增加，在玉米行内高于行间，并且在粗根（>2毫米）样本中高于细根（≤2毫米且>0.5毫米）样本。从根样本中手动排除外来有机物质的成功率与农业管理方式有关，最高约为60%。我们认为外来有机物质的组成受农业管理方式和土壤深度的强烈影响，并决定了所研究因素的效应大小。外来有机物质可能导致对回收根生物量的严重高估，因此对土壤碳建模和土壤缓解气候变化潜力的估算有很大影响。
