Biopores in the subsoil: Formation, nutrient turnover and implications for root growth of field crops

在初步研究中，我们的工作组表明，在用直根系统种植饲料作物后，底土中大型生物孔的密度在相当短的时间内增加。尽管土壤休息和作物残留物增加了蚯蚓的丰度，但它们对初级生物化石产生的贡献并不是很大。稳定生物孔和影响其孔壁特征是蚯蚓活动的潜在效应，在有利的生境条件下可能在短期内发生；但这一假设还需要进一步研究。单个生物孔的C和N含量差异很大，可能是由于孔隙的形成和殖民史的结果。无论根构型如何，大田作物的根经常在生物孔中定居，并与生物孔壁建立联系。然而，关于生物孔特性如何影响根的生长这一问题，还需要更多的研究。我们的新建议旨在量化饲料作物的作物序列对生物矿物性和后续作物表现的影响。为此，我们将使用先前建立的田间试验，包括土壤温度和湿度监测系统。持续的调查将使人们能够了解饲料种植产生的持久影响。监测三个设计相似但在2007年至2012年期间建立的系列实地试验，能够考虑到不同年份和不同天气条件的影响。此外，我们的目标是量化降雨量、表层土壤中的养分浓度和生物土壤系统之间的相互作用，以便在具有雨棚和表层土壤交换的小区中从底层土壤中获取养分。此外，我们将量化已知历史的生物孔壁的特性(蚯蚓定植与根部定植)，以及蚯蚓活动对孔壁特性的影响。从单个生物孔中采集根和孔壁材料，结合原位内窥镜检查，将为了解具有不同孔壁特性的生物孔对作物根的吸引力提供新的见解。我们希望我们的研究能够对具有直根和蚯蚓活动的作物的栽培如何影响生物孔密度和孔壁特性，以及哪些特性有利于作物根利用生物孔作为伸长途径和养分获取的热点提供新的见解。

In preliminary studies our working group has shown that after growing fodder crops with taproot systems the density of large sized biopores in the subsoil increased within quite a short period of time. Anecic earthworms did not contribute to primary biopore generation that much, although their abundance was increased by soil rest and crop residues. Stabilizing biopores and influencing their pore wall characteristics are potential effects of earthworm activity that under favorable habitat conditions may take place in the short-term; however this assumption needs further investigation. C and N contents of individual biopores vary largely, presumably as a consequence of the pores genesis and colonization history. Roots of field crops frequently colonize biopores and establish contact with the biopore wall, regardless of the root architecture. However, more research is needed on the question how biopore properties influence root growth. Our new proposal aims to quantify the effects of crop sequences with fodder crops on biopore properties and the performance of subsequent crops. For this purpose we will use previously established field experiments, including the monitoring systems for soil temperature and moisture. Continued investigation will allow understanding the lasting effects generated by fodder cropping. Monitoring three field trials with similar design but established in a series from 2007 to 2012 enables taking into account the effect of different years with different weather conditions. In addition, we aim to quantify the interactions of precipitation, nutrient concentration in the topsoil and biopore systems for nutrient acquisition from the subsoil in subplots with rain shelter and topsoil exchange. Furthermore, we will quantify the properties of walls of biopores with known history (colonization by earthworms vs. colonization by roots) and the effect of earthworm activity on pore wall properties. Harvesting roots and pore wall material from individual biopores combined with in situ-endoscopy will provide new insights about the attractiveness of biopores with different pore wall properties for crop roots. We expect our research to give new insights on how cultivation of crops with taproots and earthworm activity affect biopore density and pore wall properties and which properties are beneficial for allowing crop roots to use biopores as pathways for elongation and hot spots for nutrient acquisition.