Maize root-induced biopores do not influence root growth of subsequently grown maize plants in well aerated, fertilized and repacked soil columns

Biopore recycling is the process during which roots ingress into existing biopores instead of creating new ones. Previous studies investigated biopore recycling in rather artificial conditions, e.g., with artificially created vertical macropores, by neglecting the smaller biopore diameter classes or by focusing on high bulk density soil material only. To address these shortcomings, we designed a soil column experiment and characterized the degree of biopore recycling for two soil textures (sand, loam) and two bulk density treatments (loam: 1.26 vs 1.36 g cm−3, sand: 1.50 vs 1.60 g cm−3). We developed a novel method based on the analysis of X-ray CT 3D images which enabled us to characterize the degree of biopore recycling for root-induced biopores down to 60 µm of diameter. The degree of biopore recycling was two orders of magnitude lower than previously reported in the literature (on average 0.0036 centimeters of roots were found in 1 centimeter of biopores). Roots were crossing the biopores rather than colonizing them. Visual analysis of the images showed that the propensity of roots to grow into biopores was higher when the angle at which roots and biopores touched was inferior to 45 degrees and when the root diameter was approximately equal to or inferior to the biopore diameter. There were no statistical differences for the biopore recycling fraction between the two bulk density treatments in loam. In loam, roots degraded quickly (less than 78 days) and the biopores created were stable over time. In sand, some biopores were still filled with root residues after 216 days and many biopores had collapsed. We conclude that biopore recycling is less likely to occur in sand, as compared to in loam. We further used the model CPlantBox to simulate root system architectures with identical root length density as observed in the experiment but random arrangement with respect to biopores. By comparing the modeling results with the experimental results, we showed that roots had no preference for growing into biopores under the studied conditions.