Macrofaunal biopores: Diversity and regeneration rates across diverse pedoclimatic conditions studied with repacked soil cores

Abstract

It is well known that biopores are crucial for soil functioning. However, their dynamics is rarely studied and their origin with regards to the soil organisms involved is still hard to determine. In this study we investigated the diversity of biopores and their regeneration rates in situ in various pedoclimatic conditions. Our approach involved field incubation of repacked soil cores with lateral openings across nine study sites in five countries (France, Vietnam, India, Laos and Thailand). After 12 months, biopores were characterized by X-ray computed tomography and grouped according to their diameter, length and sphericity index using principal component analysis followed by K-means clustering. The regeneration dynamics of biopores was assessed by comparing those created after one year of incubation to the biopores determined in soil cores taken from the surrounding soils (assuming the latter are in a steady-state). Additionally, we examined the relationships between newly formed biopores and soil macrofauna taxa. Our results evidenced significant variability in biopore diameter (0.90 to 15.84 mm), length (1 to 1600 mm) and sphericity index (0.03 to 0.93). We propose 10 biopore groups allowing to distinguish most of the study sites. Complete regeneration of biopores after 12 months was achieved in seven out of nine sites. Three groups of biopores showed a positive relation with earthworm abundance (r values ranged from 0.69 to 0.90), whereas the other groups of biopores showed no association with any macrofauna taxa. We conclude that biopore formation can be assessed under field conditions with repacked soil cores, regardless the pedoclimatic conditions. However, the involvement of macrofauna other than earthworms in biopore formation still remains to be unraveled. To capture their contribution to biopore formation, improvements of the repacked soil core approach and complementary laboratory experiments were suggested.