Cover crop influence on pore size distribution and biopore dynamics: Enumerating root and soil faunal effects

Abstract

Pore structure is a key determinant of soil functioning, and both root growth and activity of soil fauna are modified by and interact with pore structure in multiple ways. Cover cropping is a rapidly growing popular strategy for improving agricultural sustainability, including improvements in pore structure. However, since cover crop species encompass a variety of contrasting root architectures, they can have disparate effects on formation of soil pores and their characteristics, thus on the pore structure formation. Moreover, utilization of the existing pore systems and its modification by new root growth, in conjunction with soil fauna activity, can also vary by cover crop species, affecting the dynamics of biopores (creation and demolition). The objectives of this study were (i) to quantify the influence of 5 cover crop species on formation and size distribution of soil macropores (>36 μm Ø); (ii) to explore the changes in the originally developed pore architecture after an additional season of cover crop growth; and (iii) to assess the relative contributions of plant roots and soil fauna to fate and modifications of biopores. Intact soil cores were taken from 5 to 10 cm depth after one season of cover crop growth, followed by X-ray computed micro-tomography (CT) characterization, and then, the cores were reburied for a second root growing period of cover crops to explore subsequent changes in pore characteristics with the second CT scanning.Our data suggest that interactions of soil fauna and roots with pore structure changed over time. While in the first season, large biopores were created at the expense of small pores, in the second year these biopores were reused or destroyed by the creation of new ones through earthworm activities and large root growth. In addition, the creation of large biopores (>0.5 mm) increased total macroporosity. During the second root growing period, these large sized macropores, however, are reduced in size again through the action of soil fauna smaller than earthworms, suggesting a highly dynamic equilibrium. Different effects of cover crops on pore structure mainly arise from their differences in root volume, mean diameter as well as their reuse of existing macropores.

The soil pore structure encountered by roots affects plant‐derived carbon inputs and fate

“…The images were reconstructed following the procedures from Lucas et al . (2022). To follow the root growth path, the μCT images taken before and after the growth experiment were registered using elastix (Klein et al ., 2010; Shamonin, 2013) as described in Lucas et al .…”

“…All intact and sieved ingrowth cores were lCT scanned twicebefore and after the ingrowth experiment at a resolution of 18.2 lm. The images were reconstructed following the procedures from Lucas et al (2022). To follow the root growth path, the lCT images taken before and after the growth experiment were registered using elastix (Klein et al, 2010;Shamonin, 2013) as described in Lucas et al (2020a).…”

“…For pore segmentation, we used the Otsu algorithm (Otsu, 1979). Biopores and roots were segmented according to the workflow of Lucas et al (2022). The respective IMAGEJ scripts can be found on 'https://github.com/Maik-Lu/Roots_and_Biopores'.…”

The distribution of particulate organic matter in the heterogeneous soil matrix - balancing between aerobic respiration and denitrification

“…5b). The reason for this is that POM is largely derived from roots that tend to grow into macropores (Lucas, Nguyen, et al 2022;Lucas, Schlüter, et al 2019a;White et al 2010, Fig. S5), and thus POM fragments are typically located close to air-filled macropores (Kravchenko, Guber, et al 2018;Schlüter, Leuther, et al 2022).…”

“…POM particles, hotspots of oxygen consumption, are distributed non-randomly within the soil matrix (Højberg et al 1994; Kravchenko and Guber 2017; Parkin 1987; Schlüter, Leuther, et al 2022). One reason for this non-random distribution is that a large share of POM originates from roots which predominately grow into more loose areas or directly into macropores (Lucas, Nguyen, et al 2022; Lucas, Schlüter, et al 2019a; White et al 2010). The distribution of POM is further modulated by land use (John et al 2005).…”