How to study deep roots—and why it matters

Abstract

The drivers underlying the development of deep root systems, whether genetic or environmental, are poorly understood but evidence has accumulated that deep rooting could be a more widespread and important trait among plants than commonly anticipated from their share of root biomass. Even though a distinct classification of “deep roots” is missing to date, deep roots provide important functions for individual plants such as nutrient and water uptake but can also shape plant communities by hydraulic lift (HL). Subterranean fauna and microbial communities are highly influenced by resources provided in the deep rhizosphere and deep roots can influence soil pedogenesis and carbon storage.Despite recent technological advances, the study of deep roots and their rhizosphere remains inherently time-consuming, technically demanding and costly, which explains why deep roots have yet to be given the attention they deserve. While state-of-the-art technologies are promising for laboratory studies involving relatively small soil volumes, they remain of limited use for the in situ observation of deep roots. Thus, basic techniques such as destructive sampling or observations at transparent interfaces with the soil (e.g., root windows) which have been known and used for decades to observe roots near the soil surface, must be adapted to the specific requirements of deep root observation. In this review, we successively address major physical, biogeochemical and ecological functions of deep roots to emphasize the significance of deep roots and to illustrate the yet limited knowledge. In the second part we describe the main methodological options to observe and measure deep roots, providing researchers interested in the field of deep root/rhizosphere studies with a comprehensive overview. Addressed methodologies are: excavations, trenches and soil coring approaches, minirhizotrons (MR), access shafts, caves and mines, and indirect approaches such as tracer-based techniques.

Functional response of Quercus robur L. to taproot pruning: a 5-year case study

“…Indeed, taproots make oak tree growth less dependent on surface soil layers that tend to dry out, and limit overexploitation of the resources present in a narrow soil profile (Cavender-Bares and Bazzaz 2000; Pierret et al 2016). The inability of a tree species, such as Q. robur, to regenerate a pruned taproot (Ogijevskij and Popova 1954) may be essential for the optimal acquisition of nutrients and water [see Maeght et al 2013 and literature cited therein]. Despite the response that occurred in our experimental system, a similar pattern of biomass partitioning might not occur under drought conditions or in less fertile soil, thus limiting the interpretation or extrapolation of the present findings.…”

The quest for understanding phenotypic variation via integrated approaches in the field environment

“…3). High-throughput soil coring (Wasson et al, 2014), root crown excavation (Das et al, 2015), and minirhizotron analysis (Maeght et al, 2013) are common ways in which roots are studied in the field, but each provides limited information relative to the actual root structure. Thus, there remains a lack of a coherent view of root phenotypes and their genetic and environmental conditioning (Topp et al, 2016).…”

Accelerating genetic gains in legumes for the development of prosperous smallholder agriculture: integrating genomics, phenotyping, systems modelling and agronomy

“…Images of roots growing along the minirhizotron wall at particular locations in the soil profile can be captured over time Iversen et al (2011), Maeght et al (2013) RhizoTube (INRA, France)…”