Which statement, if true, would best account for Mohri and colleagues… | Verbal SAT Question

Milena Mohri and colleagues conducted a meta-analysis of 330 studies to investigate the effect of soil characteristics, including pH, on the capacity of Festuca rubra and 47 other plant species to absorb chromium and other heavy metals from soil through their roots. Given that in soil, metal solubility (a key determinant of plants’ metal uptake) negatively correlates with soil pH in the rhizosphere (soil immediately proximate to roots), the researchers hypothesized that plants’ total metal content would negatively correlate with soil pH, but instead they found no correlation between the two variables overall. To explain the finding, they noted that many of the included studies didn’t specify whether the reported soil profiles were those of the rhizosphere.

Which statement, if true, would best account for Mohri and colleagues’ explanation?

Because of their distinct chemical properties, different heavy metals exhibit varying degrees of solubility response to changes in soil pH in the rhizosphere.

Relative concentrations of soluble metals in the rhizosphere are more strongly mediated by soil characteristics other than soil pH.

Biochemical interactions between plant roots and adjacent soil can considerably alter soil chemistry, including soil pH.

Plant species vary considerably in how deeply their root systems extend beyond the topsoil layer, where soil pH and metal concentrations are typically measured.