How roots capture nutrients from soil
At the simplest level, roots take up nutrients that are dissolved in soil water. But many key nutrients, like phosphorus, barely move through soil on their own, so roots must actively explore new soil to reach them. Current plant nutrition models often treat a small segment of root as representative, but this approach can miss how the whole root system forages through soil over time [1]. In other words, a root is not just a passive sponge—it is a branching, growing network that intercepts nutrients as it spreads.
The root surface itself has electrical properties that help capture nutrients. Root cell walls carry negative charges, which attract positively charged nutrient ions like calcium, magnesium, and potassium. A 2022 greenhouse study found that adding biochar to soil increased the negative charges on root surfaces by about 30–36% in safflower and mint, and this was linked to greater uptake of calcium, magnesium, and iron [3]. The biochar also raised the soil's ability to hold onto positively charged nutrients, so the effect came from both the soil and the root side.
Fungal partners extend the root's reach
Many plants outsource part of their nutrient acquisition to mycorrhizal fungi—symbiotic fungi that grow into or around root tissues and thread through the soil. In a study of 34 coexisting temperate woody species, trees that relied more heavily on mycorrhizal fungi for nutrient absorption (indicated by larger root diameter) had higher root phosphorus resorption efficiency, meaning they reabsorbed more phosphorus from dying roots before letting them go [4]. This pattern suggests that when plants lean on fungi for phosphorus uptake, they may place less value on holding onto phosphorus inside roots—though the study stops short of proving cause and effect.
The partnership can be influenced by other soil microbes. In holm oak seedlings, co-inoculating with a Pseudomonas bacterium increased the rate at which the roots were colonized by the truffle fungus Tuber melanosporum by 2.5-fold compared with seedlings given only the truffle fungus [5]. However, that same Pseudomonas treatment reduced overall plant growth, and combining the truffle fungus with Bradyrhizobium and Pseudomonas reduced the density of fine fibrous roots—the very roots most important for nutrient absorption [5]. So microbial helpers can boost fungal colonization without necessarily improving the plant's nutrient-gathering capacity, at least in the short term.
What roots take up, and what changes it
Roots absorb a mix of nutrients, and the specific ions taken up can shape plant quality. In apple trees, applying calcium nitrate to the soil increased calcium accumulation in the fruit, while monokalium phosphate promoted better formation of flower buds, and a nitrogen-free fertilizer (Kalimag) helped accumulate potassium and magnesium and influenced fruit size [2]. These are practical outcomes of root nutrition—what the roots absorb ends up in the harvestable parts of the plant.
The soil environment can shift how well roots function. The biochar study showed that adding biochar changed both soil pH and the cation exchange capacity—the soil's ability to hold positively charged nutrients—and these changes accompanied improved root activity and nutrient sorption in both a deep-rooted plant (safflower) and a shallow-rooted one (mint) [3]. The deep-rooted safflower had more functional groups on its roots and higher cation exchange capacity than mint under both control and biochar conditions, hinting that root structure and chemistry vary by species and affect nutrient capture [3].
Roots also recover nutrients from dying tissue
Roots are not only entry points for new nutrients; they also participate in recycling. Before roots die, plants can resorb nutrients from them, and this process appears coordinated with how the plant acquires nutrients in the first place. In the temperate forest study, species with lower foraging efficiency—those relying more on mycorrhizal fungi—had higher root phosphorus resorption efficiency, while species with tougher, denser root tissue had lower nitrogen and phosphorus concentrations in senesced (dying) roots and leaves [4]. The researchers suggest that outsourcing phosphorus acquisition to fungi may reduce the plant's need to recover phosphorus from dying roots, but they present this as a possible coordination rather than a proven mechanism [4].
Sources used in this answer
Acquisition of phosphorus and other poorly mobile nutrients by roots. Where do plant nutrition models fail?
Most plant nutrition models that treat a single root segment as representative may fail to capture how whole root systems acquire poorly mobile nutrients like phosphorus.
INFLUENCE OF ROOT AND NON-ROOT NUTRITION OF APPLE TREE ON PRODUCTIVITY AND QUALITY INDICATORS OF FRUIT
In apple trees, soil-applied calcium nitrate increased fruit calcium, monokalium phosphate improved flower bud formation, and a nitrogen-free fertilizer helped accumulate potassium and magnesium and influenced fruit size.
Improving electrochemical characteristics of plant roots by biochar is an efficient mechanism in increasing cations uptake by plants
Adding biochar to soil increased negative charges on root surfaces by about 30–36%, raised root cation exchange capacity, and enhanced uptake of calcium, magnesium, and iron in safflower and mint.
Nutrient resorption of leaves and roots coordinates with root nutrient‐acquisition strategies in a temperate forest
In 34 temperate woody species, trees relying more on mycorrhizal fungi for nutrient absorption had higher root phosphorus resorption efficiency, suggesting a possible coordination between acquisition strategy and nutrient recycling.
Effect of Bacteria Inoculation on Colonization of Roots by Tuber melanosporum and Growth of Quercus ilex Seedlings
Co-inoculating holm oak seedlings with a Pseudomonas bacterium increased truffle fungus colonization of roots 2.5-fold but reduced plant growth and, with Bradyrhizobium, reduced the density of fine nutrient-absorbing roots.