Introduction
The olive tree is one of the most resilient agricultural plants and can endure harsh environmental conditions. However, despite this adaptability, it faces a major nutritional challenge: phosphorus uptake. Phosphorus plays a crucial role in energy production, root development, growth of young shoots, and even the quality of olive oil. Yet in many olive-growing soils, phosphorus is either scarce or exists in forms that the roots cannot absorb.
Since olive roots have limited spread and a low capacity to search for phosphorus, the tree needs a natural partner—one that can compensate for this limitation. This partner is mycorrhizal fungi, organisms that form a symbiotic relationship with the roots and dramatically transform the phosphorus uptake cycle.
Why Is Phosphorus Uptake Difficult for Olive Trees?
Biologically, olive trees have a limited ability to access phosphorus. Phosphorus is highly immobile in soil and remains available only in very close proximity to the root surface. If the root is not located precisely in that small zone, the phosphorus becomes practically unavailable. The situation becomes even more challenging in acidic or calcareous soils, where phosphorus binds with other elements and turns into forms that roots cannot absorb. Thus, even if the soil “contains phosphorus,” the tree cannot use it.
Additionally, olive roots are relatively fine and restricted in their growth, lacking the ability to penetrate deeper or distant soil layers. This limitation makes phosphorus—more than any other nutrient—the key growth-limiting factor in olive cultivation. The root’s natural inability to access phosphorus forces the plant to rely on an auxiliary mechanism to meet its nutritional needs.
How Do Mycorrhizae Multiply Phosphorus Availability for Olive Trees?
Mycorrhizal fungi form an intimate and intelligent partnership with olive roots. After colonizing the root, these fungi extend a delicate network of microscopic filaments (hyphae) throughout the soil. These hyphae are far thinner than root hairs and can penetrate soil spaces that roots cannot reach. In effect, mycorrhizae greatly expand the absorption surface of the root system and explore a significantly larger soil volume for phosphorus.
Beyond expanding the absorption network, mycorrhizal fungi can liberate phosphorus locked in the soil. They secrete enzymes such as phosphatases and produce mild organic acids that convert insoluble phosphorus compounds into absorbable forms. The extracted phosphorus is then transported through the hyphal network to structures called arbuscules, formed inside root cells, from which it enters the plant’s nutrient stream.
This partnership is fully mutualistic: the plant receives phosphorus and minerals, and in return, supplies a portion of the sugars it produces to the fungus. This stable cooperation equips the olive root with an advanced, highly efficient nutrient uptake system.
How Mycorrhizae Enhance Phosphorus Uptake on a Cellular and Genetic Level
The cooperation between mycorrhizae and roots is not limited to physical access to phosphorus. It also induces significant changes at the cellular and molecular levels. Roots rely on specific proteins—controlled by certain genes—to absorb phosphorus. These genes behave differently when mycorrhizae are active.
In the presence of mycorrhizal fungi, certain phosphorus transporter genes (from the Pht family) become several times more active. These genes are responsible for transporting phosphorus from the cell membrane into the root cells. Increased expression of these genes allows the plant to process and utilize the incoming phosphorus more efficiently. Genes such as Pht1;11 in particular show strong responses because they are specialized for mycorrhiza-dependent uptake pathways.
Greater expression of these genes means the plant not only receives more phosphorus but can also better use, transport, and store it. The result is improved root growth, more balanced shoot development, enhanced energy production, and greater resistance to environmental stress.
Conclusion
Phosphorus is one of the most essential nutrients for olive growth. However, due to the complex behavior of phosphorus in soil and the natural limitations of olive roots, accessing this nutrient becomes a true challenge. Mycorrhizal fungi, as natural symbionts, solve this problem through multiple mechanisms: expanding the absorption surface, releasing locked phosphorus, and activating the plant’s genetic and cellular phosphorus uptake machinery.
For this reason, mycorrhiza is not just an optional aid for olives—it is a biological necessity. Olive trees associated with mycorrhiza develop stronger roots, improved nutrient uptake, stable growth, and increased resilience. Using mycorrhiza—especially during the nursery stage or early establishment—is one of the most effective strategies for ensuring long-term health and productivity in olive orchards.
Resource
Wu T, Pan L, Zipori I, Mao J, Li R, Li Y, Li Y, Jing Y, Chen H. 2022. Arbuscular mycorrhizal fungi enhanced the growth, phosphorus uptake and Pht expression of olive (Olea europaea L.) plantlets. PeerJ 10:e13813 https://doi.org/10.7717/peerj.13813
