The mechanisms of plant nutrition are more complex than simple ionic absorption — and are better understood than ever
How do plants absorb and transport nutrients?
Read any textbook on agronomy and plant nutrition and there is likely to be an opening chapter or paragraph describing how plants absorb nutrition. This section will describe how plants absorb ions (positively or negatively charged atoms) from the “soil solution,” transport these ions through the plant’s vascular tissue and transfer them into cells using “ion channels” and “pumps.”
This model of plant nutrition has been developed with lab research and mathematical modeling, generally without considering the impact of rhizosphere and phyllosphere biology. It is true that plants have the capacity to absorb and utilize nutrient ions as their primary nutrition source. After all, this is how plants are supplied with nutrients in hydroponic environments.
However, it has been obvious to close observers that this model of plant nutrition does not adequately describe how plants get nutrition in wild ecosystems. Unfertilized soils often contain very low levels of soluble ions — not nearly enough to support the nutritional requirements of the abundant vegetation growing on these soils.
And then, of course, there are those plants growing in the absence of any soil. Many of us have observed trees growing out of hard rocks and cliff faces, with zero soil present. These trees often reach impressive size and can be expected to be decades or even centuries old. Even when we assume they only grow very slowly, the question remains: where do they get access to the substantial quantities of soluble ions of nitrogen, phosphorus, potassium, calcium and magnesium needed to regenerate their leaves each year?
I would propose the answer is: they do not absorb nutrition in the form of soluble ions. Further, I would suggest that plants in undomesticated ecosystems absorb only a tiny fraction of their nutritional requirements as soluble ions from the soil solution.
The fundamental problem with the current model of plant nutrition is that it does not consider any possible contributions of soil biology. When we use this contemporary model of plant nutrition for agricultural crops, we are using a glorified hydroponic model, which makes no sense for biologically active soils. It may make sense in the context of soils that are largely biologically dead or inactive. But why would we choose to manage plant nutrition with a model that assumes dead soil? A model that assumes dead soil will create a dead soil.
The textbooks will have to be rewritten. We are living in the moment where science is describing how plants in biologically active ecosystems absorb nutrition from microbes rather than from simple ions. Science is describing how plant cells can absorb entire microbes and microbial metabolites through endocytosis directly into the cell, without any need for mathematically impossible “ion channels” and “ion pumps.” Science is describing how living microbes can be transported through the plant’s vascular system to provide microbial nutrition at any location within the plant. We now have the science to describe how plants can absorb the significant majority of their nutritional requirements from microbes and require little or no nutrition in the form of simple ions from the soil solution.
There are two areas of emerging science, and one that is well established, that we now need to be familiar with to accurately describe how we can produce the highest-yielding, best-quality crops with the smallest or no applications of simple ion fertilizers, which depletes a soil of its native biological fertility.
The first area is the work of Dr. James White and his colleagues on rhizophagy. They describe a previously unknown mechanism of how plants absorb live bacteria directly from the soil. This mechanism is in addition to the known function of fungi serving as nutrition pipelines and channeling bacteria directly into plants. These mechanisms describe how plants can absorb all of their nutritional requirements in the absence of soluble ions in a water solution. You can find an overview of James’ papers and presentations at johnkempf.com/tag/rhizophagy.
The second topic is the work of Gerald Pollack and his colleagues on the fourth phase of water, called EZ (exclusion zone) water. This work adds a critical piece to our understanding of microbes as the primary source of plant nutrition, as it describes how plants can transport live bacteria through their vascular tissue to all locations in the plant. In addition to The Fourth Phase of Water, I highly recommend Pollack’s Cells, Gels and the Engines of Life. Pollock’s work does not just influence our perspective on plant nutrition — it completely revolutionizes the very foundations of cell biology and is relevant for nutrition management of all organisms.
The third subject is the process of endocytosis, which describes how cells can absorb large molecules or entire bacteria by engulfing or enveloping them and utilizing their compounds as a source of nutrition. Endocytosis has been recognized as a foundational aspect of cellular nutrition and biology in animal cells for decades but has historically not been considered an important part of plant nutrition. Understanding that plants can absorb large quantities of living bacteria and transport them to all tissues indicates we obviously need to rethink this.
Crops express themselves quite differently when the majority of their nutrition is coming from microbes rather than from simple ions. The absorption of simple ions actually increases a plant’s water requirements and reduces its drought resiliency. As an example, for each nitrate ion absorbed, plants require three molecules of water just to convert nitrate to amino acids.
There are other obvious challenges of relying on water-soluble nutrients. What happens when there is inadequate water? As the water disappears, nutrient availability also disappears. This is mitigated with a biological-based approach to plant nutrition, as it is well established that biology can access thin films of water on soil particles and provide water that plant roots cannot access on their own. When there is excessive water, the water-soluble ions leave with the water and flow into rivers and streams.
Plants that absorb nutrition from microbes require less water, while simultaneously being able to access limited soil water better. This explains why soils with active biology consistently outperform contemporary agronomy management systems in stressed conditions, particularly in drought stress.
The agronomy of the near future will be based on the sciences of rhizophagy, EZ water and cellular endocytosis as the primary mechanisms of plant nutrition, simply because this model delivers consistently superior crop performance.
If you learned about the absorption of simple ions as the primary mechanism of plant nutrient absorption, it would be wise to mentally assign this model to the dustbin — and actively seek to learn about rhizophagy, EZ water and endocytosis.
John Kempf is the founder of Advancing Eco Agriculture and is the executive editor of Acres U.S.A. magazine.
