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Turfgrass Physiology; Diffusion & Osmosis,

In nature, it is often said that things will tend towards chaos and this is described by a mechanism known as Entropy. In one of his recent TV programs, Professor Brian Cox demonstrated this using a sand castle as his example. Simply put, Entropy says that due to natural movement by wind and weather, sand is highly unlikely to form itself into a sand castle. However, a sand castle is highly likely to be converted to a pile of sand. This is Entropy in action and it seems to say that nature prefers chaos to order; but, whose description of “order” are we using for this?

What if nature was viewing the sand castle as chaos and was instead trying to make order of it by turning it back into a nondescript (as far as we are concerned) pile of sand?

The fact is, that instead of chaos:

Natural systems will tend towards equilibrium.

A common example of this tendency towards equilibrium is the wind we feel on our faces every day. Wind is caused by uneven warming of the earth’s surface. Where one area is warmed more directly, the air above it will rise. This creates a space for cool air. When that cool air rushes in to fill the void, we feel it as wind.

So, although these processes might look like chaos to us (when our sand castle is ruined), it’s really the opposite to chaos that’s happening:

Natural systems will tend towards equilibrium.

This is the way of nature and it informs and drives a lot of what goes on in and around the grass plants on the bowling green.

Today, we will look at two mechanisms of turfgrass physiology that active in our grass plants and soil and that follow this tendency towards equilibrium, without which our turf wouldn’t be able to grow and thrive.

Diffusion

The first of these mechanisms is called Diffusion which is a term you will find throughout science. In broad scientific terms Diffusion explains the process through which molecules mix as a result of their energy and random motion.

In more simple terms related directly to the management of bowling greens, we see Diffusion in three distinct plant growth processes. We can think of it as a process that makes molecules move from an area of high concentration to an area of low concentration.

When we looked at the basics of Photosynthesis, we discovered that our grass plants absorb Carbon Dioxide (CO2) from the air through their leaves. Diffusion is responsible for this process; as the CO2 moves from an area of relatively high concentration (the air) to an area of relatively low concentration (the interior of the grass plant leaf). So Diffusion is a very important process in the cycle of food production for the plant.

The second of these growth processes affected by Diffusion is the way in which soil borne nutrients are moved towards the roots of our grass plants to enable them to be taken up by the roots. These nutrients are present as ions in the soil. These nutrient ions can spontaneously move from a point of higher concentration to a point of lower concentration by Diffusion. This happens in the soil because the immediate root area, once it is depleted (by the roots sucking them into the plant in the soil water), has a lower concentration of the nutrient ions. In this way, the soil around the roots remains in equilibrium with the greater soil mass.

The final of our three examples of Diffusion at work is called Transpiration.

Transpiration is the process by which the plant loses water to the air through the leaves. It is essentially a mechanism by which water evaporates out of the plant to the air. This evaporation happens through the leaf stomata, the same tiny holes in the undersides of the grass plant leaves that are used to take in CO2. This is another example of Diffusion in action, as the water vapour moves from an area of relatively high concentration (the interior of the leaf), to an area of low concentration (the air)  

Transpiration is an essential part of the mechanism by which plants continually take up moisture and nutrients from the soil. The combination of the Transpiration Pull (of moisture out of the plant to the air) and the sucking up of water (and nutrients) by the roots from the soil creates the effect of a continuous pump that moves water and nutrients around the plant to where they are needed. In the process, it gives the grass plants some of the functional qualities required to produce a Performance Bowling Surface.

This sucking up of soil nutrients in soil water solution brings us neatly to the second of the mechanisms that keep this natural balance, Osmosis.

Osmosis

Osmosis is the name of the process in plant growth whereby water molecules move from an area of relatively low concentration (of solute nutrients) to an area of relatively high concentration (of solute nutrients). Osmosis then is the mechanism used by the plant to take up most of the water and nutrients it needs.

Direct root interception of nutrients.

Root hairs make direct contact with nutrients in the soil, but can only impact around 3% percent of the soil volume. Symbiotic relationships with Mycorrhizae can increase the soil volume that roots are able to extract nutrients from.

Mass flow

Grass plants, sucking up water through the processes of osmosis and transpiration also move the nutrients that are dissolved in this water up through the plant. Some nutrients are more mobile than others due to the relative weakness of their electrical charge (or polarity of it) and are usually always available in soil solution. The Nitrate form of Nitrogen is quickly available to plants due to this, as are other mobile nutrients like chloride and sulphur. Calcium and magnesium are only loosely held by the soil and are easily brought into the soil water solution. However, some other nutrients are held tightly to what is called the soil colloid and are much less easily accessed by the plants.

Next time we will look at the process that dictates the availability of soil nutrients.