The Role of PAR+ and Other Biostimulants in Plant Health

PAR+ (5-aminolevulinic acid) is a precursor in the biosynthesis of chlorophyll, heme, and other organic molecules that play crucial roles in various physiological and biochemical processes, particularly in photosynthesis, respiration, and stress response.

By enhancing chlorophyll production, PAR+ improves photosynthetic efficiency, which leads to:

• Increased carbohydrate production (glucose, starch) due to more efficient light energy capture

• Improved energy availability (ATP, NADPH) for metabolic processes

• Enhanced stress tolerance through better energy status and the role of heme in antioxidant enzymes (like catalase and peroxidases).

This directly translates into better growth, colour, and recovery, especially under suboptimal conditions such as low light, heat, cold, salinity and disease pressure.

Turfgrass Stress

Before we get further into the role of plant biostimulants, let’s examine how turfgrass plants deal with stress caused by environmental and pathogen factors.

Most turfgrass managers understand the concept of ‘plant stress’, such as when under drought, heat, freezing, disease and excessive wear conditions, but how many understand what is happening inside the plant that affects its growth and health?

Healthy Growth starts with photosynthesis…

Fig 1. Photosynthesis occurs in plant leaves.

Healthy turf growth is stimulated by carbohydrate production through photosynthesis (Fig 1); but, on turfgrass surfaces, photosynthesis is restricted and carbohydrate production is limited.

In a healthy grass plant, there is a flow of carbon into the plant, which is converted to carbohydrate and proteins. Carbohydrates are excreted through leaves (the phyllosphere) and roots (the rhizosphere), which feed the host of microbes inhabiting these environments. In fact, up to 60% of CO2 absorbed by the plant (Fig. 2) and used in photosynthesis comes from the soil from respiration of plant roots & soil microbes. Low soil CO2 = poor plant growth

Fig 2. Carbon flow in a healthy plant

Turfgrass plant heath, however, is severely compromised when managed to produce playing surfaces. The everyday operation of mowing causes the plant to divert carbon energy into leaf and root growth, leaving little left for the manufacture of secondary metabolites that create disease defence mechanisms, environmental stress & pest/disease resistance, and recovery from wear. Soil microbial populations are also severely limited due to reduced root exudates, resulting in low nutrient mineralisation and protection against disease and pest attack (Fig. 3).

Fig. 3. Compromised carbon flow in mown turf

In addition, environmental factors such as lack of light and extremes of heat or cold temperatures interrupt the process of photosynthesis and, consequently, reduce carbohydrate production.

When plants are under stress, they produce Reactive Oxygen Species (ROS), also known as Free Radicals, which interrupt or damage metabolic processes.

Fig. 4 Balanced plant metabolism (homeostasis)

Reactive Oxygen Species

The production of Reactive Oxygen Species (ROS) in plants under normal growth conditions is low as the plant is able to produce sufficient antioxidants to scavenge ROS (Fig 4.). In response to various environmental stresses, however, ROS are drastically increased in plants (Fig. 4).

Fig. 5 Effects of envirnmental stress on ROS activity.

The enhanced production of ROS during environmental stresses can pose a threat to cells through the leakage of electrons from energy chains during photosynthesis, or by "stealing" electrons from the lipids in cell membranes. When the level of ROS exceeds the defence mechanisms, a cell is said to be in a state of “oxidative stress.” (Fig.5 & 6), disturbing the normal balance (homeostasis) in the intracellular environment.

Fig 6. Plant under stress and unable to balance Antioxidant production with ROS activity.

Types of ROS

There are four main types of Reactive Oxygen Species, namely, singlet oxygen (1O2), hydrogen peroxide (H2O2), superoxide radical (O2•−), and hydroxyl radical (OH•) and various stresses will trigger different ROS.

Plants respond to ROS by collaboratively using one or more antioxidants at the same time, and a lot of energy is spent by the plant in defending itself. The turfgrass surface can suffer as the plant puts energy into protection at the expense of growth, such as recovery from wear. The turfgrass manager can utilise a variety of treatments that help to increase photosynthesis, enhance antioxidant activity, increase energy reserves and protect cell components from ROS attack. The development of plant biostimulants over the past twenty years has provided a solution to plant stress.

The Role of Biostimulants in Reducing Plant Stress

The science of biostimulants has hugely developed over the past twenty years, showing that applied formulations increase:

·       nutrient availability

·       soil water-holding capacity

·       antioxidant activity

·       plant metabolism in stress conditions

·       the production of chlorophyll

Just small concentrations applied to the leaves or soil have proved to have a dramatic effect on plant growth and health. Biostimulants are corrective treatments that enhance plant health and should not be confused with fertilisers that correct nutrient deficiencies. Biostimulants help to balance the plant’s metabolism and results in the release of excess metabolites through the roots for microbial activity in the rootzone. This is Nature’s way of a healthy plant/soil interaction vital for providing high quality turfgrass surfaces.

How do we use biostimulants?

There is a confusing plethora of plant biostimulants available to turfgrass managers, all claiming to have properties that help in producing better turfgrass surfaces.

Biostimulants have diverse modes of action. For example:

• Increasing photosynthesis with PAR+

• Seaweed extracts (e.g., Ascophyllum nodosum) contain alginates and polysaccharides that stimulate disease and pest defence mechanisms, stabilises cell membranes, increases nutrient transport and regulate water uptake and transport.

• Humic and fulvic acids improve nutrient uptake by modifying root architecture and enhancing soil microbial activity.

• Amino acids and peptides serve as osmoprotectants and metabolic precursors beyond that the plant produces itself.

• Silicon-based products strengthen cell walls, offering mechanical protection against pathogens.

• Chitosan and phosphite stimulates the plants natural defence mechanisms

• Microbial inoculants can help to remediate poor rootzone conditions, ward off pathogenic organisms and help in making nutrients available to the plant (mineralisation)

• Protein hydrolysates provide a food source for soil microbes.

They all have a use depending on the sport being played on the playing surface, turfgrass species used to prepare the surface, and the environmental conditions, e.g. enclosed sports stadia or open golf course.

The best approach to developing a nutrition and biostimulant programme is to think of it as building a system:

1. Base Layer (Core Metabolism): Focus on enhancing photosynthesis and metabolic efficiency using PAR+.

2. Support Layer (Stress Management & Nutrient Efficiency): Seaweed extracts, amino acids, humic acids, microbial inoculants and protein hydrolysates to improve stress tolerance and nutrient uptake.

3. Targeted Layer (Specific Stress/Challenges): Silicon, phosphite, chitosan and microbial inoculants, applications based on seasonal stresses (e.g., drought, disease pressure).

Contact us at South West Agronomy for help on how to create a biostimulant programme that enhances all your hard work.