Turfgrass Response to Stress

Drought stresses golf course

In golf course management, maintaining optimum quality playing surfaces requires a high level of management expertise. To achieve this, finely balanced nutritional and irrigational inputs, and numerous cultural practices are required. While all these practices allow for the high standards expected, it also means our turfgrasses are often on a knife edge, balanced between healthy plants and those stressed from low inputs and disruptive management practices. Adding to this are environmental factors beyond our control which cause numerous abiotic stresses. 

Turfgrass stress can be caused by numerous factors, let’s differentiate between biotic and abiotic stress. Biotic stress is caused by living organisms such as pathogens, insects, herbivores and of course humans! Abiotic stress is caused by a non-living factor, and this is what we’re concerned with today.

How can you tell if the problem is abiotic and not biotic?

Abiotic damage occurs on numerous plant species while biotic problems are more limited to a specific species. 

  • Abiotic damage does not spread to other plants over time, biotic diseases can spread throughout a single plant and neighbouring plants of the same species.
  • Abiotic stress does not show presence of disease signs whereas biotic diseases sometimes show physical signs of a pathogen, like fungal growth, nematode cysts, or the presence of insects. 

Abiotic stress can result in poor quality surfaces due to growth inhibition, damage to cell structures and metabolic dysfunction. Often it is from extreme environmental conditions, such as high or low temperatures, soil compaction, excessive or low light, flooding, or deficient water. Sometimes it can be caused by nutrient deficiency, incorrectly applied pesticides or fertilizer, even excessive traffic. It’s worth noting that damage can often look very similar to biotic stress, making diagnosis difficult, and that plants suffering from abiotic stress are in most cases significantly more susceptible to biotic stress. 

As we are now in the summer season abiotic stresses such as heat, drought and salinity, are probably the major cause for concern. Heat and drought stress are two major limiting factors in the growth and quality of turfgrasses and they are becoming more relevant as water is becoming increasingly limited for irrigation and temperature increases with global warming. These stress factors on their own can lead to a decline in turfgrass quality and detrimentally impact turfgrass health but when combined can have devastating effects. Heat and drought stress are more common with cool-season turfgrasses, but warm-season turfgrasses, as well as other drought-tolerant turf species can also be susceptible to injury.  

Heat Stress

Cool-season grasses grow most actively within the temperature range of 60 to 75 ° F (16 to 24 °C) and temperatures exceeding this can lead to a reduction in metabolic rate and a decline in turf health. Warm season grasses tolerate a higher temperature range of 80 to 95 ° F(27 to 35 °C) but suboptimal temperatures can also limit their growth. In both turfgrass types, heat stress injury is associated with photosynthesis inhibition and various other physiological changes such as limited water and nutrient uptake and hormone synthesis and drought stress are more common with cool-season turfgrasses, but warm-season turfgrasses, as well as other drought-tolerant turf species can also be susceptible to injury.  

Wilting, heat tracking, and browning of turf can be observed, and the grasses can become dormant to conserve energy. While in dormancy, turf is more susceptible to weeds, pests and various diseases. However, even though it may appear dead, it will come out of dormancy and green up with regular watering once temperatures begin to drop. 

High air temperature is not the only factor contributing to heat stress as excessive rootzone temperatures can also be very detrimental to turf health. When soil temperatures exceed 70°F (21°C) root mass in cool-season grasses can be negatively impacted by more than 50%. Both cool- and warm-season turfgrasses perform best at specific temperatures, and ensuring soil moisture is adequate is vital, as without moisture in the soil, there’s the risk of drought stress and the synergistic effect of heat stress and drought can prove devastating.  

Drought Stress

Drought stress goes hand in glove with heat stress and although warm-season grasses can withstand the heat of summer when compared to cool-season grasses, both are subject to drought stress and injury without water. Drought stress occurs when the amount of water lost in transpiration is greater than the amount of water available and will lead to a decrease in photosynthesis and plant respiration, and an increase in plant temperature. Combined with excessive temperatures, the risk of death is significant.

Symptoms of drought stress can vary depending on the turfgrass species and the severity of water limitation. Typical symptoms would be turf discoloration, leaf blades folding lengthwise, giving the appearance of thinner turf, the cell walls losing elasticity resulting in foot printing.  

Salinity

Soil salinity can be a major turfgrass stressor and it is highly connected with drought and heat stresses of turfgrasses. Salts are added in standard application of fertilizers and soil amendments, even some pesticide applications. Recycled water for irrigation and regular fertilization are also significant contributory factors. Many areas have legislative restrictions  on the source and use of irrigation water, restricting freshwater use for turfgrass leading to turfgrass managers having to use non potable, recycled, and saline water sources.  

The presence of dissolved salts in non potable water can lead to saline or sodic soil conditions. Turfgrass exhibit many morphological, physiological, and metabolic responses to salinity stress, such as leaf scorch, wilting and restricted root growth, leading to a significant reduction of turfgrass quality.

Turfgrass responses to abiotic stress

Turfgrass responses to abiotic stress is extremely complex and occurs at physiological, morphological, and molecular levels. 

  • Physiological responses include alterations in cell membrane stability impacting their permeability and stability. Increased antioxidant enzyme activity, boosting the activity of antioxidant enzymes like superoxide dismutase, catalase, and peroxidase to counter  oxidative stress from reactive oxygen species. Accumulation of stress-related compounds such as proline, soluble sugars, and proteins. Reduction in chlorophyll content affecting photosynthetic efficiency and overall plant health, and changes in metabolic processes affecting nutrient absorption, energy production, and growth.
  • Morphological responses involve leaf and root growth inhibition, alterations in leaf size, shape, color, and structure, and impacts on root development root growth and structure, affecting nutrient uptake and water absorption. 
  • Molecular responses include changes in gene expression activating or deactivating specific genes linked to stress tolerance. Protein synthesis triggering the production of stress-related proteins that safeguard turfgrass cells from damage and signaling pathways to regulate responses to stress.

By exhibiting these responses, turfgrass can adapt to and survive under various stress conditions, maintaining its health and quality. 

How to alleviate the problem

To help prevent and/or aid stressed turfgrass and help it recover, there are several strategies and practices you can implement:

Adequate Irrigation: Provide proper and timely irrigation to maintain soil moisture levels and prevent drought stress. Water deeply and infrequently, ensuring the entire root zone receives moisture. Avoid overwatering, which can lead to issues like root rot. 

Use of Surfactants: Incorporate surfactants in your irrigation and precipitation inputs to optimize water absorption and distribution in the root zone, ensuring efficient use of water resources. 

Nutrient Management: Maintain a balanced nutrient program to supply essential nutrients for turfgrass health. Consider using elements known to facilitate stress responses, such as humic acids, kelp extract products, and phosphite.  

Silicon Applications, in particular, have been found to have positive effects in mitigating salt stress in various turfgrass species, significantly so in salt-sensitive turfgrass species such as Lolium perenne and Festuca arundinacea. Research shows benefits of Silicon by impacting chlorophyll content and regulating ion uptake, increasing antioxidant enzyme activities and decreasing oxidative stress in plants.  

Plant Growth Regulators (PGR): Consider using PGR treatments to enhance turf performance during stress conditions. PGRs can help maintain photosynthetic activities and improve cellular hydration. 

Cultural Practices: Adjust mowing frequency and height, reduce foot and machinery traffic, and minimize topdressing during stressful periods. Implement practices like aeration and dethatching to promote turf health. 

Turfgrass Preconditioning: Maximize photosynthesis in turfgrass to enhance carbohydrate storage and rooting, enabling better heat tolerance and overall summer survival.

In summary, abiotic stress conditions can inhibit the growth and development of turfgrass leading to a decline in turf quality, root length, and topgrowth. Heat, drought and salinity are major abiotic stressors during the summer months and while turf managers can do much to limit this damage, plants themselves will also respond! Turfgrasses will initiate complex defense mechanisms, producing secondary metabolites, leading to physiological and morphological responses at the molecular level. We can help this process by ensuring adequate irrigation, use of surfactants, targeted nutrient input which include know stress reduction elements such as Silicon, PGRs, and a range of stress preventing cultural practices. 

This was just a brief outline of abiotic stress and how we can help turfgrass respond to it, hopefully it was of interest, and remember there’s a lot of helpful data readily available out there online!!

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