Turfgrass Temperature Stress, Part 1: Optimal Temperatures

If you have not read the previous post highlighting a recent article published in the Wall Street Journal, it gives some basic information about how heat has declined the conditions of many courses this year.  Over the next few posts, I am going to expand on what was printed in that article and try to give some more detailed information about heat and how it can effect the turf conditions. And, moisture plays a big part in this.

Like many living things, there is a set of environmental criteria that will provide turfgrasses will optimal growing conditions.  Unfortunately nature lacks any remorse for our situation and many times conditions lay outside of the optimal criteria.  When the environmental conditions-in the case of this post-high temperatures, are outside of that criteria, turf lacks the ability to sustain normal growth.

Warm-season and Cool-season grasses

There are 2 types of grasses, warm-season grasses and cool-season grasses.  As you can probably figure out on your own, warm-season grasses can tolerate high temperatures and cool-season grasses are better suited for cooler climates.  We have cool-season grasses on the golf course.  Optimal temperatures for cool-season grasses are 65-75 degrees F for shoot growth and soil temperatures of 50-65 for root growth.  Optimal temperatures for warm-season grass are 80-95 for shoot growth and soil temperatures 75-85 for root growth.  The plants are able to survive in temperatures outside of these parameters, however if those temperatures exist for an extended period of time, the plant will begin to decline.

To establish an understanding of the differences between these two grasses and their response to heat, and other environmental factors, an understanding of their differences in photosynthesis is needed.  Turf gathers carbon dioxide from the air through the process of photosynthesis as a start to the many processes in uses to stay healthy.  When carbon dioxide is collected from the air, it first attaches itself to an enzyme that is then moved through the plant.  This enzyme is different between cool-season grasses and warm-season grasses, with cool-season grasses getting the short end of the stick.  The enzyme in cool-season grasses can also capture oxygen, when this happens, a useless compound is formed and given off by the plant (this process is called photorespiration).  During periods of intense sunlight and high temperatures, this process of diverting potentially useful energy is taxing on the root system, shoot growth, color and ultimately plant health.  The enzyme that exists in warm-season grasses cannot bind to oxygen so in the presence of high temperatures and sunlight the capture of carbon dioxide is not decreased.

This wasteful process of photorespiration decreases cool-season grasses ability to sustain the processes that are necessary to generate new shoot growth and new root growth.  To add insult to injury, the optimal temperature range for root growth is lower than the range for shoot growth.  This means that the roots of the turf plant are more sensitive to extreme soil temperatures.  Recently, we have regularly found soil temperatures in the low 80s on the course, coupled with air temperatures in the 90s.  If soil temperatures exist outside the optimal range, this can cause root death and a decrease in the amount of roots available for the plant to capture water.

So this brings us back to the beginning of the post-how moisture plays a part in this.  Hopefully with my next post I can make sense of how water fits in with all of this.