We’ve had a few scorching days here in Las Vegas and today it finally made the record books:
… Record highs broken or tied across the Las Vegas forecast area today… …
The high temperature at McCarran International Airport here in Las Vegas this afternoon reached 116 degrees. This reading tied the record high for the date last set in 1985. The 116 degree record today was one degree shy of the all time record high for Las Vegas which was 117 degrees first set on July 24 1942… and then again on July 19 2005.
Elsewhere… desert rock Nevada broke their daily record high of 104 degrees set in 2003 with a high of 112 degrees.
In California… Bishop had a high of 108 degrees breaking the old record of 106 degrees set in 1985. Daggett Airport reached a high of 118 degrees breaking the previous record of 113 degrees set in 1991.
Humidity levels have been in the single digits so it feels a few degrees cooler but even though it’s a dry heat, it’s very uncomfortable to be outside. Such low humidity, lack of rain (I’ve measured only 0.20 inches since January 1), is brutal for plants which need to transpire water to photosynthesize. So far, I’ve lost a pomegranate tree and a Lantana that I transplanted this spring.
Plants have evolved some interesting mechanisms to reduce water loss in hot, dry and bright conditions. When conditions are hot and dry, plants will close the pores on their leaves to prevent water loss. This causes problems for the plant because then it reduces the inflow of carbon dioxide (CO2) into the leaf and oxygen (O2) begins to build up in the leaf. CO2 is the raw material used by plants to create sugars. O2 is a byproduct that needs to be released into the air. Too much O2 can make the metabolism use up energy rather than store energy (photorespiration).
6 CO2(gas) + 12 H2O(liquid) + light ? C6H12O6(aqueous) + 6 O2(gas) + 6 H2O
There are two ways plants have adapted to solve this problem and continue to thrive in hot and dry conditions. C4 plants such as sugar cane and corn capture and store CO2 using an enzyme and they seperate the CO2 in a different part of the leaf. This separates the metabolic pathways and prevents them from interfering with each other. Since many different groups of plants have separately evolved this system of photosynthesis, this is an example of convergent evolution.
The other method that plants use to photosynthesize in hot and dry conditions is called CAM metabolism. This is common in cacti and succulents. This metabolism separates the metabolic cycles by time instead of spatially. The parts that require oxygen and CO2 exchange with the air occur at night when temperatures are cooler and water losses are lower. This metabolism has the benefit of saving lots of water at the expense of being a much slower growing plant.
