In the heat and drought of west Texas some fruit trees usually seem to have curled up leaves. The worst seems to be persimmon and apples. I haven’t seen much on pears, apricot, plums, or grapes. Peach/nectarines leaves normally start out folded up and can be curled until the leaf fully expands. Here are pictures mostly outdoor trees, some in the greenhouse.
We had several weeks near 100F but not much hotter than that. My soil seems a bit weak on water supplying ability. It’s a clay loam, not sand, but it seems hard to keep outdoor trees fully stress free.
The stress on my apples and persimmon doesn’t seem to damage the fruit crop or cause issues with plant hardiness or return cropping. Apples and persimmon look awful, but the trees crop heavily every year. No biennial bearing. That says the trees aren’t short on carbohydrates. So, they must be functioning well in terms of photosynthesis.
Self-protective tropisms are common in the plant world. My persimmons curled leaves during the recent heat and dry weather. We had rain for 2 days and now they have all uncurled and look normal.
Corn growing in this area is not so lucky. Most of the corn has dry brown lower leaves with a small amount of green near the top of the plant. Maize is a wonder plant, but it does not have effective drought tolerance mechanisms. Sorghum by comparison is thriving in the heat.
In west Texas sorghum is frequently grown dryland. Sorghum can produce a good crop if the soil is wet to 4ft or more at planting plus 2-3 inches of rainfall per month in summer. Yield would be 4-5,000 lbs per acre. Half that in a dry year. None if really dry.
Corn is only grown with irrigation, usually about 2-3 inches of applied water per week for a good crop. Yield should be 10,000 lbs per acre or more.
This thread is an invitation to discuss tropisms and adaptations for heat and cold.
If we look around, we can see plants that adapt to their local growing conditions. Some are adapted to temperate cold climates which would for example include most of the U.S. and Canada. Features of temperate cold plants include C3 photosynthesis which is most efficient at temperatures between 60F and 80F. Plants in this group may have adaptations for heat and drought which can include ability to close stomata to conserve moisture and ability to curl leaves to further limit moisture loss when roots are stressed and can’t slurp up enough water. Most deciduous trees fall into this general group. Why deciduous? Because dropping leaves for winter is a survival trait much needed in the climate where they grow.
Some plants are hot semi-tropical adapted such as maize which originated in the Balsas river valley of Mexico. It uses C4 photosynthesis which is highly efficient at temperatures from 80F to 100F. It’s Achilles heel is that it did not originate in a drought prone area therefore it has few adaptations to deal with drought. Maize can curl leaves which limits transpiration. The only other major drought adaptation is that some varieties produce a huge root system which is more efficient at absorbing water. Unfortunately, modern high density planting methods mean large root systems are of limited value because too many plants are trying to absorb a limited amount of water. Maize is not a winter adapted plant though you might be surprised when I say there is a species of teosinte - parent of maize - that is a true perennial.
Next we can point out some truly unique plants such as purslane which uses CAM photosynthesis. This is a very specific adaptation to a hot dry climate as purslane closes stomata in high temps and drought yet still absorbs sunlight with relatively high efficiency. Most of the growth of purslane occurs at night when stomata can open and the plant can transpire while using energy stored by CAM photosynthesis during the day.
And now we can talk about sorghum which is a member of the poaceae (grass) family, the same family as maize. Sorghum is a hot tropical drought adapted species which has so many specialized adaptations for growing in dry conditions that it is mind bending. Sorghum can suspend photosynthesis, curl leaves, close stomata, and grow day or night whenever it can slip in edgewise to do so. It has a huge root system by comparison with the size of the plant above ground and can push roots deep enough to find water if it is available.
There are other species with unique adaptations such as dropping leaves and photosynthesizing only from bark/skin on limbs and branches. Many cacti have this ability. When rare rain falls, these plants may go through an explosion of growth producing leaves, flowers, and fruit/seed in a few brief days while water is available.
Lets go back to persimmon again. It originated in the tropics. Most members of Diospyros live in the tropics as for example the ebony tree Diospyros ebenum. So how do we explain persimmon? It is a tropical plant that moved north and gradually accumulated adaptations for cold climates such as dropping leaves for winter. It retains tropical and drought adaptations of curling leaves, closing stomata, and extremely efficient absorption of water by the roots. Diospyros is one of the most varied plant groups on earth given ability to live in a wide range of climates from deserts such as in Mexico, rain forests such as India, and temperate cold climates such as D. virginiana in North America.
