It is the question of balance between moisture intake through the roots vesus the loss due to transpiration through the leaves.
If the moisture inatke is less because of less amount of roots or less amount of moisture in the soil and the moisture loss through transpiration during the hotter part of the day exceeds the the intake, then the leaves will show some kind of curl or droop. As the heat subsides, the moisture loss decreases and the leaves bounce back because of the moisture intake. It is normal. Just make sure that the soil does not dry up otherwise the the excess transpiration loss can cause the leaves to dry up and drop.

Some more information would be helpful...

How long ago did you plant the trees? Which variety(ies) do you have? Where are you located? What type of soil? How frequently do you water? Are your trees mulched? etc.

My trees are growing in full sun north of Austin, TX. This Month our lowest high temp was 97F. We've had as many days above 100F as we have below. My trees (including cuttings rooted this spring) are showing no signs of stress from the heat... even having gone the past 6 days without water.

Shade isn't necessarily the answer if there is another issue.

~james

Agreed - the first suspect would be over-watering.

Al

When young fig trees,are ,sensitive to over 90*F,Temperature.
It will burn ,(scorch),some leaves(top new ones).
But it will be a mistake to plant them in shade in Zone 7,because later in Life they will adapt and fruit abundantly in the sun.
Yet they will not be productive in the shade.
That is my experience.
If plant very young and recently planted consider shading it ,when temp. will be over 90F,using an umbrela(old),or a patio umbrella.

Again agreed. The top of the tree will take much higher temperatures (120*+) and tolerates/prefers full sun. The rub comes in the form of soil temperatures. Once (actual) soil temperatures reach 90* and start to climb, root function/metabolism drops off sharply. Shading the container, or even the pot-in-pot or pot-in-trench techniques will go a long way toward moderating high root temperatures. Watering at midday (when needed - not on a schedule), can also be helpful.

Often, growers see their trees wilting in the sun/heat. If the soil is damp, something has compromised the plants ability to move water from the roots to the canopy. That can be an undeveloped root system, but that is usually only the case for a short period after transplanting. More often, it occurs from compaction and the accompanying excessive water retention of heavy soils.

Soils that retain perched water for more than a couple of hours kill roots - period. The longer a fraction of the soil remains saturated, the greater the number of dead roots. When you kill roots or impair their ability to function because of low O2 levels, the roots cannot do their job, which in part is moving water and nutrients to the canopy. Not only does the tree wilt, but growth is greatly affected as well.

Porous soils that are durable, drain well, & support no (or little) perched water, will always yield superior results to heavy, peat-based soils from a bag. The ongoing price you pay for improved growth/vitality lies in the need to water more frequently when using that type of soil.

Al

These young trees were shipped to me bare feet and I transplanted them about 3 weeks ago. I think the root still in shock. I made the mistake of planting them in the sun immediately. A lesson I learned. I should planted them in pots in half shaded area then put them later in full sun. I have one tree which I potted in shaded area is doing very well.

You did the right thing by planting in full sun, but you may need to be more diligent in watering or more patient in waiting for them to recover from the transplanting. A temporary shade structure (as Herman suggests) might offer some short term relief until the plant gets it's feet under it.

A good part of what I said about soils applies only to containerized plants (sorry), so you can disregard, unless you planted in very heavy clay & amended the planting hole with OM, in which case what I said could be applied to your situation.

Al