Answer: I suspect that the mulch may have been too fresh or "hot" and as a result gave off some harmful gasses when placed close to the plants. The best you can do is pull it away from the stems and out from under the plants and replace it in those areas. Eventually it will decompose and be fine but for the time being there is not much you can do for the damaged plants. Make sure they are watered and fed adequately and wait and see. In the future, if a mulch has a strong odor or an odor akin to ammonia, don't use it. It should be aged about a year prior to use and should have virtually no smell.
There is another possibility and that is that the mulch (or a surrounding area) had been treated with an herbicide and this is what caused the plant reaction. On a hot day, herbicide can drift much farther than you would guess! Unfortunately, the "treatment" is virtually the same.
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