But are plants likelier to defend themselves against dry air or dry soil? Their results challenge recently held views and were derived from a place with no plants at all — the barren salt flats of Utah and Nevada. Kaighin McColl went to the salt flats in the Western U.S. desert to conduct his research. The Harvard team found their calculations lined up almost perfectly with those previous studies, but with no plants in the salt flats, they knew there had to be another explanation. They think instead that plants respond most acutely to dry soil, an environmental stressor that is known to reduce transpiration and photosynthesis.