Early Pioneers of Photosynthesis Research

Abstract

Before the early researchers on plant nutrition worked out the fundamentals of photosynthesis, plants were believed to obtain their nutrients from humus in the soil. Then, over a period of about 200 years, a succession of investigators supplied pieces of the puzzle that eventually allowed formulation of the overall equation for photosynthesis. Jan van Helmont, in the early seventeenth century, concluded that plants are composed not of humus but of water that has been transmuted into plant substance. In the early eighteenth century, Stephen Hales found evidence that “air” was a component of the plant body. The involvement of water and air remained conjectural, however, until the late eighteenth century, when the new chemical theories of Antoine Lavoisier allowed the understanding of plant nutrition to advance. Joseph Priestley found that plants and animals are interdependent through their complementary effects on the atmosphere, and his discovery of oxygen was important for Lavoisier’s formulation of the new chemistry. Jan Ingen-Housz discovered that plants need light in order to release oxygen and that the green color of plants is important. Jean Senebier showed that carbon dioxide is also essential. Nicholas de Saussure, with his embrace of the new chemical concepts and his well-targeted experiments, was able to assemble a more comprehensive picture of plant nutrition, encompassing carbon dioxide from the atmosphere, water and mineral nutrients from the soil, and light from the sun. In the mid-nineteenth century, Robert Mayer completed the outline of the overall scheme with his insight that photosynthesizing plants convert light energy into chemical energy. Some of the important eighteenth-century photosynthesis pioneers were overshadowed by the drama of the profound changes shaking chemistry and are less well known than they should be. Some of their discoveries are misattributed or misstated in the literature, even down to the present day.