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Connection to Biology Plants Seeing Red V egetable growers have long used plastic sheeting (mulch) in the rows between plants to retain moisture, retard weeds, and provide warmth for the roots of young plants. It is now becoming apparent that the color of the plastic used has a significant effect on the plants. How can this be? Why does the color of their mulch matter to plants? Michael J. Kasperbauer of the Department of Agriculture’s Coastal Plains Soil, Water, and Plant Research Laboratory in Florence, South Carolina, has spent most of his 40-year career studying the responses of plants to various colors of light. Plants use proteins called phytochromes to sense light in the red (640–670 nm) and the far red (700– 750 nm) ranges. Although far red light is not photosynthetically active—it does not provide energy for plant growth—this light gives plants important information about their environment. For example, green leaves reflect a lot of light in the far red region. Therefore, when a given plant’s phytochromes sense a high ratio of far red to red light wavelengths, the plant knows that it has many neighbors—many other plants around it are reflecting red light. Because these neighbors are competitors for the lifegiving light from the sun—their leaves will shade neighboring plants—a plant sensing this situation tends to direct its growth above ground, producing a taller, thinner structure that can compete more successfully for sunlight. In fact, Kasperbauer and his colleagues have found that by using a red plastic mulch they can fool tomatoes into “thinking” they are crowded, leading to faster seedling growth and eventually producing earlier, larger fruit. Since the opposite effect should benefit root crops, the Department of Agriculture scientists have Red plastic mulch being used in an experimental plot. grown turnips in soil covered by an orange mulch. These turnips proved much bigger than those mulched with black or red plastic, presumably because of increased reflection of red light by the orange plastic. The increased red light signaled no significant competition for light from other plants, encouraging growth of roots rather than aboveground foliage. Besides affecting the plant’s structure, the type of reflected light influences the nature of the waxy coating on the leaves and the taste of the plant product. Surprisingly, the color of the reflected light also seems to affect the plant’s response to insect damage. This research shows that plants are very sensitive to the type of red light that bathes them. Our plants may benefit from rose-colored glasses as much as we do.