Research interests Photosynthesis and plant growth underpin life on Earth and support crop production that feed billions. However, productivity varies more than tenfold among plants because external environmental resources become limiting in particular places or times, and internal physiological processes differ in each species and crop variety. Our research aims to understand how these environmental and internal factors limit plant productivity, how evolution and crop breeding have overcome the limitations, and the importance of productivity for the biology of plants in wild ecosystems and cultivated fields. Following a long tradition in plant environmental physiology, our work spans scales ranging from genes to the globe, and utilizes a broad spectrum of approaches. Right now, we have a particular emphasis on comparative experiments and global geographical analyses, though we’re beginning to broaden out to do more fieldwork. We are doing work on the evolution and ecology of C 4 plants, the domestication of crops, the control of growth by source and sink strengths, and the recruitment of trees into grasslands.