Perennial Cereals: Life History and Photosynthesis

Jaikumar, N.S. and S.S. Snapp

Presented at the All Scientist Meeting (2011-04-15 to 2011-04-15 )

Perennial wheat, kernza (Thinopyrum intermedium) and perennial rye are moderate-yielding perennial cereals currently being considered as alternatives to annual agricultural crops. The necessity that perennials invest in both reproduction and future survival raises questions of how they deal with tradeoffs between these two resource sinks. My research considers whether high photosynthetic rates and sink-regulated photosynthesis may allow perennial cereals to support both high reproductive investment and perennial growth habits. I experimentally altered crop load (reproductive investment per unit leaf area) in perennial and annual wheat and rye to determine effects of crop load on photosynthesis and seed production. Early season photosynthetic rates were also compared between perennials and annuals.

We found that perennial rye, kernza and perennial wheat maintained 15-20% higher photosynthetic levels than their annual equivalents during early season. Perennial wheat and rye continue to photosynthesize in the fall and have a longer period between emergence and flowering in their second spring, allowing additional opportunities for greater total resource accumulation. Increased crop load led to 10-23% photosynthetic increases in perennial wheat and rye, while photosynthesis in annuals was not affected by crop load; seed size was also more sensitive to crop load in annuals than in perennials, indicating that the perennials are less carbohydrate-limited and have more capacity to compensate for changes in crop load. Our results are consistent with recent studies of perennial rice relatives: they indicate that high photosynthetic rates, greater ability for compensatory photosynthesis and longer growing seasons may allow perennial cereals to accumulate large resource pools that allow them to reduce tradeoffs between reproduction and survival. These adaptations could allow perennial cereals to be selected for moderate seed yield, while maintaining perennial life history.

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