Print PagePerennial wheat and perennial rye are moderate-yielding perennial cereals developed through hybridization of annual crops with perennial relatives, which are currently being bred for higher productivity. However, the necessity for perennials to invest in both reproduction and future survival raises questions of how they deal with resource tradeoffs between these two resource sinks. My research looks at physiological traits that might allow perennial cereals to accumulate more resources than annuals, and thus to be able to support moderate yields while maintaining perennial life history. Specifically, I consider whether high photosynthetic rates, compensatory and sink-regulated photosynthesis, and longer total growing season may allow perennial wheat and perennial rye to support both high reproductive investment and a perennial growth habit. I experimentally increased and decreased crop load (reproductive investment per unit leaf area) in perennial and annual wheat and rye, at three time points during the season, to determine effects of crop load on photosynthesis. Early season photosynthetic rates, chlorophyll, specific leaf area, stored carbohydrate levels and length of growing season were also measured to determine whether photosynthetic and metabolic differences existed between perennials and annuals.
Results/Conclusions
We found that both older and younger plants of perennial rye and perennial wheat maintained 15-20% higher photosynthetic levels than their annual equivalent during the early season. Perennial wheat and rye grow back in the fall, allowing opportunities for additional resource accumulation, and started its second growing season earlier than their annual equivalents: they also flower around 7 days later than their annual equivalents, allowing more time for photosynthesis. Increased crop load in perennial wheat led to consistently 10-15% higher photosynthetic rates, while decreased crop load had no effect; in perennial rye, increased crop load had no effect on photosynthesis early in the season, but a 12-23% increase later on. Crop load manipulation in annual wheat and rye had little effect on photosynthesis, indicating that these perennials have a greater ability than their annual equivalents to compensate for increased resource demand. Our results, while surprising, are consistent with recent studies of perennial relatives of rice, which found very high photosynthetic rates in the perennials, as well as with some research on other wheat/wheatgrass hybrids. These results indicate that high photosynthetic rates, compensatory photosynthesis and longer growing seasons may allow perennial wheat and rye to accumulate large resource pools that allow them to reduce tradeoffs between reproduction and survival.
