Photosynthetic and resource acquisition traits in annual and perennial cereals

Perennial polycarpy and annual monocarpy are conflicting plant life history strategies with differing strategies of resource allocation. However, an ongoing focus of research is how perennials and annuals may differ in terms of resource acquisition rates, as well as in terms of  allocation, as reproductive output is affected both by reproductive allocation and total resource acquisition. Newly developed perennial cereals provide an ideal novel system to test how life history interacts with key ecophysiological traits related to resource acquisition. In a three year study in Hickory Corners, MI we compared annual wheat (Triticum aestivum) to two closely related perennial cereals: perennial cereals (T. aestivum x Thinopyrum elongatum) and intermediate wheatgrass (Th. intermedium). Both first- and second-year plants of both perennial cereals were included, to determine how plant age affected resource acquisition traits. Photosynthetic rates and a variety of related ecophysiological parameters were measured.

We found that perennial cereals, during the early and middle part of the spring, maintained higher photosynthetic rates (A_max) than annuals. First-year wheatgrass plant A_max was 30-50% higher than annual wheat while second-year wheatgrass A_max was 10-35% higher than annual wheat, indicating that age has an effect on leaf-level physiology in this species. Perennial wheat photosynthetic rates were generally 20% higher than annual wheat, a consistent effect maintained across years. The higher photosynthetic rates in the perennial species appear to reflect higher LMA, higher TPU and (in first year wheatgrass) higher conductance and transpiration. Differences in access to soil moisture do not appear to explain all of the difference in photosynthetic rates, and other factors are likely involved.