Effects of whole-plant age on photosynthetic traits in a perennial grass

Background/Question/Methods

The effects of aging and development on physiological processes, particularly those involving carbon and nutrient uptake, has profound effects for life history, ecosystem function and plant productivity. While many previous studies have investigated how photosynthetic traits change with whole-plant age (as distinct from leaf age) in woody perennials, as yet very few have considered effects of whole-plant age on photosynthetic traits in herbaceous perennials. Our study focuses on a hardy and long-lived perennial grass (Thinopyrum intermedium) with economic uses as a forage, in wheat breeding programs, and potentially as an edible perennial grain. We compared three cohorts of wheatgrass plants (one-, two- and three-year old plants), using annual wheat as a check, and measured photosynthetic rates at multiple points during the growing season, as well as other related traits (electron transport, triose phosphate utilization, RuBP carboxylation, quantum yield, specific leaf area, leaf protein, and concentration of several enzymes linked to photosynthesis).

Results/Conclusions

Older plants showed lower photosynthetic rates than younger plants, although even the older wheatgrass plants showed superior photosynthetic performance to their close relative, annual wheat. Differences between older and younger plants were more pronounced later in the season. The declines in photosynthesis with increasing plant age reflected lower electron transport and RuBP carboxylation rates, and at some time points lower stomatal conductance; older plants also showed less stomatal limitation. Protein concentrations were also lower in older wheatgrass plants. These results corroborate age-related declines observed in sugarcane, and constitute one of the first pieces of evidence that whole-plant age has affects on photosynthetic traits in a herbaceous perennial system, with potential implications for agriculture and ecosystem modeling.