Photosynthetic Resilience of Elymus elymoides and Pseudoroegneria spicata Seedlings Following Acute Water Stress

Demographic studies suggest that mortality of emerging bunchgrass seedlings limits restoration success across North American cold desert rangelands, but how variation in seedling resilience to ecophysiological stress contributes to this is unclear. We measured light-saturated photosynthetic rate (A_sat), apparent CO₂ assimilation quantum yield (ΦCO₂), and light-adapted PSII yield (Φ_PSII) of seedlings from two native perennial bunchgrasses (Elymus elymoides, Pseudoroegneria spicata) during and in recovery from acute water stress (6% soil moisture). All seedlings of both species survived the 14-d dry-down and recovery, and both had ∼95% reduction in A_sat and ΦCO₂ by day 3 of the dry-down but had divergent recoveries from the acute water stress. E. elymoides took a single day to recover A_sat and ΦCO₂ to prestress levels, while it took P. spicata 6 d to have 50% recovery from acute water stress. Especially notable is that after reduction in Φ_PSII on d 7 of the dry-down, E. elymoides recovered within 1 d at a lower Φ_PSII compared with pretreatment, while P. spicata had an additional 1-d lag in Φ_PSII recovery. These results suggest that E. elymoides (Turkey Lake germplasm) seedlings are more physiologically resilient to acute water stress than P. spicata (Anatone germplasm), which has implications for restoration planning and native plant breeding.