Variation in the role of the flag-leaf in reproductive effort of semiarid rangeland bunchgrasses

Understanding the mechanisms underlying viable seed production of perennial bunchgrasses is critical to improving restoration and conservation success in Great Basin sagebrush steppe rangelands. We studied the effects of pre- and post-anthesis flag-leaf removal and post-anthesis seed-head shading on reproductive effort in two important rangeland restoration species, the exotic crested wheatgrass (Agropyron cristatum) and native squirreltail (Elymus elymoides). Flag-leaf removal had distinct, species-specific effects on seed filling. Pre-anthesis flag-leaf removal in crested wheatgrass reduced the proportion of filled seeds, while post-anthesis removal did not. In contrast, squirreltail increased filled seed proportions regardless of flag-leaf removal timing. Neither flag-leaf removal treatment affected seed quality, as quantified by seed-specific mass (in grams per square meter), which significantly reduced with seed-head shading in both species. Seed-head shading reduced total propagule production (unfilled + filled seeds) in crested wheatgrass but increased it in squirreltail, possibly due to our shading method protecting from seed-head herbivory or high-light stress. Flag-leaf removal in the squirreltail also induced a negative shading effect on filled seed area, mass, and specific mass. These findings suggest flag leaves can modulate reproductive effort outside of seed provisioning, either by maintaining pre-fertilized seed viability, as in crested wheatgrass, or acting as a competitive sink to the fully emerged seed-head, as in squirreltail. Moreover, this study demonstrates photosynthetic activity by the seed-head itself is critical to the expression of seed quality traits important to seedling establishment success of semiarid perennial bunchgrasses.