Grasslands are biodiverse communities that offer many ecosystem services such as erosion prevention, carbon sequestration, and water filtration. Global change factors, such as increases in temperature, unpredictable precipitation patterns, and nitrogen deposition, impact grassland communities which can lead to species loss, dominance of non-native annual grasses, or habitat conversion. While many grassland and dryland species are adapted to low precipitation and high temperatures, they may not tolerate further shifts in environmental conditions. Morpho-physiological traits characterizing trade-offs in growth strategies are useful in predicting how species, populations, and communities will respond to shifting global change factors. While traits of adult plants are well studied, trait-performance relationships for early regeneration stages (seeds, seedlings) are less understood, and these stages may be particularly vulnerable to shifts in environmental conditions. Here, I examine how the traits and species identity of adult graminoids influence seedling establishment of nearby plants (Chapter 1), how seed traits interact with global change factors to shift seed bank composition (Chapter 2), and how differences in populations and maternal environment conditions drive intraspecific variation in seedling traits, seedling drought resilience, and first-year reproduction (Chapter 3). The main finding from Chapter 1 was that forb establishment was more likely next to graminoids with low leaf dry matter content (LDMC) and similar flowering phenology. For Chapter 2, I found that non-native seeds were larger than natives, and that N-fixing forbs had strong seed barrier traits. Additionally, community weighted seed traits shifted with resource availability, where higher nutrient availability increased seed size and higher water availability reduced seed coat thickness. For Chapter 3, in a survey of three populations of a perennial grass, I found that plants from the most arid population had root traits associated with higher resource acquisition, which were correlated with higher reproduction but not survival. Further, the maternal water environment impacted first year reproduction, e.g. transgenerational plasticity, where the direction of the reproductive response depended on the population. Collectively, my results have advanced our understanding of how traits respond to environmental variation and how they may be used to predict species, population, and community response to global change factors. My results also have important implications for management of grassland systems. As graminoids with low leaf dry matter content appear to be good nurse plants for forbs, my work suggests that incorporating these species, or increasing leaf trait diversity, in seeding mixes may enhance forb cover in dryland restoration efforts. Finally, my finding that seed provenance and maternal water availability affect first-year reproductive output reinforces the value of using locally adapted seed sources and suggests that using different watering regimes for the cultivation of seed to use in restoration plantings may enhance restoration outcomes.
