Associate Professor Santa Clara University, United States
Background/Question/Methods
Plant traits are useful for understanding how species respond to environmental change and influence ecosystem processes. Much of our understanding of how plant traits respond to climate stems from interspecific comparisons, although traits can vary significantly within species. We explored the relationships between intraspecific trait variability and climate for 74 species of grass (family: Poaceae) with a combined distribution across six continents. Using multiple regression, we assessed how three plant traits (e.g., specific leaf area (SLA), mass-based leaf nitrogen content (Nmass), and height) vary intraspecifically with mean annual temperature, precipitation and climate seasonality. We also assessed whether mean species traits (e.g., photosynthetic pathway, lifespan, SLA, Nmass, and height) would explain variation in the strength or direction of trait-climate relationships. Given that individual species respond uniquely to climate, we expected the distribution of the slopes of these trait-climate relationships to be centered near zero, with both positive and negative responses.
Results/Conclusions
We found that SLA of C4 grasses responded positively to temperature and negatively to precipitation, with the opposite response observed for C3 grasses. On average, leaf Nmass increased in warmer areas, but the effect of precipitation on leaf Nmass depended on species mean SLA. Specifically, increased rainfall led to higher Nmass for high SLA species but lower Nmass for low SLA species. Grasses generally grew taller in warmer areas, particularly grasses with acquisitive traits (high SLA and leaf Nmass), but not necessarily in wetter areas. Shorter species and/or those with high SLA tended to grow taller in wet areas whereas tall species with low SLA grew shorter with increased rainfall. Our findings suggest that intraspecific shifts in grass traits in response to climate are variable and may at first appear idiosyncratic. However, both the direction and magnitude of these shifts can be predicted from a species’ mean traits. Additionally, a species’ location along one axis of trait variation (e.g., leaf economics) may influence its ability to shift intraspecifically along another axis (e.g., plant size).
