Limits to future adaptation in the invasive plant Polygonum cespitosum: expression of functional and fitness traits at elevated CO2

For organisms to adapt to future environments, they must both evolve appropriate functional responses and phenotypically express those responses under future climatic and CO2 conditions. We examined these 2 components of future adaptation in an invasive annual plant (Polygonum cespitosum) by performing a “resurrection” experiment under field conditions simulating a future environment. Resurrection experiments reveal recent evolution by comparing genotypes from natural populations sampled across a multigeneration interval. We collected genotypes from the same 3 North American populations in 1994 and 2005 and raised inbred lines from these collections under free air CO2 enrichment to examine functional and fitness traits expressed in hot, dry conditions at both ambient and elevated CO2 (N = 295 plants). The species has rapidly evolved in its introduced range to increase photosynthetic rate (collection year effect P ≤ 0.011) and delay senescence (P = 0.017) under full-sun, dry field condit...