Growth and physiological characteristics of native and invasive plant species of the San Joaquin Valley, California

Retired farmland in the western San Joaquin Valley (SJV) of California is frequently colonized by invasive plants that may limit the establishment of native flora. Limited ecophysiological data on native and invasive SJV plant species constrains science-based restoration of native flora. This greenhouse evaluation involved a comparison of photosynthetic rates, in vivo nitrate reductase activity (NRA), and biomass accumulation of two invasive annuals and three native annual species. At 35d and 75d, 15 individuals were harvested to determine total biomass. Photosynthesis was measured using a Li-Cor Li-6400 and in vivo NRA was measured in roots and leaves. At harvest 1, the photosynthetic rate of invasives (15.5�0.56 _moles CO2�m-2 �s-1) was greater (p<0.05) than natives (10.6�0.43 _moles CO2�m-2 �s-1). Natives significantly exceeded (p<0.05) the water use efficiency of invasives by 22% and 31% at harvest 1 and 2, respectively. In all species, leaf NRA exceeded root NRA (p<0.001; p<0.05). The total biomass of invasives significantly exceeded (p<0.05) that of natives at harvest 1 and 2 (0.25�0.003 g and 0.46�0.002 g, respectively). By harvest 2, the relative growth rate (RGR) of natives (0.069�0.03 g�g-1�d-1) exceeded invasives (0.043�0.07 g�g- 1�d-1, p<0.05). Greater early season photosynthesis, biomass and RGR of invasives likely aid in out competing natives and may contribute to low rates of native species establishment on retired farmland.