Supra-optimal leaf area index of a temperate liana Pueraria lobata for competition with Solidago altissima at the expense of canopy photosynthesis.

Leaf area index (LAI) measured for the actual plant canopy is higher than the LAI that maximizes canopy photosynthesis (referred to as optimal LAI) because each individual can increase its light interception by unilaterally producing more leaf area. The LAI of an invasive woody vine Pueraria lobata (kudzu) is one of the highest among plant species, sometimes attaining nearly 10 m2 m-2. The high LAI casts heavy shade over neighboring plants, making their survival difficult. Interesting to note is that the high LAI also increases self-shading, thereby decreasing its own photosynthesis processes. In the present study, the influences of the high LAI on light interception and canopy photosynthesis, as well as on the inter-specific competition was investigated on a roadside P. lobata vegetation in Japan. With the aid of a canopy photosynthesis model and a sensitivity analysis, it was revealed that the actual LAI was 2.2-3.0 times higher than the optimal LAI for maximizing canopy photosynthesis. In the following year, a field experiment was conducted where a nearly optimal LAI was maintained throughout the growth period by regularly clipping the leaves of P. lobata. Ultimately, the field results revealed that even with a nearly optimal LAI, P. lobata was outcompeted by a competing alien weed, Solidago altissima (tall goldenrod). These results indicate that the supra-optimal leaf area, rather than maximum canopy carbon gain, makes P. lobata the dominating species in light-competing environments.