Photosynthesis and Seedling Survival of Weeds with Different Trampling Susceptibilities under Contrasting Light and Water Conditions.

Photosynthesis and seedling survival under contrasting light and water conditions were investigated for some C3 dicots and C4 monocots with different trampling susceptibilities. For the summer-annual monocots, the trampling-tolerant Eleusine indica Gaerth. appeared to be more sun-adapted than the trampling-sensitive Digitaria adscendens (H. B. K.) Henr. E. indica showed a higher optimal temperature for photosynthesis, and a lower seedling survival under shading compared with D. adscendens. In contrast, in the perennial dicots, the trampling-tolerant Plantago asiatica L. appeared to be more shade-adapted than the trampling-sensitive Artemisia princeps Pamp. P. asiatica had a higher photosynthetic rate at low irradiances and a higher seedling survival under shading than A. princeps. The optimal temperature for photosynthesis was lower in P. asiatica than in A. princeps. These results suggest that, of the tramping-tolerant species, E. indica can grow at exposed trampled habitats, while P. asiatica colonizes shaded trampled habitats. Under dry soil conditions, seedling survival of those two trampling-tolerant species was lower than that of the trampling-sensitive species (D. adscendens and A. princeps). The lowest survival was found in P. asiatica. Trampling-tolerant plants thus do not appear to be adapted to low moisture conditions.