Filho, Moacyr Bernadino Dias. “Physiological Responses of Two Tropical Weeds to Shade. II. Leaf Gas Exchange and Nitrogen Content”. Pesquisa Agropecuaria Brasileira, vol. 34, no. 6, June 1999, pp. 953-61, doi:10.1590/S1678-3921.pab1999.v34.5276.