THE RESPONSES OF CYNOGLOSSUM OFFICINALE L. AND VERBASCUM THAPSUS L. TO DEFOLIATION IN RELATION TO NITROGEN SUPPLY

The effects of defoliation of Cynoglossum officinale L. and Verbascum thapsus L. on growth, net assimilation rate and dry matter distribution were studied under various nitrogen regimes. At high levels of nitrogen supply, there was a higher net assimilation rate (NAR) and a higher leaf weight ratio in defoliated plants than in undefoliated plants resulting in a faster growth of defoliated plants. In V. thapsus growth of defoliated plants did not differ significantly from undipped plants. In a low nitrogen regime all defoliated V. thapsus plants died. In the same regime C. officinale had a low NAR and thus showed little regrowth. Leaf nitrogen content was not significantly different from control plants.