Relative contribution of meristem activities and specific leaf area to shoot relative growth rate in C3 grass species

1. Although plant growth depends on a balance between source and sink abilities, few studies have examined how sink activities influence plant shoot growth. This study is an examination of how meristem (sink) activities influence interspecific differences in shoot relative growth rate (RGR) among 16 C-3 grass species. 2. The RGR and specific leaf area (SLA) were measured on plants grown under controlled environments in each species. Meristem activities of the shoot were quantified by the length of leaf meristems, which was obtained by microscopic observation on mesophyll cells, and by leaf meristem density that was estimated from tiller density. There was an inverse relationship between single meristem size and meristem density among the species. 3. While RGR did not show a significant correlation with total meristem activity, it did show a significant correlation with SLA. These results demonstrate that the interspecific difference in shoot RGR among grass species was determined mainly by the source ability of mature leaves. 4. However, leaf meristem size and meristem density had a great effect on RGR through their influence on how the variation in SLA was generated. Species with large and few meristems tended to attain a large SLA through low leaf dry matter concentration, while fast-growing species with more, smaller meristems attained a large SLA through a reduction of leaf thickness.