CARBON AND NITROGEN-CONTENT OF CONGENERIC ANNUAL AND PERENNIAL GRASS SPECIES - RELATIONSHIPS WITH GROWTH

Seven annual-perennial pairs of grass species (six congeneric and one pair taken at random) were grown under productive conditions in the la boratory in order to investigate which plant characters were responsib le for the higher relative growth rate (RGR) of annuals as compared to perennials under these conditions. The nitrogen and carbon concentrat ions of shoot organs and of the whole plant were higher in annuals tha n in perennials. This was also the case for the specific absorption ra te for nitrate and nitrogen productivity (on whole plant and leaf basi s). The range of RGR displayed by the 14 species was large enough (0.1 5-0.33 d-1) to examine the general relationships between RGR and the v arious parameters measured in the present study. RGR was positively re lated to plant, leaf blade and sheath nitrogen concentrations, but the re was no relationship between RGR and any of the carbon concentration s. RGR also strongly correlated with specific absorption rate for nitr ate and with nitrogen productivity. A new factorization of this latter parameter led to the definition of the 'leaf nitrogen productivity' ( N(L)P), which is likely to depend on photosynthetic nitrogen use effic iency. RGR was shown to be strongly correlated with N(L)P, but not wit h the second term of the factorization, namely the proportion of plant nitrogen allocated to the leaves.