Irradiance and nitrate‐dependent variation in growth and biomass allocation of Mycelis muralis. An analysis of its significance for a functional categorization of ‘sun’ and ‘shade’ plants

summary The biomass of Mycelis muralis (L.) Dumort plants increased with increases in growth irradiance and nitrate supply. Comparisons of the data from this study with published information indicate that biomass production and growth rate of M. muralis are comparable to that of a number of slow‐growing species from resource‐poor environments. Biomass allocation varied with growth irradiance and nitrate supply. At high irradiances and low nitrate supplies there was a significantly greater allocation of plant mass to roots, resulting in a lower leaf area ratio (LAR) and leaf mass ratio (LMR). In contrast to the findings of a number of other studies, light level and nitrate supply had interactive effects on leaf mass per unit area (LMA). Changes in LAR due to variations in irradiance were mainly a consequence of changes in LMR. Given the ability of M. muralis to grow in deep shade, this suggests that large changes to within‐leaf allocation (LMA) are not an essential requirement for growth at low irradiances. Conversely, because M. muralis can also grow in fully exposed situations, these traits might not exclude some shade species from high irradiance habitats. However, a low growth rate, or traits which result in a low growth rate, might be advantageous in a number of resource‐poor environments.