Interaction of irradiance and soil nutrient supply on growth of seedlings of ten European tall-shrub species and Fagus sylvatica

1 Seedlings of 10 European tall-shrub species and the shade-tolerant tree Fagus sylvatica were grown at 0.3, 1.6, 11, and 63% daylight for 110 days on chalk grassland soil, and on a more nutrient-rich soil developed under Crataegus monogyna. 2 Crataegus monogyna, Fagus, Juniperus communis, Cornus sanguinea, Ligustrum vulgare and Rosa canina suffered high mortality in 0.3% daylight, but only the first three had losses in 1.6%. Overall mortality in deep shade (0.3, 1.6%) was considerably lower in Euonymus europaeus, Rhamnus catharticus, Viburnum lantana and V. opulus. Average mortality in deep shade on grassland soil was negatively correlated with embryo-cum-endosperm dry mass (EEM). Overall mortality in deep shade was significantly greater with higher nutrient supply. 3 In 63% daylight relative growth rate (RGR) was negatively correlated with log EEM, and positively with specific leaf area (SLA, leaf area/leaf dry mass) at time of planting but not at final harvest, i.e. differences in RGR were determined more by unit leaf rate (rate of dry mass gain/leaf area) in the latter part of the experiment. 4 The responses of the species to irradiance and nutrient supply were appreciably different. Cornus, Ligustrum, Prunus spinosa, Rhamnus, and Rosa increased yield strongly under high irradiance on nutrient-poor soil, and responded also markedly to nutrients. Viburnum lantana and Euonymus grew relatively slowly in all treatments, but the former was responsive to nutrients, even in deep shade. Viburnum opulus was more responsive to irradiance but responded to nutrients only in 11% daylight. Crataegus grew more slowly on its 'own' soil than on grassland soil. Juniperus differed consistently from the other species, growing slowly, and responding strongly to irradiance. Fagus responded moderately to irradiance and not to nutrient supply. 5 In shade allocation to roots decreased, while allocation to stem and to leaves increased generally. All species produced a smaller number and total area of leaves, and increased SLA and leaf area ratio (leaf area/total dry mass). Shoot and root lengths were reduced in shade. 6 The results are discussed in relation to the roles of the various species during secondary succession, and their regeneration niches.