THE IMPORTANCE OF TISSUE DENSITY FOR GROWTH AND LIFE-SPAN OF LEAVES AND ROOTS - A COMPARISON OF 5 ECOLOGICALLY CONTRASTING GRASSES

1. Under nutrient-poor conditions initially fast-growing species will in the long term be competitively inferior to slow-growing species. He re, we ask whether this phenomenon can be explained by constraints cau sed by tissue density. The hypothesis is that low tissue density is ne cessary for fast growth but has as a consequence short organ life span . This leads to a rapid loss of nutrients that cannot be sustained und er nutrient-poor conditions. 2. Biomass accumulation, turnover rate of leaves and roots, and tissue density were studied for five ecological ly contrasting grass species. Plants were grown in a garden experiment over two growing seasons on sand with a low nutrient supply level. 3. Species that were characteristic of nutrient-rich sites had a low lea f and root tissue density and were larger after one growing season tha n species of nutrient-poor sites. However, after two growing seasons t he species of nutrient-poor sites were larger. These species had a hig h tissue density. 4. Life span of both leaves and roots was also corre lated with tissue density. Species with low tissue density had a faste r turnover of leaves and roots. 5. It is concluded that tissue structu re is an inherent constraint that prevents simultaneous maximization o f both nutrient acquisition and nutrient conservation. The short life span of fast-growing organs explains the long-term disadvantage of a h igh growth rate for plants in low nutrient conditions.