The importance of tissue density for growth and life span of leaves and roots: A comparison of five ecologically contrasting grasses

1. Under nutrient-poor conditions initially fast-growing species will in the long term be competitively inferior to slow-growing species. Here, we ask whether this phenomenon can be explained by constraints caused by tissue density. The hypothesis is that low tissue density is necessary for fast growth but has as a consequence short organ life span. This leads to a rapid loss of nutrients that cannot be sustained under nutrient-poor conditions. 2. Biomass accumulation, turnover rate of leaves and roots, and tissue density were studied for five ecologically 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 leaf and root tissue density and were larger after one growing season than species of nutrient-poor sites. However, after two growing seasons the species of nutrient-poor sites were larger. These species had a high tissue density. 4. Life span of both leaves and roots was also correlated with tissue density. Species with low tissue density had a faster turnover of leaves and roots. 5. It is concluded that tissue structure is an inherent constraint that prevents simultaneous maximization of both nutrient acquisition and nutrient conservation. The short life span of fast-growing organs explains the long-term disadvantage of a high growth rate for plants in low nutrient conditions.