© 2004 Heron Publishing—Victoria, Canada
Terrestrial plants require nutrients in similar proportions
Magnus F. Knecht (1, 2) and Anders Göransson (3)
1. Department of Ecology and Environmental Research, P.O. Box 7072, SLU, 750 07 Uppsala, Sweden / 2. Corresponding author (Magnus.Knecht@eom.slu.se) / 3. Division of Education, P.O. Box 7070, SLU, 750 07 Uppsala, Sweden / Received June 13, 2003; accepted August 29, 2003; published online February 2, 2004
Summary
Theoretical considerations based on nutrition experiments suggest that nutrient ratios of terrestrial plants are similar to
the Redfield ratio found in marine phytoplankton. Laboratory experiments have shown that seedlings of many different plant
species have similar nutrient concentration ratios when supplied with nutrients at free access. However, at free access, nutrients
are likely to be taken up in amounts in excess of a plant’s requirements for growth. In further experiments, therefore, the
supply rate of each nutrient was reduced so that excessive uptake did not occur. Again, similar nutrient ratios were found
among the plant species tested, although the ratios differed from those found in plants given free access to nutrients. Based
on the law of the minimum, we suggest that optimum nutrient ratios be defined as the ratios found in plants when all nutrients
are limiting growth simultaneously. The literature on nutrient concentrations was surveyed to investigate nutrient ratios
in terrestrial ecosystems. Nutrients taken into consideration were nitrogen, phosphorus, potassium, calcium and magnesium.
Based on the assumption that nitrogen is either the limiting nutrient or, when not limiting, is taken up only in small excess
amounts, we calculated nutrient ratios from published data. The calculated ratios corresponded closely to the ratios determined
in laboratory and field experiments.
Keywords:
ecosystems, free access nutrition, law of the minimum, nutrient ratios, plants.
