Data collection
In mid-June 2008, after two years of treatment, aboveground plant
biomass was clipped at soil level in the inner 30 x 30 cm of each
subplot and sorted to species. To estimate daily RGR of each species in
monoculture, aboveground plant biomass was clipped at soil level within
10 x 10 cm quadrats in the outer 10 cm surrounding the inner 30 x 30 cm
of each subplot during sequential harvests on days 53, 67, 88, 109, 116,
123, 130, 145, 152, 162, and 171 in the year 2008. Day 171 was the peak
standing biomass. Each time different randomly chosen quadrats were
clipped (Fig. S1). Harvested biomass samples were dried at 80°C and
weighed. Soil cores were collected regularly during the growth season in
2008 and analysed for nitrate and ammonium concentrations (Labor für
Boden- und Umweltanalytik, Thun, Switzerland). We measured plot level
light interception ability in monoculture for each species and each
nutrient treatment before the harvest in end-April 2008 as the
percentage of transmitted photosynthetically active radiation (PAR)
reaching the soil surface.