Growth and biomass partitioning of Fagus sylvatica L. and Quercus robur L. seedlings in response to shading and small changes in the R/FR-ratio of radiation

The effects of shading levels, comparable to the light quantity and quality below the canopy of a Norway spruce (Picea abies [L.] Karst.) stand on one year old European beech (Fagus sylvatica L.) and pendunculate oak (Quercus robur L.) were tested. The treatments were: shading of plants exposed to natural shade by using green synthetic nets (PAR reduced to 32.6%, R/FR-ratio 1.04), shading of plants exposed to neutral shade by using black nets (PAR reduced to 24.7%, R/FR-ratio 1.13), no shading (control, PAR 100%, R/FR- ratio 1.15). Beech seedlings showed a strong decrease in height, diameter, stem-, branch-, leaf- and root dry mass with decreasing light quantity. Neither growth rates nor total yield indicated an impact of slightly changed light quality (R/FR- ratio 1.04) on growth and biomass partitioning of beech. Relative growth rate of the main stem dry mass of oak was considerably higher for the seedlings of the shade treatment with the reduced R/FR- ratio than for the control and the other shade treatment whereas branch dry biomass exposed to changed light quantity and quality was reduced disproportional, resulting in the lowest branch- stem- ratio. The tallest oak seedlings were found under the green nets (treatment with reduced light quantity and quality), whereas the control showed the shortest seedlings.