Productivity is great in forests with a capacity to intercept incoming radiation and harness its energy efficiently. Thus, understanding the relationships between forest diversity, tree canopy biomass and photosynthetic parameters is central to predicting how diversity will affect a key ecosystem function (i.e., productivity). Specific hypotheses to be tested: I) higher tree species diversity enables greater exploitation of light within forest canopies due to niche partitioning, increasing photosynthesis and primary production (NPP); II) photosynthetic acclimation (ecological resilience to changing environmental factors) on singular species may vary according to the varying ecological conditions, but is supposed to be maintained at plot level in mixed population (interaction of different species-specific behaviors). Photosynthetic acclimation was measured with chlorophyll fluorescence, by applying fast and reliable techniques based on the fast kinetics of the chlorophyll fluorescence induction in dark adapted leaves. This method is called JIP-test and is based on the measure of the variable fluorescence at different steps of the induction. At Kaltenborn, 36 plots of 16mx16m were established in winter 2003/2004 as part of the BIOTREE project. In each plot, the area was subdivided in an unmanaged, managed and managed plus additional species. Species mixture was achieved by patch planting (patches of 8mx8m). Seedlings of four tree species were planted in a grid with two planting densities (1 m x 1.5 m for broadleaf spp. and 2 m x 1.5 m for coniferous spp.) in 36 plots. Chlorophyll fluorescence measurements (ChlF) were carried out in 15 plots, representing different mixture levels and species combinations. Sampling was done at June 23-25 2011 at Kaltenborn, where were selected 8 trees per species per plot taking in account the neighbouring tree species. ChlF measurements were replicated on 5 different leaves per tree. The measurements were done on the twigs, directly on the crown (not cutted branch) in nighttime to achieve a dark adapted of the samples in the field. In evergreen conifers ChlF measurements took in current year needles (i.e., needles sprouted in 2011, 1-year needles). Measurements were taken by PocketPEA fluorimeter (direct or prompt fluorescence).

Chlorophyll fluorescence measurements were replicated on 5 different leaves per tree. The measurements were done on the twigs, directly on the crown (not cutted branch) in nighttime to achieve a dark adapted of the samples in the field. In evergreen conifers ChlF measurements took in current year needles (i.e., needles sprouted in 2011, 1-year needles).

Kaltenborn (Thuringia), Germany

4 tree species (total number sampled tree/specie): Fagus sylvatica (63), Quercus petraea (57), Picea abies (64), Pseudotsuga menziesii (60)