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. In July 2011 chlorophyll fluorescence were performed at Satakunta (Finland) Experimental site. Here plots 20mx20m were established in 1999, in which different species mixture were achieved by mixing the species tree by tree. Chlorophyll fluorescence measurements were done in leaves and needles south exposed, at the top of canopy, attached to the twigs/twiglets to keep them hydrated. At Satakunta twig sampling was performed in the morning (09:00 – 13:00) with extension loppers. The twigs (and leaves) were collected from 5 trees per specie per plot, randomly distributed inside the plot. The measurements were replicated in 5 leaves per tree randomly selected in the branchlets. In evergreen conifers chlorophyll fluorescence measurements took in current year needles (i.e., needles sprouted in 2011, 1-year needles). The branchlets, just collected from each tree, were put in black plastic bag (labelled with data ID plot number, and ID tree number) and stored at ambient temperature, avoiding sub exposure of the bags. After some hours of dark adaptation of the samples (minumum 4-5 hours) the measurements were taken in a darkened room at the Satakunta Environmental Research Centre (Reposaari). Measurements were taken by HandyPea fluorimeter (direct or prompt fluorescence).

We performed the chlorophyll fluorescence in 19 plots of area 1 (near Pormakku) of Satakunta Experimental site. We used 5 trees per specie per plot, earlier selected for isotopic and nitrogen analysis. For each tree we collected one twig south-exposed in the top of the a canopy. 5 leaves randomly chosen for twig were used for the chorophyll fluorescence measurements.

In July 2011 chlorophyll fluorescence were performed at Satakunta (Finland) Experimental site. Here plots 20mx20m were established in 1999, in which different species mixture were achieved by mixing the species tree by tree. Chlorophyll fluorescence measurements were done in leaves and needles south exposed, at the top of canopy, attached to the twigs/twiglets to keep them hydrated. At Satakunta twig sampling was performed in the morning (09:00 – 13:00) with extension loppers. The twigs (and leaves) were collected from 5 trees per specie per plot, randomly distributed inside the plot. The measurements were replicated in 5 leaves per tree randomly selected in the branchlets. In evergreen conifers chlorophyll fluorescence measurements took in current year needles (i.e., needles sprouted in 2011, 1-year needles). The branchlets, just collected from each tree, were put in black plastic bag (labelled with data ID plot number, and ID tree number) and stored at ambient temperature, avoiding sub exposure of the bags. After some hours of dark adaptation of the samples (minumum 4-5 hours) the measurements were taken in a darkened room at the Satakunta Environmental Research Centre (Reposaari). Measurements were taken by HandyPea fluorimeter (direct or prompt fluorescence). The samping and the measurements were carried out by Martina Pollastrini and Filippo Bussotti.

5 tree species (total number of sampled tree/specie): Betula pendula (45), Picea abies (44), Alnus glutinosa (35), Pinus sylvestris (43), Larix sibirica (40)

Overall very warm, sunny weather