Leaf area increases with species richness in young experimental stands of subtropical trees

Aims Most biodiversity-ecosystem functioning research has been carried out in grassland ecosystems,and little is known about whether forest ecosystems,in particular outside the temperate zone,respond similarly.Here,we tested whether productivity,assessed as leaf area index(LAI),increases with species richness in young experimental stands of subtropical trees,whether this response is similar for early-season leaf area(which is dominated by evergreens)and seasonal leaf area increase(which is dominated by deciduous species),and whether responses saturate at high species richness.Methods We used a planted tree biodiversity experiment in south-east China to test our hypotheses.LAI was determined three times by digital hemispheric photography in 144 plots that had been planted with 400 trees each,forming communities with 1,2,4,8 or 16 tree species.Important Findings LAI increased significantly with tree species richness in the fifth year of stand establishment.Similar,but weaker,statistically non-significant trends were observed 1 year before.We did not observe leaf area overyielding and the presence of particularly productive and unproductive species explained large amounts of variation in leaf area,suggesting that selection-type effects contributed substantially to the biodiversity effects we found in this early phase of stand establishment.Effects sizes were moderate to large and comparable in magnitude to the ones reported for grassland ecosystems.Subtropical(and tropical)forests harbor substantial parts of global net primary production and are critical for the Earth’s carbon and hydrological cycle,and our results suggest that tree diversity critically supports these ecosystem services.

No plant functional diversity effects on foliar fungal pathogens in experimental tree communities

Foliar fungal pathogens affect forest ecosystem processes by exerting highly species-specific impacts on growth and survival of trees.As many ecosystem processes in forests depend on functional diversity of specific tree species,a close relationship is expected between this and foliar fungal pathogen infestation.Testing for such a relationship in the German tree diversity experiment BIOTREE(Bechstedt),we hypothesized that pathogen richness and pathogen load decline with increasing functional diversity of tree communities.Using macro-and microscopic analyses,we assessed pathogen richness and load on 16 tree species in plots that,although differing in functional diversity,had the same tree species richness.We found no effects of functional diversity on pathogen richness or load.However,we encountered strong species identity effects in plot species composition,as susceptible tree species contributed positively to each community’s pathogen richness and load.Furthermore,testing for effects of particular leaf traits and geographical range size of host species revealed a significant effect of total leaf phenolics,which was unexpected as pathogen richness increased with increasing content in polyphenolics.Our study showed that at the community level,host species’identity was more important for foliar fungal pathogen richness and load than the functional diversity of host trees.The positive relationship between pathogen richness and phenolics in leaves,along with the finding that pathogen richness is very much conserved in tree species,point to an evolutionary arms race between hosts and fungi resulting from fungi increasing their capacity to infect tree leaves and trees boosting their defences.