3 December: Ronald Pierik

Plant Competition: regulation and functional significance of shade avoidance responses.

Ronald Pierik

Plant Ecophysiology, Institute of Environmental Biology, Utrecht University, the Netherlands

Plants growing in dense vegetations compete for resources such as water, nutrients and light. Shade-intolerant plants ensure light capture through so-called shade avoidance responses to neighbors which include upward leaf movement and increased shoot elongation. Through these morphological acclimations, the photosynthetically active leaves are positioned relatively high in a vegetation where light availability is maximal.

Neighbor detection occurs predominantly through spectral changes in the light reflected from or transmitted through neighboring vegetation. Red light (R) is absorbed for photosynthesis whereas far-red light (FR) is reflected, thus lowering the R:FR ratio which can be sensed by the phytochrome photoreceptors. Low R:FR perception regulates a variety of hormones, such as auxin, gibberellin and ethylene, to control the adaptive growth responses. I will outline current insights into the regulatory components underlying these responses and their functional significance for shade avoidance and competitive power. Furthermore I will discuss how these insights can help ask and answer questions regarding ecological trade-offs, using current work on far-red light mediated repression of defense against pathogens as an example.

19 November: Erik Dahl Kjær & Lea Vig McKinney

Genetic resilience of natural populations of Fraxinus excelsior L. against novel Ash decline - are we losing a unique habitat?

Lea Vig McKinney*, Lene Rostgaard Nielsen, Jon Kehlet Hansen, Lars N. Hansen, Iben M. Thomsen, David B. Collinge, Erik Dahl Kjær*

*Forest & Landscape, Copenhagen University

Fraxinus excelsior is an important tree species native to the Danish flora. It provides commercial and environmental services, and is a key-stone species in natural plant communities associated with moist forest habitats on fertile soils. However, the health and viability the species is presently threatened by a novel emerging disease, presumably caused by the fungus Chalara fraxinea. The disease was observed in Denmark in 2003, and has since become common throughout the country causing devastating harms.

Since 2007, we have studied genetic variation between Fraxinus excelsior trees of Danish origin in their susceptibility to the disease. By studying clone and half sib progeny trials 2007-2010, inferring from both natural and artificial infection, and using pedigree reconstructions based on SSR markers, we have established estimates of genetic variation and narrow sense heritability in degree of susceptibility. Our 5 years time series also allows us to assess the progression of the damage at the given sites. In 2010, we have initiated additional monitoring of damage level in five Danish Fraxinus stands with various ages, including the 100+ years old Stasevang stand.

In the presentation we introduce what is known about the disease, and provide a brief account of our main findings. Based on the findings, we speculate on the nature and degree (if any) of resistance and resilience to be expected in Danish Fraxinus stands due to inherent variation in susceptibility. Implications for the likely future of the Danish Fraxinus forests are discussed.