The influence of spectral composition on spring and autumn phenology in trees

Several recent reviews highlight the molecular mechanisms that underpin phenological responses to temperature and photoperiod; however, these have mostly overlooked the influence of solar radiation and its spectral composition on these processes. For instance, solar radiation in the blue and ultraviolet (UV) regions of the spectrum, as well as the red/far-red (R:FR) ratio, can influence spring and autumn phenology. Solar radiation reaching the Earth changes diurnally and seasonally; however, rising global temperatures, latitudinal range shifts and light pollution are likely to produce novel combinations of phenological cues for tree species. Here, we review the literature on phenological responses to spectral composition. Our objective was to explore the natural variation in spectral composition using radiative transfer models and to reveal any species-specific or ecotype-specific responses relating to latitudinal origin. These responses are likely to be most pronounced at high latitudes where spectral composition varies most throughout the year. For instance, trees from high latitudes tend to be more sensitive to changes in R:FR than those from low latitudes. The effects of blue light and UV radiation on phenology have not been studied as much as those of R:FR, but the limited results available suggest both could be candidate cues affecting autumn leaf colouration and senescence. Failure of more–southern species and ecotypes to adapt and use spectral cues during northwards range shifts could result in mistimed phenology, potentially resulting in frost damage, reduced fitness and limited range expansion. Future areas for research should look to establish how consistently different functional types of tree respond to spectral cues and identify photoreceptor-mediated mechanisms that allow plants to combine information from multiple light cues to coordinate the timing of phenological events. It should then be feasible to consider the synchronous or sequential action of light cues within a hierarchy of environmental factors regulating phenology.Peer reviewe

Harvesting history affects soil respiration and litterfall but not overall carbon balance in boreal Norway spruce forests

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β-aminobutyric acid does not induce defenses or increase Norway spruce resistance to the bluestain fungus Grosmannia penicillata

Priming of Norway spruce (Picea abies) inducible defenses is a promising way to protect young trees from herbivores and pathogens. Methyl jasmonate (MeJA) application is known to induce and potentially prime Norway spruce defenses but may also reduce plant growth. Therefore, we tested β-aminobutyric acid (BABA) as an alternative priming chemical to enhance spruce resistance, using 2-year-old Norway spruce plants. We compared inducible defense responses, i.e. traumatic resin duct formation and accumulation of defensive metabolites, in bark and xylem tissues of BABA- or MeJA-treated plants before and after wounding. We also evaluated the effect of these chemical treatments on Norway spruce resistance to the pathogenic bluestain fungus Grosmania penicilliata. BABA did not induce defense responses or pathogen resistance, it even reduced concentrations of total terpenes in the treated plants. In contrast, MeJA induced traumatic resin duct formation, accumulation of flavonoids, pathogen resistance, and did not affect plant growth. For the first time, flavan-3-ols (catechins) were shown to have a primed response to MeJA treatment in Norway spruce. Our results indicated that BABA is not a suitable alternative priming chemical to MeJA in Norway spruce.β-aminobutyric acid does not induce defenses or increase Norway spruce resistance to the bluestain fungus Grosmannia penicillatapublishedVersio

Experimental warming had little effect on carbon-based secondary compounds, carbon and nitrogen in selected alpine plants and lichens

Accepted version of an article published in the journal: Environmental and Experimental Botany. Published version available on Science Direct: http://dx.doi.org/10.1016/j.envexpbot.2011.04.011Global warming is expected to change plant defence through its influence on plant primary resources. Increased temperature (T) will increase photosynthesis, and thus carbon (C) availability, but may also increase soil mineralization and availability of nitrogen (N). More access to C and N is expected to mainly increase plant growth, and, according to hypotheses on resource based defence, this could lower plant concentrations of carbon-based secondary compounds (CBSCs). We used two already established warming experiment with open top chambers (OTCs) and control plots in alpine south-western Norway, one on a ridge (8 years' treatment) and a one in a leeside (3 years' treatment), to study the effects of warming on plant and lichen defensive compound concentrations. The study included five vascular plant and six lichen species. One vascular plant species had lower concentration of CBSCs under elevated T, while the others did not respond to the treatment. In lichens there were no effects of warming on CBSCs, but a tendency to reduced total C concentrations. However, there were effects of warming on nitrogen, as the concentration decreased inside OTCs for three species, while it increased for one lichen species. Lichens generally had higher CBSC and total C concentrations on the ridge than in the leeside, but no such pattern were seen for vascular plants. No elevated temperature effect on CBCSs is most probably a result of high constitutive defence under the limiting alpine conditions, suggesting that chemical defence is little subject to change under climate warming, at least on a short-term basis. We suggest that the driving forces of plant defence in the arctic-alpine should be tested individually under controlled conditions, and suggest that competition from other plants may be a greater threat under climate warming than increased herbivory or disease attacks

Establishment of spruce plantations in native birch forests reduces soil fungal diversity

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Spatial variation of surface soil carbon in a boreal forest – the role of historical fires, contemporary vegetation, and hydro-topography

Knowledge about the spatial variation of boreal forest soil carbon (C) stocks is limited, but crucial for establishing management practices that prevent losses of soil C. Here, we quantified the surface soil C stocks across small spatial scales, and aim to contribute to an improved understanding of the drivers involved in boreal forest soil C accumulation. Our study is based on C analyses of 192 soil cores, positioned and recorded systematically within a forest area of 11 ha. The study area is a south-central Norwegian boreal forest landscape, where the fire history for the past 650 years has been reconstructed. Soil C stocks ranged from 1.3 to 96.7 kg m−2 and were related to fire frequency, ecosystem productivity, vegetation attributes, and hydro-topography. Soil C stocks increased with soil nitrogen concentration, soil water content, Sphagnum- and litter-dominated forest floor vegetation, and proportion of silt in the mineral soil, and decreased with fire frequency in site 1, feathermoss- and lichen-dominated forest floor vegetation and increasing slope. Our results emphasize that boreal forest surface soil C stocks are highly variable in size across fine spatial scales, shaped by an interplay between historical forest fires, ecosystem productivity, forest floor vegetation, and hydro-topography.Spatial variation of surface soil carbon in a boreal forest – the role of historical fires, contemporary vegetation, and hydro-topographyacceptedVersio

Interannual variation in UV-B and temperature effects on bud phenology and growth in Populus tremula

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Synchronic shifts in phenolic compounds and fungal communities during litter decomposition in boreal forests

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Long term effects of ionising radiation in the Chernobyl Exclusion zone on DNA integrity and chemical defence systems of Scots pine (Pinus sylvestris)

The Chernobyl Nuclear Power Plant (ChNPP) accident in 1986 resulted in extremely high levels of acute ionising radiation, that killed or damaged Scots pine (Pinus sylvestris) trees in the surrounding areas. Dead trees were cleared and buried, and new plantations established a few years later. Today, more than three decades later, gamma and beta-radiation near the ChNPP is still elevated compared with ambient levels but have decreased by a factor of 300 and 100, respectively. In the present work, Scots pine-trees growing at High (220 μGy h−1), Medium (11 μGy h−1), and Low (0.2 μGy h−1) total (internal + external) dose rates of chronically elevated ionising radiation in the Chernobyl Exclusion zone were investigated with respect to possible damage to DNA, cells and organelles, as well as potentially increased levels of phenolic and terpenoid antioxidants. Scots pine from the High and Medium radiation sites had elevated levels of DNA damage in shoot tips and needles as shown by the COMET assay, as well as increased numbers of resin ducts and subcellular abnormalities in needles. Needles from the High radiation site showed elevated levels of monoterpenes and condensed tannins compared with those from the other sites. In conclusion, more than three decades after the ChNPP accident substantial DNA damage and (sub)cellular effects, but also mobilisation of stress-protective substances possessing antioxidant activity were observed in Scots pine trees growing at elevated levels of ionising radiation. This demonstrates that the radiation levels in the Red Forest still significantly impact the plant community.publishedVersio