Impacts of climate change on plant diseases – opinions and trends

There has been a remarkable scientific output on the topic of how climate change is likely to affect plant diseases in the coming decades. This review addresses the need for review of this burgeoning literature by summarizing opinions of previous reviews and trends in recent studies on the impacts of climate change on plant health. Sudden Oak Death is used as an introductory case study: Californian forests could become even more susceptible to this emerging plant disease, if spring precipitations will be accompanied by warmer temperatures, although climate shifts may also affect the current synchronicity between host cambium activity and pathogen colonization rate. A summary of observed and predicted climate changes, as well as of direct effects of climate change on pathosystems, is provided. Prediction and management of climate change effects on plant health are complicated by indirect effects and the interactions with global change drivers. Uncertainty in models of plant disease development under climate change calls for a diversity of management strategies, from more participatory approaches to interdisciplinary science. Involvement of stakeholders and scientists from outside plant pathology shows the importance of trade-offs, for example in the land-sharing vs. sparing debate. Further research is needed on climate change and plant health in mountain, boreal, Mediterranean and tropical regions, with multiple climate change factors and scenarios (including our responses to it, e.g. the assisted migration of plants), in relation to endophytes, viruses and mycorrhiza, using long-term and large-scale datasets and considering various plant disease control methods

Decomposers and root feeders interactively affect plant defence in Sinapis alba

Aboveground herbivory is well known to change plant growth and defence. In contrast, effects of soil organisms, acting alone or in concert, on allocation patterns are less well understood. We investigated separate and combined effects of the endogeic earthworm species Aporrectodea caliginosa and the root feeding nematode species Pratylenchus penetrans and Meloidogyne incognita on plant responses including growth and defence metabolite concentrations in leaves of white mustard, Sinapis alba. Soil biota had a strong impact on plant traits, with the intensity varying due to species combinations. Nematode infestation reduced shoot biomass and nitrogen concentration but only in the absence of earthworms. Earthworms likely counteracted the negative effects of nematodes. Infestation with the migratory lesion-nematode P. penetrans combined with earthworms led to increased root length. Earthworm biomass increased in the presence of this species, indicating that these nematodes increased the food resources of earthworms—presumably dead and decaying roots. Nitrogen-based defence compounds, i.e. glucosinolates, did not correlate with nitrogen levels. In the presence of earthworms, concentrations of aromatic glucosinolates in leaves were significantly increased. In contrast, infection with P. penetrans strongly decreased concentrations of glucosinolates (up to 81%). Infestation with the sedentary nematode M. incognita induced aromatic glucosinolates by more than 50% but only when earthworms were also present. Myrosinase activities, glucosinolate-hydrolysing enzymes, were unaffected by nematodes but reduced in the presence of earthworms. Our results document that root-feeding nematodes elicit systemic plant responses in defence metabolites, with the responses varying drastically with nematode species of different functional groups. Furthermore, systemic plant responses are also altered by decomposer animals, such as earthworms, challenging the assumption that induction of plant responses including defence traits is restricted to herbivores. Soil animals even interact and modulate the individual effects on plant growth and plant defence, thereby likely also influencing shoot herbivore attack

Enhancements in nocturnal surface ozone at urban sites in the UK

Analysis of diurnal patterns of surface ozone (O3) at multiple urban sites in the UK shows the occurrence of prominent nocturnal enhancements during the winter months (November–March). Whilst nocturnal surface ozone (NSO) enhancement events have been observed at other locations, this is the first time that such features have been demonstrated to occur in the UK and the second location globally. The observed NSO enhancement events in the UK were found to be so prevalent that they are clearly discernible in monthly diurnal cycles averaged over several years of data. Long-term (2000–2010) analysis of hourly surface ozone data from 18 urban background stations shows a bimodal diurnal variation during the winter months with a secondary nighttime peak around 0300 hours along with the primary daytime peak. For all but one site, the daily maxima NSO concentrations during the winter months exceeded 60 μg/m3 on >20 % of the nights. The highest NSO value recorded was 118 μg/m3. During the months of November, December, and January, the monthly averaged O3 concentrations observed at night (0300 h) even exceeded those observed in the daytime (1300 h). The analysis also shows that these NSO enhancements can last for several hours and were regional in scale, extending across several stations simultaneously. Interestingly, the urban sites in the north of the UK exhibited higher NSO than the sites in the south of the UK, despite their daily maxima being similar. In part, this seems to be related to the sites in the north typically having lower concentrations of nitrogen oxides

Internal conductance to CO2 transfer of adult Fagus sylvatica: variation between sun and shade leaves and due to free-air ozone fumigation

The 'In Press' version is restricted access in accordance with the Elsevier policy. The original publication is available at www.elsevier.comhttp://www.elsevier.com/wps/find/journaldescription.cws_home/267/descriptionAbstract not available due to copyright

Interactions of chronic exposure to elevated CO₂ and O₃ levels in the photosynthetic light and dark reactions of European beech (<em>Fagus sylvatica</em>).

Young trees of European beech (Fagus sylvatica) acclimated for one growing season to ambient (c. 367 mu l l(-1)) or elevated CO2 levels (c. 660 mu l l(-1)) were exposed during the subsequent year to combinations of the same CO2 regimes and ambient or twice-ambient ozone (O-3) levels (generated from the database of a rural site). By the end of June, before the development of macroscopic leaf injury, the raised O-3 levels had not affected the light and dark reactions of photosynthesis. However, acclimation to elevated CO2 had resulted in lowered chlorophyll and nitrogen concentrations, whereas photosynthetic performance, examined over a wide range of parameters from light and dark reactions, remained unchanged or showed only slight reductions (e.g. apparent electron transport rate, ETR; apparent quantum yield of CO2 gas exchange, Phi(CO2); apparent carboxylation efficiency, CE; and photosynthetic capacity at light and CO2 saturation, PC). In August, after the appearance of leaf necroses, plants grown under ambient CO2 and twice-ambient O-3 conditions declined in both the photosynthetic light reactions (optimum electron quantum yield, Fv/F-m, non-photochemical energy quenching, NPQ, reduction state of Q(A), apparent electron quantum yield, Phi(PSI)I, maximum electron transport rates) and the dark reactions as reflected by CE, Phi(CO2), as well as the maximum CO2 uptake rate (i.e. PC). CE, Phi(CO2) and PC were reduced by c. 75, 40 and 75%, respectively, relative to plants exposed to ambient CO2 and O-3 levels. By contrast, plants exposed to twice-ambient O-3 and elevated CO2 levels maintained a photosynthetic performance similar to individuals grown either under ambient CO2 and ambient O-3, or elevated CO2 and ambient O-3 conditions. The long-term exposure to elevated CO2 therefore tended to counteract adverse chronic effects of enhanced O-3 levels on photosynthesis. Possible reasons for this compensatory effect in F. sylvatica are discussed

The impact of ozone fumigation and fertilization on chlorophyll fluorescence of birch leaves (Betula pendula)

The impact of ozone fumigation on chlorophyll a fluorescence parameters and chlorophyll content of birch trees grown at high and low fertilization were studied for 6-, 8-, and 12-week old leaves. Fluorescence parameters were measured with a portable fluorometer with its fibre optics tightly inserted in a gas exchange cuvette at light intensities from 0 to 220 μmol photons m-2 s-1. Ozone caused significant changes of primary photosynthetic reactions: a decrease of the quantum yield of photosystem II and an increase of non-photochemical quenching. In all leaves a biphasic light response of nonphotochemical quenching was observed. Ozone fumigation shifted the onset of the second phase from a PFD of about 60 μmol m-2 s-1 to about 30 μmol m-2 s-1. While the fertilizer concentration had no influence on this character, high fertilization supply of plants partially reduced O3-induced damage. The light responses of Ft, Fm' and NPQ observed in birch leaves grown in O3-free air indicate the existence of at least two different processes governing energy conversion of the photosynthetic apparatus at PS II in the range of PFD 0-200 μmol photons m-2 s-1. The first phase was attributed to a rather slowly relaxing type of non-photochemical quenching, which, at least at low PFD, is thought to be related to a state 1-2 transition. The further changes of the fluorescence parameters studied at higher PFD might be explained by an increase of energy-dependent quenching, connected with the energization of the thylakoid membrane and zeaxanthin synthesis. A major effect of ozone treatment was a lowering of PS II quantum yield. This reflects a reduction of PS II electron transport and corresponds to the reduction of CO2-fixation observed in ozonated leaves.The impact of ozone fumigation on chlorophyll a fluorescence parameters and chlorophyll content of birch trees grown at high and low fertilization were studied for 6-, 8-, and 12-week old leaves. Fluorescence parameters were measured with a portable fluorometer with its fibre optics tightly inserted in a gas exchange cuvette at light intensities from 0 to 220 μmol photons m-2 s-1. Ozone caused significant changes of primary photosynthetic reactions: a decrease of the quantum yield of photosystem II and an increase of non-photochemical quenching. In all leaves a biphasic light response of non-photochemical quenching was observed. Ozone fumigation shifted the onset of the second phase from a PFD of about 60 μmol m-2 S-1 to about 30 μmol m-2 s-1. While the fertilizer concentration had no influence on this character, high fertilization supply of plants partially reduced O3-induced damage. The light responses of Ft, Fm′ and NPQ observed in birch leaves grown in O3-free air indicate the existence of at least two different processes governing energy conversion of the photosynthetic apparatus at PS II in the range of PFD 0-200 μmol photons m-2 s-1. The first phase was attributed to a rather slowly relaxing type of non-photochemical quenching, which, at least at low PFD, is thought to be related to a state 1-2 transition. The further changes of the fluorescence parameters studied at higher PFD might be explained by an increase of energy-dependent quenching, connected with the energization of the thylakoid membrane and zeaxanthin synthesis. A major effect of ozone treatment was a lowering of PS II quantum yield. This reflects a reduction of PS II electron transport and corresponds to the reduction of CO2-fixation observed in ozonated leaves.We gratefully acknowledge data on chlorophyll content from Dr. W. Landolt and the technical assistance of Mrs. C. Rhiner, Mr. U. Bühlmann, Mr. P. Bleuler and Mr. A. Bur-kart in tending the plants and operating the O3 fumigation. We also thank Mrs. M.J. Sieber for correcting the English text. The study was financed through the ‘EUREKA 447 EUROSILVA’ program of the Swiss ‘Bundesamt für Bildung und Wissenschaft’ and through a joint agreement between The Swiss Federal Institute for Forest, Snow and Landscape Research and The Ural State Forestry Engineering Academy for a sabbatical of the first author in Switzerland, and INTAS (Brussels, Proj. Nr. 93–1645) for financial support of S.S. and W.B

Upscaling Ozone Flux in Forests from Leaf to Landscape

Although stomatal conductance for ozone (O3) correlates with leaf to air water vapor difference (VPDLA) at the leaf level, uncertainty in up-scaling to the whole tree level can be overcome by means of sap flow measurements at the tree trunk. Further up-scaling to the stand level is possible by relating whole tree O3 flux to silvicultural and/or tree-allometric data. In such a way, canopy conductance and O3 uptake can be related to ground surface area. When normalized, canopy conductance is demonstrated to follow a functional relationship to VPDLA across several forest ecosystems thus allowing a generalization of model approaches. Further up-scaling to the landscape level, however, needs further investigations due to differences in the response of canopy conductance to environmental drivers in forest stands and grassland ecosystems, respectively.JRC.H.4-Transport and air qualit