Seasonal variation in the reflectance of photosynthetically active radiation from epicuticular waxes of Scots pine (Pinus sylvestris) needles

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When the sun never sets : daily changes in pigment composition in three subarctic woody plants during the summer solstice

Subarctic plants in summer (subjected to continuous light) showed photosynthetic pigment contents mainly driven by PPFD (unrelated to day/night cycles) and a xanthophyll cycle responsiveness to PPFD exacerbated during night-times. Composition and content of photosynthetic pigments is finely tuned by plants according to a subtle equilibrium between the absorbed and used energy by the photosynthetic apparatus. Subarctic and Arctic plants are subjected to extended periods of continuous light during summer. This condition represents a unique natural scenario to study the influence of light on pigment regulation and the presence of diurnal patterns potentially governed by circadian rhythms. Here, we examined the modulation of the photosynthetic apparatus in three naturally co-occurring woody species: mountain birch (Betula pubescens ssp. czerepanovii), alpine bearberry (Arctostaphylos alpina) and Scots pine (Pinus sylvestris) around the summer solstice, at 67 A degrees N latitude. Plants were continuously exposed to solar radiation during the 3-day study period, although PPFD fluctuated, being lower during night-times. Photochemical efficiencies for a given PPFD were similar during daytime and night-time for the three species. In Scots pine, for a given PPFD, net assimilation was slightly higher during daytime than during night-time. Overall, the dynamism in pigment content was mainly driven by PPFD, and was generally unrelated to day/night cycles. Weak indications of potential circadian regulation were found over a few pigments only. Interestingly, the xanthophyll cycle was active at any time of the day in the three species but its responsiveness to PPFD was exacerbated during night-times. This was particularly evident for bearberry, which maintained a highly de-epoxidised state even at night-times. The results could indicate an incomplete acclimation to a 24-h photoperiod for these species, which have colonised subarctic latitudes only recently.Peer reviewe

Leaf optical properties and dynamics of photosynthetic activity

Photosynthesis requires a balance between its light-dependent and light-independent reactions so that the energy input through photochemistry matches its consumption. Biochemical and physiological processes help to achieve this balance, as certain processes regulate the activity of light-dependent photochemical reactions, whilst others regulate the activity of temperature-dependent biochemical reactions. Biochemical and physiological processes also modulate the absorbed energy available for photosynthesis by diverting a fraction into non-photochemical pathways that dissipate energy as heat and fluorescence. Interestingly, certain biochemical and physiological processes behind the dynamics of photosynthesis correlate with leaf optical properties (LOPs), which represent an approach to characterising the dynamics of photosynthesis. Yet, how solid is our knowledge concerning the biochemical and physiological processes influencing LOPs, and how accurately do LOPs and the biochemical and physiological processes behind photosynthetic dynamics correlate when investigated across various spatio-temporal scales? This thesis investigated whether reflectance-based and fluorescence-based LOPs adequately correlate with the biochemical and physiological processes behind photosynthetic dynamics, and whether their correlations hold true at various spatio-temporal scales. This thesis demonstrates the validity of reflectance-based and fluorescence-based LOPs as optical proxies for investigating the dynamics of photosynthesis. However, it also identifies sources of variability that cause the correlations between photosynthesis and LOPs to break down. This thesis classifies the sources of variability in terms of methodological (i.e. over-simplification and technical/instrumental constraints) and spatiotemporal limitations. The over-simplification of processes behind the dynamics of photosynthesis and LOPs was addressed by studying the absorption of photosynthetically active radiation (PAR) by conifer needles. PAR absorption is generally considered to be chlorophyll concentration-dependent, yet this thesis shows it to be additionally modulated by the effect that waxes have on needle PAR reflectance. Due to the difficulties of directly measuring needle PAR absorption, PAR reflectance was used as a proxy of PAR absorption. To solve this technical/instrumental constraint, this thesis presents a new methodology that facilitates the direct estimation of PAR absorption. This thesis also demonstrates that certain LOPs appear to be insensitive to detecting the dynamics of certain biochemical and physiological processes over time. This was true for the photochemical reflectance index (PRI), which failed to detect zeaxanthin independent processes behind the thermal dissipation of the absorbed PAR. Lastly, this thesis shows that LOPs can also be influenced by leaf morphology, which could affect the optically-based monitoring of larger-than-leaf scales. Despite the caveats highlighted in this thesis, the potential to monitor the dynamics of photosynthetic activity by optical means is unquestionable, and the results presented here can contribute to reducing uncertainty in the characterisation of photosynthesis by optical means at varying spatio-temporal scales

Matching compensation sites with potential ecological compensation (EC) actions

Ecological compensation (EC) is the practice of transforming an area to recover ecological functions and characteristics that have been impaired due to the exploitation of natural resources (e.g. mining, logging) and changes in land-use (e.g. urbanization, transformation of the land into farmland). EC is usually done at large scales and seldom times at smaller scales that could involve citizen actions. Our newly launched project "Science embracing art to launch small scale ecological compensation actions" aims to reach out to citizens in Finland to raise their awareness of nature conservation, make them familiar with the EC concept and increase their willingness to get involved in EC actions. The EC concept will be explored from the perspective of a wide range of citizens, including different focus groups that will be invited to participate in a set of workshops. The project will have a pseudonym name in Finnish to evoke the EC concept, so that it is easily understood and memorable by citizens. As part of this project, we will develop an EC platform where citizens can suggest sites for EC activities. We will assess key characteristics (e.g. soil type, ecosystem type, state of degradation) in the suggested sites for EC actions. Afterwards, we will classify the sites according to shared characteristics. We will then suggest a set of potential EC actions ranging from simple/short-term to complex/long-term actions for the different sites. Thus, we aim to produce an efficient platform where sites are matched with potential EC actions. The effectiveness of the EC actions conducted on compensated sites will be assessed over time by using ecological indicators such as species richness and community structure. The above mentioned conservation ecology elements of the project, will be encompassed with the study of legal framework, social science and artistic elements. Depending on the degree of equivalency with the original ecosystem, EC actions can be classified as either in-kind or out-of-kind (Cuperus et al. 1999; Villarroya et al. 2014). Our project will make use of both types, and will also make use of private gardens as one of the focal points where EC actions can be implemented to compensate for the environmental impact of regular citizens. The project aims to raise awareness of EC and motivate citizens to volunteer for EC actions in various sites. A flow chart of the key characteristics to be used in building the EC platform will be presented in the congress. In addition, our poster will also show the key social and ecological aspects to be studied in the garden study. Cuperus R., Canters K.J., Udo de Haes H.A., Friedman D.S. 1999. Guidelines for ecological compensation associated with highways. Biological Conservation 90: 41-51. Villarroya A., Persson J., Puig J. 2014. Ecological compensation: From general guidance and expertise to specific proposals for road developments. Environmental Impact Assessment Review 45: 54-62.peerReviewe