A Multi-Scale Assessment of Solar-Induced Chlorophyll Fluorescence and Its Relation to Northern Hemisphere Forest Productivity

Photosynthesis, or gross primary productivity (GPP), plays a critical role in the global carbon cycle, since it is the sole pathway for carbon fixation by the biosphere. Quantifying GPP across multiple spatial scales is needed to improve our understanding of current and future behavior of biosphere-atmosphere carbon exchange and subsequent feedbacks on the climate system. Remote sensing represents one method to observe vegetation properties and processes, and solar-induced chlorophyll fluorescence (SIF), a light signal originating from leaves, has been shown to be proportional to GPP on diurnal and seasonal timescales. Recently, new techniques to retrieve SIF from satellite observations have provided an unprecedented opportunity to study GPP on a global scale. The relationship between SIF and GPP, however, is subject to significant uncertainty as it is influenced by a number of ecosystem traits (e.g. plant species, canopy structure, leaf age). In this dissertation, I evaluate SIF signals and their relation to GPP over Northern Hemisphere forest ecosystems. First, I compare climate-driven variations in satellite-based SIF to both longstanding satellite vegetation indices derived from reflected sunlight and tower-based estimates of GPP. Even when aggregated regionally, interannual variability (IAV) of SIF is found to be subject to low signal-to-noise performance, particularly during summer. However, through a statistical analysis, I show that increases in springtime temperature driven by warmer temperatures are offset by drier, less productive conditions later in the growing season. Summer productivity, however, is more strongly correlated with moisture than with temperature, suggesting that moisture exerts a greater influence on growing season-integrated signals. While these results demonstrate that satellite observations can be used to reveal meaningful carbon-climate interactions, they also show that currently available satellite observations of SIF do not allow for robust studies of IAV at scales comparable to surface-based observations. To investigate how SIF signals are related to ecosystem function at a local scale, I built and deployed a PhotoSpec spectrometer system to the AmeriFlux tower at the University of Michigan Biological Station (US-UMB) above a temperate deciduous forest. These observations show a strong correlation between SIF and GPP at diurnal and seasonal timescales, but SIF is more closely tied to solar radiation and exhibits a delayed response to water stress-induced losses in summer GPP. This decoupling during drought highlights the challenges in using SIF to detect changes in summertime productivity. However, an increased ratio between red and far-red SIF during drought indicates that the combination of SIF at multiple wavelengths may improve the detection of water stress. Lastly, I explore diurnal and directional aspects of the SIF signal. Observations of SIF are sensitive to sun-sensor geometry, with smaller incident angles (between solar and viewing angles) leading to stronger signals. However, afternoon SIF is typically lower than morning values at equivalent light levels due to ecosystem downregulation, which obfuscates angular dependencies in the afternoon. While satellite observations typically rely on a clear-sky sunlight proxy to scale instantaneous observations of SIF to daily values, these results demonstrate the need to account for sounding geometry and diurnal hysteresis in SIF signals in order to advance the interpretation of satellite observations. Overall, my results provide a multiscale assessment of SIF over Northern Hemisphere forests and emphasize that careful attention must be given to the spatial and temporal scales at which SIF can be used to make inferences about GPP.PHDAtmospheric, Oceanic & Space ScienceUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/168011/1/zbutterf_1.pd

Habitat Distribution And Frond Reorientation As Photoprotection And Drought-Avoidance Mechanisms In Christmas Fern (Polystichum Acrostichoides) In The Southern Appalachian Mountains

Christmas fern (Polystichum acrostichoides (Michx.) Schott) is a ubiquitous wintergreen herb found in the forests of the Appalachian Mountains, yet it is distributed asymmetrically on the landscape, favoring north-facing slopes and shady stream banks. In late autumn, the fronds of Christmas fern undergo an irreversible reorientation, bending at the base of the stipe and lying flat on the forest floor. These fronds maintain high chlorophyll concentrations throughout winter and are photosynthetically active on warm winter days and in early spring before canopy emergence. In three populations in the Appalachian State University Biological Preserve, I prevented fronds from reorienting using wooden dowels and floral wire, artificially holding them up over winter. The fronds that were prevented from reorienting to a prostrate position suffered severe photoinhibition characterized by extensive leaf necrosis coupled with significant declines in light-saturated gas exchange, chlorophyll fluorescence (Fv/Fm), and total chlorophyll, while a control group showed little or no declines as winter progressed. “Surrogate ferns” were constructed and mounted with light sensors in order to characterize the light environment at the leaf level on north- and south- facing slopes. Inclined fronds experienced much higher light levels than prostrate fronds (oriented horizontally), on both slopes, and the sensor on the south-facing slope experienced 22 days in which light exceeded 500 µmol m-2 s-1 and the air temperature at the leaf level was below freezing. Conversely, on the north-facing slope, these conditions only occurred on one day. This result suggests that frond reorientation is sufficient to prevent photoinhibition in overwintering fronds of Christmas fern by reducing winter light, and may be a significant factor limiting its distribution on south-facing slopes where it is bright and cold during winter. Christmas ferns demonstrated remarkable resilience in a controlled dry-down, with little physiological decline as midday water potentials exceeded -1.0 MPa and soil water content approached 0%. Presently, it is unclear how fern water relations contribute to frond reorientation or distribution on the landscape, but the microclimate data suggest that south- facing slopes are not dry enough to induce significant physiological stress on Christmas fern, and that winter light may have more influence. Forecasted changes in local climate may alter the range and distribution of Christmas fern. Our results provide insight into how this species might be affected, with significant ecological implications for understory herbs in our region

Chapter 9 - Light

Explore the contents of Bryophyte Ecology, Volume 1, Chapter 9 - Light by clicking the links above. For the Contents section of this ebook, as well as Volumes 1 through 5, please visit the Bryophyte Ecology Main Page. Use CTRL+F to easily search within PDF files. Ebook sponsored by Michigan Technological University and the International Association of Bryologists.https://digitalcommons.mtu.edu/bryophyte-ecology1/1008/thumbnail.jp

Volume 1, Chapter 9-3: Light: Effects of High Intensity

https://digitalcommons.mtu.edu/bryo-ecol-subchapters/1056/thumbnail.jp

In the heat of the night: wheat respiration and photosynthesis in a warming world

Temperature is crucial in determining the efficiency of plant respiration and photosynthesis. Given ongoing trends of rising global average temperature, warming nights, and longer and hotter heatwaves, understanding how these key processes respond to high temperature is increasingly important. This rings particularly true for crops, because efforts to improve yields must contend with the consequences of warming. In this thesis, measurements of leaf gas-exchange, chlorophyll fluorescence, gene expression and protein thermostability were used to characterise the responses of respiration and photosynthesis to warming in field and controlled environment grown wheat. Among 20 wheat genotypes grown over multiple seasons in the Australian wheat belt, elevated growth temperature coincided with reduced leaf dark respiration rate (Rdark) when measured as O2 consumption (Rdark-O2) at a common temperature, reflecting the predicted acclimation response. However, warming was not associated with declines in either Rdark when measured as CO2 release (Rdark-CO2) or CO2 assimilation rate. The critical temperature at which photosystem II becomes damaged (Tcrit) was also used to quantify wheat photosynthetic heat tolerance and acclimation. Tcrit varied dynamically with time of day and phenological stage, rising from heading to anthesis and grain-fill. Acclimation of Tcrit to a 36C heat shock was rapid (within two hours of heat stress), before reaching an upper threshold of approximately 43.7C after three-to-five days. A systematic review of wheat Tcrit data highlighted a 20C variation in wheat leaf Tcrit, though this was unrelated to the latitude of genotype origin. Controlled environment experiments were also conducted to examine the effects of night versus day warming on Rdark. Wheat leaf Rdark-O2 measured at a common temperature again declined with warming, though this only coincided with night warming rather than day warming. Night warming also led to a lack of acclimation of leaf Rdark-CO2, decreased plant biomass at maturity, and an increased capacity of the non-ATP producing alternative oxidase electron transport pathway. Taken together, this illustrated a predominant effect of night warming in reducing wheat growth, potentially via reduced ATP demand. Gene and protein-level analyses explored biochemical mechanisms underpinning physiological responses to elevated night temperature and daytime heatwave. A five-day 38C daytime heatwave elicited a large and rapid increase in gene expression for heat shock proteins 70 and 90 (HSP70 and HSP90), as well as for the heat tolerant isoform of Rubisco activase (Rca1-b). Elevated night growth temperature seemed to prime these responses; warm night-grown plants increased their expression of HSP70, HSP90, and Rca-1b more rapidly during the heatwave. Additionally, after five days of heatwave, the Rubisco activase of warm night-grown plants displayed a higher thermostability than that of the cool-grown plants. Overall, the results in this thesis demonstrate the dynamic and rapid responses of wheat respiration and photosynthesis to high temperature, as well as highlighting that night warming exerts greater influence over wheat energy metabolism than daytime warming does. These findings provide a framework for future efforts to improve wheat growth under elevated temperature, and also carry implications for the modelling of leaf carbon flux in a future, warmer world

Adjustment of optically measured leaf traits to patterns of solar spectral irradiance in plant taxa from high elevations and from forest understoreys

The attenuation of radiation in forest canopies has been studied in depth within the photosynthetically active radiation (PAR, 400-700 nm), but we are still lacking knowledge on how the spectral composition of ultraviolet radiation (UV-B 280-315 nm, UV-A 315-400 nm) varies. Advances in knowledge on the effects of UV radiation has led to growing interest in its study as a trigger of regulatory responses in plants, rather than as a stressor, which is now considered to be rare in plants growing under natural conditions. Furthermore, a growing number of studies suggest that there are complex interactions in perception, signalling and responses of plants to solar spectral irradiance. My dissertation research is focussed on the acclimation and adaptation of leaf flavonoids to solar radiation in plant taxa from contrasting environments assessed through the study of optically measured leaf traits. These responses were studied in forest understorey taxa growing in a seasonally dynamic, but mostly low UV radiation environment, and in taxa growing at high elevation experiencing a high UV radiation environment in a "common garden" setting. More precisely, we examined: 1) how understorey spectral irradiance changes across shade, leaf-shade and sunflecks through the spring and among different forest stands, 2) how optically measured leaf traits and leaf flavonoids in understorey plants change through the growing season, 3) how these patterns relate to seasonal changes in spectral irradiance especially those in UV region, 4) do the patterns of optically measured leaf traits from a large set of taxa, mainly growing at high elevation, follow their patterns of phylogenetic relatedness and 5) how do their leaf traits relate to climatic conditions at their original collection sites. To study these questions, we adopted relatively new monitoring approaches, enabling us both to measure simultaneously the in situ spectral irradiance from the UV to near infra-red (NIR) regions, and leaf flavonols/flavones in vivo repeatedly with a leaf-clip in the field. Our analysis revealed a hierarchy among those factors affecting spectral composition of solar radiation in forest understoreys; most importantly understorey position (sunflecks, shade or radiation transmitted through the canopy of leaves), then stand composition, and date during spring. We found the optically measured leaf flavonol/flavone index (Iflav) in forest understorey species to be plastic and to adjust to changes in climatic conditions. Furthermore, species' leaf retention strategy (e.g., summer green, overwintering leaves) and new leaf production were found to affect the Iflav of plants. All these factors are reflected in the seasonal trends we describe in leaf flavonoids, measured optically (Iflav) and via leaf extracts, across understorey plant communities. For mountain environments, our objectives were to determine factors that underpin leaf flavonoid accumulation of high elevation taxa and whether patterns in optically measured leaf traits followed their phylogenetic relatedness or climatic conditions at their origin. Both these patterns could potentially constrain plant responses. To see if either pattern was present, we tested for a phylogenetic signal particularly in Iflav from a large set of taxa growing in a high-elevation environment and the relationship of mean Iflav of plants to climatic variables. The tests for a phylogenetic signal (Pagel's λ, range from 0 to 1) gave intermediate fitted λ values with significant results for Iflav and anthocyanin index (Iant), while for the smaller set of taxa growing in Kumpula Botanical Garden (southern Finland) only chlorophyll index (Ichl) showed significant results. Despite the relatively low signal for Iflav, we identified certain genera with mainly positive local autocorrelations (local Moran's I) meaning they contained species showing either with mostly high or mostly low leaf trait values. This suggests potential limitations in their leaf flavonol/flavone accumulation responses. Hence, some of these genera may be less well prepared against higher maximum UV radiation and may encounter constraints in migrating upwards, if other compensatory photoprotection mechanisms fail. We did not find a relationship between Iflav and climate at the plants' origin, while our results suggested UV irradiance in the plants' current microhabitat to be important, albeit not the only driver for flavonoid accumulation. In most taxa, we did not find a clear indication of constraints on leaf flavonoid accumulation, thus no evidence that high UV radiation is a detrimental factor in their environment. The values of these optically measured leaf traits represent the outcome of complex interactions between the evolutionary and biogeographical history, and acclimation to the current growing conditions of the plants. In general across the three studies, these results provide evidence that optically measured leaf traits related to flavonoid accumulation are largely flexible and acclimate to local changes in the environment, as well as adjusting over the growing season.Metsien kenttäkerroksen valo-oloja ja niiden muutoksia keväällä latvuston sulkeutumisen myötä on tutkittu paljon erityisesti niillä aallonpituuksilla, joita kasvit hyödyntävät fotosynteesissä (400-700 nm). Ultraviolettisäteilyn (UV) muutoksista metsien kenttäkerroksessa tiedetään sitä vastoin verraten vähän. UV-säteily (UV-B 280-315 nm, UV-A 315-400 nm) muodostaa pienen osan maanpäällisestä auringon kokonaissäteilystä, mutta sen tiedetään olevan tärkeä kasvien vasteiden stimuloija. Auringon säteilyn eri aallonpituuksien vaikutukset kasveihin eivät ole suoraviivaisia, vaan niihin liittyy monimutkaisia vuorovaikutussuhteita aina valon havainnoinnista tuotettuun vasteeseen asti, esimerkiksi fotoreseptorien signalointireittien komponenttien välillä. Eräs usein havaittu kasvien vaste UV-säteilylle on tuottaa ja kerryttää sekundaarisia aineenvaihduntatuotteita (kuten flavonoideja), jotka osaltaan suojaavat kasveja säteilyn haitallisilta vaikutuksilta (engl. photoprotection). Tässä väitöskirjassa tutkin kasvien lehtien flavonoidien akklimaatiota ja adaptaatiota auringon säteilyyn kahdessa hyvin erilaisissa ympäristöissä. Metsän kenttäkerrosta luonnehtii tyypillisesti alhainen auringon säteilytaso ja lyhytaikainen korkea säteilytaso valoaukoissa. Vuoristoissa UV-säteilyarvot sitä vastoin ovat usein korkeita, ja siellä tutkimme eri puolilta maailmaa tuotuja kasveja samassa ympäristössä. Tutkimme 1) miten metsän kenttäkerroksen auringon säteilyn määrä ja säteilyn suhteellinen määrä spektrin eri aallonpituuksilla muuttuvat keväällä eri latvustoisissa metsiköissä, 2) miten aluskasvuston lehtien flavonoidien määrä muuttuu kasvukauden aikana, mitattuna optisesti sekä määrittäen lehtiuutteista, 3) miten nämä muutokset vertautuvat auringon säteilyn ja erityisesti UV-alueen säteilyn muutoksiin keväällä, 4) noudattavatko vuoristossa kasvavien kasvilajien optisesti mitatut lehtien ominaisuudet taksonien evolutiivisia sukulaisuussuhteita ja 5) korreloivatko nämä mitatut lehtien ominaisuudet kasvien alkuperäisen keräyspaikan ilmasto-olojen kanssa. Käytimme näiden kysymysten tutkimiseen tekniikoita, jotka mahdollistivat laajan (UV-säteilystä lyhyeen infrapunasäteilyyn) auringon säteilyspektrin mittauksen samanaikaisesti. Lehtien flavonoidipitoisuuden mittaamiseen käytimme optista laitetta (Dualex Scientific+), joka mahdollisti toistuvan seurannan kasvia vahingoittamatta. Havaitsimme, että auringon säteilyspektriin metsien kenttäkerroksessa vaikuttivat eniten varjostuksen määrä (umbra, penumbra, valolaikku) sekä laskevassa järjestyksessä metsikkö (eroavat puulajit, tiheys) ja ajankohta kevään aikana. Kasvien flavonoidi-indeksissä havaittiin plastisuutta ja muutoksia vallitsevien ympäristömuuttujien mukaisesti. Lisäksi kasvien lehtistrategiat, sekä uusien lehtien tuotanto vaikuttivat kasvien lehtien flavonoidi-indeksiin. Vuoristossa kasvavien lajien lehtien ominaisuuksien mahdollisia rajoitteita tutkittiin testaamalla niiden fylogeneettinen signaali (Pagel's λ), sekä korrelaatio kasvien alkuperäisen ympäristön ilmastomuuttujien ja lehtien ominaisuuksien välillä. Emme havainneet korrelaatiota kasvien alkuperäisten ilmasto-olojen sekä flavonoidi-indeksin välillä, mikä viittaa kasvien akklimaatioon niiden nykyiseen ympäristöönsä. Lisäksi havaitsimme, että lehtien ominaisuuksien (flavonoidi- ja antosyaani-indeksi) fylogeneettinen signaali oli heikko mutta merkitsevä, ja pienemmästä lajiryhmästä, mitkä kasvoivat Kumpulan kasvitieteellisessä puutarhassa (Etelä-Suomi) ainoastaan klorofylli-indeksi antoi merkitsevän tuloksen. Lähemmässä tarkastelussa (local Moran's I) erotimme sukuja, joiden lajit osoittivat samankaltaisuutta (paikallinen positiivinen autokorrelaatio) lehtien ominaisuuksissa, pääasiassa joko korkeita tai alhaisia indeksiarvoja. Tämä viittaa siihen, että näissä suvuissa flavonoidien kerääntyminen voi olla evolutiivisten sukulaisuussuhteiden mukaisesti rajoittunutta. Tämä voi mahdollisesti vaikeuttaa joidenkin lajien kohdalla migraatiota vuoristossa -varsinkin suvuissa, joissa havaitsimme pääasiassa matalia flavonoidi-indeksin arvoja. Emme kuitenkaan löytäneet selkeää merkkiä rajoitteista vuoristoissa kasvavien lajien lehtien flavonoidien akkumuloitumisessa, joten todisteita korkean UV-säteilyn haitoista niiden nykyisessä ympäristössä ei ollut. Kaiken kaikkiaan tuloksemme osoittavat, että optisesti mitatut lehtien ominaisuudet, liittyen lehtien flavonoidien kertymiseen, ovat joustavia ja akklimoituvat paikallisiin ympäristön muutoksiin, mukaan lukien kasvukauden aikaiset muutokset

Artificial Photosynthesis

Photosynthesis is one of the most important reactions on Earth, and it is a scientific field that is intrinsically interdisciplinary, with many research groups examining it. We could learn many strategies from photosynthesis and can apply these strategies in artificial photosynthesis. Artificial photosynthesis is a research field that attempts to replicate the natural process of photosynthesis. The goal of artificial photosynthesis is to use the energy of the sun to make different useful material or high-energy chemicals for energy production. This book is aimed at providing fundamental and applied aspects of artificial photosynthesis. In each section, important topics in the subject are discussed and reviewed by experts