Influence Of Light Availability Research Articles

Loss and replacement of macroalgal standing stock and productivity after a major environmental disturbance

AbstractHabitat‐forming macroalgae are widely recognized as one of the most productive ecosystems on earth. However, relatively little is known about the variation in productivity over large spatiotemporal scales and the relative importance of environmental and biotic factors in influencing the quantity of carbon fixed. Here we leverage a large tectonic event to understand how fluctuations in the biomass of habitat‐forming macroalgae and changes in light availability influence primary productivity along 130 km of coastline over 5 years. We also quantify the effects of changes to species composition on primary productivity. This study revealed significant implications of a compromised light environment for the biomass of macroalgae and productivity rates. Immediately post‐earthquake, there was a substantial loss of biomass (an average of −83%) of a previously dominant large brown alga, Durvillaea spp., and very limited recovery of biomass over the next 5 years. Reductions in biomass coupled with changes in light attenuation resulted in average net primary production (NPP) from Durvillaea decreasing from 1130 g C m−2 year−1 before the earthquake to 192 g C m−2 year−1 after 5 years. Partial compensation of reduced NPP was facilitated by increases in the biomass of a smaller fucoid Carpophyllum maschalocarpum, but its productivity was considerably less on average, resulting in a reduction in carbon fixation. Overall, reductions in biomass resulted in a 2‐fold to 10‐fold drop in carbon fixation by canopy‐forming macroalgae over at least 5 years, while a degradation of the light environment further compromised primary productivity, and most likely detrital subsidies of organic matter to the nearshore ecosystem.

Effects of thinning on functional and phylogenetic diversity of regenerated woody plants in plantations over time

AbstractAimsConversion of natural mixed forests into monoculture plantations results in a loss of biodiversity, and consequently leads to serious ecological problems (e.g. soil acidification and soil fertility declines) by controlling the quantity and quality of litter entering the soil. Plant diversity in the understorey is the most important component of aboveground biodiversity in plantations and plays a critical role in the sustainable development of plantations. Thinning has been proven effective in promoting the regeneration of understorey plants, and most studies have targeted the effects of thinning on a single biodiversity index (e.g. species richness) of the understorey in plantations. The effects of thinning on functional and phylogenetic diversity are less addressed, however, which could limit the full understanding of biodiversity maintenance and potential processes of community assembly integrally in plantations after thinning.LocationNortheast China.MethodsWe chose young and middle‐aged larch (Larix kaempferi) plantations based on the time after thinning (short term, 1–3 years; medium term, 4–9 years; and long term, 10 years or longer), quantified the functional and phylogenetic diversity and the structure of regenerated woody plants in the understorey, and related the functional and phylogenetic diversity to environmental factors (canopy openness and soil nutrients).ResultsFunctional richness and evenness decreased over time after thinning in two types of plantations, and in the medium term the functional divergence of young plantations was significantly lower. At short term after thinning, the phylogenetic diversity was higher in two types of plantations. Functional richness was significantly related to canopy openness in young plantations, while functional divergence was closely related to soil phosphorus content in middle‐aged plantations. Functional and phylogenetic structure of the regenerated woody community changed from dispersion to clustering and had a significant relationship with environmental conditions (e.g. light availability in both young and middle‐aged plantations), highlighting that environmental filtering gradually became the main driving force of community assembly in the regenerated community of the understorey.ConclusionThe functional and phylogenetic diversity of regenerated woody plants changed over time after thinning under the influence of light availability, and environmental filtering played a crucial role in the assembly of the understorey community. Our study expands the research of biodiversity maintenance by considering the effects of thinning over time, and provides new insights into the management and sustainable development of plantations.

Experimental test of the influence of light availability on the evolution of eye size and behaviour in Daphnia.

There exists extensive variation in eye size. Much work has provided a connection between light availability and differences in eye size across taxa. Experimental tests of the role of the light environment on the evolution of eye size are lacking. Here, we performed a selection experiment that examined the influence of light availability on shifts in eye size and the connection between eye size and phototactic (anti-predator) behaviour in Daphnia. We set-up replicate experimental populations of Daphnia, repeatedly evaluated phenotypic shifts in eye size during the ~50-day experiment, and performed a common garden experiment at the end of the experiment to test for evolutionary shifts in eye size and behaviour. Our phenotypic analyses showed that eye size rapidly diverged between the light treatments; relative eye size was consistently larger in the low versus high light treatments. Selection on eye size was also modified by variation in density as increases in Daphnia density favoured a larger eye. However, we did not observe differences in eye size between the light treatments following two generations of common garden rearing at the end of the experiment. We instead observed strong shifts in anti-predator behaviour. Daphnia from the low light treatment exhibited decreased phototactic responses to light. Our results show that decreased light relaxes selection on anti-predator behaviour. Such trends provide new insights into selection on eye size and behaviour.

Giant clams as open-source, scalable reef environmental biomonitors.

Valvometry, the electronic measurement of bivalve shell opening and closing, has been demonstrated to be a valuable biomonitoring technique in previous ecological and environmental studies. Valvometric data has been shown to relate significantly to pollution, predation, animal stress and feeding activity. However, there is a need for valvometric techniques applicable to coral reef environments, which may provide critical insights into reef resilience to ocean warming and acidification. Giant clams are endemic to coral reefs and hold great promise as valvometric recorders of light availability, productivity and other environmental variables. Despite this promise, prior valvometric work on giant clams has been limited by specialized hardware less accessible to developing countries where many coral reefs are found. Here we report on an open-source approach that uses off-the-shelf components to monitor smooth giant clam (Tridacna derasa) valve opening behavior, and tests this approach in the simulated reef environment of the Biosphere 2 Ocean. Valvometric data corroborates the influence of light availability on diurnal behavior of giant clams. The clams basked during daylight hours to expose their photosymbionts to light, and adopted a partially-closed defensive posture at night. The animals showed variations in the frequency of complete closures, with most occurring during night-time hours when the animals prioritize filter-feeding activity, clapping their valves to expel pseudofeces from their gills. Closure frequency showed a significant relation to pH and a significant lagged relationship to chlorophyll-a productivity, which are both a function of algal productivity in the Biosphere 2 Ocean tank. These results suggest that the animals fed on phytoplankton following periodic bloom events in the Biosphere 2 Ocean during the experiment. We propose that giant clams exhibit behavioral plasticity between individuals and populations, and advocate for the more widespread use of valvometry to enable comparative studies of reef environment and animal health.

Light drives vegetative phenology of

Despite Orchidaceae is a key component of the epiphytic flora of tropical and subtropical forests, phenological studies of this group are rare, mainly due to technical difficulties in observing epiphytes, the reduced abundance of wild specimens, and to the evergreen characteristic of these plants. We monitored shoot and root production of translocated young plants of the epiphytic orchid Cattleya intermedia Graham at the edge and in the interior of a subtropical Atlantic Forest fragment, and investigated their relationship with temperature, luminosity, photoperiod, rainfall and air humidity. Individuals propagated in vitro were translocated in the spring and inspected monthly for 3 years for shoot and root production. Shoot production at the edge of the forest was positively related with photoperiod and luminosity. In the interior, this relationship was characterised by a 1-month time delay. The highest concentrations of plants with shoot production occurred in spring and summer in both environments. Interior plants were more likely to produce roots in spring and summer, while edge plants were more likely to produce roots in summer. Edge plants produced fewer roots when rainfall was high, while interior plants produced more roots when interior air humidity was high. The influence of light availability for translocated plants was demonstrated by the different responses of shoot growth at the edge and in the interior of the forest and by the relationship with the seasonal variation of this variable. Thus, light becomes a key factor for the establishment of translocated C. intermedia and must be considered in the choice of their habitats.

Control of Urochloa brizantha cv. Marandu by Glyphosate and its Interaction with light availability

The use of glyphosate in the desiccation of Urochloa brizantha cv. Marandu is a common practice in Brazilian agriculture; however, the effect of night application in this species is not clearly known. Thus, this study aimed to evaluate the influence of light availability on glyphosate efficiency in the control of U. brizantha. Seven herbicide doses (0, 90, 180, 360, 720, 1,440, and 2,160 g ha-1) in plants submitted to daytime application, followed by 24, 48, or 72 h of dark and night were evaluated. The accumulation of dry matter of U. brizantha, the visual evaluation of injuries, the doses that provided 50 and 80% of control (C50 and C80), and the doses that provided 50 and 80% reduction of dry matter (GR50 and GR80) at 7, 14, 21, 28 days after application (DAA) and at 30 days after cutting (regrowth) were determined. Satisfactory control (>80%) and the absence of regrowth were established from 1,440 g ha-1 in all treatments. However, injury reduction was observed in plants that remained 72 h in the dark relative to daytime treatment in all doses. The highest dose of glyphosate (2,160 g ha-1) reduced U .brizantha by 41, 15, and 3%. For the dose of 1,440 g ha-1 the reduction was 37, 16, and 6%, at 7, 14, and 21 DAA, respectively. The values of GR50 and GR80 decreased from regrowth (37 and 28% less relative to daytime treatment) for plants that were 72 h in the dark. The light favors the behavior of glyphosate in the plant, and therefore this herbicide should not be applied at night for the control of U. brizantha.

Light availability influences the intensity of nectar robbery and its effects on reproduction in a tropical shrub via multiple pathways.

The multiple exogenous pathways by which light availability affects plant reproduction (e.g., via influence on attraction of mutualists and antagonists) remain surprisingly understudied. The light environment experienced by a parent can also have transgenerational effects on offspring via these same pathways. We evaluated (a) the influence of light availability on floral traits in Odontonema cuspidatum, (b) the relative importance of the pathways by which light influences nectar robbery and reproductive output, and (c) the role of parental light environment in mediating these relationships. We conducted a reciprocal translocation experiment using clonally propagated ramets and field surveys of naturally occurring plants. Light availability influenced multiple floral traits, including flower number and nectar volume, which in turn influenced nectar robbery. But nectar robbery was also directly influenced by light availability, due to light effects on nectar robber foraging behavior or neighborhood floral context. Parental light environment mediated the link between light availability and nectar robber attraction, suggesting local adaptation to low-light environments in floral visitor attraction. However, we found no transgenerational effect on reproduction. Our findings demonstrate that exogenous pathways by which light influences plants (particularly through effects on floral antagonists) can complicate the positive relationship between light availability and plant reproduction. Our results are among the first to document effects of light on floral antagonists and clonal transgenerational effects on flower visitor attraction traits.

Eucalyptus Are Unlikely to Escape Plantations and Invade Surrounding Forests Managed with Prescribed Fire in Southeastern US

Woody biomass production can increase through establishment of non-native tree species exhibiting greater growth potential than traditional native species. Interest in growing Eucalyptus in the southeastern US has raised concern over its potential spread and invasion, which could impact ecosystem properties and functions. Within the matrix of land use where Eucalyptus establishment is being considered in the southeastern US, surrounding pine forests managed with fire represent a likely pathway for invasion. We used greenhouse and field experiments to evaluate the potential invasion risk of Eucalyptus benthamii. We were specifically interested in determining if seeds could successfully germinate in fire-maintained pine forests and if fire-return intervals influenced germination through impacts on litter accumulation and light availability. The greenhouse experiment investigated the influence of light availability on germination success, whereas the field study investigated the influence of time since fire, and thus litter accumulation and light availability, on germination success. Percent germination was similar under non-shaded controls and moderate shade, but complete shade resulted in low germination rates. Germination was lower in the field compared to the greenhouse and was influenced by litter and light availability, which varied according to fire-return intervals. Litter increased, and light availability decreased, with time since burn. Germination was negatively related to litter depth and positively related to light availability, thereby decreasing with time since fire. Germination increased with litter removal but remained positively related to light availability after litter removal. Higher germination with litter removal suggests germination is influenced by litter, but higher germination with increased light availability, regardless of raking, suggests germination is also influenced by light availability. Despite these relationships, no seedlings persisted through the growing season. The low germination rates under a variety of field conditions coupled with the lack of persistence suggests establishment may be unlikely, regardless of the surrounding land matrix.

Influence of light availability and soil productivity on insect herbivory on bilberry (Vaccinium myrtillusL.) leaves following mammalian herbivory.

Vegetative parts of bilberry (Vaccinium myrtillus) are important forage for many boreal forest mammal, bird and insect species. Plant palatability to insects is affected by concentration of nutrients and defense compounds in plants. We expected that palatability of bilberry leaves to insect herbivores is influenced by light availability and soil productivity (both affecting nitrogen concentration and constitutive carbon-based defense compound concentration) and herbivory by mammals (affecting nitrogen concentration and induced carbon-based defense compound concentration). We studied bilberry leaf herbivory under different light availability, soil productivity and mammalian herbivory pressure in small sampling units (1m x 1m) in boreal forest in Norway. We used generalized linear mixed models and generalized additive mixed models to model insect herbivory on bilberry leaves as a function of shade, soil productivity and mammalian herbivory. Observed insect herbivory on bilberry leaves increased with increasing shade levels. Predicted insect herbivory increased with increasing previous mammalian herbivory at high shade levels and this response was magnified at higher soil productivity levels. At low to intermediate shade levels, this response was only present under high soil productivity levels. Our results indicate that light availability is more important for variation in bilberry leaf palatability than soil nutrient conditions.

Water Flow and Light Availability Influence on Intracellular Geosmin Production in River Biofilms.

Hydro-morphological alterations in water bodies caused by climate change and human activities affects the ecosystem functioning and generate important water quality problems. Some of these alterations can generate an increase in cyanobacterial blooms, which are associated with the appearance of bad taste and odorous compounds such as geosmin. The factors that trigger their production are still unclear, and this inability to predict geosmin episodes provokes economic problems for water supply companies. This study aims to evaluate the effects of water flow and light availability on biofilm development and intracellular geosmin formation. A mesocosm experiment was performed between February–April, 2019. The mesocosms were a set of 10 outdoor 3 m long flumes, with a continuous water supply from the Ter river (Catalonia, NE Spain). Two light intensities were established: natural light and light reduced to 80%, combined with five gradual water flows from 0.09 to 1.10 L/s. Water samples were taken to analyze nutrients, and biofilm samples, to analyze geosmin concentration, chlorophyll a and the community. Geosmin in biofilm was detected in those treatments in which Oscillatoria sp. appeared. The concentration of intracellular geosmin was higher at lower water flows (0.09 and 0.18 L/s), and the highest (2.12 mg/g) was found in the flume with the lowest water flow (0.09 L/s) and irradiation (20%). This flume was the one that presented a greater concentration of Oscillatoria sp. (21% of the community). It stands out that, when geosmin in biofilm was found, the dissolved inorganic nitrogen and soluble reactive phosphorus ratio decreased, from an average of 417:1 to 14:1. This was mainly due to an increase in inorganic phosphorus concentration generated by a change in the nutrient uptake capacity of the community’s biofilm. The results obtained in this study indicated the potential implications for stream ecosystem management to control geosmin appearance. Likewise, they could be used as an early warning system, establishing that in times of drought, which lead to a general decrease in river water flow, the situation could be optimal for the appearance and development of geosmin producing cyanobacteria in low-flow areas near the river banks.

Unraveling Shade Tolerance and Plasticity of Semi-Evergreen Oaks: Insights From Maritime Forest Live Oak Restoration.

Quercus spp. (oaks) are generally intermediate in shade tolerance, yet there is large variation within the genus in shade tolerance and plasticity in response to varying resource availability. Ecophysiological knowledge specific to semi-evergreen Quercus spp. from subtropical maritime forests is lacking relative to temperate deciduous oaks. We studied the influence of light availability and plant competition on leaf physiology and performance of semi-evergreen Quercus virginiana on a barrier island along the US southern Atlantic coast. Seedlings were underplanted in pine (Pinus taeda) plantation stands with varying overstory density (clear-cut, heavy thin, light thin, and non-thinned; creating a gradient of understory light availability) and vegetation (no competition removal or herbaceous competition removal) treatments. After 2 years, seedling survival was higher with increasing light availability (clear-cut = heavy thin > light thin > non-thinned). Seedling growth (i.e., diameter, height, and crown width) increased similarly with increasing thinning intensity, while vegetation control was mainly beneficial to seedling growth in clear-cuts. These responses were partially explained by foliar nitrogen and leaf trait measurements, which followed the same pattern. Q. virginiana seedlings demonstrated high plasticity in their ability to acclimate to varying resource availability, as indicated by light response curves, specific leaf area, stomatal density, stomatal pore index, and maximum theoretical stomatal conductance. Light compensation and saturation points illustrated seedling capacity to increase net CO2 assimilation with increased light availability. Leaves on trees in the high light environment had the highest net CO2 assimilation, stomatal density, stomatal pore index, maximum theoretical stomatal conductance, and lowest specific leaf area. Although we demonstrated the relative shade tolerance of Q. virginiana in lower light environments (i.e., heavy and light thin plots), this semi-evergreen species shows high plasticity in capacity to respond to varying resource availability, similar to other Quercus spp. from mesic and Mediterranean environments.

New insights about the primary production dependence on abiotic factors: Ria de Aveiro case study

Abstract The Ria de Aveiro is a mesotidal coastal lagoon located in the north coast of Portugal. Although the biophysics of this coastal system has been extensively researched in previous studies, there is still a lack of knowledge about the fate of biomass of fluvial origin in the lagoon and on the on the limiting factors of growth of their plankton communities. Based on this assumption, this study presents a first attempt to perform an integrated assessment of the temporal and spatial evolution of water temperature, salinity, pH and chlorophyll a concentration in Ria de Aveiro lagoon, incorporating analysis of in situ data and numerical model predictions of local biophysics. Additionally, the influence of light availability, nutrient limitation and water temperature in lagoon’s phytoplankton biomass was also evaluated. Water temperature, salinity, pH and chlorophyll a were measured in water samples collected monthly from February 2016 until February 2017, in 12 stations strategically located along the lagoon main channels. Chlorophyll a concentration was measured by extraction with aqueous acetone and quantified spectrophotometrycally. A model implementation based on Delft 3D suite was developed to simulate Ria de Aveiro hydrodynamics and water quality, and one-year simulation was performed including the sampling period. The results show a seasonal and longitudinal variability of the biophysical variables under analysis, allowing its quantification under different conditions in such a complex system. Particularly, the phytoplankton biomass showed a typical seasonal variability, characterized by a spring/summer bloom with a maximum of 8 μg/L, when environmental conditions are suitable to their growth, in opposition to nutrients concentration, that shows a 90% uptake of the total available by the phytoplankton communities. During these periods, Ria de Aveiro lagoon was found to be nutrient limited. Despite the seasonal light limitation, the primary production is strongly ruled by water temperature and nutrients concentration variability. These are strongly dependent on the riverine input, which is the most important natural source controlling the water temperature and nutrients concentration variability. The spatial and temporal distribution of the different variables is strongly influenced by the tidal dynamics, but also by geomorphologic features, such as depth and narrowness of the channels, which play therefore a major role in water quality characteristics. In summary, the water temperature establishes the seasonal variability, limiting photosynthesis in winter to values close to 0, while nutrients concentrations rule the primary production during spring and summer, since the nutrients uptake by phytoplankton and other marine organisms is about 90% higher than the replenishment from oceanic and riverine origin. These conclusions upgrade the state of the art about local processes, which generally referred that plankton community’s growth in Ria de Aveiro is nutrients limited.

The Influence of Light on Olive (Olea europaea L.) Fruit Development Is Cultivar Dependent.

In olive, the response to environmental conditions, such as light availability, is under genetic control and requires a combination of biochemical and physiological events. We investigated the effect of irradiance in fruit development in two Italian cultivars, Leccino and Frantoio. Morphological and cyto-histological analyses, as well as water and oil content determination, were carried out in fruits exposed to a different light regime (named as light and shade fruits). Results demonstrated that the influence of light availability on fruit development depends on the cultivar. In Leccino, the fresh and the dry weight, the percentage of dry matter, the kernel and fruit diameter, the mesocarp thickness and the mesocarp cell size were higher in the light exposed fruits than in the ones grown in the shade. In Frantoio, differences between light and shade fruits were observed only at 140 DAF (Days After Flowering) and only in the kernel and fruit diameter and in the dry and fresh weight, which were higher in the light exposed fruits. Leccino, therefore, showed a greater sensitivity to the light availability. This may be related to the observed delay in the endocarp lignification as compared to the Frantoio cultivar. In each cultivar, moreover, shade and light fruits did not show differences in the timing of cell differentiation. Finally, the investigation of oil storage carried out in cyto-histological studies demonstrated that differences in oil content between fruit subjected to different light regimes correlated with the number of oil containing cells, rather than the oil content per cell. A different behaviour was observed in the two cultivars: in Leccino, the mesocarp cell size was almost twice of Frantoio, while oil drops were only 30% larger; therefore, the percentage of cell volume occupied by the oil drops was lower in Leccino than in Frantoio. The chemical analysis confirmed this observation.

Influence of light availability on the specific density, size and sinking loss of Anabaena flos-aquae and Scenedesmus obliquus

Harmful algal blooms in eutrophic waters pose a serious threat to freshwater ecosystems and human health. In-situ light availability control is one of the most commonly used technologies to suppress algae in lakes and reservoirs. To develop a better understanding of the effects of light on algal growth, specific density, colony size and sinking loss, Anabaena flos-aquae (cyanobacteria) and Scenedesmus obliquus (green algae) were evaluated in varying light scenarios. The results showed that the specific density and colony size of these two species varied during growth, and there were obvious differences among the light scenarios. At the end of exponential phase, S. obliquus incubated under light-limited condition maintained a higher specific density and formed larger aggregates, whereas A. flos-aquae formed a longer filament length. Both species exhibited higher sinking loss rates with lower light availability. These results implied that the sinking loss rate was not always constant but should be considered as a variable response to the change of light availability, and in-situ light availability control might result in a significant increase of the sinking loss of algae due to the change of size and specific density, thereby further affecting the algal biomass in the water column.

Environmental Control on Microbial Turnover of Leaf Carbon in Streams - Ecological Function of Phototrophic-Heterotrophic Interactions.

In aquatic ecosystems, light availability can significantly influence microbial turnover of terrestrial organic matter through associated metabolic interactions between phototrophic and heterotrophic communities. However, particularly in streams, microbial functions vary significantly with the structure of the streambed, that is the distribution and spatial arrangement of sediment grains in the streambed. It is therefore essential to elucidate how environmental factors synergistically define the microbial turnover of terrestrial organic matter in order to better understand the ecological role of photo-heterotrophic interactions in stream ecosystem processes. In outdoor experimental streams, we examined how the structure of streambeds modifies the influence of light availability on microbial turnover of leaf carbon (C). Furthermore, we investigated whether the studied relationships of microbial leaf C turnover to environmental conditions are affected by flow intermittency commonly occurring in streams. We applied leaves enriched with a 13C-stable isotope tracer and combined quantitative and isotope analyses. We thereby elucidated whether treatment induced changes in C turnover were associated with altered use of leaf C within the microbial food web. Moreover, isotope analyses were combined with measurements of microbial community composition to determine whether changes in community function were associated with a change in community composition. In this study, we present evidence, that environmental factors interactively determine how phototrophs and heterotrophs contribute to leaf C turnover. Light availability promoted the utilization of leaf C within the microbial food web, which was likely associated with a promoted availability of highly bioavailable metabolites of phototrophic origin. However, our results additionally confirm that the structure of the streambed modifies light-related changes in microbial C turnover. From our observations, we conclude that the streambed structure influences the strength of photo-heterotrophic interactions by defining the spatial availability of algal metabolites in the streambed and the composition of microbial communities. Collectively, our multifactorial approach provides valuable insights into environmental controls on the functioning of stream ecosystems.

Low Light Availability Alters Root Exudation and Reduces Putative Beneficial Microorganisms in Seagrass Roots.

Seagrass roots host a diverse microbiome that is critical for plant growth and health. Composition of microbial communities can be regulated in part by root exudates, but the specifics of these interactions in seagrass rhizospheres are still largely unknown. As light availability controls primary productivity, reduced light may impact root exudation and consequently the composition of the root microbiome. Hence, we analyzed the influence of light availability on root exudation and community structure of the root microbiome of three co-occurring seagrass species, Halophila ovalis, Halodule uninervis and Cymodocea serrulata. Plants were grown under four light treatments in mesocosms for 2 weeks; control (100% surface irradiance (SI), medium (40% SI), low (20% SI) and fluctuating light (10 days 20% and 4 days 100%). 16S rDNA amplicon sequencing revealed that microbial diversity, composition and predicted function were strongly influenced by the presence of seagrass roots, such that root microbiomes were unique to each seagrass species. Reduced light availability altered seagrass root exudation, as characterized using fluorescence spectroscopy, and altered the composition of seagrass root microbiomes with a reduction in abundance of potentially beneficial microorganisms. Overall, this study highlights the potential for above-ground light reduction to invoke a cascade of changes from alterations in root exudation to a reduction in putative beneficial microorganisms and, ultimately, confirms the importance of the seagrass root environment – a critical, but often overlooked space.

Establishment and Biomass Allocation of Black and Red Mangroves: Response to Propagule Flotation Duration and Seedling Light Availability

ABSTRACT Simpson, L.T.; Osborne, T.Z., and Feller, I.C., 2017. Establishment and biomass allocation of black and red mangroves: Response to propagule flotation duration and seedling light availability. Global climate change is driving the expansion of mangroves into salt-marsh habitats around the world, and the ability of mangroves to displace salt marsh is attributable to a combination of factors. Early life history is critical to initial establishment; the mangroves' hydrochorous propagules allow for long-distance dispersal, and plasticity allows for establishment in varying environmental conditions. To examine differences in propagule flotation duration and the influence of light availability on seedling establishment and growth, the growth dynamics of Avicennia germinans (black mangrove) and Rhizophora mangle (red mangrove) seedlings were documented in a manipulative laboratory experiment. Propagules were collected on the Atlantic coast of Florida and were grown under two light levels (sun and shade) ...

Effect of Light Availability on the Interaction between Maritime Pine and the Pine Weevil: Light Drives Insect Feeding Behavior But Also the Defensive Capabilities of the Host.

Light is a major environmental factor that may determine the interaction between plants and herbivores in several ways, including top-down effects through changes in herbivore behavior and bottom-up effects mediated by alterations of plant physiology. Here we explored the relative contribution of these two regulation processes to the outcome of the interaction of pine trees with a major forest pest, the pine weevil (Hylobius abietis). We studied to what extent light availability influence insect feeding behavior and/or the ability of pines to produce induced defenses in response to herbivory. For this purpose, 3-year old Pinus pinaster plants from three contrasting populations were subjected to 6 days of experimental herbivory by the pine weevil under two levels of light availability (complete darkness or natural sunlight) independently applied to the plant and to the insect in a fully factorial design. Light availability strongly affected the pine weevil feeding behavior. The pine weevil fed more and caused larger feeding scars in darkness than under natural sunlight. Besides, under the more intense levels of weevil damage (i.e., those registered with insects in darkness), light availability also affected the pine’s ability to respond to insect feeding by producing induced resin defenses. These results were consistent across the three studied populations despite they differed in weevil susceptibility and inducibility of defenses. Morocco was the most damaged population and the one that induced more defensive compounds. Overall, results indicate that light availability modulates the outcome of the pine–weevil interactions through both bottom-up and top-down regulation mechanisms.

High light intensity mediates a shift from allochthonous to autochthonous carbon use in phototrophic stream biofilms

Changes in the riparian vegetation along stream channels, diurnal light availability, and longitudinal fluctuations in the local light regime in streams influence primary production and carbon (C) cycling in benthic stream biofilms. To investigate the influence of light availability on the uptake dynamics of autochthonous and allochthonous dissolved organic carbon (DOC) in benthic biofilms, we experimentally added 13C-labeled allochthonous DOC to biofilms grown under light intensities ranging from 5 to 152 μmol photons m- 2 s- 1. We calculated the net C flux, which showed that benthic biofilms released autochthonous DOC across the entire light gradient. Light availability and diurnal light patterns influenced C uptake by benthic biofilms. More allochthonous DOC was respired under low light availability and at night, whereas under high light availability and during the day mainly autochthonous C was respired by the benthic biofilm community.

Phytoplankton primary productivity around submarine groundwater discharge in nearshore coasts

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 563:25-33 (2017) - DOI: https://doi.org/10.3354/meps11980 Phytoplankton primary productivity around submarine groundwater discharge in nearshore coasts Ryo Sugimoto1,*, Katsuhiro Kitagawa1, Saori Nishi1, Hisami Honda1,2, Makoto Yamada2, Shiho Kobayashi3, Jun Shoji4, Shinji Ohsawa5, Makoto Taniguchi2, Osamu Tominaga1 1Faculty of Marine Biosciences, Fukui Prefectural University, Obama, Fukui 917-0003, Japan 2Research Institute for Humanity and Nature, Kyoto 603-8047, Japan 3Field Science Education and Research Center, Kyoto University, Kyoto 606-0068, Japan 4Graduate School of Biosphere Science, Hiroshima University, Hiroshima 739-8528, Japan 5Institute for Geothermal Sciences, Kyoto University, Oita 874-0903, Japan *Corresponding author: sugiryo@fpu.ac.jp ABSTRACT: Nutrients supplied from submarine groundwater discharge (SGD) are generally thought to enhance primary production in coastal seas. However, there is little evidence for a direct association between SGD and phytoplankton primary productivity. To elucidate the response of in situ primary productivity to SGD, we conducted comparative experiments at 3 coastal sites in Japan with different SGD types (Site A: Obama Bay; Site B: coast along the western foot of Mt. Chokai; Site C: Beppu Bay) during the summers of 2013-2015. At Site A, which is characterized by seepage-type SGD, we found a significant positive relationship between in situ primary productivity and 222Rn concentration. This was likely driven by nutrient-limited water column conditions. On the other hand, at the volcanic coastal Sites B and C, which are dominated by spring-type SGD, no clear relationships between in situ primary productivity and 222Rn concentration were found. Although significant relationships between nutrient concentrations and 222Rn concentration suggest that SGD acts as a primary nutrient source in these regions, the non-trivial influence of light availability complicates those relationships. Furthermore, lower biomass-specific primary productivity around submarine springs at both sites suggests that submarine springs have negative impacts on phytoplankton growth rates around vent sites, possibly due to changes in local environmental conditions. Our study clarified that the mechanism by which SGD affects phytoplankton production differs from one ecosystem to another because of variable hydrogeographical properties, such as the type of groundwater discharge (i.e. spring or seepage). KEY WORDS: In situ primary productivity · Submarine groundwater discharge · 222Rn Full text in pdf format PreviousNextCite this article as: Sugimoto R, Kitagawa K, Nishi S, Honda H and others (2017) Phytoplankton primary productivity around submarine groundwater discharge in nearshore coasts. Mar Ecol Prog Ser 563:25-33. https://doi.org/10.3354/meps11980 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 563. Online publication date: January 20, 2017 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2017 Inter-Research.