Friday, June 15, 2007

Brown the new green in an ultraviolet world

As we have discussed here and here the changes and effects of UV flux is the precursor mechanism for the oscillations in CO2 absorption and emission from the biosphere and hence changes in the atmospheric levels.

The ability of biological species to adapt to adverse environments is one of the paradoxes of Ecological science.

How the exclusion of some “players” from the” marketplace” will allow for smaller players to dominate the market due to enhanced adaptability.

Changes to the ozone levels and UV penetration are cyclical over the solar cycles from the 27 day rotation, the 11 year cycle ,the Gleissberg cycle and longer orbital parameters.

Solar variability is observed on three main time scales: solar rotation (27-day), solar cycle (11year) and the Grand Minima time scale. The magnitude of the variability progressively increases from the short to long scales. Earth's climate responses are now found on all these scales. The most recognized are the responses to solar irradiance variations. These variations strongly depend on wavelength rising from 0.1% per solar cycle in total irradiance (mostly infrared-optical range) to 10% in UV and 100% per solar cycle in X-ray range. The variations in the total irradiance produce a small global effect. More substantial is the effect of solar UV variability on large-scale climate patterns. These patterns are naturally excited in the Earth's atmosphere as deviations (anomalies) from its mean state.

How does the distribution of UVB, UVA, and photosynthetically active radiation vary on sensitive surfaces within the biosphere in the agricultural and forest canopies over the growing season? Plants have widely varying sensitivity to solar UV radiation. This can result in shifts in the competitive advantage of one plant species over another and consequently composition and health of both manages ecosystems.

Daylength is the major environmental factor affecting the seasonal photosynthetic performance of Antarctic macroalgae. For example, the "season anticipation" strategy of large brown algae such as Ascoseira mirabilis and Desmarestia menziesii are based on the ability of their photosynthetic apparatus to make use of the available irradiance at increasing daylengths in late winter-spring. The seasonal development and allocation of biomass along the lamina of A. mirabilis are related to a differential physiological activity in the plant. Thus, intra-thallus differentiation in O2-based photosynthesis and carbon fixation represents a morpho-functional adaptation that optimizes conversion of radiant energy to primary productivity.

It is now known that various of the reproductive- and life history events in Antarctic macroalgae are seasonally determined: microscopic gametophytes and early stages of sporophytes in Desmarestia (Wiencke et al. 1991, 1995, 1996), Himantothallus (Wiencke & Clayton 1990) and P. antarcticus (Clayton & Wiencke 1990) grow under limited light conditions during winter, whereas growth of adult sporophytes is restricted to late winter-spring. Culture studies under simulated fluctuating Antarctic daylength demonstrated that macroalgae exhibit two different strategies to cope with the strong seasonality of the light regime in the Antarctic (Wiencke 1990a, 1990b). The so-called "season responders" are species with an opportunistic strategy growing only under optimal light conditions mainly in summer, whereas the "season anticipators", grow and reproduce in winter and spring.

By virtue of their fine morphology, have a high content of pigments per weight unit, a high photosynthetic efficiency, very low light requirements for photosynthesis, and they are better suited to dim light conditions than adult sporophytes. This strategy ensures the completion of the life-cycle under seasonally changing light conditions. Low light requirements for growing and photosynthesizing are developed to cope with Antarctic seasonality and constitute adaptations to expand depth zonation of macroalgae.

This suggests that the microalgae have adapted to predicting not only the early spring photosynthetically active radiation, but also high spring flux of UV due to ozone loss as seen by the levels of melanin pigmentation.

Envisat has captured the first images of Sargassum from space reports the ESA. The brown kelp famous in nautical lore for entangling ships in its dense floating vegetation, has been detected from space for the first time thanks to an instrument aboard ESA’s environmental satellite.

The discovery was made using the MERIS maximum chlorophyll index (MCI) which provides an assessment of the amount of chlorophyll in vegetation to produce detailed images of chlorophyll per unit area. MERIS is uniquely suited for this because it provides images of above-atmosphere spectral radiance in 15 bands, including three bands at wavelengths of 665, 681 and 709 nanometres in order to measure the fluorescence emission from chlorophyll a.

Chlorophyll is the green photosynthetic compound in plants that captures energy from sunlight necessary for photosynthesis. The amount of chlorophyll present in vegetation plays an important role in determining how healthy it is. Accurately monitoring chlorophyll from space, therefore, provides a valuable tool for modelling primary productivity.

"The 709 band used by MERIS is not present on other ocean-colour sensors. It was essential to our detecting Sargassum," Gower said. "The MCI index has allowed us to find so many interesting things, including Sargassum and Antarctic super blooms. It really gives us a new and unique view of the Earth."

In the arctic with similar radiation properties affecting the aquatic biosphere we see similar properties in the growth function of brown alga.

ABSTRACT. The effect of artificial ultraviolet (UV) and natural solar radiation on photosynthesis, respiration and growth was investigated in 14 red, green and brown macroalgal species on Spitsbergen (Norway) during summer 1998. In June, maximum mean solar radiation at sea level was 120 W m-2 of visible (370 to 695 nm) and 15 W m-' of UV radiation (300 to 370 nm), and decreased gradually until the end of the summer. In spite of incident irradiance, levels were low in comparison with other latitudes, and UV radiation stress on growth of Arctic macroalgae was evident. Transplantation experiments of plants from deeper to shallow waters showed, for most algae, an inhibitory effect of both UVA and UVB on growth, except in the intertidal species Fucus djstichus. The growth rate of selected n~acroalgaew as directly correlated to the variations in natural solar radiation during the summer. Underwater experiments both in situ and using UV-transparent incubators revealed a linear relationship between the depth distribution and the growth rate of the algae. In almost all species the photosynthetic oxygen production decreased after 2 h incubation in the laboratory under 38 pm01 m-' s-' photosynthetic active radiation (PAR 400 to 700 nm) supplemented with 8 W m-' UVA (320 to 400 nm) and 0.36 W m-' UVB (280 to 320 nm) compared to only PAR without UV. Like in the growth experiments. the only exception was the brown alga F. distichus, in which photosynthesis was not affected by UV. The degree of inhibition of photosynthesis showed a relation to the depth distribution, i.e. algae from deeper waters were more inhibited than species from shallow waters. In general, no inhibitory UV effect on respiratory oxygen consumption in all macroalgae studied was detected under the artificial radiation regimes described above, with the exception of the brown alga Desmarestia aculeata and the green alga Monostroma arcticum, both showing a significant stimulation of respiration after 2 h of UV exposure. The ecological relevance of the seasonal variations in the solar radiation and the optical characteristics of the water column with respect to the vertical zonation of the macroalgae is discussed.

Jose Aguilera et al MARINE ECOLOGY Vol. 191: 109-119, 1999

In summary we can conclude that high latitude species are adapted to changes in UV flux. That the response in species with elevated melanin pigmentation is more suited to early levels of available PAR where photosynthesis is present. In other species due to defensive response the populations do not significantly decrease ,however photosynthesis is not present as the organisms metabolize on dark respiration.


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