Carbon Flux in the Temperate Zooxanthellate Sea Anemone Anthopleura aureoradiata

<p>This study investigated the algal density and growth, photophysiology and contribution of algae to animal respiration requirements (CZAR), in the symbiosis between the sea anemone Anthopleura aureoradiata and its dinoflagellate symbionts (zooxanthellae) under field and laboratory conditions. A. aureoradiata was collected during summer and winter on sunny and cloudy days from a rocky shore and mudflat environment. Algal densities displayed a trend of being 2.6 and 1.7 times greater during summer than winter on the mudflat on a sunny and cloudy day respectively. Algal division was asynchronous under field conditions over a daily period, and was 2.1 and 1.3 times greater on the rocky shore and mudflat respectively, during winter than summer on sunny days. Under field conditions, the efficiency and maximum rate of photosynthesis (per cell and per association) as well as respiration rate, were all greater during summer than winter. Cloud cover resulted in a difference in a higher maximum rate of photosynthesis per cell on a sunny day than a cloudy day within summer at Kau Bay. Additionally, these photosynthetic parameters and respiration rate were all greater on the rocky shore than mudflat while the photosynthetic compensation irradiance was greater on the mudflat. The CZAR was greatest on the rocky shore during summer on a sunny day (151%) and was also > 100% on a cloudy day in summer at this same site (129%); on the mudflat the CZAR was greatest during summer on a sunny day (89%). The CZAR was measured to be zero during winter at both sites during winter on cloudy days. Additionally, under laboratory conditions A. aureoradiata was exposed to gradual (GTC) and rapid (RTC) temperature changes. While under GTC and RTC, the algal density did not vary, though higher temperatures led to an increase in algal division. Under both GTC and RTC, the photosynthetic efficiency, maximum photosynthetic rate (per cell and per association) and respiration rate all increased with temperature, however under GTC these parameters all decreased between 32.5 [degrees]C and 35 [degrees] C. Photosynthetic compensation irradiance increased with temperature under both GTC and RTC until 30 [degrees] C, after which respiration exceeded maximum photosynthesis, meaning that photosynthetic compensation did not occur. Furthermore, photosynthetic saturation irradiance increased with temperature and peaked at 15 [degrees] C before declining with temperature under both GTC and RTC. The CZAR under GTC increased with temperature until it peaked at 15 [degrees] C (128%), before decreasing to zero at 30 [degrees] C - 35 [degrees] C. Under RTC, the CZAR was zero for all temperatures except at 10 [degrees] C where it was 25.1%. A CZAR < 100% may suggest that the symbiosis between A. aureoradiata and its zooxanthellae is parasitic under most conditions and at most times of the year. Alternatively, there may be some benefit to the symbiosis due to a competitive advantage over other macro-invertebrate species as a result of carbon translocation from the symbiont providing extra support for reproduction and growth. This study also showed A. aureoradiata to have a wide temperature tolerance reflecting the fluctuating conditions of a variable temperate environment. The wide temperature tolerance of this species suggests that it will tolerate short term (50 - 100 years) increases in ocean temperatures however, the threat beyond this time frame with other factors such as ocean acidification remains to be determined.</p>

Carbon Flux in the Temperate Zooxanthellate Sea Anemone Anthopleura aureoradiata

<p>This study investigated the algal density and growth, photophysiology and contribution of algae to animal respiration requirements (CZAR), in the symbiosis between the sea anemone Anthopleura aureoradiata and its dinoflagellate symbionts (zooxanthellae) under field and laboratory conditions. A. aureoradiata was collected during summer and winter on sunny and cloudy days from a rocky shore and mudflat environment. Algal densities displayed a trend of being 2.6 and 1.7 times greater during summer than winter on the mudflat on a sunny and cloudy day respectively. Algal division was asynchronous under field conditions over a daily period, and was 2.1 and 1.3 times greater on the rocky shore and mudflat respectively, during winter than summer on sunny days. Under field conditions, the efficiency and maximum rate of photosynthesis (per cell and per association) as well as respiration rate, were all greater during summer than winter. Cloud cover resulted in a difference in a higher maximum rate of photosynthesis per cell on a sunny day than a cloudy day within summer at Kau Bay. Additionally, these photosynthetic parameters and respiration rate were all greater on the rocky shore than mudflat while the photosynthetic compensation irradiance was greater on the mudflat. The CZAR was greatest on the rocky shore during summer on a sunny day (151%) and was also > 100% on a cloudy day in summer at this same site (129%); on the mudflat the CZAR was greatest during summer on a sunny day (89%). The CZAR was measured to be zero during winter at both sites during winter on cloudy days. Additionally, under laboratory conditions A. aureoradiata was exposed to gradual (GTC) and rapid (RTC) temperature changes. While under GTC and RTC, the algal density did not vary, though higher temperatures led to an increase in algal division. Under both GTC and RTC, the photosynthetic efficiency, maximum photosynthetic rate (per cell and per association) and respiration rate all increased with temperature, however under GTC these parameters all decreased between 32.5 [degrees]C and 35 [degrees] C. Photosynthetic compensation irradiance increased with temperature under both GTC and RTC until 30 [degrees] C, after which respiration exceeded maximum photosynthesis, meaning that photosynthetic compensation did not occur. Furthermore, photosynthetic saturation irradiance increased with temperature and peaked at 15 [degrees] C before declining with temperature under both GTC and RTC. The CZAR under GTC increased with temperature until it peaked at 15 [degrees] C (128%), before decreasing to zero at 30 [degrees] C - 35 [degrees] C. Under RTC, the CZAR was zero for all temperatures except at 10 [degrees] C where it was 25.1%. A CZAR < 100% may suggest that the symbiosis between A. aureoradiata and its zooxanthellae is parasitic under most conditions and at most times of the year. Alternatively, there may be some benefit to the symbiosis due to a competitive advantage over other macro-invertebrate species as a result of carbon translocation from the symbiont providing extra support for reproduction and growth. This study also showed A. aureoradiata to have a wide temperature tolerance reflecting the fluctuating conditions of a variable temperate environment. The wide temperature tolerance of this species suggests that it will tolerate short term (50 - 100 years) increases in ocean temperatures however, the threat beyond this time frame with other factors such as ocean acidification remains to be determined.</p>

Algal stacks and fungal stacks as adaptations to high light in lichens

Some lichens that occur in mountains and arid regions have developed an unusual anatomy resembling window-leaved plants. In these lichens, algal cells occur in thick vertical stacks (algal stacks) separated by vertical channels of light-transferring fungal hyphae (fungal stacks). We present experimental evidence that this anatomy permits higher rates of area-based CO2 assimilation in strong light, but that it also leads to higher respiration resulting in higher compensation irradiance. The net effect of this anatomy must be beneficial in regions of high insolation, as it has arisen many times in different parts of the world, and in unrelated lichens, and these lichens often dominate the communities in which they occur.

Effects of Exogenous Nitric Oxide at Different Concentrations on the Photosynthesis of Pinus koraiensis Sieb. Et Zucc. Seedlings

In the study, the gas exchange parameters and chlorophyll contents in the needles of Pinus koraiensis Sieb. et Zucc. exposed to exogenous nitric oxide (NO) were determined. The Pinus koraiensis Sieb. et Zucc. seedlings were treated with sodium nitroprusside (SNP), a NO donor, at 5 different concentrations ranging from 0 mM to 1 mM. The result showed that at different concentrations exogenous NO had different effects on the photosynthetic parameters and photosynthetic pigments. The content of chlorophyll was maximal in the treatment with SNP at 0.01 mM. At low concentrations (0.1 mM) SNP significantly increased the photosynthetic rate (PN) and decreased the Respiration rate (RD) and Compensation irradiance (IC) of the needles (p<0.05). The experiment proved that at low concentrations exogenous NO signals increased the photosynthesis of Pinus koraiensis Sieb. et Zucc. seedlings. The present results suggested that the lower concentrations SNP might decrease the level of reactive oxygen species (ROS) and promote the growth of the Pinus koraiensis Sieb. et Zucc.

Light-use efficiency of native and hybrid poplar genotypes at high levels of intracanopy competition

In southern Wisconsin, U.S.A., tree growth and associated canopy traits were compared among five native and hybrid genotypes of poplar (Populus spp.) in replicated, monoclonal stands planted at a 1 × 1 m spacing. The overall objective of this study was to assess clonal suitability to cultural conditions entailing high levels of intracanopy competition (such as high-density plantations or long rotations) and to identify selection criteria suitable to such conditions. Two of the clones were Populus deltoides Bartr., two were P. deltoides × Populus nigra L. (DN) crosses, and the fifth was a P. nigra × Populus maximowiczii A. Henry (NM) cross. In the third year after establishment, variation in aboveground biomass gain (ANBG) was analyzed in relation to canopy light interception (IPAR) and canopy light-use efficiency (LUE) during a 31-day period when growing conditions were most favorable (late June through late July). ANBG in this interval varied by twofold among genotypes (2.76–5.78 Mg·ha–1), and it was highest in the two P. deltoides clones, followed by the NM and DN hybrids, respectively. Across genotypes, ANBG was unrelated to IPAR, which varied by only 5%. Instead, it was strongly and positively related (r2 = 0.99) to the twofold variation in LUE (1.06–2.22 g·MJ–1). Among measured canopy traits, the best predictor of LUE (r2 = 0.88) was an additive combination of factors associated to the optimization of canopy photosynthesis: LUE was negatively related to both the canopy light-extinction coefficient and compensation irradiance at the canopy base. We infer from these findings that poplar genotypes can vary considerably in LUE and, correspondingly, in the extent to which photosynthesis is optimized in dense canopies. Furthermore, the low LUE among hybrid genotypes at this level of intracanopy competition may reflect a bias in "tree improvement" efforts towards maximizing biomass production under conditions of relatively low competition.

Studies on a nudibranch that contains zooxanthellae. I. Photosynthesis, respiration and the translocation of newly fixed carbon by zooxanthellae in Pteraeolidia ianthina

Zooxanthellae of the genus Symbiodinium are present in the tissues of the aeolid nudibranch Pteraeolidia ianthina . Individuals with widely differing densities of zooxanthellae are found living off the mid-central coast of eastern Australia. Nudibranchs with low densities of zooxanthellae (0.02-0.5 x 10 6 cells mg -1 protein) are common in winter populations, whereas those with comparatively higher densities (1–3 x 10 6 cells mg -1 protein) are the most common form at other times of the year. Zooxanthellae at all densities in the host exhibit the capacity for photosynthesis, and they grow while resident in the host. The mitotic indices of the zooxanthellae were found to vary as a function of the population density of the algae in the host and were highest in those animals with the lowest densities of zooxanthellae. Oxygen flux was measured as a function of irradiance. Maximum photosynthetic capacity ( P max ), light utilization efficiency ( α ) and compensation irradiance ( I c ) varied between animals, although most of the variation was attributable to differences in the density of zooxanthellae between animals. P max and α were positively correlated with density ( r 2 = 0.82 and 0.88 respectively); I c exhibited an exponential decrease with the density of zooxanthellae in the host ( r 2 > 0.81). I c for animals with 1–2 x 10 6 cells mg-1 protein had values of I c between 30 and 50 μE m -2 s -1 (1 μE = 6 x 10 17 photons), similar to values of I c measured for shade-adapted corals in other studies. Between 25 and 50% of the total photosynthetic products synthesized over 1 h were shown to move from the alga to the animal in that hour. The total respiratory rate of the association was positively correlated with the density of zooxanthellae ( r 2 = 0.94). This relation was used to estimate the respiratory rate of a zooxanthella in vivo . Estimates were, however, unreasonably high; this result suggests that zooxanthellae may directly influence the respiratory rate of the host, possibly by increasing the supply of respiratory substrates.

Growth and morphogenesis of shoot initials of Douglas fir, Pseudotsuga menziesii (Mirb.) Franco, in vitro.

A method of micropropagation of Douglas fir is described. Differences in morphogenesis and photosynthesis were found in shoot initials that had been isolated from buds in 10 topophysical positions on 2-yr-old trees. These differences were influenced by medium composition and light intensity, and by forcing, topping or growth regulator treatment of the mother trees. Shoots originating from buds in less exposed parts of the tree generally had a higher relative growth rate, max. net photosynthesis and photochemical efficiency and a lower compensation irradiance. Seasonal changes were found in the optima for nitrate and sucrose concn. in the medium and for light intensity. (Abstract retrieved from CAB Abstracts by CABI’s permission)