Responses of dark respiration in the light to desiccation and temperature in the intertidal macroalga, Ulva lactuca (Chorophyta) during emersion

Dark respiration (nonphotorespiratory mitochondrial CO2 release) in the light (R-L) of the intertidal macroalga Ulva lactuca (Chorophyta) during emersion was investigated with respect to its response to variations in temperature and desiccation. R-L was estimated by CO2 gas-exchange analysis using the Kok effect method, whereas dark respiration in darkness (R-D) was determined from CO2 release at zero light. Rates of R, were significantly and consistently lower than those of R-D in emersed U. lactuca across all the temperature and desiccation levels measured. This demonstrated that dark respiration was partially depressed in the light, with the percentage inhibition ranging from 32 to 62%. Desiccation exerted a negative effect on R-L and R-D at a high temperature, 33 degrees C, whereas it had much less effect on respiration at low and moderate temperatures, 23 and 28 degrees C. In general, R-L and R-D increased with increasing temperature in U. lactuca during all stages of emersion but responded less positively to temperature change with increasing desiccation. Additionally, the Q(10) value (i.e. the proportional increase of respiration for each 10 degrees C rise in temperature) for R-L calculated over the temperature range of 23 to 33 degrees C was significantly higher than that for R-D in U. lactuca during the initial stages of emersion. Respiratory carbon loss as a percentage of gross photosynthetic carbon gain increased with increasing temperature and/or desiccation but was significantly reduced when estimated using R-L rather than R-D. It is suggested that measurements of R-L and how it changes in a variable environment are as important as estimates of R-D and photosynthesis in determining simultaneous balance between photosynthetic carbon uptake and respiratory carbon loss and in modeling the net daily carbon gain for an intertidal macroalga.Dark respiration (nonphotorespiratory mitochondrial CO2 release) in the light (R-L) of the intertidal macroalga Ulva lactuca (Chorophyta) during emersion was investigated with respect to its response to variations in temperature and desiccation. R-L was estimated by CO2 gas-exchange analysis using the Kok effect method, whereas dark respiration in darkness (R-D) was determined from CO2 release at zero light. Rates of R, were significantly and consistently lower than those of R-D in emersed U. lactuca across all the temperature and desiccation levels measured. This demonstrated that dark respiration was partially depressed in the light, with the percentage inhibition ranging from 32 to 62%. Desiccation exerted a negative effect on R-L and R-D at a high temperature, 33 degrees C, whereas it had much less effect on respiration at low and moderate temperatures, 23 and 28 degrees C. In general, R-L and R-D increased with increasing temperature in U. lactuca during all stages of emersion but responded less positively to temperature change with increasing desiccation. Additionally, the Q(10) value (i.e. the proportional increase of respiration for each 10 degrees C rise in temperature) for R-L calculated over the temperature range of 23 to 33 degrees C was significantly higher than that for R-D in U. lactuca during the initial stages of emersion. Respiratory carbon loss as a percentage of gross photosynthetic carbon gain increased with increasing temperature and/or desiccation but was significantly reduced when estimated using R-L rather than R-D. It is suggested that measurements of R-L and how it changes in a variable environment are as important as estimates of R-D and photosynthesis in determining simultaneous balance between photosynthetic carbon uptake and respiratory carbon loss and in modeling the net daily carbon gain for an intertidal macroalga

Comparative physiological behaviors of Ulva lactuca and Gracilariopsis lemaneiformis in responses to elevated atmospheric CO2 and temperature

Physiological metabolisms of seaweeds usually suffered climate changes in the field. Gracilariopsis lemaneiformis and Ulva lactuca, collected from Nan'ao Island, Shantou, China, were cultured under ambient and elevated CO2 supply (390 and 800 mu l L-1), with low and high temperatures (15 A degrees C and 25 A degrees C) for 2 weeks, aiming to compare the difference of the main physiological metabolism between two seaweed species in response to the elevated CO2 and high temperature. At 15 A degrees C, the pH reduction in the culture medium caused by elevated CO2 was larger in G. lemaneiformis than in U. lactuca. At 25 A degrees C, elevated CO2 significantly increased photosynthetic rates (P-n or P-g) and maintained constant respiratory rates (R-d) in G. lemaneiformis. However, for 25 A degrees C-grown U. lactuca, the increment of CO2 did not enhance the P-n (P-g) rates but rapidly decreased the R-d rates itself. With the higher R-d/P-g ratios in G. lemaneiformis than U. lactuca, the warming thereby promoted more allocation of photosynthetic products to respiratory consumption in G. lemaneiformis. Both P-g and R-d rates exhibited lower temperature acclimation in two seaweeds. In addition, elevated CO2 markedly increased the relative growth rate (RGR) and phycobiliprotein (PB) contents at 25 A degrees C, but exhibited no enhancement of chlorophyll a (Chl a), carotenoids (Car), soluble carbohydrate (SC), and soluble protein (SP) contents in G. lemaneiformis, with the reduction of SC when temperature increased only. We suggested that climate changes were probably a more benefit to U. lactuca than to G. lemaneiformis, inherently justifying the metabolism during G. lemaneiformis maricultivation

Thermal acclimation of respiration and photosynthesis in the marine macroalga Gracilaria lemaneiformis (Gracilariales, Rhodophyta)

Chinese 973 Project [2009CB421207]; National Natural Science Foundation of China [41076094, 41276148, 30970450]; Fundamental Research Funds for the Central Universities, SCUT [2011ZG0013]The responses of respiration and photosynthesis to temperature fluctuations in marine macroalgae have the potential to significantly affect coastal carbon fluxes and sequestration. In this study, the marine red macroalga Gracilaria lemaneiformis was cultured at three different temperatures (12, 19, and 26 degrees C) and at high- and low-nitrogen (N) availability, to investigate the acclimation potential of respiration and photosynthesis to temperature change. Measurements of respiratory and photosynthetic rates were made at five temperatures (7 degrees C33 degrees C). An instantaneous change in temperature resulted in a change in the rates of respiration and photosynthesis, and the temperature sensitivities (i.e., the Q10 value) for both the metabolic processes were lower in 26 degrees C-grown algae than 12 degrees C- or 19 degrees C-grown algae. Both respiration and photosynthesis acclimated to long-term changes in temperature, irrespective of the N availability under which the algae were grown; respiration displayed strong acclimation, whereas photosynthesis only exhibited a partial acclimation response to changing growth temperatures. The ratio of respiration to gross photosynthesis was higher in 12 degrees C-grown algae, but displayed little difference between the algae grown at 19 degrees C and 26 degrees C. We propose that it is unlikely that respiration in G.lemaneiformis would increase significantly with global warming, although photosynthesis would increase at moderately elevated temperatures

The photosynthetic and respiratory responses to temperature and nitrogen supply in the marine green macroalga Ulva conglobata (Chlorophyta)

Chinese 973 Project [2009CB421207]; National Natural Science Foundation of China [41276148, 41076094]Temperature effects on photosynthesis and respiration were investigated in the green macroalga, Ulva conglobata, collected from low rocky coast of Nanao Island, Shantou, China. Thalli were cultured at 15 and 25 degrees C and at low nitrogen (LN) and high nitrogen (HN) availability. Dark respiration and light-saturating photosynthesis were measured as oxygen exchange; the characteristics of chlorophyll fluorescence were also assayed. The maximal photochemical yield (F-v/F-m) and maximum relative electron transport rates (rETR(max)) remained stable with moderate fluctuations of temperature (15-30 degrees C) in the short term. However, the values of F-v/F-m and rETR(max) declined with the high temperature (>= 35 degrees C), and such a decline was more accentuated in 15 degrees C- than 25 degrees C-grown algae. Both the rates of photosynthesis and respiration were sensitive to measurement temperature, with the Q(10) values being higher in 25 degrees C-grown algae (HN) than 15 degrees C-grown algae. It appeared that 25 degrees C-grown algae displayed an optimum temperature (T-opt) of 30 degrees C for photosynthesis, while 15 degrees C-grown algae exhibited the T-opt of a range of 20-30 degrees C. When measured at their respective growth temperature, the rates of photosynthesis were significant higher in 25 degrees C-than 15 degrees C-grown algae, while the rates of respiration were identical between 25 degrees C- and 15 degrees C-grown algae. Our results demonstrated that respiration displayed full acclimation; whereas, photosynthesis exhibited partial acclimation to changing growth temperatures in U. conglobata. Consequently, the balance between respiration and gross photosynthesis was re-established by changing growth temperature, with the ratio being lowered with warmer growth temperature. The results also showed that HN availability in culture significantly increased pigments and soluble protein contents and enhanced photosynthesis and respiration. We suggested that the acclimation potential of metabolisms in U. conglobata favored carbon acquisition and net carbon balance with the increasing seawater temperature resulting from climate change and/or increasing N loading from coastal eutrophication

Effects of selenite on growth, photosynthesis and antioxidant system in seaweeds, Ulva fasciata (Chlorophyta) and Gracilaria lemaneiformis (Rhodophyta)

Selenium (Se) is an essential trace element for plants, animals and humans. Se enrichment has been deemed as a new approach to enhance the nutrient and economic value of seaweed to make it commercially competitive. To explore the effects of Se on seaweed photosynthesis, Ulva fasciata (Chlorophyta) and Gracilaria lemaneiformis (Rhodophyta) were cultured over 1 week in selenite (Na2SeO3) concentrations of 0, 200, 500, 800 mg L-1 . Our results showed that, U. fasciata and G. lemaneiformis effectively accumulated Se and transformed inorganic Se to organic Se at the rate of about 80% during cultivation. Se exerted positive effect on growth and photosynthesis in the three Se concentrations (200, 500, 800 mg L-1 selenite) with the optimum concentration 200 mg L-1 in Ulva and 500 mg L-1 in Gracilaria, and Se promoted growth of seaweeds Gracilaria and Ulva, accumulating more soluble protein (SP) and carbohydrate (SC). Also, photosynthesis was improved by promotion of photosynthetic pigments (Chl a, Car, PE, PC), stimulation of photosystem II (PSII) (F-v/F-m a, rETRm), and enhancement of photosynthetic oxygen evolution (Pn, AE). In addition, Se stimulated activities of SOD, POD, CAT and GPX with all Se concentrations in Ulva and Gracilaria, and substantially decreased MDA levels in 200 mg L-1 selenite, indicating that Se could increase antioxidative activity and enhance antioxidant system. We proposed that enhanced defensive system of antioxidants by Se could improve and protect photosynthesis to some extent

Effects of CO2 levels and light intensities on growth and amino acid contents in red seaweed Gracilaria lemaneiformis

The seaweed Gracilaria lemaneiformis is largely maricultivated in China, for use as food and as a material in the agar industry. This alga experiences ocean acidification caused by rising atmospheric CO2 levels, and experiences changing light levels caused by self-shading during the later period of mariculture. In this study, growth and amino acid (AA) content responses of G. lemaneiformis to different CO2 levels (the present and the predicted increased levels) and varying light levels at 28 (+/- 1)degrees C temperature conditions were investigated. The results showed that a higher light level enhanced algal growth and decreased water loss, but reduced AA accumulation. Decreased pH levels (as a result of CO2 elevation) also enhanced algal growth and reduced AA contents, but the decreases in the AA score at the lower pH levels were not significant under the two light level treatments. In this study, the light treatments had greater influences on growth and AA contents than CO2 levels. The results suggest that G. lemaneiformis quality will be negatively affected during the later mariculture production period as levels of CO2 rise and global temperatures increase

Temperature response of photosynthetic light- and carbon-use characteristics in the red seaweed Gracilariopsis lemaneiformis (Gracilariales, Rhodophyta)

Chinese 973 Project [2009CB421207]; National Natural Science Foundation of China [41276148, 41076094]The red seaweed Gracilariopsis is an important crop extensively cultivated in China for high-quality raw agar. In the cultivation site at Nanao Island, Shantou, China, G.lemaneiformis experiences high variability in environmental conditions like seawater temperature. In this study, G.lemaneiformis was cultured at 12, 19, or 26 degrees C for 3weeks, to examine its photosynthetic acclimation to changing temperature. Growth rates were highest in G.lemaneiformis thalli grown at 19 degrees C, and were reduced with either decreased or increased temperature. The irradiance-saturated rate of photosynthesis (P-max) decreased with decreasing temperature, but increased significantly with prolonged cultivation at lower temperatures, indicating the potential for photosynthesis acclimation to lower temperature. Moreover, P-max increased with increasing temperature (~30 mu mol O-2 center dot g(-1)FW center dot h(-1) at 12 degrees C to 70 mu mol O-2 center dot g(-1)FW center dot h(-1) at 26 degrees C). The irradiance compensation point for photosynthesis (I-c) decreased significantly with increasing temperature (28 mu mol photons center dot m(-2)center dot s(-1) at high temperature vs. 38 mu mol photons center dot m(-2)center dot s(-1) at low temperature). Both the photosynthetic light- and carbon-use efficiencies increased with increasing growth or temperatures (from 12 degrees C to 26 degrees C). The results suggested that the thermal acclimation of photosynthetic performance of G.lemaneiformis would have important ecophysiological implications in sea cultivation for improving photosynthesis at low temperature and maintaining high standing biomass during summer. Ongoing climate change (increasing atmospheric CO2 and global warming) may enhance biomass production in G.lemaneiformis mariculture through the improved photosynthetic performances in response to increasing temperature