We tested the role of solar irradiance and ammonium inputs on phytoplankton bloom formation in Antarctic coastal waters (62°39.576′ S; 60°22.408′ W, Livingston Island, South Sethlands) through the combination of a large‐scale, in situ mesocosm experiment and a small‐scale experiment. Phytoplankton growth, nutrient use, and biomass development remained low at ambient irradiances and increased greatly (greater than thirtyfold) to yield large (up to 93 μ g chlorophyll a l −1 ) phytoplankton blooms in response to moderate shading. The phytoplankton communities tested were light limited when irradiance was reduced below 30% of the incident irradiance and stressed by high irradiance at the full ambient irradiance. Ammonium additions greatly stimulated phytoplankton growth, biomass, and stimulated the use of the large nitrate pool present in the Antarctic waters and lead to a decline in the specific UV absorption by mycosporine‐like amminoacids. The small‐scale experiment confirmed the role of UV irradiance in inhibiting phytoplankton growth and the capacity of ammonium inputs to overcome this inhibition. The alleviation of the high‐irradiance stress by ammonium additions provided evidence of a key role of ammonium inputs in allowing phytoplankton to resume growth and nutrient use. The results demonstrate that there is a narrow window of irradiance where phytoplankton growth is adequate and that coastal Antarctic phytoplankton communities, examined here, are either light limited or stressed by high irradiance at irradiances outside this range. More research is needed to analyze the interplay between light climate, ammonium, and bloom initiation in Antarctic coastal waters to test the generality of the results obtained.
Abstract. The metabolic balance of the open waters supporting submerged macrophytes of the Doñana marsh (SW Spain) was investigated in spring, when community production is highest. The marsh community (benthic + pelagic) was net autotrophic with net community production rates averaging 0.61 g C m−2 d−1, and gross production rates exceeding community respiration rates by, on average, 43%. Net community production increased greatly with increasing irradiance, with the threshold irradiance for communities to become net autotrophic ranging from 42 to 255 μE m−2 s−1, with net heterotrophic at lower irradiance. Examination of the contributions of the benthic and the pelagic compartments showed the pelagic compartment to be strongly heterotrophic (average P/R ratio = 0.27), indicating that the metabolism of the pelagic compartment is highly subsidised by excess organic carbon produced in the strongly autotrophic benthic compartment (average P/R = 1.58).
Abstract. The direct CO2 released by respiration of humans and domesticated animals, as well as the CO2 derived from the decomposition of their resulting wastes was calculated in order to ascertain the direct and indirect metabolic contribution of humanity to CO2 release. Human respiration was estimated to release 0.6 Gt C year−1 and that of their associated domestic animals was estimated to release 1.5 Gt C year−1, to which an indirect release of 1.0 Gt C year−1, derived from decomposition of the organic waste and garbage produced by humans and their domestic animals, must be added. These combined direct and indirect metabolic sources, estimated at 3.1 Gt C year−1, has increased 7 fold since pre-industrial times and is forecasted to continue to rise over the 21st century.
The Novel Coronavirus (COVID-19) daily data of confirmed cases for affected countries and provinces of China reported between 31st December 2019 and 31st May 2020. The data was collected from the European Centre for Disease Prevention and Control (ECDC), and John Hopkin CSSA. The monthly mean temperature of February to May 2020 of capital cities for the various nations.
Volatile and semi-volatile gas-phase organic carbon (GOC) is a largely neglected component of the global carbon cycle, with poorly resolved pools and fluxes of natural and anthropogenic GOC in the biosphere. Substantial amounts of atmospheric GOC are exchanged with the surface ocean, and subsequent utilization of specific GOC compounds by surface ocean microbial communities has been demonstrated. Yet, the final fate of the bulk of the atmospheric GOC entering the surface ocean is unknown. Our data show experimental evidence of efficient use of atmospheric GOC by marine prokaryotes at different locations in the NE Subtropical Atlantic, the Arctic Ocean and the Mediterranean Sea. We estimate that between 2 to 27% of the prokaryotic carbon demand was supported by GOC with a major fraction of GOC inputs being consumed within the mixed layer. The role of the atmosphere as a key vector of organic carbon subsidising marine microbial metabolism is a novel link yet to be incorporated into the microbial ecology of the surface ocean as well as into the global carbon budget.
A comparison of available data on iron concentration in seagrass tissues shows iron concentrations in seagrass leaves growing on carbonate sediments to be below critical levels for angiosperms [< 100 µ g Fe (g DW) − 1 ]. Iron concentrations of leaves in Caribbean seagrasses declined by 5–10‐fold from terrigenous to carbonate sediments (inner Gulf of Mexico to the Caribbean coast off the Yucatan Peninsula). This observation provided evidence of possible iron deficiency in seagrasses, which was confirmed by an experimental demonstration that adding iron to the sediments stimulates growth of the Caribbean seagrass Thalassia testudinum and increases the chlorophyll a concentration of both T. testudinum and Syringodium filiforme growing above coralline carbonate sediments. We conclude that seagrasses growing above carbonate sediments are likely to experience iron deficiency.
1. This study provides evidence for the existence of general intrinsic patterns controlling the maximum growth rate of photosynthetic organisms, based on a compilation of data from more than 120 reports, the species ranging from unicellular algae to trees and thick-leaved desert plants. 2. We used thickness and nutrient concentration of the photosynthetic tissue to scale differences in maximum growth rate among plants, based on the demonstrated importance of these plant traits in regulating the maximum growth rates of particular plant groups. 3. The growth rate declined with increasing thickness of the photosynthetic structures and increased with increasing nitrogen and phosphorus concentration. The strong dependence of growth rate and nutrient concentrations on tissue thickness reflect broad-scale patterns and not the adaptive response of individual or closely related species of similar tissue thickness to varying environmental conditions. 4. The scaling of maximum growth rate is similar to the scaling of metabolic rate to animal size. Thickness of the photosynthetic structures therefore plays an important role in the environmental control of plant performance and evolution, setting thresholds for the growth and productivity of photosynthetic organisms.
Long‐term and experimental approaches were used to examine the metabolic balance of the planktonic community in the Bay of Blanes (Spanish Mediterranean). Incubation measurements at weekly intervals for 6 yr revealed that community respiration, R, was consistently larger than gross primary production (GPP) by a factor of 2. The plankton community was net heterotrophic for 2/3 of the study period, with a median P/R ratio of 0.65. The biomass of autotrophs comprised, on average, 41% ± 3% of the planktonic biomass, and the total microplankton biomass was about 2.5‐fold greater than that of the primary producers. The monthly average GPP and R were positively correlated with day length, and the planktonic respiration and gross production per unit microplankton biomass increased with increasing water temperature. Experimental nutrient additions had a greater effect on GPP than respiration rates; the increase in R along the nutrient gradient was 7.8% (± 0.4%) of the increase in GPP. As a result, net community production increased in parallel with GPP, shifting from net heterotrophic at low GPP to net autotrophic when GPP increased because of nutrient additions. Our results show that the R that would be supported by llocthonous inputs was 3.83 ± 0.67 µmol O 2 L −1 d −1 , and the average GPP required to shift the community from net heterotrophic to net autotrophic was about 4 µmol O 2 L −1 d −1 . This is well above the average GPP recorded in the Bay of Blanes along this study (2.56 ± 0.13 µmol O 2 L −1 d −1 ), explaining the net heterotrophic nature of the community.
