Effect of pH on Photosynthesis of Euglena mutabilis Schmitz, an Acidophilic Benthic Flagellate

The dependence of the photosynthetic rate of Euglena mutabilis Schmitz on pH across a range of 2.0–10.0 was investigated. Populations of E. mutabilis isolated from sediments of acidic mine drainage in Sensui (pH = 3.95) and a volcanic cold spring in Bougatsuru (pH = 5.32) were cultured in a pH-adjusted growth media for 96 h, and photosynthetic rate and dark respiration rate were measured. The maximum gross photosynthetic rate of E. mutabilis cells from the Sensui drainage population did not vary significantly over the pH range of 2.0–7.0, and their dark respiration rate showed high values at pH = 7.0. The maximum gross photosynthetic rate of E. mutabilis cells from the Bougatsuru spring population did not vary significantly within the pH range of 2.0–6.0, and their dark respiration rate tended to show high values at pH = 7.0. E. mutabilis can colonize under circumneutral conditions up to and including pH = 6.0.

Photosynthetic and Morphological Acclimation to High and Low Light Environments in Petasites japonicus subsp. giganteus

Within each species, leaf traits such as light-saturated photosynthetic rate or dark respiration rate acclimate to local light environment. Comparing only static physiological traits, however, may not be sufficient to evaluate the effects of such acclimation in the shade because the light environment changes diurnally. We investigated leaf photosynthetic and morphological acclimation for a perennial herb, butterbur (Petasites japonicus (Siebold et Zucc.) Maxim. subsp. giganteus (G.Nicholson) Kitam.) (Asteraceae), in both a well-lit clearing and a shaded understory of a temperate forest. Diurnal changes in light intensity incident on the leaves were also measured on a sunny day and an overcast day. Leaves in the clearing were more folded and upright, whereas leaves in the understory were flatter. Leaf mass per area (LMA) was approximately twofold higher in the clearing than in the understory, while light-saturated photosynthetic rate and dark respiration rate per unit mass of leaf were similar between the sites. Consequently, both light-saturated photosynthetic rate and dark respiration rate per unit area of leaf were approximately twofold higher in the clearing than in the understory, consistent with previous studies on different species. Using this experimental dataset, we performed a simulation in which sun and shade leaves were hypothetically exchanged to investigate whether such plasticity increased carbon gain at each local environment. As expected, in the clearing, the locally acclimated sun leaves gained more carbon than the hypothetically transferred shade leaves. By contrast, in the understory, the daily net carbon gain was similar between the simulated sun and shade leaves on the sunny day due to the frequent sunflecks. Lower LMA and lower photosynthetic capacity in the understory reduced leaf construction cost per area rather than maximizing net daily carbon gain. These results indicate that information on static photosynthetic parameters may not be sufficient to evaluate shade acclimation in forest understories.

Comparison of the Photosynthetic Capacity of Phragmites australis in Five Habitats in Saline‒Alkaline Wetlands

Water shortages have an important impact on the photosynthetic capacity of Phragmites australis. However, this impact has not been adequately studied from the perspective of photosynthesis. An in-depth study of the photosynthetic process can help in better understanding the impact of water shortages on the photosynthetic capacity of P. australis, especially on the microscale. The aim of this study is to explore the photosynthetic adaptation strategies to environmental changes in saline‒alkaline wetlands. The light response curves and CO2 response curves of P. australis in five habitats (hygrophilous, xerophytic, psammophytic, abandoned farmland, paddy field drainage) in saline‒alkaline wetlands were measured at different stages of their life history, and we used a nonrectangular hyperbolic model to fit the data. It was concluded that P. australis utilized coping strategies that differed between the growing and breeding seasons. P. australis in abandoned farmland during the growing season had the highest apparent quantum efficiency (AQE) and photosynthetic utilization efficiency for weak light because of the dark environment. The dark respiration rate of P. australis in the drainage area of paddy fields was the lowest, and it had the highest values for photorespiration rate, maximum photosynthetic rate (Pmax), photosynthetic capacity (Pa), biomass, maximum carboxylation rate (Vcmax), and maximum electron transfer rate (Jmax). The light insensitivity of P. australis increased with the transition from growing to breeding season, and the dark respiration rate also showed a downward trend. Moreover, Vcmax and Jmax would decline when Pmax and Pa showed a declining trend, and vice versa. In other words, Vcmax and Jmax could explain changes in the photosynthetic capacity to some extent. These findings contribute to providing insights that Vcmax and Jmax can directly reflect the variation in photosynthetic capacity of P. australis under water shortages in saline‒alkaline wetlands and in other parts of world where there are problems with similarly harmful environmental conditions.

Combined effects of elevated <i>p</i>CO₂ and temperature on biomass and carbon fixation of phytoplankton assemblages in the northern South China Sea

The individual influences of ocean warming and acidification on marine organisms have been investigated intensively, but studies regarding the combined effects of both global change variables on natural marine phytoplankton assemblages are still scarce. Even fewer studies have addressed possible differences in the responses of phytoplankton communities in pelagic and coastal zones to ocean warming and acidification. We conducted shipboard microcosm experiments at both off-shore (SEATS) and near-shore (D001) stations in the northern South China Sea (NSCS) under three treatments, low temperature (30.5 °C at SEATS and 28.5 °C at D001) and low pCO2 (390.0 µatm at SEATS and 420.0 µatm at D001) (LTLC), high temperature (33.5 °C at SEATS and 31.5 °C at D001) and low pCO2 (390 µatm at SEATS and 420 µatm at D001) (HTLC), and high temperature (33.5 °C at SEATS and 31.5 °C at D001) and high pCO2 (1000 µatm at SEATS and 1030 µatm at D001) (HTHC). Biomass of phytoplankton at both stations were enhanced by HT. HTHC did not affect phytoplankton biomass at station D001 but decreased it at station SEATS. At this offshore station HT alone increased daily primary productivity (DPP, µgC (µg chl a)−1 d−1) by ~ 64 %, and by ~ 117 % when higher pCO2 was added. In contrast, HT alone did not affect DPP and HTHC reduced it by ~ 15 % at station D001. HT enhanced the dark respiration rate (µg C (µg chl a)-1 d−1) by 64 % at station SEATS, but had no significant effect at station D001, and did not change the ratio of respiration to photosynthesis at either station. HTHC did not affect dark respiration rate (µg C (µg chl a)−1 d−1) at either station compared to LTLC. HTHC reduced the respiration to photosynthesis ratio by ~ 41 % at station SEATS but increased it ~ 42 % at station D001. Overall, our findings indicate that responses of coastal and offshore phytoplankton assemblages in NSCS to ocean warming and acidification are contrasting, with the pelagic phytoplankton communities being more sensitive to these two global change factors.

Impact of atmospheric ammonia on growth, C and N accumulation and photosynthesis of two maize cultivars with different N root supply

Impact of enriched atmospheric NH₃ in combination with low and high N medium on growth, total C and N accumulation (C_totA and N_totA) and photosynthetic characteristics of two maize cultivars i.e. SD19 (cult. 1) and NE5 (cult. 2) with low N and N high use efficiency, respectively, was investigated. Plants were exposed to 10 nl/L and 1000 nl/L NH₃ fumigation, respectively, for 30 days in open-top chambers (OTCs). Under exposure to the low N medium, increase of the atmospheric NH₃ concentration to 1000 nl/L from the ambient level significantly (P &lt; 0.05) increased dry matter (DM) (by 18% in cult. 1 and 14% in cult. 2 respectively), C_totA, N_totA, net photosynthetic rate (P_n), stomatal conductance (G_s) and apparent quantum yield (AQY) but decreased intercellular CO₂ concentration (C_i) in both cultivars. These effects were more pronounced in cult. 1 as compared to those in cult. 2. In contrast, in the high N solution, enriched atmospheric NH₃ led to a decrease in DM, C_totA, N_totA, P_n, G_sand AQY but an increase in C_iof cult. 2 only. Dark respiration rate remained unaffected by enrichment of NH₃ in each treatment. Therefore, it is concluded that appropriately enriched atmospheric NH₃ can improve plant growth of maize by enhancing C_totA, N_totA, and photosynthesis in the low N medium, especially for low N use efficiency cultivars.

Dark respiration of leaves and traps of terrestrial carnivorous plants: are there greater energetic costs in traps?

In this study, O2-based dark respiration rate (RD) in leaf and trap cuttings was compared in 9 terrestrial carnivorous plant species of 5 genera to decide whether traps represent a greater energetic (maintanence) cost than leaves or photosynthetic parts of traps. RD values of cut strips of traps or leaves of terrestrial carnivorous plants submerged in water ranged between 2.2 and 8.4 nmol g−1 s−1 (per unit dry weight) in pitcher traps of the genera Sarracenia, Nepenthes, and Cephalotus, while between 7.2 and 25 nmol g−1 DW s−1 in fly-paper or snapping traps or leaves of Dionaea and Drosera. No clear relationship between RD values of traps (or pitcher walls) and leaves (or pitcher wings or petioles) was found. However, RD values of separated Drosera prolifera tentacles exceeded those of leaf lamina 7.3 times.

Thermal dissipation, leaf rolling and inactivation of PSII reaction centres in Amomum villosum

Amomum villosum Lour. (Zingiberaceae) is an obligate shade plant. Its leaves naturally roll up upon exposure to bright sun. This paper characterizes the effects of its leaf rolling and light on photoinhibition of photosynthesis and thermal dissipation activity under field conditions with sufficient soil moisture. Between the plants from bright and shaded parts of a canopy gap, both maximum photosynthetic rate (mean ≈ 6.5 μmol m-2 s-1) and stomatal conductance (148 vs. 131 mmol m-2 s-1) were not significantly different, but apparent quantum yield (0.021 vs. 0.025) and dark respiration rate (0.49 vs. 0.30 μmol m-2 s-1) were. In the foggy morning, when the incident irradiance was low, photoinhibition had already occurred in plants in the bright part of the canopy gap and also in plants in the shaded part of the gap but to a much lesser degree. Photoinhibition accelerated with increase of incident irradiance and relaxed in the afternoon. Thermal dissipation as indicated by non-photochemical fluorescence quenching (NPQ) increased rapidly in the morning and continued at a high rate in the afternoon. Prevention of leaf rolling resulted in acceleration of photoinhibition. Artificial inhibition of the xanthophyll cycle led to acceleration of both photoinhibition and inactivation of PSII reaction centres, and decrease of NPQ. Photoinhibited leaves in either control or treatment plants recovered overnight. These results show that A. villosum is able effectively to prevent photodamage through the mechanisms of leaf rolling, thermal dissipation and reversible inactivation of PSII reaction centres.