Effects Of CO2 Enrichment Research Articles

The determiner of photosynthetic acclimation induced by biochemical limitation under elevated CO2 in japonica rice

Photosynthetic acclimation to prolonged elevated CO2 could be attributed to the two limited biochemical capacity, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) carboxylation and ribulose-1,5-bisphosphate (RuBP) regeneration, however, which one is the primary driver is unclear. To quantify photosynthetic acclimation induced by biochemical limitation, we investigated photosynthetic characteristics and leaf nitrogen allocation to photosynthetic apparatus (Rubisco, bioenergetics, and light-harvesting complex) in a japonica rice grown in open-top chambers at ambient CO2 and ambient CO2+200 μmol mol−1 (e [CO2]). Results showed that photosynthesis was stimulated under e [CO2], but concomitantly, photosynthetic acclimation obviously occurred across the whole growth stages. The content of leaf nitrogen allocation to Rubisco and biogenetics was reduced by e [CO2], while not in light-harvesting complex. Unlike the content, there was little effects of CO2 enrichment on the percentage of nitrogen allocation to photosynthetic components. Additionally, leaf nitrogen did not reallocate within photosynthetic apparatus until the imbalance of sink-source under e [CO2]. The contribution of biochemical limitations, including Rubisco carboxylation and RuBP regeneration, to photosynthetic acclimation averaged 36.2% and 63.8% over the growing seasons, respectively. This study suggests that acclimation of photosynthesis is mainly driven by RuBP regeneration limitation and highlights the importance of RuBP regeneration relative to Rubisco carboxylation in the future CO2 enrichment.

Coupled effects of CO2 and biochar amendment on the yield and quality of Pseudostellaria heterophylla

Previous studies reveal that atmospheric CO2 enrichment can improve plant growth with enhanced photosynthesis. However, it is not well-understood whether biochar could be coupled with elevated CO2 to further promote growth and quality of medicinal plants. This study aims to investigate the interactive effects of CO2 enrichment and biochar amendment on the growth and quality of a common medicinal plant (Pseudostellaria heterophylla (Miq.) Pax). Two CO2 concentrations (400 and 1000 ppm) and three biochar dosages (0, 3% and 5%) were considered and tested. Compared with the control in the ambient CO2 without biochar addition, coupled CO2 enrichment and 3% biochar enhanced available nutrient levels (e.g., P) most efficiently by up to 1740% in rhizosphere. This was due to the increased soil enzyme activity and relative abundance of beneficial bacteria for nutrient activation. Elevated CO2 (1000 ppm) coupled with 3% biochar induced the highest tuber yield of P. heterophylla, which was 228% higher than the control. Coupled elevated CO2 and 5% biochar group shows an increasing yield by 84%. The coupled treatments could increase the yield by up to 213% as compared with the only biochar or only elevated CO2 treated groups. The concentrations of polysaccharides in root tuber were improved by 56–124% under the CO2 enrichment. They all satisfy the requirements of Hong Kong Chinese Materia Medica Standards. However, the concentrations of saponins decreased by 14–20% in low dosages of biochar treated groups (0, 3%) under the elevated CO2 concentration, as compared with those under the ambient CO2. On the contrary, CO2 enrichment increased the concentrations of saponins by 22% when biochar dosage increased to 5%. This study recommends that 3% biochar amendment coupled with 1000 ppm CO2 should be adopted to enhance the yield and biosynthesis of polysaccharides in root tuber of P. heterophylla.

How Does Carbon Dioxide-Induced Acidification Affect Postecdysial Exoskeletal Mineralization in the Blue Crab (Callinectes sapidus)?

Carbon dioxide (CO2 ) enrichment in seawater because of increased use of fossil fuels can possibly cause detrimental effects on the physiological processes of marine life, especially shell builders, due to CO2 -induced ocean acidification. We investigated, for the first time, specifically the effect of CO2 enrichment on postecdysial shell mineralization in Crustacea using the blue crab, Callinectes sapidus, as the model crustacean. It was hypothesized that CO2 enrichment of seawater would adversely affect exoskeletal mineralization in the blue crab. We used two groups of postecdysial crabs, with one group exposed to seawater at a pH of 8.20 and the other group treated with CO2 -acidified seawater with a pH of 7.80-7.90. After a period of 7 days, samples of exoskeleton and hemolymph were collected from the survivors. Enrichment was found to significantly increase exoskeletal magnesium content by 104% relative to control, whereas a statistically nonsignificant elevation of 31% in exoskeletal calcium was registered. Because CO2 treatment did not change the content of magnesium and calcium in the hemolymph, we postulate that increased exoskeletal mineralization in postecdysial blue crabs must stem from an increased influx of bicarbonate ions from the medium through the gill, to the hemolymph, and across the epidermis. In addition, the observed significant increase in the mass of exoskeleton following CO2 treatment must be at least partly accounted for by enhanced postmolt carbonate salt deposition to the shell. Environ Toxicol Chem 2022;41:2950-2954. © 2022 SETAC.

Response of rice grain quality to elevated atmospheric CO2 concentration: A meta-analysis of 20-year FACE studies

Compared with growth and yield, far less attention has been devoted to the impact of elevated CO2 on rice grain quality. Exposure to elevated CO2 induces numerous physiological changes in plants that can alter the chemical composition and thus the quality of rice grains. This meta-analysis was conducted to synthesize the effect of free air CO2 enrichment (FACE, approximately 550 μmol mol−1) on grain quality of rice grown under open field conditions. Factors that could modify the CO2 effects were also investigated. They included cultivars, nitrogen applications, environmental temperatures and grain types. On average, elevated CO2 decreased head rice percentage by 8%, which led to no increase in head rice yield, despite substantial increases of brown rice yield and white rice yield that were obtained under FACE conditions. Elevated [CO2] increased chalky grain percentage by 26% and chalkiness degree by 30%, which significantly impaired rice appearance. However, the cooking and eating quality was improved by elevated [CO2], as indicated by the changes in starch RVA profiles and the palatability of cooked rice. The nutritional value of FACE rice declined as shown by the 2–9% decreases in the concentrations of nitrogen, phosphorus, magnesium, sulfur, zinc, iron, copper, manganese and amino acids; meanwhile the anti-nutrient phytate and the molar ratio of phytate to zinc were increased. High nitrogen application alleviated negative effects of elevated [CO2] on milling quality and rice appearance but further decreased the bioavailability of essential nutrients. The CO2-induced decreases in element concentrations of white rice were generally higher than those in brown rice. In general, CO2-induced changes on grain quality were seldom modified by rice cultivars, temperatures or experimental locations.

Impacts of Land-Use Change on the Spatio-Temporal Patterns of Terrestrial Ecosystem Carbon Storage in the Gansu Province, Northwest China

Land-use change is supposed to exert significant effects on the spatio-temporal patterns of ecosystem carbon storage in arid regions, while the relative size of land-use change effect under future environmental change conditions is still less quantified. In this study, we combined a land-use change dataset with a satellite-based high-resolution biomass and soil organic carbon dataset to determine the role of land-use change in affecting ecosystem carbon storage from 1980 to 2050 in the Gansu province of China, using the MCE-CA-Markov and InVEST models. In addition, to quantify the relative size of the land-use change effect in comparison with other environmental drivers, we also considered the effects of climate change, CO2 enrichment, and cropland and forest managements in the models. The results show that the ecosystem carbon storage in the Gansu province increased by 208.9 ± 99.85 Tg C from 1980 to 2020, 12.87% of which was caused by land-use change, and the rest was caused by climate change, CO2 enrichment, and ecosystem managements. The land-use change-induced carbon sequestration was mainly associated with the land-use category conversion from farmland to grassland as well as from saline land and desert to farmland, driven by the grain-for-green projects in the Loess Plateau and oasis cultivation in the Hexi Corridor. Furthermore, it was projected that ecosystem carbon storage in the Gansu province from 2020 to 2050 will change from −14.69 ± 12.28 Tg C to 57.83 ± 53.42 Tg C (from 105.62 ± 51.83 Tg C to 177.03 ± 94.1 Tg C) for the natural development (ecological protection) scenario. By contrast, the land-use change was supposed to individually increase the carbon storage by 56.46 ± 9.82 (165.84 ± 40.06 Tg C) under the natural development (ecological protection) scenario, respectively. Our results highlight the importance of ecological protection and restoration in enhancing ecosystem carbon storage for arid regions, especially under future climate change conditions.

Waning advantages of CO2 enrichment on photosynthesis and productivity due to accelerated phase transition and source-sink imbalance in sweet pepper

CO2 concentration, which can be raised by CO2 enrichment, has been considered to affect photosynthetic physiology, morphology, and yield of crops in greenhouses. However, inconsistent influence of CO2 enrichment on crop productivity has been demonstrated owing to the complicated and dynamic interaction between physiological and morphological responses of crops. Therefore, integrative analysis on the systemic responses of crops to CO2 enrichment is required for clarifying the reasons for the inconsistency. The objective of this study was to analyze the effect of CO2 enrichment on the photosynthesis and yield of sweet pepper plants according to growth phase and to investigate how photosynthetic physiology and plant morphology contribute to the CO2 enrichment effect via functional structural plant model (FSPM), an integrative plant modeling tool. CO2 was enriched to sweet pepper plants with a daily average concentration of about 900 μmol mol−1. Growth, yield, and photosynthesis were periodically measured during the cultivation. The structural and photosynthetic properties obtained through 3D-phenotyping and gas-exchange measurement were applied to the 3D-framework for FSPM. The change in the CO2 enrichment efficiency for photosynthesis and the contribution of photosynthetic and morphological acclimation to CO2 enrichment effect were calculated. The overall influence of CO2 enrichment on the plants changed by growth stage mostly mediated by photosynthate source-sink balance. In early stages, CO2 enrichment accelerated the growth phase transition and increased the fruit yield through the increase in photosynthate partitioning to fruits. In later stages, however, the efficiency of CO2 enrichment on fruit yield gradually decreased due to the restricted leaf area expansion caused by excessive photosynthate partition to fruits. The systemic influence of CO2 enrichment on the plants including photosynthetic acclimation, structural acclimation, and fruit yield could be reasonably elucidated through the method used in this study. Thus, balancing the photosynthate source-sink balance in the early stages with appropriate cultivation practices could improve the long-term productivity of sweet pepper under CO2 enrichment.

Effects of CO2 Enrichment on Yield, Photosynthetic Rate, Translocation and Distribution of Photoassimilates in Strawberry ‘Sagahonoka’

The method of automatically controlling the CO2 concentration in a greenhouse depending on ventilation was examined in order to efficiently improve the productivity of strawberries under the weather conditions in the northern part of Kyushu in Japan. The effects of CO2 enrichment on the yields, fruit Brix, and economic value of the strawberry ‘Sagahonoka’ were investigated. In addition, in order to clarify the physiological response of ‘Sagahonoka’ to the CO2 concentration, the photosynthetic rate, translocation, and photoassimilate distribution rate were measured. It was found that maintaining the CO2 concentrations above 800 μmol mol−1 and 400 μmol mol−1 during no ventilation and ventilation, respectively, resulted in 25% increases in marketable fruit yields and a 0.2–1.2% higher fruit Brix compared to control, which was kept in 400 μmol mol−1 CO2 or above all day regardless of ventilation. Additionally, the economic value of ‘Sagahonoka’ was increased. The photosynthetic rate of ‘Sagahonoka’ increased linearly up to 800 μmol mol−1 CO2, and high CO2 concentrations affected the distribution for the primary fruit, the most significant sink. It was clarified that CO2 enrichment at 800 μmol mol−1 for ‘Sagahonoka’ was effective in increasing the photosynthetic rate and distribution of photoassimilates to fruits, and the yields of strawberries could be increased efficiently by automatically controlling the CO2 concentration depending on ventilation in a southern region of Japan.

Soil water stress overrides the benefit of water-use efficiency from rising CO2 and temperature in a cold semi-arid poplar plantation.

The counteractive effect of atmospheric CO2 (ca ) enrichment and drought stress on tree growth results in great uncertainty in the growth patterns of forest plantations in cold semi-arid regions. We analysed tree ring chronologies and carbon isotopes in Populus simonii plantations in cold semi-arid areas in northern China over the past four decades. We hypothesized that the hydraulic stress from drought would override the stimulating effect of increasing ca and temperature (T) on stem growth (basal area increment [BAI]). We found the stimulating effect of rising ca and T on the growth, indicated by continuous increase of intrinsic water-use efficiency in all stands and a positive correlation between T and BAI. However, these effects failed to alleviate the negative impacts of drought on tree growth. Concurrent acceleration of BAI reversed during the intensive drought episodes. Water stress resulted from inaccessibility of roots to deep soil water rather than from lack of precipitation, suggested by the decoupling of BAI from precipitation and vapour pressure deficit. Local soil water limitation might also cause greater stomatal regulation in declining trees, indicated by lower intercellular CO2 concentration. Thus, site-specific soil moisture conditions growth sensitivity to global warming resulting in site-specific decline episodes in drought-prone areas.

Impacts of Carbon Dioxide Enrichment on Landrace and Released Ethiopian Barley (Hordeum vulgare L.) Cultivars.

Barley (Hordeum vulgare L.) is an important food security crop due to its high-stress tolerance. This study explored the effects of CO2 enrichment (eCO2) on the growth, yield, and water-use efficiency of Ethiopian barley cultivars (15 landraces, 15 released). Cultivars were grown under two levels of CO2 concentration (400 and 550 ppm) in climate chambers, and each level was replicated three times. A significant positive effect of eCO2 enrichment was observed on plant height by 9.5 and 6.7%, vegetative biomass by 7.6 and 9.4%, and grain yield by 34.1 and 40.6% in landraces and released cultivars, respectively. The observed increment of grain yield mainly resulted from the significant positive effect of eCO2 on grain number per plant. The water-use efficiency of vegetative biomass and grain yield significantly increased by 7.9 and 33.3% in landraces, with 9.5 and 42.9% improvement in released cultivars, respectively. Pearson’s correlation analysis revealed positive relationships between grain yield and grain number (r = 0.95), harvest index (r = 0.86), and ear biomass (r = 0.85). The response of barley to eCO2 was cultivar dependent, i.e., the highest grain yield response to eCO2 was observed for Lan_15 (122.3%) and Rel_10 (140.2%). However, Lan_13, Land_14, and Rel_3 showed reduced grain yield by 16, 25, and 42%, respectively, in response to eCO2 enrichment. While the released cultivars benefited more from higher levels of CO2 in relative terms, some landraces displayed better actual values. Under future climate conditions, i.e., future CO2 concentrations, grain yield production could benefit from the promotion of landrace and released cultivars with higher grain numbers and higher levels of water-use efficiency of the grain. The superior cultivars that were identified in the present study represent valuable genetic resources for future barley breeding.

Biogeochemical feedbacks to ocean acidification in a cohesive photosynthetic sediment

Ecosystem feedbacks in response to ocean acidification can amplify or diminish diel pH oscillations in productive coastal waters. Benthic microalgae generate such oscillations in sediment porewater and here we ask how CO2 enrichment (acidification) of the overlying seawater alters these in the absence and presence of biogenic calcite. We placed a 1-mm layer of ground oyster shells, mimicking the arrival of dead calcifying biota (+Calcite), or sand (Control) onto intact silt sediment cores, and then gradually increased the pCO2 in the seawater above half of +Calcite and Control cores from 472 to 1216 μatm (pH 8.0 to 7.6, CO2:HCO3− from 4.8 to 9.6 × 10−4). Porewater [O2] and [H+] microprofiles measured 16 d later showed that this enrichment had decreased the O2 penetration depth (O2-pd) in +Calcite and Control, indicating a metabolic response. In CO2-enriched seawater: (1) sediment biogeochemical processes respectively added and removed more H+ to and from the sediment porewater in darkness and light, than in ambient seawater increasing the amplitude of the diel porewater [H+] oscillations, and (2) in darkness, calcite dissolution in +Calcite sediment decreased the porewater [H+] below that in overlying seawater, reversing the sediment–seawater H+ flux and decreasing the amplitude of diel [H+] oscillations. This dissolution did not, however, counter the negative effect of CO2 enrichment on O2-pd. We now hypothesise that feedback to CO2 enrichment—an increase in the microbial reoxidation of reduced solutes with O2—decreased the sediment O2-pd and contributed to the enhanced porewater acidification.

Forest stand and canopy development unaltered by 12years of CO2 enrichment.

Canopy structure—the size and distribution of tree crowns and the spatial and temporal distribution of leaves within them—exerts dominant control over primary productivity, transpiration and energy exchange. Stand structure—the spatial arrangement of trees in the forest (height, basal area and spacing)—has a strong influence on forest growth, allocation and resource use. Forest response to elevated atmospheric CO2 is likely to be dependent on the canopy and stand structure. Here, we investigated elevated CO2 effects on the forest structure of a Liquidambar styraciflua L. stand in a free-air CO2 enrichment experiment, considering leaves, tree crowns, forest canopy and stand structure. During the 12-year experiment, the trees increased in height by 5 m and basal area increased by 37%. Basal area distribution among trees shifted from a relatively narrow distribution to a much broader one, but there was little evidence of a CO2 effect on height growth or basal area distribution. The differentiation into crown classes over time led to an increase in the number of unproductive intermediate and suppressed trees and to a greater concentration of stand basal area in the largest trees. A whole-tree harvest at the end of the experiment permitted detailed analysis of canopy structure. There was little effect of CO2 enrichment on the relative leaf area distribution within tree crowns and there was little change from 1998 to 2009. Leaf characteristics (leaf mass per unit area and nitrogen content) varied with crown depth; any effects of elevated CO2 were much smaller than the variation within the crown and were consistent throughout the crown. In this young, even-aged, monoculture plantation forest, there was little evidence that elevated CO2 accelerated tree and stand development, and there were remarkably small changes in canopy structure. Questions remain as to whether a more diverse, mixed species forest would respond similarly.

AMF colonization and community of a temperate invader and co-occurring natives grown under different CO2 concentrations for 3 years

AbstractGlobal changes such as atmospheric CO2 enrichment often facilitate exotic plant invasions and alter soil arbuscular mycorrhizal fungi (AMF) community. However, it is still unclear whether the effects of CO2 enrichment on exotic plant invasions are associated with its effects on root-AMF symbiosis of invasive and native plants. To address this issue, the annual invasive plant Xanthium strumarium and two phylogenetically related annual natives were compared under ambient and elevated CO2 concentrations for three consecutive years. Atmospheric CO2 enrichment increased AMF colonization rates for the species only in few cases, and the invader did not benefit more from CO2 enrichment in terms of AMF colonization. Under ambient CO2 concentration, however, the invader had a higher AMF colonization rate than the natives in the first year of the study, which disappeared in the second and third year of the study due to the increase of AMF colonization rates in the natives but not in the invader. The influences of species, CO2 concentrations and planting year on AMF colonization were associated with their effects on both soil nutrient and AMF community, and the former may be more important as it also influenced the latter. Our results indicate that the invader could more quickly form symbiosis with soil AMF, contributing to adaptation and occupation of new habitats, and that it is necessary to consider the roles of AMF and the effects of time when determining the effects of global changes such as atmospheric CO2 enrichment on exotic plant invasions.

The effect of long-term CO2 enrichment on carbon and nitrogen content of roots and soil of natural pastureland

Abstract Increasing levels of atmospheric CO2 may change C and N dynamics in pasture ecosystems. The present study was conducted to examine the impact of four years of CO2 enrichment on soil and root composition and soil N transformation in natural pastureland. Plots of open-top growth chambers were continuously injected with ambient CO2 (350 µL L–1) and elevated CO2 (625 µL L–1). Soil cores exposed to ambient and elevated CO2 treatment were incubated and collected each year. Net N-mineralization rates in soil (NH4 +-N plus NO3ˉ–-N), in addition to total C and N content (%) of soil and root tissues were measured. Results revealed that elevated CO2 caused a significant reduction in soil NO3 (P < 0.05), however, no significant CO2 effect was found on total soil C and N content (%). Roots of plants grown under elevated CO2 treatment had higher C/N ratios. Changes in root C/N ratios were driven by changes in root N concentrations as total root N content (%) was significantly reduced by 30% (P < 0.05). Overall, findings suggest that the effects of CO2 enrichment was more noticeable on N content (%) than C content (%) of soil and roots; elevated CO2 significantly affected soil N-mineralization and total N content (%) in roots, however, no substantial change was found in C inputs in CO2-enriched soil.

Effects of CO2 enrichment on the anaerobic digestion of sewage sludge in continuously operated fermenters

The effect of CO2 enrichment in sewage sludge anaerobic digestion (AD) as a potential strategy to improve the biogas yield was assessed at increasing organic loading rates (OLR). Effects on process performance and resilience were evaluated in long-term continuous AD experiments at lab-scale. The specific methane production (SMP) was sustainably enhanced in the test digester compared to a control at elevated OLRs, reaching an increase of 6 ± 12% on average at the highest OLR tested (4.0 kgVS/(m3·d)). The reduction of CO2 via homoacetogenesis, facilitating acetoclastic CH4 formation is proposed as the dominant conversion pathway. Results suggest that sufficient load of easily degradable substances is a prerequisite for intrinsic formation of the reduction equivalent H2 via acidogenesis. The enhanced resilience of the process under CO2-enriched conditions in response to acid accumulation further qualifies this approach as a viable option for improving AD performance by converting a waste stream into a valuable product.

Long-term compound interest effect of CO2 enrichment on the carbon balance and growth of a leafy vegetable canopy

The response of crops to elevated atmospheric CO2 concentrations (Ca) is of great concern for horticultural vegetable production in greenhouse facilities, where Ca levels are often artificially elevated. To elucidate the long-term effect of the elevated Ca on canopy photosynthesis and growth, we conducted long-term continuous measurements of the canopy photosynthesis (A) and leaf area index (L) of hydroponically grown spinach canopies under elevated Ca (approximately 800 μmol mol−1) and ambient Ca (approximately 400 μmol mol−1) treatments by combining the open chamber method and image analysis of the top of view of canopies. There existed a positive feedback loop between A and L, where an increase in L caused an increase in A, which subsequently accelerated the increase in L. The enhancing effect of elevated Ca on A, which was evaluated with enhancement ratios (i.e., A in the elevated Ca treatment divided by A in the ambient Ca treatment; Aelev/Aamb), showed a short-term increase under high-light conditions during the daytime and a long-term increase with canopy growth toward the harvest. The long-term increase in Aelev/Aamb was attributed to the enhancement of Aelev brought on by not only the short-term enhancing effect of elevated Ca but also the more rapidly increasing and thus larger L in the elevated Ca treatment compared with that in the ambient Ca treatment. Both the long-term increase in Aelev/Aamb and the more rapidly increasing L in the elevated Ca treatment were caused by the “compound interest effect” of elevated Ca, where the enhancing effects of elevated Ca on A and L were gradually amplified over a long-term period through the positive feedback loop between A and L. This compound interest effect of elevated Ca also caused a long-term increase in canopy nighttime respiration in proportion to daytime photosynthesis. Through these changes in the canopy-scale carbon balance, the compound interest effect detected in the elevated Ca treatment likely contributed to a substantial increase in the final aboveground dry weight at the harvest time. This study highlights the importance of the long-term compound interest effect of elevated Ca on canopy photosynthesis, carbon balance, and growth.

Impact of Different Daily Light Integrals and Carbon Dioxide Concentrations on the Growth, Morphology, and Production Efficiency of Tomato Seedlings.

Indoor growing systems with light-emitting diodes offer advantages for the growth of tomato seedlings through uniform and optimized environmental conditions which increase consistency between plants and growing cycles. CO2 enrichment has been shown to improve the yield of crops. Thus, this research aimed to characterize the effects of varied light intensities and CO2 enrichment on the growth, morphology, and production efficiency of tomato seedlings in indoor growing systems. Four tomato cultivars, “Florida-47 R,” “Rebelski,” “Maxifort,” and “Shin Cheong Gang,” were subjected to three different daily light integrals (DLIs) of 6.5, 9.7, and 13 mol m–2 d–1 with a percent photon flux ratio of 40 blue:60 red and an end-of-day far-red treatment of 5 mmol m–2 d–1. The plants were also subjected to three different CO2 concentrations: 448 ± 32 (400-ambient), 1010 ± 45 (1000), and 1568 ± 129 (1600) μmol mol–1. Temperature was maintained at 24.3°C ± 0.48/16.8°C ± 1.1 (day/dark; 22.4°C average) and relative humidity at 52.56 ± 8.2%. Plant density was 1000 plants m–2 until canopy closure. Morphological measurements were conducted daily to observe the growth response over time. In addition, data was collected to quantify the effects of each treatment. The results showed increases in growth rate with increases in the DLI and CO2 concentration. In addition, CO2 enrichment to 1000–1600 μmol mol–1 increased the light use efficiency (gDM mol–1 applied) by 38–44%, and CO2 enrichment to 1600 μmol mol–1 did not result in any additional increase on shoot fresh mass, shoot dry mass, and stem extension. However, the net photosynthetic rate obtained with 1600 μmol mol–1 was 31 and 68% higher than those obtained with 1000 and 400 μmol mol–1, respectively. Furthermore, the comparison of the light and CO2 treatment combinations with the control (13 mol m–2 d–1–400CO2) revealed that the plants subjected to 6.5DLI–1600CO2, 9.7DLI–1000CO2, and 9.7DLI–1600CO2 treatment combinations exhibited the same growth rate as the control plants but with 25–50% less DLI. Furthermore, two treatment combinations (13.0DLI–1000CO2 and 13.0DLI–1600CO2) were associated with the consumption of comparable amount of energy but increased plant growth by 24–33%.

Effects of long-term CO2 enrichment on forage quality of extensively managed temperate grassland

Different studies revealed an increased biomass production in grasslands due to elevated CO2 (eCO2). Thus, the question arises whether forage quality of grassland biomass is also influenced.In the present study, we assessed the long-term effects of eCO2 in context of the accompanied site conditions soil moisture, air temperature and precipitation on different forage quality and energy parameters of grassland biomass in an extensively managed temperate grassland. The study took place at the Free-Air Carbon dioxide Enrichment site near Giessen [GiFACE], which was set up in 1998. Our main objective was to assess the differences in the quality and energy content of grassland forage, exposed to elevated CO2 [+ 20%; eCO2] and ambient CO2 (aCO2) concentrations. Crude protein, C/N-ratio, crude fat, total non-structural carbohydrates, ash, crude fibre, metabolisable energy [ME] and net energy for lactation [NEL] were determined to assess the forage quality and energy content of grassland biomass separated in grasses and forbs, which was harvested twice per year (end of May, beginning of September), over the period of 2006–2015.Forbs showed a significant decrease for most tested parameters under eCO2 at both harvests, except for crude fibre, which showed a significant increase at the second harvest of the year under eCO2. Grasses showed a significant negative CO2 effect for ash content at the first harvest of the year. In addition to eCO2, site and climatic conditions, e.g. soil moisture, affected the investigated parameters.Based on the last 10 observation years (2006–2015) within the 18 year long experiment, eCO2 is likely to cause a decline in forage quality, especially of forbs caused by reduced crude protein and fat contents and increased crude fibre content, in extensively managed grassland ecosystems. However, site and climatic conditions should also be considered showing the importance of long-term observations that contain the full range of climatic conditions. Periods of heat, drought and precipitation, which are expected to increase in the future, lead to a decrease of the CO2 fertilization effect on grassland biomass and also to a negative impact on forage quality.

Ocean acidification may slow the pace of tropicalization of temperate fish communities

Poleward range extensions by warm-adapted sea urchins are switching temperate marine ecosystems from kelp-dominated to barren-dominated systems that favour the establishment of range-extending tropical fishes. Yet, such tropicalization may be buffered by ocean acidification, which reduces urchin grazing performance and the urchin barrens that tropical range-extending fishes prefer. Using ecosystems experiencing natural warming and acidification, we show that ocean acidification could buffer warming-facilitated tropicalization by reducing urchin populations (by 87%) and inhibiting the formation of barrens. This buffering effect of CO2 enrichment was observed at natural CO2 vents that are associated with a shift from a barren-dominated to a turf-dominated state, which we found is less favourable to tropical fishes. Together, these observations suggest that ocean acidification may buffer the tropicalization effect of ocean warming against urchin barren formation via multiple processes (fewer urchins and barrens) and consequently slow the increasing rate of tropicalization of temperate fish communities.

Effects of warming and CO2 enrichment on O2 consumption, porewater oxygenation and pH of subtidal silt sediment

We investigated the effects of seawater warming and CO2 enrichment on the microbial community metabolism (using O2 consumption as a proxy) in subtidal silt sediment. Intact sediment cores, without large dwelling infauna, were incubated for 24 days at 12 (in situ) and 18 °C to confirm the expected temperature response. We then enriched the seawater overlying a subset of cold and warm-incubated cores with CO2 (+ ΔpCO2: 253–396 µatm) for 16 days and measured the metabolic response. Warming increased the depth-integrated volume-specific O2 consumption (Rvol), the maximum in the volume-specific O2 consumption at the bottom of the oxic zone (Rvol,bmax) and the volume-specific net O2 production (Pn,vol), and decreased the O2 penetration depth (O2-pd) and the depth of Rvol,bmax (depthbmax). Benthic photosynthesis oscillated the pH in the upper 2 mm of the sediment. CO2 enrichment of the warm seawater did not alter this oscillation but shifted the pH profile towards acidity; the effect was greatest at the surface and decreased to a depth of 12 mm. Confoundment rendered the CO2 treatment of the cold seawater inconclusive. In warm seawater, we found no statistically clear effect of CO2 enrichment on Rvol, Rvol,bmax, Pn,vol, O2-pd, or depthbmax and therefore suspect that this perturbation did not alter the microbial community metabolism. This confirms the conclusion from experiments with other, contrasting types of sediment.

Air warming and CO2 enrichment cause more ammonia volatilization from rice paddies: An OTC field study

Ammonia (NH3) volatilization in rice paddies may be affected by elevated atmospheric CO2 concentration ([CO2]) and temperature due to changes in plant and soil nitrogen (N) metabolism. At present, little is known about the individual and combined effects of CO2 enrichment and warming on NH3 volatilization under field conditions. An experiment was conducted in a rice paddy in Central China, after 4 years of warming and CO2 enrichment using open-top chamber (OTC) devices. Compared with ambient conditions, elevated [CO2] had no significant effects on NH3 volatilization, although increases in soil pH and urease activity were observed. The stimulation on plant N assimilation under CO2 enrichment might offset the possible enhancement on NH3 volatilization, as more soil N was absorbed by plant thus reducing NH3 loss potential. Elevated temperature increased NH3 volatilization significantly, which could be attributed to increased soil ammonium nitrogen (NH4+-N) concentration, pH, and urease activity. Combination of CO2 enrichment and warming caused the highest cumulative NH3 loss, which increased by 26.5% compared with ambient conditions, but the interaction was not significant. Higher plant N uptake, soil NH4+-N concentration, pH and urease activity were also observed with co-elevation of [CO2] and temperature, but the combined effects were variable and not synergistic. Our findings confirm that field warming and CO2 enrichment cause more NH3 volatilization in rice paddies, among which warming effects are dominant, and suggest that improved N management or field practices are required to reduce NH3 losses under future climate change.