Carbon Uptake Efficiency Research Articles

The photosynthetic uptake of inorganic carbon from Pyropia seaweed aquaculture beds: Scaling up population-level estimations

Seaweed aquaculture beds (SABs) contribute positively to CO2 removal (CDR) worldwide. Among cultivated seaweed species, Pyropia represents approximately 8% of the global seaweed production and has the capacity to sequester a significant amount of carbon from the surface layer of the coastal ocean. In this study, we evaluated the carbon uptake efficiency of Pyropia SABs by measuring their photosynthetic rates. Pyropia individuals were collected from Pyropia SABs on the south and west coasts of South of Korea from December to March (cultivation period) in 2016 to 2019, and the photosynthetic light response curves (P-E curves) were measured. Oxygen-based photosyntheses were converted into carbon-based photosynthetic rates using theoretical photosynthetic quotients. Pyropia thallus consumed an average 37 mg C g−1ww d−1, with a high ratio of gross primary production to respiration (P/R ratio; 5–14). To quantify the carbon uptake potential in the coastal areas of South Korea during the cultivation period, we extrapolated the carbon uptake rates using the estimated biomass, total area of Pyropia SABs, and meteorological irradiance data. The highest carbon uptake rate (2143 kt C month−1) was observed in the Southwestern Sea of South Korea in December. Considering all productivity data from the entire cultivation period, approximately 6789 kt C was taken up by the Pyropia SABs. Therefore, our study indicates a significant potential to mitigate climate change by reducing greenhouse gas emissions using Pyropia SABs.

Diffuse Fertilization Effect in Maize and Soybean Is Driven by Improved Light Use Efficiency Rather Than by Light Absorption

AbstractDiffuse radiation can improve the efficiency of terrestrial carbon uptake. Both light absorption and canopy light use efficiency (LUE) are affected by the fraction of diffuse radiation (DF). However, the relative contribution of these two factors to the diffuse fertilization effect (DFE) in the short term is not well understood. To investigate the mechanism of DFE in cropland, we collected gross primary productivity, fraction of absorbed photosynthetically active radiation (FAPAR), and other meteorological parameters from June to August in three crop sites. Our results indicated that the short‐term DFE in soybean and maize was primarily driven by the improvement of LUE rather than light absorption. The LUE increased significantly with DF, while the FAPAR changed a little with DF. The increased DF is typically associated with reduced photosynthetically active radiation (PAR). Our results showed that the potential gain in light absorption and canopy LUE from DF could not fully offset the reduced PAR in soybean and maize. The findings in this study contribute to our understanding of the mechanisms underlying the DFE.

The impact of tillage practices on daytime CO2 fluxes, evapotranspiration (ET), and water-use efficiency in peanut

Peanut (Arachis hypogaea L.) growers use different tillage systems in the Southeastern United States, the impact of which needs to be assessed with regard to evapotranspiration (ET), carbon uptake, and water-use efficiency (WUE). The eddy-covariance method was used to measure these fluxes in peanut in two common tillage systems (strip tillage vs. conventional tillage) over the course of three consecutive growing seasons (2019–2021). Results suggest that during the dry year of 2019 with rainfall of only 30 cm, strip tillage peanut had a significantly higher daytime ecosystem WUE, 105%, 51%, and 32% higher than that of the conventional tillage in early, mid, and late growth stages, respectively. In 2020, with mean rainfall the overall difference in average WUE was nonsignificant between the tillage systems. Heavy rainfall of 112 cm in 2021 led to waterlogged conditions in the conventional tillage field due to poorer infiltration. This likely reduced the CO2 uptake. Waterlogging did not occur in the strip tillage field due to improved infiltration. As a result, in 2021, 18%, 33%, and 48% greater ecosystem WUE in strip tillage during early, mid, and later stages was found. Thus, this study suggests that strip tillage fields can achieve higher net CO2 uptake and WUE in Georgia during dry or very wet years. However, no difference in WUE was found between different tillage systems in a typical year with average rainfall for Georgia. The present study has implications for regions characterized by long growing seasons and low rainfall.

Influence of planting pattern on peanut ecosystem daytime net carbon uptake, evapotranspiration, and water-use efficiency using the eddy-covariance method

Peanut is planted in a pattern of either single or twin rows in Georgia, USA. However, limited attention has been paid to the impact of planting pattern on the carbon footprint and how the net carbon uptake is intertwined with the amount of water used to determine the ecosystem water-use efficiency (WUE) in peanut. This paper reports on the relationship between the amount of carbon produced to the amount of water used in peanut, carbon dioxide flux, and crop evapotranspiration of peanut in a single- or in a twin-row planting pattern measured using the eddy-covariance method. To the best of our knowledge, the present study is unique in that it examines for the first time the effect of planting pattern on the net carbon uptake and WUE. The two-year study took place in contrasting weather conditions with the 2016 year experiencing a higher vapor pressure deficit and lower precipitation than in the 2018 year. In this study, field-scale daytime net carbon ecosystem exchange (CO2 fluxes), ET and WUE of single- and twin-row peanut were compared using the eddy-covariance technique. Results showed that in 2018, both the net carbon uptake from the atmosphere and the WUE of twin-row peanut were significantly greater than those in the single-row peanut by 7-10% and ~9% respectively, for pod filling and seed maturity growth stages (aGDD 1000-2000 and aGDD > 2000). In 2016, the net daytime carbon uptake and WUE of peanut were similar for both planting patterns during pod filling (aGDD 1000-2000). Higher precipitation and lower VPD in 2018 likely resulted in greater peanut yield in twin-row as compared to single-row with abundant precipitation. Owing to the fast canopy growth rate in twin-row peanut, results suggest that during the vegetative stage (aGDD<500) in 2016, both daytime net carbon uptake from the atmosphere and WUE were considerably greater in twin-row than single-row by 32% and 27%, respectively. Given that in both years, the ET from both planting patterns was similar, it appears that the determination of WUE in both planting patterns was more impacted by changes in daytime net carbon uptake than evapotranspiration. The results of this study suggest the possibility that the higher WUE at the critical stages of twin-row peanut in 2018 are likely to lead to greater yield than single-row peanut. This should be confirmed with further year-to-year investigations.

Continued glacial retreat linked to changing macronutrient supply along the West Antarctic Peninsula

At the West Antarctic Peninsula (WAP), continued atmospheric and oceanic warming is causing significant physical and biogeochemical changes to glaciers and the marine environment. We compare sediment sources and drivers of macronutrient distributions at two bays along the WAP during austral summer 2020, using radioactive radium and stable oxygen isotopes to trace sedimentary influences and quantify different freshwater inputs. In the Ryder Bay, where the Sheldon Glacier is marine-terminating, radium activities at the sediment-water interface indicate considerable benthic mixing. Using radium isotope activity gradients to resolve radium and macronutrient fluxes, we find buoyant meltwater proximal to the glacier drives vigorous mixing of sediment and entrainment of macronutrient deep waters, on the order of 2.0 × 105 mol d−1 for nitrate. Conversely, in the Marian Cove, where the Fourcade Glacier terminates on land, low salinities and oxygen isotopes indicate a meltwater-rich surface layer <1 m thick and rich in sediment, and strong vertical mixing to the seafloor. A continued shift to land-terminating glaciers along the WAP may have a significant impact upon nutrient and sediment supply to the euphotic zone, with impacts upon primary productivity and carbon uptake efficiency. The future of primary production, carbon uptake, and food web dynamics is therefore linked to glacier retreat dynamics in the many fjords along the WAP.

Boosts in leaf-level photosynthetic capacity aid Pinus ponderosa recovery from wildfire

Forests mitigate climate change by sequestering massive amounts of carbon, but recent increases in wildfire activity are threatening carbon storage. Currently, our understanding of wildfire impacts on forest resilience and the mechanisms controlling post-fire recovery remains unresolved due to a lack of empirical data on mature trees in natural settings. Here, we quantify the physiological mechanisms controlling carbon uptake immediately following wildfire in mature individuals of ponderosa pine (Pinus ponderosa), a wide-spread and canopy-dominant tree species in fire-prone forests. While photosynthetic capacity was lower in burned than unburned trees due to an overall depletion of resources, we show that within the burned trees, photosynthetic capacity increases with the severity of damage. Our data reveal that boosts in the efficiency of carbon uptake at the leaf-level may compensate for whole-tree damage, including the loss of leaf area and roots. We further show that heightened photosynthetic capacity in remaining needles on burned trees may be linked with reduced water stress and leaf nitrogen content, providing pivotal information about post-fire physiological processes. Our results have implications for Earth system modeling efforts because measurements of species-level physiological parameters are used in models to predict ecosystem and landscape-level carbon trajectories. Finally, current land management practices do not account for physiological resilience and recovery of severely burned trees. Our results suggest premature harvest may remove individuals that may otherwise survive, irrevocably altering forest carbon balance.

Meandering development of tidal creeks splits bacterial communities and functional characteristics: Evidence from a field study in Jiangsu Coast, China

Tidal creeks are common and important geomorphic features in intertidal zones, which provide a broad range of ecosystem services. The meandering development of tidal creeks can cause a discrepancy in sediment properties between the two banks in tidal creek bends, which affects a few geomorphic and biological processes and seems to be another incentive for the ecological effects of tidal creeks. However, how this discrepancy affects the distribution of bacterial communities in tidal creek bends remains unclear. To this end, we collected sediment samples from a typical tidal creek bend in Jiangsu Coast, China. The bacterial communities were characterized by 16S rRNA gene sequencing and the sediment properties were determined. Results showed that bacterial communities and their functions exhibited significant differences between the convex bank (VB) and the concave bank (CB). Bacterial diversity was higher in VB than in CB, mainly attributed to higher nutrients (TOC and TN), moisture, and finer sediment in VB. The oligotrophic (e.g., Chloroflexi), drought-resistant (e.g., Actinobacteria), and mobile (e.g. Nitrospirae) bacteria had higher abundances in CB. In contrast, bacteria with opposite niche preferences (e.g., Proteobacteria and Acidobacteria) tended to inhabit VB. Network analysis revealed that CB bacterial communities had a higher efficiency of nutrient cycling and carbon uptake but were more vulnerable to environmental disturbances. FAPROTAX results showed that bacterial functions associated with carbon cycles were more abundant in CB, whereas those associated with nitrogen and sulfur cycles were more abundant in VB. Overall, these results demonstrate that the meandering development of tidal creeks splits bacterial communities and functional characteristics in tidal creeks bends. These findings are expected to provide useful information for further understanding and predicting the ecological effects of tidal creeks.

A dynamically controlled anaerobic/aerobic granular sludge reactor efficiently treats brewery/bottling wastewater.

This study investigated the application of a dynamic control strategy in an aerobic granular sludge (AGS) reactor treating real variable brewery/bottling wastewater. For 482 days, the anaerobic and aerobic reaction steps in a lab-scale AGS system were controlled dynamically. A pH-based control was used for the anaerobic step, and an oxygen uptake rate (OUR) based control for the aerobic step. Additionally, the effect of an elongated aerobic step, and the effect of the removal of the suspended solids from the influent, on AGS formation were also investigated. In comparison to a static operation, the dynamic operation resulted in similar reactor performance, related to effluent quality and the anaerobic dissolved organic carbon (DOC) uptake efficiency, while the organic loading rate was significantly higher. The removal of suspended solids from the influent by chemical coagulation with FeCl3 turned hybrid floccular-granular sludge into fully granular sludge. The granulation coincided with a significant increase in the abundance of the glycogen-accumulating Candidatus Competibacter and an increase in the content of gel-forming EPS to respectively around 14% and 30%. In conclusion, this study showed the successful application of a dynamic control strategy based on common and low-cost sensors for AGS treatment of industrial wastewater.

Alkalinization Scenarios in the Mediterranean Sea for Efficient Removal of Atmospheric CO2 and the Mitigation of Ocean Acidification

It is now widely recognized that in order to reach the target of limiting global warming to well below 2°C above pre-industrial levels (as the objective of the Paris agreement), cutting the carbon emissions even at an unprecedented pace will not be sufficient, but there is the need for development and implementation of active Carbon Dioxide Removal (CDR) strategies. Among the CDR strategies that currently exist, relatively few studies have assessed the mitigation capacity of ocean-based Negative Emission Technologies (NET) and the feasibility of their implementation on a larger scale to support efficient implementation strategies of CDR. This study investigates the case of ocean alkalinization, which has the additional potential of contrasting the ongoing acidification resulting from increased uptake of atmospheric CO2 by the seas. More specifically, we present an analysis of marine alkalinization applied to the Mediterranean Sea taking into consideration the regional characteristics of the basin. Rather than using idealized spatially homogenous scenarios of alkalinization as done in previous studies, which are practically hard to implement, we use a set of numerical simulations of alkalinization based on current shipping routes to quantitatively assess the alkalinization efficiency via a coupled physical-biogeochemical model (NEMO-BFM) for the Mediterranean Sea at 1/16° horizontal resolution (~6 km) under an RCP4.5 scenario over the next decades. Simulations suggest the potential of nearly doubling the carbon-dioxide uptake rate of the Mediterranean Sea after 30 years of alkalinization, and of neutralizing the mean surface acidification trend of the baseline scenario without alkalinization over the same time span. These levels are achieved via two different alkalinization strategies that are technically feasible using the current network of cargo and tanker ships: a first approach applying annual discharge of 200 Mt Ca(OH)2 constant over the alkalinization period and a second approach with gradually increasing discharge proportional to the surface pH trend of the baseline scenario, reaching similar amounts of annual discharge by the end of the alkalinization period. We demonstrate that the latter approach allows to stabilize the mean surface pH at present day values and substantially increase the potential to counteract acidification relative to the alkalinity added, while the carbon uptake efficiency (mole of CO2 absorbed by the ocean per mole of alkalinity added) is only marginally reduced. Nevertheless, significant local alterations of the surface pH persist, calling for an investigation of the physiological and ecological implications of the extent of these alterations to the carbonate system in the short to medium term in order to support a safe, sustainable application of this CDR implementation.

Increased carbon uptake under elevated CO2 concentration enhances water-use efficiency of C4 broomcorn millet under drought

Broomcorn millet (Panicum miliaceum L.) has been cultivated in arid or semi-arid area due to its high drought tolerance. Yet information on how elevated atmospheric CO2 concentration ([CO2]) affects the responses to drought of the productivity, photosynthesis, water-use efficiency and drought tolerance of broomcorn millet is lacking. We investigated the effects of elevated [CO2] and drought on gas exchange parameters, water-use efficiency, physiological indices related to drought tolerance, leaf area and aboveground biomass of broomcorn millet using an open-top chamber experimental facility in North China in 2015 and 2016. Broomcorn millet was grown in pots with or without drought stress under ambient or elevated [CO2]. Elevated [CO2] could compensate the negative effect of drought on the leaf area and aboveground biomass of broomcorn millet. This was attributed to the direct stimulation in photosynthesis due to increased carbon uptake under elevated [CO2]. Elevated [CO2] significantly enhanced the water-use efficiency of broomcorn millet at both leaf and plant levels, especially under drought condition. Elevated [CO2] did not significantly affect evapotranspiration, but increased water-use efficiency at the plant level by 15% (2015) and 35% (2016) of broomcorn millet under drought. Elevated [CO2] did not significantly affect PSII efficiency, antioxidative defense capacity (peroxidase, malondialdehyde) or osmotic adjustment (soluble sugar content and proline). We conclude that elevated [CO2] -induced increase in carbon uptake and water-use efficiency would increase the productivity of broomcorn millet in semi-arid areas under future high-CO2 climate.

Evaluation of the light profile and carbon assimilation of tomato plants in greenhouses with respect to film diffuseness and regional solar radiation using ray-tracing simulation

Diffuse fraction, which can be increased by using diffuse films, has been considered to influence light interception and photosynthesis of crops in greenhouses. However, quantifying the influence of diffuse films is challenging owing to the complicated optical interactions between climatic factors inside and outside greenhouses. Thus, versatile methods for evaluating the effect of diffuse films are required. The objective of this study was to evaluate the effect of diffuse films on the improvement of the light profile and photosynthesis of tomatoes in greenhouses according to film diffuseness and regional solar radiation using ray-tracing simulation. The structural and optical properties of the greenhouse components were applied in a 3D-framework combined with a ray-tracing module. The light transmission patterns of diffuse films and solar radiation properties were incorporated. The reliability of the simulation was confirmed by comparing measured and estimated irradiances inside greenhouses covered with films having different haze factors. For scenarios, the diffuse film efficiency was assessed under typically different solar radiations, a low irradiance, high diffuse radiation fraction (LIHD) and a high irradiance, low diffuse radiation fraction (HILD). The light interception was estimated through the simulation and used to calculate the photosynthesis using the Farquhar-von Caemmerer-Berry model. The simulation was found to be reliable with R2 of 0.95 and 0.94 for the two greenhouses covered with different diffuse films. The light distribution on the tomato plants were less affected by film diffuseness under LIHD than HILD. With increasing film diffuseness, carbon uptake and light use efficiency increased by 5.30% and 4.58% under HILD, but did not change under LIHD. The light distribution and photosynthesis in diffuse film-covered greenhouses under different light environments could be reasonably estimated by the simulation. Thus, this method can be used to evaluate the applicability of diffuse films to various regions with diverse meteorological characteristics.

Phenotypic plasticity of leaf anatomical traits helps to explain gas-exchange response to water shortage in grasses of different photosynthetic types

C3 and C4 plants, as their intermediates, respond differently to short-term changes in environmental conditions. This difference is linked to contrasting levels of phenotypic plasticity and photosynthetic apparatus specialization. Phenotypic plasticity is an underexplored topic although its understanding is crucial to predict plant behaviour in future climatic scenarios. In this research, the phenotypic plasticity of anatomical traits and its influence to carbon uptake efficiency was studied in plants with different photosynthetic types, under contrasting water regimes. Oryza sativa cvs. Soberana (drought-sensitive) and Douradao (drought-tolerant) (C3), Homolepis isocalycia (C3 proto-Kranz) and Andropogon gayanus (C4), grown at three water treatments (100, 75 and 50% of substrate water holding capacity), were phenotyped for leaf anatomy and gas-exchange parameters. The results showed that plasticity trends indicated different strategies between O. sativa cultivars to deal with water shortage, explaining their classification as drought-sensitive or tolerant. We also mapped typical characteristics of C3–C4 intermediate plant, H. isocalycia, mainly in the ratio mesophyll:bundle sheath cells and hypothesize how it may influence photosynthesis. Finally, we have confirmed previous claims that C4 carbon uptake advantages may be limited under severe drought conditions, as A. gayanus have drastically reduced its photosynthetic rates at lower water levels. By studying C3–C4 intermediates, this study may also be a starting point to unravel the trade-offs of anatomical changes during the evolutionary process from C3 to C4 photosynthesis, and also improve the understanding of their impact in carbon uptake in different water conditions.

Increased carbon uptake and water use efficiency in global semi-arid ecosystems

The semi-arid ecosystems dominate the inter-annual variability of the global carbon sink and the driving role of semi-arid ecosystems is becoming increasingly important. However, the impacts of climate change on the dynamics of carbon and water fluxes in global semi-arid ecosystems are still not well understood. We used a data-driven (or machine learning) approach, along with observations from a number of FLUXNET sites and spatially continuous satellite and meteorological data, to generate gridded carbon and water flux estimates for semi-arid regions globally, and then examined the magnitude, spatial patterns, and trends of carbon and water fluxes and their responses to climate change during the period 1982–2015. The average annual gross primary productivity (GPP), net ecosystem productivity (NEP), evapotranspiration (ET), and water use efficiency (WUE) were 628.6 g C m−2 yr−1, 9.6 g C m−2 yr−1, 463.1 mm yr−1, and 1.60 g C Kg−1 H2O, respectively. The climate conditions during the period 1982–2015 enhanced gross and net carbon uptake in global semi-arid regions. The spatially-averaged annual GPP, NEP, ET, and WUE in semi-arid regions showed significant increases both globally and regionally (Asia, Africa, and Australia). As with GPP and ET, WUE significantly increased in North America, Asia, Africa, and Australia. Australia was the most sensitive semi-arid region in terms of changes in carbon and water fluxes and their responses to climate. Semi-arid forests, shrublands, and savannas were net carbon sinks; croplands were minor carbon sources; grasslands were nearly carbon neutral. Overall, precipitation was the most important climate factor influencing the carbon and water fluxes; WUE in 40.9% of the semi-arid region was significantly influenced by precipitation. The global climate change is expected to influence global semi-arid ecosystems in many ways and our findings have implications for semi-arid ecosystem management and policy making.

Direct and carry-over effects of summer rainfall on ecosystem carbon uptake and water use efficiency in a semi-arid woodland

Biological activity in semi-arid and arid ecosystems is strongly dependent on rainfall, particularly in summer. A period of favourable rainfall can alter ecosystem carbon balance and is likely influence inner-annual variability of the regional and global carbon cycle. The effect of rainfall variability on ecosystem carbon and water fluxes in semi-arid ecosystems, particularly in woody ecosystems has not been adequately investigated. In this study, we used eddy covariance data from four springs (September–November), four summers (December of that year–February of the following year) and three following autumns (March–May) between 2010 and 2013 in a semi-arid woodland of southern Australia to better understand the effect of pre-summer, summer and post-summer rainfall variability on diurnal pattern of carbon flux. In 2010/11 summer, La Niῆa conditions resulted in extensive rainfall, which marked an historic record over the last 100 years. The 2011/12 summer was also moist. In contrast, the two following summers (2012/13 and 2013/14) were dry. Cumulative net ecosystem productivity (NEP) was lower in dry summers than in moist summers, due to lower maximum carbon flux rate and total hours of net carbon uptake. Maximum NEP and gross primary productivity rates on a given day were reached earlier in dry summers, indicating that photosynthetic activity was not suppressed by high temperatures but by water availability. Ecosystem water use efficiency, calculated as the ratio of daily NEP to evapotranspiration, was higher in moist than dry summers. In addition, the effect of summer rain extended into the following autumn. Cumulative NEP and ecosystem water use efficiency in autumn following a dry summer were lower than when following a moist summer. We conclude that summer rainfall has a strong impact on the carbon cycle in semi-arid woodlands due to its direct and carry-over effect. Therefore seasonal rainfall variation is likely to determine inter-annual variability of annual net carbo uptake of this ecosystem.

Ecophysiological plasticity of Amazonian trees to long-term drought.

Episodic multi-year droughts fundamentally alter the dynamics, functioning, and structure of Amazonian forests. However, the capacity of individual plant species to withstand intense drought regimes remains unclear. Here, we evaluated ecophysiological responses from a forest community where we sampled 83 woody plant species during 5years of experimental drought (throughfall exclusion) in an eastern Amazonian terra firme forest. Overall, the experimental drought resulted in shifts of some, but not all, leaf traits related to photosynthetic carbon uptake and intrinsic water-use efficiency. Leaf δ13C values increased by 2-3‰ within the canopy, consistent with increased diffusional constraints on photosynthesis. Decreased leaf C:N ratios were also observed, consistent with lower investments in leaf structure. However, no statistically significant treatment effects on leaf nitrogen content were observed, consistent with a lack of acclimation in photosynthetic capacity or increased production of nitrogen-based secondary metabolites. The results of our study provide evidence of robust acclimation potential to drought intensification in the diverse flora of an Amazonian forest community. The results reveals considerable ability of several species to respond to intense drought and challenge commonly held perspectives that this flora has attained limited adaptive plasticity because of a long evolutionary history in a favorable and stable climate.

Airborne Hyperspectral Evaluation of Maximum Gross Photosynthesis, Gravimetric Water Content, and CO2 Uptake Efficiency of the Mer Bleue Ombrotrophic Peatland

Peatlands cover a large area in Canada and globally (12% and 3% of the landmass, respectively). These ecosystems play an important role in climate regulation through the sequestration of carbon dioxide from, and the release of methane to, the atmosphere. Monitoring approaches, required to understand the response of peatlands to climate change at large spatial scales, are challenged by their unique vegetation characteristics, intrinsic hydrological complexity, and rapid changes over short periods of time (e.g., seasonality). In this study, we demonstrate the use of multitemporal, high spatial resolution (1 m2) hyperspectral airborne imagery (Compact Airborne Spectrographic Imager (CASI) and Shortwave Airborne Spectrographic Imager (SASI) sensors) for assessing maximum instantaneous gross photosynthesis (PGmax) in hummocks, and gravimetric water content (GWC) and carbon uptake efficiency in hollows, at the Mer Bleue ombrotrophic bog. We applied empirical models (i.e., in situ data and spectral indices) and we derived spatial and temporal trends for the aforementioned variables. Our findings revealed the distribution of hummocks (51.2%), hollows (12.7%), and tree cover (33.6%), which is the first high spatial resolution map of this nature at Mer Bleue. For hummocks, we found growing season PGmax values between 8 μmol m−2 s−1 and 12 μmol m−2 s−1 were predominant (86.3% of the total area). For hollows, our results revealed, for the first time, the spatial heterogeneity and seasonal trends for gravimetric water content and carbon uptake efficiency for the whole bog.

Ocean acidification of a coastal Antarctic marine microbial community reveals a critical threshold for CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; tolerance in phytoplankton productivity

Abstract. High-latitude oceans are anticipated to be some of the first regions affected by ocean acidification. Despite this, the effect of ocean acidification on natural communities of Antarctic marine microbes is still not well understood. In this study we exposed an early spring, coastal marine microbial community in Prydz Bay to CO2 levels ranging from ambient (343 µatm) to 1641 µatm in six 650 L minicosms. Productivity assays were performed to identify whether a CO2 threshold existed that led to a change in primary productivity, bacterial productivity, and the accumulation of chlorophyll a (Chl a) and particulate organic matter (POM) in the minicosms. In addition, photophysiological measurements were performed to identify possible mechanisms driving changes in the phytoplankton community. A critical threshold for tolerance to ocean acidification was identified in the phytoplankton community between 953 and 1140 µatm. CO2 levels ≥ 1140 µatm negatively affected photosynthetic performance and Chl a-normalised primary productivity (csGPP14C), causing significant reductions in gross primary production (GPP14C), Chl a accumulation, nutrient uptake, and POM production. However, there was no effect of CO2 on C : N ratios. Over time, the phytoplankton community acclimated to high CO2 conditions, showing a down-regulation of carbon concentrating mechanisms (CCMs) and likely adjusting other intracellular processes. Bacterial abundance initially increased in CO2 treatments ≥ 953 µatm (days 3–5), yet gross bacterial production (GBP14C) remained unchanged and cell-specific bacterial productivity (csBP14C) was reduced. Towards the end of the experiment, GBP14C and csBP14C markedly increased across all treatments regardless of CO2 availability. This coincided with increased organic matter availability (POC and PON) combined with improved efficiency of carbon uptake. Changes in phytoplankton community production could have negative effects on the Antarctic food web and the biological pump, resulting in negative feedbacks on anthropogenic CO2 uptake. Increases in bacterial abundance under high CO2 conditions may also increase the efficiency of the microbial loop, resulting in increased organic matter remineralisation and further declines in carbon sequestration.

Polyploidy influences plant-environment interactions in quaking aspen (Populus tremuloides Michx.).

Quaking aspen (Populus tremuloides Michx.), a widespread and keystone tree species in North America, experienced heat and drought stress in the years 2002 and 2003 in the southwestern United States. This led to widespread aspen mortality that has altered the composition of forests, and is expected to occur again if climate change continues. Understanding interactions between aspen and its environments is essential to understanding future mortality risk in forests. Polyploidy, which is common in aspen, can modify plant structure and function and therefore plant-environment interactions, but the influence of polyploidy on aspen physiology is still not well understood. Furthermore, the ploidy types of aspen have different biogeographies, with triploids being most frequent at lower latitudes in generally warmer and drier climates, while the northerly populations are virtually 100% diploid. This suggests that ploidy-environment interactions differ, and could mean that the ploidy types have different vulnerabilities to environmental stress. In this study, to understand aspen ploidy-environment interactions, we measured 38 different traits important to carbon uptake, water loss and water-use efficiency in diploid and triploid aspen in Colorado. We found that triploid aspen had lower stand density, and greater leaf area, leaf mass, leaf mass per area, percent nitrogen content, chlorophyll content and stomatal size. These differences corresponded to greater potential net carbon assimilation (A, measured using A/Ci curves, and chlorophyll fluorescence) and stomatal conductance (gs) in triploids than diploids. While triploid aspen had higher intrinsic water-use efficiency (iWUE, calculated from measurements of δ13C in leaf tissue), they also had greater potential water loss from higher measured gs and lower stomatal sensitivity to increasing vapor pressure deficit. Therefore, despite greater iWUE, triploids may have lower resilience to climate-induced stress. We conclude that ploidy type strongly influences physiological traits and function, and mediates drought stress responses in quaking aspen.

Asymmetric sensitivity of ecosystem carbon and water processes in response to precipitation change in a semi‐arid steppe

Summary Semi‐arid ecosystems play an important role in regulating the dynamics of the global terrestrial CO2 sink. These dynamics are mainly driven by increasing inter‐annual precipitation variability. However, how ecosystem carbon processes respond to changes in precipitation is not well understood, due to a lack of substantial experimental evidence that combines increased and decreased precipitation treatments. This study, a 3‐year field manipulation experiment with five precipitation levels conducted in a semi‐arid steppe, examined the impacts of increased and decreased precipitation on ecosystem CO2 (GEP: gross ecosystem photosynthesis; ER: ecosystem respiration; NEE: net ecosystem CO2 exchange), water exchange (ET: evapotranspiration), and resource use efficiency (CUE: carbon use efficiency; WUE: water use efficiency). We found that decreased precipitation reduced ecosystem CO2, water exchange and resource use efficiency significantly, while increased precipitation did not cause significant influence on them. That is, they responded more sensitively to decreased precipitation. Soil water availability was the most important driver determining changes in GEP, ER and ET. Changes in NEE, CUE and WUE were predominately regulated by soil temperature. Photosynthesis at leaf and ecosystem levels showed significantly greater sensitivity to changed precipitation than respiration and ET, and therefore determined the trends of net carbon uptake and resource use efficiency. This study highlighted an asymmetric response of ecosystem carbon and water processes to altered precipitation. This is potentially important for improving our understanding of how possible future changes in precipitation will affect the carbon cycle. Taking this asymmetric response into consideration will inevitably reduce uncertainties in predicting the dynamics of the global carbon cycle. A lay summary is available for this article.

Soil networks become more connected and take up more carbon as nature restoration progresses

Soil organisms have an important role in aboveground community dynamics and ecosystem functioning in terrestrial ecosystems. However, most studies have considered soil biota as a black box or focussed on specific groups, whereas little is known about entire soil networks. Here we show that during the course of nature restoration on abandoned arable land a compositional shift in soil biota, preceded by tightening of the belowground networks, corresponds with enhanced efficiency of carbon uptake. In mid- and long-term abandoned field soil, carbon uptake by fungi increases without an increase in fungal biomass or shift in bacterial-to-fungal ratio. The implication of our findings is that during nature restoration the efficiency of nutrient cycling and carbon uptake can increase by a shift in fungal composition and/or fungal activity. Therefore, we propose that relationships between soil food web structure and carbon cycling in soils need to be reconsidered.