Infrared Gas Analyzer Research Articles

Flux Puppy – An open-source software application and portable system design for low-cost manual measurements of CO2 and H2O fluxes

Manual chamber-based measurements of CO2 (and H2O) fluxes are important for understanding ecosystem carbon metabolism. Small opaque chambers can be used to measure leaf, stem and soil respiration. Larger transparent chambers can be used to measure net ecosystem exchange of CO2, and small jars often serve this purpose for laboratory incubations of soil and plant material. We developed an Android application (app), called Flux Puppy, to facilitate chamber-based flux measurements in the field and laboratory. The app is designed to run on an inexpensive handheld Android device, such as a tablet or phone, and it has a graphical user interface that communicates with a LI-COR LI-820 and LI-830 (CO2) or LI-840 and LI-850 (CO2/H2O) infrared gas analyzer. The app logs concentrations of CO2 and H2O, cell temperature and pressure at 1 Hz, displays the output graphically, and calculates the linear regression slope, R-squared, and standard error of the CO2 time series. A metadata screen allows users to enter operator, site, and plot information, as well as take a photograph using the Android device’s built-in camera, and log measurement location using the device GPS. Additionally, there is a notes field, which can be revised after the measurements are taken. Data files (the 1 s raw data, photograph, and metadata including statistics calculated from the raw data) are then transmitted off the device through file sharing options (Gmail, Outlook, Google Drive, Dropbox etc.). Because Flux Puppy code is open-source (available on GitHub) and the flux measurement system we describe is relatively inexpensive and straightforward to assemble, it should be of broad interest to the carbon cycling community.

Proteomic Analysis of Horseweed (Conyza canadensis) Subjected to Caprylic Acid Stress.

Caprylic acid (CAP) is anticipated to be a potential biocontrol herbicide in the control of weeds, however the molecular mechanism of how CAP affects weeds is poorly understood. Here, the physiological and biochemical (protein-level) changes in horseweed (Conyza canadensis L.) are studied under CAP treatment, with infrared gas analyzer and label-free quantitative proteomics methods. In total, 112 differentially-accumulated proteins (DAPs) (>1.5 fold change, p < 0.05) are present between treated horseweed and control samples, with 46 up-regulated and 66 down-regulated proteins. These DAPs are involved in 28 biochemical pathways, including photosynthesis pathways. In particular, six photosynthesis proteins show significant abundance changes in the CAP-treated horseweed. The qRT-PCR results confirm three of the six genes involved in photosynthesis. Moreover, by measuring photosynthesis characteristics, CAP was shown to decrease photosynthetic rate, stomatal conductance, intercellular CO2 concentration, and the transpiration rate of horseweed. These results suggest that photosystem I is one of the main biological processes involved in the response of horseweed to CAP.

Silicon Supplementation Alleviates Ammonium Toxicity in Sugar Beet (Beta vulgaris L.)

The purpose of this study is to evaluate the relationship between Si and NH4+ toxicity in the context of the nutrition, physiology, and production of sugar beet grown using hydroponics. We hypothesized that NH4+ affects the physiology of the plant, accumulation of nutrients, and dry matter, with the possibility for Si to mitigate this toxicity. The experimental design used was completely randomized, in a factorial scheme of 2 × 5, corresponding with the absence and presence of Si (2 mmol L−1) and five concentrations of NH4+ with four replicates. The following series of physiological evaluations were carried out: photosynthesis, stomatal conductance, transpiration, with the use of an infrared gas analyzer (LICOR, Inc., LI-6400), the dry biomass, N and Si accumulation, and Si use efficiency in the roots. Accumulation of N and photosynthesis in the leaves was higher in the presence of Si. An increase of NH4+ increased transpiration, especially in the plants cultivated without the incorporation of Si. Stomatal conductance was lower in the presence of Si. Dry matter was reduced when plants were exposed to higher concentrations of NH4+, showing a greater reduction in the root than in the aerial part. The use of NH4+ equal to or higher than 15 mmol L−1 damaged the photosynthesis. Transpiration and stomatal conductance were less affected in the presence of Si and in the accumulation of N and Si in the roots. Dry matter was reduced when plants were exposed to higher concentrations of NH4+, and this effect was mitigated in the presence of Si.

Contrasting responses of soil fungal communities and soil respiration to the above‐ and below‐ground plant C inputs in a subtropical forest

The roles of soil fungal diversity and community composition in regulating soil respiration when above‐ and below‐ground plant carbon (C) inputs are excluded remain unclear. In the present study, we aimed to examine the following. (a) How does the exclusion of above‐ and below‐ground plant C inputs affect soil respiration and soil fungi singly and in combination? (b) Are changes in soil fungal diversity aligned with changes in soil respiration? A field experiment with manipulation of plant C inputs was established in a subtropical forest in southwest China in 2004 with litter removal and tree stem‐girdling to exclude inputs of the above‐ and below‐ground plant C, respectively. In 2009, we measured the rates of soil respiration with an infrared gas analyser and soil fungal community structure using Illumina sequencing. We found that the rates of soil respiration were reduced significantly by litter removal and girdling, by similar magnitudes. However, they were not decreased further by the combination of these two treatments compared to either treatment alone. In contrast, litter removal increased the diversity of soil fungal communities, whereas girdling decreased the abundance of symbiotrophic fungi but increased the abundance of saptrotrophic and pathotrophic fungi. These changes in soil fungal community might initiate CO2 emission from soil C decomposition, offsetting further decline in soil respiration when plant C inputs are excluded. These results revealed that the exclusion of the above‐ and below‐ground plant C inputs led to contrasting soil fungal communities but similar soil function. Our findings suggest that both above‐ and below‐ground plant C are important in regulating soil respiration in subtropical forests, by limiting substrates for soil fungal growth and altering the diversity and composition of the soil fungal community.Highlights Litter removal and girdling decreased soil respiration by similar magnitudes The combination of litter removal and girdling did not further decrease soil respiration Litter removal significantly increased species richness of soil fungal communities Girdling changed the abundance of functional guilds of soil fungal communities

Soil respiration from winter wheat-based cropping systems in the US Southern Great Plains as influenced by tillage managements

ABSTRACTThis study compared soil respiration (SR) fluxes from winter wheat-based cropping systems in the US Southern Great Plains (SGP) under reduced and conventional tillage. The study consisted of four sets of paired paddocks assigned to conventional or reduced tillage with a four-year crop rotation applied over time. During the 2016–2017 study year, four sets of paired paddocks were planted to: winter wheat managed for grazing, dual-purpose (grazing and grain production), and grain-only systems of production, and winter canola. Heterotrophic SR fluxes were measured using a plant and root exclusion method on eight permanently deployed PVC cores per paddock. Fluxes from the cores were measured manually using a closed chamber connected to an infrared gas analyser on 12–13 dates during the winter wheat growing season (October through May). There were strong seasonal patterns of SR flux, with lower rates during dry and cold periods, and higher rates during warm and wet periods. Large rainfall induced pulses of SR flux were observed for both tillage systems. There was no consistent large-scale difference in SR flux between tillage treatments applied to paired paddocks. Results from this study indicate SR fluxes from winter wheat-based cropping systems are controlled more by soil environmental conditions than form of tillage.

Comparison of vineyard evapotranspiration estimates from surface renewal using measured and modelled energy balance components in the GRAPEX project

Surface renewal (SR) is a biometeorological technique that uses high frequency air temperature measurements above a crop surface to estimate sensible heat flux (H). The H derived from SR is then combined with net radiation (Rn) and ground heat flux (G) measurements to estimate latent heat flux (LE) as the residual of an energy balance equation. Recent advances in SR theory enabled its use beyond research settings, and led to the development of an inexpensive, stand-alone SR system for use in commercial agricultural settings. However, these commercial applications require replacing expensive net radiometers with clear sky models designed to estimate Rn for the energy balance approach, while also assuming G is zero on a daily basis. The accuracy of substituting Rn measurements with modelled values is unknown, and the assumption of an inconsequential G requires additional testing. Here, we compare the accuracy of the SR derived estimates of H and LE when Rn is either measured directly or modelled, and we compare results to two eddy covariance (EC) LE observations, namely LE measured via EC with an infrared gas analyzer (ECIRGA) and LE solved as a residual in the surface energy balance (ECresid). These measurements were collected at the Grape Remote sensing Atmospheric Profile & Evapotranspiration eXperiment (GRAPEX) conducted over a vineyard within the Lodi, CA wine growing region. LE from SR using tower Rn data measured directly onsite was significantly correlated with LE from ECresid and from ECIRGA with a least squares regression slope ~ 1. LE derived with the modelled incoming solar radiation (SWi) and DisALEXI Rn approaches were also significantly correlated with LE from ECresid, but both modelling approaches overestimated LE at higher fluxes. Patterns were similar, but with more scatter for correlations between LE from ECIRGA and LE from SR using either modelled or remotely sensed Rn. Incorporating direct measurements of G had minimal impact on the agreement of several SR approaches and LE from both EC approaches, however, when differences did occur direct measures of G reduced scatter and bias especially for the empirical SR approach. Our results suggest that LE derived from the new SR method requires fairly accurate Rn modelling approaches to obtain reliable and unbiased estimates of daily LE in comparison to measured LE using EC techniques.

Deep root growth, ABA adjustments and root water uptake response to soil water deficit in giant reed.

Giant reed (Arundo donax L.) is a deep-rooted crop that can survive prolonged dry periods probably as a result of its capacity to uptake water from below ground, but specific information on the functioning of deep/shallow roots is missing. The objective of this study was to understand the dynamic interrelationships of root water acquisition, canopy water conservation and abscisic acid (ABA) signals from both shallow and deep roots. In transparent split top-bottom rhizotron systems (1-m-high columns), where hydraulically isolated and independently watered layers were created with the aid of calibrated soil moisture sensors, water uptake trends were monitored. Rooting patterns were traced on the walls of the rhizotrons. Leaf gas exchange was determined using a portable infrared gas analyser. Leaf and root ABA concentrations were monitored. Under well-watered conditions, water uptake from both upper and deeper soil layers was similar. Water uptake from deeper soil layers increased gradually by up to 2.2-fold when drought stress was imposed to upper layers compared to the control conditions. Despite the significant increase in water uptake from deeper layers, surface root length density of drought-treated plants remained unchanged, suggesting increased root water uptake efficiency by these roots. However, these adjustments were not sufficient to sustain photosynthesis and therefore biomass accumulation, which was reduced by 42 %. The ABA content in shallower drought-treated roots increased 2.6-fold. This increase closely and positively correlated with foliar ABA concentration, increased intrinsic water use efficiency and leaf water potential (LWP). Giant reed is able to change its water sources depending on water availability and to maximize water uptake efficiency to satisfy canopy evapotranspirative demands. The regulation of deep root functioning and distribution, adjustment of canopy size, and root/foliar synthesized ABA play a central role in controlling LWP and leaf transpiration efficiency.

The role of decoupling factor on sugarcane crop water use under tropical conditions

AbstractThe expansion of sugarcane crop to regions with lower water supply in Brazil has increased the importance of correct estimation of crop water requirements. Currently, the irrigation management is generally done using the crop coefficient (Kc) based on the FAO 56 bulletin. Kc is used to determine the potential water demand of the crop for a given period of time and is considered constant for each crop stage. However, some recent studies have shown that Kc can be significantly variable under different evapotranspiration (ETo) rates. This paper aimed to analyse sugarcane water consumption at different scales: plant (sap flow measurements by energy balance method); canopy (Bowen ratio energy balance method); and plant–atmosphere coupling (infrared gas analyser) to reduce the uncertainties on the irrigation practices. Measurements were taken at two experimental sites, where a modern Brazilian cultivar CTC 12 was grown under drip irrigation and an old main Brazilian cultivar (RB867515) was grown under sprinkler irrigation by a central pivot. The mean crop evapotranspiration (ETc) values by the Bowen ratio energy balance method were 2.92 and 3.68 mm d−1 for RB867515 and CTC 12, respectively, resulting in a mean Kc of 0.99 at the full vegetative growth stage. Kc values were dependent on ETo and varied between 0.2 and 1.7 for both cultivars. This occurred in a crop coupled to the atmosphere (Ω = 0.37) and was the same found in other coupled crops such as coffee and citrus. In conclusion, the sugarcane Kc for southeast Brazil presented temporal variability due to coupling conditions according to reference evapotranspiration, and this should be considered in irrigation management.

Foliar gas exchange, fruit quality and water use efficiency of cape Gooseberry under different irrigation depths and mulching at greenhouse conditions

Abstract The current study aimed at evaluating gas exchanges, yield, water use efficiency and fruit quality of cape gooseberry in response to different irrigation depths with or without mulching of oat residues on pots at greenhouse conditions. Four irrigation depths were tested: 50%, 100%, 125% e 150% of reference evapotranspiration (ETo). Leaf gas exchanges were evaluated by an infrared gas analyzer at different stages of the crop. Throughout the harvest, yield per plant and yield components were assessed in conjunction with water-use efficiency (WUE) and fruit quality responses. Stomata conductance at the flowering and fructification stages showed a smaller limitation under the treatments 125 and 150%ETo. It should be noticed that the aforementioned treatments increased in 83% fresh fruit mass per plant in comparison to 50%ETo. We found a higher instantaneous water-use efficiency throughout flowering under 150%ETo, as well as at the fructification under 125%ETo treatments. Nevertheless, under 125%ETo conditions without mulching the greatest WUE was found, whereas the lowest WUE was obtained under the 50%ETo treatment with no mulching. The treatment 125%ETo resulted in the highest SS and pH, whilst the treatment 150%ETo with mulching evidenced the highest Ratio along with the lowest total acidity observed.

Preparation of highly crystalline NiO meshed nanowalls via ammonia volatilization liquid deposition for H2S detection

Novel NiO meshed nanowalls, with characteristics of open geometry, porosity, single crystal and highly crystalline framework, are grown in situ on different substrates (including Al2O3 tube, glass slide, ITO, stainless steel mesh, nickel foam and carbon cloth) via a simple ammonia volatilization liquid deposition process at room temperature and a postcalcination treatment. The calcination temperature can strongly influence the pore size and crystallinity of the product, leading to different gas-sensing performances. The product that obtained at 700 °C (NiO-700) has the advantage in the combination of the largest pore size and high crystallinity, and shows the highest response to H2S gas. In 0.01–100 ppm H2S gas, the NiO-700 meshed nanowalls based sensor can give evident and reversible response signals at a low optimal operating temperature of 50 °C, the response towards 100 ppm H2S can reach to 137.3, the detection limit is as low as 10 ppb. Furthermore, the sensor also exhibits excellent selectivity, repeatability, anti-humidity and long-term stability for H2S detection. The results of gas chromatograph-mass spectrometry (GC-MS) and infrared gas analysis (IRGA) reveal that the H2S gas can be oxidized to SO2 after interacting with NiO-700 meshed nanowalls material. Therefore, the possible H2S sensing mechanism should be proposed as: H2S gas molecules undergo a redox reaction with adsorbed oxygen anion on the surface of NiO-700 meshed nanowalls to form SO2; meanwhile, the electrons restricted by adsorbed oxygen return to the bulk and recombine with the holes, resulting in a decrease in effective carrier concentration of holes and thus generating a change in resistance.

In situ durability of various carbon supports against carbon corrosion during fuel starvation in a PEM fuel cell cathode

In this study, the degradation of different cathode carbon supports is investigated in proton exchange membrane fuel cells (PEMFCs). A platinum catalyst is synthesized using various carbon supports, such as Vulcan XC-72, graphite nanopowder and carbon nanotube, which are evaluated based on the fabrication of membrane electrode assemblies. During the startup and shutdown of PEMFCs, the individual electrode potential can be measured in situ using a dynamic hydrogen electrode. The cathode potential increases instantaneously to 1.4 V in one attempt, when H2/air boundaries are developed on the anode side during the fuel starvation, leading to significant carbon corrosion. The corrosion rates of various carbon supports are calculated from the concentration of gases, such as CO2, CO and SO2, emitted from the cathode outlet, measured directly in situ by Fourier transform infrared gas analysis. The carbon nanotube-supported Pt catalyst shows the best performance against carbon corrosion during fuel starvation, compared to commercial Pt/C catalyst and other types of carbon supports.

Annual respiration of Japanese mud snail Batillaria attramentaria in an intertidal flat: its impact on ecosystem carbon flows

The Japanese mud snail Batillaria attramentaria, a common gastropod in northeastern Asia, often predominates in isolated or degraded intertidal flat ecosystems in Japan and in other countries where it has invaded as an alien species. To evaluate the effects of B. attramentaria on carbon flow in intertidal flat ecosystems, we estimated the annual respiration of B. attramentaria from field surveys and laboratory experiments. The densities of the snails, as determined at an intertidal flat of the Seto Inland Sea, western Japan, were 235–485 individuals m−2. Temperature and snail size strongly affected their respiration rates, as determined by measuring their CO2 emission rates using an open-flow infrared gas analyzer method. The respiration rates were higher in the submerged condition than in the air-exposed condition. Based on the size structure of the natural population, laboratory experiment results, and environmental factors in the field (temperature and duration of the ebb/flood tide), we estimated the respiration in spring, summer, and autumn, respectively, as 1.9, 2.4, and 4.0 g C m−2. The total amount of carbon mineralized annually by the respiration of B. attramentaria exceeds 10% of that mineralized through sediment respiration. Based on these data and respiration/ingestion ratios in previous reports, we conclude that B. attramentaria has a significant impact on the carbon flows in intertidal flat ecosystems.

Microbial Response to Sodic Soil Amendments: Flue-Gas Gypsum, By-Product Lime, and Langbeinite

ABSTRACT Amendments are commonly applied to soil to ameliorate sodic conditions, but their effect on improving microbial activity depends on the severity of sodicity and the types and rates of amendments applied. Changes in metabolic activity in response to three chemical amendments (flue-gas gypsum (FG), spent lime, and langbeinite) applied at three rates to two sodic soils were measured using infrared gas analyzer during 76 days of incubation. Spent lime had the greatest influence on microbial activity at rates of 33.6 and 67.2 Mg ha−1, and at the highest rate of application (67.2 Mg ha−1) cumulative respiration was over two times greater than the control for both soils. High rates of langbeinite yielded the lowest respiration but were not significantly different than the control and the FG had no significant influence on respiration. The use of spent lime increased microbial activity which, in turn, may improve soil health through increased microbial activity.

Dried, closed-path eddy covariance method for measuring carbon dioxide flux over sea ice

Abstract. The Arctic marine environment plays an important role in the global carbon cycle. However, there remain large uncertainties in how sea ice affects air–sea fluxes of carbon dioxide (CO2), partially due to disagreement between the two main methods (enclosure and eddy covariance) for measuring CO2 flux (FCO2). The enclosure method has appeared to produce more credible FCO2 than eddy covariance (EC), but is not suited for collecting long-term, ecosystem-scale flux datasets in such remote regions. Here we describe the design and performance of an EC system to measure FCO2 over landfast sea ice that addresses the shortcomings of previous EC systems. The system was installed on a 10 m tower on Qikirtaarjuk Island – a small rock outcrop in Dease Strait located roughly 35 km west of Cambridge Bay, Nunavut, in the Canadian Arctic Archipelago. The system incorporates recent developments in the field of air–sea gas exchange by measuring atmospheric CO2 using a closed-path infrared gas analyzer (IRGA) with a dried sample airstream, thus avoiding the known water vapor issues associated with using open-path IRGAs in low-flux environments. A description of the methods and the results from 4 months of continuous flux measurements from May through August 2017 are presented, highlighting the winter to summer transition from ice cover to open water. We show that the dried, closed-path EC system greatly reduces the magnitude of measured FCO2 compared to simultaneous open-path EC measurements, and for the first time reconciles EC and enclosure flux measurements over sea ice. This novel EC installation is capable of operating year-round on solar and wind power, and therefore promises to deliver new insights into the magnitude of CO2 fluxes and their driving processes through the annual sea ice cycle.

Physiological Variables in Pineapples Submitted to the Application of Diuron

ABSTRACT Diuron is a widely used herbicide on pineapple cultivations. However, its application is recommended only for the implementation of the crop. The objective of this work was to evaluate the gas exchanges of four pineapple cultivars submitted to the application of the herbicide diuron at their reproductive stage. The experiment was conducted with the IAC Fantástico, Vitória, MD2 and Pérola pineapple cultivars using the active ingredient diuron at a dose of 7.5 mL L-1. Measurements of CO2 assimilation rate, stomatal conductance, transpiration, vapor pressure deficit and water use efficiency were carried out weekly, by the hour, on two plants per cultivar, over a 24 hour period. These determinations were carried out two days before the application of the herbicide and 8, 15, 22, 29 and 36 days after application of the herbicide. Measurement of photochemical efficiency was performed weekly on the same dates and all these determinations were made on the ‘D’ leaf. Measurements of gas exchange were performed with an infrared gas analyzer (IRGA) and of chlorophyll a fluorescence with a fluorometer. The application of diuron reduced the assimilation of CO2 in the pineapple varieties IAC Fantástico, Vitória, MD2 and Pérola, at their reproductive phase, in all CAM metabolism stages. Diuron promoted a temporary reduction of the stomatal conductance and a temporary increase in water use efficiency. The photochemical efficiency of the studied pineapple cultivars was negatively affected by the herbicide diuron, with the recovery of the initial values by cultivar IAC Fantástico.

Morpho-physiological and proteomic analysis to identify and characterise the traditional rice genotypes for drought tolerance

Rice is the major staple food for one-third of the world’s population. Rice requires high amount of water as compared to other cereal crops. In this context, we screened traditional rice genotypes collected from RARS, Pattambi and Ambalavayal for drought tolerance. Based on the morpho-physiological characters, the plants which showed wilting symptoms were screened according to international standard i.e., IRRI leaf score 7.0. The genotype which showed no wilting symptom even after 90% of the plants were showing wilting was identified as tolerant and the plant which showed early wilting symptom was identified as susceptible genotype. The genotype Chuvanna Modan has taken 25 days and the genotype Parambuvattan has taken only 10 days for wilting. After 90% of plants reached IRRI score 7.0 phenotypic observations i.e., electrical conductivity, measurement of stomatal conductance and transpiration rate using Infra red gas analyser were recorded. Root traits were also measured. The identified tolerant and susceptible genotypes were further subjected to 2D gel electrophoresis to identify and characterize the differentially expressed proteins for drought tolerance. Totally four differentially expressed protein spots were identified in Chuvanna Modan. The differential protein spots were sequenced by Matrix Assisted Laser Desorption/Ionization–Time of Flight Mass Spectrometry (MALDI–TOF/MS). Spot 1 and 2 were identified as ribulose bisphosphate carboxylase small subunit, spot 3 was identified as Protein tyrosine phosphatases and spot 4 was identified as Photosystem II stability/assembly factor HCF136.

Short-term response of soil respiration to simulated acid rain in Cunninghamia lanceolata and Michelia macclurei plantations

Acid rain is a primary environmental problem in Southern China. However, the effect of acid rain on soil respiration rarely received attention, especially in ecosystems with different buffering capacities to acid rain. Thus, we explored how the response of soil respiration to simulated acid rain (SAR) in Cunninghamia lanceolata and Michelia macclurei plantations, which had great difference in the buffering capacities of their litter layers to acid rain. The field experiment was subjected to a split-block experiment, with four main blocks in each plantation. Each block was split into A1 (SAR treatment, pH = 3) and A0 (deionized water, pH = 6.6) plots. Each plot was separated into subplots with (L0) and without (L1) litter treatments. SAR and deionized water were applied twice a month to A1 and A0 plots, respectively. From June 2016 to June 2017, soil respiration was measured twice per month using Li-8100 infrared gas analyzer. Soil temperature and moisture at a 5-cm depth were monitored using temperature and moisture sensors connected to Li-8100 during the measurement of soil respiration. The result showed that SAR did not significantly influence soil respiration neither in C. lanceolate nor in M. macclurei plantations. However, the reasons for this result were probably different in the two plantations. The unchanged soil respiration in C. lanceolata plantation was mainly attributed to the negligible effect of SAR on fine root biomass and microbial biomass carbon (MBC) in C. lanceolata plantation because of the acclimation of fine root and microorganism to acid soil environment. In addition, the increase in fine root biomass and decrease in MBC may have resulted in the absence of the influence of SAR on soil respiration in M. macclurei plantation, because the variation of soil respiration derived from fine root under SAR may have offset that derived from microorganism. Although C. lanceolata and M. macclurei plantations had different buffering capacities to SAR, SAR did not significantly affect soil respiration in both plantations after 1 year of SAR treatment. Therefore, the long-term effect of SAR on soil respiration should be considered, particularly in forest types with different buffering capacities to acid rain.

Measuring turbulent CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; fluxes with a closed-path gas analyzer in a marine environment

Abstract. In this study, we introduce new observations of sea–air fluxes of carbon dioxide using the eddy covariance method. The measurements took place at the Utö Atmospheric and Marine Research Station on the island of Utö in the Baltic Sea in July–October 2017. The flux measurement system is based on a closed-path infrared gas analyzer (LI-7000, LI-COR) requiring only occasional maintenance, making the station capable of continuous monitoring. However, such infrared gas analyzers are prone to significant water vapor interference in a marine environment, where CO2 fluxes are small. Two LI-7000 analyzers were run in parallel to test the effect of a sample air drier which dampens water vapor fluctuations and a virtual impactor, included to remove liquid sea spray, both of which were attached to the sample air tubing of one of the analyzers. The systems showed closely similar (R2=0.99) sea–air CO2 fluxes when the latent heat flux was low, which proved that neither the drier nor the virtual impactor perturbed the CO2 flux measurement. However, the undried measurement had a positive bias that increased with increasing latent heat flux, suggesting water vapor interference. For both systems, cospectral densities between vertical wind speed and CO2 molar fraction were distributed within the expected frequency range, with a moderate attenuation of high-frequency fluctuations. While the setup equipped with a drier and a virtual impactor generated a slightly higher flux loss, we opt for this alternative for its reduced water vapor cross-sensitivity and better protection against sea spray. The integral turbulence characteristics were found to agree with the universal stability dependence observed over land. Nonstationary conditions caused unphysical results, which resulted in a high percentage (65 %) of discarded measurements. After removing the nonstationary cases, the direction of the sea–air CO2 fluxes was in good accordance with independently measured CO2 partial pressure difference between the sea and the atmosphere. Atmospheric CO2 concentration changes larger than 2 ppm during a 30 min averaging period were found to be associated with the nonstationarity of CO2 fluxes.

An introductory guide to gas exchange analysis of photosynthesis and its application to plant phenotyping and precision irrigation to enhance water use efficiency

AbstractLeaf gas exchange is central to the analysis of photosynthetic processes and the development of more productive, water efficient and stress tolerant crops. This has led to a rapid expansion in the use of commercial plant photosynthesis systems which combine infra-red gas analysis and chlorophyll fluorescence (Chl-Flr) capabilities. The present review provides an introduction to the principles, common sources of error, basic measurements and protocols when using these plant photosynthesis systems. We summarise techniques to characterise the physiology of light harvesting, photosynthetic capacity and rates of respiration in the light and dark. The underlying concepts and calculation of mesophyll conductance of CO2 from the intercellular air-space to the carboxylation site within chloroplasts using leaf gas exchange and Chl-Flr are introduced. The analysis of stomatal kinetic responses is also presented, and its significance in terms of stomatal physiological control of photosynthesis that determines plant carbon and water efficiency in response to short-term variations in environmental conditions. These techniques can be utilised in the identification of the irrigation technique most suited to a particular crop, scheduling of water application in precision irrigation, and phenotyping of crops for growth under conditions of drought, temperature extremes, elevated [CO2] or exposure to pollutants.

Respiration of downed logs in pine and oak forests in the Qinling Mountains, China

Approximately 70% of the carbon (C) stored in logs is released into the atmosphere, representing an important source of CO2 lost from terrestrial ecosystems. Log respiration (Rlog) has gained attention as a core issue in global C cycle research. In forest ecosystems that contain many logs, the Rlog flux can convert forests from C sinks into C sources; thus, Rlog should be considered in relevant research to avoid underestimating the CO2 losses in the forest C cycle. Limited information is available regarding Rlog from natural forests, and many uncertainties remain about the magnitude of Rlog. In our study, Rlog was measured in situ by infrared gas analysis in Pinus armandi and Quercus aliena var. acuteserrata forests in the Qinling Mountains, China. The objectives of this study were (1) to reveal the seasonal variation patterns of Rlog; (2) to systematically analyze the relationships between Rlog and various factors, including the tree species, decay class, temperature, water content, and chemical composition; and (3) to estimate the annual Rlog flux in P. armandi and Q. aliena var. acuteserrata forests in the Qinling Mountains, China. This study presents a full year time series of Rlog measurements for 30 logs (3 replicate logs × 5 decay classes × 2 tree species). The Rlog measurements were repeated 468 times for each log from May 2014 to April 2015. The log temperature (Tlog), air temperature (TA), soil temperature (TS) at a depth of 10 cm, and log water content (Wlog) were measured simultaneously with Rlog. Moreover, the log density (Dlog) and chemical composition (C, nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg)) were determined. Our results showed significant seasonal variation in Rlog for both species, which corresponded to variations in Tlog during the study period. The annual mean Rlog of Q. aliena var. acuteserrata (1.69 ± 1.60 μmol m−2·s-1) was higher than that of P. armandi (1.55 ± 1.43 μmol m−2·s−1), but the difference was not significant (P = 0.61). The decay classes, Tlog, Wlog, and the N, P, Ca, and Mg concentrations were positively correlated with Rlog. Moreover, the K concentration was negatively correlated with Rlog, and the C concentration in logs was not correlated with Rlog. The total annual Rlog flux did not differ significantly between the P. armandi (67.25 ± 7.28 g C·m−2·y−1) and Q. aliena var. acuteserrata (74.69 ± 9.31 g C·m−2·y−1) forests (P = 0.26). These results provide insight into the factors responsible for seasonal changes in Rlog and can improve estimates of the annual Rlog flux in natural forests.