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Tidal wetlands are comprised of complex interdependent pathways where measurements of carbon exchange are often scale dependent. Common data collection methods (i.e., chambers and eddy covariance) are inherently constrained to different spatial and temporal scales which could generate biased information for applications of carbon accounting, identifying functional relationships and predicting future responses to climate change. Consequently, it is needed to systematically evaluate measurements derived from multiple approaches to identify differences and how techniques complement each other to reconcile interpretations. To accomplish this, we tested ecosystem‐scale eddy covariance with plot‐scale chamber measurements within a temperate salt marsh. We found good agreement (R2 = 0.71–0.95) when comparing measurements of CH4 emissions and CO2 exchange but this agreement was dependent upon canopy phenology with discrepancies mainly arising during senescence and dormancy phenophases. The environmental drivers for CH4 and CO2 fluxes were mostly preserved across different measurement techniques, but the number of drivers increases while their individual strength decreases at the ecosystem scale. Empirical upscaling models parameterized with chamber measurements overestimated annual net ecosystem exchange (NEE; 108%) and gross primary production (GPP; 12%) while underestimating ecosystem respiration (Reco; 14%) and CH4 emissions (69%) compared to eddy covariance measurements. Our results suggest that the environmental complexity of CH4 and CO2 fluxes in salt marshes may be underestimated by chamber‐based measurements, and highlights how different techniques are complementary while considering limitations at each level of measurement. Plain Language Summary: Tidal wetlands are important landscape features which play a significant role in regional carbon cycling between land, ocean and the atmosphere. These ecosystems are very productive, with high rates of photosynthesis during the growing season, but they also emit methane and carbon dioxide which can offset carbon gains. Therefore, it is important to accurately measure and understand what factors regulate carbon cycling processes to better characterize how these systems function, calculate carbon budgets and help predict possible reposes to climate change. We compare several common measurement techniques including chamber and eddy covariance which incorporate information across different scales to evaluate the level of agreement and how these techniques can be combined to increase our understanding of ecosystem functionality. We found that techniques agree well when comparing time‐matched measurement windows but different plant development stages across the ecosystem likely impacted agreement during autumn and early winter. We found that primary factors regulating fluxes were similar across techniques but when considering data collected over more hours of the day with eddy covariance, additional factors were identified indicating measurements from chambers which are limited in both coverage across space and time may present an oversimplified view within tidal wetlands. Key Points: Plot‐level and eddy covariance measurements had good overall agreement, but the strength of agreement was dependent upon plant phenologyThe relevance and influence of environmental drivers varied for all fluxes across different techniquesModels parameterized with plot‐level data overestimated ecosystem‐scale net ecosystem exchange but underestimated CO2 and CH4 emissions [ABSTRACT FROM AUTHOR]

Improving canopy photosynthetic light use efficiency and energy conversion efficiency (εc) is a major option to increase crop yield potential. However, so far, the diurnal and seasonal variations of canopy light use efficiency (LUE) and εc are largely unknown due to the lack of an efficient method to estimate εc in a high temporal resolution. Here we quantified the dynamic changes of crop canopy LUE and εc during a day and a growing season with the canopy gas exchange method. A response curve of whole-plant carbon dioxide (CO2) flux to incident photosynthetically active radiation (PAR) was further used to calculate εc and LUE at a high temporal resolution. Results show that the LUE of two wheat cultivars with different canopy architectures at five stages varies between 0.01 to about 0.05 mol CO2 mol–1 photon, with the LUE being higher under medium PAR. Throughout the growing season, the εc varies from 0.5 to 3.7% (11–80% of the maximal εc for C3 plants) with incident PAR identified as a major factor controlling variation of εc. The estimated average εc from tillering to grain filling stages was about 2.17%, i.e., 47.2% of the theoretical maximal. The estimated season-averaged radiation use efficiency (RUE) was 1.5–1.7 g MJ–1, which was similar to the estimated RUE based on biomass harvesting. The large variations of LUE and εc imply a great opportunity to improve canopy photosynthesis for greater wheat biomass and yield potential.

Improving canopy photosynthetic light use efficiency and energy conversion efficiency (ε c ) is a major option to increase crop yield potential. However, so far, the diurnal and seasonal variations of canopy light use efficiency (LUE) and ε c are largely unknown due to the lack of an efficient method to estimate ε c in a high temporal resolution. Here we quantified the dynamic changes of crop canopy LUE and ε c during a day and a growing season with the canopy gas exchange method. A response curve of whole-plant carbon dioxide (CO2) flux to incident photosynthetically active radiation (PAR) was further used to calculate ε c and LUE at a high temporal resolution. Results show that the LUE of two wheat cultivars with different canopy architectures at five stages varies between 0.01 to about 0.05 mol CO2 mol–1 photon, with the LUE being higher under medium PAR. Throughout the growing season, the ε c varies from 0.5 to 3.7% (11–80% of the maximal ε c for C3 plants) with incident PAR identified as a major factor controlling variation of ε c . The estimated average ε c from tillering to grain filling stages was about 2.17%, i.e., 47.2% of the theoretical maximal. The estimated season-averaged radiation use efficiency (RUE) was 1.5–1.7 g MJ–1, which was similar to the estimated RUE based on biomass harvesting. The large variations of LUE and ε c imply a great opportunity to improve canopy photosynthesis for greater wheat biomass and yield potential. [ABSTRACT FROM AUTHOR]

High temperature and accompanying high vapor pressure deficit often stress plants without causing distinctive changes in plant canopy structure and consequential spectral signatures. Sun‐induced chlorophyll fluorescence (SIF), because of its mechanistic link with photosynthesis, may better detect such stress than remote sensing techniques relying on spectral reflectance signatures of canopy structural changes. However, our understanding about physiological mechanisms of SIF and its unique potential for physiological stress detection remains less clear. In this study, we measured SIF at a high‐temperature experiment, Temperature Free‐Air Controlled Enhancement, to explore the potential of SIF for physiological investigations. The experiment provided a gradient of soybean canopy temperature with 1.5, 3.0, 4.5, and 6.0°C above the ambient canopy temperature in the open field environments. SIF yield, which is normalized by incident radiation and the fraction of absorbed photosynthetically active radiation, showed a high correlation with photosynthetic light use efficiency (r = 0.89) and captured dynamic plant responses to high‐temperature conditions. SIF yield was affected by canopy structural and plant physiological changes associated with high‐temperature stress (partial correlation r = 0.60 and −0.23). Near‐infrared reflectance of vegetation, only affected by canopy structural changes, was used to minimize the canopy structural impact on SIF yield and to retrieve physiological SIF yield (ΦF) signals. ΦF further excludes the canopy structural impact than SIF yield and indicates plant physiological variability, and we found that ΦF outperformed SIF yield in responding to physiological stress (r = −0.37). Our findings highlight that ΦF sensitively responded to the physiological downregulation of soybean gross primary productivity under high temperature. ΦF, if reliably derived from satellite SIF, can support monitoring regional crop growth and different ecosystems' vegetation productivity under environmental stress and climate change. [ABSTRACT FROM AUTHOR]

A transient state canopy-chamber was developed to monitor CO2 exchange of shrubland ecosystems. The chamber covered 0.64 m2 and it was modular with a variable height. Several tests were carried out to check the potential errors in the flux estimates due to leakages and the environment modifications during the measurements inside the chamber. The laboratory leakages test showed an error below 1% of the flux; the temperature increases inside the chamber were below 1.3 °C at different light intensity and small pressure changes. The radial blowers inside the chamber created different wind speed at different chamber height, with faster speed at the top of the chamber and the minimum wind speed that was recorded at soil level, preventing detectable effects on soil CO2 emission rates. Moreover, the chamber was tested for two years in a semi-arid Mediterranean garrigue, identifying a strong seasonality of CO2 fluxes with the highest rates during spring and lowest rates recorded during the hot dry non-vegetative summer.

A transient state canopy-chamber was developed to monitor CO2 exchange of shrubland ecosystems. The chamber covered 0.64 m² and it was modular with a variable height. Several tests were carried out to check the potential errors in the flux estimates due to leakages and the environment modifications during the measurements inside the chamber. The laboratory leakages test showed an error below 1% of the flux; the temperature increases inside the chamber were below 1.3 °C at different light intensity and small pressure changes. The radial blowers inside the chamber created different wind speed at different chamber height, with faster speed at the top of the chamber and the minimum wind speed that was recorded at soil level, preventing detectable effects on soil CO2 emission rates. Moreover, the chamber was tested for two years in a semi-arid Mediterranean garrigue, identifying a strong seasonality of CO2 fluxes with the highest rates during spring and lowest rates recorded during the hot dry non-vegetative summer. [ABSTRACT FROM AUTHOR]

Traditional farming has been ceased in large areas regarding several Central-European countries during the last decades. Nevertheless, only minimal knowledge is available about the impacts of these land use changes on the fluxes of grasslands. Within the framework of this research the dependence of stand level CO2 flux (NEE) on temperature, light (PPFD), leaf area (LAI), evapotranspiration and soil moisture has been examined in a dry sandy pasture grazed by grey cattle for decades. The examinations have been completed both in a grazed area and in a 6 hectare patch excluded from grazing. Measurements have been taken for 3 years during the vegetation periods in the area of the Kiskunság National Park by a mobile Plexiglas chamber as well as infrared gas analysers. Among the examined abiotic and biotic parameters the dependence of NEE on PPFD and LAI has been significant in both areas. Exponential and linear correlation turned out to be the strongest in both grassland types between CO2 fixation and light dependence and CO2 fixation and leaf area, respectively. The strongest correlation has been observed between the PPFD and NEE in both types of grassland. The dependence of CO2 flux on light and leaf area has been stronger in the extensively grazed area compared to the other examined grass excluded from grazing. Based on this fact it can be assumed that the conversion of land use in traditionally grazed grasslands has negative influence on the relation among NEE and the key abiotic and biotic parameters. It can be explained, beside the accumulation of litter, by the altered vegetation dynamic processes. Extreme dry periods effect, in a negative way, the dependence of CO2 flux on temperature, soil moisture and evapotranspiration. It calls the attention to the impacts of weather extremities on the mechanisms in semi-natural sandy grasslands. [ABSTRACT FROM AUTHOR]

Aims: Gas exchange measurements on individual plants depend largely on chamber systems, and uncertainties and corrections in current flux calculation procedures require further assessment. Methods: We present a practical study with novel methods for analyses of flux uncertainties in an original chamber design excluding soil fluxes and allowing simultaneous measurements of whole-plant photosynthesis and transpiration. Results: Results indicate that random errors caused by IRGA noise and the lack of criteria to optimize the time window (TW) of chamber enclosure lead to significant flux uncertainties (12 %). Although enclosure should be rapid to minimize plant disturbances, longer TWs (3 min) increase confidence in flux estimates. Indeterminate stabilization periods in existing calculation protocols cause significant systematic errors. Stabilization times were identified via the change-point detection method, and flux uncertainties were reduced. Photosynthesis was overestimated by up to 28 % when not correcting the evolving CO molar fraction for water vapour dilution. Leakage can compromise flux estimates, but was negligible (ca. 2 %) here due to the large chamber-headspace and relatively small values of both collar contact length and closure time. Conclusions: A bootstrapping, resampling-based flux calculation method is presented and recommended to better assess random errors and improve flux precision. We present practical recommendations for the use of whole-plant chambers. [ABSTRACT FROM AUTHOR]

The accurate assessment of respiration by woody vegetation, still a challenge in plant productivity models, is generally a problem of correctly scaling-up the process from organs to the whole plant. We used a large (41.6 m), canopy chamber to enclose mature olive trees and to measure aboveground respiration ( R) under natural environmental conditions in an irrigated olive orchard in Córdoba (Spain). The 3-year study assessed nocturnal and seasonal R patterns in terms of temperature ( T), plant dry matter composition, and phenology. The relative contributions of maintenance and growth respiration to R were determined empirically via an independent experiment. Although short-term variations in R rates were explained mainly by T variations, over seasonal time-scales this relationship was modulated by the vegetative composition of the olive trees and the contribution of growth respiration to R when the plants, in different seasons, allocated most of the new assimilates to actively growing shoots, flowers or fruits. Leaf mass and fruit load were the main determinants of R, which was weakly affected by differences in woody biomass since woody tissue respiration accounted for just 15 % of R. Respiration in olive trees during fruit setting periods is composed of approximately 30 % growth and 70 % maintenance. This study provides an independent evaluation of how, and to what degree, seasonally varying plant organ composition determines total respiration. Improved modelling of ecosystem respiration can be achieved by accounting for plant biological patterns characterising energy-requiring growth and maintenance processes, since biochemical kinetics alone cannot explain the observed seasonal variability. [ABSTRACT FROM AUTHOR]

Among the most extended ecosystems of the temperate zone, the seminatural, dry grasslands constitute a substantial proportion in the Carpathian Basin. The aim of our present study was to investigate the short-term effect of extensive fertilization on the species composition and CO 2 exchange of loess grassland at community level. The in situ investigation of the latter parameter have not been yet carried out in Pannonian loess grasslands. Most of the parameters studied showed a considerable interannual variation both in the fertilized and in the control stands. As a result of the treatment, the average species number of the fertilized stand decreased by 22%, which was more significant in the autumn (26%) than in the spring. Diversity values, including Shannon index and species richness, increased by nearly 1.5 times in the year with adequate rainfall compared with the initial values. In general, species richness and the ratio of dicots decreased, while the ratio of therophytes, alien competitors, and C 4 plants increased with the addition of fertilizers. Significant carbon sequestration potential was only detected during wet periods in the fertilized grass. The rate of CO 2 uptake was found to be nearly five times higher in the fertilized stand and nearly three times higher in the control stand during the wet year compared with the previous, extremely dry year. The CO 2 uptake potential of the fertilized grassland exceeded that of the control stand by 12% in the year with high rainfall, while the rate of CO 2 exchange dropped by 50% in the dry year in the fertilized stand. Our study reinforced the idea that the decline in species richness was not necessarily followed by the reduction of stand level carbon uptake in a short period due to an insignificant change in ecophysiological functional groups. [ABSTRACT FROM AUTHOR]

Abstract: A transient-state chamber was developed to measure canopy gas exchange of single trees in the field. The chamber, with a volume of 41.6m3, is designed to enclose a medium-size orchard tree; chamber top and windows can be left open, causing minimum disturbance to the tree environment. Transitory closures allow simultaneous measurement of CO2 exchange and transpiration of the enclosed tree. The chamber was tested during a 2-year study in an olive orchard submitted to different irrigation treatments: control with no water stress (CI) and regulated deficit irrigation (RDI). Leakage had a minimal impact on flux calculations (0.8%min−1); adsorption was not detectable. Maximum increases in canopy temperature of 0.58°Cmin−1 for CI and 1.3°Cmin−1 for RDI generated very small effects on fluxes. Changes in the transpiration rate induced by the chamber''s modification of the canopy environment were evaluated by continuous sap flow measurements with heat pulse gauges inserted in the trunk of two trees enclosed by chambers. Results showed a sap flow decrease of about 8% after 180s of chamber closure. The artificial turbulence generated by fans into the chamber to facilitate air mixing did not alter the transpiration rate. The enclosure had a very small impact on the tree canopy conductance (G c ). The initial lag and mixing time was estimated as 30s; the optimal duration of the calculation window was 70s. Hourly carbon assimilation (A), transpiration (E), and water use efficiency (WUE) for two olive trees in the field subjected to different levels of water stress were measured. [Copyright &y& Elsevier]

Abstract: An automated, portable, and non-steady-state through-flow canopy-chamber assembly for measurements of CO2 and water vapour fluxes on field crops and for simultaneous recording of environmental variables within the chambers and in the field is described. The system comprises of four units operating independently of each other. Each unit consists of (i) a central measurement device containing the CO2 and water vapour sensors, gas valves and pumps and a PC-controlled data acquisition system, (ii) an air conditioner for cooling and drying of incoming air, and (iii) the canopy chamber. Within each chamber, sensors for air, leaf, and soil temperature as well as for soil moisture are installed. All operations of the system are controlled by a PC. Chamber effects on the microclimate were carefully studied. Downwelling and upwelling total radiation, its balance, and incoming photosynthetically active radiation (PAR) inside the chamber were reduced by 2%, 3% and 10%, respectively. Diffuse fraction of PAR on clear days at noon was about 5% higher than in the open field, whereas it decreased by about 10% under cloudy conditions. Maximum over-temperatures of the air inside the chamber were less than 3K. Based on an analysis of the dynamic properties of the CO2 and H2O sensors and of the chamber, a data analysis approach was developed that allows for bias compensation in CO2 and H2O gas exchange rates occurring under non-steady-state measurement conditions in the field. The system was used successfully over several years in studies on canopy gas exchange of barley (Hordeum vulgare L.) and oilseed rape (Brassica napus L.). [Copyright &y& Elsevier]

Significant part of our work was developing a new type of CO2 and H2O gas exchange chambers fit for measuring stand patches. Ground areas of six chambers (ranged between 0.044–4.531 m2) constituted a logarithmic series with doubling diameters from 7.5 to 240.0 cm. We demonstrate one of the first results for stand net ecosystem CO2 exchange (NEE) rates and temporal variability for two characteristic Central European grassland types: loess and sand. The measured mean NEE rates and their ranges in these grasslands were similar to values reported in other studies on temperate grasslands. We also dealt with the spatial scale dependence from ecophysiological point of view. Our chamber-series measurement was performed in a perennial ruderal weed association. The variability of CO2-assimilation of this weed vegetation showed clear spatial scale-dependence. We found the lowest variability of the vegetation photosynthesis at the small-middle scales. The results of spatial variability suggest the 0.2832 m2 patch size is the characteristic unit of the investigated weed association and there is a kind of synphysiological minimi-area with characteristic size for each vegetation type. [ABSTRACT FROM AUTHOR]