Seasonal variations in net ecosystem exchange of CO2 and conservation of water use efficiency of cotton in the Mississippi Delta

The continuous field measurements of net ecosystem exchange (NEE) of CO 2 were provided at ridge-hollow oligotrophic bog in the Middle Taiga zone of West Siberia, Russia in 2017-2018. The model of net ecosystem exchange of CO 2 was suggested to describe the influence of different environmental factors on NEE and to estimate the total carbon budget of the bog over the growing season. The model uses air and soil temperature, incoming photosynthetically active radiation (PAR) and water table depth, as the key factors influencing gross primary production (GPP) and ecosystem respiration (ER). The model coefficients were calibrated using the data collected by automated soil CO 2 flux system with two transparent long-term chambers placed at large hollow and small ridge sites. Experimental and modeling results showed that the Mukhrino bog acted over the study period as a carbon sink, with an average NEE of –87.7 gC m -2 at the hollow site and –50.2 gC m -2 at the ridge site. GPP was – 344.8 and –228.5 gC m -2 whereas ER was 287.6 and 140.9 gC m -2 at ridge and hollow sites, respectively. Despite of a large difference in NEE estimates between 2017 and 2018 the growing season variability of NEE were quite similar.

<p>Long term flux measurements are needed to improve our understanding of the carbon balance of arable lands. The objective of our study was to determine the seasonal dynamics of carbon cycling in a Hungarian cropland and to examine the effect of crop rotation on net ecosystem exchange of CO<sub>2</sub> (NEE), furthermore to assess the influences of C outputs and inputs derived from lateral fluxes on soil organic carbon (SOC) stock. In this study we update the results presented in our poster of last year’s conference (EGU21-10977).</p><p>The experiment began in 2017 and crop rotation of the measured field consisted of winter wheat (2017-2018 and 2019-2020), rapeseed (2018), sorghum (2019) and sunflower (2021). CO<sub>2</sub> fluxes and annual net ecosystem exchange (NEE) of CO<sub>2</sub> were measured by a field-scale eddy covariance (EC) station at a Central Hungarian cropland site. Both vertical and lateral C fluxes were taken into account when calculating the net ecosystem carbon budget (NECB).</p><p>As presented in our previous study the largest sink activity was observed in the sorghum season (-277 g C m<sup>-2</sup> from sowing to harvest). The cropland acted as a source of CO<sub>2</sub> during the rapeseed season (140 g C m<sup>-2</sup>) due to incomplete germination caused by extreme autumnal drought.</p><p>We found that during the study period both meteorological variables and lateral carbon fluxes such as C inputs derived from seed and crop residues and outputs (harvest) had significant influence on the C dynamics. The higher temperatures and precipitation amount that characterised the fall of 2019 caused large differences in NEE dynamics for winter wheat when compared to 2017. The impact of climatic factors could be seen in the sunflower period since lack of precipitation in 2021 led to remarkably low carbon uptake.</p><p>Fallow periods in total covered a relatively long period of time (approximately 1 year out of the 4 year long study period). These fallow periods had a significant effect on NECB values due to immense C loss. During the four years of our experiment cumulative NEE was -222 g C m<sup>-2</sup> and NECB was 726 g C m<sup>-2</sup> as carbon loss during fallow periods (437 g C m<sup>-2</sup> in total) and carbon export through harvest (964 g C m<sup>-2</sup> in total) counterbalanced the crop’s CO<sub>2</sub> uptake.</p><p>We can conclude that while this Hungarian cropland was a sink of carbon it could not maintain the soil organic carbon content as it was not able to sequester enough carbon to do so. Cover plants and crop residue retention could be a solution to reduce the risk of soil carbon stock depletion but further studies are needed in the field of soil management practices.</p>

Net ecosystem exchange of CO2 and carbon balance for eight temperate organic soils under agricultural management

Sustainable use of water resources in agriculture is a necessity for many arid countries. In order to investigate the effect of water deficit, irrigation after 120 (control), 155 (moderate water stress) and 190 mm (sever water stress) pan evaporation and super absorbent polymer rates (SAP) (0, 30, 60 and 90 kg ha-1) on growth, yield and water use efficiency of cotton, an experiment was conducted as split plot based on a randomized complete block design with three replications. Moreover, the effect of water quality (distilled water and solutions of 0.25, 0.5, 0.75, 1 and 1.25% NaCl) was investigated on water holding capacity by SAP. Results revealed that moderate water stress (irrigation intervals of aprox. 15 days) along with 60 kg ha-1 SAP application was the best treatment in terms of growth and yield indices of cotton. The results for plant height, plant dry weight, boll number per plant and fiber yield in this treatment were 16, 28, 42 and 10% higher than control treatment, respectively. Water deficit and SAP application improved the water use efficiency (WUE) of cotton. The amount of WUE in moderate water stress treatment along with consumption of 60 or 90 kg ha-1 SAP was 26% higher than for control treatment. In addition, water holding capacity by SAP in distilled water treatment was 7 times higher than in the case of 1.25% NaCl solution. The overall results showed that irrigation deficit and SAP application are two appropriate strategies for crop production in areas affected by drought stress, especially if low saline water sources are used.

Sustainable use of water resources in agriculture is a necessity for many arid countries. In order to investigate the effect of water deficit, irrigation after 120 (control), 155 (moderate water stress) and 190 mm (sever water stress) pan evaporation and super absorbent polymer rates (SAP) (0, 30, 60 and 90 kg ha-1) on growth, yield and water use efficiency of cotton, an experiment was conducted as split plot based on a randomized complete block design with three replications. Moreover, the effect of water quality (distilled water and solutions of 0.25, 0.5, 0.75, 1 and 1.25% NaCl) was investigated on water holding capacity by SAP. Results revealed that moderate water stress (irrigation intervals of aprox. 15 days) along with 60 kg ha-1 SAP application was the best treatment in terms of growth and yield indices of cotton. The results for plant height, plant dry weight, boll number per plant and fiber yield in this treatment were 16, 28, 42 and 10% higher than control treatment, respectively. Water deficit and SAP application improved the water use efficiency (WUE) of cotton. The amount of WUE in moderate water stress treatment along with consumption of 60 or 90 kg ha-1 SAP was 26% higher than for control treatment. In addition, water holding capacity by SAP in distilled water treatment was 7 times higher than in the case of 1.25% NaCl solution. The overall results showed that irrigation deficit and SAP application are two appropriate strategies for crop production in areas affected by drought stress, especially if low saline water sources are used.

干旱叠加海平面上升、氮负荷增加对河口潮汐沼泽生态系统净CO₂交换的影响

This study was conducted in the Aegean region conditions of Turkey in 2020. It was carried out on May-505, a local cotton variety. The study examined the variation of seed yield, water use efficiency (WUE), and irrigation water use efficiency (IWUE) of cotton with different irrigation programs and water levels. The field trial, which was designed as two factors and three replications, was designed according to the randomized complete block trial design. Four different irrigation levels (IL) (100%, 67%, 33%, and 0%) and two different irrigation scheduling approaches (gravimetric and pan evaporation) were investigated in the study. Seasonal water use values in treatments varied between 215 (0%) and 746 (100% - Pan evaporation approach) mm during the production period. The average yield values obtained with irrigation levels, which have essential effects on cotton seed yield, are listed as follows; 2057 kg ha-1 (IL-0%), 3471 kg ha-1 (IL-33%), 3771 kg ha-1 (IL-67%), and 5083 kg ha-1 (IL-100%). It was determined pan evaporation applications performed higher yields than gravimetric applications. WUE values were between 0.63 – 1.04 kg m-3. The gravimetric method’s yield response factor (ky) was 0.73, and the pan evaporation method’s yield response factor (ky) was 0.89. These results show that cotton is tolerant of water stress. In conclusion, although the pan evaporation approach with 100% treatment is suggested for cotton production in the parts of the Aegean region within the semi-arid climate zone, while water resources are sufficient. When the results are evaluated in terms of seed cotton yield for a deficit irrigation strategy, IL-67% treatment with a gravimetric approach can be used.

Present study is a maiden attempt to assess net ecosystem exchange (NEE) of carbon dioxide (CO2) flux from jute crop (Corchorus olitorius L.) in the Indo-Gangetic plain by using open-path eddy covariance (EC) technique. Diurnal variations of NEE were strongly influenced by growth stages of jute crop. Daytime peak NEE varied from - 5µmolm-2s-1 (in germination stage) to - 23µmolm-2s-1 (in fibre development stage). The ecosystem was net CO2 source during nighttime with an average NEE value of 5-8μmolm-2s-1. Combining both daytime and nighttime CO2 fluxes, jute ecosystem was found to be a net CO2 sink on a daily basis except the initial 9days from date of sowing. Seasonal and growth stage-wise NEEs were computed, and the seasonal total NEE over the jute season was found to be - 268.5gC m-2(i.e. 10.3 t CO2 ha-1). In different jute growth stages, diurnal variations of NEE were strongly correlated (R2 > 0.9) with photosynthetic photon flux density (PPFD). Ecosystem level photosynthetic efficiency parameters were estimated at each growth stage of jute crop using the Michaelis-Menten equation. The maximum values of photosynthetic capacity (Pmax, 63.3 ± 1.15µmol CO2 m-2s-1) and apparent quantum yield (α, 0.072 ± 0.0045µmol CO2 µmol photon-1) were observed during the active vegetative stage, and the fibre development stage, respectively. Results of the present study would significantly contribute to understanding of the carbon flux from the Indian agro-ecosystems, which otherwise are very sparse.

Net ecosystem exchange (NEE) of C varies greatly among Arctic ecosystems. Here, we show that approximately 75 per cent of this variation can be accounted for in a single regression model that predicts NEE as a function of leaf area index (LAI), air temperature and photosynthetically active radiation (PAR). The model was developed in concert with a survey of the light response of NEE in Arctic and subarctic tundras in Alaska, Greenland, Svalbard and Sweden. Model parametrizations based on data collected in one part of the Arctic can be used to predict NEE in other parts of the Arctic with accuracy similar to that of predictions based on data collected in the same site where NEE is predicted. The principal requirement for the dataset is that it should contain a sufficiently wide range of measurements of NEE at both high and low values of LAI, air temperature and PAR, to properly constrain the estimates of model parameters. Canopy N content can also be substituted for leaf area in predicting NEE, with equal or greater accuracy, but substitution of soil temperature for air temperature does not improve predictions. Overall, the results suggest a remarkable convergence in regulation of NEE in diverse ecosystem types throughout the Arctic.

Climatic variables not only directly affect the interannual variability (IAV) in net ecosystem exchange of CO2 (NEE) but also indirectly drive it by changing the physiological parameters. Identifying these direct and indirect paths can reveal the underlying mechanisms of carbon (C) dynamics. In this study, we applied a path analysis using flux data from 65 sites to quantify the direct and indirect climatic effects on IAV in NEE and to evaluate the potential relationships among the climatic variables and physiological parameters that represent physiology and phenology of ecosystems. We found that the maximum photosynthetic rate was the most important factor for the IAV in gross primary productivity (GPP), which was mainly induced by the variation in vapour pressure deficit. For ecosystem respiration (RE), the most important drivers were GPP and the reference respiratory rate. The biome type regulated the direct and indirect paths, with distinctive differences between forests and non-forests, evergreen needleleaf forests and deciduous broadleaf forests, and between grasslands and croplands. Different paths were also found among wet, moist and dry ecosystems. However, the climatic variables can only partly explain the IAV in physiological parameters, suggesting that the latter may also result from other biotic and disturbance factors. In addition, the climatic variables related to NEE were not necessarily the same as those related to GPP and RE, indicating the emerging difficulty encountered when studying the IAV in NEE. Overall, our results highlight the contribution of certain physiological parameters to the IAV in C fluxes and the importance of biome type and multi-year water conditions, which should receive more attention in future experimental and modelling research.

Over the last two and half decades, strong evidence showed that the terrestrial ecosystems are acting as a net sink for atmospheric carbon. However the spatial and temporal patterns of variation in the sink are not well known. In this study, we examined latitudinal patterns of interannual variability (IAV) in net ecosystem exchange (NEE) of CO2 based on 163 site‐years of eddy covariance data, from 39 northern‐hemisphere research sites located at latitudes ranging from ∼29°N to ∼64°N. We computed the standard deviation of annual NEE integrals at individual sites to represent absolute interannual variability (AIAV), and the corresponding coefficient of variation as a measure of relative interannual variability (RIAV). Our results showed decreased trends of annual NEE with increasing latitude for both deciduous broadleaf forests and evergreen needleleaf forests. Gross primary production (GPP) explained a significant proportion of the spatial variation of NEE across evergreen needleleaf forests, whereas, across deciduous broadleaf forests, it is ecosystem respiration (Re). In addition, AIAV in GPP and Re increased significantly with latitude in deciduous broadleaf forests, but AIAV in GPP decreased significantly with latitude in evergreen needleleaf forests. Furthermore, RIAV in NEE, GPP, and Re appeared to increase significantly with latitude in deciduous broadleaf forests, but not in evergreen needleleaf forests. Correlation analyses showed air temperature was the primary environmental factor that determined RIAV of NEE in deciduous broadleaf forest across the North American sites, and none of the chosen climatic factors could explain RIAV of NEE in evergreen needleleaf forests. Mean annual NEE significantly increased with latitude in grasslands. Precipitation was dominant environmental factor for the spatial variation of magnitude and IAV in GPP and Re in grasslands.

Cotton (Gossypium hirsutum L.) production in the Southeast United States can be limited by periodic drought. Irrigation and furrow diking tillage may improve economic yield and water use efficiency of cotton. Timing of rainfall may interfere with the efficiency of irrigation. Field studies were conducted during 2001 to 2010 near Shellman, Georgia to examine four irrigation rates based on Irrigator Pro for Cotton consisting of 100, 66, 33, and 0%. The objectives were to determine the value of irrigation and the economic water use efficiency of irrigation among irrigation rates over years. In-season rainfall ranged from 270 to 760 mm and irrigation volume ranged from 110 to 455 mm. Total water applied (rainfall + irrigation) ranged between 560 and 870 mm. In all but 2003, irrigation improved yield by 247-645 kg lint ha -1 . Years with average or below average rainfall had incrementally higher yields as irrigation rate increased except for 2007. Water use efficiency for irrigation was highest for the 33% rate in 2001 and 2002 and higher in 2004 and 2007 for the 66% rate. In severe drought years, the 33% rate did not sufficiently relieve drought stress. Irrigation provided profit in all but one year of the study. Although 100% irrigation is not the most efficient irrigation level, it often provides the most economic return. Furrow diking improved yield and water use efficiency in 3 of 6 years tested.

<p>Peatlands North of 45˚ represent one of the largest terrestrial carbon (C) stores. They play an important role in the global C-cycle, and their ability to sequester carbon is controlled by multiple, often competing, factors including precipitation, temperature and phenology. Land-atmosphere exchange of carbon dioxide (CO<sub>2</sub>) is dynamic, and exhibits marked seasonal and inter-annual variations which can effect the overall carbon sink strength in both the short- and long-term.</p><p>Due to increased incidences of climate anomalies in recent years, long-term datasets are essential to disambiguate natural variability in Net Ecosystem Exchange (NEE) from shorter-term fluctuations. This is particularly important at high latitudes (>45˚N) where the majority of global peatlands are found. With increasing pressure from stressors such as climate and land-use change, it has been predicted that with a ca. 3<sup>o</sup>C global temperature rise by 2100, UK peatlands could become a net source of C.</p><p>NEE of CO<sub>2</sub> has been measured using the eddy-covariance (EC) method at Auchencorth Moss (55°47’32 N, 3°14’35 W, 267 m a.s.l.), a temperate, lowland, ombrotrophic peatland in central Scotland, continuously since 2002. Alongside EC data, we present a range of meteorological parameters measured at site including soil temperature, total solar and photosynthetically active radiation (PAR), rainfall, and, since April 2007, half-hourly water table depth readings. The length of record and range of measurements make this dataset an important resource as one of the longest term records of CO<sub>2</sub> fluxes from a temperate peatland.</p><p>Although seasonal cycles of gross primary productivity (GPP) were highly variable between years, the site was a consistent CO<sub>2</sub> sink for the period 2002-2012. However, net annual losses of CO<sub>2</sub> have been recorded on several occasions since 2013. Whilst NEE tends to be positively correlated with the length of growing season, anomalies in winter weather also explain some of the variability in CO<sub>2</sub> sink strength the following summer.</p><p>Additionally, water table depth (WTD) plays a crucial role, affecting both GPP and ecosystem respiration (R<sub>eco</sub>). Relatively dry summers in recent years have contributed to shifting the balance between R<sub>eco</sub> and GPP: prolonged periods of low WTD were typically accompanied by an increase in R<sub>eco</sub>, and a decrease in GPP, hence weakening the overall CO<sub>2</sub> sink strength. Extreme events such as drought periods and cold winter temperatures can have significant and complex effects on NEE, particularly when such meteorological anomalies co-occur. For example, a positive annual NEE occurred in 2003 when Europe experienced heatwave and summer drought. More recently, an unusually long spell of snow lasting until the end of March delayed the onset of the 2018 growing season by up to 1.5 months compared to previous years. This was followed by a prolonged dry spell in summer 2018, which weakened GPP, increased R<sub>eco</sub> and led to a net annual loss of 47.4 ton CO<sub>2</sub>-C km<sup>-2</sup>. It is clear that the role of Northern peatlands within the carbon cycle is being modified, driven by changes in climate at both local and global scales.</p>

Atmospheric water vapor and soil moisture jointly determine the spatiotemporal variations of CO2 fluxes and evapotranspiration across the Qinghai-Tibetan Plateau grasslands

Changes in plant biomass induced by soil moisture variability drive interannual variation in the net ecosystem CO2 exchange over a reclaimed coastal wetland