CO2 Fertilization Research Articles

Quantitative analysis of the contributions of land use change and CO2 fertilization to carbon use efficiency on the Tibetan Plateau

Carbon use efficiency (CUE) is a key element in the vegetation carbon cycle, and determines how vegetation allocates carbon. Here, our research provides the spatio-temporal variations of CUE on the Tibetan Plateau (TP) based on ensemble simulations from 12 terrestrial ecosystem models. Moreover, the experimental design of simulations adds one time-varying driver at a time, thus quantitative analysis of the response of CUE to climate factors (i.e., temperature, precipitation and radiation), land use and land cover change (LULCC), and CO2 fertilization can be investigated. Results show that average CUE value of the multi-model simulations (0.583 ± 0.064) on the TP is slightly lower than that derived from the satellite-based product, the Moderate Resolution Imaging Spectroradiometer (0.646). However, CUE varies greatly among models due to differences in simulating plant photosynthetic productivity and respiratory rate, with range of 0.489–0.661. LULCC and CO2 fertilization contribute 4.24% and 0.79% of the annual mean CUE, respectively. Among the climatic factors, temperature and precipitation have positive correlations with CUE over most areas of the TP while solar radiation shows a negative impact.

The fate of carbon in a mature forest under carbon dioxide enrichment.

Atmospheric carbon dioxide enrichment (eCO2) can enhance plant carbon uptake and growth1-5, thereby providing an important negative feedback to climate change by slowing the rate of increase of the atmospheric CO2 concentration6. Although evidence gathered from young aggrading forests has generally indicated a strong CO2 fertilization effect on biomass growth3-5, it is unclear whether mature forests respond to eCO2 in a similar way. In mature trees and forest stands7-10, photosynthetic uptake has been found to increase under eCO2 without any apparent accompanying growth response, leaving the fate of additional carbon fixed under eCO2 unclear4,5,7-11. Here using data from the first ecosystem-scale Free-Air CO2 Enrichment (FACE) experiment in a mature forest, we constructed a comprehensive ecosystem carbon budget to track the fate of carbon as the forest responded to four years of eCO2 exposure. We show that, although the eCO2 treatment of +150 parts per million (+38 per cent) above ambient levels induced a 12 per cent (+247 grams of carbon per square metre per year) increase in carbon uptake through gross primary production, this additional carbon uptake did not lead to increased carbon sequestration at the ecosystem level. Instead, the majority of the extra carbon was emitted back into the atmosphere via several respiratory fluxes, with increased soil respiration alone accounting for half of the total uptake surplus. Our results call into question the predominant thinking that the capacity of forests to act as carbon sinks will be generally enhanced under eCO2, and challenge the efficacy of climate mitigation strategies that rely on ubiquitous CO2 fertilization as a driver of increased carbon sinks in global forests.

Assessing Impacts of Plant Stoichiometric Traits on Terrestrial Ecosystem Carbon Accumulation Using the E3SM Land Model

AbstractCarbon (C) enters into the terrestrial ecosystems via photosynthesis and cycles through the system together with other essential nutrients (i.e., nitrogen [N] and phosphorus [P]). Such a strong coupling of C, N, and P leads to the theoretical prediction that limited nutrient availability will limit photosynthesis rate, plant growth, and future terrestrial C dynamics. However, the lack of reliable information about plant tissue stoichiometric constraints remains a challenge for quantifying nutrient limitations on projected global C cycling. In this study, we harmonized observed plant tissue C:N:P stoichiometry from more than 6,000 plant species with the commonly used plant functional type framework in global land models. Using observed C:N:P stoichiometry and the flexibility of these ratios as emergent plant traits, we show that observationally constrained fixed plant stoichiometry does not improve model estimates of present‐day C dynamics compared with unconstrained stoichiometry. However, adopting stoichiometric flexibility significantly improves model predictions of C fluxes and stocks. The 21st century simulations with RCP8.5 CO2 concentrations show that stoichiometric flexibility, rather than baseline stoichiometric ratios, is the dominant controller of plant productivity and ecosystem C accumulation in modeled responses to CO2 fertilization. The enhanced nutrient limitations and plant P use efficiency mainly explain this result. This study is consistent with the previous consensus that nutrient availability will limit xfuture land carbon sequestration but challenges the idea that imbalances between C and nutrient supplies and fixed stoichiometry limit future land C sinks. We show here that it is necessary to represent nutrient stoichiometric flexibility in models to accurately project future terrestrial ecosystem carbon sequestration.

N-decanoyl-homoserine lactone alleviates elevated CO2-induced defense suppression to Botrytis cinerea in tomato

Tropospheric CO2 concentrations were remarkably increasing, especially since the Industrial Revolution. The CO2 fertilization technology was increasingly used in greenhouse agriculture cultivation because of its benefit to crop quality and yield. But, as a consequence of elevated CO2, the plant-pathogen interactions in natural or agricultural ecosystems have large potential to be affected. So far, the effects of elevated CO2 on plant defense against pathogen are complicated and the underlying mechanism remained poorly understood. Here, using tomato plants, we found that elevated CO2 significantly suppressed the plant defense against necrotrophic pathogen Botrytis cinerea, which is accompanied by the disturbed homeostasis between defense-related salicylic acid- and jasmonic acid- (JA-) signaling. But, exogenous application of bacterial secreta N-decanoyl-homoserine lactone (DHL) drastically rescued B. cinerea disease susceptibility under elevated CO2 condition. Moreover, JA biosynthesis mutant spr2 and JA signaling gene-silenced plants blocked DHL-induced plant defense under elevated CO2 condition, which suggested JA signaling was indispensable to the alleviated effect of DHL on plant susceptibility to B. cinerea under elevated CO2 condition. Overall, this information will be benefit to manipulate DHL as an attractive disease management strategy in agriculture cultivation under changing CO2 conditions.

Liana species decline in Congo basin contrasts with global patterns.

Lianas, woody climbing plants, are increasing in many tropical forests, with cascading effects such as decreased forest productivity, carbon sequestration, and resilience. Possible causes are increasing forest fragmentation, CO2 fertilization, and drought. Determining the primary changing species and their underlying vital rates help explain the liana trends. We monitored over 17,000 liana stems for 13 yr in 20 ha of old‐growth forest in the Congo Basin, and here we report changes and vital rates for the community and for the 87 most abundant species. The total liana abundance declined from 15,007 lianas in 1994 to 11,090 in 2001 to 9,978 in 2007. Over half (52%) of the evaluated species have significantly declining populations, showing that the community response is not the result of changes in a few dominant species only. Species density change (i.e., the change in number of individuals per hectare) decreased with mortality rate, tended to increase with recruitment rate, but was independent of growth rate. Species change was independent of functional characteristics important for plant responses to fragmentation, CO2, and drought, such as lifetime light requirements, climbing and dispersal mechanism, and leaf size. These results indicate that in Congo lianas do not show the reputed global liana increase, but rather a decline, and that elements of the reputed drivers underlying global liana change do not apply to this DR Congo forest. We suggest warfare in the Congo Basin to have decimated the elephant population, leading to less disturbance, forest closure, and declining liana numbers. Our results imply that, in this tropical forest, local causes (i.e., disturbance) override more global causes of liana change resulting in liana decline, which sharply contrasts with the liana increase observed elsewhere.

Scaling carbon fluxes from eddy covariance sites to globe: synthesis and evaluation of the FLUXCOM approach

Abstract. FLUXNET comprises globally distributed eddy-covariance-based estimates of carbon fluxes between the biosphere and the atmosphere. Since eddy covariance flux towers have a relatively small footprint and are distributed unevenly across the world, upscaling the observations is necessary to obtain global-scale estimates of biosphere–atmosphere exchange. Based on cross-consistency checks with atmospheric inversions, sun-induced fluorescence (SIF) and dynamic global vegetation models (DGVMs), here we provide a systematic assessment of the latest upscaling efforts for gross primary production (GPP) and net ecosystem exchange (NEE) of the FLUXCOM initiative, where different machine learning methods, forcing data sets and sets of predictor variables were employed. Spatial patterns of mean GPP are consistent across FLUXCOM and DGVM ensembles (R2>0.94 at 1∘ spatial resolution) while the majority of DGVMs show, for 70 % of the land surface, values outside the FLUXCOM range. Global mean GPP magnitudes for 2008–2010 from FLUXCOM members vary within 106 and 130 PgC yr−1 with the largest uncertainty in the tropics. Seasonal variations in independent SIF estimates agree better with FLUXCOM GPP (mean global pixel-wise R2∼0.75) than with GPP from DGVMs (mean global pixel-wise R2∼0.6). Seasonal variations in FLUXCOM NEE show good consistency with atmospheric inversion-based net land carbon fluxes, particularly for temperate and boreal regions (R2>0.92). Interannual variability of global NEE in FLUXCOM is underestimated compared to inversions and DGVMs. The FLUXCOM version which also uses meteorological inputs shows a strong co-variation in interannual patterns with inversions (R2=0.87 for 2001–2010). Mean regional NEE from FLUXCOM shows larger uptake than inversion and DGVM-based estimates, particularly in the tropics with discrepancies of up to several hundred grammes of carbon per square metre per year. These discrepancies can only partly be reconciled by carbon loss pathways that are implicit in inversions but not captured by the flux tower measurements such as carbon emissions from fires and water bodies. We hypothesize that a combination of systematic biases in the underlying eddy covariance data, in particular in tall tropical forests, and a lack of site history effects on NEE in FLUXCOM are likely responsible for the too strong tropical carbon sink estimated by FLUXCOM. Furthermore, as FLUXCOM does not account for CO2 fertilization effects, carbon flux trends are not realistic. Overall, current FLUXCOM estimates of mean annual and seasonal cycles of GPP as well as seasonal NEE variations provide useful constraints of global carbon cycling, while interannual variability patterns from FLUXCOM are valuable but require cautious interpretation. Exploring the diversity of Earth observation data and of machine learning concepts along with improved quality and quantity of flux tower measurements will facilitate further improvements of the FLUXCOM approach overall.

HETEROFOR 1.0: a spatially explicit model for exploring the response of structurally complex forests to uncertain future conditions – Part 1: Carbon fluxes and tree dimensional growth

Abstract. Given the multiple abiotic and biotic stressors resulting from global changes, management systems and practices must be adapted in order to maintain and reinforce the resilience of forests. Among others, the transformation of monocultures into uneven-aged and mixed stands is an avenue to improve forest resilience. To explore the forest response to these new silvicultural practices under a changing environment, one needs models combining a process-based approach with a detailed spatial representation, which is quite rare. We therefore decided to develop our own model (HETEROFOR for HETEROgeneous FORest) according to a spatially explicit approach, describing individual tree growth based on resource sharing (light, water and nutrients). HETEROFOR was progressively elaborated within Capsis (Computer-Aided Projection for Strategies in Silviculture), a collaborative modelling platform devoted to tree growth and stand dynamics. This paper describes the carbon-related processes of HETEROFOR (photosynthesis, respiration, carbon allocation and tree dimensional growth) and evaluates the model performances for three broadleaved stands with different species compositions (Wallonia, Belgium). This first evaluation showed that HETEROFOR predicts well individual radial growth (Pearson's correlation of 0.83 and 0.63 for the European beech and sessile oak, respectively) and is able to reproduce size–growth relationships. We also noticed that the net to gross primary production (npp to gpp) ratio option for describing maintenance respiration provides better results than the temperature-dependent routine, while the process-based (Farquhar model) and empirical (radiation use efficiency) approaches perform similarly for photosynthesis. To illustrate how the model can be used to predict climate change impacts on forest ecosystems, we simulated the growth dynamics of the mixed stand driven by three IPCC climate scenarios. According to these simulations, the tree growth trends will be governed by the CO2 fertilization effect, with the increase in vegetation period length and the increase in water stress also playing a role but offsetting each other.

Effects of CO2 enrichment by fermentation of CRAM on growth, yield and physiological traits of cherry tomato.

Carbon dioxide (CO2) concentration in greenhouses is sub-optimal for vegetable production. Many techniques have been used to increase CO2 concentration in greenhouses but most of them are expensive with certain limitations and drawbacks. We adopted a new strategy to elevate CO2 concentration in the greenhouse throughout the day via crop residues and animal manure composting (CRAM). During the whole cultivation period, CRAM-treated greenhouse had doubled CO2 concentration which significantly increased the yield of cherry tomatoes (Lycopersiconesculentum L.) i.e. up to 38%. The influence of CRAM procedure on cherry tomato quality was also investigated and the concentrations of total soluble solids (TSS) and soluble sugar were found to be significantly higher in cherry tomatoes grown under composting greenhouse than that of non-composting greenhouse. Additionally, CRAM-CO2 enrichment also resulted in increased concentrations of ascorbic acid (Vitamin C) and titrate acid as compared with the control. In contrast, the concentration of nitrate was considerably decreased in cherry tomato grown under CO2 enriched condition than that of control. The increase in active oxygen metabolisms such as POD, CAT and SOD while a decrease in MDA, as well as APX was observed for cherry tomatoes grown under CO2 enriched condition. Hence, CO2 fertilization by using CRAM in greenhouse significantly improved quality and increased the yield of cherry tomatoes.

Research and Application of Biochar in Soil CO2 Emission, Fertility, and Microorganisms: A Sustainable Solution to Solve China’s Agricultural Straw Burning Problem

This study aimed to explore a new way to address the burning of agricultural waste in China while achieving the sustainable use of it. Three agricultural wastes (Wheat straw, peanut shell, and rice husk) were slowly pyrolyzed into biochar, which was subsequently added to the soil to reduce CO2 emissions from the soil, and to improve soil fertility as well as microbial community structure. The biochar and raw materials were added to the soil and cultured under controlled conditions, and then the CO2 emissions produced from the mixing. At the same time, this study used pot experiments to determine the effects of biochar on tobacco soil physical and chemical properties and, therefore, the microbial communities of the soil. This study suggests that (1) biochar can effectively reduce soil CO2 emission rate. Compared with the control, peanut shell biochar could reduce the total CO2 emissions of soil by 33.41%, and the total CO2 emissions of wheat straw biochar treatment was 90.25% lower than that of wheat straw treatment. (2) The soil’s physical and chemical properties were improved. The soil bulk density of wheat straw biochar treatment kept 34.57% lower than that of the control as well as 21.15% lower than that of wheat straw treatment. The soil’s organic carbon of peanut shell biochar treatment was 87.62% more than that of peanut shell treatment. (3) Biochar changed soil microbial community structure. (4) Biochar is suitable for tobacco growth. Peanut husk biochar significantly increased the total biomass of tobacco, and wheat straw biochar significantly increased tobacco root vigor. This study concluded that processing Chinese agricultural waste into biochar and adding it to the soil instead of burning it directly would be an effective means to reduce greenhouse gas emissions, to improve soil, and to promote crop growth.

Effects of Anthropogenic Activity on Global Terrestrial Gross Primary Production

AbstractGross primary production (GPP) has been identified as the largest terrestrial carbon flux and the major driver of the growing biosphere uptake of carbon. Factorial simulations using several biosphere models have been used to estimate the effects of long‐term (>50 years) climate change on global terrestrial GPP. However, no study has integrated large‐ensemble climate simulation data into a biosphere model to realistically estimate global terrestrial GPP with associated uncertainty. Here we present a novel approach to estimate the global terrestrial long‐term GPP with associated climate data‐induced uncertainty that combines a diagnostic‐type biosphere model with a large‐ensemble climate simulation data set. We distinguish the effects of recent anthropogenic activity on global GPP (the anthropogenic GPP effect) from the effects of interannual climate variability (the natural GPP effect) by comparing GPP model estimates forced by historical and “nonwarming” climate data. We provide evidence for an increasing anthropogenic effect on global terrestrial GPP. The anthropogenic GPP effect is driven by CO2 fertilization, which is projected to weaken or saturate by 2050–2150, depending on the representative concentration pathway scenario used. Model results suggest that shortwave radiation couples with El Niño–Southern Oscillation conditions and volcanic eruptions to drive the natural GPP effect. Because shortwave radiation at the surface is related to cloud cover, we encourage future studies to focus on cloud‐radiation feedbacks on the carbon cycle.

Pathway dependence of ecosystem responses in China to 1.5 °C global warming

Abstract. China is currently the world's largest emitter of both CO2 and short-lived air pollutants. Ecosystems in China help mitigate a part of the country's carbon emissions, but they are subject to perturbations in CO2, climate, and air pollution. Here, we use a dynamic vegetation model and data from three model inter-comparison projects to examine ecosystem responses in China under different emission pathways towards the 1.5 ∘C warming target set by the Paris Agreement. At 1.5 ∘C warming, gross primary productivity (GPP) increases by 15.5±5.4 % in a stabilized pathway and 11.9±4.4 % in a transient pathway. CO2 fertilization is the dominant driver of GPP enhancement and climate change is the main source of uncertainties. However, differences in ozone and aerosols explain the GPP differences between pathways at 1.5 ∘C warming. Although the land carbon sink is weakened by 17.4±19.6 % in the stabilized pathway, the ecosystems mitigate 10.6±1.4 % of national emissions in the stabilized pathway, more efficient than the fraction of 6.3±0.8 % in the transient pathway. To achieve the 1.5 ∘C warming target, our analysis suggests a higher allowable carbon budget for China under a stabilized pathway with reduced emissions in both CO2 and air pollutants.

More fertilizer and impoverished roots required for improving wheat yields and profits under climate change

To mitigate adverse effects of climate change on agricultural productivity, it is essential to obtain a better understanding of how plant traits influence crop yields and profits. To explore such interactions, we used a coupled ecohydrological and biogeochemical model, ecosys, and applied it to an agricultural farm cultivating wheat in Ardmore, Oklahoma, USA. Our results show that positive impacts of elevated CO2 on winter wheat cannot offset negative influences of warming that shortens grain filling periods and thereby grain content. We found that CO2 fertilization effects were weaker than expected without additional fertilizer addition. To identify conditions that simultaneously optimize wheat yields and profits, we performed model optimization analyses by varying root radius, nutrient transfer conductance, and fertilizer application rates. Optimum conditions were found for root radius in the range 0.1–0.25 mm and nutrient transfer conductance in the range 0.004–0.008 h−1. However, under climate change, an additional 5.6 gN m−2 of fertilizer was required to maximize net profits compared to present-day climate conditions. These optimum conditions led to yield improvements of 38%, 23%, 20%, and 17% under RCP2.6, 4.5, 6.0, and 8.5, respectively, which in turn improved net profits by 98%, 90%, 76%, and 31% compared to baseline, respectively. That is, crop breeding alone may not be sufficient to meet growing food demands without additional N fertilizer applications. However, these higher fertilization application rates lead to increased nitrogen losses as leachate and N2O, motivating analyses on the net radiative balance of these systems and their sensitivity to future climate.

Higher than expected CO2 fertilization inferred from leaf to global observations.

Several lines of evidence point to an increase in the activity of the terrestrial biosphere over recent decades, impacting the global net land carbon sink (NLS) and its control on the growth of atmospheric carbon dioxide (ca). Global terrestrial gross primary production (GPP)—the rate of carbon fixation by photosynthesis—is estimated to have risen by (31 ± 5)% since 1900, but the relative contributions of different putative drivers to this increase are not well known. Here we identify the rising atmospheric CO2 concentration as the dominant driver. We reconcile leaf‐level and global atmospheric constraints on trends in modeled biospheric activity to reveal a global CO2 fertilization effect on photosynthesis of 30% since 1900, or 47% for a doubling of ca above the pre‐industrial level. Our historic value is nearly twice as high as current estimates (17 ± 4)% that do not use the full range of available constraints. Consequently, under a future low‐emission scenario, we project a land carbon sink (174 PgC, 2006–2099) that is 57 PgC larger than if a lower CO2 fertilization effect comparable with current estimates is assumed. These findings suggest a larger beneficial role of the land carbon sink in modulating future excess anthropogenic CO2 consistent with the target of the Paris Agreement to stay below 2°C warming, and underscore the importance of preserving terrestrial carbon sinks.

Recent divergence in the contributions of tropical and boreal forests to the terrestrial carbon sink.

Anthropogenic land use and land cover changes (LULCC) have a large impact on the global terrestrial carbon sink, but this effect is not well characterized according to biogeographical region. Here, using state-of-the-art Earth observation data and a dynamic global vegetation model, we estimate the impact of LULCC on the contribution of biomes to the terrestrial carbon sink between 1992 and 2015. Tropical and boreal forests contributed equally, and with the largest share of the mean global terrestrial carbon sink. CO2 fertilization was found to be the main driver increasing the terrestrial carbon sink from 1992 to 2015, but the net effect of all drivers (CO2 fertilization and nitrogen deposition, LULCC and meteorological forcing) caused a reduction and an increase, respectively, in the terrestrial carbon sink for tropical and boreal forests. These diverging trends were not observed when applying a conventional LULCC dataset, but were also evident in satellite passive microwave estimates of aboveground biomass. These datasets thereby converge on the conclusion that LULCC have had a greater impact on tropical forests than previously estimated, causing an increase and decrease of the contributions of boreal and tropical forests, respectively, to the growing terrestrial carbon sink.

Climate sensitivity, agricultural productivity and the social cost of carbon in FUND

We explore the implications of recent empirical findings about CO2 fertilization and climate sensitivity on the social cost of carbon (SCC) in the FUND model. New compilations of satellite and experimental evidence suggest larger agricultural productivity gains due to CO2 growth are being experienced than are reflected in FUND parameterization. We also discuss recent studies applying empirical constraints to the probability distribution of equilibrium climate sensitivity and we argue that previous Monte Carlo analyses in IAMs have not adequately reflected the findings of this literature. Updating the distributions of these parameters under varying discount rates is influential on SCC estimates. The lower bound of the social cost of carbon is likely negative and the upper bound is much lower than previously claimed, at least through the mid-twenty-first century. Also the choice of discount rate becomes much less important under the updated parameter distributions.

Impacts of 1.5 and 2.0°C global warming on rice production across China

The primary goal of the 2015 Paris Climate Agreement is to limit future global warming to less than 2.0 °C above pre-industrial levels. Thus, understanding the impacts of relatively low warming level on rice production is essential to future food security of China. Here, with the latest global warming scenarios from the Half a degree Additional warming, Projections, Prognosis and Impacts (HAPPI) project, we assess the impacts of the two HAPPI scenarios (1.5 °C and 2.0 °C warming above pre-industrial levels) on rice production for two major rice-cropping systems, including single-season rice and double-season rice (early- and late-season rice). A multi-model ensemble approach (three crop models and four climate models) was used to predict the changes of rice production across the main rice-growing regions of China under 1.5 °C and 2.0 °C warming scenarios. Results show that increases in mean rice growing season temperature (GST) under 1.5 °C and 2.0 °C warming scenarios are highest in central China. Likewise, the increase in GST during the reproductive growth phase (GST-r) is greater than that during the vegetative growth phase (GST-v). The whole rice-growing season duration (GSD-w) is shortened by about 3–15 and 4.5–18 days under 1.5 °C and 2.0 °C warming scenarios, respectively. Most of the shortening in GSD-w occurs due to a shortening of the vegetative growth phase (GSD-v). Using a stepwise multiple regression procedure, we find that the yield changes of single-season rice and late-season rice are significantly negatively correlated with both GST-r and GSD-v. When examining early-season rice, yield changes are significantly negatively correlated with both GST-v and GSD-r. Under 1.5 °C and 2.0 °C warming scenarios without carbon dioxide (CO2) fertilization effects, the impact of warming has a negative effect across the main rice-growing regions of China. The reduction is greater in the southern area than that in the northern section of the study regions. However, climatic warming has a positive effect on rice yield in low thermal regions of northeast China with CO2 fertilization effects. In other regions, CO2 fertilization will not offset the negative impacts on rice production due to climatic warming. Our results will aid in making the future adaptation strategies to moderate the negative impacts of climate warming on regional rice production across China.

Assessing the Impacts of Future Climate on Cotton Production in the Arizona Low Desert

HighlightsCotton yield was reduced significantly under projected future climate conditions for the Arizona low desert (ALD). Of all the weather variables, yield reduction was primarily due to projected increases in daily maximum and minimum air temperatures.Cotton reproductive stages were more susceptible to heat stress than vegetative stages. Projected increases in air temperature may result in a slight increase in cotton growth or biomass production; however, heat stress significantly reduced fruit retention, leading to lower boll number and yield.Although future increases in CO2 may improve plant growth and productivity, the potential benefit of CO2 fertilization on cotton growth and yield in the ALD was offset by the projected increase in air temperature.The projected average seasonal irrigation requirement increased by at least 10%. This suggests that greater demand for freshwater withdrawal for agriculture can be expected in the future. Therefore, given the projected change in future climate, cotton cultivars tolerant of longer periods of high air temperature, changes in planting dates, and improved management practices for higher water productivity are critical needs for sustainable cotton production in the ALD.Abstract. Cotton is an important crop in Arizona, with a total cash value of approximately $200 million for fiber and cottonseed in 2018. In recent years, heat stress from increasing air temperature has reduced cotton productivity in the Arizona low desert (ALD); however, the effects of future climate on ALD cotton production have not been studied. In this study, the DSSAT CSM-CROPGRO-Cotton model was used to simulate the effects of future climate on cotton growth, yield, and water use in the ALD area. Projected climate forcings for the ALD were obtained from nine global climate models under two representative concentration pathways (RCP 4.5 and 8.5). Cotton growth, yield, and water use were simulated for mid-century (2036 to 2065) and late century (2066 to 2095) and compared to the baseline (1980 to 2005). Results indicated that seed cotton yield was reduced by at least 40% and 51% by mid-century and late century, respectively, compared to the baseline. Of all the weather variables, the seasonal average maximum (R2 = 0.72) and minimum (R2 = 0.80) air temperatures were most correlated with yield reductions. Under the future climate conditions of the ALD, cotton growth or biomass accumulation slightly increased compared to the baseline. Irrigation requirements in the ALD increased by at least 10% and 14% by mid-century and late century, respectively. Increases in irrigation requirements were due to an increase in crop water use; hence, greater demand for freshwater withdrawal for agricultural purposes is anticipated in the future. Therefore, cotton cultivars that are tolerant of long periods of high air temperature and improved management practices that promote efficient crop water use are critical for future sustainability of cotton production in the ALD. Keywords: . Arid region, CSM-CROPGRO-Cotton, Future climate, Gossypium hirsutum L., Heat stress, Irrigation demand.

Assessing the Climate Change Impacts on Grain Sorghum Yield and Irrigation Water Use under Full and Deficit Irrigation Strategies

HighlightsIrrigated grain sorghum yield and irrigation water use decreased under climate change.Increase in growing season temperature beyond 26°C resulted in a sharp decline in grain sorghum yield.Irrigating during early reproductive stages resulted in the most efficient use of limited water.Irrigating to replenish soil water to 80% of field capacity was found suitable for both current and future climates. Groundwater overdraft from the Ogallala Aquifer for irrigation use and anticipated climate change impacts pose major threats to the sustainability of agriculture in the Texas High Plains (THP) region. In this study, the DSSAT-CSM-CERES-Sorghum model was used to simulate climate change impacts on grain sorghum production under full and deficit irrigation strategies and suggest optimal deficit irrigation strategies. Two irrigation strategies were designed based on (1) crop growth stage and (2) soil water deficit. For the first strategy, seven deficit irrigation scenarios and one full irrigation scenario were simulated: three scenarios with a single 100 mm irrigation scheduled between panicle initiation and boot (T1), between boot and early grain filling (T2), and between early and late grain filling (T3) growth stages; three 200 mm irrigation treatments with combinations of T1 and T2 (T4), T1 and T3 (T5), and T2 and T3 (T6); one 300 mm irrigation scenario (T7) that was a combination of T1, T2, and T3; and a full irrigation scenario (T8) in which irrigation was applied throughout the growing season to maintain at least 50% of plant-available water in the top 30 cm soil profile. For the second strategy, the irrigation schedule obtained from auto-irrigation (T8) was mimicked to create a full irrigation scenario (I100) and six deficit irrigation scenarios. In the deficit irrigation scenarios, water was applied on the same dates as scenario I100; however, the irrigation amounts of scenario I100 were reduced by 10%, 20%, 30%, 40%, 50%, and 60% to create deficit irrigation scenarios I90, I80, I70, I60, I50, and I40, respectively. Projected climate forcings were drawn from nine global climate models (GCMs) and two representative concentration pathways (RCP 4.5 and RCP 8.5). Climate change analysis indicated that grain sorghum yield under full irrigation was expected to be reduced by 5% by mid-century (2036 to 2065) and by 15% by late-century (2066 to 2095) under RCP 8.5 compared to the baseline period (1976 to 2005). Simulated future irrigation water demand of grain sorghum was reduced due to the shorter growing season and improved dry matter- and yield-transpiration productivity, likely due to CO2 fertilization. Based on the simulated grain sorghum yield and irrigation water use efficiency, the most efficient use of limited irrigation was achieved by applying irrigation during the early reproductive stages of grain sorghum (panicle initiation through early grain filling). A 20% deficit irrigation scenario was found to be optimal for current and future conditions because it was more water use efficient than full irrigation with a minor yield reduction of <11%. In summary, these results indicated that strategic planning of when and how much to irrigate could help in getting the most out of limited irrigation. Keywords: CERES-Sorghum, Critical growth stages, Crop yield, Global climate model, Irrigation demand, Soil water depletion.

Validation of spring wheat responses to elevated CO2, irrigation, and nitrogen fertilization in the Community Land Model 4.5

Validation of spring wheat responses to elevated CO2, irrigation, and nitrogen fertilization in the Community Land Model 4.5

Effects of CO2 fertilization on tomato fruit quality under reduced irrigation

CO2 fertilization has been widely used in greenhouse cultivation of tomato (Solanum lycopersicum) to enhance fruit yield; its effects on fruit quality remain largely elusive yet, particularly in combination with reduced irrigation regimes. To explore the response of tomato to the CO2 fertilization under reduced irrigation, tomato (cv. Zhou Si Dun) plants were grown under ambient CO2 (a[CO2], 400 ppm) and elevated CO2 (e[CO2], 800 ppm) environment, respectively and subjected to three irrigation levels since anthesis: I1 (irrigated to 90–95 % water holding capacity of the mixture in the pot, WHC), I2 (irrigated to 70–75 % WHC) and I3 (irrigated to 50–55 % WHC). The results showed that fruit yield was significantly higher in plants with I1 than those with I3. Moreover, the e[CO2] enhanced the number of fruit and decreased the percentage of small fruit (< 70 g), resulting in higher fruit yield as compared to a[CO2]. Leaf area (LA), fruit dry weight (FDW), water use efficiency (WUE), as well as harvest index (HI) were increased under e[CO2], whereas irrigation regime had no influence on FDW, WUE or HI. Both reduced irrigation and e[CO2] increased total soluble solid, vitamin C and lycopene content, while decreased nitrate content in fruit. The results of PCA (Principal Component Analysis) indicated that there was a significant improvement in the comprehensive performance of plants with reduced irrigation at e[CO2] environment. It can be concluded that reduced irrigation, combined with CO2 fertilization, could be a promising strategy to enhance fruit quality in greenhouse tomato production under water-limited conditions.