CO2 Fertilization Research Articles

An abrupt shift in gross primary productivity over Eastern China-Mongolia and its inter-model diversity in land surface models

The terrestrial ecosystem in East Asia mainly consists of semi-arid regions that are sensitive to climate change. Therefore, gross primary productivity (GPP) in East Asia could be highly variable and vulnerable to climate change, which can significantly affect the local carbon budget. Here, we examine the spatial and temporal characteristics of GPP variability in East Asia and its relationship with climate factors over the last three decades. We detect an abrupt decrease in GPP over Eastern China-Mongolia region around the year 2000. This is attributed to an abrupt decrease in precipitation associated with the phase shift of the Pacific decadal oscillation (PDO). We also evaluate the reproducibility of offline land surface models to simulate these abrupt changes. Of the twelve models, eight were able to simulate this abrupt response, while the others failed due to the combination of an exaggerated CO2 fertilization effect and an underrated climate impact. For accurate prediction, it is necessary to improve the sensitivity of the GPP to changes in CO2 concentrations and the climate system.

The global greening continues despite increased drought stress since 2000

Increases or decreases in remote sensing-based vegetation greenness are usually referred to as greening or browning. The CO2 fertilization along with land management determined that greening is dominant. However, recently global browning signals due to drought stress have also been widely reported. In this study, We used the four latest leaf area index (LAI) datasets to explore this controversial topic, and found that global greening was not only present (trend between 3.1–6.4 ×10−3 m2 m−2 yr−1) but also continued (growth rate trend between 3.3–6.4 ×10−4 m2 m−2 yr−2) during 2001–2020. Greening acceleration occurred in 55.15% of the globe (positive trend and positive growth rate trend), while browning acceleration occurred in only 7.28% (negative trend and positive growth rate trend). Combined with meteorological variables, we found that CO2 change dominated the LAI trend, while climate change largely determined the LAI growth rate trend. Importantly, our study highlighted that drought trend did not necessarily trigger vegetation browning, but slowed down the rate of greening.

Trends in Atmospheric CO2 Fertilization Effects with Stand Age Based on Tree Rings

The increase in global carbon emissions has intensified the effects of CO2 fertilization on the carbon cycle. CO2 fertilization is shaped by several factors, including the physiological differences among trees of varied forest ages and types, as well as the influence of different climatic conditions. It is essential to investigate the differences in CO2 fertilization effects across diverse climate zones and delve into the association between these effects and forest age and type. Such exploration will deepen our knowledge of forest responses to environmental changes. This study used annual ring width data from the International Tree-Ring Data Bank, employing the generalized additive mixed models and the Random Forest model to discern the pattern of the CO2 fertilization effect concerning forest age in the Northern Hemisphere. This study also explored the variations in the effect of CO2 fertilization across unique climate zones and the disparities among various forest types within the same climatic zone. The results indicated a link between forest age and the CO2 fertilization effect: it tends to increase in sapling forests and middle-aged forests and diminish in mature forests. Warmer, drier environments had a more marked effect of increased CO2 on tree fertilization. Additionally, coniferous forests demonstrated a more substantial CO2 fertilization effect than broadleaf forests, and deciduous needle-leaf forests surpassed evergreen needle-leaf forests in this regard. This research is pivotal in understanding the shifting patterns of CO2 fertilization effects and how forests respond to atmospheric changes.

Feeding of leaf beetle to two species of alder grown under two different soils in a free-air CO2 enrichment

ABSTRACT The effects of elevated CO2 concentration on the defensive ability of two Alnus species (A. maximowiczii, A. hirsuta) against herbivory attacks (alder leaf beetle; Agelastica coerulea) were investigated using a free-air CO2 enrichment. Elevated CO2 significantly affected consumed leaf area index (CLI) of A. maximowiczii but soil fertility did not, while more significant effects on CLI of A. hirsuta were found in both CO2 and soil fertility. As found in natural conditions, A. hirsuta was grazed five times more than A. maximowiczii in both CO2 levels, which was explained with the low condensed tannin (CT) concentration of the leaves. The value of leaf mass per area in fertile soil was 10 g m−2 lower than that in infertile soil under ambient CO2 in July. Leaf C/N ratio was not affected by elevated CO2 for both species but that of A. hirsuta was little higher in infertile soil when compared to fertile soil in July. CT of A. maximowiczii tended to increase in September under elevated CO2. CT of A. hirsuta was higher in infertile soil than in fertile soil in July and showed an overall decrease in September compared to July. Nitrogen-fixing activity by a nodule of Frankia sp. on A. maximowiczii was higher in elevated CO2 treatments than in ambient CO2 independent of soil fertility. As a result of changes in these parameters, except for fertile soil, the peak of the herbivorous damage was later in elevated CO2 for the Alnus species than in the control.

Economic impacts of climate change on EU agriculture: will the farmers benefit from global climate change?

This paper analyses how climate change might impact EU agricultural markets by mid-century, considering a large ensemble of climate change projections from different models, market adjustments and trade feedbacks. Applying consistent climate change driven productivity shocks to a global multi-commodity agricultural market model we show that the negative direct effects from climate change on crop production in the EU could be offset by market and trade adjustments. The simulations reveal that climate change has heterogeneous impacts across regions. EU farming sector, in particular, might actually benefit from climate change as the impacts on agricultural productivity are expected to be more severe in important non-EU production regions such as US, Russia and Ukraine, depending on the crop. Higher producer prices for important crops such as wheat, barley, grain maize, rice and soybeans, lead to an increase in EU production and exports. For instance EU wheat production could increase by 13% and exports by 28%, with 19% higher farm incomes on average than in a business-as-usual situation. Our study has several limitations. In particular, we do not consider CO2 fertilization effects and direct effect from climate change on livestock sector, climate variability and extreme weather effects. Notwithstanding, our findings highlight the heterogeneity of climate change impacts across regions, specifically Northern versus Southern Europe, and the importance of market and trade adjustments as economic adaptation mechanisms to climate change.

Constraining long-term model predictions for woody growth using tropical tree rings.

The strength and persistence of the tropical carbon sink hinges on the long-term responses of woody growth to climatic variations and increasing CO2 . However, the sensitivity of tropical woody growth to these environmental changes is poorly understood, leading to large uncertainties in growth predictions. Here, we used tree ring records from a Southeast Asian tropical forest to constrain ED2.2-hydro, a terrestrial biosphere model with explicit vegetation demography. Specifically, we assessed individual-level woody growth responses to historical climate variability and increases in atmospheric CO2 (Ca ). When forced with historical Ca , ED2.2-hydro reproduced the magnitude of increases in intercellular CO2 concentration (a major determinant of photosynthesis) estimated from tree ring carbon isotope records. In contrast, simulated growth trends were considerably larger than those obtained from tree rings, suggesting that woody biomass production efficiency (WBPE = woody biomass production:gross primary productivity) was overestimated by the model. The estimated WBPE decline under increasing Ca based on model-data discrepancy was comparable to or stronger than (depending on tree species and size) the observed WBPE changes from a multi-year mature-forest CO2 fertilization experiment. In addition, we found that ED2.2-hydro generally overestimated climatic sensitivity of woody growth, especially for late-successional plant functional types. The model-data discrepancy in growth sensitivity to climate was likely caused by underestimating WBPE in hot and dry years due to commonly used model assumptions on carbon use efficiency and allocation. To our knowledge, this is the first study to constrain model predictions of individual tree-level growth sensitivity to Ca and climate against tropical tree-ring data. Our results suggest that improving model processes related to WBPE is crucial to obtain better predictions of tropical forest responses to droughts and increasing Ca . More accurate parameterization of WBPE will likely reduce the stimulation of woody growth by Ca rise predicted by biosphere models.

Integrated crop and livestock systems increase both climate change adaptation and mitigation capacities

Integrated crop-livestock systems (ICLS) are proposed as key solutions to the various challenges posed to present-day agriculture which must guarantee high and stable yields while minimizing its impacts on the environment. Yet the complex relationships between crops, grasslands and animals on which they rely demand careful and precise management. In this study, from a 18-year ICLS field experiment in Brazil, that consists in annual no-till soybean-pastures grazed by beef cattle, we investigated the impacts of contrasted pastures grazing intensities (defined by sward heights of 10, 20, 30 and 40 cm, plus an ungrazed treatment) on the agroecosystem productivity and soil organic carbon (SOC) under both historical and future (2040–2070, RCP8.5) climatic conditions. We used an innovative methodology to model the ICLS with the STICS soil-crop model, which was validated with field observations. Results showed that the total system production increased along with grazing intensity because of higher stocking rates and subsequent live weight gains. Moderate and light grazing intensities (30 and 40 cm sward heights) resulted in the largest increase in SOC over the 18-year period, with all ICLS treatments leading to greater SOC contents than the ungrazed treatment. When facing climate change under future conditions, all treatments increased in productivity due to the CO2 fertilization effect and the increases in organic amendments that result from the larger stocking rate allowed by the increased pasture carrying capacity. Moderate grazing resulted in the most significant enhancements in productivity and SOC levels. These improvements were accompanied by increased resistance to both moderate and extreme climatic events, benefiting herbage production and live weight gain. Globally, our results show that adding a trophic level (i.e. herbivores) into cropping systems, provided that their carrying capacities are respected, proved to increase their ability to withstand climate change and to contribute to its mitigation.

Grassland Greening and Water Resource Availability May Coexist in a Warming Climate in Northern China and the Tibetan Plateau

AbstractGreening of Northern China and the Tibetan Plateau (NCTP) has been observed by increases in the remotely sensed leaf area index (LAI), driven primarily by CO2 fertilization effects, anthropogenic warming, and the implementation of ecological restoration programs. Continued growth of LAI throughout the 21st century is also projected by the Coupled Model Intercomparison Project Phase 6 (CMIP6) scenarios. However, the question of whether local water resources can sustain ongoing grassland greening has not been adequately investigated. Here we assessed the sustainability of water resources under grassland greening across NCTP under various climate scenarios using water yield (WY, defined as precipitation minus actual evapotranspiration) as the key metric. Unexpectedly, we observe the coexistence of increases in LAI and WY in most of NCTP. In a warming climate with increasing precipitation and CO2, we find that grasses maintain high water use efficiency to sustain their growth, contributing to continued local water resource availability. Thus, livestock production may also continue to increase under the simultaneous growth of LAI and WY in the future.

Modelling adaptation strategies towards climate smart red gram production in Tamil Nadu

Assessing the pulse of an important legume crop, red gram (Cajanus cajan L.) of Tamil Nadu under changing climate and framing adaptation strategies were formulated using the DSSAT model. The assessment was done for the popular variety of red gram, viz., CO(RG)7 with August 1st as sowing date, under constant CO2 (380ppm) and CO2 enrichment. The adaptation strategies such as altering the sowing date and 25 per cent increment in nitrogenous fertilizer were carried out with CO2 enrichment conditions. The yield was found to be adversely affected by the warming scenario of the climate system without CO2 fertilization. With the incorporation of enriched CO2 data, the average yield increases until the end of the century, but with temporal and spatial variations. Among the different agro climatic zones of Tamil Nadu, highest yield was recorded in Western Zone and lowest in Southern Zone. There was no response to application of Nitrogenous fertilizer. July 15 sowing was identified to be the best sowing for the base as well as future period for CO(RG)7.

A constraint on historic growth in global photosynthesis due to rising CO2

Theory predicts that rising CO2 increases global photosynthesis, a process known as CO2 fertilization, and that this is responsible for much of the current terrestrial carbon sink. The estimated magnitude of the historic CO2 fertilization, however, differs by an order of magnitude between long-term proxies, remote sensing-based estimates and terrestrial biosphere models. Here we constrain the likely historic effect of CO2 on global photosynthesis by combining terrestrial biosphere models, ecological optimality theory, remote sensing approaches and an emergent constraint based on global carbon budget estimates. Our analysis suggests that CO2 fertilization increased global annual terrestrial photosynthesis by 13.5 ± 3.5% or 15.9 ± 2.9 PgC (mean ± s.d.) between 1981 and 2020. Our results help resolve conflicting estimates of the historic sensitivity of global terrestrial photosynthesis to CO2 and highlight the large impact anthropogenic emissions have had on ecosystems worldwide.

Greening of human-dominated ecosystems in India

Satellite data show the Earth has been greening and identify croplands in India as one of the most prominent greening hotspots. Though India’s agriculture has been dependent on irrigation enhancement to reduce crop water stress and increase production, the spatiotemporal dynamics of how irrigation influenced the satellite observed greenness remains unclear. Here, we use satellite-derived leaf area data and survey-based agricultural statistics together with results from state-of-the-art Land Surface Models (LSM) to investigate the role of irrigation in the greening of India’s croplands. We find that satellite observations provide multiple lines of evidence showing strong contributions of irrigation to significant greening during dry season and in drier environments. The national statistics support irrigation-driven yield enhancement and increased dry season cropping intensity. These suggest a continuous shift in India’s agriculture toward an irrigation-driven dry season cropping system and confirm the importance of land management in the greening phenomenon. However, the LSMs identify CO2 fertilization as a primary driver of greening whereas land use and management have marginal impacts on the simulated leaf area changes. This finding urges a closer collaboration of the modeling, Earth observation, and land system science communities to improve representation of land management in the Earth system modeling.

Projecting the impact of climate change and elevated CO2 concentration on rice irrigation water requirement in China

Climate change and elevated CO2 concentrations significantly affect rice growth and water consumption. Understanding the specific impacts of climate change and elevated CO2 concentrations on rice physiological phenology, crop water demand (ETC), and irrigation water requirement (IR) is of great significance for the sustainable utilization of water resources and food security. This is particularly true in China, the world's largest rice producer. In this study, with the help of two rice phenological models, the modified Penman-Monteith equation, and the paddy water balance model, we project the changes in rice phenological period, ETC, and IR in four main rice-producing regions of China in the period 2015–2100 based on the 11 GCM outputs. The results show that the rice growing period is shortened in most rice-producing regions, except for the parts of the middle and lower reaches of the Yangtze River. Meanwhile, the trend of ETC and IR of rice varies slightly among regions in the future scenario, with almost all regions decreasing yearly except for the middle and lower reaches of the Yangtze River, where the trend is increasing. The progressively increasing atmospheric CO2 concentration has a “fertilization effect” on the crop, which can reduce the water requirements of rice. In the SSP585 scenario, the “ CO2 fertilization effect” can reduce up to 8.87 × 108 m3 of ETC and 6.94 × 108 m3 of IR in the middle and lower reaches of the Yangtze River in the period of 2090s. This study provides beneficial references to understand the response of rice ETC and IR to future climate change and CO2 concentration elevation in China and highlights that the simulation in terms of crop irrigation must account for the “CO2 fertilization effect”.

VPD modifies CO2 fertilization effect on tomato plants via abscisic acid and jasmonic acid signaling pathways

Atmospheric CO2 concentration is elevated globally, which has “CO2 fertilization effects” and potentially improves plant photosynthesis, yield, and productivity. Despite the beneficial effect of CO2 fertilization being modulated by vapor pressure deficit (VPD), the underlying mechanism is highly uncertain. In the present study, the potential roles of hormones in determining CO2 fertilization effects under contrasting high and low VPD conditions were investigated by integrated physiological and transcriptomic analyses. Beneficial CO2 fertilization effects were offset under high VPD conditions and were constrained by plant water stress and photosynthetic CO2 utilization. High VPD induced a large passive water driving force, which disrupted the water balance and consequently caused plant water deficit. Leaf water potential, turgor pressure, and hydraulic conductance declined under high VPD stress. The physiological evidence combined with transcriptomic analyses demonstrated that abscisic acid (ABA) and jasmonic acid (JA) potentially acted as drought-signaling molecules in response to high VPD stress. Increased foliar ABA and JA content triggered stomatal closure to prevent excessive water loss under high VPD stress, which simultaneously increased the diffusion resistance for CO2 uptake from atmosphere to leaf intercellular space. High VPD also significantly increased mesophyll resistance for CO2 transport from stomatal cavity to fixation site inside chloroplast. The chloroplast “sink” CO2 availability was constrained by stomatal and mesophyll resistance under high VPD stress, despite the atmospheric “source” CO2 concentration being elevated. Thus, ABA- and JA-mediated drought-resistant mechanisms potentially modified the beneficial effect of CO2 fertilization on photosynthesis, plant growth, and yield productivity. This study provides valuable information for improving the utilization efficiency of CO2 fertilization and a better understanding of the physiological processes.

Trend in seasonal amplitude of northern net ecosystem production: Simulated results from IAP DGVM in CAS-ESM2

Net ecosystem production (NEP) over northern latitudes has an obvious seasonal variation, which dominantly drives the seasonal variation in atmospheric CO2. Investigating these carbon processes and understanding the underlying drivers is a key issue of climate research. This study focuses on the seasonal amplitude of northern NEP (40°–90°N) and investigates its trend in the period 1990–2014 by using the dynamic global vegetation model (IAP DGVM) in the second version of the Chinese Academy of Sciences Earth System Model (CAS-ESM2). Basing on a spin-up simulation, the authors conduct a control simulation to evaluate the modeled trend in the seasonal amplitude of northern NEP, and three sensitivity simulations to detect the contributions of the climate and atmospheric CO2. The results show that the modeled seasonal amplitude of northern NEP increases significantly from 1990 to 2014, with a trend of 9.69 TgC month−1 yr−1, which is mainly because of the increasing maximum NEP. The positive trend is largely reduced when CO2 fertilization effects and climatic effects are separately excluded. These significant reductions suggest important effects of atmospheric CO2 and climate change on the seasonal amplitude of northern NEP. Even though model uncertainties remain, the results favor further development of IAP DGVM in accurately simulating the terrestrial carbon cycle, and also provide an important reference for the application of CAS-ESM in further investigating carbon–climate interactions.摘要北方陆地净生态系统生产力(NEP)具有明显的季节变化特征, 这是大气CO2季节变化的关键驱动. 研究这些碳循环过程并理解潜在的驱动因素是气候研究的一个关键问题. 本文利用第二代中国科学院地球系统模式(CAS-ESM2)中的全球植被动态模型(IAP DGVM), 研究了1990−2014年北方NEP(40°−90°N)的季节振幅及其变化趋势. 在初始化试验的基础上, 本文开展了一个控制试验来评估模拟的北方NEP季节幅度的变化趋势, 同时开展了三个敏感性试验来研究气候和大气CO2的贡献. 结果表明: 1990−2014年, 模拟的北方NEP季节振幅显著增加, 趋势为9.69 万吨碳/月/年, 这主要是由于最大NEP增加所致. 当分别排除CO2施肥效应和气候效应时, 上述增加趋势大大减弱.这些显著的减少表明大气CO2和气候变化对北方NEP的季节性振幅有重要影响. 尽管模式存在不确定性, 但这些结果有利于进一步提升IAP DGVM对陆地碳循环的精确模拟, 也为CAS-ESM研究碳-气候相互作用的应用提供了重要参考.

Increased Vegetation Productivity of Altitudinal Vegetation Belts in the Chinese Tianshan Mountains despite Warming and Drying since the Early 21st Century

Gaining a deep understanding of how climate change affects the carbon cycle in dryland vegetation is of utmost importance, as it plays a pivotal role in shaping the overall carbon cycle in global ecosystems. It is currently not clear how plant communities at varying elevations in arid mountainous regions will respond to climate change in terms of their productivity. The aim of this study was to investigate the effect of climate change on vegetation productivity in different altitudinal vegetation belts of the Tianshan Mountains between 2000 and 2021, utilizing satellite-derived vegetation productivity and climate data. The findings suggest a notable increase in vegetation productivity across diverse altitudinal vegetation belts. The productivity of vegetation in the coniferous forest and alpine meadow belts displayed a notably higher interannual trend compared to other vegetation belts. Notably, an increase in vegetation productivity was accompanied by warming and drying. The productivity of altitudinal vegetation belts, however, appears to be resilient to current climate trends and was not significantly impacted by the severity of atmospheric drought. The trend of increased vegetation productivity was primarily driven by CO2 fertilization. Our results highlight that the extent of climate change may need to reach a threshold to noticeably affect variations in vegetation productivity in arid mountainous.

Comparing stem growth of strip-bark and whole-bark growth morphologies in a subarctic conifer (Pinus banksiana), Yellowknife, Northwest Territories

Generally, organisms living near the periphery of their range experience increased environmental stress compared to individuals of the same species growing at the core of their geographic distribution. The greater environmental stress at the ecological limits of a species distribution normally leads to greater sensitivity to growth-limiting factors. For some tree species, this can lead to the development of unique growth morphologies such as strip-bark or partial cambial dieback. Previous studies have concluded that the growth differences induced by CO2 fertilization effects in high elevation strip-bark trees makes them unsuitable for climate reconstructions. However, comparisons of strip-bark and whole-bark growth morphologies at high latitude and low elevation sites are limited. This study compares the growth of strip-bark and whole-bark jack pine (Pinus banksiana Lamb.) trees near Yellowknife, Canada. Annual ring widths from trees of each morphological type were measured, and the results indicate the growth of the two populations are statistically different from one another prior to the late 19th century. After the late 19th century, growth of the two populations remains statistically different, but the average mean growth of strip-bark trees increases 44% after 1891 while average mean growth of whole-bark trees decreases nearly 11%. Climate sensitivity of the two populations was tested using monthly and seasonal climate indices from 1943 to 2015 and results indicate the two populations share similar responses to climate. The results of this research suggest these strip-bark and whole-bark trees share similar climate-growth relations at inter-annual timescales, however, their growth trends diverge at decadal to centennial timescales. The timing of cambial dieback was dated to a short time interval in the early 19th century which coincided with a period of cool summer temperatures across the northern hemisphere. Increased growth in strip-bark trees after ∼1891 could be related to CO2 fertilization effects, although further studies into intrinsic water use efficiency would be helpful in assessing this possibility more accurately.

Land use significantly improved grassland degradation and desertification states in China over the last two decades

China possesses extensive grasslands primarily located in dryland regions, which are highly susceptible and fragile to climate change and human intervention, making them prone to degradation and desertification. In recent decades, China has implemented numerous ecological projects to improve the states of ecosystems. Additionally, recent studies have revealed the critical roles of rising CO2 on dryland greening. However, it is still limited to understand the contributions of anthropogenic recovery and CO2 fertilization, as well as other climate factors, to the dynamics of grassland degradation and desertification in China. To address these gaps, we employed a two-step approach to differentiate between grassland degradation and desertification as distinct processes across the grasslands and sparsely vegetated lands in China. This involved assessing degradation within existing grassland areas and identifying the conversion of grasslands into desert regions. The study period of 2000–2020 was examined to determine the occurrence of grassland desertification, which suggested a significant decrease in the desertification area in China. Subsequently, the time series of the Enhanced Vegetation Index (EVI) during the growing season was analyzed to track vegetation dynamics. Since the beginning of the 21st century, a significant greening trend has been observed in approximately 97% of the study area. Furthermore, we quantified the effects of anthropogenic climate change (ACC), climate change, and land use change on grassland degradation and desertification in China. The analyses indicated that 50.7% of the observed vegetation changes in the study area from 2000 to 2020 were primarily driven by land use, followed by the effects of rising CO2, accounting for 42.1% of the changes. These findings provided some insights on developing regionally-targeted strategies for grassland conservation in China.

Recent shift from dominant nitrogen to CO2 fertilization control on the growth of mature Qinghai spruce in China's Qilian Mountains

Terrestrial vegetation growth is stimulated by rising atmospheric CO2 concentration, a warmer climate, and increased soil nutrient availability. However, as plants age, progressive nutrient limitation is known to occur, especially in mature forests where soil nitrogen is deficient. Yet the long-term growth response of mature trees to rising CO2 accompanied by changing climate and nitrogen availability in semi-arid mountain regions is unclear. Here we used tree-ring widths and stable carbon (δ13C) and nitrogen (δ15N) isotopes to investigate the drivers of radial growth of mature Qinghai spruce (Picea crassifolia) in the central Qilian Mountains, northwest China, from 1840 through 2019. Tree growth benefited from improved nitrogen availability, chiefly via changes in bioavailable nitrogen pools modified by a favorable climate during 1930–1964. Enhanced intrinsic water-use efficiency (iWUE), driven by reduced stomatal conductance (gs) related to water deficit, lead to radial growth declines in 1985–2002. Recent acceleration of tree growth was largely attributed to a CO2 fertilization effect through enhanced iWUE during 2003–2019. Nitrogen availability was positively related to tree growth from the 1920s onward until greater CO2 fertilization ensued from 2000 onward. Hence, the negative effects of low nitrogen availability on growth could be mitigated or reversed by a high atmospheric CO2 concentration and warmer climate conditions. Our results suggest that mature spruce forests still harbor potential to increase ecosystem-level carbon sequestration and thereby partially mitigate climate warming. Such a nature-based solution in drought-prone forests would be achieved under warmer-wetter climate conditions in northwest China.

Identifying the main drivers of the spatiotemporal variations in wetland methane emissions during 2001–2020

Wetlands act as an important natural source of global methane (CH4). The emission rate of wetland CH4 is jointly affected by climate change, carbon dioxide (CO2) fertilization, and wetland distribution. In this study, we implemented a wetland CH4 emission module into the Yale Interactive Biosphere (YIBs) model to quantify the spatiotemporal variations of global wetland CH4 emissions in 2001–2020. Site-level validations showed that the YIBs model reasonably captures the seasonality and magnitude of CH4 emissions at 28 out of 33 sites with significantly positive correlations and low relative biases. On the global scale, the YIBs predicts an annual mean wetland CH4 emission of 147.5 Tg yr−1 in 2000–2017, very close to the estimate of 147.9 Tg yr−1 from the ensemble of 13 process-based models. Global wetland CH4 emissions showed a positive trend of 0.74 Tg yr−2 in the past 2 decades, leading to an increase of 7.4 Tg yr−1 (5.2%) in 2008–2017 than 2000–2009. Climate change and CO2 fertilization accounted for over 70% of global wetland CH4 emission changes. Among them, the impact of CO2 grew steadily and became the dominant factor after the year 2008. The most significant changes in wetland CH4 emissions were located in the tropical regions following the perturbations in temperature that drives the ecosystem productivity. We found limited changes in CH4 emissions over high latitudes because of the moderate variations in wetland area fraction. The rise of wetland CH4 emissions poses an emerging threat to the global warming and likely escalates the tropospheric air pollutants.

Does drought stress eliminate the benefit of elevated CO2 on soybean yield? Using an improved model to link crop and soil water relations

Crop simulation models are indispensable tools that facilitate studies to assess climate impacts and adaptation responses, but have not been adequately tested in terms of accurately predicting crop growth and water stress responses to high carbon dioxide concentrations [CO2]. The soybean model, GLYCIM, previously modified with a coupled leaf-level gas exchange – energy balance model, was integrated with a two-dimensional convective-diffusive root growth module which linked soil and leaf water potentials with the regulation of stomatal conductance. We evaluated the accuracy of this modified GLYCIM using experimental data from a Free-Air CO2 Enrichment (FACE) site, SoyFACE, and used the calibrated model to quantify current and projected elevated CO2 effects on soybean yields in the United States (US) Midwest. The model accurately matched SoyFACE observed data including canopy temperature (RMSE, 2.26 -2.42 °C; IA, 0.89-0.90), photosynthesis rate (RMSE, 6.33 -12.88 µmol m−2 s−1; IA, 0.82-0.92), seasonal LAI (RMSE, 0.96 -1.08 cm2 cm−2; IA, 0.91-0.93), biomass (RMSE, 2.06 -2.34 Mg ha−1; IA, 0.87-0.90), soil water contents (RMSE, 5.42 -7.82 %; IA, 0.80-0.85) and root length (RMSE, 2.12 -5.64 m plant−1; IA, 0.70-0.86). GLYCIM also reproduced the observed declining response of yield to CO2 fertilization with increasing drought. Using an ensemble of five climate model projections, GLYCIM showed that the CO2 fertilization effect on yield was highest in northern counties and declined in southern and the western counties by late 21st century in response to increased drought characterized by higher daily maximum temperature and decreased rainfall. This study highlights the need to continue to test and improve crop models and use geospatially referenced adaptive strategies to capitalize the benefits from elevated [CO2] to better counteract increasing drought.