Crops have been well studied at abruptly elevated CO2 (eCO2). In fact, atmospheric CO2 concentration is rising gradually, but its ecological effect is little known. Thus, rice growth and yield were ...investigated under gradual eCO2 (GE) and abrupt eCO2 (AE) using open-top chambers. Gradual eCO2 involved an ambient CO2 (aCO2) + 40 μmol mol−1 per year in 2016 until aCO2 + 200 μmol mol−1 in 2020, while AE maintained aCO2 + 200 μmol mol−1 from 2016 to 2020. We found that steady-state photosynthetic rates responded similarly and increased significantly under GE and AE, however, photosynthetic induction time in dynamic photosynthesis was reduced by AE. Gradual eCO2 had little effect on biomass before the grain filling stage, while AE significantly stimulated biomass because of the stronger tillering ability and faster photosynthetic induction rate. Neither eCO2 increased biomass at maturity, however, a significant increase in panicle density was observed under AE. Surprisingly, rice yield was not promoted by both eCO2, possibly resulting from the reduced carbon assimilation caused by accelerated phenology from grain filling to maturity. These results promote a new understanding of the CO2 fertilization effect with small and slow increases in CO2 concentration, closer to what happens in nature. This may partly challenge the classic view of elevated CO2 fertilization effects from AE.
Display omitted
•Japonica rice was tested under gradual elevated CO2 (eCO2) and abrupt eCO2.•Gradual eCO2 had little effect on growth during the entire growing season.•Abrupt eCO2 had strong effect on growth before the filling stage.•Both eCO2 plots did not stimulate yield in maturity.•This provides a new CO2 effect from small and slow CO2 increases.
Rice paddies contribute to ∼48% of greenhouse gas emissions from cropland, with ∼94% from methane (CH4). Elevated atmospheric CO2 concentrations (eCO2) due to human activities, generally stimulate ...the rice growth, and in turn affect CH4 emissions from rice paddies. However, the effects of eCO2 on CH4 emissions from rice paddies are still unclear under in situ straw incorporation, the popular agricultural practice. Therefore, we conducted a 3-yr field experiment to investigate the effects of eCO2 on CH4 emissions under in situ straw incorporation in the rice-wheat cropping system, using the open-top chamber technology. We found that eCO2 reduced the CH4 emissions from rice paddies by 10.9–23.8%, but increased rice plant biomass by 4.2–35.6%. The eCO2 reduced the soil NH4+ and NO3- concentrations, but did not affect the soil dissolved organic C. The eCO2 did not affect the abundance of methanogens and CH4 production potential, whereas it stimulated the abundance of methanotrophs and CH4 oxidation potential by 102.5% and 15.1%, respectively. The eCO2 also shifted the community composition of methanotrophs and reduced the relative abundance of type Ⅱ methanotrophs by 8.5%. The random forest analysis identified that soil CH4 oxidation potential is the most important factor affecting CH4 emissions. Our findings indicate that eCO2 can reduce the CH4 emissions from rice paddies under in situ straw incorporation mainly through increasing the soil CH4 oxidation potential. Our study suggests the effects of eCO2 on CH4 emissions from global paddies may be overestimated and underline the need for smart agricultural management to reduce CH4 emissions.
•Elevated CO2 reduced CH4 emission from paddies under in situ straw incorporation.•Elevated CO2 stimulated abundance of methanotrophs and CH4 oxidation potential.•Soil CH4 oxidation potential is the most important factor affecting CH4 emissions.
Soil organic carbon (SOC), as the largest terrestrial carbon pool, plays an important role in global carbon (C) cycling, which may be significantly impacted by global changes such as nitrogen (N) ...fertilization, elevated carbon dioxide (CO2), warming, and increased precipitation. Yet, our ability to accurately detect and predict the impact of these global changes on SOC dynamics is still limited. Investigating SOC responses to global changes separately for mineral-associated organic carbon (MAOC) and the particulate organic carbon (POC) can aid in the understanding of overall SOC responses, because these are formed, protected, and lost through different pathways. To this end, we performed a systematic meta-analysis of the response of SOC, MAOC, and POC to global changes. POC was particularly responsive, confirming that it is a better diagnostic indicator of soil C changes in the short-term, compared to bulk SOC and MAOC. The effects of elevated CO2 and warming were subtle and evident only in the POC fraction (+5.11% and − 10.05%, respectively), while increased precipitation had no effects at all. Nitrogen fertilization, which comprised the majority of the dataset, increased SOC (+5.64%), MAOC (+4.49%), and POC (+13.17%). Effect size consistently varied with soil depth and experiment length, highlighting the importance of long-term experiments that sample the full soil profile in global change SOC studies. In addition, SOC pool responses to warming were modified by degree of warming, differently for air and soil warming manipulations. Overall, we suggest that MAOC and POC respond differently to global changes and moderators because of the different formation and loss processes that control these pools. Coupled with additional plant and microbial measurements, studying the individual responses of POC and MAOC improves understanding of the underlying dynamics of SOC responses to global change. This will help inform the role of SOC in mitigating the climate crisis.
Display omitted
•Used meta-analysis to investigate soil carbon fractions responses to global change.•All soil organic carbon fractions increase under nitrogen fertilization.•Particulate organic carbon decreases with atmospheric warming.•Particulate organic carbon increases with elevated carbon dioxide.•Soil depth and experiment length were consistently important moderators.
•Exposure of plants to elevated oscillating CO2 depresses photosynthesis and yield.•Plant response is also underestimated in fluctuating Free-Air CO2Enrichment (FACE).•Yields in fluctuating FACE are ...decreased to about 0.65 of steady levels of elevated CO2.•Reasons for depressed photosynthesis and yield in fluctuating CO2 are unknown.•Basic physiology research is needed to determine causes of depressed photosynthesis.
Free-Air CO2 Enrichment (FACE) was conceived as an experimental method to measure plant responses to elevated CO2 in natural environments rather than in chambered or controlled environments. However, due to the difficulty of controlling elevated CO2 concentrations in turbulent air, the range of fluctuations of CO2 in FACE experiments are more than 10-fold greater than plants experience in natural conditions. One early study reported that photosynthetic increases of leaves in 40- and 80-s periods of oscillating elevated CO2 were only about 68% of those in leaves exposed to constant elevated CO2 with the same mean CO2 concentration. Later whole-plant studies reported smaller increases of responses in 60-s periods of oscillating elevated CO2 compared to constant elevated CO2 with the same mean concentration. After eliminating problematic data from studies that predicted plant responses in FACE to be only 45% of responses in open top chambers, we calculated that yields increased 65% as much in fluctuating elevated CO2 of FACE as in constant elevated CO2. The smaller plant responses in fluctuating elevated CO2 can be attributed partially to the non-linear, convex-upward curved response of photosynthesis to CO2 concentration, but other unknown mechanisms must exist. Future leaf chamber studies and FACE studies should include fundamental photosynthetic physiologists who can focus on uncovering the mechanisms responsible for lower photosynthetic, biomass, and yield response in both regular waveform oscillating and irregular fluctuating elevated CO2. Because CO2 fluctuates in FACE and recent experiments indicate reduced photosynthesis and growth under fluctuating CO2, responses of plants in FACE are likely to underestimate the benefits of rising CO2. We found that a correction factor of about 1.5 needs to be applied to FACE results. While responses to elevated CO2 in FACE experiments are smaller than those in chamber experiments, FACE responses are obtained in natural conditions not available in chambers and thus are conservative regarding future projections of agricultural productivity.
Small, natural CO2 variations (left panel) contrasted with large CO2 fluctuations in a FACE plot (right panel), Maricopa, AZ USA. A 20-s moving average (black trace, right panel) illustrates poorly-defined major oscillations. Fluctuating CO2 in FACE depressed plant response to CO2. L.H. Allen, B.A. Kimball, et al., Agricultural and Forest Meteorology, Volume xxx, Issue y, “Month” 2019, Pages 000–000. http://dx.doi.org/10.1016/j.agrformet.2020.107899 Display omitted
•20% CO2 delayed the changes of color value in strawberry fruit.•Elevated CO2 delayed chlorophyll degradation by inhibiting chlorophyll catabolism.•The accumulation of five individual anthocyanins ...was suppressed by elevated CO2.•CO2 treatment inhibited the phenylpropanoid and flavonoid pathways.•The inhibition effect of 20% CO2 was eliminated after transferring fruit to air.
Colour is an important quality attribute for the consumer’s acceptability of fruit. Elevated CO2 was applied to strawberry fruit to explore its influence on chlorophyll catabolism and anthocyanin synthesis. The results showed that 20% CO2 delayed the changes of a* and b* values in strawberry fruit. The degradation of chlorophyll was delayed in CO2 treated fruit by inhibiting the activities of chlorophyllase and down-regulating the expression of FaChl b reductase, FaPAO and FaRCCR. In addition, lower concentration of anthocyanins and lower activity of PAL, C4H, 4CL and CHS were recorded under the effect of 20% CO2. Meanwhile, qRT-PCR analysis showed that 13 genes involved in the phenylpropanoid pathway and the flavonoid biosynthesis pathway were also down-regulated under CO2 stress. However, no residual effect on pigment metabolism was observed when elevated CO2 was removed. Our study provided new insights into the regulation of elevated CO2 in the role of pigment metabolism in postharvest.
While plant growth is promoted by elevated carbon dioxide (CO2), it is constrained by low nitrogen (N, 1 mmol L−1 NO3-) availability. Here, we investigated N absorption responses to elevated CO2 ...under low-N conditions. Brassica napus L. was cultured hydroponically in a low-N nutrient solution at normal and elevated ambient CO2 levels, at normal CO2 in the presence of exogenous auxin (Indole-3-acetic acid, IAA), and at elevated CO2 in the presence of N-1-naphthylphthalamic acid (NPA), an inhibitor of auxin polar transport. Photosynthetic rate, biosynthesis of 3-deoxy-d-arabinoheptanoic acid-7-phosphate (DAHP), tryptophan and IAA, and IAA polar transport from shoots to roots were enhanced under elevated CO2 compared with controls. Furthermore, increased root growth, Plasma membrane (PM) H+-ATPase activity, and expression of NRT1.1 and NRT2.1 resulting in higher total N were observed under elevated CO2 and normal CO2 + IAA treatment compared with controls. Moreover, the usual promotion of root growth, H+-ATPase activity, and expression of NRT1.1 and NRT2.1 by elevated CO2 vanished once IAA polar transport was inhibited; total N did not differ between elevated CO2 + NPA-treated plants and controls. Elevated CO2 promoted IAA biosynthesis and its polar transport from shoots to roots under low-N conditions, promoting root growth, PM H+-ATPase activity, and the expression of NRT1.1 and NRT2.1, thereby enhancing N uptake and plant growth.
•Elevated CO2 promoted NO3- uptake of Brassica napus L. under low nitrogen condition.•Elevated CO2 advanced the metabolism of shikimic acid pathway.•Elevated CO2 enhanced the IAA synthesis and its polar transport.•Elevated CO2 stimulated root growth and expression of NO3- transporters.
Elevated CO2 concentrations may inhibit photosynthesis due to nitrogen deficiency, but legumes may be able to overcome this limitation and continue to grow. Our study confirms this conjecture well. ...First, we placed the two-year-old potted saplings of Ormosia hosiei (O. hosiei) (a leguminous tree species) in the open-top chamber (OTC) with three CO2 concentrations of 400 (CK), 600 (E1), and 800 μmol·mol−1 (E2) to simulate the elevated CO2 concentration environment. After 146 days, the light saturation point (LSP), light compensation point (LCP), apparent quantum efficiency (AQE), and dark respiration rate (Rd) of O. hosiei were increased under increasing CO2 concentration and obtain the maximum ribulose diphosphate (RuBP) carboxylation rate (Vc max) and RuBP regenerated photosynthetic electron transfer rate (Jmax) were also significantly increased under E2 treatment (P < 0.05). This results in a significant increase of the maximum assimilation rate (Amax) under elevated CO2 concentrations. Sucrose phosphate synthase (SPS) activity in sucrose metabolism increased in the leaves, more soluble sugars, starches, and sucrose was produced, but sucrose content only in leaves increased at E2, and more carbon flows to the roots. The activity of the NH4+ assimilating enzymes glutamine synthetase (GS), glutamate synthetase (GOGAT), and glutamate dehydrogenase (GDH) in the leaves of O. hosiei increases under elevated CO2 concentrations to promote nitrogen synthesis that reduces the content of ammonium nitrogen and increases the content of nitrate nitrogen. In addition, under E1 conditions, sucrose synthase (SS), direction of synthesis activity was highest and sucrose invertase (INV) activity was lowest, this means that the balance of C and N metabolism is maintained. While under E2 conditions SS activity decreased and INV activity increased, this increased C/N and nitrogen use efficiency. So, the elevated CO2 concentration promotes the accumulation of O. hosiei biomass, especially in the aboveground part, but did not have a significant effect on the accumulation of root biomass. This means that O. hosiei is able to cope under the elevated CO2 concentration without showing photosynthetic adaptation during the experimental period.
•The legume of O.hoeisi did not show photosynthetic adaptation under elevated CO2 concentration.•In elevated CO2 environment, O.horeisi 's strong C input promoted nodule nitrogen fixation.•Elevated CO2 concentration was beneficial to the biomass accumulation of O.houeisi, especially the aboveground part.
The projected rise in atmospheric CO2 levels to 550 ppm by mid-century may reduce protein, iron, and zinc levels in certain cereal crops by 3–17 %. In China, staple foods provide nearly 50 % of total ...energy and 40 % of essential nutrients, and their cultivation exacerbates environmental stress; adjusting staple food consumption may bring environmental and health benefits. Using China Health and Nutrition Survey (CHNS) data, this study compared current staple food consumption (SBAU) to an optimized balanced diet scenario with the consumption of whole grains and legumes replaces excessive refined grains. Findings reveal that SBAU falls short of recommended nutrient intake (RNI), while the optimized scenario offsets the nutritional impact of the elevated CO2, exceeding 95 % of the RNI for zinc and iron from staple food. Additionally, transition to the optimized scenario also reduces greenhouse gas emissions and blue water consumption by 7 % and 39 %, respectively.
Display omitted
Land models are often used to simulate terrestrial responses to future environmental changes, but these models are not commonly evaluated with data from experimental manipulations. Results from ...experimental manipulations can identify and evaluate model assumptions that are consistent with appropriate ecosystem responses to future environmental change. We conducted simulations using three coupled carbon‐nitrogen versions of the Community Land Model (CLM, versions 4, 4.5, and—the newly developed—5), and compared the simulated response to nitrogen (N) and atmospheric carbon dioxide (CO2) enrichment with meta‐analyses of observations from similar experimental manipulations. In control simulations, successive versions of CLM showed a poleward increase in gross primary productivity and an overall bias reduction, compared to FLUXNET‐MTE observations. Simulations with N and CO2 enrichment demonstrate that CLM transitioned from a model that exhibited strong nitrogen limitation of the terrestrial carbon cycle (CLM4) to a model that showed greater responsiveness to elevated concentrations of CO2 in the atmosphere (CLM5). Overall, CLM5 simulations showed better agreement with observed ecosystem responses to experimental N and CO2 enrichment than previous versions of the model. These simulations also exposed shortcomings in structural assumptions and parameterizations. Specifically, no version of CLM captures changes in plant physiology, allocation, and nutrient uptake that are likely important aspects of terrestrial ecosystems' responses to environmental change. These highlight priority areas that should be addressed in future model developments. Moving forward, incorporating results from experimental manipulations into model benchmarking tools that are used to evaluate model performance will help increase confidence in terrestrial carbon cycle projections.
Plain Language Summary
How do changes in the availability of nitrogen in soils or carbon dioxide in the atmosphere affect the amount of carbon that can be stored on land? Answering this question is critical, but it remains difficult for land models that are used to make climate change projections—in part because of limited understanding in how terrestrial ecosystems will respond to environmental change. Experimental manipulations that increase the availability of nitrogen or carbon dioxide, however, provide insights into how ecosystems are likely to respond to changes in resource availability. We expect that models should exhibit similar responses to those observed in the real world. Our results show that over the course of model development later versions of the Community Land Model do a better job of simulating the global carbon cycle and capturing appropriate ecosystem responses to nitrogen and carbon dioxide enrichment. This improves our confidence in the future carbon cycle projections made by more recent versions of the Community Land Model. Our results also identify assumptions in the model that are not well supported by observations and can help to prioritize future model developments.
Key Points
Experimental manipulations provide critical insights into ecosystem responses to environmental change that can evaluate land models
Parametric and structural changes to the Community Land Model version 5 improve the simulated response to environmental change
Model assumptions related to nutrient acquisition strategies and trade‐offs between carbon and nitrogen limitation deserve further attention
•We applied T-FACE to evaluate the effects of combination of elevated CO2 and increased temperature on rice yield, dry matter distribution and photosynthetic characteristics.•Rising temperature lead ...to the decrease in rice yield, no matter alone or combined with elevated CO2.•Increased temperature alone or combined with elevated CO2 significantly reduced DM at heading stage compared to ambient conditions.•The negative effect of increased temperature alone or combined with elevated CO2 was attributed to the decrease of leaf area index.•Future climate conditions will be advantageous for the leaf photosynthesis but not for growth and yields of rice.
Carbon dioxide (CO2)-induced stimulation of the leaf net photosynthetic rate (Amax) is projected to further increase with increasing temperature. Although the impact of rising temperature or CO2 on leaf photosynthesis parameters and dry matter (DM) accumulation and distribution has been widely investigated, less research has been conducted to evaluate the combined effects of these climate change factors on rice in field sites. In this study, the effects of the combination of two levels of CO2 (390 μmol mol−1 and 590 μmol mol-1) and two levels of temperature (no increase and increase of ˜1.5 °C) on the Amax, respiration rate (Rd), leaf biochemical parameters, DM accumulation and distribution and yield of rice were tested in a free air CO2-enrichment (FACE) system. Elevated CO2 dramatically increased DM accumulation before heading; however, rising temperature alone or in combination with CO2 concentration enrichment remarkably reduced DM at the heading stage compared to that under ambient conditions. Therefore, rising temperature leads to a decrease in rice yield, regardless of whether it occurs alone or in combination with high CO2 concentration. The negative effect of rising temperature alone or in combination with elevated CO2 was attributed to a reduced leaf area index, as both treatments had minor or positive effects on Amax and Rd. Increases in Amax and Rd under the combination of elevated CO2 and temperature were linked to improvements in the maximum carboxylation rate of Rubisco (Vc,max) and the maximum electron transport rate (Jmax). Furthermore, the increase in both CO2 and temperature significantly increased Amax compared to that under elevated CO2. Alleviation of the decrease in leaf nitrogen and Rubisco content by the increase in both CO2 and temperature compared to that observed with elevated CO2 alone accounted for the increase in Vc,max and Jmax. These results suggest that future climate conditions will be advantageous for leaf photosynthesis but not for the growth and yield of rice.
![Elevated [CO2] reduces CH4 ...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0167-8809/small "Elevated [CO2] reduces CH4 emissions from rice paddies under in situ straw incorporation")
PDF
