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Article

Short-Term Elevated CO2 or O3 Reduces Undamaged Rice Kernels, but Together They Have No Effect

by
Mengbi Long
1,
Mikeleban Yunshanjiang
1,
Dezhao Yu
1,
Shenshen Li
1,
Mairemu Tuerdimaimaiti
1,
Aoqi Wu
1,2 and
Guoyou Zhang
1,3,*
1
School of Ecology and Applied Meteorology, Nanjing University of Information Science and Technology, Nanjing 211544, China
2
Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China
3
Key Laboratory of Agrometeorology of Jiangsu Province, School of Ecology and Applied Meteorology, Nanjing University of Information Science and Technology, Nanjing 210044, China
*
Author to whom correspondence should be addressed.
Agronomy 2023, 13(12), 2981; https://doi.org/10.3390/agronomy13122981
Submission received: 21 October 2023 / Revised: 29 November 2023 / Accepted: 30 November 2023 / Published: 1 December 2023
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Abstract

:
The spatiotemporal heterogeneity in the concentrations of atmospheric CO2 and tropospheric O3 is increasing under climate change, threatening food security. However, the impacts of short-term elevated CO2 or O3 on undamaged kernels in rice remain poorly understood, especially the impacts of their combination. We conducted an open-top chamber experiment to examine the impacts of short-term elevated CO2 (+200 ppm, eCO2) and O3 (+40 ppb, eO3) on undamaged kernels in rice cultivars (NJ5055 and WYJ3). We found eCO2 significantly reduced undamaged kernels by 35.2% and 66.2% in NJ5055 and WYJ3, respectively. EO3 significantly reduced undamaged kernels by 52.4% and 47.7% in NJ5055 and WYJ3, respectively. But the combination of eCO2 and eO3 did not affect the undamaged kernels in both cultivars. Moreover, we found that undamaged kernels were significantly correlated with chalky kernels (r = −0.9735). These results highlighted that changes in chalky kernels are most responsible for the changes in undamaged kernels in rice under eCO2 and eO3. This study demonstrated that undamaged kernels in rice are fragile to climate change factors like short-term eCO2 and eO3, and reducing chalky kernels is one of the most important adaptations to sustain food security in the future.

1. Introduction

Rice (Oryza sativa L.) sustainably provides staple food for over half of the world’s population [1,2]. Steady growth in rice production is an important guarantee for eradicating hunger and achieving global food security. However, short- and long-term environmental stresses induced by climate change are threatening the yields of rice and other food crops [3,4,5]. Among the many environmental factors, the effects of elevated atmospheric carbon dioxide (CO2) and tropospheric ozone (O3) concentrations on crops and plants have received much attention. The effect of elevated CO2 concentrations usually has a positive effect on plant productivity, showing a carbon fertilization effect (CFE). However, elevated O3 reduces rice yield through impacts on plant growth and development, physiological metabolism, and antioxidant capacity. Climate change has destabilized O3 concentrations, and the average O3 concentration in major rice-growing areas has been increasing year by year. Anthropogenic emissions of volatile organic compounds (VOCs) and nitrogen oxides (NOx) are important contributors to ozone pollution, and since these precursors are produced by urbanization and industrial and agricultural production and we are not in a position to change the trend of environmental change in the short term, we need to gain a better understanding of the impacts of their changes on rice in order to actively safeguard food security [3].
Grain yield in rice and other crops is usually increased by CFE, whose mechanisms involve several aspects, including the photosynthesis rate, nutrient uptake and partitioning, plant structure, and physiological metabolism [6,7,8]. Briefly, the grain yield increase by CFE could be achieved by increasing the number of grains or increasing the grain weight. For example, some studies have found that the number of grains harvested from rice under elevated CO2 concentrations was significantly higher, while grain weight did not change significantly [9,10,11]. However, some studies found that the weight and size of rice grains significantly increased under elevated CO2 concentrations [12,13]. It has also been reported that there is a trade-off between grain number and grain weight [14,15], and the CFE can be easily diminished or even eliminated by other environmental factors [16,17,18], such as heat, drought, O3, etc. Some studies have shown that elevated O3 inhibits pollen germination and pollen tube growth in rice [19], and reduces pollination and the number of ovules formed, ultimately leading to a reduction in grain number [20]. Other studies reported that elevated O3 inhibits photosynthesis and nutrient uptake in rice [21], leading to slow plant growth and thus affecting grain weight and size [22,23,24].
The simultaneous action of elevated CO2 and O3 on rice is more complex. In general, elevated CO2 can partially mitigate the negative effects of elevated O3 on rice. However, the exact effect depends on factors such as the concentration of CO2 and O3, the duration of exposure, and the mode of action [6]. Some studies have found that rice growth rates and yields increased under the simultaneous action of elevated CO2 and O3 compared to exposure to elevated O3 alone [25,26]. This may be due to the fact that elevated CO2 can promote photosynthesis and carbohydrate accumulation in plants [27], thereby increasing their antioxidant capacity and resilience. However, other studies have shown that elevated CO2 may exacerbate the negative effects of elevated O3 [6,28,29,30]. For example, some studies have found that root growth is inhibited under the simultaneous action of elevated CO2 and O3 [28,31,32], which may lead to a reduction in the ability of plants to absorb and utilize nutrients, ultimately affecting yield and quality.
These uncertainties may be induced by different experimental conditions and plant varieties on the one hand, and on the other hand, differences in rice harvesting methods and yield measurement. The inconsistency of the research results makes it more difficult to understand and evaluate the impacts of climate change on rice production. The increased frequency of extreme weather events due to climate change is increasing the spatial and temporal heterogeneity of the concentrations of CO2 and O3. In order to assess the impacts of climate change more accurately and develop effective adaptations, there is an urgent need to understand the impacts of elevated CO2 and O3.
Therefore, we conducted this study using the open-top chamber (OTC) method. We examined the effects of short-term elevated CO2 and O3 on rice cultivars through field experiments. In order to reduce the discrepancy between similar studies that was induced by the inconsistency of analytical methods for grain yield and grain quality, we focused on the response of rice kernels. Our research questions were as follows: (1) What are the effects of short-term elevated CO2 and O3 concentrations separately and together on undamaged kernels in rice? (2) What are the causes of changes in undamaged kernels? (3) What are the specific adaptation recommendations to safeguard rice production in the face of elevated CO2 and O3?

2. Materials and Methods

The field experiment was conducted in 2021 at a rice paddy in Jiangdu County, Jiangsu Province, an inferior section of China’s Yangtze River Delta (119°43′ E, 32°25′ N, with a total yearly precipitation of 1131.3 mm and a mean temperature of 16.2 °C from 2009 to 2021). The open-top chamber (OTC) method was adopted to examine the effects of the main factors in this study. Embedding in the paddy field, the OTC (octagonal with 2.3 m in height and 4.8 m in diameter) was constructed with tempered glass and aluminum alloy frames (Figure S1). The atmospheric CO2 concentration has already increased by more than 200 ppm in the past decades, and is now 50% higher than preindustrial levels (417 ppm, https://www.noaa.gov/news-release/greenhouse-gases-continued-to-increase-rapidly-in-2022, accessed on 28 November 2023). Moreover, tropospheric O3 concentrations are also increasing, and to improve our understanding of the impacts of climate change on rice in order to identify adaptation responses in advance, we simulate high-concentration gas environments several decades in the future. With three OTC replicates, the same 12 OTCs were assigned to the ambient air (control), elevated carbon dioxide (ambient air + 200 ppm, eCO2), elevated ozone (ambient air + 40 ppb, eO3), and jointly elevated CO2 and O3 (eCO2 + eO3). The fumigation was only given on daytime and non-rainy days, and the duration of the fumigation by eCO2 and eO3 was from 20th July to 30th October 2021. More details about the experimental site and the OTC facilities can be found in our previous studies [33,34]. Because Nanjing 5055 and Wuyujing 3 (NJ5055, WYJ3, japonica) are among the most common forms of rice and are widely grown in the experimental region, they were chosen for this investigation. Both NJ5055 and WYJ3 were transplanted on 16 June 2021, and the cultivation of the crops and the field management were in accordance with the practices of local farmers. The harvest was conducted at plant physiological maturity, when 85% of the grains had turned straw-colored and the grain moisture content fell to about 20%.
Briefly, the plants were collected from each OTC. All grains per plant were airdried to a constant weight. The sample was collected for the undamaged kernel analysis. The grains were dehulled manually, and classified into different types of kernels, including undamaged, shriveled, crackle, deformed, and chalky kernels by visual inspection (Figure S2). In order to avoid human error and bias, investigators were trained well before analyzing samples, and a blinded sample analysis was used when analyzing samples, i.e., the investigator only knew the sample number and did not know the treatment from which the sample was collected. On the basis of the position of the chalky appearance within a kernel, the chalky kernel was further classified into different types (Figure S3). Milky white kernel, white-back kernel, white-base kernel, white-belly kernel, and white-core kernel are the types of chalky kernel in this study. For more details about the chalky types, please see our previous studies [16,35].
The results of an undamaged kernels analysis were subjected to ANOVA by fitting the mixed-linear model with rice cultivar “Cultivar”, short-term eCO2 or/and eO3 treatment “Treat”, and their interaction “Cultivar × Treat”, examining the effects of the cultivar, treatment, and interaction. Tukey’s multiple comparisons test was used to examine the differences among the variables. A statistical analysis was performed with JMP (13) software (SAS Institute, Cary, NC, USA). In order to examine the specific impacts of the treatment on the variables, comparisons among least squares means were conducted, and the differences were checked by the t-test.

3. Results

3.1. Effects of eCO2, eO3, and Their Combination on Undamaged Kernels in Rice Cultivars

The ratios of undamaged kernels (UDKs) were significantly reduced by eCO2 and eO3 in both rice cultivars (Figure 1a), and the effects of treatment (p < 0.0001), cultivar (p < 0.0001), and their interaction (p < 0.01) were significant. While the negative effects of eO3 on UDK (−52.4%, p < 0.05) were larger than those of eCO2 (−35.2%, p < 0.05) in NJ5055, eCO2 effects on UDK (−66.2%, p < 0.01) were larger than eO3 (−47.7%, p < 0.05) in WYJ3 (Table 1). Although the UDKs at eCO2 + eO3 in NJ5055 and WYJ3 were 15.7% and 12.3% smaller than those at the control, respectively (Table 1), for both cultivars, UDK was not significantly affected by eCO2 + eO3, compared to the control (Figure 1a). These results indicate that undamaged kernels in rice were reduced by eCO2 or eO3, but not affected by their combination.

3.2. Effects of eCO2, eO3, and Their Combination on Various Types of Damaged Kernels in Rice

All four types of damaged kernels were sensitive to eCO2 and eO3 (Figure 2). For chalky kernels (CKs), the effects of treatment (p < 0.0001), cultivar (p < 0.0001), and their interaction (p < 0.0001) were all significant (Figure 2a). In NJ5055, CK was significantly increased by eCO2 (19.3%, p < 0.05), eO3 (47.0%, p < 0.05), and eCO2 + eO3 (15.5%, p < 0.05). However, CK in WYJ3 was only significantly increased by eCO2 (50.3%, p < 0.01) and eO3 (29.9%, p < 0.05). For shriveled kernels (SKs), the effects of treatment (p < 0.001) and the interaction between treatment and cultivar (p < 0.0001) were significant (Figure 2b). In NJ5055, SK was significantly reduced by eCO2 (88.9%, p < 0.01), but increased by eCO2 + eO3 by 73.3% (p < 0.01, Table 1). For crackle kernels (CRKs) and deformed kernels (DKs), the effects of treatment (p < 0.0001), cultivar (p < 0.0001), and their interaction (p < 0.0001) were all significant (Figure 2c,d).

3.3. Contribution of Chalky Kernels to Undamaged Kernels in Rice under eCO2 and eO3

The ratios and compositions of CK were altered by eCO2, eO3, and eCO2 + eO3 (Figure 3). In NJ5055, the types of chalky kernels that take the largest proportions, at control, eCO2, eO3, and eCO2 + eO3, were white-belly kernels (WBL, 23.1%), white-core kernels (WCO, 29.3%), WBL (35.8%), and WCO (21.3%), respectively. In WYJ3, the types of chalky kernels that take the largest proportions, at control, eCO2, eO3, and eCO2 + eO3, were WBL (23.1%), WBL (44.0%), WBL (32.4%), and WBL (24.6%), respectively. For milky white kernels (MW), the effects of treatment (p < 0.0001), cultivar (p < 0.0001), and their interaction (p < 0.05) were all significant. For both cultivars, eO3 increased MW most compared to other treatments (Table 2). For white-back kernels (WBC), the effects of treatment (p < 0.0001) and the interaction between treatment and cultivar (p < 0.0001) were all significant. While eCO2 + eO3 reduced the WBC mostly in NJ5055, eCO2 reduced the WBC most in WYJ3. For white-base kernels (WBS), the effects of treatment (p < 0.0001), cultivar (p < 0.0001), and their interaction (p < 0.0001) were all significant. The largest effects were caused by the eO3 treatment in both cultivars, which were negative. For WBL and WCO, the effects of treatment (p < 0.0001), cultivar (p < 0.0001), and their interaction (p < 0.0001) were all significant; eCO2 increased WBL in WYJ3 and WCO in both cultivars, respectively (Table 2).
The contributions of chalky kernels to undamaged kernels (Figure 4a) were significantly affected by the treatment (p < 0.0001), cultivar (p < 0.05), and their interaction (p < 0.0001). The contribution of CK to UDK was significantly altered by eCO2: the contribution of CK to UDK decreased in NJ5055 but increased in WYJ3. The contributions of MW (Figure 4b), WBC (Figure 4c), WBS (Figure 4d), WBL (Figure 4e), and WCO (Figure 4f) kernels to chalky kernels (Table 2) were significantly affected by the treatment, cultivar, and their interaction. In NJ5055, at control, WBC contributed the most (19.5%) to the chalky kernels compared to other types of chalky kernels. At eCO2 and eCO2 + eO3, WCO contributed the most to chalky kernels by 50% and 37.6%, respectively. At eO3, MW contributed the most to the chalky kernels (29.2%). In WYJ3, at control, eCO2, and eO3, WBL contributed the most to the chalky kernels, which were 35.3%, 53.9%, and 45.8%, respectively. The contribution of MW to chalky kernels was significantly increased to 40.7% by eO3, compared to that at control (21.2%), and was larger (39.6%) at eCO2 + eO3 than other types of chalky kernels.

4. Discussion

From grain (seed) to kernel, depending on how the rice was harvested and the method of yield estimation, grain weight in rice (thousand grain weight) may be the average of the sifted (wind-selected, water-selected, etc.) grains, the average of all the unsifted grains, or the average of the brown rice that was hulled after screening [36,37,38,39]; these inconsistencies in research methods and analytical traits may confuse our understanding of the response of rice to climate change. Although there have been previous studies on the effects of abiotic factors on grain yield and quality [3,40,41], this study is the first to report on the effects of short-term eCO2 and eO3 on undamaged kernels in rice. To minimize errors due to threshing, etc., we manually harvested all rice grains and randomly selected subsamples for the analysis without any screening. Manual hulling was adopted to observe and examine different types of kernels. Our results show that undamaged kernels in rice were reduced by eCO2 or eO3, but not affected by their combination (Figure 1a). These results indicate that both yield (e.g., brown rice yield and milled rice yield) and quality of rice kernels are sensitive to short-term eCO2 and eO3, i.e., rice production is very fragile to climate change.
Moreover, the interaction between treatment and cultivar was significant; for NJ5055, the reduction in undamaged kernels by eO3 (52.4%) was larger than that by eCO2 (35.2%). Oppositely, eCO2 reduced undamaged kernels (66.2%) more severely than eO3 (47.7%) in WYJ3 (Table 1). These reductions suggest that the impact of eO3 on the undamaged kernels was similar for the two cultivars, but WYJ3 was more sensitive to eCO2 compared to NJ5055. Cultivar-dependent sensitivity to eCO2 was normal; e.g., grain yield enhancement in rice by CFE could range from 3% to 36% [42]. Undamaged kernels in rice could be decreased by short-term eCO2 by at least one third, which in turn increased damaged kernels by more than one third. Damaged kernels are more likely to break during storage, transportation, and processing and become broken rice or waste [43,44,45]. Our results thus demonstrate that previous estimates of the CFE for rice yield enhancement are likely to be overestimated [3,46,47].
It should be noted that eCO2 and eO3 together had no significant effect on undamaged kernels in rice. This may be due to the fact that the effect of eCO2 on kernels is to alter plant growth rhythms by increasing grain filling resources, whereas eO3, on the contrary, affects the plant growth and grain filling rate by decreasing grain filling resources [25,28]; when both occur at the same time, eCO2 moderates or counteracts the effects of eO3. This phenomenon is actually important because it gives us the possibility that it is possible to regulate the effect of one of the gases by regulating the concentration and duration of the other gas. Currently, CO2 is still expensive to prepare and fumigate, but O3 is relatively easy to prepare and can be replaced with chemical substitutes such as ethylenediurea. With future technological advances, local conditioning of CO2, O3, and the microclimate of crop canopies will become easier.
Chalky kernels were significantly increased by both short-term eCO2 and eO3 (Figure 2a), and undamaged kernels were found to be significantly correlated (r = −0.9735, p < 0.0001) with chalky kernels (Figure 1b), suggesting that the reduction in undamaged kernels in rice is closely correlated with the increase in chalky kernels. Chalky kernels are easily broken during polishing and processing, and unbroken chalky kernels degrade the appearance, cooking, and nutritional qualities of rice [48,49]. Chalky rice is usually sold at a lower market price than non-chalky rice [50,51], reducing farmers’ income. Studies on rice chalkiness as affected by eCO2 and eO3 have shown that eCO2 can stimulate photosynthesis in plants, increase leaf area and dry matter accumulation, and thus affect the grain filling characteristics [10,12]. On the other hand, eO3 damages the cell membranes and chlorophyll of plants, reducing photosynthetic capacity and affecting the grain quality [26,35]. Our results show short-term eCO2 and eO3 significantly increased chalky kernels, and the negative correlation between chalky kernels and undamaged kernels suggests that reducing chalky kernels under eCO2 and eO3 is an important adaptation to maintain the production of undamaged kernels in rice.
Previous studies have focused on the grain chalkiness, chalky degree, and proportion of chalky grains, but little has been reported on specific different types of chalky kernels under climate change [52,53]. In short, the starch granules of chalky endosperm cells are loosely packed, whereas the starch granules of normal translucent endosperm are tightly packed; the large amount of airspace between the starch granules causes random light reflections, creating a chalky appearance [54,55,56]. It is suggested that the appearance of chalky kernels caused by exposure to high temperatures is due to the lack of starch in the endosperm, the reduction in some genes related to starch synthesis, and the improvement of genes that store starch-degrading α-amylase [57,58,59]. Different types of chalky kernels are induced by various physiological mechanisms, investigation of which could provide information on the happenings of chalky kernels under eCO2 and eO3 and indicate potential adaptation strategies.
We found that eCO2 and eO3 altered the proportion of different types of chalky kernels, and the alteration was cultivar-dependent. In NJ5055, at control, white-back kernels contributed the most to the chalky kernels; at eCO2 and eCO2 + eO3, white-core kernels contributed the most to chalky kernels, respectively; at eO3, milky white kernels contributed the most to the chalky kernels. In WYJ3, at control, eCO2, and eO3, white-belly kernels contributed the most to the chalky kernels, respectively; at eCO2 + eO3, milky white kernels shared the largest proportion compared to other types. White-back and milky white kernels usually appear once the rice plant is exposed to higher temperatures [60,61], whose mechanisms include resource portioning among grains. The source ability, e.g., the amount of starch substrates per grain, significantly affects the occurrence of milky white grains [54,62].
Because there are trade-offs between grain number and grain weight in rice, the source ability per grain is easily affected by eCO2 and eO3, inducing the occurrence of milky white kernels [16,35]. The occurrence of white-base and white-back kernels is negatively correlated with plant nitrogen concentrations [63], and the increment of grain weight in some rice cultivars by CFE usually shows a dilution effect on the concentrations of nitrogen and other elements in rice kernels [16,64]. Maximum proportions of chalky kernels were occupied by white-core kernels in NJ5055 at eCO2 and eCO2 + eO3 (Table 2). This could probably be induced by the warming effect of eCO2. In comparison to white-back and milky white kernels, white-core kernels were found to be more sensitive to temperatures [65]. In fact, temperature affects rice in more ways than one can imagine. A rise in the optimum temperature (28/22 °C) by about 1 °C may lead to a 10% decrease in rice yield [66] if the chalky kernel is considered, which may further lower the milled rice yield. Elevated CO2 increases the air temperature of the plant leaves and rice canopy [67,68,69]. Thus, white-core kernels were increased by eCO2, while further studies need to be conducted to clarify the mechanisms, especially under the combination of eCO2, eO3, warming stresses, and other abiotic and biotic factors.

5. Conclusions

Through a field experiment, we examined the impacts of short-term elevated CO2 and O3 on undamaged kernels in rice cultivars. We found that short-term elevated CO2 or O3 reduces undamaged rice kernels, but together they have no effect. The undamaged kernels were closely correlated with chalky kernels, indicating that the increment of chalky kernels may be the main reason why the undamaged kernels decreased, and reducing the occurrence of chalky kernels is an important adaptation to safeguard the rice production under climate change.
Because the effects of short-term elevated CO2 and O3 on undamaged kernels were cultivar-dependent, we could develop adaptations by screening tolerant cultivars. Moreover, through the analysis of different types of chalky kernels, we inferred that the altered source sink balance and grain growth under elevated CO2 and O3 are probably the mechanisms in the increasement in chalky kernels. Different types of kernels occur at specific conditions, e.g., white-base kernels occur at a deficiency of nitrogen in plant growth, and white-core kernels are sensitive to temperature. Agronomic adaptations like management of fertilization, plant density, and canopy temperature could be developed in future studies.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/agronomy13122981/s1, Figure S1. A picture of the open-top chamber (OTC) adopted for this study. The photo was taken by Guoyou Zhang in 2021. Figure S2. Examples of different types of kernels in rice (from left to right, undamaged, shriveled, cracked, and deformed, referenced from the Ministry of Agriculture, Forestry, and Fisheries, Japan). Figure S3. Grayscale images (upper row) and binary images (lower row) of rice grains. Since the grains were illuminated from behind, the chalky parts of the grains appear darker than normal parts. Cited from Yoshioka et al. [70].

Author Contributions

M.L.: Conceptualization, Methodology, Investigation, Data curation. M.Y.: Validation, Methodology, Visualization. D.Y., S.L., M.T. and A.W.: Investigation, Formal analysis. G.Z.: Conceptualization, Project administration, Funding acquisition, Writing—review and editing. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by National Natural Science Foundation of China, grant number: 42077209.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Acknowledgments

We want to express our acknowledgement to Zhaozhong Feng, Yanshen Xu, Bo Shang, Fangzhen Yang, Longxin He, and other technicians specializing at the experimental site. We also want to thank Meng Wang, Zhe Wu, and Subati Mamati Aili for their assistance in the sample analysis.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Effects of eCO2, eO3, and their combination on the ratio of undamaged kernels in rice cultivars (a) and the correlation of the ratios between different types of damaged kernels and undamaged kernel mean across the treatments and cultivars (b). * (p < 0.05), *** (p < 0.001), **** (p < 0.0001), and ns (not significant) are the results of multiple comparisons.
Figure 1. Effects of eCO2, eO3, and their combination on the ratio of undamaged kernels in rice cultivars (a) and the correlation of the ratios between different types of damaged kernels and undamaged kernel mean across the treatments and cultivars (b). * (p < 0.05), *** (p < 0.001), **** (p < 0.0001), and ns (not significant) are the results of multiple comparisons.
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Figure 2. Effects of eCO2, eO3, and their combination on the ratio of chalky (a), shriveled (b), crackle (c), and deformed (d) kernels. * (p < 0.05), ** (p < 0.01), *** (p < 0.001), **** (p < 0.0001), ns (not significant) are the results of multiple comparisons.
Figure 2. Effects of eCO2, eO3, and their combination on the ratio of chalky (a), shriveled (b), crackle (c), and deformed (d) kernels. * (p < 0.05), ** (p < 0.01), *** (p < 0.001), **** (p < 0.0001), ns (not significant) are the results of multiple comparisons.
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Figure 3. Chalky kernel compositions under different treatments in NJ5055 (a) and WYJ 3 (b).
Figure 3. Chalky kernel compositions under different treatments in NJ5055 (a) and WYJ 3 (b).
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Figure 4. Effects of eCO2, eO3, and their combination on the contribution of chalky kernels to undamaged kernels (a), and milky white (b), white-back (c), white-base (d), white-belly (e), and white-core (f) to chalky kernels. * (p < 0.05), ** (p < 0.01), *** (p < 0.001), **** (p < 0.0001), ns (not significant) are the results of multiple comparisons.
Figure 4. Effects of eCO2, eO3, and their combination on the contribution of chalky kernels to undamaged kernels (a), and milky white (b), white-back (c), white-base (d), white-belly (e), and white-core (f) to chalky kernels. * (p < 0.05), ** (p < 0.01), *** (p < 0.001), **** (p < 0.0001), ns (not significant) are the results of multiple comparisons.
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Table 1. Effects of eCO2, eO3, and their combination on the ratio of undamaged and various types of damaged kernels in rice cultivars, as shown by the least squares mean (LSM) and effects.
Table 1. Effects of eCO2, eO3, and their combination on the ratio of undamaged and various types of damaged kernels in rice cultivars, as shown by the least squares mean (LSM) and effects.
CultivarTreatmentUndamaged
Kernel		Shriveled KernelCrackle KernelDeformed KernelChalky Kernel
LSM (%)Effects (%)LSM (%)Effects (%)LSM (%)Effects (%)LSM (%)Effects (%)LSM (%)Effects (%)
NJ5055Control47.9 1.5 1.5 0.0 49.1
eCO231.0−35.2 *0.2−88.9 **9.3517.8 *0.82 × 1018 *58.619.3 *
eO322.8−52.4 *4.6204.40.0−100.00.48 × 1017 *72.247.0 *
eCO2 + eO340.4−15.72.673.3 **0.0−100.00.35 × 101756.715.5 *
WYJ3Control40.9 2.5 0.0 2.2 54.4
eCO213.8−66.2 **2.0−18.71.53 × 1017 *1.0−53.781.750.3 **
eO321.4−47.7 *3.228.01.23 × 1017 *3.558.270.629.9 *
eCO2 + eO335.9−12.32.4−2.70.0−1 × 1020.5−77.6 *61.212.6
* (p < 0.05) and ** (p < 0.01) are the results of t-test of the eCO2 (eO3, and their combination)—control contrasted in each cultivar.
Table 2. Effects of eCO2, eO3, and their combination on the ratio of different types of chalky kernels (and the contribution to chalky, CTC) in rice cultivars, as shown by the least squares mean (LSM) and effects.
Table 2. Effects of eCO2, eO3, and their combination on the ratio of different types of chalky kernels (and the contribution to chalky, CTC) in rice cultivars, as shown by the least squares mean (LSM) and effects.
CultivarTreatmentMilky WhiteWhite-BackWhite-BaseWhite-BellyWhite-Core
LSM (%)Effects (%)CTC (%)LSM (%)Effects (%)CTC (%)LSM (%)Effects (%)CTC (%)LSM (%)Effects (%)CTC (%)LSM (%)Effects (%)CTC (%)
NJ5055Control6.6 13.49.6 19.52.5 5.123.1 47.17.3 14.8
eCO212.488.4 ***21.2 **2.6−73.3 **4.4 ***3.642.7 *6.1 *10.8−53.1 **18.5 **29.3301.4 **50.0 **
eO321.1219.2 ***29.2 *3.5−63.9 **4.8 **0.4−85.3 **0.5 **35.855.1 *49.511.557.1 *15.9
eCO2 + eO317.0157.1 *29.9 **2.0−78.8 **3.6 ***1.8−26.73.214.6−36.9 *25.7 *21.3192.2 *37.6 **
WYJ3Control11.5 21.27.3 13.57.5 13.819.2 35.38.8 16.3
eCO214.223.117.33.0−59.1 ***3.7 **2.1−72.0 *2.6 **44.0129.6 **53.9 **18.3107.5 **22.5
eO328.8149.4 ***40.7 ***3.9−46.8 **5.5 **1.3−82.1 **1.9 **32.468.9 *45.8 *4.3−51.3 **6.1 **
eCO2 + eO324.3110.4 **39.6 ***3.3−54.5 *5.4 **5.0−32.9 **8.2 **24.628.240.24.0−54.7 *6.5 *
* (p < 0.05), ** (p < 0.01), and *** (p < 0.001) are the results of t-test of the eCO2 (eO3, and their combination)—control contrasted in each cultivar.
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Long, M.; Yunshanjiang, M.; Yu, D.; Li, S.; Tuerdimaimaiti, M.; Wu, A.; Zhang, G. Short-Term Elevated CO2 or O3 Reduces Undamaged Rice Kernels, but Together They Have No Effect. Agronomy 2023, 13, 2981. https://doi.org/10.3390/agronomy13122981

AMA Style

Long M, Yunshanjiang M, Yu D, Li S, Tuerdimaimaiti M, Wu A, Zhang G. Short-Term Elevated CO2 or O3 Reduces Undamaged Rice Kernels, but Together They Have No Effect. Agronomy. 2023; 13(12):2981. https://doi.org/10.3390/agronomy13122981

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Long, Mengbi, Mikeleban Yunshanjiang, Dezhao Yu, Shenshen Li, Mairemu Tuerdimaimaiti, Aoqi Wu, and Guoyou Zhang. 2023. "Short-Term Elevated CO2 or O3 Reduces Undamaged Rice Kernels, but Together They Have No Effect" Agronomy 13, no. 12: 2981. https://doi.org/10.3390/agronomy13122981

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