Elevated CO₂ increases rice yields, and the response level varies across locations and genotypes. Previous analyses of genotypic variations from diverse Free-Air CO₂ Enrichment (FACE) studies lacked specificity, limiting their applicability in simulating the responses of crop growth to elevated CO₂. Using meta-analysis approach and the ORYZA (v3) model with historical and projected climatic data, this study evaluated the differences in the responses of rice ecotypes to elevated CO₂ and identified adaptive measures. Meta-analytical findings indicated that Chinese inbred indica (indica_i) and hybrid indica (indica_h) rice exhibited comparable yield response rates (28.4% and 31.1%, respectively) to elevated CO₂, surpassing those of Chinese japonica rice and Japanese indica_i and japonica rice. Achieving higher adaptation to elevated CO₂, exemplified by Chinese indica_h rice, necessitates the consideration of balanced yield components, with individual contributions to yield responses ranging from 9.8% to 36.2%. This study highlighted the susceptibility of japonica rice to adverse effects of maximum temperatures on yield component responses to elevated CO₂ compared to indica_i or indica_h rice. Strategic adjustments in sowing dates can enhance rice production under climate change, with high-response genotypes benefiting more from optimal sowing periods. Furthermore, for genotypes with less responsiveness to elevated CO₂, augmenting nitrogen application in conjunction with sowing date adjustments was beneficial for yield optimization. This research not only advances our understanding of the diverse adaptation strategies of rice genotypes under varying climatic conditions but also enhances the precision of crop growth simulations by accounting for the varied responses to CO₂ enrichment. These insights are pivotal for developing targeted breeding and management practices aimed at enhancing climate resilience in rice production.

Photosynthetic adaptations to light fluctuations do not occur instantaneously, leading to reduced carbon gain and lower productivity in agricultural crops. Enhancing the rapidity of photosynthetic responses to these fluctuations could potentially increase carbon assimilation by 13-32%, indicating a substantial opportunity for yield improvement of major crops. Most crops can be categorized into C₃ or C₄ crops by their photosynthetic pathways. This review provides a comparative overview of the photosynthetic responses of both C₃ and C₄ crops to light fluctuations, highlighting the unique and shared challenges for these two photosynthetic pathways. In C₃ crops, fast adjustments in non-photochemical quenching, stomatal and mesophyll conductance, and Rubisco activation are essential for optimizing photosynthesis under variable light conditions. In contrast, C₄ crops, including maize, sorghum, and sugarcane, benefit from their carbon concentration mechanism under high light conditions but face challenges in coordinating the C₄ and Calvin-Benson-Bassham cycles. Strategies to enhance the activation of pyruvate phosphate dikinase and Rubisco, as well as to improve electron transport capacity and flexibility, could markedly boost the photosynthetic efficiency and productivity. Through a detailed understanding of the distinct mechanisms involved in C₃ and C₄ photosynthesis, this review underscores the need for tailored strategies to optimize the photosynthetic efficiency specific to each crop type. Exploring and leveraging these differences is crucial for propelling agricultural productivity forward.

Climate warming affects rice seed vigor during ripening, which plays a crucial role in seed quality. However, the actual response of rice seed vigor to warming is still unclear. In this study, seeds after warming treatment in a double rice cropping system were used to determine seed vigor and related physiological traits during germination. Warming treatment significantly improved the germination index (GI), seed vigor index (VI), and seedling dry weight (SDW) for the late-season rice seeds but had no effect on hull thickness, grain weight, and starch and protein contents for both early- and late-season rice seeds, and these parameters were highly associated with germination rate, GI, VI, and SDW. Warming treatment increased gibberellin (GA) content and α-amylase and β-amylase activities in endosperm and coleoptile in both seasons during the later stage of germination, reaching a significant level on the 7^th d. Moreover, indole-3-acetic acid (IAA) content was consistently increased in the coleoptile but decreased in the endosperm in response to warming, and warming did not affect zeatin content. These results suggest that future global warming will improve rice seed vigor by regulating the synthesis of endogenous hormones and amylases, especially in the late-season rice.

Photorespiration begins with the oxygenation reaction catalyzed by 1,5-bisphosphate carboxylase/oxygenase (Rubisco) and serves as a repair pathway for carbon retrieval by converting 2-phosphoglycolate to 3-phosphogly-cerate allowing plants to thrive in an oxygen-rich environment. Photorespiration metabolism is intimately linked to plant primary metabolism, particularly carbon and nitrogen assimilation, and cellular redox equilibrium, and such interactions are dynamically regulated by environmental changes. Although the basic genetics and biochemistry of photorespiration have been well characterized, it is still essential to further improve our understanding of the regulatory mechanisms of photorespiration and the roles in responding to changing environments, which are required for the future genetic manipulation of photorespiration. Here, we summarize recent progress regarding the evolutionary aspects of photorespiration and its multifaceted regulation, highlighting its intricate interactions with environmental CO₂, light, and nitrogen nutrition. This review provides a comprehensive perspective on the functional implications of photorespiration for plants to adapt to the environment and opens new avenues for our in-depth exploration of photorespiration to develop better strategies to enhance plant productivity and adaptability in the face of changing environmental conditions.

Compared with high-stubble ratoon rice (RR), low-stubble RR is superior in yield potential, grain quality, and economic benefit. However, the unstable ratooning ability limits the grain yield of low-stubble RR production. Light condition during the grain-filling stage of main crop (GFMC) may be important for rice ratooning. To elucidate the role of light condition during GFMC in affecting ratooning ability, the key response periods, and their underlying mechanisms, field experiments were conducted using two indica cultivars in 2021 and 2022. To create varied light conditions at the canopy base during GFMC, two planting density treatments combining three nitrogen (N) treatments were established in 2021, and three density treatments combining two N treatments and four shading treatments were established in 2022 for the main crop. Light intensity (LI), light quality as reflected by the ratio of red light/far red light (R/FR), and light transmission ratio (LTR) at the canopy base during GFMC, and ratooning ability were dramatically altered by N fertilization but not by planting density. With increased N application, LTR, root bleeding rate, and maximum ratooning rate significantly decreased in 2021. In 2022, low N rate increased LI, R/FR, and maximum ratooning rate by 155.7-241.4%, 47.4-65.3%, and 15.6-27.5%, respectively, but reduced missing hill percentage (proportion of hills without regenerated tillers to the total number of hills) by 30.0-62.1% compared with high N rate. The missing hill percentage was negatively correlated with the indices of light condition, while the maximum ratooning rate was positively correlated with them for both cultivars. Root activity and the ratios of abscisic acid (ABA) to cytokinins (CTK), indole-3-acetic acid (IAA), and IAA + CTK could explain the effect of light condition during GFMC on ratooning ability. Shading experiment confirmed the effect of light condition on ratooning ability and further revealed that only shading during middle and late GFMC affected ratooning ability. These findings provide new insights into the regulation of ratooning ability, which are useful for developing management practices to increase the grain yield and yield stability of low-stubble RR.

The application of polymer-coated urea (PCU) to crops is likely restricted because the product's capsules cause plastic pollution. Although conventional fertilizer use reduces plastic pollution, it may increase nitrogen (N) pollution owing to its lower N recovery than that of PCU. Therefore, we need to develop optimal N application methods to reduce both plastic and N pollution. Here, we aimed to (1) compare the agronomic, economic, and environmental outcomes of PCU application with those of conventional urea application and (2) provide quantitative targets for developing alternatives to PCU application in dry direct-seeded rice production. We developed a model incorporating yield, brown-rice protein content, farmer profit, and environmental damage cost due to N and polymer losses according to N fertilizer application. Data were collected from field experiments at a farm in Iwate, Japan from 2020 to 2022. The average apparent N recovery was 0.43 for PCU and 0.37 for conventional urea. Despite the plastic damage cost, the estimated total environmental cost of PCU was lower than that of normal urea owing to the former's higher N recovery. However, our ability to simulate plastic pollution is limited, as few of the environmental effects of microplastics are understood. If new N application methods with N recovery above 0.5 are developed, an N fertilization cost within $5 × 10⁻³ g⁻¹ N can maintain the same benefit as that obtained in the current simulation. This model can be used to evaluate the quantitative relationships among N recovery, benefits, and implementation costs of each candidate N application method.