Transcriptomic analysis of salt-tolerant and sensitive high-yield japonica rice (Oryza sativa L.) reveals complicated salt-tolerant mechanisms.

Developing and cultivating rice varieties is a potent strategy for reclaiming salinity-affected soils for rice production. Nevertheless, the molecular mechanisms conferring salt tolerance, especially in conventional high-yield japonica rice varieties, remain obscure. In this study, Zhendao 23309 (ZD23309) exhibited significantly less grain yield reduction under a salt stress gradient than the control variety Wuyunjing 30 (WYJ30). High positive correlations between grain yield and dry matter accumulation at the jointing, heading and maturity stages indicated that early salt tolerance performance is a crucial hallmark for yield formation. After a mild salt stress (85 mM NaCl) of young seedlings, RNA sequencing (RNA-seq) of shoot and root separately identified a total of 1952 and 3647 differentially expressed genes (DEGs) in ZD23309, and 2114 and 2711 DEGs in WYJ30, respectively. Gene ontology (GO) analysis revealed numerous DEGs in ZD23309 that play pivotal roles in strengthening salt tolerance, encompassing the response to stimulus (GO:0050896) in shoots and nucleoside binding (GO:0001882) in roots. Additionally, distinct expression patterns were observed in a fraction of genes in the two rice varieties under salt stress, corroborating the efficacy of previously reported salt tolerance genes. Our research not only offers fresh insights into the differences in salt stress tolerance among conventional high-yield rice varieties but also unveils the intricate nature of salt tolerance mechanisms. These findings lay a solid groundwork for deciphering the mechanisms underlying salt tolerance.

Simplified panicle fertilization is applicable to japonica cultivars, but splits are preferred in indica rice for a higher paddy yield under wheat straw return.

Introduction: The panicle fertilization strategy for japonica and indica rice under wheat straw return (SR) has not been updated, especially on the elaboration of their impacts on spikelet differentiation and degeneration. This study aimed to verify the hypothesis that SR increases spikelet number by reducing spikelet degeneration and to explore the possibility of simplifying panicle fertilization. Methods: In three consecutive years, four varieties of japonica and indica rice were field-grown in Yangzhou, Jiangsu Province, China. Six panicle fertilization rates and split treatments were applied to SR and no straw return (NR) conditions. Results: The results showed that SR promoted rice yield significantly by 3.77%, and the highest yields were obtained under the T2 (split panicle fertilization at the panicle initiation (PI) and spikelet primordium differentiation (SPD) stages) and T1 (panicle fertilization only at the PI stage) treatments, for indica and japonica rice, respectively. Correlation and path analysis revealed that the number of spikelets per panicle was the most attributable to yield variation. SR significantly increased the concentration of alkali hydrolyzable N in the soil 40 days after rice transplantation, significantly increased the nitrogen accumulation per stem (NA) during the SPD-pollen mother cell meiosis (PMC) stage, and increased the brassinosteroids level in the young panicles at the PMC stage. SR also reduced the degeneration rate of spikelets (DRS) and increased the number of surviving spikelets (NSS). The dry matter accumulation per stem was more important to increasing the NA in japonica rice at the PMC stage, whereas NA was more affected by the N content than the dry matter accumulation in indica rice. In japonica rice, panicle N application once only at the PI stage combined with the N released from SR was enough to improve the plant N content, reduce the DRS, and increase the NSS. For indica rice, split application of N panicle fertilization at both the PI and SPD stages was still necessary to achieve a maximum NSS. Discussion: In conclusion, under wheat SR practice, panicle fertilization could be simplified to once in japonica rice with a significant yield increase, whereas equal splits might still be optimal for indica rice.

Validation of Novel Reference Genes in Different Rice Plant Tissues through Mining RNA-Seq Datasets.

Reverse transcription quantitative real-time PCR (RT-qPCR) is arguably the most prevalent and accurate quantitative gene expression analysis. However, selection of reliable reference genes for RT-qPCR in rice (Oryza sativa) is still limited, especially for a specific tissue type or growth condition. In this study, we took the advantage of our RNA-seq datasets encompassing data from five rice varieties with diverse treatment conditions, identified 12 novel candidate reference genes, and conducted rigorous evaluations of their suitability across typical rice tissues. Comprehensive analysis of the leaves, shoots, and roots of two rice seedlings subjected to salt (30 mmol/L NaCl) and drought (air-dry) stresses have revealed that OsMED7, OsACT1, and OsOS-9 were the robust reference genes for leaf samples, while OsACT1, OsZOS3-23, and OsGDCP were recommended for shoots and OsMED7, OsOS-9, and OsGDCP were the most reliable reference genes for roots. Comparison results produced by different sets of reference genes revealed that all these newly recommended reference genes displayed less variation than previous commonly used references genes under the experiment conditions. Thus, selecting appropriate reference genes from RNA-seq datasets leads to identification of reference genes suitable for respective rice tissues under drought and salt stress. The findings offer valuable insights for refining the screening of candidate reference genes under diverse conditions through the RNA-seq database. This refinement serves to improve the accuracy of gene expression in rice under similar conditions.

Progress of Research on the Physiology and Molecular Regulation of Sorghum Growth under Salt Stress by Gibberellin.

Plant growth often encounters diverse abiotic stresses. As a global resource-based ecological problem, salinity is widely distributed and one of the major abiotic stresses affecting crop yields worldwide. Sorghum, a cereal crop with medium salt tolerance and great value for the development and utilization of salted soils, is an important source of food, brewing, energy, and forage production. However, in soils with high salt concentrations, sorghum experiences low emergence and suppressed metabolism. It has been demonstrated that the effects of salt stress on germination and seedling growth can be effectively mitigated to a certain extent by the exogenous amendment of hormonal gibberellin (GA). At present, most of the studies on sorghum salt tolerance at home and abroad focus on morphological and physiological levels, including the transcriptome analysis of the exogenous hormone on sorghum salt stress tolerance, the salt tolerance metabolism pathway, and the mining of key salt tolerance regulation genes. The high-throughput sequencing technology is increasingly widely used in the study of crop resistance, which is of great significance to the study of plant resistance gene excavation and mechanism. In this study, we aimed to review the effects of the exogenous hormone GA on leaf morphological traits of sorghum seedlings and further analyze the physiological response of sorghum seedling leaves and the regulation of sorghum growth and development. This review not only focuses on the role of GA but also explores the signal transduction pathways of GA and the performance of their responsive genes under salt stress, thus helping to further clarify the mechanism of regulating growth and production under salt stress. This will serve as a reference for the molecular discovery of key genes related to salt stress and the development of new sorghum varieties.

Elevated atmospheric CO2 concentration triggers redistribution of nitrogen to promote tillering in rice.

Elevated atmospheric CO2 concentration (eCO2) often reduces nitrogen (N) content in rice plants and stimulates tillering. However, there is a general consensus that reduced N would constrain rice tillering. To resolve this contradiction, we investigated N distribution and transcriptomic changes in different rice plant organs after subjecting them to eCO2 and different N application rates. Our results showed that eCO2 significantly promoted rice tillers (by 0.6, 1.1, 1.7, and 2.1 tillers/plant at 0, 75, 150, and 225 kg N ha-1 N application rates, respectively) and more tillers were produced under higher N application rates, confirming that N availability constrained tillering in the early stages of growth. Although N content declined in the leaves (-11.0 to -20.7 mg g-1) and sheaths (-9.8 to -28.8 mg g-1) of rice plants exposed to eCO2, the N content of newly emerged tillers on plants exposed to eCO2 equaled or exceeded the N content of tillers produced under ambient CO2 conditions. Apparently, the redistribution of N within the plant per se was a critical adaptation strategy to the eCO2 condition. Transcriptomic analysis revealed that eCO2 induced less extensive alteration of gene expression than did N application. Most importantly, the expression levels of multiple N-related transporters and receptors such as nitrate transporter NRT2.3a/b and NRT1.1a/b were differentially regulated in leaf and shoot apical meristem, suggesting that multiple genes were involved in sensing the N signal and transporting N metabolites to adapt to eCO2. The redistribution of N in different organs could be a universal adaptation strategy of terrestrial plants to eCO2.

Transcriptomic and Co-Expression Network Profiling of Shoot Apical Meristem Reveal Contrasting Response to Nitrogen Rate between Indica and Japonica Rice Subspecies.

Reducing nitrogen (N) input is a key measure to achieve a sustainable rice production in China, especially in Jiangsu Province. Tiller is the basis for achieving panicle number that plays as a major factor in the yield determination. In actual production, excessive N is often applied in order to produce enough tillers in the early stages. Understanding how N regulates tillering in rice plants is critical to generate an integrative management to reduce N use and reaching tiller number target. Aiming at this objective, we utilized RNA sequencing and weighted gene co-expression network analysis (WGCNA) to compare the transcriptomes surrounding the shoot apical meristem of indica (Yangdao6, YD6) and japonica (Nipponbare, NPB) rice subspecies. Our results showed that N rate influenced tiller number in a different pattern between the two varieties, with NPB being more sensitive to N enrichment, and YD6 being more tolerant to high N rate. Tiller number was positively related to N content in leaf, culm and root tissue, but negatively related to the soluble carbohydrate content, regardless of variety. Transcriptomic comparisons revealed that for YD6 when N rate enrichment from low (LN) to medium (MN), it caused 115 DEGs (LN vs. MN), from MN to high level (HN) triggered 162 DEGs (MN vs. HN), but direct comparison of low with high N rate showed a 511 DEGs (LN vs. HN). These numbers of DEG in NPB were 87 (LN vs. MN), 40 (MN vs. HN), and 148 (LN vs. HN). These differences indicate that continual N enrichment led to a bumpy change at the transcription level. For the reported sixty-five genes which affect tillering, thirty-six showed decent expression in SAM at tiller starting phase, among them only nineteen being significantly influenced by N level, and two genes showed significant interaction between N rate and variety. Gene ontology analysis revealed that the majority of the common DEGs are involved in general stress responses, stimulus responses, and hormonal signaling process. WGCNA network identified twenty-two co-expressing gene modules and ten candidate hubgenes for each module. Several genes associated with tillering and N rate fall on the related modules. These indicate that there are more genes participating in tillering regulation in response to N enrichment.

Global Transcriptome and Co-Expression Network Analysis Reveal Contrasting Response of Japonica and Indica Rice Cultivar to γ Radiation.

Japonica and indica are two important subspecies in cultivated Asian rice. Irradiation is a classical approach to induce mutations and create novel germplasm. However, little is known about the differential response between japonica and indica rice after γ radiation. Here, we utilized the RNA sequencing and Weighted Gene Co-expression Network Analysis (WGCNA) to compare the transcriptome differences between japonica Nipponbare (NPB) and indica Yangdao6 (YD6) in response to irradiation. Japonica subspecies are more sensitive to irradiation than the indica subspecies. Indica showed a higher seedling survival rate than japonica. Irradiation caused more extensive DNA damage in shoots than in roots, and the severity was higher in NPB than in YD6. GO and KEGG pathway analyses indicate that the core genes related to DNA repair and replication and cell proliferation are similarly regulated between the varieties, however the universal stress responsive genes show contrasting differential response patterns in japonica and indica. WGCNA identifies 37 co-expressing gene modules and ten candidate hub genes for each module. This provides novel evidence indicating that certain peripheral pathways may dominate the molecular networks in irradiation survival and suggests more potential target genes in breeding for universal stress tolerance in rice.

Identification of QTL Associated with Nitrogen Uptake and Nitrogen Use Efficiency Using High Throughput Genotyped CSSLs in Rice (Oryza sativa L.).

Nitrogen (N) availability is a major factor limiting crop growth and development. Identification of quantitative trait loci (QTL) for N uptake (NUP) and N use efficiency (NUE) can provide useful information regarding the genetic basis of these traits and their associated effects on yield production. In this study, a set of high throughput genotyped chromosome segment substitution lines (CSSLs) derived from a cross between recipient 9311 and donor Nipponbare were used to identify QTL for rice NUP and NUE. Using high throughput sequencing, each CSSL were genotyped and an ultra-high-quality physical map was constructed. A total of 13 QTL, seven for NUP and six for NUE, were identified in plants under hydroponic culture with all nutrients supplied in sufficient quantities. The proportion of phenotypic variation explained by these QTL for NUP and NUE ranged from 3.16-13.99% and 3.76-12.34%, respectively. We also identified several QTL for biomass yield (BY) and grain yield (GY), which were responsible for 3.21-45.54% and 6.28-7.31%, respectively, of observed phenotypic variation. GY were significantly positively correlated with NUP and NUE, with NUP more closely correlated than NUE. Our results contribute information to NUP and NUE improvement in rice.

Correction: Mapping Quantitative Trait Loci Associated with Toot Traits Using Sequencing-Based Genotyping Chromosome Segment Substitution Lines Derived from 9311 and Nipponbare in Rice (Oryza sativa L.).

[This corrects the article DOI: 10.1371/journal.pone.0151796.].

Mapping Quantitative Trait Loci Associated with Toot Traits Using Sequencing-Based Genotyping Chromosome Segment Substitution Lines Derived from 9311 and Nipponbare in Rice (Oryza sativa L.).

Identification of quantitative trait loci (QTLs) associated with rice root morphology provides useful information for avoiding drought stress and maintaining yield production under the irrigation condition. In this study, a set of chromosome segment substitution lines derived from 9311 as the recipient and Nipponbare as donor, were used to analysis root morphology. By combining the resequencing-based bin-map with a multiple linear regression analysis, QTL identification was conducted on root number (RN), total root length (TRL), root dry weight (RDW), maximum root length (MRL), root thickness (RTH), total absorption area (TAA) and root vitality (RV), using the CSSL population grown under hydroponic conditions. A total of thirty-eight QTLs were identified: six for TRL, six for RDW, eight for the MRL, four for RTH, seven for RN, two for TAA, and five for RV. Phenotypic effect variance explained by these QTLs ranged from 2.23% to 37.08%, and four single QTLs had more than 10% phenotypic explanations on three root traits. We also detected the correlations between grain yield (GY) and root traits, and found that TRL, RTH and MRL had significantly positive correlations with GY. However, TRL, RDW and MRL had significantly positive correlations with biomass yield (BY). Several QTLs identified in our population were co-localized with some loci for grain yield or biomass. This information may be immediately exploited for improving rice water and fertilizer use efficiency for molecular breeding of root system architectures.

[Effects of free-air CO2 enrichment on nitrogen uptake and utilization of wheat].

In this paper, the effects of free-air CO2 enrichment (FACE) and its interaction with nitrogen supply on the nitrogen content, uptake, allocation, and use efficiency of winter wheat variety Ningmai 9 at its different growth stages were studied in 2001-2003. The results showed that under FACE treatment, the nitrogen content in wheat plant sampled at different growth stages all decreased significantly, with an average decrement of 4.4% to 13.4% compared with the control. The nitrogen accumulation under FACE increased significantly (9.2% -32.3%), and the increasing rate was larger at middle growth stage than at early and late growth stages. Nitrogen fraction was higher in stem, but lower in leaf. As for spike, the accumulation of nitrogen depended on the growth stage. FACE resulted in a significant increase (5.5% -10.3%) of nitrogen use efficiency for biomass production at all growth stages, of nitrogen harvest index (16.3%) at maturing stage, and of nitrogen use efficiency (9.3%) for grain yield. Nitrogen application increased the nitrogen content of wheat plant and its N uptake at all growth stages, decreased the nitrogen use efficiency, but had less effect on the nitrogen allocation in different organs.

[Effects of free-air CO2 enrichment (FACE) on yield formation of wheat].

To investigate the effects of predicted higher CO2 levels on the growth duration, plant height, yield, and yield components of wheat (Triticum aestivum L.), a free-air CO2 enrichment (FACE) experiment with weak gluten variety Ningmai 9 was conducted at Anzhen of Wuxi in Jiangsu Province in 2001-2002 and 2002-2003 growth seasons. The target [CO2] in FACE plots was 200 microl x L(-1) above that in ambient air. Three levels of N were supplied, i.e., 90 kg x hm(-2) (2001-2002) and 125 kg x hm(-2)(2002-2003) (low level, LN), 180 kg x hm(-2) 2002-2003) (medium level, MN), and 250 kg x hm(-2)(high level, HN). The durations from sowing to heading and from heading to maturity and the whole growth period of wheat in FACE plots shortened 1.3 , 1.3 and 2.6 days, respectively, compared with the control. FACE increased the plant height (+4.0% significantly, due to the increases of panicle length and of the first and second internode lengths. FACE also greatly increased the grain yield by an average of 24.6%. Across the two years, there was a positive [CO2] x N interaction for grain yield, with a yield increase of 15.2%, 21.4% and 35.4% at LN, MN and HN, respectively. The ears per square meter in FACE plots was increased by an average of 17.8% mainly due to the increase of maximum tiller number per unit ground area rather than that of the percentage of productive tiller (panicle bearing). In addition, FACE increased the grain number per ear (+2.9% and the individual grain mass (+4.8%).

[Effects of free-air CO2 enrichment (FACE) on dry matter production and allocation in wheat].

A free-air CO2 enrichment (FACE) experiment was conducted in 2001-2003 to study the effects of predicted higher CO2 levels on the dry matter (DM) production and allocation in winter wheat variety Ningmai 9. The results showed that under FACE, the DM production had an increase of 10. 8% , 31. 6% , 40. 5% and 27. 2% during the growth periods from sowing to wintering ( Period 1 ) , wintering to jointing ( Period 2) , jointing to booting ( Period 3) , and booting to heading (Period 4) , respectively, but a decrease of 5. 5% in the period from heading to grain maturity (Period 5). As a result, the final total biomass at maturity was increased by 13. 6%. FACE had no significant effect on leaf area index (LAI) and net assimilation rate (NAR) in Period 1, but made the LAI in Period 2 increased obviously, and the NAR decreased dramatically in Period 3. Under FACE, the proportion of leaf to total above-ground DM decreased, while that of stem (including sheath) to total above-ground DM showed an opposite trend in the whole growth period. The percentage and total amount of soluble sugar and starch in the stem at grain-filling stage were also increased obviously under FACE.

[Dynamic model of rice tiller in FACE].

With Japonica cultivar Wuxiangjing 14 as test material, a free-air CO2 enrichment (FACE) experiment was conducted at Anzhen and Wuxi of Jiangsu Province in 2001 to approximately 2003. The target CO2 concentration of FACE plots was 570 micromol x mol(-1), 200 micromol x mol(-1) higher than that of ambient air. Three levels of N were supplied as LN (150 kg x hm(-2)), MN (250 kg x hm(-2)) and HN (350 kg x hm(-2)). The effects of FACE treatment on the dynamics of rice tiller was studied, and the simulation model was established as Tt = ((A1/1 + e(a1-b1t)) - (A2/1 + e(a2-b2t)) + C) x ((B1/(1 + e(a3-b3t) - (B2/1 + e(a4-b4t))+D) Where Tt was the numbers of rice tiller in t days after transplanting; A1 and A2 were the maximal tillers of production and death under ambient air, respectively; B1 and B2 were the maximal potential tillers of production and death under FACE, respectively; C was the coefficient of CO2 concentration; D was the initial tillers after transplanting; and a1, a2, a3, a4, b1, b2, b3 and b4 were the control coefficients of the model. The dynamics of tiller numbers with the days after transplanting was described, and the model fitted well under ambient air and FACE conditions. Through testing with different year experimental data, the maximum and minimum RMSE was forecasted as 44.27 and 13.96 ind x m(-2), respectively, suggesting that the model was accurate and applicable.

Toxicity of copper on rice growth and accumulation of copper in rice grain in copper contaminated soil.

Pot soil experiments showed that copper (Cu) is highly toxic to rice. Rice grain yields decreased exponentially and significantly with the increase of soil Cu levels. Rice grain yield was reduced about 10% by soil Cu level of 100 mg kg(-1), about 50% by soil Cu level of 300-500 mg kg(-1) and about 90% by soil Cu concentration of 1,000 mg kg(-1). Root was more sensitive to soil Cu toxicity than other parts of rice plant at relatively lower soil Cu levels (less than 300-500 mg kg(-1)), but the growth of whole rice plant was severely inhibited at high soil Cu levels (300-500 mg kg(-1) or above). Cu concentrations in rice grain increased with soil Cu levels below 150-200 mg kg(-1), but decreased with soil Cu levels above 150-200 mg kg(-1), with peak Cu concentration at soil Cu level of 150-20 mg kg(-1). Cu was not distributed evenly in different parts of rice grain. Cu concentration in cortex (embryo) was more than 2-fold that in chaff and polished rice. More than 60% of the Cu in grain was accumulated in polished rice, about 24% in cortex (embryo), and about 12% in chaff. So, about 1/3 of the Cu in rice grain was eliminated after grain processing (chaff, cortex and embryo was removed).

[Dry matter accumulation and allocation models of rice in FACE].

A fertilization experiment with 150 kg N x hm(-2), 250 kg N xhm(-2) and 350 kg N x hm(-2) was conducted on the free-air CO2 enrichment (FACE) platform at Wuxi of Jiangsu Province in 2001-2003, aimed to build a simulation model of dry matter accumulation and allocation of rice in FACE. Physiological development time and CO2 concentration were selected as the driving factor and the main affecting factor, respectively, and nitrogen application rate was introduced as the factor adjusting the dry matter accumulation and allocation in green leaf, stem and panicle. The results showed that with the increase of atmospheric CO2 concentration, the dry matter accumulation in above-ground part of rice increased remarkably, but the allocation index dropped in green leaf, changed little in panicle, while increased in stem at early stage and equaled to the CK at last. The model was tested with different experimental data, and the results indicated that the model had high fitting degree and preferable applicability and predictability.

[Effects of free-air CO2 enrichment (FACE) on phosphorus nutrition of Oryza sativa at its different growth stages].

Using free-air CO2 enrichment (FACE) platform and under different nitrogen supply level, this paper studied the phosphorus nutrition of Oryza sativa at its different growth stages. The CO2 concentration of FACE platform was 200 micromol.mol(-1) more than that in ambient air, and the nitrogen supply levels were 150 kg.hm(-2), 250 kg.hm(-2) and 280 kg.hm(-2). The results showed that during rice growth period, FACE significantly increased the phosphorus content of rice plant and its phosphorus uptake by 3.9%-20.6% and 28.9%-71.4%, respectively. Before heading, FACE had little effect on the phosphorous accumulation in leaf or stake, but after heading, made the proportion of phosphorus accumulation in reproductive organ decreased by 9.8%-26.3% and that in vegetative organ increased by 2.2%-23.9% at 0.01 or 0.05 significant level. Under FACE treatment, the phosphorus use efficiency for biomass production (PUEp) at different growth stages, the phosphorus use efficiency for grain output (PUEg), and the phosphorus harvest index (PHI) were decreased by 3.7%-16.6%, 6.5% -15.5%, 5.4%-9.0%, respectively. Nitrogen supply level and its interaction with FACE had less effect on the phosphorus-nutrition of rice at its different growth stages.

[Response of rice grain quality traits to free-air CO2 enrichment].

The study showed that under field condition, when the CO2 concentration was elevated 200 micromol x mol(-1) above control, the average brown rice rate of japonica variety Wuxiangjing 14 was 1.4% higher, while lead milled rice rate was 12.3% lower than control. The brown rice rate increased at lower nitrogen supply level (LN), while lead milled rice rate increased at higher nitrogen supply level (HN). The percentage of chalky grain was 11.9% higher, and chalkiness degree was 2.8% higher than control, but no obvious difference was found in chalkiness area between the FACE and the control. The chalkiness area, percentage of chalky grain and chalkiness degree decreased at HN plus higher phosphorus supply level (HP). The gelatinization temperature was elevated 0.52 degrees C, gel consistency increased, while amylose content was not statistically significant. The amylose content decreased at HN plus HP, while gel consistency and gelatinization temperature decreased at LN plus HP and at LN, respectively. The protein content was decreased 0.6% under FACE treatment and at LN plus lower phosphorus supply level.

[Effect of free-air CO2 enrichment on biomass accumulation and distribution in rice].

Investigation on the effect of free-air CO2 enrichment (FACE) on biomass accumulation and distribution in different parts of rice plant treated with 200 mumol.mol-1 CO2 elevation under field condition showed that the dry matter accumulated from transplanting to 20th day after heading and the total biomass increased significantly, while the dry mater accumulated from 20th day after heading to maturity was significantly depressed under FACE treatment. The enhancement of both leaf area index (LAI) and net assimilation rate (NAR) under FACE treatment resulted in the increase of dry matter accumulated from transplanting to heading, while the dominant reason for the increase of dry matter accumulated during 20 days after heading was the slowed decline of LAI. The decline of dry matter accumulated from 20th day to maturity was mainly caused by the decrease of NAR. The percentage of dry matter distributed in stem and sheath increased under FACE treatment, while that in leaf decreased, and that in panicle showed no significant change. The content (%) and amount of soluble sugar and starch in stem and sheath at heading was significantly elevated under FACE. The grain yield of rice under FACE treatment could be significantly improved by raising biomass.

[Effects of free-air CO2 enrichment (FACE) on yield formation in rice (Oryza sativa)].

Effect of Free-Air CO2 enrichment (FACE, 200 mumol.mol-1 higher than CK) on rice yield and its components under field condition were studied with a Japonica variety 99-15. Results showed that FACE treatment had no obvious effect on plant height and number of leaves on main stem, but could quicken growth process of rice, shorten the whole growth duration. Increment of nitrogen application rate could weaken the effect of FACE on whole growth duration. The number of tillers and panicles, and fulfilled-grain percentage increased significantly under FACE treatment, whereas spikelets per panicle decreased. FACE treatment could significantly increase grain yield of rice, especially when higher rate of nitrogen fertilizer was applied. Increasing spikelets per panicle and spikelets per unit area under FACE treatment would result in marked increment of rice yield. Increasing nitrogen application rate was an important approach to increase spikelets per panicle and spikelets per unit area under FACE treatment.