豆科作物轮作强化农田生态系统功能的研究进展

集约化农业对保障国家粮食安全至关重要,但其导致的生态环境代价与绿色可持续发展之间的矛盾日益突出。引入豆科作物到农田生态系统对于实现地力保育、作物丰产稳产和资源优化利用等多目标协同具有重要意义。本文系统总结了豆科作物轮作对作物生产和土壤功能的主要影响:1)豆科作物通过生物固氮、高质量的根际分泌物输入、秸秆还田等过程改善了土壤氮素水平,产生正向的残留效应,有利于后茬作物增产,且增产效应在低产区更显著;2)豆科作物轮作可以通过氮肥减施降低系统N_(2)O排放,但豆科的生物固氮过程有增加CO_(2)排放的风险;3)低C/N、高氮含量的豆科秸秆还田能够提高土壤微生物活性和残体积累,提高土壤固碳效率,但其固碳效应也受到较低的秸秆生物量投入限制;4)豆科作物可以提高后茬作物的水肥利用效率,同时利用前后茬作物根系深浅合理搭配,实现轮作周年水肥高效利用。因此,将豆科作物引入到轮作系统可实现氮肥减施和增产,但其产生的土壤固碳和温室气体减排效应受到作物种类、肥料投入、土壤和气候条件等多种因素的综合影响。为更好地发挥豆科作物轮作优势,应深入探究豆科促进后茬作物增产和驱动地下部生态功能提升的耦合机制,开发豆科作物轮作配套田间管理技术,并定向设计适合我国典型生态区的新型生态高效种植体系,对推动豆科作物轮作模式构建与应用及农业绿色发展具有重要理论意义和实践价值。

“现代作物学-栽培耕作与生理”全英文课程建设实践及建议

全英文课程是“双一流”建设的重要组成部分,我国作物学全英文课程建设比较滞后。中国农业大学率先借鉴国际一流大学全英文课程建设经验,开设了全英文课程“现代作物学-栽培耕作与生理”,搭建了高水平外教团队+国内高水平教学团队的双教学团队模式,构建了以学术报告+案例教学+Journal Club研讨+课堂练习+课程报告为主线的参与式教学方法,取得了较好的成效。系统总结“现代作物学-栽培耕作与生理”课程建设经验和成效,提出了未来进一步完善我国作物学全英文课程建设的建议。

Effects of Nitrogen Application on Chlorophyll Fluorescence Parameters and Leaf Gas Exchange in Naked Oat

Naked oat（Avena nuda L.） was originated from China,where soil nitrogen（N） is low availability.The responses of chlorophyll（Chl.） fluorescence parameters and leaf gas exchange to N application were analysed in this study.After the N application rate ranged from 60 to 120 kg ha-1,variable fluorescence（F v）,the maximal fluorescence（F m）,the maximal photochemical efficiency（F v /F m）,quantum yield（Φ PS II） of the photosynthetic system II（PS II）,electron transport rate（ETR）,and photochemical quenching coefficient（qP） increased with N application level,however,non-photochemical quenching coefficient（qN） decreased.Moreover,there was no difference in initial fluorescence（F o） with further more N enhancement.The maximum net photosynthetic rate（P max）,apparent dark respiration rate（R d） and light saturation point（LSP） were improved with 40-56 kg N ha-1as basal fertilizer and 24-40 kg N ha-1as top dressing fertilizer applied at jointing stage.Initial quantum yield（α） was decreased with 24 kg N ha-1as basal fertilizer and 56 kg N ha-1as top dressing fertilizer.Flag-leaf net photosynthetic rate（P n） was significantly enhanced at the jointing and heading stages with 40-56 kg N ha-1as basal fertilizer; in addition,increased at grain filling stage of naked oat with 40-56 kg N ha-1as top dressing fertilizer.90 kg N ha-1（50-70% as basal fertilizer and 30-50% as top dressing fertilizer） application is recommended to alleviate photodamage of photosystem and improve the photosynthetic rate in naked oat.

Estimates on nitrogen uptake in the subsequent wheat by aboveground and root residue and rhizodeposition of using peanut labeled with^(15)N isotope on the North China Plain

Leguminous crops play a vital role in enhancing crop yield and improving soil fertility. Therefore, it can be used as an organic N source for improving soil fertility. The purpose of this study was to(i) quantify the amounts of N derived from rhizodeposition, root and above-ground biomass of peanut residue in comparison with wheat and(ii) estimate the effect of the residual N on the wheat-growing season in the subsequent year. The plants of peanut and wheat were stem fed with 15 N urea using the cotton-wick method at the Wuqiao Station of China Agricultural University in 2014. The experiment consisted of four residue-returning strategies in a randomized complete-block design:(i) no return of crop residue(CR0);(ii) return of above-ground biomass of peanut crop(CR1);(iii) return of peanut root biomass(CR2); and(iv) return of all residue of the whole peanut plant(CR3). The 31.5 and 21% of the labeled 15 N isotope were accumulated in the above-ground tissues(leaves and stems) of peanuts and wheat, respectively. N rhizodeposition of peanuts and wheat accounted for 14.91 and 3.61% of the BG15 N, respectively. The 15 N from the below-ground 15 N-labeled of peanuts were supplied 11.3, 5.9, 13.5, and 6.1% of in the CR0, CR1, CR2, and CR3 treatments, respectively. Peanut straw contributes a significant proportion of N to the soil through the decomposition of plant residues and N rhizodeposition. With the current production level on the NCP, it is estimated that peanut straw can potentially replace 104 500 tons of synthetic N fertilizer per year. The inclusion of peanut in rotation with cereal can significantly reduce the use of N fertilizer and enhance the system sustainability.

Effects of different LEDs light spectrum on the growth,leaf anatomy,and chloroplast ultrastructure of potato plantlets in vitro and minituber production after transplanting in the greenhouse

Light spectrum plays an important role in regulating the growth and development of in vitro cultured potato(Solanum tuberosum L.) plantlets. The status of potato plantlets at the end of in vitro stage influences the minituber production after transplanting. With 100 μmol m^-2s^-1 total photosynthetic photon flux density(PPFD), a light spectrum study of 100% red light emitting diodes(LEDs) light spectrum(RR), 100% blue LEDs light spectrum(BB), 65% red+35% blue LEDs light spectrum(RB), and 45% red+35% blue+20% green LEDs light spectrum(RBG) providing illumination at the in vitro cultured stage of potato plantlets for 4 weeks using fluorescent lamp as control(CK) was performed to investigate the effects of LEDs light spectrum on the growth, leaf anatomy, and chloroplast ultrastructure of potato plantlets in vitro as well as the minituber yield after 2 months transplanting in the greenhouse. Compared to CK, RB and RBG promoted the growth of potato plantlets in vitro with increased stem diameter, plantlet fresh weight, plantlet dry weight, and health index. Furthermore, BB induced the greatest stem diameter as well as the highest health index in potato plantlets in vitro. Root activity, soluble protein, and free amino acid were also significantly enhanced by BB, whereas carbohydrates were improved by RR. In addition, thickness of leaf, palisade parenchyma and spongy parenchyma was significantly increased by BB and RBG. Chloroplasts under BB and RBG showed well-developed grana thylakoid and stroma thylakoid. Unexpectedly, distinct upper epidermis with greatest thickness was induced and palisade parenchyma and spongy parenchyma were arranged neatly in RR. After transplanting in the greenhouse for 2 months, potato plantlets in vitro from BB, RB, and RBG produced high percentage of large size tuber. BB improved fresh and dry weights of the biggest tuber but decreased tuber number per plantlet. In addition, RBG increased tuber number as well as tuber fresh and dry weight slightly. Our results suggested monochromatic blue LEDs as well as combined red, blue or/and green LEDs light spectrum were superior to fluorescent lamp spectrum in micro-propagation of potato plantlets. Therefore, the application of RBG was suitable;BB and RB could be used as alternatives.

Non-leguminous winter cover crop and nitrogen rate in relation to double rice grain yield and nitrogen uptake in Dongting Lake Plain, Hunan Province, China

Annual ryegrass（Lolium multiflorum Lam.）, a non-leguminous winter cover crop, has been adopted to absorb soil native N to minimize N loss from an intensive double rice cropping system in southern China, but a little is known about its effects on rice grain yield and rice N use efficiency. In this study, effects of ryegrass on double rice yield, N uptake and use efficiency were measured under different fertilizer N rates. A 3-year（2009–2011） field experiment arranged in a split-plot design was undertaken. Main plots were ryegrass（RG） as a winter cover crop and winter fallow（WF） without weed. Subplots were three N treatments for each rice season： 0（N_0）, 100（N_（100）） and 200 kg N ha–1（N_（200））. In the 3-year experiment, RG reduced grain yield and plant N uptake for early rice（0.4–1.7 t ha–1 for grain yield and 4.6–20.3 kg ha–1 for N uptake） and double rice（0.6–2.0 t ha–1 for grain yield and 6.3–27.0 kg ha–1 for N uptake） when compared with WF among different N rates. Yield and N uptake decrease due to RG was smaller in N_（100） and N_（200） plots than in N_0 plots. The reduction in early rice grain yield in RG plots was associated with decrease number of panicles. Agronomic N use efficiency and fertilizer N recovery efficiency were higher in RG plots than winter fallow for early rice and double rice among different N rates and experimental years. RG tended to have little effect on grain yield, N uptake, agronomic N use efficiency, and fertilizer N recovery efficiency in the late rice season. These results suggest that ryegrass may reduce grain yield while it improves rice N use efficiency in a double rice cropping system.

Transcriptome analysis reveals effects of red and blue lightemitting diodes(LEDs)on the growth,chlorophyll fluorescence and endogenous plant hormones of potato(Solanum tuberosum L.)plantlets cultured in vitro

Red and blue light illumination has been reported to significantly affect plantlet growth.Potato is an important food and feed crop in the world and potato plantlet cultured in vitro plays an important role in potato production.However,few studies have documented the effects of red and blue light on the growth of potato plantlets revealed at the transcriptome level.The objective of this study was to determine the growth and physiological responses of potato plantlets cultured in vitro under monochromatic red(RR),monochromatic blue(BB)as well as combined red and blue(RB)LEDs using the RNA-Seq technique.In total,3150 and 814 differentially expressed genes(DEGs)were detected in potato plantlets under RR and BB,respectively,compared to RB(used as control).Compared to the control,the DEGs enriched in"photosynthesis"and"photosynthesis-antenna proteins"metabolic pathways were up-regulated and down-regulated by BB and RR,respectively,which might be responsible for the increases and decreases of maximum quantum yield(F_(v)/F_(m)),photochemical quantum yield(φ_(PSII)),photochemical quenching(q_(P))and electron transfer rate(ETR)in BB and RR,respectively.Potato plantlets exhibited dwarfed stems and extended leaves under BB,whereas elongated stems and small leaves were induced under RR.These dramatically altered plantlet phenotypes were associated with variable levels of endogenous plant hormones gibberellin(GAs),indoleacetic acid(IAA)and cytokinins(CKs),as assessed in stems and leaves of potato plantlets.In addition,monochromatic red and blue LEDs trigged the opposite expression profiles of DEGs identified in the"plant hormone signal transduction"metabolic pathway,which were closely related to the endogenous plant hormone levels in potato plantlets.Our results provide insights into the responses of potato plantlets cultured in vitro to red and blue LEDs at the transcriptomic level and may contribute to improvements in the micro-propagation of potato plantlets cultured in vitro from the light spectrum aspect.

Screening of Highly Effective Sinorhizobium meliloti Strains for 'Vector' Alfalfa and Testing of Its Competitive Nodulation Ability in the Field

Seventeen Sinorhizobium meliloti strains from seven provinces in China were used to screen highly effective strains for alfalfa cultivar in a greenhouse study and their symbiotic relationship and competitive ability were studied in the field. CCBAU30138 was the most effective strain, as evidenced by increase in dry weights. A field experiment showed that the inoculation of alfalfa with CCBAU30138 resulted in increases of 11.9% and 19.6% of dry matter production and crude protein production, respectively, in forage of monocultured plants. The total dry matter yields of alfalfa and tall fescue in binary culture were increased by 16.3% by inoculation of alfalfa with this strain. These results showed that S. rneliloti strain CCBAU30138 was an effective inoculant both in the greenhouse and in the field. The analysis of randomly amplified polymorphic DNA （RAPD） by polymerase chain reaction （PCR） from nodule extracts showed that the strain CCBAU30138 had high competitiveness in the field. It occupied 47.5% of nodules in alfalfa monoculture and 44.4% of nodules in alfalfa-tall fescue binary culture after 20 weeks of growth. In conclusion, a simple system to select highly effective and competitive symbiotic strains specific to alfalfa was established. Using this system, a s.train suitable for the alfalfa cultivar ‘Vector＇ grown in Wuqiao County of Hebei Province was obtained.

Winter cover crops alter methanotrophs community structure in a double-rice paddy soil

Methanotrophs play a vital role in the mitigation of methane emission from soils. However, the influences of cover crops incorporation on paddy soil methanotrophic community structure have not been fully understood. In this study, the impacts of two winter cover crops（Chinese milk vetch（Astragalus sinicus L.） and ryegrass（Lolium multiflorum Lam.）, representing leguminous and non-leguminous cover crops, respectively） on community structure and abundance of methanotrophs were evaluated by using PCR-DGGE（polymerase chain reaction-denaturing gradient gel electrophoresis） and real-time PCR technology in a double-rice cropping system from South China. Four treatments were established in a completely randomized block design： 1） double-rice cropping without nitrogen fertilizer application, CK; 2） double-rice cropping with chemical nitrogen fertilizer application（200 kg ha^（–1） urea for entire double-rice season）, CF; 3） Chinese milk vetch cropping followed by double-rice cultivation with Chinese milk vetch incorporation, MV; 4） ryegrass cropping followed by double-rice cultivation with ryegrass incorporation, RG. Results showed that cultivating Chinese milk vetch and ryegrass in fallow season decreased soil bulk density and increased rice yield in different extents by comparison with CK. Additionally, methanotrophic bacterial abundance and community structure changed significantly with rice growth. Methanotrophic bacterial pmo A gene copies in four treatments were higher during late-rice season（3.18×10^7 to 10.28×10^7 copies g^–1 dry soil） by comparison with early-rice season（2.1×10^7 to 9.62×10^7 copies g^–1 dry soil）. Type Ⅰ methanotrophs absolutely predominated during early-rice season. However, the advantage of type Ⅰ methanotrophs kept narrowing during entire double-rice season and both types Ⅰ and Ⅱ methanotrophs dominated at later stage of late-rice.