Variation Characteristics of Root Traits of Different Alfalfa Cultivars under Saline-Alkaline Stress and their Relationship with Soil Environmental Factors

Soil salinization is the main factor that threatens the growth and development of plants and limits the increase of yield.It is of great significance to study the key soil environmental factors affecting plant root traits to reveal the adaptation strategies of plants to saline-alkaline-stressed soil environments.In this study,the root biomass,root morphological parameters and root mineral nutrient content of two alfalfa cultivars with different sensitivities to alkaline stress were analyzed with black soil as the control group and the mixed saline-alkaline soil with a ratio of 7:3 between black soil and saline-alkaline soil as the saline-alkaline treatment group.At the same time,the correlation analysis of soil salinity indexes,soil nutrient indexes and the activities of key enzymes involved in soil carbon,nitrogen and phosphorus cycles was carried out.The results showed that compared with the control group,the pH,EC,and urease(URE)of the soil surrounding the roots of two alfalfa cultivars were significantly increased,while soil total nitrogen(TN),total phosphorus(TP),organic carbon(SOC),andα-glucosidase activity(AGC)were significantly decreased under saline-alkaline stress.There was no significant difference in root biomass and root morphological parameters of saline-alkaline tolerant cultivar GN under saline-alkaline stress.The number of root tips(RT),root surface area(RS)and root volume(RV)of AG were reduced by 61.16%,44.54%,and 45.31%,respectively,compared with control group.The ratios of K^(+)/Na^(+),Ca^(2+)/Na^(+)and Mg^(2+)/Na^(+)of GN were significantly higher than those of AG(p<0.05).The root fresh weight(RFW)and dry weight(RDW),root length(RL),RV and RT of alfalfa were positively regulated by soil SOC and TN,but negatively regulated by soil pH,EC,and URE(p<0.01).Root Ca^(2+)/Na+ratio was significantly positively correlated with soil TN,TP and SOC(p<0.01).The absorption of Mg and Ca ions in roots is significantly negatively regulated by soilβ-glucosidase activity(BGC)and acid phosphatase activity(APC)(p<0.05).This study improved knowledge of the relationship between root traits and soil environmental factors and offered a theoretical framework for elucidating how plant roots adapt to saline-alkaline stressed soil environments.

QTL mapping of seedling biomass and root traits under different nitrogen conditions in bread wheat(Triticum aestivum L.)

Plant nitrogen assimilation and use efficiency in the seedling's root system are beneficial for adult plants in field condition for yield enhancement.Identification of the genetic basis between root traits and N uptake plays a crucial role in wheat breeding.In the present study,198 doubled haploid lines from the cross of Yangmai 16/Zhongmai 895 were used to identify quantitative trait loci(QTLs)underpinning four seedling biomass traits and five root system architecture(RSA)related traits.The plants were grown under hydroponic conditions with control,low and high N treatments(Ca(NO_(3))_(2)·4H_(2)O at 0,0.05 and 2.0 mmol L^(-1),respectively).Significant variations among the treatments and genotypes,and positive correlations between seedling biomass and RSA traits(r=0.20 to 0.98)were observed.Inclusive composite interval mapping based on a high-density map from the Wheat 660 K single nucleotide polymorphisms(SNP)array identified 51 QTLs from the three N treatments.Twelve new QTLs detected on chromosomes 1 AL(1)in the control,1 DS(2)in high N treatment,4 BL(5)in low and high N treatments,and 7 DS(3)and 7 DL(1)in low N treatments,are first reported in influencing the root and biomass related traits for N uptake.The most stable QTLs(RRS.caas-4 DS)on chromosome 4 DS,which were related to ratio of root to shoot dry weight trait,was in close proximity of the Rht-D1 gene,and it showed high phenotypic effects,explaining 13.1%of the phenotypic variance.Twenty-eight QTLs were clustered in 12 genetic regions.SNP markers tightly linked to two important QTLs clusters C10 and C11 on chromosomes 6 BL and 7 BL were converted to kompetitive allele-specific PCR(KASP)assays that underpin important traits in root development,including root dry weight,root surface area and shoot dry weight.These QTLs,clusters and KASP assays can greatly improve the efficiency of selection for root traits in wheat breeding programmes.

Quantitative trait loci analysis for root traits in synthetic hexaploid wheat under drought stress conditions

Synthetic hexaploid wheat(SHW),possesses numerous genes for drought that can help breeding for drought-tolerant wheat varieties.We evaluated 10 root traits at seedling stage in 111 F9 recombinant inbred lines derived from a F2 population of a SHW line(SHW-L1)and a common wheat line,under normal(NC)and polyethylene glycol-simulated drought stress conditions(DC).We mapped quantitative trait loci(QTLs)for root traits using an enriched high-density genetic map containing 120370 single nucleotide polymorphisms(SNPs),733 diversity arrays technology markers(DArT)and 119 simple sequence repeats(SSRs).With four replicates per treatment,we identified 19 QTLs for root traits under NC and DC,and 12 of them could be consistently detected with three or four replicates.Two novel QTLs for root fresh weight and root diameter under NC explained 9 and 15.7%of the phenotypic variation respectively,and six novel QTLs for root fresh weight,the ratio of root water loss,total root surface area,number of root tips,and number of root forks under DC explained 8.5–14%of the phenotypic variation.Here seven of eight novel QTLs could be consistently detected with more than three replicates.Results provide essential information for fine-mapping QTLs related to drought tolerance that will facilitate breeding drought-tolerant wheat cultivars.

Evaluation of root traits and water use efficiency of different cotton genotypes in the presence or absence of a soil-hardpan

Cotton(Gossypium spp.) is an important fiber and oil crop grown worldwide. Water and nutrient stresses are major issues affecting cotton production globally. Root traits are critical in improving water and nutrient uptake and maintaining plant productivity under optimal as well as drought conditions.However, root traits have rarely been utilized in cotton breeding programs, a major reason being the lack of information regarding genetic variability for root traits. The objective of this research was to evaluate ten selected cotton genotypes for root traits and water use efficiency. The tested genotypes included germplasm lines(PD 1 and PD 695) and cultivars that are currently grown in the southeastern USA(PHY 499 WRF, PHY 444 WRF, PHY 430 W3 FE, DP 1646 B2 XF, DP 1538 B2 XF, DP 1851 B3 XF, NG5007 B2 XF, and ST 5020 GLT). Experiments were conducted under controlled environmental conditions in 2018 and 2019. A hardpan treatment was included in the second year to evaluate the effect of a soil hardpan on root traits and water use efficiency. Genotype PHY 499 WRF ranked at the top and NG5007 B2 XF ranked at the bottom for root morphological traits(total and fine root length, surface area,and volume) and root weight. PHY 499 WRF was also one of the best biomass producers and had high water use efficiency. PHY 444 WRF, PHY 430 W3 FE, and PD-1 were the other best genotypes in terms of root traits and water use efficiency. All genotypes had higher values for root traits and water use efficiency under hardpan conditions. This trend indicates a horizontal proliferation of root systems when they incur a stress imposed by a hardpan. The genotypic differences identified in this research for root traits and water use efficiency would be valuable for selecting genotypes for cotton breeding programs.

Lodging Resistance Related to Root Traits for Mechanized Wet-Seeding of Two Super Rice Cultivars

Mechanical hill wet-seeded rice machine is beneficial for establishing and growing uniform rows of seedlings.However,there is limited knowledge regarding the effects of the establishment of furrows on growth,lodging and yield,and their relationships with root traits.In this study,field experiments were conducted during 2012 and 2013 using two super rice varieties(hybrid rice Peizataifeng and inbred rice Yuxiangyouzhan)under three furrow establishment treatments(T1,both water and seed furrows were established by the machine;T2,only seed furrows were established by the machine;and T3,neither water nor seed furrows were established by the machine).Lodging index,lodging-related traits,grain yield,above-ground dry weight and root traits were measured.The results showed that the lodging index was significantly affected by the treatments with furrows(T1 and T2).The strongest lodging resistance was detected in the mechanical hill wet-seeded rice with furrow treatment(T1)in both 2012 and 2013.Lodging resistance was strongly related to the breaking resistance.No significant difference was found in grain yield or dry weight of the mechanical hill wet-seeded rice.Therefore,the mechanical hill wet-seeded rice with furrow treatment increased rice lodging resistance,which was related to root traits.

Shear resistance characteristics and influencing factors of root-soil composite on an alpine metal mine dump slope with different recovery periods

Artificial vegetation restoration is the main measure for vegetation restoration and soil and water conservation in alpine mine dumps on the Qinghai-Tibet Plateau,China.However,there are few reports on the dynamic changes and the influencing factors of the soil reinforcement effect of plant species after artificial vegetation restoration under different recovery periods.We selected dump areas of the Delni Copper Mine in Qinghai Province,China to study the relationship between the shear strength and the peak displacement of the root-soil composite on the slope during the recovery period,and the influence of the root traits and soil physical properties on the shear resistance characteristics of the root-soil composite via in situ direct shear tests.The results indicate that the shear strength and peak displacement of the rooted soil initially decreased and then increased with the increase of the recovery period.The shear strength of the rooted soil and the recovery period exhibited a quadratic function relationship.There is no significant function relationship between the peak displacement and the recovery period.Significant positive correlations(P<0.05)exists between the shear strength of the root-soil composite and the root biomass density,root volume density,and root area ratio,and they show significant linear correlations(P<0.05).There are no significant correlations(P>0.05)between the shear strength of the root-soil composite and the root length density,and the root volume ratio of the coarse roots to the fine roots.A significant negative linear correlation(P<0.05)exists between the peak displacement of the rooted soil and the coarse-grain content,but no significant correlations(P>0.05)with the root traits,other soil physical property indices(the moisture content and dry density of the soil),and slope gradient.The coarse-grain content is the main factor controlling the peak displacement of the rooted soil.

Rhizosphere microbe populations but not root traits induced by drought in Populus euphratica males

How sex-related root traits and soil microbes and their interactions respond to drought remains unclear.Here,we investigated how fine root traits and the composition of rhizosphere microbial communities in Populus euphratica females and males respond to drought in concert in 17-year-old plantations.Females increased specific root length(SRL)in response to drought.However,males showed no changes in their roots but significant increases in arbuscular mycorrhizal hyphal biomass and population of Gram-negative bacteria in the rhizosphere.Also,fungal symbiotroph communities associated with root systems in males differed from those in females under drought.We further demonstrated that the Gram-positive to Gram-negative bacteria ratios positively correlated with the SRL,while fungi to bacteria ratios were negatively correlated.Meanwhile,the relative abundance of symbiotrophs was negatively correlated with the SRL,while saprotroph abundance was positively correlated.Nevertheless,the relative abundance of symbiotrophs was positively correlated with the root carbon content(RCC).These findings indicate that microbial responses to drought depend highly upon the sex of the plant and microbial group and are related to root trait adjustments to drought.This discovery also highlights the role of plant-microbial interactions in the ecosystems of P.euphratica forest plantations.

Tolerance to low phosphorus in rice varieties is conferred by regulation of root growth

Phosphorus use efficiency(PUE)can be improved through cultivation techniques and breeding.However,little is known about rice(Oryza sativa L.)agronomic and physiological traits associated with high PUE.We characterized the agronomic and physiological traits of rice varieties with different tolerances to low phosphorus in nutrient solution.Two varieties with strong tolerance to low phosphorus(STVs)and two with weak tolerance(WTVs)were grown at normal(NP,control)and low phosphorus(LP,1/20 of NP)concentrations.Plants grown at LP produced significantly lower grain yield than those grown at NP.WTVs yields were lower than STVs yields.Compared to NP,LP significantly increased phosphorus translocation efficiency(PTE),internal phosphorus efficiency(IPE)and phosphorus harvest index(PHI).Under the LP condition,PTE and IPE were higher for STVs than for WTVs.LP also reduced tiller number,shoot biomass,leaf area index(LAI),leaf photosynthetic rate,and mean root diameter of both kinds of varieties at the main growth stages,but to a lower extent in STVs.LP significantly increased the number of productive tillers,root biomass,root-shoot ratio,root bleeding rate,and root acid phosphatase(RAP)activity.Total root length,root oxidation activity(ROA),and root total and active absorbing surface areas for STVs were significantly increased under LP,whereas the opposite responses were observed for WTVs.Total root length,ROA,root bleeding rate,root active absorbing surface area,and RAP activity were positively and significantly correlated with grain yield,PTE,and IPE.These results suggest that the tolerance of rice varieties to a low-phosphorus growth condition is closely associated with root growth with higher biomass and activity.

Melatonin mitigates cold-induced damage to pepper seedlings by promoting redox homeostasis and regulating antioxidant profiling

This study assessed the influence of exogenous ME in the mitigation of cold damage in pepper seedlings. Melatonin(ME) is a dynamic molecule that helps plants cope with stress in several ways. Cold stress(CS) is one of the most important environmental factors that restrict plant growth and yield. Pepper(Capsicum annuum L.) is a valuable commercial crop, highly sensitive to CS. Thus, identifying an efficient strategy to mitigate cold damage is critical for long-term pepper production. For this purpose, the roots of pepper seedlings were pretreated with ME(5 μmol · L^(-1)) and exposed to CS for 7 d. The results indicated that CS suppressed pepper growth, hampered photosynthetic capacity, and damaged root architecture in pepper plants. In contrast, the production of reactive oxygen species(ROS), malondialdehyde(MDA), electrolyte leakage(EL), proline, and soluble sugars were enhanced in plants under CS. ME(5 μmol · L^(-1)) pretreatment reduced the negative effects of CS by recovering plant growth, root traits, gas exchange elements, and pigment molecules compared to CS control treatment. Furthermore, ME application efficiently reduced oxidative stress markers [hydrogen peroxide(H_(2)O_(2)), superoxide ion(O_(2)^(·-)), EL, and MDA] while increasing proline and soluble sugar content in pepper leaves. ME application combined with CS further increased antioxidant enzymes and related gene expression. Collectively, our results confirmed the mitigating potential of ME supplementation for CS by maintaining pepper seedling growth,improving the photosynthesis apparatus, regulating pigments, and osmolyte content.

Genome-wide and candidate gene association studies identify BnPAP17 as conferring the utilization of organic phosphorus in oilseed rape

Phosphorus(P)is essential for living plants,and P deficiency is one of the key factors limiting the yield in rapeseed production worldwide.As the most important organ for plants,root morphology traits(RMTs)play a key role in P absorption.To investigate the genetic variability of RMT under low P availability,we dissected the genetic structure of RMTs by genome-wide association studies(GWAS),linkage mapping and candidate gene association studies(CGAS).A total of 52 suggestive loci were associated with RMTs under P stress conditions in 405 oilseed rape accessions.The purple acid phosphatase gene BnPAP17 was found to control the lateral root number(LRN)and root dry weight(RDW)under low P stress.The expression of BnPAP17 was increased in shoot tissue in P-efficient cultivars compared to root tissue and P-inefficient cultivars in response to low P stress.Moreover,the haplotype of BnPAP17^(Hap3)was detected for the selective breeding of P efficiency in oilseed rape.Over-expression of the BnPAP17^(Hap3)could promote the shoot and root growth with enhanced tolerance to low P stress and organic phosphorus(Po)utilization in oilseed rape.Collectively,these findings increase our understanding of the mechanisms underlying BnPAP17-mediated low P stress tolerance in oilseed rape.

Deciphering the morpho–physiological traits for high yield potential in nitrogen efficient varieties(NEVs):A japonica rice case study

The use of nitrogen(N)-efficient rice(Oryza sativa L.) varieties could reduce excessive N input without sacrificing yields. However, the plant traits associated with N-efficient rice varieties have not been fully defined or comprehensively explored. Here, three japonica N-efficient varieties(NEVs) and three japonica N-inefficient varieties(NIVs) of rice were grown in a paddy field under N omission(0 N, 0 kg N ha^(-1)) and normal N(NN, 180 or 200 kg N ha^(-1)) treatments. Results showed that NEVs exhibited higher grain yield and nitrogen use efficiency(NUE) than NIVs under both treatments, due to improved sink size and filled-grains percentage in the former which had higher root oxidation activity and greater root dry weight, root length and root diameter at panicle initiation(PI), as well as higher spikelet-leaf ratio and more productive tillers during the grain-filling stage. Compared with NIVs, NEVs also exhibited enhanced N translocation and dry matter accumulation after heading and improved flag leaf morpho-physiological traits, including greater leaf thickness and specific leaf weight and higher contents of ribulose^(-1),5-bisphosphate carboxylase/oxygenase, chlorophyll, nitrogen, and soluble sugars, leading to better photosynthetic performance. Additionally, NEVs had a better canopy structure, as reflected by a higher ratio of the extinction coefficient for effective leaf N to the light extinction coefficient, leading to enhanced canopy photosynthesis and dry matter accumulation. These improved agronomic and physiological traits were positively and significantly correlated with grain yield and internal NUE, which could be used to select and breed N-efficient rice varieties.

Trade-offs among fine-root phosphorus-acquisition strategies of 15 tropical woody species

Aims: Plant roots show various functional strategies in soil phosphorus(P) acquisition. Under limited soil phosphatase activity, P deficiency is the main concern, and roots either invest carbon(C) to produce higher levels of phosphatase or establish more symbioses with mycorrhizal fungi. However, these strategies and their interactions are not clear. Furthermore, few studies have investigated trade-offs of functional traits in woody species associated with different types of mycorrhizal partners.Methods: Here we examined the abilities to release acid phosphatase(AP) and the colonization ratio by arbuscular and ectomycorrhizal fungi for fine roots of 15 woody species growing in a tropical common garden in Xishuangbanna, China. We also measured acid phosphatase activities of bulk soils under the canopy of target trees.Results: Soil and root AP activities exhibited a positive correlation, indicating that roots actively produced AP to acquire P even bulk soil AP was increasing. We found a significantly negative correlation(P=0.02) between mycorrhizal colonization ratio and root-released AP activity across target species, reflecting a trade-off between these two P acquisition strategies.Conclusions: Our findings suggest a trade-off of resource allocation between these two strategies at both species and individual levels, and provide information on the overall mechanism of P acquisition by fine roots that they either ‘do it by themselves’ or ‘rely on mycorrhizal partners’. These two strategies might be integrated into the collaboration gradient of the root economics space.

Effects of Auxin at Different Concentrations on the Growth,Root Morphology and Cadmium Uptake of Maize(Zea mays L.)

Indoleacetic acid(IAA)is an important regulator that plays a crucial role in plant growth and responses to abiotic stresses.In the present study,a sand cultivation experiment was carried out to investigate the effects of IAA at different concentrations(0,0.01,0.1,0.5,1,and 2.5 mmol/L)on maize growth,root morphology,mineral elements(Ca,Mg)and Cd uptake under 20 mg/kg Cd stress.The results showed that 0.01 mmol/L is the optimal IAA concentration for enhancing the Cd tolerance of maize.Compared with the control treatment,0.01 mmol/L IAA promoted maize growth,with significant increases in the height,shoot and root biomass by 34.6%,25.0%and 16.3%;altered the root morphology,with increases in root length,root tip number,and root tip density by 8.9%,31.4%and 20.7%,respectively;and enhanced the mineral element uptake of maize,resulting in signifi-cant increases in the Ca content in shoots and roots by 640.6%and 1036.4%and in the Mg content in shoots by 205.8%,respectively.In addition,0.01 mmol/L IAA decreased the Cd content and uptake in the shoots by 51.9%and 39.6%,respectively.Furthermore,the Cd content and uptake exhibited a significant negative correlation with Ca content in roots and a significantly positive correlation with root morphology,and the Cd content in shoots was significantly and negatively correlated with root tip number.Thus,0.01 mmol/L IAA was effective in enhancing the Cd tolerance and plant growth of maize.

Correlation between Root Trait and Yield of Alfalfa

Growth traits of root system of 13 autumn-sowing alfalfa cultivars were analyzed. The results indicated that there were significant difference in growth parameters of root system among alfalfa cultivars( P < 0. 05). The cultivars,Prime and WL323,showed the highest root biomass( higher than 32 g); cultivar WL323 had the largest lateral root number( 17. 8 branches). Cultivars Prime,WL323,Super7 and L90 had better root traits than other cultivars based on comprehensive evaluation. Among three times of mowing within a year,root growth and development of alfalfa had mutual promotion with the first and second time growth of aboveground part,but had competition with the third time growth. Overwintering alfalfa root restricted the grass yield in the following year,especially the third-cut yield in the next year.

Rhizobacteria facilitate physiological and biochemical drought tolerance of Halimodendron halodendron (Pall.) Voss

Growth-promoting bacteria(GPB)have shown promising effects on serving plants against environmental constraints such as drought.Nevertheless,simultaneous effects of different GPB have less been considered for arid land plants and under field conditions.We investigated the effects of single and combined application of GPB,including free-living nitrogen-fixing bacteria(NFB),phosphate solubilizing bacteria(PSB),potassium solubilizing bacteria(KSB),a combination of NFB,PSB,and KSB(NPK),and control,at three drought stress treatments.In order to better understand the interactions between drought and GPB,we measured the morphological,biochemical,and physiological plant traits.The target plant was salt tree(Halimodendron Halodendron(Pall.)Voss),a legume shrub native to arid lands of Central and West Asia.All biofertilizer treatments enhanced the growth,physiology,and biochemistry of salt tree seedlings,and there were significant differences among the treatments.KSB and PSB treatments increased photosynthetic pigments,but KSB treatment was more efficient in transpiration rate and stomatal regulation and increased the soluble carbohydrates.PSB treatment had the highest effect on root traits,such as taproot length,root volume,cumulative root length,and the ratio of root to shoot.NFB treatment enhanced root diameter and induced biomass translocation between root systems.However,only the application of mixed biofertilizer(i.e.,NPK treatment)was the most significant treatment to improve all plant morphological and physiological characteristics of salt tree under drought stress.Therefore,our results provided improvement of some specific plant traits simultaneous with application of three biofertilizers to increase growth and establishment of salt tree seedlings in the degraded arid lands.

Effects of nitrogen addition on the soil detachment in the typical grasslands of the Loess Plateau

Nitrogen deposition will alleviate the nitrogen limitation in terrestrial ecosystems and greatly affect vegetation growth,thereby soil erosion.It is important to clarify the effects of nitrogen addition to the plant roots and soil properties on the soil erosion process.A nitrogen addition experiment was conducted in the grassland dominated by Bothriochloa ischaemum(Linn.)Keng(BI),which has received 0,2.5,5,and 10 g N m^(-2) yr^(-1)(N_(0),N_(2.5),N_(5)and N_(10),respectively)for three consecutive years.Then,a total of 150 undisturbed soil samples were collected(including bare soil control)and subjected to flowing water to test their soil detachment capacities under six shear stress levels(10.2 Pa to 29.9 Pa).Three-year nitrogen addition increased the soil bulk density,soil cohesion and nitrate nitrogen while decreasing the saturated hydraulic conductivity,soil water-stable aggregates,soil organic carbon,total nitrogen and ammonium nitrogen.The root mass density and root diameter decreased with nitrogen addition.And the root length,surface area and volume density of the N_(0) and N_(5) treatments were larger than those of the other treatments,while the plant roots were significantly inhibited by N_(10).Additionally,the soil detachment capacity(D_(c))and rill erodibility(K_(r))of the N_(0) and N_(5) treatments were significantly less than those of the N_(2.5) and N_(10)treatments,of which the Dc(0.020 kg m^(-2) s^(-1))of the N_(0) treatment was 69.0%,24.3%and 66.8%less than that of the N_(2.5),N_(5) and N_(10) treatments,respectively.The Kr of the N_(0) treatment was 0.0012 s m^(-1),which was 72.1%,25.0%and 70.0%less than that of the others.This study implies that an increase in nitrogen addition likely exacerbates soil erosion in the early(approximately 2.5 g N m^(-2) yr^(-1))and late phases(more than 10 g N m^(-2) yr^(-1)).However,when the nitrogen addition rate is approximately 5 g m^(-2) yr^(-1),soil erosion may be inhibited because of the responses of the plant roots and soil to nitrogen addition.

Co-planted barnyardgrass reduces rice yield by inhibiting plant above-and belowground-growth during post-heading stages

Barnyardgrass (Echinochloa spp.) is the most common noxious weed in rice paddies as it inhibits rice growth and reduces grain yield.To date,little information is available on above-and belowgroundgrowth changes in rice due to neighboring barnyardgrass.This study aimed to investigate the changes in root traits and shoot growth of rice when it is grown with different kinds of barnyardgrass.Japonica rice plants (var.Nanjing 9108) were co-cultured with two varieties of Echinochloa crusgalli (L.) Beauv.(EP,var.mitis (pursh) Petern;EH,var.zelayensis (H.B.K.) Hitchc),and E.colonum (L.) Link (EL) in the field in 2017 and 2018.Four treatments included control (i.e.,weed free rice plants) and co-cultures with each of three barnyardgrasses (EP,EH,and EL).The results revealed that EP,EH,and EL treatments significantly reduced rice grain yields by 30.6%–36.2%,42.5%–46.5%,and 10.6%–14.3%,respectively.Shoot growth including shoot dry weight,leaf photosynthetic rate,zeatin (Z) and zeatin riboside (ZR) in grains,and activities of key enzymes involved in sucrose-to-starch conversion in grains and root traits,such as length density,root dry weight,total absorbing surface area,active absorption surface area,oxidation activity,and Z+ZR contents in roots were dramatically reduced during post-heading stages of rice when grown with the three kinds of barnyardgrass.Moreover,above-mentioned rice shoot growth indices were strongly and positively correlated with root traits.These results suggested the decrease in rice shoot growth and root traits during post-heading stages contributes to the reduction in the rice yield when it grows with barnyardgrass neighbors.

Morpho-Physiological Response of Oryza glaberrima to Gradual Soil Drying

Soil drought occurrence during dry season has been the main constraint, besides prolonged flooding during rainy season, in increasing cropping intensity and rice productivity in tropical riparian wetland. Use of drought tolerant rice genotype might be a suitable option for overcoming such problem. This study focused on the effects of gradual soil drying during early vegetative growth stage on morphological and physiological traits of five Oryza glaberrima genotypes, namely RAM12, RAM14, RAM59, RAM97 and RAM101, and two Oryza sativa subsp japonica genotypes, i.e. Koshihikari and Minamihatamochi. The plants were subjected to 6 d of gradual soil drying condition from 15 days after transplanting(DAT) to 20 DAT, and were allowed to recover until 22 DAT. Gradual soil drying reduced plant growth as indicated by dry mass accumulation. Drought reduced stomatal conductance and increased leaf rolling score of all the genotypes. All the genotypes showed comparable response on stomatal conductance, but O. glaberrima genotypes performed higher in leaf rolling recovery. Meanwhile, O. sativa genotypes decreased total leaf area and specific leaf area, but increased specific leaf weight in order to avoid further damages due to drought stress. Drought tolerance mechanisms in RAM101, RAM12, RAM59 and RAM14 were associated with leaf morpho-physiological responses, root traits and dry biomass accumulation.

Effects of water and nitrogen on growth and relative competitive ability of introduced versus native C_(4)grass species in the semi-arid Loess Plateau of China

Switchgrass is an introduced C_(4)grass in the semi-arid Loess Plateau of China,but there is a lack of information to assess its ecological invasive risk.In this study,Old World bluestems(native C_(4)grass)and switchgrass were sowed at five mixture ratios(8:0,6:2,4:4,2:6 and 0:8)under two soil water levels(80%field capacity(FC)and 40%FC)and two nitrogen(N)treatments(0 and 100 mg N/kg dry soil,termed N0-unfertilized and N1-fertilized treatments,respectively)in a pot experiment in 2012.Biomass,root morphological traits and relative competitive abilities of these two species were analyzed.Results showed that biomass of both species was significantly greater under 80%FC or N fertilization,and switchgrass had a relatively larger root:shoot ratio(RSR).Total root length(TRL)and root surface area(RSA)of switchgrass were significantly higher under 80%FC irrespective of N treatment,while those of Old World bluestems were only significantly higher under N fertilization.N had no significant effect on TRL and RSA of switchgrass,while RSA of Old World bluestems significantly increased under 80%FC and N fertilization.Under 40%FC and N0-unfertilized treatment,the aggressivity of Old World bluestems was larger than zero at 2:6 and 4:4 mixture ratios of two species,whereas it was close to zero at 6:2 mixture ratio.Root competitive ability of switchgrass significantly increased under 80%FC or N fertilization.The aggressivity of Old World bluestems was negative at 6:2 mixture ratio under 80%FC and N fertilization,while it was positive at 2:6 mixture ratio.Switchgrass may become more aggressive when N deposition or rainfall increases,while a proper mixture ratio with appropriate water and N management could help with grassland management in the semi-arid Loess Plateau.

Root and leaf functional trait relations in Poaceae species: implications of differing resource- acquisition strategies

Aims root systems play an essential role in grassland functioning in both acquisition and storage of resources.Nevertheless,root functional traits have not received as much attention as those measured on above-ground organs,and little is known about their relations.our objec-tives were to test whether morphological and root system traits allowed identification of grass species’functional strategies and to determine whether a relation exists between above-and below-ground traits.Methods Functional traits of root tissues(specific root length,diameter,tissue density and nitrogen concentration),whole root systems(root mass,root length density,root mass percentage below a depth of 20 cm and fine root%)and two major leaf traits(specific leaf area and leaf dry matter content)were determined under field conditions and their rela-tions were analysed in eleven perennial temperate Poaceae species.Important Findings Canonical correspondence analysis along axis 1 revealed a gra-dient of species,from those with deep,dense and coarse root systems with a large root mass to those with shallow root sys-tems,thin roots and high specific root length;this suggests strong correlations among root traits.Correlations between specific root length and specific leaf area reveal two groups of species,which probably indicates different drought-tolerance capacities.root trait syndromes enable ranking grasses along a gradient from conservative-strategy species(from stressful habitats),which display a deep and coarse root system,to acquisitive species(from rich and moist meadows),which display a shallow and thin root system.although both types display similar above-ground strategies,drought-tolerant species have lower specific root lengths than drought-sensitive species,revealing more conservative root strategies.