苗期玉米叶片光合特性对水分胁迫的响应

以2个抗旱性不同的玉米品种为材料进行盆栽试验,在苗期设置4个水分梯度,研究气体交换和叶绿素荧光参数及光响应特征。结果表明:随水分胁迫的加剧,除细胞间CO2浓度(Ci)和非光化学淬灭(qN)上升外,其它参数均下降,先玉335(XY335)各参数的变化幅度小于陕单902(SD902);轻度胁迫下品种间气体交换参数差异最大,严重干旱下叶绿素荧光参数差异最大;净光合速率(Pn)和相对电子传递速率(rETR)的光响应曲线拟合结果显示,水分胁迫导致玉米叶片最大光合速率和光能利用率下降,XY335各参数的下降幅度小于SD902;轻度干旱下Pn光响应拟合参数品种间差异最大,严重干旱下rETR光响应拟合参数差异最大。综上表明,水分胁迫导致玉米叶片对强光的敏感性增加,干旱和光抑制对光系统Ⅱ造成的叠加伤害随干旱加重和品种抗旱性弱而加剧,是制约光合作用的主要原因;旱区强光下的玉米幼苗应及时补水,以避免严重干旱和高光强的叠加伤害。     

Canopy and leaf photosynthetic characteristics and water use efficiency of sweet sorghum under drought stress

The objective of this paper was to examine the relationship between Water Use Efficiency (WUE) at the canopy and leaf levels, to determine soil moisture conditions, which can optimize yield, and WUE of sweet sorghum (Sorghum bicolor (Linn.) Moench), thus providing some theoretical foundation for using marginal land effectively and developing production of sweet sorghum. Three levels of soil moisture conditions were established, and photosynthetic characteristics and yield were measured. The canopy apparent photo-synthetic rate (CAP) and leaf photosynthetic rate (P _N) were reduced gradually with increased drought stress, and the CAP was lower than the P _N under every soil moisture conditions. The P _N had a midday depression phenomenon, but the CAP did not exhibit this midday depression phenomenon under severe drought stress. The linear regression relationship of CAP and P _N was CAP = 1.5945 + 0.1496 P _N. The canopy apparent WUE_C and leaf WUE_L were the highest under moderate drought stress. The first was 5.3 and 5.8 times higher than the WUE_L in mid-July and late August, respectively. The stem fresh biomass yield was 77 tons/ha under moderate drought stress and WUE of aboveground biomass yield (WUE_B) was also the highest. Our results showed that moderate drought stress did not result in a significant reduction in biomass yield but increased WUE significantly.     

结实期水分胁迫对不同氮肥水平下水稻产量及其品质的影响

以生产上广泛使用的3个水稻品种为材料,研究了结实期适度水分胁迫对不同氮肥水平下稻米产量及其品质的影响.结果表明,正常施氮水平下,水分胁迫使3个品种籽粒产量降低11.6%～14.7%,虽整精米率有所提高,但垩白度却显著增加(18.7%～33.1%),外观品质变劣;而高氮水平下,水分胁迫处理的产量增加18.8%～22.2%,垩白粒率和垩白度分别降低15.3%～37.2%和13.7%～29.9%,外观品质变优.稻米RVA谱特征值和米饭质地也明显受到结实期土壤水分和施氮水平的影响.正常施氮水平下,水分胁迫处理的最高粘度和崩解值(扬稻6号除外)要低于水层灌溉处理,而其消减值却明显高于水层灌溉处理,水分胁迫使得正常施氮处理的米饭口感较硬,弹性较差,粘性降低,且咀嚼有渣感.而高氮水平下,水分胁迫利于米粉糊化过程中早期粘度的上升,最高粘度增加,崩解值也明显高于水层灌溉,消减值却明显减小,米饭的硬性和凝聚性减小,松弛性和粘附性增大,米饭质地有变优的趋势.     

夏玉米叶片含水率及光合特性对不同强度持续干旱的响应

基于七叶期开始的夏玉米全生育期不同强度的干旱发生发展模拟试验资料,分析了不同强度的干旱发生发展对夏玉米叶片含水率及光合特性的影响。结果表明:夏玉米生育期内叶片含水率随干旱发生发展呈线性下降趋势,并与土壤相对湿度通过0.005水平的显著性检验,可表征玉米的受旱程度。玉米全生育期内叶片的光合速率、蒸腾速率和气孔导度均随干旱的发生发展呈显著下降趋势,且不同强度干旱的影响差异随时间推移而减小;而叶片水分利用效率则随干旱发生发展呈升高趋势,且随着干旱的发展不同强度干旱间的差异呈增加趋势。玉米全生育期内均出现了光合作用由气孔限制向非气孔限制的转换,转换时间分别为46、38、30和35 d,与干旱强度及持续时间呈反比。     

田间不同条件下玉米叶片的气孔阻力及与光合、蒸腾作用的关系

以玉米17个自交系和10个杂交种为试材,在田间条件下研究了不同光强、不同叶位、不同生育期、不同源库比例和株间差异状态下的气孔阻力及其与光合(PH)、蒸腾(TR)和叶片水分利用效率(WUE)的关系,结果表明,不同自交系之间RS具有显著的差异,相差最大可达2.3倍以上;光照条件变弱、穗叶位差增加、生育期推延和源/库比例改变等均可引起RS值的增加;在各种情况下导致RS变化的同时也引起TR和PH产生相应的变化,RS与TR、PH表现出显著或极显著的负相关,且相关系数r_RS-TR>r_RS-PH;RS与WUE的相关关系在不同的条件下表现出不稳定性.     

Quantifying photosynthetic capacity and its relationship to leaf nitrogen content for global-scale terrestrial biosphere models

Photosynthetic capacity and its relationship to leaf nitrogen content are two of the most sensitive parameters of terrestrial biosphere models (TBM) whose representation in global‐scale simulations has been severely hampered by a lack of systematic analyses using a sufficiently broad database. Here, we use data of qualitative traits, climate and soil to subdivide the terrestrial vegetation into functional types (PFT), and then assimilate observations of carboxylation capacity, V_max (723 data points), and maximum photosynthesis rates, A_max (776 data points), into the C₃ photosynthesis model proposed by Farquhar et al. to constrain the relationship of (V_max normalised to 25 °C) to leaf nitrogen content per unit leaf area for each PFT. In a second step, the resulting functions are used to predict per PFT from easily measurable values of leaf nitrogen content in natural vegetation (1966 data points). Mean values of thus obtained are implemented into a TBM (BETHY within the coupled climate–vegetation model ECHAM5/JSBACH) and modelled gross primary production (GPP) is compared with independent observations on stand scale. Apart from providing parameter ranges per PFT constrained from much more comprehensive data, the results of this analysis enable several major improvements on previous parameterisations. (1) The range of mean between PFTs is dominated by differences of photosynthetic nitrogen use efficiency (NUE, defined as divided by leaf nitrogen content), while within each PFT, the scatter of values is dominated by the high variability of leaf nitrogen content. (2) We find a systematic depression of NUE on certain tropical soils that are known to be deficient in phosphorous. (3) of tropical trees derived by this study is substantially lower than earlier estimates currently used in TBMs, with an obvious effect on modelled GPP and surface temperature. (4) The root‐mean‐squared difference between modelled and observed GPP is substantially reduced.     

QTL mapping for yield and photosynthetic related traits under different water regimes in wheat

The improvement for drought tolerance requires understanding of the genetic control of wheat (Triticum aestivum L.) reaction to drought. In this study, a set of 131 recombinant inbred lines of wheat were investigated under well-watered (WW) and drought stress (DS) environments across 2 years to map quantitative trait loci (QTLs) for yield and physiological traits. A total of 225 QTLs were detected, including 32 non-environment-specific loci that were significant in both DS and WW, one drought-specific locus and two watering-specific loci. Three consistently-expressed QTLs (QTkw-3A.2, QTss-1A, and QScn-7A.1) were identified in at least three environments and the QTkw-1D.1 was significant in DS across the 2 years. By unconditional and conditional QTL analysis, spike number per plant and kernel number per spike were more important than thousand-kernel weight for grain yield (GY) at the given genetic background. Meta-analysis identified 67 meta-QTLs that contained QTLs for at least two traits. High frequency co-location of QTLs was found among either the spike-related traits or the six physiological traits. Four photosynthesis traits (CHL, LWUE, P _N, and C _i) were co-located with GY and/or yield components on various MQTLs. The results provided QTLs that warrant further study for drought tolerance breeding and are helpful for understanding the genetic basis of drought tolerance and the genetic contribution of yield components to GY at individual QTL level in wheat.     

Nitrogen nutrition and water stress effects on leaf photosynthetic gas exchange and water use efficiency in winter wheat

The responses of gas exchange and water use efficiency to nitrogen nutrition for winter wheat were investigated under well-watered and drought conditions. The photosynthetic gas exchange parameters of winter wheat are remarkably improved by water and nitrogen nutrition and the regulative capability of nitrogen nutrition is influenced by water status. The effects of nitrogen nutrition on photosynthetic characteristics and on the limited factors to photosynthesis are not identical under different water status. Intrinsic water use efficiency (WUE(i)) of the plants at the high-N nutrition was decreased by a larger value than that of the plants in the low-N treatment due to a larger decrease in photosynthetic rate than in transpiration rate. Carbon isotope composition of plant material (delta(p)) is increased by the increase of drought intensity. The delta(p) at a given level of C(i)/C(a) is reduced by nitrogen deficiency. Leaf carbon isotope discrimination (Delta) is increased by the increase of nitrogen nutrition and decreased by the increase of drought intensity. Transpirational water use efficiency (WUE(t)) is negatively correlated with Delta in both nitrogen supply treatments and increased with the nitrogen supply.     

Effects of different levels of water stress on leaf photosynthetic characteristics and antioxidant enzyme activities of greenhouse tomato

Two greenhouse experiments were conducted in order to investigate the effects of different levels of water stress on gas exchange, chlorophyll fluorescence, chlorophyll content, antioxidant enzyme activities, lipid peroxidation, and yield of tomato plants (Solanum lycopersicum cv. Jinfen 2). Four levels of soil water content were used: control (75 to 80% of field water capacity), mild water stress (55 to 60%), moderate water stress (45 to 50%), and severe water stress (35 to 40%). The controlled irrigation was initiated from the third leaf stage until maturity. The results of two-year trials indicated that the stomatal conductance, net photosynthetic rate, light-saturated photosynthetic rate, and saturation radiation decreased generally under all levels of water stress during all developmental stages, while compensation radiation and dark respiration rate increased generally. Water stress also declined maximum quantum yield of PSII photochemistry, electron transfer rate, and effective quantum yield of PSII photochemistry, while nonphotochemical quenching increased in all developmental stages. All levels of water stress also caused a marked reduction of chlorophyll a, chlorophyll b, and total chlorophyll content in all developmental stages, while activities of antioxidant enzymes, such as superoxide dismutase, peroxidase, and catalase, and lipid peroxidation increased.     

田间不同条件下玉米叶片的气孔阻力及与光合,蒸腾作用的关系

以玉米 1 7个自交系和 1 0个杂交种为试材 ,在田间条件下研究了不同光强、不同叶位、不同生育期、不同源库比例和株间差异状态下的气孔阻力及其与光合 (PH)、蒸腾(TR)和叶片水分利用效率 (WUE)的关系 ,结果表明 ,不同自交系之间RS具有显著的差异 ,相差最大可达 2 .3倍以上 ;光照条件变弱、穗叶位差增加、生育期推延和源 /库比例改变等均可引起RS值的增加 ;在各种情况下导致RS变化的同时也引起TR和PH产生相应的变化 ,RS与TR、PH表现出显著或极显著的负相关 ,且相关系数rRS TR>rRS PH;RS与WUE的相关关系在不同的条件下表现出不稳定性     

小麦品种氮利用效率的评价指标及其氮营养特性研究

选用40个不同小麦基因型在2个不同生态区进行田间试验,系统地分析了不同N利用效率指标的基因型与环境差异及其与N营养特性的关系．结果表明,N收获指数在基因型间的变异相对较小。其余指标受品种影响较大．N吸收效率、氮流效率受环境影响较小,其余指标受环境影响较大．所有指标均受基因型和环境互作的显著影响．氮流效率与N吸收效率、植株N生产力和土壤N生产力极显著相关,综合反映了植株干物质生产和N利用状况,可作为一个有效的N利用效率评价指标．指出提高开花后,N同化量和转运量有利于提高氮流效率．     

干旱胁迫对不同施氮水平麻疯树幼苗光合特性及生长的影响

采用盆栽控水的方法,研究了干旱胁迫（连续干旱0 d,5 d,10 d,…,45 d）对不同施氮水平(对照 0 kg N·hm^-2、低氮 96 kg N·hm^-2、中氮 288 kg N·hm^-2、高氮 480 kg N·hm^-2)麻疯树幼苗光合特性及其生长的影响.结果表明: 随干旱胁迫强度的增加,各施氮水平麻疯树幼苗叶片相对含水量、苗高生长量、地径生长量、叶面积、净光合速率、蒸腾速率和气孔导度均降低,且各水分处理间差异极显著(P<0.01);随干旱时间的延长,叶绿素含量和水分利用效率表现出先升高后降低的趋势,而胞间CO₂浓度呈先降低后升高的趋势.正常供水时,施氮处理均不同程度提高了麻疯树幼苗的光合能力,促进了麻疯树幼苗的生长,且施氮量越高效果越好;干旱条件下,氮素营养对植株光合能力和生长的影响与干旱程度和施氮水平有关.轻度干旱时,提高施氮水平对植株光合能力和生长具有明显的促进作用;中度干旱时,中氮的促进作用明显高于其他施氮水平;严重干旱时,低氮的促进效果最好,高氮的促进作用减弱并逐渐转向抑制.     

Toxicity of nitrapyrin to sunflower under different N nutrition regimes

Summary The purpose of this study was to investigate the phytotoxicity of nitrapyrin 2-chloro-6-(trichloromethyl)pyridine to sunflower (Helianthus annuus L.) under different N regimes and to see if N forms affect the phytotoxicity of nitrapyrin. Sunflower was grown in pot culture for 21 days and was fertilized with (NH₄)₂SO₄, NH₄NO₃ and NaNO₃ to provide 0, 100 and 200 ppm N and with nitrapyrin application of 0 and 20 ppm. All N-treated sunflower plants in all N regimes and regardless of titrapyrin treatment produced more root and shoot dry weights and contained a significantly higher N than untreated check. Nitrapyrin toxicity appeared as a curling of leaf margin and a tendril type of stem growth, the visible toxicity symptoms decreased in the order: (NH₄)₂SO₄>NH₄NO₃>NaNO₃. Furthermore nitrapyrin addition suppressed sunflower growth in each N regime, the suppressing effect being greater with (NH₄)₂SO₄ and NH₄NO₃ than as with NaNO₃. Although, shoot growth from plants receiving nitrapyrin was not significantly affected by any N regime, root growth of nitrapyrin-treated plants was somewhat restricted by NH₄ ⁺−N nutrition relative to NO₃ ⁻−N nutrition.     

不同施氮量下灌水量对小麦耗水特性和氮素分配的影响

研究了不同施氮量条件下灌水量对高产小麦耗水特性和氮素分配利用的影响。设置4个施氮水平:0kg·hm-2(N0)、120kg·hm-2(N1)、210kg·hm-2(N2)和300kg·hm-2(N3),在每个施氮水平下设置4个灌水量处理:不浇水(W0)、底墒水+拔节水(W1)、底墒水+拔节水+开花水(W2)、底墒水+拔节水+开花水+灌浆水(W3),每次灌水量60mm。结果表明:(1)在N0水平下W0处理日耗水量以拔节至开花期最高,在N1水平下,拔节至开花期日耗水量与开花至成熟期的无显著差异。同一施氮水平下,小麦开花后总耗水量、耗水模系数和日耗水量随灌水量的增加而提高,但产量随灌水量的增加先升高后降低。(2)同一施氮水平下,成熟期W1处理20—140cm各土层土壤含水量低于W2和W3处理,140—200cm土层土壤含水量与W2处理无显著差异;W1处理0—40cm土层土壤硝态氮含量及植株氮素在籽粒中的分配比例高于W2和W3处理,100—140cm土层土壤硝态氮含量及植株氮素在营养器官中的分配量和分配比例低于W2和W3处理。表明灌溉底墒水和拔节水的W1处理,促进了小麦对20—140cm土层土壤水的吸收利用,减少了土壤硝态氮向100cm以下土层的淋溶,而且有利于营养器官中氮素向籽粒的再分配,水分和氮素利用效率较高。(3)在试验条件下,施纯氮210kg·hm-2、灌溉底墒水和拔节水的N2W1处理,籽粒产量最高,水分利用效率和氮素利用效率较高,可供生产中参考。     

Influence of water stress on leaf photosynthetic characteristics in wheat cultivars differing in their susceptibility to drought

A gradual reduction in leaf water potential (Ψ_leaf), net photosynthetic rate (P _N), stomatal conductance, and transpiration rate was observed in two drought tolerant (C 306 and K 8027) and two susceptible (RW 893 and 899) genotypes subjected to water stress. The extent of reduction was lower in K 8027 and C 306 and higher in RW 893 and RW 899. Rewatering the plants after 5 d of stress restored P _N and other gas exchange traits in all four cultivars. Water stress had no significant effect on variable to maximum fluorescence ratio (F_v/F_m) indicating that water stress had no effect on primary photochemistry of photosystem 2 (PS2). However, water stress reduced the efficiency of excitation energy transfer (F′_v/F′_m) and the quantum yield of electron transport (Φ_PS2). The reduction was more pronounced in susceptible cultivars. Water stress had no significant effect on photochemical quenching, however, the non-photochemical quenching increased by water stress.     

不同土壤水分处理对水稻光合特性及产量的影响

为探明土壤水分对水稻生长发育的影响机理,以武香粳14和两优培九为试验材料,分析了不同土壤水分处理下(W1、W2、W3和CK分别表示土壤体积含水量为20%、30%、40%和5cm水层灌溉)的水稻光合特性、产量及水分生产率等。结果表明,轻度水分胁迫(W3)具有处理间最大的叶片气孔导度、蒸腾速率和净光合速率,其他处理规律不显著。灌浆初期各水分处理下叶位间光合指标均表现为:剑叶＞顶2叶＞顶3叶>顶4叶,其他生育期规律不显著。与对照处理(CK)相比,武香粳14的W1、W2和W3处理的产量分别减少61.14%和29.13%、增加0.96%,水分生产率分别减少10.69%、增加1.53%和20.61%;两优培九的产量分别减少64.11%和28.76%,增加2.08%,水分生产率分别减少16.39%,增加2.46%和22.13%。研究结果为水稻精确灌溉和节水生产提供了技术支撑。     

Chilling-stress responses by rice seedlings grown with different ammonium concentrations and its relationship to leaf spermidine content

We previously determined that, under salt stress, a growth medium containing a high level of ammonium enhances oxidative damage in rice (Oryza sativa L.) seedlings. This suggested that, to be salt-tolerant, plants must assimilate excess nitrogen efficiently. Here, we investigated the effect of different ammonium concentrations on the chilling-stress sensitivity of rice seedlings. We also examined the relationship between leaf polyamine contents and stress tolerance under low temperatures (13/8°C day/night). Chilling treatment resulted in a striking decrease in chlorophyll fluorescence (ΦII) in the leaf blades. This was especially true for seedlings grown in a high-ammonium medium. Thus, the chilling-stress sensitivity of rice was heightened under excess N, similar to that noted in our earlier salt-stress experiments. Exposure to low temperature caused contents of putrescine and spermidine to increase in leaf blades under all ammonium concentrations, whereas the level of spermine declined under such treatment. The rate of increase in putrescine and spermidine contents was slower when the medium contained a high amount of ammonium, and a positive correlation was observed between leaf ΦII values and leaf spermidine contents. These results imply that an adaptive mechanism operates in rice seedlings and that spermidine is of physiological importance in conveying chilling-stress tolerance.     

不同淹水条件下河竹叶片光合生理特性的变化

为阐明淹水条件下河竹( Phyllostachys rivalis H. R. Zhao)叶片的光合生理特性,设置对照组( CK,正常供水)及中度淹水(T1,水面高出基质表面5 cm)和重度淹水(T2,水面高出基质表面10 cm)处理组,对持续淹水360 d内2年生河竹幼苗叶片的光合气体交换参数、光响应曲线、光合特征参数、资源利用效率参数、光合色素含量及比值的变化进行了分析;在此基础上,探讨了河竹对淹水环境的适应性。结果表明：随淹水时间延长,2个处理组的多数光合生理参数呈“升高—降低—升高”的变化趋势,且多数参数在淹水90 d时达到峰值、在淹水270 d时达到谷值;T1组的各项光合生理参数总体上高于T2组。淹水30~180 d,与CK组相比,2个处理组的净光合速率( Pn)、蒸腾速率( Tr)、气孔导度( Gs)、胞间CO2浓度( Ci)和叶面饱和水汽压亏缺( Vpdl)总体上降低,表观量子效率( AQY)显著降低;气孔限制值(Ls)升高,而光饱和点(LSP)和光补偿点(LCP)显著升高;T1组的最大净光合速率(Pmax)略降低,而T2组的Pmax值则显著降低;但2个处理组的水分利用效率( WUE)、表观CO2利用效率( CUE)和表观光能利用效率(LUE)却无明显变化。淹水270和360 d,与CK组相比,2个处理组的Pn、Tr、Gs、Ls和Vpdl值降低,Pmax、LSP、LCP、WUE、CUE和LUE值显著降低,仅Ci值升高;T1组的AQY值略降低,而T2组的AQY值则显著降低。2个处理组的光响应曲线变化趋势与CK组相似,但随淹水时间延长,2个处理组的Pn值变幅不同,其中T1组的Pn值总体上高于T2组。淹水30和90 d,与CK组相比,T1组的叶绿素b( Chlb)和总叶绿素( Chl)含量总体上显著升高,而T2组的Chlb和Chl含量总体上显著降低;2个处理组的叶绿素a(Chla)和类胡萝卜素(Car)含量以及Chla/Chlb和Chl/Car值也显著降低。淹水180~360 d,仅2个处理组的Chla/Chlb值显著升高,而其他光合色素含量及比值总体上显著降低。综合分析结果显示：河竹叶片Pn值在淹水前期和中期下降的主要原因为气孔限制,而在淹水后期下降的主要原因为非气孔限制。河竹对淹水环境有较强耐受性,并对长期淹水有一定的适应性;此外,中度淹水条件下河竹叶片的光能转化效率、对光辐射的利用范围和对光变化的适应能力均高于重度淹水条件。     

盐胁迫下水稻叶片光合参数对光强的响应

以耐盐性不同的两个水稻品种秋光和辽盐2号为试材,在设定条件下测定长时间NaCl胁迫下水稻剑叶的净光合速率(P_n)、蒸腾速率（T_r）、气孔导度（G_s）和胞间CO₂浓度（C_i）在不同光照强度（PFD）诱导下的反应差异与水稻抗性的关系.结果表明,在不同浓度NaCl胁迫下,随着PFD的升高,两品种的P_n和G_s均呈上升趋势,与对照相比,耐盐品种辽盐2号的P_n增加了14.87%,而秋光的P_n则下降了17.91%.C_i、L_s及P_n/G_s比值的变化趋势表明,气孔因素和非气孔因素对辽盐2号的光合变化起到了积极作用,而气孔因素则是引起秋光光合变化的主要原因.     

Responses of rice cultivars with different nitrogen use efficiency to partial nitrate nutrition

BACKGROUND AND AIMS: There is increased evidence that partial nitrate (NO3-) nutrition (PNN) improves growth of rice (Oryza sativa), although the crop prefers ammonium (NH4+) to NO3- nutrition. It is not known whether the response to NO3- supply is related to nitrogen (N) use efficiency (NUE) in rice cultivars. Methods Solution culture experiments were carried out to study the response of two rice cultivars, Nanguang (High-NUE) and Elio (Low-NUE), to partial NO3- supply in terms of dry weight, N accumulation, grain yield, NH4+ uptake and ammonium transporter expression [real-time polymerase chain reaction (PCR)]. KEY RESULTS: A ratio of 75/25 NH4+ -N/NO3- -N increased dry weight, N accumulation and grain yield of 'Nanguang' by 30, 36 and 21 %, respectively, but no effect was found in 'Elio' when compared with those of 100/0 NH4+ -N/NO3- -N. Uptake experiments with 15N-NH4+ showed that NO3- increased NH4+ uptake efficiency in 'Nanguang' by increasing Vmax (14 %), but there was no effect on Km. This indicated that partial replacement of NH4+ by NO3- could increase the number of the ammonium transporters but did not affect the affinity of the transporters for NH4+. Real-time PCR showed that expression of OsAMT1s in 'Nanguang' was improved by PNN, while that in 'Elio' did not change, which is in accordance with the differing responses of these two cultivars to PNN. Conclusions Increased NUE by PNN can be attributed to improved N uptake. The rice cultivar with a higher NUE has a more positive response to PNN than that with a low NUE, suggesting that there might be a relationship between PNN and NUE.