Phosphorus (P) is a nonrenewable resource and a critical element for plant growth that plays an important role in improving crop yield. Excessive P fertilizer application is widespread in agricultural production, which not only wastes phosphate resources but also causes P accumulation and groundwater pollution. Here, we hypothesized that the apparent P balance of a crop system could be used as an indicator for identifying the critical P input in order to obtain a high yield with high phosphorus use efficiency (PUE). A 12-year field experiment with P fertilization rates of 0, 45, 90, 135, 180, and 225 kg P2O5 ha-1 was conducted to determine the crop yield, PUE, and soil Olsen-P value response to P balance, and to optimize the P input. Annual yield stagnation occurred when the P fertilizer application exceeded a certain level, and high yield and PUE levels were achieved with annual P fertilizer application rates of 90-135 kg P2O5 ha-1. A critical P balance range of 2.15-4.45 kg P ha-1 was recommended to achieve optimum yield with minimal environmental risk. The critical P input range estimated from the P balance was 95.7-101 kg P2O5 ha-1, which improved relative yield (>90%) and PUE (90.0-94.9%). In addition, the P input-output balance helps in assessing future changes in Olsen-P values, which increased by 4.07 mg kg-1 of P for every 100 kg of P surplus. Overall, the P balance can be used as a critical indicator for P management in agriculture, providing a robust reference for limiting P excess and developing a more productive, efficient and environmentally friendly P fertilizer management strategy.

IntroductionHumic substances (HSs), components of plant biostimulants, are known to influence plant physiological processes, nutrient uptake and plant growth, thereby increasing crop yield. However, few studies have focused on the impact of HS on overall plant metabolism, and there is still debate over the connection between HS’ structural characteristics and their stimulatory actions.MethodsIn this study, two different HSs (AHA, Aojia humic acid and SHA, Shandong humic acid) screened in a previous experiment were chosen for foliar spraying, and plant samples were collected on the tenth day after spraying (62 days after germination) to investigate the effects of different HSs on photosynthesis, dry matter accumulation, carbon and nitrogen metabolism and overall metabolism in maize leaf.Results and discussionThe results showed different molecular compositions for AHA and SHA and a total of 510 small molecules with significant differences were screened using an ESI-OPLC-MS techno. AHA and SHA exerted different effects on maize growth, with the AHA inducing more effective stimulation than the SHA doing. Untargeted metabolomic analysis revealed that the phospholipid components of maize leaves treated by SHA generally increased significantly than that in the AHA and control treatments. Additionally, both HS-treated maize leaves exhibited different levels of accumulation of trans-zeatin, but SHA treatment significantly decreased the accumulation of zeatin riboside. Compared to CK treatment, AHA treatment resulted in the reorganization of four metabolic pathways: starch and sucrose metabolism, TCA cycle, stilbenes, diarylheptanes, and curcumin biosynthesis, and ABC transport, SHA treatment modified starch and sucrose metabolism and unsaturated fatty acid biosynthesis. These results demonstrate that HSs exert their function through a multifaceted mechanism of action, partially connected to their hormone-like activity but also involving hormoneindependent signaling pathways.

IntroductionMaize has a high demand for nitrogen during the growth period. The study of metabolic changes in maize can provide a theoretical basis for rational nitrogen nutrition regulation.MethodsIn order to investigate the changes of different metabolites and their metabolic pathways in maize leaves under nitrogen stress, we used ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) for metabolomic analysis of maize leaves under different nitrogen treatments at three critical growth stages (V4, V12 and R1) in a pot experiment under natural conditions.Results and discussionThe results showed that nitrogen stress significantly affected sugar metabolism and nitrogen metabolism, and affected carbon and nitrogen balance, and the effects of stress on maize leaves metabolism increased with the growth process. Metabolic pathways such as the TCA cycle and starch and sucrose metabolism were mainly affected at the seeding stage (V4). The stress response to nitrogen deficiency also showed significant upregulation of flavonoids such as luteolin and astragalin during the booting stage (V12) and anthesis-silking stage (R1). During R1 stage, the synthesis of tryptophan and phenylalanine and the degradation of lysine were significantly affected. Compared with nitrogen stress, the metabolic synthesis of key amino acids and jasmonic acid were intensified and the TCA cycle was promoted under nitrogen sufficiency conditions. This study initially revealed that the response mechanism of maize to nitrogen stress at the metabolic level.

【Objective】 Soil water in the field experiences spatiotemporal variation due to irrigation and rainfall evens, but its impact on crop growth is unclear. Using millet as a model plant, this paper investigates the effect of temporal soil moisture fluction on its water use efficiency. 【Method】 Experiments were conducted in pots with two soil water treatments: keeping the soil water content stable (SW), or temporally fluctuating it (FW). The former was achieved by keeping the pressure of irrigation water negative (NPI), and the latter by manual irrigation. In both treatments, the average soil water content was kept at 24.94%~25.61% (W1) or 21.12%~22.60%. The changes in growth, photosynthesis, stomatal characteristics, biomass allocation and physiological traits of the millet were measured in each treatment. 【Result】 ① Keeping soil water content stable significantly promoted crop growth. 60 days after start of the experiment, keeping soil water content stable in the range of 24.94%~25.61% (SW1) increased plant height, stem diameter and leaf area by 33.0%, 13.04% and 127.36%, respectively, compared to FW1, while SW2 increased plant height, stem diameter and leaf area by 51.94%, 144.70% and 13.91%, respectively, compared to FW2. ② Compared to FW, SW increased photosynthesis, dry matter accumulation and water use efficiency. During the experimental period, the photosynthetic traits of the millet in SW were significantly higher than those in FW. ③ In addition, SW1 increased fresh biomass and water use efficiency by 222.45% and 200.00%, respectively, compared to FW1, while SW2 increased the fresh biomass and water use efficiency by 352.54% and 260.00%, respectively, compared to FW2. On average, SW increased length and width of leaf stomata while reducing leaf stomatal density. SW and FW treatments did not show significant influence on root malondialdehyde (MDA), root antioxidant enzymes (SOD, POD, CAT), leaf malondialdehyde (MDA), leaf proline (Pro), leaf superoxide dismutase (SOD) and leaf catalase (CAT) contents, but impacted root pro, leaf POD and leaf abscisic acid contents significantly. 【Conclusion】 The broomcorn millet responded differently to stable and fluctuating soil water content, with stable soil water content being more favorable to growth, photosynthesis and water use efficiency of the crop.

Nitrogen (N) fertilizer application has revolutionized agricultural productivity, but excessive N fertilizer application has resulted in low N use efficiency (NUE) and high N accumulation, increasing the risk of N losses. Here, we hypothesize that the apparent N balance can be used as an indicator to identify the N input for obtaining high yield with a high NUE. Thus, a 12-year field experiment involving seven N treatments (0, 120, 240, 360, 480, 600, and 720 kg N ha-1 per year) in a typical winter wheat-summer maize rotation system in North China was conducted to investigate the response of crop yield and NUE to the N balance under different N application rates and to identify the N input-output framework. The annual yield increased in a linear-platform and NUE decreased with increasing N fertilizer application. The N balance and yield are strongly correlated to predict changes in yield, and a critical N balance of 44.4-64.9 kg N ha-1 per year was recommended for optimal yield with minimal risk of N loss. The N balance and NUE can be presented in the framework of N input-output, and the critical N input estimated from the N balance of 217-252 kg N ha-1 could obtain high productivity with high NUE (74.3-79.6 %). Overall, the apparent N balance could be used as a key indicator for optimizing N input, providing a strong reference for limiting N excess in intensive production areas and evaluating agronomic and environmental performance in N management. Data Availability: The datasets generated during and analyzed during the current study are available from the corresponding author on reasonable request.

The physiological and metabolic differences in maize under different nitrogen(N)levels are the basis of reasonable N management,which is vital in improving fertilizer utilization and reducing environmental pollution.In this paper,on the premise of defining the N fertilizer efficiency and yield under different long-term N fertilization treatments,the corresponding differential metabolites and their metabolic pathways were analyzed by untargeted metabolomics in maize.N stress,including deficiency and excess,affects the balance of carbon(C)metabolism and N metabolism by regulating C metabolites(sugar alcohols and tricarboxylic acid(TCA)cycle intermediates)and N metabolites(various amino acids and their derivatives).L-alanine,L-phenylalanine,L-histidine,and L-glutamine decreased under N deficiency,and L-valine,proline,and L-histidine increased under N excess.In addition to sugar alcohols and the above amino acids in C and N metabolism,differential secondary metabolites,flavonoids(e.g.,kaempferol,luteolin,rutin,and diosmetin),and hormones(e.g.,indoleacetic acid,trans-zeatin,and jasmonic acid)were initially considered as indicators for N stress diagnosis under this experimental conditions.This study also indicated that the leaf metabolic levels of N2(120 kg ha-1 N)and N3(180 kg ha-1 N)were similar,consistent with the differences in their physiological indexes and yields over 12 years.This study verified the feasibility of reducing N fertilization from 180 kg ha-1(locally recommended)to 120 kg ha-1 at the metabolic level,which provided a mechanistic basis for reducing N fertilization without reducing yield,further improving the N utilization rate and protecting the ecological environment.

[目的]研究冬小麦–夏玉米轮作体系下砂质潮土长期施磷的作物产量效应、磷肥利用效率、土壤有效磷农学阈值及有效磷对土壤磷素盈亏的响应关系,为农田磷素养分管理提供依据.[方法]磷肥长期定位试验自2008年起在河北廊坊进行,种植制度为冬小麦–夏玉米轮作,供试土壤为砂质潮土,设置6个施磷(P2O5)水平(0、45、90、135、180、225?kg/hm2),依次表示为P0、P45、P90、P135、P180、P225.在2020年(试验的第12年)测定作物产量、作物吸磷量、土壤有效磷含量,分析了周年产量和土壤有效磷演变特征、作物有效磷农学阈值、土壤有效磷与累积磷盈亏的关系.[结果]施磷显著提高了冬小麦–夏玉米周年产量和作物吸磷量,产量与吸磷量随施磷水平提高先升高后降低.达到最高周年产量(14627?kg/hm2)的施磷量为152?kg/hm2.以该最高产量的90％为实际生产目标,适宜施磷量为90?kg/hm2.磷肥利用率随轮作周期延长而提高,12年平均磷素表观利用率和累积利用率变幅分别为36.98％～98.10％和26.26％～71.85％.周年施磷量超过90?kg/hm2时,施磷对作物吸磷量影响不显著,且磷肥表观利用率、累积利用率显著降低.P0～P225处理表观磷盈余12年平均值分别为–11.30、–7.38、0.94、20.05、37.21、57.68?kg/hm2;至2020年累积磷盈亏分别为–144.92、–88.57、11.33、240.56、446.48、692.15?kg/hm2.砂质潮土有效磷含量随累积磷盈余量的变化呈现两段线性关系,拐点出现在土壤累积磷盈余量P?218.81?kg/hm2.低于此值时,土壤每盈余P?100?kg/hm2,有效磷含量上升0.48?mg/kg;当土壤累积磷盈余高于此值时,土壤每盈余P?100?kg/hm2,有效磷含量上升3.37?mg/kg.冬小麦、夏玉米有效磷农学阈值分别为10.20、5.93?mg/kg,施磷量为90?kg/hm2时,冬小麦、夏玉米季土壤有效磷含量最接近农学阈值.[结论]在作物秸秆还田条件下,砂质潮土冬小麦–夏玉米轮作体系周年施磷量为90?kg/hm2,可以兼顾冬小麦–夏玉米轮作周年对磷素的需求,维持土壤磷素的表观平衡,在保证产量的前提下实现磷素平衡和磷肥高效施用.砂质潮土磷的储存阈值为218.81?kg/hm2,当土壤磷累积量低于该阈值时,施磷提高土壤有效磷含量的效果较低;而当磷累积量高于该阈值时,施磷可显著提升土壤磷的有效性.

【Objective】This paper explored the dynamic prediction model and characteristic parameters of dry matter and nitrogen accumulation in summer maize with different nitrogen supply levels based on effective accumulated temperature, in order to provide a theoretical basis for using effective accumulated temperature to predict summer maize dry matter and nitrogen accumulation.【Method】This study was based on a two-year field experiment in Langfang, Hebei Province (2019-2020), using Zhengdan 958 as the test material, and using the normalization method to fit the dry matter and nitrogen accumulation of summer maize with different nitrogen supply levels through model screening. Based on the normalized Gompertz model of effective accumulated temperature after sowing, and using the growth rate curve and its characteristic parameters, the dry matter and nitrogen accumulation characteristics of summer maize were quantitatively analyzed.【Result】(1) Under the experimental conditions, when the amount of phosphorus and potassium fertilizer was appropriate, the maximum dry matter and nitrogen accumulation of summer maize continued to increase with the increase of nitrogen application rate. (2) The normalized Gompertz model of summer maize dry matter and nitrogen accumulation established with effective accumulated temperature as the independent variable had the good biological significance. The coefficients of determination of the equation were 0.9962-0.9988 and 0.9887-0.9922, respectively. Using the second-year data for model verification, the correlation coefficients of the simulated and measured values were 0.9933-0.9959 and 0.9830-0.9923, and the standardized root mean square errors were 6.64%-16.86% and 7.31%-12.68%, respectively. The prediction effect was good. (3) The growth rate of dry matter and nitrogen accumulation of summer maize at different nitrogen supply levels all showed a “single peak curve”, and its change was closely related to the nitrogen supply level. The performance between treatments was: under the condition of moderate fertilization, the growth rate curve had the characteristics of fast rising and falling, and the growth rate curve of weight loss treatment had the characteristics of slow rising and falling. (4) The effective accumulated temperature ranges of dry matter and nitrogen accumulation during the rapid increase period of summer maize after sowing were 709.35-1 722.54 and 482.50-1 507.61 ℃·d, respectively, and the effective accumulated temperature required for the maximum rate showed that nitrogen accumulation (995.05 ℃·d) was less than dry matter accumulation (1 215.94 ℃·d). Nitrogen supply level obviously affected the accumulation of dry matter and nitrogen in summer maize to enter the accumulation temperature required for the rapid increase period, the accumulated temperature required for the slow increase period, the accumulated temperature required for the maximum increase rate, the maximum increase rate, and the average increase rate during the rapid increase period. Compared with nitrogen fertilizer treatment, the effective accumulated temperature required for summer maize to enter each critical period was significantly reduced, and the growth rate during the critical period increased significantly.【Conclusion】The normalized Gompertz model could not only simulate and predict the dynamic changes of summer maize dry matter and nitrogen accumulation with effective accumulated temperature with different nitrogen supply levels, but also clarify the quantitative relationship between effective accumulated temperature and dry matter and nitrogen accumulation. The Gompertz model based on effective accumulated temperature could be used to predict crop growth and optimal fertilization period, and had strong application value..

[目的]探究基于有效积温的不同氮磷钾处理夏玉米株高和叶面积指数(LAI)的生长动态预测模型及其特征参数,以期为利用有效积温定量模拟夏玉米生长发育动态提供理论依据.[方法]在河北廊坊两年大田试验(2019-2020年)基础上,以郑单958为试验材料,分为氮、磷、钾3个单因素肥效试验,每个因素设4个水平,分别为不施肥、低肥、适量肥和高肥处理.采用Logistic模型拟合不同氮磷钾营养水平下夏玉米株高和叶面积指数基于有效积温的动态方程,并利用增长速率曲线及其特征参数定量分析了夏玉米生长发育特征.[结果](1)在本试验条件下,与其他处理相比,适量施肥处理(N2、P2和K2)夏玉米株高最大值均为最大.过量施用钾肥对夏玉米最大株高有显著的抑制作用.适量施肥处理夏玉米株高进入平台期所需积温为952.43-958.83℃·d.适量施肥能有效增加夏玉米叶面积指数,养分过量或过少均影响叶面积的形成.适量施肥处理夏玉米叶面积指数进入平台期所需积温为849.18-952.43℃·d.(2)各施肥处理条件下以有效积温为自变量建立的夏玉米株高和叶面积指数方程的拟合度R2分别为0.9949-0.9970和0.9840-0.9939,方程均达到极显著水平,具有生物学意义.基于有效积温的株高拟合方程得出的模拟值和实测值的相关系数(r)在0.9961-0.9983;基于有效积温的叶面积指数拟合方程的模拟值和实测值的r在0.9815-0.9981.(3)各施肥条件下,夏玉米株高和叶面积指数增长速率均表现为"单峰曲线",适量施肥处理条件下,增长速率曲线呈现上升快下降也快的特点,不施氮肥、不施磷肥和不施钾肥处理增长速率曲线呈现上升慢下降也慢的特点.(4)适量施肥处理条件下夏玉米株高进入快增期积温、进入缓增期积温和达到最大增长速率积温分别为394.17、776.63和585.40℃·d,均与NO、P0和K0处理差异显著,株高最大增长速率和快增期平均增长速率分别为0.4907和0.4302 cm·(℃·d)-1,均与NO、P0和K0处理差异不显著.(5)适量施肥处理条件下夏玉米叶面积指数进入快增期积温、进入缓增期积温和达到最大增长速率积温分别为609.69、855.08和732.38℃·d,叶面积指数最大增长速率和快增期平均增长速率分别为0.0135和0.0118℃·d.[结论]养分供应不足能够增加夏玉米株高和叶面积指数进入平台期所需有效积温.基于有效积温的Logistic模型能够很好地模拟和预测不同氮磷钾处理下夏玉米株高和叶面积指数的动态变化.适量施肥条件下方程的拟合度和稳定性优于养分过量或过少的拟合方程.不施肥处理相比适量施肥处理,夏玉米株高和LAI达到关键期所需积温(进入快增期所需积温、进入缓增期所需积温、最大增长速率所需积温)明显增加,关键期增长速率(最大增长速率、快增期平均增长速率)明显减小.本研究为有效积温定量模拟夏玉米生长发育动态提供了理论依据.