It is estimated that 据估计，施用于土壤的常规常量养分N、P和K分别损失了40 to 70 per cent, 80 to 90 per cent and 50 to 90 per cent of the conventional macronutrients N, P and K applied to soil are lost, respectively, resulting in considerable resource losses. Compared with traditional fertilizers, nano fertilizers have small volume (-70%、80-90%和50-90%，导致资源损失相当大。与传统肥料相比，纳米肥料具有控释、养分利用率高、成本低、环境污染相对较小等优点，因为它们的体积小（1-100 nm) and high specific surface area, and have the advantages of controlled release, high nutrient utilization, low cost and relatively small environmental pollution. The application of nanofertilizers is an emerging area of agricultural research and is an attractive and economical alternative to traditional fertilizers that could sustainably increase global food productivity. Foliar fertilization is a popular method to meet the needs of higher plants. Due to the small amount of leaf application, nutrient absorption is faster than the soil, and environmental pollution is relatively small, so it is more popular in plants. It can be seen that nano-fertilizer and foliar fertilization are the focus of attention at present, and the study on the foliar application of nano-fertilizer is not as extensive as that of soil application.）和比表面积高。纳米肥料的应用是农业研究的一个新兴领域，是普通肥料的有吸引力且经济的替代品，可以可持续地提高全球粮食生产力。叶面施肥是满足高等植物需求的一种流行方法。由于叶面施用量小，养分吸收快于土壤，环境污染相对较小，因此在植物中较受欢迎。可以看出，纳米肥和叶面施肥是目前关注的热点，目前对纳米肥叶面施用的研究还不如土壤施用广泛。
1. The way of nano fertilizer entering the plant纳米肥料进入植物的途径
必需营养素最常用于土壤和植物叶片，土壤施肥更受欢迎，对更大的养分需求更有效[19]。然而，在某些情况下，叶面施肥因其更具成本效益和效率的特点而成为一种广泛而常见的作物管理方法[19]。
E植物的叶子可以保护植物免受水分流失、害虫和病原体的侵害，同时允许气体交换以进行光合作用反应[20]。叶子的表面通常由特征组成：毛状体、气孔和韧皮部孔。NPs
sential以两种方式被叶子吸收，即角质层途径和气孔途径[21]（图2）。直径小于4.8 n
utrients are m
ost commonly applied to 的NPs可以通过角质层通道直接进入叶片[22]，而粒径较大的NPs
oil and plant leave可以通过气孔进入。由于气孔本身密度高，气孔通路被认为是吸收NP的更有效途径[23]。NF被气孔吸收后，通过韧皮部转移到植物的其余部分。纳米颗粒可以通过两种方式进入韧皮部，直接从韧皮部细胞进入韧皮部，或者通过韧皮部细胞的间隙进入韧皮部[24]。纳米肥料可以促进植物生长部位快速获取养分，从而增加叶绿素的产生、光合速率，并最终增加植物的生长发育[25]。
2. 叶面纳米肥的农业应用
纳米肥料由于其独特的特性，在提高养分利用效率方面变得越来越重要[28]。纳米肥料有助于以缓慢、可控的方式释放养分，以便将养分输送到目标位置，从而将损失降至最低[29]。纳米肥料由于尺寸小，比传统肥料具有更大的吸收和保留能力[30]。纳米肥可以改善植物的生理生化指标，如光合速率和养分吸收效率等，增强植物的防御系统[7]。一些研究报道，锌NFs
, and soil fertilization is more desirable and effective for larger n具有更好的理化性质，在促进种子发芽和植物生长方面起着积极作用[31\u
trient needs [1]. In some cases, 201232]。Ah
owever, foliar fertilization has become
a widespread and common method of crop management dd等人表明，硫纳米肥料不仅可以减轻砷的毒性，还可以提高水稻的产量和质量[33]。Hu
e to it等人证明，低水平的 TiO2NPs
more cost-effective and efficient characteristic s [1].在不引起显著氧化应激的情况下改善了植物营养品质[34]。总体而言，纳米肥料比传统肥料更有效，具有良好的发展前景。
叶面施肥比土壤施肥更有效，是满足高等树种需求的有用方法[35]（图3）。与叶面施用相比，土壤施用对环境的危害更大，纳米肥料在土壤中的生物利用度较低，而叶面施用的环境风险较低，因此植物通常更喜欢叶面施用纳米肥料[36]。叶面施肥的暴露剂量低，可反复施用，并可根据天气定时施用，避免养分流失[11]。此外，叶面施用比土壤施用提供更快的养分吸收[37]。图3说明了叶面施肥的优点及其对植物的积极影响。
2.1. 提高作物产量和质量
叶面施用纳米肥可以提高肥料的利用效率以及作物的产量和品质，并在一定程度上减少不良影响。
The leaves of the pla锌（Zn
t protect the plant from water loss, pests and pathogens, while allowing gas exchange for the photosynthetic）作为一种必需的微量营养素，对植物有重大影响，包括蛋白质、DNA和RNA的合成，也是许多抗氧化酶所必需的辅助因子。关于叶面喷施锌基纳米肥对作物的有利影响的研究很多。Lorenzo等人发现，由于ZnO NPs穿透叶片的能力提高，ZnO NPs改善了咖啡的生长和生理机能，对果实和品质的影响比ZnSO更积极4 reactio[Garcia-Lopez等人证明，叶面喷施Zn
O [2]. The surface of a leaf is usually composed of features: trichosomes, stomata, and phloem pores. NPs
（1000 is absorbed by leaves in two ways, namely the cuticle pathway and the stomatal pathway [3]（Figure 1mg/L和2000 mg/L）
. NPs with a diameter 可提高哈瓦那辣椒果实的抗氧化能力，并显著改善果实品质[38]。Ko
f le
ss than 4.8 nm can enter the leaf directly through the cuticle chancik等人发现，TiO2Zn
nel,O while NPs with a larger diameter can enter through the NPs处理提高了向日葵的产量和营养参数，但TiO2NPs
tomata. Due to the high de处理具有潜在毒性，而Zn
sity of the stomata itself, the stomatal pathway is considered to be a more efficient way to absorb NP [4]. NF iO NPs
处理未检测到毒性[39]。Da
bsorbed by the stomva
ta and transferred to the rest of the plant through the phloem. Nanoparticles can enter phloem in two waysrpanah等得出结论，叶面喷施较低浓度的B或Zn纳米肥可以促进石榴的产量，且果实的特性不受影响[40]。还有其他研究表明，叶面施用锌纳米肥不仅增加了叶片数量和精油含量，还显著提高了植物的生长、产量和养分含量[41,42,43,44,45,
either directly from phloem cells or thro46]。可以看出，叶面施用锌纳米肥对作物产量、品质、养分量和生理参数的改善有正向影响，可能没有潜在的毒性，但需要注意的是，不同植株的最佳浓度差异可能较大。
2.2. 减轻环境压力
环境胁迫效应会改变生态系统过程[53]，破坏生态系统平衡，进而破坏与粮食生产相关的环境平衡，可能导致作物减产[54]。重金属、盐碱化、干旱和高温都是对全球作物生产力和质量产生严重影响的关键环境压力源[55]。人们已经寻求各种策略来提高植物承受这些众多环境压力的能力[56]。纳米肥料效率高、释放慢，已成为减轻环境胁迫效应[57\u201258]和促进恶劣环境下作物栽培的合适选择[59\u
gh the inter201260]。多项研究证实了NPs
titiums of phloem cells 对温度胁迫下植物的积极作用，包括提高光合能力[61]和促进生长发育[
2462]
. Nano-f。然而，对热应激的研究还不够;因此，本文介绍了纳米肥料在缓解重金属胁迫、盐胁迫和干旱胁迫中的应用，这些都是目前研究中比较关注的方面。
2.2.1. Heavy Metal Stress
He
rtilizer ca
n promote the rapid acquisition of nutrients in plant growth parts, thereby increasing chlorophyll production, photosynthetic rate, and ultimately increase plant growth and developmentvy metals are taken up by plants and [5].
Figure 1. Methods and influencing factors of foliar application of nanoparticles.
2. Agricultural application of foliar nano-fertilizer
Na
no-fertilizers are becc
oming more and more important in improving nutrient utilization efficiency due to their unique propertieumulate in grain crops
[6]. Rice f
eor
tilizer helps to release nutrients in a slow, controlled manner in order to deliver nutrients to the target location, thereby minimizing losses [7]. N human and anima
no-fertil
izers have greater absorption and retention capacity than traditional fertilizers due to their small size [30]. Nano-fertilizer can improve the physiological and biochemical indexes of plants, such as photosynthetic rate and nutrient absorption efficiency, and enhance the defense system of plants [8]. Som consumption, seriously e
studies have reported that zin
c NFs has better physical and chemical properties and plays a positive role in promoting seed germination and plantdangering crop growth
[9][10]. Ahmed et a
l. have shown
that sulfur nanofertilizers can not only reduce arsenic toxicity, but also improve the yieldd human health [63,64]. Man
d quality of rice [11]. Hu et al. proved that low ley inve
ls
of TiO2NPs improved plant nutritional quality without causing significant oxidative stress [12]. In tigations have sugge
neral, nano-fertilizer is
more effective than traditional fertilizer and has good prospects for development.
Folited that nanopar
ferti
lization is more effective than soil fertilization and is a useful method to meet the needs of higher tree species (Figure 2). Compared with foliar application, soil application is more harmful to the environment, and nano-fertilizer has lower bioavailability in the soil, while foliar application has lower environmental risk, so cles can mitigate heavy metal stress on plants
generally[65,66]. prefer fFoliar application of
nano-fertilizer. Foliate fertilization has a low exposure dose, can be applied repeatedly, and can be applied regularly according to the weather to avoid nutrient loss. In addition, foliar application provides faster nutrient uptake than soil application [13]. Figure 2 illuSe and Si NPs alleviates metal str
ates
the advantages of foliar fertilization and its positive effects on plants.
Figure 2. Foliar application.
2.1. Improve crop yield and quality
Folias in r
applic
ation of nano-fertilizer cane and improve
fertilizer utilization efficiency and crop s brown rice yield and quality
, and [67]. reduce adverse effects tFo
a certain extent.
Zinc (Zn), as an essential
mi
cronutrient, has a major impact on plants, including protein, DNA, and RNA synthesis, and is also an essential cofactor for many antioxidant enzymes. There are many studies on the beneficial effects of zinc-based nano-fertilizer spraying on crops. Lorenzo et al found that ar application of ZnO NPs
improved the growth and physiology of coffee due to the increased ability of ZnO NPs to penetrate leaves, and had a more positive effect on fruit and quality than ZnSO4 [Garcia-Lopez et al demonstrated, ZnO NPs (1000 mg/L and 2000 mg/L) sprayed on the leaf surface increased the antioxidant capacity of Habanos pepper fruit and significantly improved the fruit quality [14].Davarpanah mitigated Cd contamination and increase
t al. conclud
ed that spraying a lower concentration of B or Zn nano-fertilizer on the leaf surface could promote the yield of pomegranates without affecting the characteristics of the fruit [15]. Other stu plant height and
ies have shown that leaf surface application of zinc nano-fertilizer not only increases the number of leaves and essential oil content, but also significantly improves plant growth, yield and nutrient content [16][17][18][19][20][21]. It biomass as well as chlorophyll conc
an be
seen that leaf surface applicantration of
zinc nano-fertilizer has a positive effect on the improvement of crop yield, quality, nutrient contentmaize plants [68]. and physiFol
ogical parameters, and there may be no potential toxicity, but it should be noted that the optimal concentration of iar application of TiO2NPs显著降低茎畲含量，对降低Cd
诱导的毒性有显著贡献;然而，土壤中Ti
fferent plantO的施用2NPs
may vary greatly.增加了玉米在Cd污染土壤中对Cd的吸收[69]。综上所述，叶面施用纳米肥对土壤重金属污染有缓解作用，在一定程度上可能比土壤施用更有用。然而，需要注意的是，重金属的存在可能会促进植物中纳米颗粒的吸收和富集，并产生共毒性，从而导致食品安全问题[70]。
2.2. Reduce environmental stress
2.2.2. 盐胁迫
Environmental stress effects will change ecosystem processes [22], destroy ecosystem 盐度被认为是限制全球作物产量的主要非生物胁迫之一[71\u201272]。盐胁迫限制了生长，减少了生物量，导致叶绿素降解并改变了水的状态[73]。针对盐胁迫的更环保的缓解策略以提高作物产量对农业部门至关重要[74]。Ab
alance, and
then destroy the environmental balance relelaal等人证明，叶面施用硅可以通过改善水分状态、提高光合速率、调节某些渗透压和植物激素以及提高抗氧化酶活性来减轻盐胁迫对甜椒的不利影响[75]。Ha
ted to food productji
on, which may lead to crop yield reduction [23]. Heavy metalhas
, salinization, drough
t, and high temperatures are all key environmemi等人证明，叶面喷施二氧化硅纳米肥料可以通过改善酶和非酶抗氧化系统来显着提高小麦植物的抗盐性[76]。Pe
ntal stre
ssors that have serious impacts on global crop productivity and quality [24]. Varioz-Labrada等人认为，叶面施用Cu
s str纳米颗粒通过提高Na
t+/K+比率以及刺激植物的抗氧化机制来增强耐盐性[77]。She
gi
es have been sought to enhance the ability of plants to withstand these numerous environmental stresses [25]. khalipour等研究证明，叶面施用Cs-Se N
ano-fertilizer haPs
high efficiency and slow release, and ha可提高叶片光合色素含量，促进植物生产，并通过提高SOD、POD和CAT酶的活性来减轻盐胁迫条件下的氧化损伤[78]。Mus
become a suita
ble choice to reduce environmental stress effects [26][27] fa
nd promote crop cult等人发现，叶面施用低剂量Ti
vatioO2纳米颗粒改善了小麦的发芽特性以及水分和渗透潜力，并有助于提高植物对盐胁迫的耐受性[79]。此外，一项综述表明，施用Zn
i和Zn
harsh environments [28][29]. O NPs可以减轻盐胁迫对作物产量和品质的不利影响，并增加蛋白质含量和抗氧化能力[37]。硅纳米肥在缓解盐胁迫方面具有积极作用[55,80,81]。例如，A
number of ls
tudies have confirmed the positive effects of NPs oaeedi等人的研究结果表明，无定形二氧化硅纳米颗粒（Si NPs）有助于黄瓜植株在盐胁迫下的正常生长，在整个生长季节没有任何明显的缺水症状[82]。然而，叶面施用硅肥尚未得到充分研究，是一个新的研究方向。硅纳米颗粒作为喷涂其他纳米颗粒的涂层也相对较新。一项研究表明，叶面施用Zn
O plants under temperature stress, iNPs和ZnO-Si NPs对盐胁迫下的豌豆植株有不同的影响[83]。较高浓度的Zn
cludingO improving photosynthetic capacity [30] and promoting growth and development [31]. However, heat NPs会产生一定的植物毒性作用，而ZnO-Si NPs
tress has 在生理条件下对植物无毒性，在较高浓度下甚至具有轻微的刺激作用。叶面施用纳米肥是缓解盐胁迫的趋势之一。
2.2.3. 干旱胁迫
干旱条件也是制约作物产量的关键因素，导致植物在形态、生理和分子水平上经历许多不利胁迫[84]，影响植物生长、生理和产量[85]。干旱胁迫通常是干旱诱导的气孔闭合导致氧化应激的结果，进而导致叶绿体和线粒体中ROS的产生增加[86,87]。干旱胁迫通过改变叶绿素和其他光合色素的含量来限制光合过程，从而导致植物停止生长[88,89,90]。此外，随着干旱的恶化，土壤盐碱化和钙化加剧，这反过来又导致生产力显着下降[91]。在缺水的半干旱热带地区，叶面施用纳米肥料可能是提高产量的最佳选择，因为其溶解和被根系吸收需要大量的水[92]。叶面施用纳米肥料作为生长调节剂，可促进干旱条件下的作物发育和生产力[92]。例如，叶面喷施Zn
otO been studied enNPs可提高产量和作物品质[41,93]以及种子的营养品质[94]，并改善气孔导度和作物干旱胁迫指数[94]。此外，Mo
ugh; Therefore, thi
s paper introduces the application of nano-fertilizer in alleviating heavy metal stress, salt stress and drought stress, which artazedi等人发现，叶面施用锌肥可显著改善干旱胁迫对膜稳定指数（MSI）的影响[95]。研究还表明，在缺水条件下，叶面喷施Fe
relatively co和Zn
cerned aspects in current research.纳米肥可改善正常灌溉的豆类生理特性和种子产量[85\u201296]。叶面施用K-纳米螯合物可改善生长、生理生化特性，增加定量和定性性状，减轻水分胁迫的负面影响[97]。叶面施用镁纳米肥和壳聚糖肥可提高叶绿素总产量、种子产量和含油量，并缓解干旱胁迫[98]。除了几种金属纳米肥料外，非金属纳米肥料也已用于许多应用。
2.2.1. Heavy Metal Stress
Heavy metals are absorbed by plants and accumulate in food crops for human and animal consumption, seriously endangering crop growth and human health [32][33]. Many studies have shown that nanoparticles can reduce plant stress to heavy metals [34][35]. Leaf application of SE and SI, NPK can alleviate metal stress of rice and improve the yield and quality of brown rice [36]. Spraying ZnO NPs on the foliage reduced Cd pollution and increased the plant height, biomass and chlorophyll concentration of maize plants [37]. Foliar application of TiO2NPs significantly reduced She content and CD-induced toxicity in stems. However, the application of TiO 2NPs to soil increased the absorption of Cd by corn in CD-contaminated soil [38]. In summary, the application of nano-fertilizer on the surface of leaves has a alleviating effect on soil heavy metal pollution, and may be more useful than soil application to a certain extent. However, it should be noted that the presence of heavy metals may promote the absorption and enrichment of nanoparticles in plants and produce co-toxicity, leading to food safety issues [39].
2.2.2. Salt stress
Salinity is considered to be one of the major abiotic stresses that limit crop yields globally. Salt stress limits growth, reduces biomass, causes chlorophyll degradation and alters the state of water [40]. Abdelaal et al proved that leaf surface application of silicon alleviated the adverse effects of salt stress on sweet pepper by improving water state, increasing photosynthetic rate, regulating certain osmotic pressure and plant hormones, and increasing antioxidant enzyme activity [41]. Perez-Labrada et al. Foliar application of Cu nanoparticles enhanced salt tolerance by increasing the Na+/K+ ratio and stimulating the antioxidant mechanism of plants [42]. Sheikhalipour et al. proved that foliar application of Cs-Se NPs could increase photosynthetic pigment content in leaves, promote plant production, and reduce oxidative damage under salt stress by increasing SOD, POD and CAT enzyme activities [43]. Mustafa et al. found that leaf spraying with low-dose TiO2 nanoparticles could improve the germination characteristics, water and permeability potential of wheat, and help improve plant tolerance to salt stress [44]. Nano-silicon fertilizer plays a positive role in alleviating salt stress [24][45][46]. For example, Alsaeedi et al. showed that amorphous silica nanoparticles (Si NPs) contribute to the normal growth of cucumber plants under salt stress without any significant symptoms of dehydration throughout the growing season [47]. However, foliar application of silicon fertilizer has not been fully studied and is a new research direction. Silicon nanoparticles are also relatively new as a coating for spraying other nanoparticles. A study showed that ZnO NPs and Zno-Si NPs had different leaf application effects on pea plants under salt stress [48]. Higher concentrations of ZnO NPs can produce certain phytotoxic effects, while Zno-Si NPs is non-toxic to plants under physiological conditions, and even has a slight irritating effect at higher concentrations. The application of nano-fertilizer on leaf surface is one of the trends to alleviate salt stress.
2.2.3. Drought stress
Drought condition is also a key factor restricting crop yield, causing many adverse stresses on plant morphology, physiology and molecular level [49], affecting plant growth, physiology and yield [50]. In addition, as drought worsens, soil salinization and calcification increase, which in turn leads to a significant decline in productivity [51]. In semi-arid tropical regions where water is scarce, foliar application of nanomaterials may be the best option for increasing yield, as it requires a large amount of water to dissolve and be absorbed by the root system [52]. Foliar application of nano-fertilizer as a growth regulator can promote crop development and productivity under drought conditions [52]. For example, leaf spraying ZnO NPs can improve yield and crop quality [16][53] and seed nutritional quality [54], as well as stomatal conductance and crop drought stress index [54]. In addition, Moitazedi et al found that zinc fertilizer applied to foliage could significantly improve the influence of drought stress on membrane stability index (MSI) [55]. Studies have also shown that under water shortage conditions, spraying Fe and Zn nano-fertilizer on leaf surface can improve the physiological characteristics and seed yield of legumes under normal irrigation [50][56]. Leaf surface application of K nanochelate can improve growth, physiological and biochemical characteristics, increase quantitative and qualitative traits, and reduce the negative effects of water stress [57]. The application of magnesium nano-fertilizer and chitosan fertilizer on the surface of leaves can improve the total chlorophyll yield, seed yield and oil content, and alleviate drought stress [58]. In addition to several metallic nano-fertilizers, non-metallic nano-fertilizers have also been used in many applications.
In conclusion, the application of nano-fertilizer on leaf surface under abiotic stress can improve plant enzyme activity and enhance plant antioxidant capacity. These improvements can increase crop resistance to adversity, resulting in higher yields and quality.
综上所述，在非生物胁迫下叶面施用纳米肥可以提高植物酶活性，增强植物抗氧化能力。这些改良可以提高作物对逆境的抵抗力，从而提高产量和质量。
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