1,? 2 2 2 2 1 2 ?1 ?1 2 ?1 ?1 ? Silicon(Si)is classified as a beneficial or useful element for plant growth(Marschner,1995;Mendes et al.,2011).The beneficial effects of Si on crops include yield gain,increased resistance to pests and diseases(biotic factors),and the mitigation of metal toxicity,salt stress,and drought stress(abiotic factors),among others(Epstein,2001).Rice(Oryza sativa L.)accumulates Si(Mengel and Kirkby,1987;Ma et al.,2001;Mendes et al.,2011),leading to improved crop nutrition and induction of the formation of organosilicon in the leaves,which cooperate to improve crop yield under biotic or abiotic benefits of Si application to rice may studies indicate a lack of response of rice plant to Si(Ramos et al.,2012;Artigiani et al.,2014)because of the absence of reports claim grain yield increase in response to Si application in the presence of stressors(Kornd¨orfer et al.,1999b;Guimar?aes et al.,2013;Moro et al.,2015).The increase of rice sheath lignification is one of the beneficial effects of Si is associated with the lignincarbohydrate complex in leaf epidermal cell walls and increases lignification in these structures,consequently improving resistance to pests and pathogens(biotic factors)(Schurt et al.,2013).The presence of Si in the leaf blades,sheaths,and stems reduces the C content present in these parts of the ,metabolic costs are lowered since Si compounds are energetically cheaper to form compared with C ,higher Si supply increases shoot growth of Phragmites australis by altering the C:N:P stoichiometry in plant tissues(Schaller et al.,2012). The most common Si source in agriculture is calcium silicate,some of which is derived from industrial or mining waste,such as steel slag.In this case,calcium silicate is likely to be contaminated with phytotoxic heavy metals(Prado et al.,2001).Other Si sources include wollastonite,a naturally occurring rock of limited availability,and manufactured sources such as potassium high doses of Si(960 kg ha ?1 Studies on soluble Si sources supplied to rice crops,especially potassium silicate,have focused on foliar applications(Pawar and Hegde,1978;Hegde and Pawar,1981).No research has been reported on silicate application to soil,while few studies have addressed the use of Si nanoparticles in investigation of the use of Si nanoparticles is an important first step to expand Si application to rice ,the effect of new Si sources on rice crops,aiming to meet crop demands,increase the production of basic organic compounds,and boost yield,may be more prominent under biotic and/or abiotic hypothesis is that nanosilica will perform better compared with other soluble Si sources,regarding Si uptake by plants,lignin biosynthesis,C:N:P stoichiometry,and grain yield in rice.The objective of this study was to evaluate the effects of highly soluble silicate and nanosilica,applied to rice seeding furrows,on plant Si uptake,lignin content,C:N:P stoichiometry,physiological attributes,and grain yield of rice. MATERIALS AND METHODS Experimental site and soil The experiment was carried out between January and April 2016 under greenhouse conditions at S?ao Paulo State University(UNESP),Jaboticabal, minimum and maximum temperatures and relative humidity during the experimental period were 21 ? ? ?1 2 ?1 ?3 c ?3 c ?3 c ?3 c ?3 c ?3 min max Experimental design The experimental design was completely randomized and consisted of a 2×4 factorial scheme(two sources and four doses of Si)with four treatments included the application of nanosilica(Si=106.0 g L ?1 ?1 2 ?1 ?1 2 ?1 ?1 ? Before sowing and spraying,fertilizers were macerated and set aside for each pot,and then mixed into the entire soil volume before rice follo-wing fertilizer doses were used for 1 dm 3 ?3 ?3 ?3 Determinations of C,N,and lignin contents At blooming,all flag leaves of six plants were harvested and two plants remained intact until grain harvest in each pot.The flag leaves were washed with distilled water,dried in a forced air circulation oven at 65–70 ? To determine the lignin content,the acid detergent fiber(ADF)was first measured,followed by the“Klason”or acid detergent lignin(Silva and Queiroz,2002).For the ADF determination,50 mL acid detergent solution was added to 0.5 g sample of dried leaves,and then autoclaved at 1.5 atm for 40 min.The suspension was washed with 30–40 mL distilled water at 95–100 ? ? 2 4 ? ? ? ? ? Scanning electron microscopy(SEM)analysis The analysis process followed the protocol routinely used at the Laboratory of Electronic Microscopy of Faculdade de Ci?encias Agràrias e Veterinàrias of UNESP de Jaboticabal in Brazil(Maia and Santos,1997).Flag leaf blade segments of approximately 1 cm long were collected at blooming from the treatments with Si dose of 2420 g ha ?1 2 Determinations of experimental parameters The net C assimilation and transpiration rates were determined at the grain filling stage(milky grain),using two randomly selected flag leaves per plant in each pot.Gas exchange performance is better assessed when the photosynthetic photon flux density is higher and before the temperature increases to a limiting value for C3 photosynthesis(Feistler and Habermann,2012).Therefore,the plants were evaluated between 9:00 a.m.and 11:00 a portable infrared gas analyzer(LI-6400,LI-COR,USA).During the gas exchange measurement period,the temperature ranged from 31.4 to 37.9 ? ?2 ?1 ?2 ?1 At the grain physiological maturity stage,two plants from each pot were cut at the soil and stems were separated from the plants,except for the panicles,were dried in a forced air circulation oven at 65 ? ?1 Soil samples were collected from the top 15 cm of each pot,where the Si sprays were applied at samples were then air-dried and sieved through a 2-mm mesh Si content was determined using 0.01 mol L ?1 2 Data analysis Data were subjected to analysis of variance(ANOVA).The Si treatments were compared using the Tukey’s test at P<0.05.The effects of Si doses were evaluated by regression analysis,since the magnitudes of regression coefficients were significant at P<0.05 as determined by the statistical analyses were performed by the SISVAR 4.3(Ferreira,2008). RESULTS AND DISCUSSION Si in soil and plant and Si accumulation in plant shoot Nanosilica application increased the Si content in soil to a maximum of 4.31 g kg ?1 ?1 ?1 Regardless of the Si source,the maximum levels of Si in soil were not high as the products were applied locally and at moderate silicate significantly increased the Si content in leaf when compared with nanosilica(Fig.2),with a maximum of 8.49 g kg ?1 ?1 ?1 ?1 Regardless of the Si source,spray application increased Si accumulation in silicate increased Si accumulation in plant to a maximum of 282.93 g kg ?1 ?1 ?1 N and P accumulation Nanosilica was the most promising Si source for promoting greater increase in Si accumulation both in the soil and rice shoot when compared with other Si of the Si source,Si doses did not affect N and P accumulation in rice plant(Fig.3). The lack of correlation between Si dose and N accumulation in rice plant was reported by Artigiani et al.(2014),and the lack of correlation between Si dose and P accumulation in rice plant was reported by Alovisi et al.(2007). C and lignin contents in rice leaf The C content in the leaf blades of rice plants treated with nanosilica was lower than that of plants treated with soluble silicate(Fig.4).The reduction in C content at high Si levels may be due to the partial substitution of Si for C in the organic compounds of plant tissues(Schaller et al.,2012).According to Raven(1983),this change is advantageous to plant,since Si compounds are energetically cheaper to form,compared with C compounds,and provide structural protection such as lignified structures(Schoelynck et al.,2010).Inanaga et al.(1995)reported that Si was associated with a lignin-carbohydrate complex in rice epidermal leaf cell walls and may increase lignification. At all doses,nanosilica resulted in higher leaf lignin content than soluble silicate(Fig.4).At the Si dose of 2420 g ha ?1 C:N:P stoichiometry in rice shoot Determination of the C:N:P stoichiometry as a function of Si application may reveal the correlations between plant Si uptake,C fixation,and N and P forms phytoliths,which are energetically cheaper than the C compounds derived from enzymatic syntheses(Raven,1983).In the soil,phytoliths can promote the desorption of P from retention sites and increase its availability(Alovisi et al.,2007);they can also promote great accumulation of nitrate in the roots(′Avila et al.,2010).Nevertheless,in the present study,soluble silicate at the Si doses of 1210 and 2420 g ha ?1 In an experiment with ,Schaller et al.(2012)reported that Si availability might significantly affect C:N:P stoichiometric ratios in different tissues(leaf blades,sheaths,and culms).These findings corroborate those reported for wheat by Neu et al.(2017).In the present work,the C:N:P stoichiometric ratio refers to the mean shoot values excluding the panicle,which is possibly the reason why the Si treatments showed no pronounced addition,the Si doses(up to 2420 g ha ?1 Scanning electron microscopy analysis The SEM analysis showed large amounts of amorphous silica in the flag leaf blades of rice plants treatedwith soluble silicate and nanosilica at a Si dose of 2420 g ha ?1 ?1 ?1 The results from this study and that reported by Schaller et al.(2012)for suggest that rice plants can absorb Si.Mali and Aery(2008)indicated that transpiration promoted mineral transport to the shoot of correlations between Si doses,plant tissue content,and substrate concentration were reported for bamboo(Ding et al.,2008)and several crop species(Liang et al.,2006).Schaller et al.(2012)observed that Si uptake and deposition may vary according to the location and may depend on Si availability and transpiration. ?1 ?1 The plants passively absorb Si as monosilicic acid(H 4 4 4 4 4 4 Net C assimilation rate and transpiration in rice leaf A significant interaction was observed between the net C assimilation rate and the transpiration rate in rice leaf(Fig.6).Soluble silicate application increased the net C assimilation rate to a maximum of 26.45μmol CO 2 ?1 ?1 ?1 ?1 2 ?2 ?1 ?1 2 ?2 ?1 ?1 Previous studies reported a positive effect of Si on net C assimilation and leaf transpiration et al.(2014)observed improvements in C assimilation and transpiration rates in wheat plants supplied with Si.Moro et al.(2015)stated that the net C assimilation rate in rice increased with Si supplementation. Plant dry matter and grain yield The shoot dry matter weight of rice was not affected by the Si source(Fig.7).The same result was reported by Liang et al.(1994),Alovisi et al.(2007),and′Avila et al.(2010).The result,however,contradicts the findings reported by other authors(Deren et al.,1994;Liang,1994;Kornd¨orfer and Datno ff,1995;Kornd¨orfer et al.,1999a,b;Gerami and Rameeh,2012;Moro et al.,2015). The changes in rice physiology were not significant(Fig.6),because they did not influence the plant dry matter addition,grain yield was not signi ficantly influenced by Si source and dose(Fig.7).These results are in accordance with those reported by Ramos et al.(2012)and Artigiani et al.(2014).The fact that Si did not affect rice growth or grain yield may be attributed to the relative lack of biotic or abiotic stress in rice plants during the benefits of Si to crops subjected to several stresses,such as drought(Souza et al.,2013;Moro et al.,2015),hypersalinity(Alves et al.,2014),and others,have been widely reported in literature. CONCLUSIONS Little information is available on the physiological and agronomic changes that occur in plants exposed to is the first report on the effect of nanosilica applied to the soil on rice plant mineral nutrition in Brazilian application increased Si accumulation in rice plants,but affected neither the accumulation of N and P,nor the C:N:P increased the lignin content in rice leaf.No significant influence was observed on rice plant dry matter weight or grain yield with Si application,owing to the lack of biotic and abiotic study provides evidence that rice plants absorb and accumulate Si derived from nanoparticles applied to the studies should be performed to determine the potential of nanoparticles to enhance nutrition in other plant species. 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