Potential of root acid phosphatase activity to reduce phosphorus fertilization in maize cultivated in Brazil

It is urgent to mitigate the environmental impacts resulting from agriculture, especially in highly biodiverse and threatened areas, as the Brazilian Cerrado. We aim to investigate whether root acid phosphatase activity is an alternative plant strategy for nutrient acquisition in maize genotypes cultivated under fertilized and unfertilized conditions in Brazil, potentially contributing to reducing the use of phosphate fertilizers needed for production. Three experiments were performed: the first was conducted in a glasshouse, with 17 experimental maize inbred lines and two phosphorus (P) treatments; the second in the field, with three maize inbred lines and two treatments, one without fertilization and another with NPK fertilization; and the third was also carried out in the field, with 13 commercial hybrids, grown either under NK or under NPK treatment. Plant variables were measured and tested for the response to fertilization, differences amongst genotypes and response to root acid phosphatase activity. The activity of root acid phosphatase was modulated by the availability of P and nitrogen (N) in the soil and promoted grain filling of commercial hybrids in soils with low P availability. These results demonstrate that it is possible to select genotypes that are more adapted to low soil P availability aiming at organic production or to use genotypes that have high phosphatase activity under P fertilization to reduce the amount of added P needed for maize production in Brazil. 

Glasshouse study

A glasshouse study was conducted from August to October 2018 in Ilha Solteira, São Paulo State, Brazil (20°25’04.77’’S 51°20’30.65’’W, 375 m elevation). We used 3.5 L pots filled with 3.2 kg dry soil of 2 mm-sieved Cerrado soil (dystrophic Red Latosol – Oxisol) [27]. From seeds, seventeen genotypes were cultivated under each of two treatments (control – only distilled water added, or P fertilization – 768 mg sodium phosphate (Na₂HPO₄), equivalent to 200 mg.P.kg^-1 soil, as suggested by Novais et al. [28]), in three replicates, in a total of 102 pots. These inbred lines were chosen because they are experimental genotypes developed at São Paulo State University (UNESP – Campus of Ilha Solteira) and are potential candidates for a future breeding program (S1 Table).

In the 9-leaf stage of the plants, the pot was removed, and the roots were collected and washed first with tap water and then with distilled water. We then evaluated rPME activity, plant height, number of leaves, stem diameter, root water content, aerial dry biomass, root dry biomass and total dry biomass. The measurements were performed during this plant stage because it represents the end of the plant vegetative stage and the start of the most P-demanding stage of the crop.

Root PME activity was measured using 100 mg fresh roots in 5 ml p-NPP (para-nitrophenylphosphate). Root samples were taken to the laboratory for immediate measurements, and 3–5 analytical replicates were used per plant (p-NPP) bioassay [29]. Plant height and stem diameter were measured with a flexible ruler. Aerial dry biomass, root dry biomass, root plant water content and total dry biomass were measured after drying the material at 60 °C for 72 h.

The chemical attributes of the soil used for the experiment are: 11 mg.dm^-3 resin-P; 19 g.dm^-3 organic matter; water-pH 5.0; K, Ca, Mg, H⁺, Al = 1.4; 11.0; 9.0 and 22.0 mmol_c.dm^-3, respectively; Cu, Fe, Mn, Zn = 1.6; 16.0; 20.0 and 0.7 mg.dm^-3, respectively; 0.17 mg.dm^-3 B, CEC= 43.4 0 mmol_c.dm^-3, 49% bases saturation and granulometry of 420, 50 and 530 g.kg^-1 of sand, silt and clay respectively. Extractable P was measured colorimetrically after extraction with ion exchange resin and then washed with 0.8 M NH₄Cl and 0.2 M HCl. N concentration was measured using the micro-Kjeldahl procedure. Extractable sulfur (S) was measured colorimetrically after extraction with activated charcoal and 0.01 M Ca(H₂PO₄). Soil pH was measured in a soil–water suspension (10 g dry soil in 50 ml deionized water) using a Metrohm Herisau pH meter with a Mettler Toledo electrode. Soil organic matter content was determined colorimetrically after extraction for 10 min with 0.667 M sodium dichromate and 5 M sulfuric acid. Soil extractable B was measured after extraction of 10 cm⁻³ dry soil with 20 ml barium chloride 6 mM solution by heating in a microwave at 490 W for 5 min. The B concentration was measured colorimetrically using the azomethine‐H method and adsorption at 420 nm on a spectrophotometer (Varian 50 Probe). Extractable Ca, Cu, Fe, Mg, Mn, K, and Zn concentrations were measured by means of atomic adsorption. Extractable Al was measured after extraction with 1 M KCl and titration with NaOH using the phenolphthalein method. All soil chemical characteristics were determined through standard methods at the UNESP Soil Laboratory according to Raij et al. [30], Lannes et al. [31] and Teixeira et al. [32]. At the end of the experiment, one soil sample per pot was collected for determinations of nutrients following the same methods.

Field study 1

Field study 1 was performed from November 2018 to January 2019 in Selvíria, in the State of Mato Grosso do Sul, Brazil (20°20’50.65’’S 51°24’06.32’’W, 344 m elevation), located 11 km on the Northwestern of Glasshouse study area. Soils are classified as dystrophic Red Latosol – Oxisol [27]. Climate is characterized as Aw [33], tropical wet with a rainy season generally occurring from November to March and a pronounced dry season from April to October.

From seeds, we cultivated four genotypes under two fertilization treatments and three replications, in a total of 24 plants used for analysis. The genotypes were constituted by three inbred lines, L4, L8 and L12 (S1 Table) – which were selected because they had significantly lower rPME in the control than in P fertilized pots in the Glasshouse study, and a flint maize population (Pop), selected for low technology, genetically variable and equilibrated. The treatments used were control – only water added, or NPK fertilization – 20 kg.ha^-1 (N): 51.6 kg.ha^-1 (PO₄): 33.2 kg.ha^-1 (K). The plants were grown on lines with 3-meter length each with inter-row distance of 0.90 m (S2 Fig). This experiment was not randomized due to the aim of performing the cross-pollination manually, to obtain maize single-cross, where each genotype on its line was parallel with another line of an inbred line of interest for cross-pollination, with all possible combinations being carried out. The flint maize population was sown around the inbred lines and their harvest was random within each soil fertilization treatment (S2 Fig). To prevent water stress, all plots were irrigated two to three times a week according to the normal on-farm practice in this area, i.e., irrigation per demand following the evapotranspiration rate of the area according to our meteorological station (https://clima.feis.unesp.br/), which corresponds to a year average of 3 mm per day. In the 10-leaf stage of the plants we measured plant height and rPME using the abovementioned methods after removing parts of the roots using a shovel and washing first with tap water and then with distilled water.

At the end of the experiment, thirty top-20 cm soil samples were collected with a 5 cm diameter auger and combined in a composite sample. Samples were air dried, sieved and sent to the UNESP Soil Laboratory for determination of chemical attributes as previously described. 

Field study 2

A second field study was conducted from April to September 2019 in an area located close to where Field Study 1 took place. We used 13 commercial hybrids (S2 Table), widely used in the region [34–44], with cycle is semi-early, early or super-early, single-cross and double-cross. In three randomized blocks and two treatments: Control – NK addition (20 kg.ha^-1 (N): 0 (PO₄): 33.2 kg.ha^-1 (K)), or NPK fertilization (20 kg.ha^-1 (N): 51.6 kg.ha^-1 (PO₄): 33.2 kg.ha^-1 (K)). The plants were grown on 6 lines with 5-meter length each with inter-row distance of 0.45 m, in a total density equivalent to 60,000 plants per hectare (S3 Fig). To prevent water stress, all plots were irrigated two to three times a week according to the normal on-farm practice in this area. In the 10-leaf stage, one random plant from each block (total of 78 plants) was used for measuring rPME, number of leaves and root plant water content, and at the beginning of the reproductive stage, the plant height and ear height were measured using five random plants from each block. Ear height refers to height of insertion of the first ear and plant height is the height of the last fully open leaf. For the destructive methods, the whole field plant was gently removed from the soil using a shovel, the roots were washed first with tap water and then with distilled water. After harvest, we measured the weight of 100 randomly selected grains; we selected this variable to allow the analysis of the influence of phosphatase upon grain weight independently on the amount of grains each genotype produces.

At the end of the experiment, thirty top-20 cm soil samples were collected with a 5 cm diameter auger and combined in a composite sample. Samples were air-dried, sieved and sent to the UNESP Soil Laboratory under the current methods mentioned in the previous sections.

Data analyses

The effect of fertilization upon measured variables was analysed through Student t-tests, and the differences amongst genotypes were assessed through ANOVA followed by Tukey test using IBM SPSS Statistics 20. Cohen’s d effect sizes [45] were calculated as standardized differences between means of total biomass, aerial biomass, root biomass, stem biomass, number of leaves, height and root phosphatase activity between P fertilized and control plots. Linear regression analyses were employed to assess the effects of rPME on growth and productivity parameters. Data were log-transformed when necessary to reach normal distribution and homoscedasticity.

References

[27] - Santos HG, Jacomine PKT, Anjos LHC, Oliveira VA, Lumbreras JF, Coelho MR, Almeida JÁ, Filho JCA, Cunha TJF, Oliveira JB. Sistema brasileiro de classificação de solos. 5th ed. Embrapa. 2018. Available from: https://ainfo.cnptia.embrapa.br/digital/bitstream/item/199517/1/SiBCS-2018-ISBN-9788570358004.pdf

[28] - Novais RF, Ferreira PR, Neves JCL, Barros NF. Absorção de fósforo e crescimento do milho com sistema radicular parcialmente exposto a fonte de fósforo. Pesquisa Agropecuária Brasileira. 1985;20(7): 749–754.

[29] - Olde Venterink H. Legumes have a higher root phosphatase activity than other forbs, particularly under low inorganic P and N supply. Plant and Soil. 2011;347: 137–146. https://doi.org/10.1007/s11104-011-0834-7

[30] - Raij B, Andrade JC, Cantarella H, Quaggio JA. Análise química para avaliação da fertilidade de solos tropicais. 1st ed. Instituto Agronômico. 2001. https://www.iac.sp.gov.br/publicacoes/arquivos/Raij_et_al_2001_Metod_Anal_IAC.pdf

[31] - Lannes LS, Olde Venterink H, Leite MR, Silva JN, Oberhofer M. Boron application increases growth of Brazilian Cerrado grasses. Ecology and Evolution. 2020;10(13): 6364–6372. http://doi.org/10.1002/ece3.6367

[32] - Teixeira DS, Rezende AA, Lannes LS. Response of vegetation to sheep dung addition in a degraded Cerrado area. Revista Brasileira de Engenharia Agrícola e Ambiental. 2019;23: 47–52. https://doi.org/10.1590/1807-1929/agriambi.v23n1p47-52  

[33] - Köppen W. Klassifikation der klimate nach temperatur, niederschlag und jahreslauf. Petermanns Mitt. 1918;64: 193–203.

[34] - Almeida IPC, Silva PSL, Negreiros MZ, Barbosa Z. Baby corn, green ear, and grain yield of corn cultivars. Horticultura Brasileira. 2005;23(4): 960–964. https://doi.org/10.1590/S0102-05362005000400020

[35] - Fidelis RR, Miranda GV, Erasmo EAL. Seleção de populações base de milho sob alta e baixa dose de fósforo em solo de cerrado. Pesquisa. Agropecuária Tropical. 2009;39(4): 285–293. https://www.revistas.ufg.br/pat/article/view/3496/5826

[36] - Silva PSL, Silva KMB, Silva PIB, Oliveira VR, Ferreira JLB. Green ear yield and grain yield of maize cultivars in competition with weeds.  Planta Daninha. 2010;28(1). https://doi.org/10.1590/S0100-83582010000100010

[37] - Mendes SM, Boregas KGB, Lopes ME, Waquil MS, Waquil JM. Fall armyworm responses to genetically modified maize expressing the toxin Cry 1A(b). Pesquisa Agropecuária Brasileira. 2011;46(3). https://doi.org/10.1590/S0100-204X2011000300003

[38] - Costa CTS, Teodoro I, Silva S, Cunha FN, Teixeira MB, Soares FAL, Morais WA, Silva NF, Gomes FHF, Cabral LBS. Agronomic performance, production components and agricultural productivity of maize (Zea mays L.) cultivars. African Journal of Agricultural Research. 2016;11(43): 4375–4383. https://doi.org/10.5897/AJAR2016.11587

[39] - Galindo FS, Teixeira Filho MCM, Buzetti S, Rodrigues WL, Fernandes GC, Boleta EHM, Barco Neto M, Biagini ALC, Baratella EB, Souza JS. Nitrogen rates associated with the inoculation of Azospirillum brasilense and application of Si: Effects on micronutrients and silicon concentration in irrigated corn. Journal Open Agriculture. 2018;3(1): 510–523. https://doi.org/10.1515/opag-2018-0056

[40] - Mijone AP, Nogueira APO, Hamawaki1 OT, Maes ML, Pinsetta Junior JS. Adaptability and stability of corn hybrids in the off season across various agricultural regions in Brazil. Genetics and Molecular Research. 2019;18(3): gmr18193. http://dx.doi.org/10.4238/gmr18193

[41] - Pereira NCM, Galindo FS, Gazola RPD, Dupas E, Rosa PAL, Mortinho ES, Teixeira Filho MCM. Corn yield and phosphorus use efficiency response to phosphorus rates associated with plant growth promoting bacteria. Frontiers in Environmental Science. 2020;8: 40. https://doi.org/10.3389/fenvs.2020.00040

[42] - Queiroz P, Alves Filho I, Pereira Junior S, van Cleef FS, Ezequiel J, Kaneko F, van Cleef EHCB. PSIX-10 in vitro dry matter digestibility, gas production and pH of silages of several maize hybrids. Journal of Animal Science. 2020;98(4): 415–416. https://doi.org/10.1093/jas/skaa278.725

[43] - Pereira CS, Zanetti VH, Schoffen ME, Wiest G, Fiorini IVA. Characters of production and ClorofiloG®index of thirteen maize hybrids in northern Mato Grosso. Agrarian. 2021;14(52): 233–240. https://doi.org/10.30612/agrarian.v14i52.10333

[44] - Faria RD, Fanela TLM, Sartori MMP, Lopes JRS, Lourenção AL, Baldin ELL. Evaluation of resistance of BT and non-BT maize genotypes to Dalbulus maidis (Hemiptera: Cicadellidae) and associated mollicutes, Phytoparasitica. 2022. https://doi.org/10.1007/s12600-022-00999-z

[45] - Cohen J. Statistical power analysis for the behavioral sciences. Hilldale: Lawrence Earlbaum Associates. 1988.