Original Article
Raúl Cárdenas-Navarro1 , Jesús Alonso Luna-Béjar2 , Vilma del Carmen Castellanos-Morales1 , Nayda Luz Bravo- Hernandez1 and Luis López-Pérez1
1 Instituto de Investigaciones Agropecuarias y Forestales, Universidad Michoacana de San Nicolás de Hidalgo, Km 9.5 Carr. Morelia Zinapécuaro, 58880 Tarímbaro, Michoacán, México.
2 Facultad de Agrobiología “Presidente Juárez”, Universidad Michoacana de San Nicolás de Hidalgo, Paseo Lázaro Cárdenas 2290, Emiliano Zapata, Melchor Ocampo, 60170 Uruapan, Michoacán, México.
Efecto de la concentración y forma iónica del nitrógeno (N) en la fotosíntesis, crecimiento y producción de frutos de arándano (Vaccinium corymbosum L.)
The aim of this work was to evaluate the main effects and the
tendencia inicial registrada. La concentración de N modifica el efecto de la proporción NH +:NO - y se propone que los
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interactions of nitrogen (N) concentration and ammonium (NH +): nitrate (NO -) proportion in the nutrient solution, on
efectos de ambos factores sobre la fotosíntesis, el crecimiento
y la producción de frutos del arándano estuvieron mediados
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net photosynthesis, plant growth, production and quality
of fruits on blueberry (Vaccinium corimbosum L.) plants. The studied factors were N concentration (0.6 and 6.0 mM) and NH +: NO - proportion (100 % NH +, 50 % NH + - 50 % NO - and
por su interacción por la disponibilidad de carbohidratos de
la planta.
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100 % NO -). 243 d after the experiment was established, net photosynthesis (PN) was measured and a day after, leaf area (LA), shoots fresh weight (SFW) and roots fresh weight (RFW) were determined. Fruit yield (FY), fruit diameter (FD) and Brix degrees (oBrix) were evaluated in four harvests along fruit production period. The results showed higher values on PN, LA, SFW, FY and FD in plants that received 6.0 mM N as NH +;
nevertheless, N concentration altered the NH +: NO - propor-
Nitrogen (N) is considered the most important mineral nutrient for plants, it is found in a higher proportion than other essential elements (1 % to 3 % dry matter), depending on the plant species, phenological stage, and the organ. It is part of fundamental molecules for growth and development
such as nucleic acids, amino acids, proteins, chlorophylls and
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tion effects and at 0.6 mM N only FY and FD maintained such a pattern. It is concluded that N concentration modifies the
effect of NH +: NO - proportion and it is proposed that the
alkaloids (Marschner, 2011). Plants have developed physio- logical mechanisms to uptake mineral N from the soil, mainly in the forms of nitrate (NO -) or ammonium (NH +) (Errebhi
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effects of both factors on photosynthesis, growth and fruit
production of blueberry were mediated by their interaction
and Wilcox, 1990; Cárdenas-Navarro et al., 2006; Lobit et al., 2007). The N absorbed as NO - is reduced to NH + by the
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with plant carbohydrates availability.
En este trabajo se evaluó la concentración de nitrógeno
(N) (0.6 y 6.0 mM), la proporción de amonio (NH +): nitrato
enzymes nitrate reductase (NR) and nitrite reductase (NiR).
When this process takes place in the leaves, as in most plants, it depends on reductant compounds generated by photo- synthesis, and when it takes place in the roots, the reductants compounds are provided by respiration (Scheurwater et al., 2002; Li et al., 2013). The NH + absorbed, or previously pro-
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- + + - - -
(NO3 ) (100 % NH4 , 50 % NH4 - 50 % NO3 y 100 % NO3 ) y su
duced by the reduction of NO3 is assimilated directly into
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interacción, sobre la fotosíntesis neta, el crecimiento de las plantas, la producción y la calidad de los frutos, en arándano (Vaccinium corimbosum L.). Las plantas se mantuvieron por 243 d en un sistema hidropónico y después se midió la fo- tosíntesis neta (FN), el área foliar (AF), el peso fresco de los brotes (PFB) y el peso fresco de las raíces (PFR). También se evaluó, el rendimiento (RF), diámetro de fruto (DF) y grados Brix (oBrix). Se encotraron los mayores valores en FN, AF, PSB, RF y DF, en las plantas que recibieron 6.0 mM como NH +; sin embargo, la concentración de N alteró los efectos de la pro- porción NH +:NO - y a 0.6 mM N, solo RF y DF mantuvieron la
amino acids by the enzyme glutamine synthetase (GS) and requires C compounds to get C skeletons and energy, which can come from previously stored carbohydrates or directly from photosynthesis (Li et al., 2013; Doyle et al., 2021). On the one hand, N deficiency directly and negatively affects pho- tosynthesis reducing stomatal conductance, content of light harvesting proteins and content and/or activity of photosyn- thetic enzymes (Mu and Chen, 2021) and indirectly, due to photoassimilates accumulation, through a feedback down- regulation mechanism (Araya et al., 2010). On the other hand,
N assimilation consumes carbohydrates originally produced
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*Author for correspondence: Luis López Pérez e-mail: luis.lopez.perez@umich.mx
Received: May 20, 2024
Accepted: September 7, 2024
Published: October 8, 2024
Volume XXVI
DOI: 10.18633/biotecnia.v26.2325
Journal of biological and health sciences http://biotecnia.unison.mx
Universidad de Sonora
ISSN: 1665-1456
by photosynthesis and competes with other physiological processes associated with plant growth and development for these compounds (Li et al., 2013).
Plants preferences for NH + or NO - depend on the
8:30 a.m. and 8:30 p.m.), using an automated drip irrigation system. In order to homogenize the plant material, three days after transfer to the greenhouse, thinning was carried out to leave a single stem per plant. Seven days later, the
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species, phenological stage, habitat of species origin and conditions of roots environment such as pH, aeration, tem- perature (Li et al., 2013). V. corymbosum L. is native from the temperate forests of North America and grows in the under- growth, where low temperatures limit the mineralization of the plenty organic matter; in soils with low salinity, acidic pH, abundant organic forms of N, as amino acids and proteins and scarce mineral N, which is mainly found as NH + (Korcak,
apical part of the stem was cut, leaving ten viable buds, and seven days later the buds and shoots were removed, leaving only one shoot per plant, which was supported with plastic stakes during its growth.
The experiment was bi-factorial and the studied factors were the N concentration and the NH +:NO - proportion in the
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1989; Rosen et al., 1990; Metcalfe et al., 2011). Therefore, this
plant species has evolutionarily adapted to grow in soils with low N availability (Banados et al., 2012; Vargas and Bryla, 2015)
irrigation solution. The first factor had two levels: 0.6 mM and
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6.0 mM, and the second factor had three levels: 100 % NH +, 50 % NH + : 50 % NO - and 100 % NO -. The combination of
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and to prefer NH + instead NO -, which allows it to conserve these factors produced six treatments, repeated four times
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energy, which is an advantage in a low-temperature environ- ment, since the processes of absorption and assimilation of NH +:NO - require less energy than those of NO -; in addition,
resulting in 24 experimental units (EU), which were integrat- ed with four plants each and randomly distributed. The treat- ments application began on day 22 after plant transfer to
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the assimilation of NO - is restricted by the low content of NR in its leaves and roots (Poonnachit and Darnell, 2004; Osorio et al., 2020; Doyle et al., 2021; Leal-Ayala et al., 2021). Indeed, it has been documented that when N is supplied as NH +, blueberry plants show greater net photosynthesis, leaf area, biomass and content of chlorophyll and mineral nutrients, than when N is provided only as NO - (Osorio et al., 2020; Leal-Ayala et al., 2021; Yuan-Yuan et al., 2021). However, it is
the greenhouse. Six irrigation solutions (one per treatment) were prepared based on nutrient solution proposed by Cárdenas-Navarro et al. (1998). All solutions were prepared with demineralized water (pH 5.0, electrical conductivity
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1.80 dSm-1, H2PO - concentration 1 Eq m-3 and anions and cations balance 16 Eq m-3). In order to maintain this balance, NO - concentrations variations were compensated by varying SO 2- concentrations, and NH + concentrations changes were
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unknown if these effects are kept when N availability in the
root medium is variable and if there is interaction between the concentration and the ionic form of this element. There- fore, the aim of this work was to study the main effects and the interaction of N concentration and NH +:NO - proportion
balanced by varying the concentrations of K+, Ca++ and Mg++,
always keeping the proportion 25 %, 50 %, 25 %, respectively. Microelements concentrations were as follows: H3BO3, 42.0 μM; CuSO4.5H2O, 1.0 μM; Fe-EDTA, 15.0 μM; MnSO4.H2O, 23.0 μM; (NH ) Mo O .4H O, 0.3 μM and, 6.0 μM.
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in the nutrient solution, on net photosynthesis, plant growth, fruit production and quality of blueberry plants var. Biloxi grown in hydroponics.
An experiment was developed using 96 blueberry plants (V. corymbosum L.) var. Biloxi, produced in vitro and hardened in a greenhouse. The 0.3 m high plants with root ball were transplanted in 7.0 L plastic pots containing a substrate composed with a mixture of volcanic gravel “tezontle” (0.005
- 0.007 m diameter) and river sand at 1:2 (v/v) ratio, which was previously disinfected with a 10 % sodium hypochlorite solution. The pots were established in a tunnel-type green- house covered with plastic (30 % shading, 7 mil) and located at the Instituto de Investigaciones Agropecuarias y Forestales (IIAF), Universidad Michoacana de San Nicolás de Hidalgo (UMSNH), Morelia, Michoacán, México (Lat. 19°46’11.3 “N, Long. 101°09’00.1 “O; 1860 m.s.n.m.). During the experiment, the average daily temperature inside the greenhouse was 27
°C and the average daily relative humidity was 47 %.
Throughout the first 22 d after transfer to the greenhouse, all plants received 0.3 L of demineralized water every 12 h (at
At fruit production phase, 242 d after treatments application (DAT), net photosynthesis (PN) was measured by EU, using a portable photosynthesis system (Li -6400; LI-COR). The mea- surement was carried out inside the greenhouse between 7:00 - 9:00 am, on a fully expanded mature leaf randomly selected, keeping 1,000 μmol m-2s–1 light intensity, 400 μmol mol-1 CO2 concentration and 25 ºC temperature. A day after, 243 DAT, one plant per EU was taken and organs dissected, to determine: leaf area (LA) with a digital planimeter (LICOR, LI- 3100C) and with a precision balance (Mettler Toledo, PR8002) shoots fresh weight (SFW) and roots fresh weight (RFW). The fruit yield (FY) was evaluated on one randomly selected plant (from the beginning of the experiment) per EU and four harvests were make (every 15 d) along the production phase. The fruits of each plant were weighed (Mettler Toledo, PR8002), its equatorial diameter was measured with a digital vernier (Truper, 14388) and, in a representative sample, the total soluble solids content (°Brix) was determined with a digital refractometer (HI, 96801).
The data were subjected to a two-ways analysis of variance (ANOVA) and when significant statistical differences were
found, the Tukey mean test (P ≤ 0.05) was applied, using SAS® OnDemand for Academics for Macintosh.
The obtained results on PN showed statistically significant
effects of N concentration, NH +:NO - proportion and interac-
In both variables the effects of the studied factors and their interaction were statistically significant (Table 1), thus, the plants irrigated with 0.6 mM N and those receiving only NO - showed the lowest values (Fig. 2A, 2B, 3A, 3B). Nevertheless, the reduction of LA and SFW observed in plants receiving just NO - in the nutrient solution was only perceived in plants
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tion of both factors (Table 1). The main effects observed is that plants irrigated with 0.6 mM N and those that received this element only as NO - showed lower rate of net CO
irrigated with 6.0 mM N, whereas non statistically significant differences were detected between NH +:NO - proportion treatments when plants were irrigated with 0.6 mM N (Fig.
3 2 2C, 3C). On the other hand, the RFW did not showed statisti-
assimilation (Fig. 1A, 1B). However, when examining factors
interaction, it’s clear that the effect of the NH +:NO - propor-
cally significant effects associated with the studied factors or
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tion is different in the two N concentrations studied. The PN drop observed with the increase of NO - proportion in the irrigation solution was only showed by plants that received
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6.0 mM of N, while in plants irrigated with 0.6 mM of N non statistically significant differences were detected between NH +:NO - proportion treatments (Fig. 1C).
The plant biomass production analysis revealed that the variables representing the aerial part growth of plant (the LA and the SFW), showed a similar response that PN.
When examining fruits production and quality it was observed that FY showed statistically significant effects as- sociated to N concentration, to NH +:NO - proportion and to interaction of both factors (Table 1). The main effects analysis revealed that FY was higher in plants that received solutions with 6.0 mM N (Fig. 5A) and decreased as the proportion of NO - in the irrigation solution increased (Fig. 5B). However, the factors interaction analysis showed that the effect of
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Table 1. P values from bi-factorial ANOVA analysis of: net photosynthesis (PN), leaf area (LA), shoots fresh weight (SFW), roots fresh weight (RFW), fruit yield (FY), fruit diameter (FD) and degrees brix (ºBrix). The factors were N concentration in irrigation solution ([N]) (0.6 mM and 6.0 mM), and NH +∶NO -
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proportion in irrigation solution (NH +∶NO -) (100 %:0 %, 50 %:50 %, 0 %:100 %); [N] * NH +∶NO - indica-
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tes the interaction of both factors.
Tabla 1. Valores de P del análisis bifactorial ANOVA de: fotosíntesis neta (FN), área foliar (AF), peso fres- co de tallo (PFT), peso fresco de raíz (PFR), producción de frutos (PF), diámetro de fruto (DF) y grados Brix (ºBrix). Los factores fueron concentración de N en la solución de riego ([N]) (0.6 mM and 6.0 mM) y la proporción de NH +∶NO - en la solución de riego (NH +∶NO -) (100 %:0 %, 50 %:50 %, 0 %:100 %), [N] *
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NH +∶NO - indica la interacción entre factores.
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Factor | PN | LA | SFW | RFW | FY | FD | °BRIX |
[N] | 0.018 | 0.002 | 0.009 | 0.660 | <0.0001 | 0.064 | 0.189 |
NH4 : NO3 | 0.001 | 0.001 | 0.000 | 0.356 | <0.0001 | <0.0001 | 0.132 |
[N] * NH4 : NO3 | 0.054 | 0.018 | 0.035 | 0.356 | 0.004 | 0.320 | 0.623 |
+ -
+ -
Figure 1. Effect of N concentration in irrigation solution (A); NH +∶NO -proportion in irrigation solution (B) and interaction of both factors (C), grey bars 6.0 mM
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N concentration and white bars 0.6 mM N concentration on net photosynthesis (PN). Values are the mean ± standard error; different letters in the bars indicate statistically significant differences according with Tukey test at P ≤ 0.05.
Figura 1. (A). Efecto de la concentracion de N en la solución de riego; (B), proporción de NH +∶NO - en la solución de riego y (C), interacción de factores, barras
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grises concentración de N a 6.0 mM y barras blancas concentration de N a 0.6 mM en la fotosíntesis neta (FN). Los valores representan la media ±el error estan- dar; diferentes letras en las barras indican diferencia estadística significativa de acuerdo con la prueba de Tukey a una P ≤ 0.05.
Figure 2. Effect of N concentration in irrigation solution, (A); NH +∶NO - proportion in irrigation solution, (B) and interaction of both factors, grey bars 6.0 mM
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N concentration and white bars 0.6 mM N concentration (C) on leaf area (LA). Values are the mean ± standard error; different letters in the bars indicate statis- tically significant differences according with Tukey test at P ≤ 0.05.
Figura 2. (A). Efecto de la concentracion de N en la solución de riego; (B), proporción de NH +∶NO - en la solución de riego y (C), interacción de factores, barras
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grises concentración de N a 6.0 mM y barras blancas concentration de N a 0.6 mM en el área foliar (AF). Los valores representan la media ±el error estandar; diferentes letras en las barras indican diferencia estadística significativa de acuerdo con la prueba de Tukey a una P ≤ 0.05.
Figure 3. Effect of N concentration in irrigation solution, (A); NH +∶NO - proportion in irrigation solution, (B) and interaction of both factors, grey bars 6.0 mM
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N concentration and white bars 0.6 mM N concentration (C) on shoots fresh weight (SFW). Values are the mean ± standard error; different letters in the bars indicate statistically significant differences according with Tukey test at P ≤ 0.05.
Figura 3. (A). Efecto de la concentracion de N en la solución de riego; (B), proporción de NH +∶NO - en la solución de riego y (C), interacción de factores, barras
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grises concentración de N a 6.0 mM y barras blancas concentration de N a 0.6 mM en el peso fresco de tallos (PFT). Los valores representan la media ±el error estandar; diferentes letras en las barras indican diferencia estadística significativa de acuerdo con la prueba de Tukey a una P ≤ 0.05.
Figure 4. Effect of N concentration in irrigation solution (A); NH +∶NO -proportion in irrigation solution (B) and interaction of both factors, grey bars 6.0 mM
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N concentration and white bars 0.6 mM N concentration (C) on roots fresh weight (RFW). Values are the mean ± standard error; different letters in the bars indicate statistically significant differences according with Tukey test at P ≤ 0.05.
Figura 4. (A). Efecto de la concentracion de N en la solución de riego; (B), proporción de NH +∶NO - en la solución de riego y (C), interacción de factores, barras
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grises concentración de N a 6.0 mM y barras blancas concentration de N a 0.6 mM en el peso fresco de raíces (PFR). Los valores representan la media ±el error estandar; diferentes letras en las barras indican diferencia estadística significativa de acuerdo con la prueba de Tukey a una P ≤ 0.05.
Figure 5. Effect of N concentration in irrigation solution (A); NH +∶NO -proportion in irrigation solution (B) and interaction of both factors, grey bars 6.0 mM N
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concentration and white bars 0.6 mM N concentration (C) on fruit yield (FY). Values are the mean ± standard error; different letters in the bars indicate statisti- cally significant differences according with Tukey test at P ≤ 0.05.
Figura 5. (A). Efecto de la concentracion de N en la solución de riego; (B), proporción de NH +∶NO - en la solución de riego y (C), interacción de factores, barras
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grises concentración de N a 6.0 mM y barras blancas concentration de N a 0.6 mM en la producción de frutos (PF). Los valores representan la media ±el error estandar; diferentes letras en las barras indican diferencia estadística significativa de acuerdo con la prueba de Tukey a una P ≤ 0.05.
NH +:NO - proportion is different in the two studied concen-
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trations of this element. The plants that received 6.0 mM N had lower FY when this element was provided only in the form of NO -, while in the plants that received 0.6 mM of N, the lower fruits production was observed in treatments with 100 % and also 50 % NO - (Fig. 5C). The FD only showed signif-
icant effects associated to NH +:NO - proportion, but not to N
Blueberry is considered a plant with low nutritional require- ments, particularly N (Banados et al., 2012; Vargas and Bryla, 2015), however, in this work plants that received 0.6 mM N in the irrigation solution showed a lower PN (Fig. 1A). The photo- synthesis drop in N-deficient plants is produced by a reduced stomatal conductance, a low availability of energy molecules
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concentration or to interaction of both factors (Table 1). The main effects analysis reveals that plants that received only NO - produced the smallest diameter fruits (Fig. 6B) and as the interaction of the studied factors was not significant, this pattern was replicated in both studied N concentrations (Fig. 6C). The ºBrix of fruits did not shows statistically significant
effects associated with N concentration, NH +:NO - propor-
and light harvesting proteins, as well as reduced content and/ or low activity of enzymes involved in carboxylation process (Mu and Chen, 2021). Low photosynthesis in N-deficient blue- berry plant is also associated with feedback downregulation mechanism generated by leaf carbohydrates accumulation (Araya et al., 2010; Jorquera-Fontena et al., 2018). In addition to display a decline in PN, plants that received 0.6 mM N also
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tion, or the interaction of both factors (Table 1, Fig. 7A, 7B,
7C).
exhibited less development of the plant aerial part, specif-
ically LA and SFW (Figs. 1A, 2A); therefore, it is evident that
Figure 6. Effect of N concentration in irrigation solution (A); NH +∶NO -proportion in irrigation solution (B) and interaction of both factors, grey bars 6.0 mM
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N concentration and white bars 0.6 mM N concentration (C) on fruit diameter (FD). Values are the mean ± standard error; different letters in the bars indicate statistically significant differences according with Tukey test at P ≤ 0.05.
Figura 6. (A). Efecto de la concentracion de N en la solución de riego; (B), proporción de NH +∶NO - en la solución de riego y (C), interacción de factores, barras
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grises concentración de N a 6.0 mM y barras blancas concentration de N a 0.6 mM en el diámetro del fruto (D). Los valores representan la media ±el error estandar; diferentes letras en las barras indican diferencia estadística significativa de acuerdo con la prueba de Tukey a una P ≤ 0.05.
Figure 7. Effect of N concentration in irrigation solution(A); NH +∶NO -proportion in irrigation solution (B) and interaction of both factors, grey bars 6.0 mM
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N concentration and white bars 0.6 mM N concentration (C) on degrees brix (ºBrix). Values are the mean ± standard error; different letters in the bars indicate statistically significant differences according with Tukey test at P ≤ 0.05.
Figura 7. (A). Efecto de la concentracion de N en la solución de riego; (B), proporción de NH +∶NO - en la solución de riego y (C), interacción de factores, barras
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grises concentración de N a 6.0 mM y barras blancas concentration de N a 0.6 mM en los grados Brix (ºBrix). Los valores representan la media ±el error estandar; diferentes letras en las barras indican diferencia estadística significativa de acuerdo con la prueba de Tukey a una P ≤ 0.05.
such a N concentration in the irrigation solution generates a deficiency of this element, which is insufficient to meet the N demand created by plant growth. Moreover, plants that received solutions with 6.0 mM N, together with higher PN, LA and SFW, also showed higher FY (Fig. 5A, 6A, 7A). In most crops, growth and fruit yield rise with the increase of N rate until to a critical level beyond which more N supply increases do not generate augmentations in these variables and may even decline (Cárdenas-Navarro et al., 2004). In blueberry several works, carried out under different agronomic condi- tions, have reported N rates, varying between 34 and 93 kg of N ha-1year-1, beyond which increases in plant growth and/ or fruit yield were not observed (Bryla and Machado, 2011; Banados et al., 2012; Ehret et al., 2014; Vargas and Bryla, 2015; Messiga et al., 2018). In accordance with these reports, the
6.0 mM N treatments of this work were equivalent to 18.4 g plant-1year-1, meaning 51 Kg N ha-1year-1 if a common plant- ing density of 2,777 plants ha-1 is considered (Banados et al., 2012; Vargas and Bryla, 2015). Some reports in the literature indicate that in blueberry N supply reduce the fruits size and affect its sugars accumulation (Ehret et al., 2014; Vargas
2021). Secondly, as is well known, photosynthesis is the main physiological process associated to biomass accumulation and crops production; in this work, plants that received nutrient solutions with NH +, in addition to display higher PN also produced a higher aerial biomass: LA and SFW (Fig. 2B). These results are in accordance with a wide number of previously published reports on blueberry, in which plants biomass increase when supplied with NH +, alone or predom- inantly, and decrease when received only NO - (Osorio et al., 2020; Doyle et al., 2021; Yuan-Yuan et al., 2021). This behavior is surely associated with V. corymbosum L. adaptation to its origin habitat, which is the temperate forests undergrowth and soils with acidic pH, low temperatures, low microbial activity, slow process of organic matter mineralization and NH + as the predominant inorganic form of N (Korcak, 1989; Metcalfe et al., 2011).
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The blueberry plant NH + preference reflects its adap- tation to such environmental conditions and is expressed in physiological process as absorption, translocation from the root to the aerial part and assimilation in organic N (Doyle et al., 2021). Thirdly, NH +:NO - proportion effects on PN, LA and
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and Bryla, 2015; Zhang et al., 2023); however, in this work N treatments did not generate statistical differences neither in FD (Fig. 6A) nor in ºB (Fig. 7A).
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Plants uptake mineral N from the soil mainly as NH + or NO -, the preference between these two ionic forms of N depends on plant species, its origin habitat, its phenological stage and the roots environmental conditions such as pH, temperature, aeration and microbial activity (Li et al., 2013). In the literature, most authors claim that blueberry develops better when N is provided only or mainly as NH + (Doyle et al., 2021). In this work, such a preference is confirmed according to the responses registered in the evaluated variables. Firstly,
plants that received nutrient solutions in the presence of
SFW were likewise observed on the production and quality of fruits. The FY of plants that received only NH + was three- fold than those received only NO - (Fig. 5B), these plants also showed bigger FD (Fig. 6B), although non-statistical differ- ences were observed in ºBrix (Fig. 7B), which agrees with pre- vious reports (Bolaños-Alcántara et al., 2019). The increases of FY and FD are surely associated with the higher availability of photo-assimilates, as a result of PN increase; the greater development of LA and the higher number of flower buds and consequently of fruits, as outcome of SFW increase of plants that received NH + in the irrigation solution.
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However, the analysis of studied factors interaction showed that the effect of NH +:NO - proportion on PN, LA,
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NH + showed higher PN (Fig. 1B), compared to those that received only NO -, which agrees with previously published reports on this crop (Osorio et al., 2020; Yuan-Yuan et al.,
SFW and FY depends on N availability in roots environment. PN of plants that received irrigation solutions with 6.0 mM N was more than twice higher when this element was supplied
as NH +, than when it was provided as NO -. In plants that fundamentally by leaves photosynthesis (Maust et al., 1999
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received 0.6 mM N, no statistical differences were observed
between NH +:NO - proportion treatments (Fig. 1C). It is well
a; b). In this context, the production and quality of the fruits
is based on a source (leaves) sink (fruit) relationship, whose
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established that N is essential in plants photosynthesis and that when its availability in the root milieu is limited, as is the case of plants that received 0.6 mM N in this work, CO2 fixation decrease, regardless of the ionic form of N supplied in the irri- gation solution. In such a condition, as it has been previously reported by several authors in blueberries, photosynthesis
decline, either due to the lack of essential compounds that
balance depends fundamentally on the factors that affect the photosynthetic activity of the leaves and the number of fruits (Jorquera-Fontena et al., 2018; Kumarihami et al., 2021). As previously showed, plants that received 6.0 mM N as NH +, displayed the highest values of PN per unit of leaf surface and in plants that received 0.6 mM N there were no statis-
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tically differences between NH +:NO - proportion treatments
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participate both in the transformation of light energy into energetic molecules and in the carboxylation process, or by the feedback downregulation mechanism exerted by the excessive accumulation of carbohydrates (Araya et al., 2010; Jorquera-Fontena et al., 2018; Petridis et al., 2020; Leal-Ayala et al., 2021; Mu and Chen, 2021). On the other hand, when plant growth is not limited by the N availability in the root medium, as in the case of 6.0 mM N treatments, the develop- ment of the photosynthetic process is not obstructed by the lack of N compounds nor downregulated by carbohydrates accumulation in leaves cells. In such conditions, PN showed by plants that received only NH + was more than two folds
greater than by those supplied only with NO - (Fig. 1C), which
(Fig. 1C). The same pattern was observed in LA (Fig. 2C) and in SFW (Fig. 3C), therefore, according to the source-sink ap- proach, it can be assumed that the behavior of LA and SFW was associated with photoassimilates availability.
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FY and FD showed similar effects than PN, LA and SFW; plants that received 6.0 mM N as NH + were more than three times and 15 % higher, respectively, than those that received it as NO - (Fig. 5C, 6C); therefore, it could be assumed that the effects showed by FY and FD depends likewise on carbohy- drates availability (Maust et al., 1999 a; b). However, interest- ingly and in contrast to PN, LA and SFW, plants that received
0.6 mM N did show statistically significant differences
between NH +:NO - proportion treatments in both variables.
4
3
4
3 4 3
4
could be associated to carbohydrates consumption by NH + assimilation processes (Li et al., 2013), stimulating CO2 fixa- tion, according to the sugar-sensing mechanism previously proposed in blueberry (Jorquera-Fontena et al., 2018; Petridis et al., 2020).
The pattern observed on PN, was similar to plant aerial biomass production both in LA and in SFW. In these variables, plants irrigated with solutions at 6.0 mM N showed six- and five-times greater values, respectively, when N was supplied
only as NH + than when it was provided just as NO - (Fig. 2C,
The FY and FD of plants that received only NH + were four times and 9.5 % higher, respectively, than those that received only NO - (Fig. 5C, 6C). These results could be explained by an indirect effect of NH + on flower buds induction and fruit development, through a stimulus to the photosynthetic ac- tivity and the increase of photoassimilates availability, which may act as energy providers and/or signaling molecules (Li et al., 2013; Jorquera-Fontena et al., 2018; Maust et al., 1999 a; 1999b; Petridis et al., 2020; Wang et al., 2021). However, more
research is needed to clarify and quantify this process.
4 3
4
3
3C). Furthermore, when the N concentration in the irrigation solution was 0.6 mM none of these variables exposed statis- tically significant differences between NH +:NO - proportion treatments (Fig. 2C, 3C). These results are surely associated with the previously shown behavior of PN, as this physio- logical process is considered the most important for plant biomass accumulation (Evans and Clarke, 2019; Flood et al., 2011; Yamori, 2020); although probably there are also interactions between the factors and variables studied in this work, with other physiological processes as respiration, water absorption and transpiration.
In blueberry, fruit production depends mainly on the number of plant floral buds (Salvo et al., 2011; 2012; Kumar- ihami et al., 2021), whose induction is stimulated by factors such as temperature, light intensity and carbohydrates availability (Pescie et al., 2011; Salvo et al., 2012; Kumarihami et al., 2021). Carbohydrates metabolism plays a fundamental role, since it is a source of soluble sugars such as glucose and fructose, which act as energy providers and as signaling molecules that stimulate the metabolic processes involved in breaking bud dormancy (Wang et al., 2021). The first phases of the flower buds induction are sustained mainly by the re- serve carbohydrates, and later by fruits photosynthesis, but
4
3
The results of this work show that, in blueberry grown under hydroponic conditions, plant growth and fruit production were higher when N was supplied as NH +, than when it was provided only as NO -. These effects were manifested through higher values of net photosynthesis, leaf area, shoots fresh weight, fruit yield and fruit diameter. However, N concentration in the irrigation solution altered the effect of its ionic form and this pattern was only observed at high N concentration (6.0 mM), whereas at low N concentration (0.6 mM), these effects were only maintained in fruit yield and fruit diameter, but not in net photosynthesis, leaf area and shoots fresh weight. Considering that photosynthesis is a fundamental physiological process for plant growth and development and the intimate relationship between N and C metabolism, it is proposed that the effects of the concentra- tion and the ionic form of N, on growth and fruit production of blueberry plants, were closely related to internal carbohy- drates availability.
The present work was carried out as a part of the MSc thesis of
Mr. Jesús Alonso Luna Béjar, who was supported by a fellows- hip from the Consejo Nacional de Humanidades, Ciencias y Tecnología (CONAHCYT) of the Mexican government and was directed by Dr. Raúl Cárdenas-Navarro. Special thanks to M.A in ELT. Mauricio Montes Cortés, from the Languages Department of the Universidad Michoacana de San Nicolás de Hidalgo, for English editing service. This study was funded by the Consejo de la Investigación Científica (CIC) of the Uni- versidad Michoacána de San Nicolás de Hidalgo.
The authors will not declare conflicts of interest.
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