Fitociencia

 

Water relations and photosynthesis of young coffee plants under two water regimes and different N and K doses

 

Relaciones hídricas y fotosíntesis de las plantas jóvenes de café bajo dos regímenes hídricos y diferentes dosis de N y K

 

Marcela A. Frois de Andrade¹, Paulo A. Ramos-Cairo^2*, Jerffson L. Santos¹

 

¹ Sowthwest Bahia State University, Vitória da Conquista, Bahia, Brazil.

² Sowthwest Bahia State University, Department of Phytotechny and Zootechny, Post Office 95, Zip Code 45083-900, Vitória da Conquista, Bahia, Brazil. * Author for correspondence (pcairo@uol.com.br)

 

Received: October, 2014.
Approved: February, 2015.

 

Abstract

Nitrogen (N) and potassium (K) are the major nutrients required for coffee plants growth and development. Soil water deficit reduces nutrients uptake, causing negative effects on photosynthesis and water relations of plants. Within certain limits, the increase in N and K concentration in soil solution could result in higher nutrient uptake, softening physiological disturbs caused by the water deficit. This study aimed to evaluate water relations and photosynthesis of young coffee plants grown in 16 L pots in a greenhouse. Treatments were three N and three K doses: conventional (urea 12 g plant^-1 and KCl 4 g plant^-1), doubled and tripled; and two water regimes: irrigated (soil at field capacity) and non-irrigated. Thus, treatments were arranged in a factorial 3 x 3 x 2, with three replicates in a completely randomized design. Water stress effects on leaf water potential and relative water content are softened by increase in N and K doses. However, transpiration, stomatal conductance and net photosynthesis are decreased by water stress, regardless of N and K doses. Increase in K doses reduces transpiration and stomatal conductance, regardless of water regime. This study suggests that increases in N and K could partially protect young coffee plants against the water stress, as they contribute to mitigate negative effects in plant water status; however, they do not prevent a decrease in net photosynthesis.

Key words: Coffea arabica, water stress, mineral nutrition.

 

Resumen

El nitrógeno (N) y el potasio (K) son los principales nutrientes requeridos para el crecimiento y el desarrollo de las plantas de café. El déficit hídrico reduce la absorción de nutrientes, causando efectos negativos en la fotosíntesis y las relaciones hídricas de las plantas. Dentro de ciertos límites, el aumento en la concentración de N y K en la solución del suelo podría resultar en una mayor absorción de nutrientes, suavizando las perturbaciones fisiológicas causadas por el déficit del agua. El objetivo de estudio fue evaluar las relaciones hídricas y la fotosíntesis de plantas jóvenes de café cultivadas en macetas de 16 L en un invernadero. Los tratamientos fueron tres dosis de N y tres dosis de K: convencional (urea 12 g planta^-1 y KCl 4 g planta^-1), doble y triple; y dos regímenes hídricos: con irrigación (suelo a capacidad de campo) y sin irrigación. Así, los tratamientos se organizaron en un arreglo factorial de 3 x 3 x 2 con tres réplicas en un diseño completamente aleatorio. Los efectos del estrés hídrico en el potencial hídrico de la hoja y en el contenido relativo de agua se suavizan con el aumento en las dosis de N y K. Pero la transpiración, la conducción estomática y la fotosíntesis neta se reducen con el estrés hídrico, sin importar la dosis de N y K. El aumento en dosis de K reduce la transpiración y la conducción estomática, independientemente del régimen hídrico. Este estudio sugiere que el aumento en N y K podría proteger parcialmente a las plantas jóvenes de café contra el estrés hídrico, ya que contribuye amitigar los efectos negativos en el estado hídrico de la planta; pero no evita una disminución en la fotosíntesis neta.

Palabras clave: Coffea arabica, estrés hídrico, nutrición mineral.

 

INTRODUCTION

Nitrogen (N) and potassium (K) are the major nutrients required for growth and development of coffee plants. Soil moisture affects either nutrients availability in soil solution as ion uptake by plant roots (Pérez-Zamora et al., 2004). Thus, drought stress decreases nutrient uptake by crops (Prado, 2008). Low supply of these nutrients causes negative effects on photosynthesis and water relations of plants and coffee yield is seriously affected (Clemente et al., 2008).

Maize leaf photosynthetic capacity and N concentration show a significant positive correlation; thus, most of the N is used for synthesis of components in photosynthesis (Sugiharto et al., 1990). Limited levels of N supply decrease the absolute capacity and quantum yield of photosynthesis (Khamis etal., 1990). Besides the direct effects on the structure of the photosynthetic apparatus, N-deprivation reduces the amount of Calvin cycle enzymes, which, at the same time, lowers the C assimilation capacity (Terashima and Evans, 1988). Rubisco enzyme plays a major role in C assimilation and is strongly affected by N deficiency (Seemann et al., 1987).

Plants suffering from drought stress enhanced need for K, since this nutrient is required for maintenance of photosynthetic CO₂ fixation (Waraich et al., 2011). Drought stress is associated with stomatal closure and thereby with decreased CO₂ fixation (Marschner, 1995).

Rubi 1192 coffee plants, under different NPK doses and water regimes, during the first year after transplantation, alter plant shoot dry matter partitioning, increasing buds/fruit mass ratio in non-irrigated treatments (Nazareno et al., 2003). If N doses are increased, amount of fruit, length of internodes and crown diameter of young coffee plants are also increased (Fahl et al., 2001). According to Jessi (2011), plant response to N fertilization is affected by water stress and there is a positive interaction between water regimes and P and K fertilization. Proper plant nutrition is a good strategy to enhance water use efficiency and productivity in crop plants (Waraich et al., 2011). Within certain limits, the increase in N and K concentration in soil solution could result in higher nutrient uptake (Marschner, 1995).

Therefore, this study aimed to evaluate water relations and photosynthesis of young coffee plants growing in a greenhouse, with three N and K doses (conventional, doubled and tripled) and two water regimes (irrigated and non-irrigated).

 

MATERIALS AND METHODS

The study started in October 2010, in a greenhouse of the State University of Southwest Bahia, Vitoria da Conquista, Brazil. After leaving the nursery, coffee (Catuaí Red IAC 144) 6 months old seedlings were prepared in plastic bags with the following composition for each m³ of substrate: soil 700 L, cattle manure 300 L, P₂O₅ 1.0 kg and K₂O 0.3 kg (Ribeiro et al., 1999). The coffee seedlings acclimation in the greenhouse was 5 d with 40 % sunlight restriction, followed by 5 d with 20 % sunlight restriction and 5 d full sunlight. Afterwards, coffee seedlings were transferred from plastic bags to 16 L pots (one plant pot^-1) containing yellow oxisol, sandy-clay texture. NPK fertilization was adopted according to Van Raij et al. (1997) recommendations.

Treatments were arranged in a factorial 3 x 3 x 2 (three N doses, three K doses and two water regimes), with three replicates in a completely randomized design. Three N and K doses were: conventional, doubled and tripled. Conventional N and K doses were urea 12 g plant^-1 and KCl 4 g plant^-1, respectively, and applied at 30, 60, 90 and 120 d after planting.

The water regimes were irrigated and non-irrigated. Irrigated regime was soil at field capacity, determined by direct gravimetric method. For determining the soil water content, four 16 L pots without plants containing the same substrate of the experimental pots were moistened to saturation; then, the saturated soils were drained completely for 24 h. The soil water content was determined based on the average of four pots. Non-irrigated regime was no irrigation at all.

Water regimes started 30 d after N and K last application. Ten days after stopping irrigation, plants began to show visible symptoms of water stress, such as wilting and curling of the leaves and the following variables were evaluated: leaf water potential (Y_w), relative water content (RWC), transpiration (E), stomatal conductance (g_S) and net photosynthesis (A). For Y_w and RWC measurements, fully expanded leaves from middle third of each plant were collected at 05:00 h and a pressure camera (Model 1000, PMS) was used for Y_w measurement (Scholander et al., 1965). For RWC measurements, 10 foliar discs were collected from leaf blade (main veins were discarded) and the weight of fresh mass (FM) was recorded. Thereafter, foliar discs were immersed in distilled water for 24 h and the weight of turgid mass (TM) was recorded; then, foliar discs were placed in a kiln 48 h at 70 °C and the weight of dry mass (DM) was recorded. FM, TM and DM were used for this formula: RWC = [(FM-DM) / (TM-DM)] * 100. For E, g_s and A measurements, a portable photosynthesis meter, infra-red gas analyzer type (Infrared Gas Analyzer. IRGA LI-6400, LI-COR^®, Nebraska / USA) was used.

Data were used for an analysis of variance, based on F test. When necessary, data were transformed using , to attain a normal distribution. Mean comparisons were performed using SAEG program, version 9.1. When mean comparisons were significantly different, regression was performed and F test (p≤0.05) was utilized.

 

RESULTS AND DISCUSSION

In non-irrigated plants, Y_w was lower than in irrigated ones (Table 1). Decreases in leaf Y_w are common when plants are subjected to water deficit, due to increase in solute concentration in leaf tissues, which results in decrease in solute potential (Y_s) (DaMatta, 2000b; DaMatta et al., 2003; Silva et al., 2013). Furthermore, leaf Y_w became significantly lower when N and K doses were increased (Figures 1A and 1B). When leaf Y_w decreases slowly, it generates a gradient between internal and external Y_w which may mitigate plant water loss and promote water uptake from soil to roots (Morgan, 1984).

Premachandra et al. (1991) reported that K is the major nutrient for osmotic regulation in maize under water stress. Meinzer et al. (1990) observed changes both in cell wall elasticity as in Y_w, in five coffee cultivars during dry season. In tomato plant, Garcia et al. (2007) showed that increases in N doses also cause changes in cell wall elasticity. According to Saneoka et al. (2004), higher N doses may increase drought tolerance of plants, since this nutrient prevents damages to cell membrane.

According to the analysis of variance (data not shown), the interaction between N doses and water regimes was significant, both in relation to Y_w (Figure 1C) as to RWC (Figure 1E). The interaction between K doses and water regimes was not significant, indicating that the effects of this nutrient on these two variables are similar, both in irrigated as in non-irrigated plants.

In non-irrigated plants, RWC was lower than in irrigated ones (Table 1), as is usual in plants under water deficit. Nevertheless, data suggest a possible occurrence of osmoregulation in non-irrigated plants affected by N doses, since the difference in RWC between irrigated and non-irrigated plants became lower with increases in N doses, despite of decrease in Y_w (Figure 1E). According to DaMatta et al. (2002a), N supply effects on drought tolerance capacity are related to increase in cell wall rigidity, allowing osmotic adjustment. Increments in K doses contributed to osmoregulation and its effect on maintaining cell turgor (Figure 1D), independently of water regime. In most instances, cell extension is the consequence of the accumulation in the cells of K⁺, which is required for both stabilizing the pH in the cytoplasm and decreasing the osmotic potential in the vacuoles (Marschner, 1995). Therefore, plants with adequate supply of K are less susceptible to water stress.

Water deficit caused decrease in E, g_s and A, independently of N and K doses (Table 2). In plants under water stress, photosynthesis rate is highly regulated by stomatal closure, with aim to reduce transpiration, but this closure also compromises CO₂ influx into substomatal chamber (Cornic, 2000). Miguel et al. (2007) reported that a decrease in stomatal conductance is the major cause for a drop in net photosynthesis rate in young rubber tree. In Coffea canephora water stress also leads to a decrease in net photosynthesis, but not as intense as in stomatal conductance, regardless of N dose (DaMatta et al., 2002b).

Increments in K doses led to a decrease in stomatal conductance and transpiration, regardless of water regime (Figures 2A and 2B). Accumulation of K⁺ in guard cells and its release causes oscillation in cell turgor, which leads to stomatal opening and closing (Taiz and Zeiger, 2013). Abscisic acid stimulates K⁺ release from guard cells, causing stomatal closure and decrease in transpiration (Assmann and Shimazaki, 1999).

Increases in K (Figure 2C) and N (Figure 2D) doses led to decrease in photosynthetic rates. In C. canephora, water deficit lead to a decrease in photosynthesis, even when N availability is increased (DaMatta et al., 2002a). Given that 70 % of N content in leaf tissues are found in chloroplasts, there may be a positive correlation between leaf N content and photosynthesis (Marenco and Lopes, 2009), mostly when N content in plants are adequate (Matiello et al., 2010).

 

CONCLUSIONS

Water stress effects on leaf Y_w and RWC are softened by increase in N and K doses. However, E,g_s and A are decreased by water stress, regardless of N and K doses. Increase in K doses reduces E and g_s, regardless of water regime. This study suggests that increases in N and K could partially protect young coffee plants against water stress, as they contribute to mitigate negative effects in plant water status, despite do not prevent a decrease in A.

 

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