Absorción de agua y rendimiento de maíz en campos bajos ¿Es el horizonte nátrico una limitante?

Los campos bajos son una de las últimas áreas de expansión de la frontera agrícola en nuestro país. Un ejemplo es la Cuenca del Salado, que es una región que en la última década mostró incrementos de la superficie sembrada con cultivos agrícolas. Este trabajo, investigó los patrones de absorción de agua del cultivo de maíz en suelos Natracuoles, bajo dos regímenes hídricos contrastantes. Se realizaron mediciones semanales de humedad gravimétrica y se comparó la evolución del agua disponible para el cultivo a lo largo del ciclo. El rendimiento y la biomasa total disminuyeron ante incrementos del PSI, el pH y la CE. El régimen hídrico no redujo los niveles de producción (8260 a 8872 kg ha-1). El horizonte A, alcanzó aportes de hasta 90% del agua disponible, mientras que el horizonte Bt solo aportó el 50%. Este horizonte, redujo 141 kg ha-1 los rendimientos de maíz por cada unidad de sodio intercambiable, pero no los limitó totalmente. Una parte del aporte hídrico al cultivo provino de capas más profundas del suelo, demostrando que el horizonte nátrico no limitó totalmente la profundidad efectiva del cultivo. Estos resultados abren nuevas perspectivas para el desarrollo de la agricultura en la región.Fil: Garello, F.J. Universidad de Buenos Aires. Facultad de Agronomía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Cuenca del Salado. Agencia de Extensión Rural Chascomus; ArgentinaFil: Aguero, M.A. Universidad Nacional de La Plata; ArgentinaFil: Crespo, M. Universidad de Buenos Aires. Facultad de Agronomía; ArgentinaFil: Cicchino, M.A. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Cuenca del Salado. Agencia de Extensión Rural Chascomus; ArgentinaFil: Melani, Esteban. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Cuenca del Salado. Agencia de Extensión Rural Chascomus; ArgentinaFil: Ploschuk, Edmundo. Universidad de Buenos Aires. Facultad de Agronomía. Cátedra de Cultivos Industriales; ArgentinaFil: Taboada, Miguel Angel. Instituto Nacional de Tecnología Agropecuaria (INTA). Instuto de Suelos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Soil water availability and water absorption by maize in sodic soils with high water table

Context: Because of the increasing prices of commodities over the last decades, crops like maize (Zea mays L.) are being cultivated in lowland sodic soils with physical-chemical constraints, such as those having natric horizon (Btn); however, the magnitude of the reductions in maize productivity in the face of these limitations under different water regimes is not known. Maize is a highly water-demanding crop in midsummer, so the ability of the Btn horizon to provide enough water to the crop in times of high atmospheric demand is still unclear. Objective: The objectives were to evaluate (i) the contribution of the Btn horizon to water absorption by maize, and (ii) the effect of soil exchangeable sodium percentage (ESP) in the Btn horizon on leaf area index (LAI) and maize grain yield (GY) under contrasting imposed soil water conditions. Methods: Field trials were carried out during the growing seasons 2018/19 and 2019/20 at Chascomús, Argentina (35º 44′ S; 58º 03′ O), where sodic soils with natric horizons and high-water table are plentiful. Treatments included a bare soil without cultivation and maize crops under two water regimes: i) rainfed control (C), ii) drought (D), under a wide range of exchangeable sodium percentage (ESP) in the Btn horizon (from ESP 3–34 %). Results: Maize crops could uptake water from the Btn horizon in both water regimes (C and D), but absorption decreased by ≈ 1 % for every 1 % increase in subsoil ESP. This increase in sodicity also decreased the LAI by 0.053 cm cm−2, and GY by 134.5 kg ha−1. In the treatment with imposed drought, maize roots passed down the Btn horizon and reached the groundwater from where they absorbed water. Conclusions: The Btn horizon can be considered a source of water for the maize crop, mainly with low levels of ESP. The detrimental effect of ESP in the GY was independent of water regimes in the crop cycle. SIGNIFICANCE: These results are useful for farmers to adjust crop management, considering the soil ESP, available water in the Btn horizon, and the groundwater depth, making use of water and soil resources more efficient and sustainable.EEA Cuenca del SaladoFil: Garello, F.J. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Cuenca del Salado. Agencia de Extensión Rural Chascomus; ArgentinaFil: Garello, F.J. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina.Fil: Garello, F.J. Universidad de Buenos Aires. Facultad de Agronomía; ArgentinaFil: Ploschuk, Edmundo. Universidad de Buenos Aires. Facultad de Agronomía. Cátedra de Cultivos Industriales; ArgentinaFil: Melani, Esteban. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Cuenca del Salado. Agencia de Extensión Rural Chascomus; ArgentinaFil: Taboada, Miguel Angel. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Taboada, Miguel Angel. Universidad de Buenos Aires. Facultad de Agronomía, Cátedra de Edafología; Argentin

Short-term responses to flooding stress of three Prunus rootstocks

In fruit trees, flooding stress can affect plant survival and growth, and tolerance to root anoxia is determined by rootstock characteristics. Similarly to almond, peach trees are also among the Prunus species proving most susceptible to root anoxia in flooded soils. The aim of our study was to investigate the short-term responses to flooding of different Prunus rootstocks, in terms of growth and development and physiological variables. Flood treatments were continuously applied for 6 days to myrobalan plum Sansavini 2/5 (Mr. S. 2/5), Monegro and Nemared peach rootstocks. Trees that were not exposed to flooding served as controls. Physiological and growth variables were evaluated. Flooding negatively affected net photosynthesis (Pn), leaf conductance (gs) and water potential (Ѱw) in Monegro and Nemared but not in Mr. S. 2/5 rootstock. However, flooding treatments did not affect the intercellular concentration of CO2 (Ci) in any of the rootstocks. We propose that the lack of alterations in Ci indicates that the processes related to photosynthetic metabolism are affected simultaneously with stomatal closure. Flooding only reduced the leaf growth of Monegro and Nemared rootstocks. The Mr. S. 2/5 rootstock had the highest constitutive root porosity, which increased its tolerance to flooding compared to the other rootstocks. The differences in the responses to flooding of various rootstocks should be considered in production settings where it is not possible to properly control irrigation to prevent short periods of flooding or in soils that do not drain irrigation or rain water quickly.Fil: Ziegler, Victor H. Universidad de Buenos Aires. Facultad de Agronomía. Cátedra de Fruticultura; ArgentinaFil: Ploschuk, Edmundo. Universidad de Buenos Aires. Facultad de Agronomía. Cátedra de Cultivos Industriales; ArgentinaFil: Weibel, Antonio Marcelo. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Junín; ArgentinaFil: Insausti, Pedro. Universidad de Buenos Aires. Facultad de Agronomía. Cátedra de Fruticultura; Argentina.Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentin

Mesophyll conductance modulates photosynthetic rate in cotton crops exposed to heat stress under field conditions

Cotton is often exposed to high temperatures during the reproductive stage, which can negatively affect its productivity. The objectives were to: i) test whether heat stress impacts during the reproductive stage on photosynthesis are due to instant temperature effects or to acclimation produced during the heat stress period, ii) evaluate the role of stomatal and mesophyll conductance on net photosynthetic rate and iii) identify possible interactions between heat stress and different source/sink ratios during the reproductive period. Two field experiments were carried out in 2016 (Exp. 1) and 2017 (Exp. 2). Two heating treatment periods were imposed as follows: pre-flowering between 15 days before flower bud and flowering (H1) and post-flowering between flowering and 15 days later (H2). Each treatment had a control group (C1 and C2, respectively). In Exp. 1, two genotypes with contrasting crop cycles were compared. In Exp. 2, 50% defoliated plants (D-) were compared with intact plants (D+) under the same temperature treatments using one genotype. Average daily maximum temperature of heated treatments for both experiments was 37.9 ± 0.79ºC, 5.8ºC higher than the controls. Independently of the period, thermal stress had a negative impact on photosynthesis in both genotypes through an acclimation response, reducing it up to 35% compared with controls when heath-stressed and control plants were measured at the same temperature. Instant responses to temperature were not observed. This decrease was mainly determined by mesophyll conductance, and no recovery was observed 15 days after the end of treatments. Photosynthesis depletion was conditioned by the source/sink ratio, showing a complete recovery only in defoliated plants. It is concluded that thermal stress had a negative acclimation impact on photosynthesis, without responses to changes in instant temperature, and this acclimation is modulated mainly by mesophyll conductance.EEA ReconquistaFil: Mercado Álvarez, Kelly. Universidad de Buenos Aires. Facultad de Agronomía. Cátedra de Cultivos Industriales; ArgentinaFil: Bertero, Héctor Daniel. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal. Cátedra de Producción Vegetal; Argentina.Fil: Paytas, Marcelo Javier. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Reconquista; ArgentinaFil: Ploschuk, Edmundo. Universidad de Buenos Aires. Facultad de Agronomía. Cátedra de Cultivos Industriales; Argentin

Heterologous Expression of AtBBX21 Enhances the Rate of Photosynthesis and Alleviates Photoinhibition in Solanum tuberosum

B-box (BBX) proteins are zinc-finger transcription factors containing one or two B-box motifs. BBX proteins act as key factors in the networks regulating growth and development. The relevance of BBX21 to light and abscisic acid signaling in seedling development is well established; however, its importance in adult plant development and agronomic species is poorly understood. Therefore, we studied the effect of heterologous expression of Arabidopsis (Arabidopsis thaliana) BBX21 in potato (Solanum tuberosum) var Spunta. Three independent AtBBX21-expressing lines and the wild-type control were cultivated under sunlight and at controlled temperatures in a greenhouse. By anatomical, physiological, biochemical, and gene expression analysis, we demonstrated that AtBBX21-expressing plants were more robust and produced more tubers than wild-type plants. Interestingly, AtBBX21-expressing plants had higher rates of photosynthesis, with a significant increase in photosynthetic gene expression, and higher stomatal conductance, with increased size of the stomatal opening, without any associated decline in water use efficiency. Furthermore, AtBBX21-expressing potato plants had reduced photoinhibition associated with higher production of anthocyanins and phenolic compounds, and higher expression of genes in the phenylpropanoid biosynthesis pathway. To gain insights into the mechanism of BBX21, we evaluated the molecular, morphological, metabolic, and photosynthetic behavior in adult BBX21-overexpressing Arabidopsis. We conclude that BBX21 overexpression improved morphological and physiological attributes, and photosynthetic rates in nonoptimal, high-irradiance conditions, without associated impairment of water use efficiency. These characteristics of BBX21 may be useful for increasing production of potatoes, and potentially of other crops.Fil: Crocco, Carlos Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Gómez Ocampo, Jorge Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Ploschuk, Edmundo L.. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal. Cátedra de Cultivos Industriales; ArgentinaFil: Mantese, Anita. Universidad de Buenos Aires. Facultad de Agronomía; ArgentinaFil: Botto, Javier Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentin

Increased Phytochrome B Alleviates Density Effects on Tuber Yield of Field Potato Crops

The possibility that reduced photomorphogenic responses could increase field crop yield has been suggested often, but experimental support is still lacking. Here, we report that ectopic expression of the Arabidopsis PHYB (phytochrome B) gene, a photoreceptor involved in detecting red to far-red light ratio associated with plant density, can increase tuber yield in field-grown transgenic potato (Solanum tuberosum) crops. Surprisingly, this effect was larger at very high densities, despite the intense reduction in the red to far-red light ratios and the concomitant narrowed differences in active phytochrome B levels between wild type and transgenics at these densities. Increased PHYB expression not only altered the ability of plants to respond to light signals, but they also modified the light environment itself. This combination resulted in larger effects of enhanced PHYB expression on tuber number and crop photosynthesis at high planting densities. The PHYB transgenics showed higher maximum photosynthesis in leaves of all strata of the canopy, and this effect was largely due to increased leaf stomatal conductance. We propose that enhanced PHYB expression could be used in breeding programs to shift optimum planting densities to higher levels

Freeze tolerance differs between two ecotypes of Paspalum vaginatum (Poaceae)

Morphological and physiological responses to freezing were evaluated in two ecotypes of the perennial turfgrass Paspalum vaginatum. Leaf extension rate, number of active meristems, leaf water potential and net photosynthesis were measured on plants of both a commercial cultivar, 'Sea Isle 2000', and a wild ecotype from the Flooding Pampa grasslands of Argentina. Plants were propagated by cloning, cultivated in pots, and examined during 18 consecutive days under two treatments: a non-frozen control treatment (15.5±7 ºC) and a frozen treatment with two stages: Stage 1 with four hours of freezing stress for 10 nights (-5ºC), and Stage 2 with 12 hours of freezing stress for eight nights (five nights at -5ºC and three nights at -8ºC). After these treatments, plants were returned to the outside environment to evaluate shoot injury and post-freezing recovery. Leaf water potential, net photosynthesis and leaf extension rate were significantly higher in the wild ecotype than in the commercial cultivar. Meristem density was reduced after freezing in both ecotypes, but was more pronounced in the commercial cultivar (98.5%) than in the wild ecotype (80%). Thus, the two ecotypes coming from different environments, exhibited different morphological and physiological responses to exposure to freezing temperatures

Phototropins But Not Cryptochromes Mediate the Blue Light-Specific Promotion of Stomatal Conductance, While Both Enhance Photosynthesis and Transpiration under Full Sunlight12[C][W][OA]

Leaf epidermal peels of Arabidopsis (Arabidopsis thaliana) mutants lacking either phototropins 1 and 2 (phot1 and phot2) or cryptochromes 1 and 2 (cry1 and cry2) exposed to a background of red light show severely impaired stomatal opening responses to blue light. Since phot and cry are UV-A/blue light photoreceptors, they may be involved in the perception of the blue light-specific signal that induces the aperture of the stomatal pores. In leaf epidermal peels, the blue light-specific effect saturates at low irradiances; therefore, it is considered to operate mainly under the low irradiance of dawn, dusk, or deep canopies. Conversely, we show that both phot1 phot2 and cry1 cry2 have reduced stomatal conductance, transpiration, and photosynthesis, particularly under the high irradiance of full sunlight at midday. These mutants show compromised responses of stomatal conductance to irradiance. However, the effects of phot and cry on photosynthesis were largely nonstomatic. While the stomatal conductance phenotype of phot1 phot2 was blue light specific, cry1 cry2 showed reduced stomatal conductance not only in response to blue light, but also in response to red light. The levels of abscisic acid were elevated in cry1 cry2. We conclude that considering their effects at high irradiances cry and phot are critical for the control of transpiration and photosynthesis rates in the field. The effects of cry on stomatal conductance are largely indirect and involve the control of abscisic acid levels

Phytochrome B Enhances Photosynthesis at the Expense of Water-Use Efficiency in Arabidopsis1[W][OA]

In open places, plants are exposed to higher fluence rates of photosynthetically active radiation and to higher red to far-red ratios than under the shade of neighbor plants. High fluence rates are known to increase stomata density. Here we show that high, compared to low, red to far-red ratios also increase stomata density in Arabidopsis (Arabidopsis thaliana). High red to far-red ratios increase the proportion of phytochrome B (phyB) in its active form and the phyB mutant exhibited a constitutively low stomata density. phyB increased the stomata index (the ratio between stomata and epidermal cells number) and the level of anphistomy (by increasing stomata density more intensively in the adaxial than in the abaxial face). phyB promoted the expression of FAMA and TOO MANY MOUTHS genes involved in the regulation of stomata development in young leaves. Increased stomata density resulted in increased transpiration per unit leaf area. However, phyB promoted photosynthesis rates only at high fluence rates of photosynthetically active radiation. In accordance to these observations, phyB reduced long-term water-use efficiency estimated by the analysis of isotopic discrimination against 13CO2. We propose a model where active phyB promotes stomata differentiation in open places, allowing plants to take advantage of the higher irradiances at the expense of a reduction of water-use efficiency, which is compensated by a reduced leaf area