Abstract: Despite its economic importance, the microclimate in soybean canopies has not yet been studied in detail. Such a study can yield valuable information regarding the interaction of a crop with its environment. In this context, the aim of this study was to evaluate the solar radiation dynamic and yield responses for each canopy strata for two soybean cultivars with determined and undetermined growth habits. A field study was conducted during the 2013/2014 and 2014/2015 growing seasons in the city of Frederico Westphalen, Rio Grande do Sul, Brazil. The cultivar NA6411, with a determinate growth habit, presented a greater interception of radiation in the middle and lower canopies strata which results in higher soybean yield when compared to the cultivar TEC6029, and thus, can be recommended for cultivation in crop production systems. The contribution of the middle and upper canopy strata to the total yield formation was greater than that observed in the lower canopy strata due to the greater interception of solar radiation by these strata. To increase soybean yields, new studies regarding the microclimatic conditions of the soybean canopy should be developed to improve the maximum potential yield of the new soybean cultivars.

Abstract: This work aimed to determine variance components and genetic parameters, as well as phenotypic, genetic and environmental correlations among black oat (Avena strigosa) families grown in different crop season. Seventy-six black oat families and three controls (BRS Madrugada, BRS Centauro, BRS 139 Neblina) were evaluated in two crop seasons (2016 and 2017), using families with intercalary controls experimental design. The results reveled high potential of black oat families to compose a breeding program, due to families and controls variance were similar, variance components expressed greater genetic variance origin for crop season. Panicle weight and panicle grain weight presented high heritability and, these are correlated with panicle length. Thus, these traits can be used to select superior genotypes. Divergent meteorological conditions between crop seasons expressed few variations among phenotypic, genetic and environmental correlations, and it did not alter magnitude and sense of phenotypic and genetic correlations.

Abstract: The objective of the study was to evaluate the growth and production efficiency of forage-grain dual-purpose wheat in two arrangements and four agroforestry systems (Intercrop-I and Intercrop-II), as well as to evaluate crop management for the wheat crops in two planting seasons (Crop Season I-2014 and Crop Season II-2015. The experiment was conducted in a randomized complete block design, factorial scheme 7x2x2, with seven cultivation systems Eucalyptus urophylla x Eucalyptus grandis Intercrop-II and Intercrop-I; Peltophorum dubium Intercrop-II and Intercrop-I; P. rigida Intercrop-I; S. parahyba Intercrop-I; a wheat monoculture with no tree species present; and two harvest management techniques (with and without harvesting of the forage species). Agroforestry systems generated shading for wheat plants, with a higher phyllochron and lower values of leaf area index of those individuals kept under trees with higher crown shading (non-deciduous trees) due to the lower transmissivity of solar radiation. The systems composed with Schizolobium parahyba in Intercrop-I and Parapiptadenia rigida in Intercrop-I provide a minor phyllochron to the wheat, resulting in a higher leaf area index and dry matter yield. Thus, the cultivation of tree species and dual-skilled agricultural crops, such as wheat, provides promising alternatives for the future use of land in tropical countries.

Abstract Sugarcane (Sacharum officinarum L.) monocropping has had a great socio-economic and environmental impact in Brazil, and agroforestry systems have been considered as an alternative for more sustainable production; however, there is a lack of field research under such conditions. The aim of this study was to evaluate the growth rates, radiation use efficiency and yield traits in sugarcane cultivated in the understory of Aleurites fordii, in two agroforestry arrangements and monocropping systems. A field experiment was conducted from July 2015 to June 2016 in the city of Frederico Westphalen, Rio Grande do Sul, Brazil. The radiation use efficiency, assimilate partitioning, leaf area index, absolute growth rate, net assimilation rate, number of tillers, plant height, % of intercepted solar radiation, extinction coefficient, and yield in each system was evaluated. In agroforestry systems, the dynamic interactions between multiple plant species change with the time and can result in unique microclimates. The use of agroforestry systems in 12 x 12m arrangements should be prioritized because it enables greater yields and radiation availability in the understory. This study sought to provide new sustainable alternatives for farmers in order to increase the diversification of the rural property and maintain the preservation of existing agroecosystems.

Abstract Soybean (Glycine max L.) monocropping have had a great socio-economic and environmental impact on the world and agroforestry systems has been considered an alternative for more sustainable production. The aim of this study was to evaluate the effect of different arrangements of agroforestry systems of the species E. urophylla x E. grandis and P. dubium and the pruning of the trees on the dynamics of solar radiation and soybean yield. A field experiment was conducted in Southern Brazil. In order to achieve the objective of the study, the solar radiation transmissivity and the productive performance of the soybean were evaluated. In this study, the soybean yield was determined by the arrangement of the agroforestry system and forest species utilized. The soybean crop cultivated in the understory of the P. dubium trees showed the highest yield response. The use of silvicultural practices for the management of forest species should be considered to generate the balance of the productive system. In this context, tree pruning is a viable side for agroforestry systems, as it promotes an increase in the incidence of solar radiation in the understory, resulting in an increase in soybean yield, especially when integrated with P. dubium.

RESUMO O objetivo deste trabalho foi determinar a temperatura base da chicória e aplicá-la na análise fenológica da cultura, durante quatro períodos de cultivo. O trabalho foi realizado com a cultura da chicória (Chicorium endivia) cultivar Escarola Lisa, na Universidade Federal de Santa Maria, campus Frederico Westphalen-RS. O experimento foi conduzido em delineamento de blocos ao acaso com quatro períodos de cultivo (P1: 15/2/2015; P2: 29/04/2015, P3: 22/07/2015, P4: 16/10/2015) em 10 repetições, com uma planta por repetição. As avaliações consistiram da contagem do número de folhas, realizada três vezes por semana após transplante até o ponto de colheita. Para determinação de temperatura base utilizaram-se os métodos desvio padrão em graus dias (DPgd), desvio padrão em dias (DPd), coeficiente da variação em graus dias (CVgd), coeficiente de variação em dias (CVd), coeficiente de regressão (CR), X-intercepto. Desta forma, a temperatura base para emissão de duas folhas sucessivas na escarola é de 4,7°C, obtida através dos valores de 4,0 e 5,5°C, observados nos métodos DPgd e CR. Para a emissão de duas folhas é necessário entre 16,6 e 27,8°C dia folha-1.

ABSTRACT The objective of this study was to determine the base temperature of escarole and to apply in the phenological analysis of crop during four growing periods. The study was carried out with escarole (Chicorium endivia) ‘Escarola Lisa’ cultivar, at the Federal University of Santa Maria, campus Frederico Westphalen-RS. The experiment was performed in a randomized block design with four sowing periods (P1: 2/15/2015; P2: 04/29/2015, P3: 07/22/2015, P4: 10/16/2015) and 10 replicates, each replicate being one plant. The evaluations consisted of counting the number of leaves, performed three times a week after transplanting date until the harvesting point. To determine the base temperature, the following methods were used: standard deviation in degree-days (SDgd), standard deviation in days (SDd), coefficient of variation in degree-days (CVgd), coefficient of variation in days (CVd), regression coefficient (RC) and X-intercept. The base temperature for emission of two successive leaves in the escarole is 4.7°C, obtained by values of 4.0 and 5.5°C, observed in the SDgd and RC methods. For two leaves emission, the temperature between 16.6 and 27.8°C day leaf-1 is necessary.

ABSTRACT The aim of this study was to evaluate the efficacy and safety of several anesthetics in the brachyuran crab Neohelice granulata, an emergent experimental model. The essential oils (EOs) of Lippia alba, Aloysia tryphilla, and Melaleuca alternifolia (tea tree oil; TTO), the isolated compounds eugenol, menthol, terpinen-4-ol, and the nanoencapsulated form of TTO, were administered in one or more of the following ways: added to the water (immersion), through an arthrodial membrane (injected), or by oral gavage. Unexpectedly, most EOs did not produce an anesthetic effect after immersion. Only TTO and eugenol induced anesthesia by immersion, with very long induction and recovery times compared to anesthesia of other crustaceans. However, a good anesthetic effect was observed with the injection of terpinen-4-ol and nanoencapsulated TTO in N. granulata; both demonstrated ideal induction and recovery times. These substances appear to be promising anesthetic alternatives for crustaceans.

Abstract The appropriate choice of tree species and planting arrangement for use in agroforestry systems is very important in order to maximize productivity and sustainability. The aim of this study was to evaluate the growth of five tree species and its effect on sugarcane yields in different planting arrays in agroforestry systems. The study was conducted from 2007 to 2011 in the city of Frederico Westphalen, RS, Brazil. The five studied tree species were: guapuruvu (Schizolobium parahybae), bracatinga (Mimosa scabrella), canafístula (Peltophorum dubium), angico-vermelho (Parapiptadenia rigida) and eucalypt (Eucalyptus urophylla S.T. Blake x Eucalyptus grandis Hill ex Maiden). Root collar diameter, diameter at breast height, plant height and mean diameter of crown were evaluated for four years with an interval of 90 days between assessments. Yield data for sugarcane were collected in June 2009, 2010, and 2011. Eucalypt presented the greatest root collar diameter values, diameter at breast height, crown development, and plant height. Angico-vermelho, canafístula and eucalypt presented a higher growth in the strip system, while guapuruvu presented the greater growth in the line system. Bracatinga was not influenced by an arrangement in the agroforestry systems. Sugarcane presented greater production in the understory of angico and bracatinga.

RESUMEN El objetivo de este estudio fue evaluar el efecto de tratamientos de boro edáfico y frecuencia del calcio foliar en floración, sobre la producción y ocurrencia de la pudrición apical de híbridos de tomate italiano, cultivados en el sistema convencional en dos temporadas de cultivo. Se realizaron dos experimentos en el área experimental perteneciente a la Universidade Federal de Santa Maria, campus de Frederico Westphalen (Brasil), en los años 2012 y 2013. El diseño experimental fue de bloques al azar con un arreglo factorial 2x2x3x3 cuyo factores fueron dos híbridos (San Vito y Neptuno), en dos épocas de cultivo (primavera-verano y verano-otoño), tres dosis de boro (0; 2,0 y 4,0 g/planta) y tres frecuencias de aplicación de calcio (ausencia de aplicación, aplicación semanal y quincenal) y cuatro repeticiones. El trasplante de plántulas se realizó el día 04 de septiembre de 2012 para la primavera-verano y el 26 de enero para el verano-otoño. El híbrido Neptuno es más productivo en comparación con el híbrido San Vito, pero más susceptible a la pudrición apical. Las dos épocas de cultivo pueden ser recomendadas para el cultivo del tomate italiano en Rio Grande do Sul, aunque el cultivo de primavera-verano presenta mayor productividad cuando se compara al verano-otoño. La frecuencia de aplicación quincenal de CaCl2 al 0,6% se constituye en la mejor opción de manejo de fertilización, en el sentido de obtener mayor productividad y menor número de frutos con incidencia de pudrición apical. El incremento de la dosis de boro condiciona mayor número de frutos por planta y aumento de la productividad.

ABSTRACT The objective of this study was to evaluate the effect of boron soil treatments and the frequency of calcium applications on the flowering, agronomic performance, and incidence of blossom end rot in Italian tomato hybrids grown in conventional systems during two growing seasons. Two experiments were carried out in the experimental area of the Federal University of Santa Maria, Frederico Westphalen campus (Brazil) during 2012 and 2013. A randomized block experiment design was used in a 2x2x3x3 factorial scheme with two hybrids (San Vito and Netuno) in two growing seasons (Spring-Summer and Summer-Fall), three boron doses (0.0, 2.0, or 4.0 g/hole), and three frequencies of calcium application (absence of application, weekly, or biweekly application) with four replicates. The seedlings were transplanted on September 4, 2012 for the Spring-Summer growing season and on January 26, 2013 for the Summer-Fall growing season. The Netuno hybrid was more productive in comparison to the San Vito hybrid, but more susceptible to blossom end rot. Both growing seasons can be recommended for Italian tomato production in Rio Grande do Sul although the Spring-Summer growing season was more productive than the Summer-Fall growing season. The biweekly application frequency of 0.6% CaCl2 was the best option for fertilizer management, resulting in higher yields and a lower number of fruits with an incidence of blossom end rot. The increment of the boron dose defined the higher number of fruits per plant and yield increase.

RESUMO Com o propósito de compreender e relacionar o desempenho fisiológico das plantas às adversidades meteorológicas, objetivou-se determinar a resposta fisiológica de plantas de cidró (Aloysia triphylla) submetidas a diferentes níveis de reposição hídrica no verão e inverno. O trabalho foi desenvolvido em ambiente protegido, no município de Frederico Westphalen-RS. O delineamento utilizado foi blocos completos ao acaso em um esquema fatorial 2x4x2, sendo duas estações do ano (verão e inverno), quatro disponibilidades hídricas (50, 75, 100, 125% da ETo) e duas faces da folha (abaxial e adaxial), com quatro repetições. Avaliou-se a resistência à difusão de vapor pelos estômatos (s/cm), transpiração (µg/cm2/s) e a temperatura da folha (°C), em ambas as faces da folha, no período compreendido entre 10 às 11, 13 às 14 e 16 às 17 horas, aos 45 dias após o início da estação. A resposta fisiológica das plantas de cidró foi influenciada pelo nível de reposição hídrica, de forma diferenciada entre as estações do ano. A estação do verão foi responsável pelos maiores valores de radiação fotossinteticamente ativa incidente, temperatura da folha, transpiração e resistência à difusão de vapor pelos estômatos. A redução na disponibilidade hídrica promoveu o aumento nos valores de resistência estomática ao fluxo de vapor, reduzindo a taxa de transpiração das folhas. A radiação fotossinteticamente ativa incidente, temperatura da folha e transpiração apresentaram maiores valores na face abaxial da espécie estudada.

ABSTRACT We aimed to determine the response of cidró (Aloysia triphylla) submitted to different water replacement levels in summer and winter, in order to understand and relate the plant physiological performance under adverse weather conditions. The research was developed in a protected environment, in the city of Frederico Westphalen, Rio Grande do Sul State, Brazil. The experimental design was completely randomized, arranged in a 2x4x2 factorial scheme, two seasons of the year (summer and winter), four water availability (50, 75, 100, 125% of ETo) and two faces of leaf (abaxial and adaxial), with four replications. There were evaluated stomatal vapor diffusion resistance (s/cm), transpiration (µg/cm2/s) and leaf temperature (°C), on both faces of the leaf from 10 a.m. to 11 a.m., 1 p.m. to 2 p.m. and 4 p.m. to 5 p.m., 45 days after the beginning of the season. We concluded that the physiological response of cidró plants was influenced by water replacement levels, in a different way according to the seasons of the year. The summer season was responsible for the highest values of incident photosynthetically active radiation, leaf temperature, transpiration and stomatal vapor diffusion resistance. The reduction in water availability promoted the increase in values for stomatal resistance to vapor flow, reducing leaf transpiration rate. The incident photosynthetically active radiation, leaf temperature and transpiration showed highest values on the abaxial face of the studied species.

RESUMO O objetivo deste trabalho foi avaliar o filocrono e o requerimento térmico de híbridos de tomateiro italiano nas diferentes fases fenológicas e em diferentes ciclos de cultivo. Os experimentos foram conduzidos na área experimental da Universidade Federal de Santa Maria, campus de Frederico Westphalen-RS, nos anos 2012 e 2013. O delineamento foi em blocos casualizados, em esquema 2x2x5, com dois híbridos de tomateiro, dois ciclos de cultivo e cinco fases fenológicas, em quatro repetições. Foram avaliados os híbridos San Vito e Netuno, com hábito de crescimento indeterminado, no inverno-primavera e no verão-outono. A soma térmica para cada fase fenológica foi calculada pelo acúmulo de temperatura no decorrer das mesmas. O híbrido San Vito apresentou filocrono superior ao Netuno no inverno-primavera, e no verão-outono ambos foram semelhantes. O requerimento térmico total para o cultivo de inverno-primavera foi de 1749,4 e 1717,5 graus dias para os híbridos San Vito e Netuno e de 1534,6 e 1495,2 graus dias no verão-outono, respectivamente. O híbrido Netuno foi mais precoce e apresentou período produtivo mais longo. No ciclo inverno-primavera, o maior requerimento térmico ocorreu na fase de maturação dos frutos, enquanto que no verão-outono ocorreu na fase de crescimento vegetativo. No verão-outono, o ciclo de ambos os híbridos foi menor, com produção mais precoce e concentrada dos frutos.

ABSTRACT The objective of this study was to evaluate the phyllochron and the thermal requirement of Italian tomato hybrids in different phenological phases and different cycles of cultivation. The experiments were carried out in the experimental area of the Federal University of Santa Maria campus Frederico Westphalen, Rio Grande do Sul State, Brazil, in the years 2012 and 2013. The experimental design was a randomized block 2x2x5, with two tomato hybrids, two crop cycles and five phenological stages, with four replications. Hybrids San Vito and Neptune were evaluated, with indeterminate growth habit, during winter-spring and summer-autumn. Thermal needs for each phenological phase was calculated by the accumulation of temperature throughout each phase. Hybrid San Vito showed a phyllochron superior to Neptune in the winter-spring, but, both were similar in summer-autumn. The total thermal requirement for the winter-spring crop was 1749.4 and 1717.5 degrees days for San Vito and Neptune hybrids and 1534.6 and 1495.2 degrees days in the summer-autumn, respectively. Neptune hybrid was earlier and presented a longer production period. In the winter-spring cycle, the highest thermal requirement occurred in fruit maturation phase, while in the summer-fall, the highest thermal requirement occurred in the vegetative growth stage. During summer-autumn, the cycle of both hybrids was shorter, with early production and concentrated fruiting period.

RESUMO O objetivo deste estudo foi avaliar a influência de diferentes cores de perfil de cultivo em NLT sobre o microclima, o crescimento e a produção de quatro cultivares de rúcula, em duas estações do ano. O experimento foi conduzido durante quatro meses em ambiente protegido, no sistema NLT, constituído por bancadas, compostas por oito perfis hidropônicos para a condução das plantas. Os tratamentos foram arranjados em esquema fatorial 4x2x2, sendo quatro cultivares (Cultivada, Folha Larga, Rococó e Runway), duas cores de perfis (preto e branco) e duas estações de cultivo (outono e inverno). Os experimentos foram conduzidos em delineamento experimental em blocos casualizados, com três repetições. As avaliações foram realizadas a cada quatro dias, durante todo o período de crescimento. Avaliou-se a massa fresca e seca de folhas, caules e raízes, altura de planta, número de folhas e índice de área foliar. As diferentes cores de perfis provocaram variações no crescimento e produção da rúcula em razão das modificações térmicas no interior do perfil hidropônico. O maior crescimento e maior produtividade foram obtidos em plantas cultivadas em canais de cultivo de cor branca, durante o outono. As cultivares Cultivada, Folha Larga e Rococó apresentam desempenho produtivo semelhante, sendo superiores a ‘Runway’.

ABSTRACT The aim of this study was to evaluate the influence of different profile colors based on nutrient flux on microclimate, growth and yield of four rocket cultivars. The experiment was conducted during four months in a protected environment in the NLT system, which consisted of benches composed of eight hydroponic profiles for the plants conduction. The treatments were arranged in a 4x2x2 factorial design, with four cultivars (Cultivada, Folha Larga, Rococo and Runway), two color profiles (black and white) and two growing seasons (autumn and winter). The experiments were conducted in a randomized block design with three replications. The evaluations were realized on every four days, throughout the growth period. Leaves fresh and dry mass, stems and roots, plant height, leaf number and leaf area index were evaluated. The different color profiles resulted in variations on crop growth and production due to the thermal changes within the hydroponic profile. The greatest growth and increased productivity were obtained from plants cultivated in white growing channels during the autumn. The cultivars Cultivada, Folha Larga and Rococo have similar performance, better than ‘Runway’.

RESUMO O objetivo deste estudo foi avaliar se Lippia alba apresenta diferentes quimiotipos de acordo com a composição química do óleo essencial (OE), considerando local de coleta e se o OE causa diferentes efeitos nos parâmetros sanguíneos e plasmáticos em jundiá, Rhamdia quelen, durante e imediatamente após a anestesia. Os quimiotipos citral (OE-C) e linalol (OE-L) foram identificados e ambos apresentaram efeito anestésico semelhante para jundiá. Os peixes foram expostos a duas concentrações de cada OE, que induziram anestesia lenta e rápida (100 e 300 mL L-1, respectivamente). Íons sanguíneos não se alteraram em nenhum tempo e consequentemente, o equilíbrio eletrolítico não foi alterado. Os gases sanguíneos oscilaram durante todo tempo de exposição e recuperação, mas houve aumento na pO2 após 10 min de recuperação em peixes anestesiados com OE-C. Níveis sanguíneos de glicose aumentaram nos peixes expostos a ambos OEs quando comparados com o grupo controle. De um modo geral, a exposição a ambos OEs (exceto 100 µL L-1 OE-L na maioria dos tempos) reduziu o cortisol plasmático comparado aos grupos controle e etanol. No entanto, como os níveis de creatinina plasmática em peixes anestesiados com OE-C foram maiores que nos peixes controle, é preferível o uso do OE-L.

ABSTRACT The aim of this study was to evaluate if Lippia alba has different chemotypes according to the chemical composition of the essential oil (EO) considering collection site, and if the EO may have different effects on blood and plasma parameters in silver catfish, Rhamdia quelen, during and immediately after anesthesia. The citral (EO-C) and linalool (EO-L) chemotypes were identified, and both presented similar anesthetic effects for silver catfish. Fish were exposed to two concentrations of each EO, which induced slow and fast anesthesia (100 and 300 µL L-1, respectively). Blood ions did not change at any time of anesthesia induction and recovery and, therefore, the electrolyte balance was not altered. Blood gases oscillated through all exposure and recovery times, but there was an increase in pO2 after 10 min recovery in fish anesthetized with EO-C. Glucose increased in fish exposed to both EOs when compared with the control group. Overall, exposure to both EOs (except 100 µL L-1 EO-L at most times) reduced plasma cortisol levels compared to the control and/or ethanol groups. However, as plasma creatinine levels in fish anesthetized with EO-C were higher than control fish, the use of EO-L is preferable.

RESUMO O objetivo deste estudo foi avaliar o efeito do óleo essencial de Lippiaalba (OELA) como aditivo em rações na ionoregulação, parâmetros metabólicos e expressão de hormônios hipofisários em jundiás, Rhamdiaquelen, submetidos a uma situação estressante (densidade de estocagem de 10,6 kg m-3 e espaço limitado). Os peixes foram alimentados com diferentes concentrações de OELA (0,0 - controle, 0,25 e 0,50 mL kg de ração-1) durante 20 dias. Parâmetros metabólicos não foram afetados pela dieta, com a exceção da alanina aminotransferase, que foi mais elevada no fígado dos peixes alimentados com 0,50 mL de OELA kg de ração-1. Íons plasmáticos e a atividade da H+-ATPase não apresentaram nenhuma alteração, mas os peixes alimentados com 0,25 mL OELA kg de ração-1 apresentaram maior atividade da Na+/K+-ATPase. A expressão da somatolactina na hipófise de peixes alimentados com 0,25 mL OELA kg de ração-1 aumentou, porém a expressão do hormônio de crescimento e da prolactina não mudou. Portanto, a adição do OELA na ração não tem um efeito protetor em jundiás submetidos a uma situação estressante, pois não influiu na maioria dos parâmetros medidos. O uso de 0,25 mL OELA kg de ração-1 parece ser mais adequado que 0,50 mL OELA kg de ração-1, uma vez que este nível de inclusão pode estar relacionado a danos hepáticos.

ABSTRACT The aim of this study was to evaluate the effect of the essential oil of Lippia alba (EOLA) as a feed additive on ionoregulatory and metabolic parameters and pituitary hormones expression in silver catfish, Rhamdia quelen , submitted to a stressful condition (stocking density of 10.6 kg m-3 and limited space). Fish were fed with different concentrations of EOLA (0.0 - control, 0.25 and 0.50 mL kg food-1) for 20 days. Metabolic parameters were not affected by the diet, with the exception of alanine aminotransferase, which was higher in the liver of fish fed 0.50 mL EOLA kg food-1. Plasma ions and activity of H+-ATPase did not change, but fish fed 0.25 mL EOLA kg food-1 presented higher Na+/K+-ATPase activity. Somatolactin expression in the pituitary was higher in the fish fed 0.25 mL EOLA kg food -1, but the expression of growth hormone and prolactin did not change. Therefore, dietary EOLA does not exert a protective effect in R. quelen submitted to a stressful situation because it did not alter most measured parameters. The use of 0.25 mL EOLA kg food-1 seems to be more suitable than 0.50 mL EOLA kg food-1 since the latter may be related to liver damage.

RESUMOO objetivo é estudar a dinâmica da radiação fotossintética alcançando a superfície do solo em povoamentos de Acacia mearnsii De Wild e sua influência no crescimento em altura em povoamentos. Este fato dá origem à formulação da seguinte hipótese para este estudo: "A redução da incidência de luz no interior do suporte de acácia negra vai fazer com que o ponto de inflexão no seu crescimento quando esta atinge a altura de 4 a 5 m de altura, isto é, quando o povoamento se encontra entre 2 e 3 anos de idade". O estudo foi realizado em povoamentos no Estado do Rio Grande do Sul, Brasil, onde os diâmetros a altura do peito, altura total e radiação fotossinteticamente ativa disponível ao nível do solo foram medidos. A frequência tendeu a ser mais intensa com o aumento da idade dos povoamentos. Ficou evidente que ocorreu redução da incidência de luz no interior da floresta causada pelo fechamento do dossel. Consequentemente, o dossel fechado propiciou a concorrência das plantas. Isso afetou as condições para o crescimento em diâmetro e altura dessa espécie, razão pela qual se torna possível conceber a ocorrência de um ponto de inflexão no crescimento dessas duas variáveis, confirmando a hipótese formulada.

ABSTRACTThe objective is to study the dynamics of photosynthetic radiation reaching the soil surface in stands of Acacia mearnsii De Wild and its influence on height growth in stands. This fact gives rise to the formulation of the following hypothesis for this study: "The reduction of the incidence of light inside the stand of black wattle will cause the inflection point in its height growth when this reaches 4 to 5 m in height, i.e. when the stand is between 2 and 3 years of age". The study was conducted in stands in the state of Rio Grande do Sul, Brazil, where diameters at breast height, total height and photosynthetically active radiation available at ground level were measured. The frequency tended to be more intense when the age of the stands increases. It was evident that a reduction of light incidence inside the forest occurred, caused by canopy closure. Consequently, closed canopy propitiated the competition of plants. This has affected the conditions for growth in diameter and height of this species, reason why it becomes possible to conceive the occurrence of an inflection point in the growth of these two variables, confirming the formulated hypothesis.