Strategies to improve olive orchards sustainability under a changing environment
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2019-01-28
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As condições ambientais são um dos maiores desafios para a agricultura. Na Região Mediterrânea, onde a oliveira é uma cultura emblemática, é muito comum o stresse estival severo que inclui défice hídrico, elevadas temperaturas e altos níveis de radiação solar, um cenário tendencialmente agravado no futuro pelas alterações climáticas. Se a esta razão acrescentarmos o aumento da demanda de azeite no mundo, torna-se evidente a necessidade de aumentar a sustentabilidade e a competitividade dos olivais tradicionais de sequeiro que contribuem para a economia de regiões remotas e para a preservação dos ecossistemas autóctones. Dos componentes do stresse estival, o défice hídrico é talvez o mais crítico, uma vez que é extremamente agravado pelos outros. Compreender as respostas da oliveira ao défice hídrico ajuda a projetar e a selecionar práticas agronómicas que melhorem a rentabilidade da cultura. Neste particular, as respostas fisiológicas noturnas têm sido pouco exploradas pela comunidade científica. Com baixa disponibilidade de água, a oliveira aumentou a abertura estomática durante as primeiras horas da noite, bem como a proporção das perdas de água durante a noite relativamente à totalidade das perdas diárias. Embora alguns potenciais benefícios possam estar associados a este comportamento, como a redução da respiração noturna e a melhoria da absorção de minerais, elevadas perdas de água durante a noite podem ser prejudiciais em condições de seca severa. Juntamente com a compreensão da resposta da oliveira às condições de stresse, é importante agir a curto prazo, avaliando e selecionando estratégias que aliviem e/ ou melhorem a adaptabilidade da oliveira ao stresse estival, incluindo as vertentes de capacidade de resistência e capacidade de recuperação. Neste sentido, pode considerar-se a aplicação de certos produtos naturais na superfície foliar. Neste trabalho avaliou-se o uso de caulino (KL) e ácido salicílico (SA) como agentes protetores do stresse estival. O KL forma um filme de partículas brancas que reflete o excesso de radiação, reduzindo a carga de calor, e o SA é uma hormona vegetal de sinalização com diversos papéis reguladores na resposta ao stresse. Inicialmente, a influência dos produtos foi avaliada em plantas jovens envasadas e submetidas a ciclos de seca e reidratação, de forma a avaliar a capacidade de resistência à seca e a capacidade de recuperação. No caso do SA, testaram-se três concentrações diferentes (10, 100 e 1000 µM), uma vez que a sua eficácia para diferentes genótipos depende da concentração aplicada e não há recomendação por parte do fabricante, o que acontece para o KL (5% p/v). De forma a confirmar os resultados obtidos na experiência em vasos, e para avaliar a influência na produtividade e qualidade das colheitas, oliveiras em regime de sequeiro, em condições reais, foram pulverizadas com KL e SA a 100 µM, a concentração mais eficiente do estudo em vasos, durante dois anos. Reunindo os resultados das experiências efetuadas, compreendeu-se melhor as respostas induzidas pelo KL e pelo SA. O KL induziu o desenvolvimento de características foliares associadas a condições de sombra, contribuiu para melhorar o estado hídrico das plantas, reduziu as limitações estomáticas e não estomáticas para a atividade fotossintética, melhorou o estado nutritivo da planta e reduziu a necessidade de investimento em metabolismo secundário durante o stresse e na reparação de danos extra durante a fase de recuperação. As principais diferenças nas duas experiências foram encontradas na restauração das trocas gasosas após o alívio do stresse, atendendo a que no ensaio de vasos a recuperação foi enfraquecida pelo sombreamento causado pelo KL, e na produção de biomassa, considerando que não se verificou influência significativa na acumulação de biomassa, enquanto que em condições de campo a aplicação de KL contribuiu para aumentar o volume da copa e a produção de azeitona. Em relação às respostas ao SA, verificou-se uma fraca influência da concentração de 10µM, enquanto a concentração de 1000 µM induziu algumas respostas negativas. Por sua vez, o SA a 100 µM melhorou o estado hídrico das plantas, em estreita associação com a acumulação de osmólitos, aumentou a concentração de proteínas solúveis totais, melhorou o estado nutritivo, a desintoxicação de ROS e capacidade fotossintética durante o stresse, contribuindo ainda para melhorar a capacidade de recuperação depois do alívio do stresse. No ensaio de vasos, a concentração de 100 µM aumentou a acumulação de biomassa, principalmente ao nível radicular, enquanto que em condições de campo aumentou a produção de frutos, não influenciando o crescimento da copa. A influência do KL e do SA na qualidade das colheitas dependeu da severidade do stresse. Com stresse estival moderado, o KL e o SA aumentaram as concentrações de antioxidantes e a capacidade antioxidante das azeitonas e dos azeites, enquanto que o oposto se verificou com o aumento da severidade do stresse. O KL e o SA também contribuíram para reduzir a degradação dos compostos fenólicos durante os eventos de geadas. Por outro lado, estes produtos não afetaram significativamente os índices de qualidade do azeite, acidez, índice de peróxidos e o coeficiente de extinção relacionado com a formação de dienos conjugados. Resumindo, o trabalho desenvolvido no âmbito desta tese revelou que o balanço hídrico noturno deve ser incluído na gestão agronómica. Além disso, este estudo expôs estratégias rentáveis que atenuam o efeito negativo do stresse estival em oliveiras e contribuiu para aumentar a compreensão do modo de ação do KL e do SA na mitigação do stresse.
One of the major challenges for agriculture are the environmental conditions. In the Mediterranean Region, where olive is an emblematic crop, is commonly notice a severe summer stress that includes drought, heat and high irradiance levels, a scenario tendentially worsened by climate change. In addition, as the demand for olive oil is increasing all over the world, urge the necessity to increase the sustainability and competitiveness of the traditional rainfed olive orchards that highly contribute to the economy of remote regions and for the autochthone ecosystems preservation. Among the constituents of summer stress, drought is perhaps the most critical, as is highly exacerbated by the others. A better understanding of how olive tree responds to drought help to design and select agronomic practices to improve the crop profitability. In this regard, nighttime physiological responses has been less discussed. Under drought, olive tree increases both nighttime stomatal open in the first hours of night and the proportion of nighttime water loss in relation to whole-day losses. Although some potential benefits to plants can be associated to this response, as the reduction in nighttime respiration and the improvement in minerals uptake, a continuous nighttime water loss might be detrimental under severe drought conditions. Along with the understanding of olive tree response to stress conditions, it is important to act in the short-term, by evaluating and selecting strategies that contribute to alleviate and/or to improve olive tree adaptability (stress resistance and recovery capacity) to summer stress. The application of exogenous products on leaf surface can be considered in this sense. The use of kaolin (KL) and salicylic acid (SA) as summer stress mitigating agents was evaluated in this thesis. KL forms a white protective particle film which increases the reflection of excess radiation, reducing the heat load, and SA is a signaling phytohormone with diverse regulatory roles in stress response. The influence of these products was primarily evaluated in young potted plants subjected to repeated cycles of drought-rewatering, to properly assess the drought resistance and the recovery capacity. In the case of SA, three different concentrations were tested (10, 100 and 1000 µM) since concentration highly determine its effectiveness and no manufacture recommended dosage is available, as for KL (5% w/v). To confirm the pots experiment results under realistic field conditions, and to evaluate the influence on yield and harvests quality, rainfed olive trees were sprayed with KL and the most effective SA concentration, 100 µM, for two consecutive growing seasons. Pulling up together the results of both experiments, a better understanding about KL and SA induced responses was achieved. KL particle film induced shade-related leaf characteristics and contributed to improve plant water status, reduced the stress-induced stomatal and nonstomatal limitations to photosynthesis, improved plant mineral status and reduced the necessity to invest in secondary metabolism during stress and in extra repair damages under stress recovery. The major differences of KL effects between experiments were found in gas exchange restauration after stress relief, as under pot conditions the recovery was weakened by the KL shaded effect, and also in biomass yield as no influence was recorded in biomass accumulation, while in field conditions KL contributed to higher canopy volume and crop yield. Regarding SA, although the influence of 10µM SA was less noticeable and 1000 µM SA induced some negative responses, 100 µM SA improved water status in line with osmolites accumulation, increased total soluble proteins concentration, plant mineral status and ROS detoxification and photosynthetic capacity during stress, contributing also to improved recovery capacity after stress relief. In pots experiment, 100 µM SA increased biomass accumulation, mainly at root level, while under field conditions enhanced crop yield and no influence was noticed in canopy growth. KL and SA influenced harvests quality depending on the severity of stress conditions. Under moderate summer stress, KL and SA improved antioxidants and antioxidant capacity of olives and olive oil, while the opposite was verified with higher stress severity. The effects of KL and SA was also associated with phenolics protection against severe frost events. By other side, both products did not significantly affect the oil quality indices, free acidity, peroxide value and the extinction coefficient related with the formation of conjugation diene compounds. In summary, the work developed in the scope of this thesis revealed that nighttime water balance is worth being considered in agronomic management. Moreover, this study exposes cost-effective strategies to attenuate the negative effects of summer stress in olive trees, and contributed to increase the understanding about KL and SA action mode in stress mitigation
One of the major challenges for agriculture are the environmental conditions. In the Mediterranean Region, where olive is an emblematic crop, is commonly notice a severe summer stress that includes drought, heat and high irradiance levels, a scenario tendentially worsened by climate change. In addition, as the demand for olive oil is increasing all over the world, urge the necessity to increase the sustainability and competitiveness of the traditional rainfed olive orchards that highly contribute to the economy of remote regions and for the autochthone ecosystems preservation. Among the constituents of summer stress, drought is perhaps the most critical, as is highly exacerbated by the others. A better understanding of how olive tree responds to drought help to design and select agronomic practices to improve the crop profitability. In this regard, nighttime physiological responses has been less discussed. Under drought, olive tree increases both nighttime stomatal open in the first hours of night and the proportion of nighttime water loss in relation to whole-day losses. Although some potential benefits to plants can be associated to this response, as the reduction in nighttime respiration and the improvement in minerals uptake, a continuous nighttime water loss might be detrimental under severe drought conditions. Along with the understanding of olive tree response to stress conditions, it is important to act in the short-term, by evaluating and selecting strategies that contribute to alleviate and/or to improve olive tree adaptability (stress resistance and recovery capacity) to summer stress. The application of exogenous products on leaf surface can be considered in this sense. The use of kaolin (KL) and salicylic acid (SA) as summer stress mitigating agents was evaluated in this thesis. KL forms a white protective particle film which increases the reflection of excess radiation, reducing the heat load, and SA is a signaling phytohormone with diverse regulatory roles in stress response. The influence of these products was primarily evaluated in young potted plants subjected to repeated cycles of drought-rewatering, to properly assess the drought resistance and the recovery capacity. In the case of SA, three different concentrations were tested (10, 100 and 1000 µM) since concentration highly determine its effectiveness and no manufacture recommended dosage is available, as for KL (5% w/v). To confirm the pots experiment results under realistic field conditions, and to evaluate the influence on yield and harvests quality, rainfed olive trees were sprayed with KL and the most effective SA concentration, 100 µM, for two consecutive growing seasons. Pulling up together the results of both experiments, a better understanding about KL and SA induced responses was achieved. KL particle film induced shade-related leaf characteristics and contributed to improve plant water status, reduced the stress-induced stomatal and nonstomatal limitations to photosynthesis, improved plant mineral status and reduced the necessity to invest in secondary metabolism during stress and in extra repair damages under stress recovery. The major differences of KL effects between experiments were found in gas exchange restauration after stress relief, as under pot conditions the recovery was weakened by the KL shaded effect, and also in biomass yield as no influence was recorded in biomass accumulation, while in field conditions KL contributed to higher canopy volume and crop yield. Regarding SA, although the influence of 10µM SA was less noticeable and 1000 µM SA induced some negative responses, 100 µM SA improved water status in line with osmolites accumulation, increased total soluble proteins concentration, plant mineral status and ROS detoxification and photosynthetic capacity during stress, contributing also to improved recovery capacity after stress relief. In pots experiment, 100 µM SA increased biomass accumulation, mainly at root level, while under field conditions enhanced crop yield and no influence was noticed in canopy growth. KL and SA influenced harvests quality depending on the severity of stress conditions. Under moderate summer stress, KL and SA improved antioxidants and antioxidant capacity of olives and olive oil, while the opposite was verified with higher stress severity. The effects of KL and SA was also associated with phenolics protection against severe frost events. By other side, both products did not significantly affect the oil quality indices, free acidity, peroxide value and the extinction coefficient related with the formation of conjugation diene compounds. In summary, the work developed in the scope of this thesis revealed that nighttime water balance is worth being considered in agronomic management. Moreover, this study exposes cost-effective strategies to attenuate the negative effects of summer stress in olive trees, and contributed to increase the understanding about KL and SA action mode in stress mitigation
Descrição
PhD Thesis Agricultural Production Chains - From Fork to Farm
Palavras-chave
Ácido salicílico , balanço hídrico noturno , caulino , oliveira , stresse estival , seca