Scanning electron microscopy of leaf and petal cuts of citrus trees fertigated with two nitrogen sources

Abstract

Calcium exerts a structural role on cell walls and medium lamellae in plants, which might have implications for tolerance to abiotic and biotic stresses in the field. Based on this later, our work was taken from a long-term field study on fertigation of a citrus orchard that compared the use of ammonium nitrate (AN) and calcium nitrate (CN) fertilizers via fertigation in Valencia sweet orange trees. Sample of leaves and flower petals of trees were collected and observed under scanning electron microscopy, from selected treatments receiving either 80 (N80) or 320 (N320) kg ha-1 year-1 of N, which correspond to 100 or 400 kg ha-1 year-1 of soluble Ca via CN. Trees fertigated with N320 as CN developed leaves and petals with higher mechanical resistance than those with AN. Results also demonstrated that structured cell walls were associated with higher calcium contents and greater mechanical resistance of the tissue during sample preparation for microscopy. From a more practical point of view, such improved structure of leaves and flower petals of CN-treated trees could contribute to an enhanced plant tolerance to diseases commonly affecting the citrus orchards. Additionally, such finding is important for a more sustainable citrus production, because it raises the possibility of reducing pesticides inputs by adjusting nutritional management of citrus orchards. Microscopia eletrônica de varredura de folhas e de pétalas de plantas cítricas fertirrigadas com duas fontes de nitrogênio RESUMO O cálcio exerce papel estrutural nas paredes celulares e lamelas médias das plantas, o que pode ter implicações para a tolerância destas a estresses bióticos e abióticos no campo. Nosso trabalho fez parte de um estudo de campo de longo prazo sobre fertirrigação dos citros, o qual comparou o uso das fontes fertilizantes nitrato de amônio (NA) e de nitrato de cálcio (NC) em laranjeiras Valencia. Amostras de folhas e de pétalas de flores de tratamentos que receberam 80 (N80) ou 320 (N320) kg ha-1 ano-1 de N (os quais corresponderam a 100 ou 400 kg ha-1 ano-1 de Ca solúvel para NC) foram coletadas e observadas em microscópio eletrônico de varredura. As árvores fertirrigadas