Campomanesia xanthocarpa O. Berg. (“Gabirobeira”, Myrtaceae) is a versatile fruit tree species native in Cerrado. Studies of mineral fertilization and luminous conditions with the species are incipient. Thus, the aim was to evaluate the initial growth and photochemical aspects in C. xanthocarpa cultivated under phosphate fertilization and shading levels. The experiment was carried out in plastic pots and the factors under study consisted of five doses of phosphorus: 0, 50, 100, 150 and 200 mg kg soil-1, and two shadings levels: 0% (full sun) and 50%. The treatments were arranged in a 5 x 2 factorial scheme, in a randomized block design, with four replications. The greatest growth characteristics occurred at 240 days after transplantation. The highest chlorophyll index was seen in shaded leaves. The highest values of variable and maximum chlorophyll-a fluorescence were with 10.8 and 11.6 mg P kg-1 in shaded environments, and with 120.0 and 81.81 mg P kg-1, under full sun. The highest photochemical efficiency in photosystem II (Fv/Fm) was under full sun with 33.33 mg P kg-1. The analysis of main components explained 78.82% of the remaining variability. The shaded C. xanthocarpa plants showed higher photochemical yields with the addition of low phosphorus doses. Phosphate fertilization contributed to the mitigation of photochemical damage in young plants of C. xanthocarpa cultivated under full sun.
O alumínio (Al) presente nos solos ácidos reduz o potencial fisiológico de sementes e limita o crescimento plântulas de diversas espécies de interesse agronômico. Entretanto, informações quanto à toxicidade do Al em Arctium lappa L. (bardana, Asteraceae) são escassos. Objetivou-se nesse estudo avaliar o efeito do estresse por alumínio na germinação e no vigor de plântulas de A. lappa. Foram testadas cinco concentrações de sulfato de alumínio hidratado Al2(SO4)3·16H2O: 0 (controle), 5, 10, 15 e 20 mmol L-1. O teste de germinação foi feito em caixas do tipo Gerbox (sobre papel – SP) e em rolo papel – RP, utilizando papel germitest® umedecidos 2,5 vezes seu peso seco. As sementes foram mantidas em câmaras de B.O.D, sob 20-30ºC e luz branca constante. O potencial fisiológico das sementes e vigor de plântulas foi avaliado por meio dos testes de primeira contagem de germinação (4 dias), germinação (7 dias) e comprimento de plântulas. Observamos redução da germinação conforme aumento das concentração de Al em substrato SP. Os menores comprimentos da parte aérea das plântulas ocorreram com 20 mmol L-1 de Al e no substrato SP. Ocorreu inibição radicular das plântulas conforme aumento das concentração de Al nos dois substratos, especialmente no SP. O estresse por alumínio e substrato SP afetou negativamente a germinação de sementes e vigor das plântulas de A. lappa.
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