Partição de biomassa seca e nutriente em minicepas de eucalipto influenciada pela adubação NPK

Abstract

O estado nutricional da planta-matriz é de grande importância para a manutenção do seu vigor vegetativo, o que determina a produção de brotos e também os índices de enraizamento e velocidade de formação das raízes, uma vez que os macronutrientes e os micronutrientes estão envolvidos nos processos bioquímicos e fisiológicos vitais à planta. Nesse sentido, o objetivo deste trabalho foi avaliar a influência da adubação NPK sobre a partição de biomassa seca e nutriente em minicepa de eucalipto em solução nutritiva. O trabalho foi realizado de novembro de 2008 a janeiro de 2009, em casa de vegetação. Foi utilizado delineamento inteiramente casualizado em esquema fatorial fracionado (4x4x4) ½ , perfazendo 32 tratamentos com três repetições. Os tratamentos se constituíram de quatro doses dos nutrientes de N (50; 100; 200 e 400 mg L-1) na forma de ureia, P (7,5; 15; 30 e 60 mg L-1) na forma de ácido fosfórico e K (50; 100; 200 e 400 mg L-1) na forma de cloreto de potássio em solução nutritiva. Houve efeito significativo apenas para as doses de N isoladamente, para a biomassa seca das miniestacas e biomassa seca da parte aérea e raiz das minicepas com efeito linear decrescente, com o aumento das doses de N. A dose de 50 mg L-1 de N proporcionou maior acúmulo de biomassa seca das miniestacas e minicepas. A distribuição percentual da biomassa seca e dos nutrientes na biomassa seca das miniestacas, parte aérea e raízes das minicepas variou em relação às doses de N. A extração de macronutrientes pelas miniestacas de 6 cm na dose de 50 mg L-1 de N seguiu a seguinte ordem decrescente de N > S > P > K > Ca > Mg e micronutrientes de Cu > B > Mn > Fe > Zn.

Nutrient partitioning among the roots, hedge and cuttings of Corymbia citriodora stock plants

“…Between 17% and 31% of total plant mass was collected as cuttings at each harvest, with this percentage declining during the experiment (Table 1). These percentages were similar to those from the cuttings of E. urophylla stock plants (~18-25%) across a range of N application rates (Neto et al, 2012). Nitrogen was most concentrated in the hedge leaves and cutting leaves (HL and CL) and least concentrated in the stems of the hedge (HS) (Figure 2a), so that between 32 ± 4 and 88 ± 7 mg of N (CS + CL) was lost from the stock plant during each harvest of cuttings (Figure 2b).…”

“…Boron was more highly concentrated in the hedge leaves (HL) than the cutting leaves (CL) or other plant parts (R, HS and CS) (Figure 3c), resulting in much of the B content of the stock plant being confined to the hedge (HL and HS; Figure 3d). The proportion of total plant B removed through the harvest of cuttings (15-31%) reflected the biomass allocation to cuttings (Table 1), as it did during the harvest of cuttings from E. urophylla (Neto et al, 2012). B is an immobile nutrient in many plant species where sucrose is the primary photoassimilate, but it is mobile in species that contain polyols such as sorbitol and mannitol (Miwa et al, 2009;Lehto et al, 2010) E. grandis and E. grandis × E. urophylla are rich in sorbitol and mannitol (Leite et al, 2008(Leite et al, , 2010, and B appears to be mobile in E. grandis × E. urophylla (Mattiello et al, 2009).…”

“…Therefore, Ca loss through the harvest of cuttings (Figure 3b) was lower as a proportion of the plant's total nutrient content than it was for N, P and K (Figures 2b, 2d, 2f; Table 1). In fact, disproportionately low amounts of Ca (8-20%) were lost through the harvest of cuttings (Table 1) in contrast with high losses (~24-43%) observed with E. urophylla (Neto et al, 2012). Ca is considered an immobile nutrient that tends to be retained at high levels in mature and senescing organs (McLaughlin and Wimmer, 1999;Karley and White, 2009).…”

“…These nutrients are highly mobile and are often concentrated in growing tissues such as young shoots (Karley and White, 2009;Li et al, 2010). Much greater percentages of total plant N (~75-86%) are removed during the harvest of E. urophylla cuttings, which also lose disproportionately high amounts of total plant P (~33-56%) and K (~30-43%) at each harvest (Neto et al, 2012). Replacement of these mobile macronutrients may be critical for sustained stock plant growth as well as for root formation by cuttings, since adventitious rooting has been correlated with P and K concentrations in the cuttings of C. citriodora (Trueman et al, 2013a) and with N, P and K concentrations in E. cloeziana (Trueman et al, 2013b).…”

“…Rooting is also correlated with N, P and K concentrations in E. cloeziana, and with P and K concentrations in C. citriodora, but it is not correlated with concentrations of these macronutrients in E. dunnii, E. grandis, E. grandis × E.urophylla or E. urophylla (Cunha et al, 2009a, b;Trueman et al, 2013a, b). The partitioning of nutrients among the roots, pruned hedge and cuttings of stock plants has been described recently for E. urophylla (Neto et al, 2012) but, otherwise, little is known about the uptake and distribution of nutrients by eucalypt stock plants, despite their importance for determining the nutrient status and adventitious rooting potential of cuttings.…”