Crescimento do tomateiro (Lycopersicum esculentum Mill.) adubado com fósforo e colonizado com fungos micorrízicos vesículo-arbusculares

Abstract

Three experiments were conducted in the greenhouse, in desinfested soils, to evaluate the effectivity of vesiculararbuscular mycorrhizal fungi (VAMF) to the tomato plant (Lycopersicum esculentum Mill., cv. Angela I-5100). In the first experiment, eight species of VAMF and a control were tested. Glomus clarum, Glomus etunicatum, and Gigaspora margarita were selected, due to their improve on shoot P concentration and content and their infectivity. In the second experiment, these three VAMF species and a control were compared at four levels of added P (30, 60, 120 and 240 mg P.kg-1 soil). Responses to P levels were observed on shoot and root dry matter up to 120 mg.kg-1, and on leaf area, P concentration and content up to 240 mg.kg-1. At 60 mg.kg-1, mycorrhizal plants showed higher shoot dry matter than the nonmycorrhizal ones, with no increases in P concentration and content. At 30 mg.kg-1, G. clarum and G. margarita were superior to G. etunicatum, and at 120 mg.kg-1, G. etunicatum was superior to G. clarum, with respect to shoot dry matter. G. clarum increased root dry matter and root P content, when compared to the control. The mycorrhizal infection was higher at 30 and 60 mg.kg-1 than at 240 mg.kg-1. In the third experiment, tomato plants, inoculated or not with G. etunicatum, were cultivated at two levels of added P (60 and 120 mg P.kg-1 soil). A functional method of growth analysis was used, with ten weekly harvests (27 until 90 days after transplant) and fotometric measurement of root area. From the mathematical models tested for data adjustment - Gompertz, Logistic, second degree and third degree exponential polynomials - the last one was chosen. A continuous reduction of root:shoot (R:S) ratio (dry matter), specific leaf area, root radius, and P concentration in plant portions were observed. At 120 mg.kg-1, leaf area, dry matter, and root radius were increased, and R:S ratio was decreased. VAMF increased root dry matter and root area, and reduced root radius. At 60 mg.kg-1, VAMF increased stem dry matter, and at 120 mg.kg-1, increased R:S ratio and specific leaf area. VAMF increased stem P content. At 120 mg.kg-1, VAMF increased leaf, fruit and total P content. At 120 mg.kg-1, the relative growth rate, the P accumulation rates, and the net P flux were increased, and the specific P utilization rate was decreased. The net assimilation rate was little affected. In the early stages, VAMF reduced the growth, the net assimilation and the P utilization rates, mainly at 120 mg.kg-1. Thereafter, an increase of these rates was observed, and also a delay in plant senescence. At 120 mg.kg-1, VAMF enhanced P accumulation, with no photosynthetic stimulation, reducing the specific P utilization rate. The VAMF stimulation to root production caused a decrease in the net P flux.