Abstract
ABSTRACT Some forages release allelopathic substances into the environment, and may prevent consortium with arboreal species in pastures. The objective of this work was to evaluate photosynthetic characteristics of pequizeiro plants (hereafter pequi) influenced by concentrations of residues of the forage species Urocholoa decumbens, Melinis minutiflora and Paspalum notatum. The treatments consisted of pequi cultivation under aerial residues of the three forage species mixed to the substrate in four concentrations (1, 2, 3 and 4% mass/mass), plus an additional treatment (comparative control) with pequi cultivated on the substrate without waste. The following parameters were evaluated: photosynthetic rate, stomatal conductance, transpiration rate, relationship between internal and external CO2 concentration (Ci/Ca), maximum quantum yield, effective quantum yield of FS II, electron transport rate, nonchemical quenching and chlorophyll index, concerning the content of chlorophyll a, b and total in pequi plants at 50 and 100 days after transplanting (DAT), and the relative production of dry matter at 100 DAT. At 50 DAT, the following photosynthetic variables were affected in pequi plants: A, gs, chlorophyll a, chlorophyll b and total chlorophyll when cultivated in the presence of forage residues. At 100 DAT, the following photosynthetic variables were affected in pequi plants: A, Fv/Fm, ETR, NPQ, chlorophyll a, chlorophyll b and total chlorophyll, when cultivated in the presence of forage residues. Pequi plants had reduced relative dry matter yield when grown in the presence of U. decumbens. This variable was also affected when pequi was grown in increasing concentrations of residues of the species U. decumbens, M. minutiflora and P. notatum.
Highlights
Allelopathy can be defined as any direct or indirect, beneficial or detrimental effect of a plant or microorganism on another plant or microorganism by the release of secondary compounds into the environment (RICE, 1984)
At 50 days after transplanting (DAT), pequi plants grown in soil with residues of the species Urochloa decumbens and Melinis minutiflora had a lower photosynthetic rate (A) and stomatal conductance with lower values than the control, but the respiratory rate (E) and the Ci/Ca ratio and were not affected by the residues of these two species (Table 2)
At 100 DAT the pequi plants grown on soils with U. decumbens, M. minutiflora and P. notatum were negatively affected for A, but not for gs or E affected
Summary
Allelopathy can be defined as any direct or indirect, beneficial or detrimental effect of a plant or microorganism on another plant or microorganism by the release of secondary compounds into the environment (RICE, 1984). Chemicals involved in allelopathic interactions are secondary compounds and are present in all parts of the plant, such as leaves, roots, stems, flowers, fruit and pollen grains (RICE, 1984). The forage species Urochloa decumbens (brachiaria-grass), Melinis minutiflora (fat-grass) and Paspalum notatum (grass-batatais) are among the plants of interest to the national cattle ranch (VALLE; JANK; RESENDE, 2009). These species may release allelopathic substances causing inhibitory effects in other species, such as corn, rice, wheat, soybean, beans, cotton, lettuce, and carrot (SOUZA et al, 1999; SOUZA et al, 2006; BARBOSA; PIVELLO; MEIRELLES, 2008). These may interfere in the physiological processes and in the growth of the pequi tree when living with these forages and arboreal species
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