Com o objetivo de definir qual o melhor volume de tubete e o tempo de permanência das mudas de Senegalia bahiensis em viveiro, foram instalados dois experimentos em delineamento inteiramente casualizado. No primeiro experimento, as mudas foram produzidas em três volumes de tubetes (55, 180 e 280 cm³), constituindo os tratamentos, quatro repetições e 49 mudas por repetição. No segundo experimento, foi realizada uma simulação de campo utilizando duas mudas por repetição, totalizando 24 mudas. As variáveis analisadas foram: altura, diâmetro, massa seca da parte aérea e do sistema radicular, número de folhas, incremento médio diário em altura e incremento médio diário em diâmetro. As mudas produzidas no recipiente de menor volume (55cm³) obtiveram as menores médias para todas as variáveis analisadas, tanto na fase de produção de mudas, como na simulação de campo. Em função dos resultados obtidos nos experimentos, conclui-se que para a espécie Senegalia bahiensis, por sua produção de mudas apresentar qualidade semelhante quando foram utilizados tubetes de 180 e 280 cm³, recomenda-se o uso do tubete de 180 cm³, o qual, além de apresentar redução do ciclo de produção em no mínimo 33 dias, reduz o uso de insumos, nas condições em que os experimentos foram conduzidos.
Background and Aims Although hypernodulating phenotype mutants of legumes, such as soybean, possess a high leaf N content, the large number of root nodules decreases carbohydrate availability for plant growth and seed yield. In addition, under conditions of high air vapour pressure deficit (VPD), hypernodulating plants show a limited capacity to replace water losses through transpiration, resulting in stomatal closure, and therefore decreased net photosynthetic rates. Here, we used hypernodulating (nod4) (282.33 ± 28.56 nodules per plant) and non-nodulating (nod139) (0 nodules per plant) soybean mutant lines to determine explicitly whether a large number of nodules reduces root hydraulic capacity, resulting in decreased stomatal conductance and net photosynthetic rates under high air VPD conditions. Methods Plants were either inoculated or not inoculated with Bradyrhizobium diazoefficiens (strain BR 85, SEMIA 5080) to induce nitrogen-fixing root nodules (where possible). Absolute root conductance and root conductivity, plant growth, leaf water potential, gas exchange, chlorophyll a fluorescence, leaf ‘greenness’ [Soil Plant Analysis Development (SPAD) reading] and nitrogen content were measured 37 days after sowing. Key Results Besides the reduced growth of hypernodulating soybean mutant nod4, such plants showed decreased root capacity to supply leaf water demand as a consequence of their reduced root dry mass and root volume, which resulted in limited absolute root conductance and root conductivity normalized by leaf area. Thereby, reduced leaf water potential at 1300 h was observed, which contributed to depression of photosynthesis at midday associated with both stomatal and non-stomatal limitations. Conclusions Hypernodulated plants were more vulnerable to VPD increases due to their limited root-to-shoot water transport capacity. However, greater CO2 uptake caused by the high N content can be partly compensated by the stomatal limitation imposed by increased VPD conditions.
The effects of root deformation caused by errors in the pricking-out process in forest nurseries are still unknown for tropical tree seedlings. We analyzed the effects of light availability and root deformation on growth and biomass allocation in seedlings of Senna multijuga, a pioneer tropical tree commonly used in forest restoration programs. Our hypotheses were: (a) as a typical light-demanding species, the seedlings of S. multijuga may have their growth compromised by low light availability; (b) root deformation impairs growth rates and induces changes in biomass allocation; and (c) the effects of low light availability on growth and biomass allocation are increased by root deformation. Seedlings with and without root deformation were cultivated for 43 days under three levels of total daily photosynthetically active radiation (PAR) (28, 12, and 1 mol photons m-2 day-1). Seedlings of S. multijuga had their growth rates severely affected by values of PAR at about 1 mol photons m-2 day-1, but root deformation did not affect the relative growth rates of the whole plant. Instead, root deformation caused a decrease in the relative growth rate of roots in all light availabilities. The changes in root growth affected biomass allocation to the roots. The interactive effects of light availability and root deformation on the allocation of biomass to leaves are more pronounced at low light availability. Root deformations may lead to the production of seedlings with a low competitiveness capacity regardless of light conditions.
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