EFFECTS OF ROOT DEFORMATION AND LIGHT AVAILABILITY ON GROWTH AND BIOMASS ALLOCATION OF Senna multijuga SEEDLINGS (Rich) H. S. Irwin & Barneby

ABSTRACT 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. RESUMO Os efeitos e consequências da deformação da raiz causada por erros no processo de repicagem em viveiros florestais ainda são desconhecidos para as mudas de árvores tropicais. Analisamos os impactos da disponibilidade de luz e de deformação das raízes no crescimento e alocação de biomassa em mudas de Senna multijuga, uma árvore tropical pioneira comumente utilizada em programas de restauração florestal. Nossas hipóteses foram: (a) como espécie típica exigente de luz, as plântulas de S. multijuga podem ter seu crescimento comprometido em baixa disponibilidade de luz, (b) a deformação da raiz induz prejuízos nas taxas de crescimento e mudanças na alocação de biomassa, e (c) os efeitos da baixa disponibilidade de luz no crescimento e alocação de biomassa são potencializados pela deformação da raiz. As plântulas, com e sem deformação das raízes, foram cultivadas durante 43 dias sob três níveis de radiação fotossinteticamente ativa