Role of nodes in accumulation and distribution of cadmium and its relationship with nutrient distribution and photosynthesis in the growth and regrowth of Brachiaria decumbens

Abstract

Nodes play an important role in the accumulation and distribution of cadmium (Cd) in graminaceous-like rice (Oryza sativa L.), but what about grasses used for Cd phytoextraction? In this study we evaluated i) if possible Cd accumulation in the basal node compromises the growth of Brachiaria decumbens; ii) the role of nodes in Cd and nutrient accumulation and distribution in leaves; and iii) the relationship between Cd-induced nutritional disorders and photosynthetic impairment. B. decumbens cv. Basilisk was grown for two periods in an Oxisol presenting 0.02 (control), 2.28, 5.17 and 11.23 mg kg−1 soil with bioavailable Cd. The tillering of B. decumbens was not compromised, despite the basal node presenting high Cd concentrations, although Cd did induce stem shortening, especially in the regrowth period. Nodes restricted Cd upward transportation in the initial growth period, but Cd reached the upper nodes in the regrowth period. This result did not affect nutrient distribution into the aerial tissues of the grass. However, nutritional disorders induced by Cd appeared in the lower plant parts (especially in the growth period) due to Cd absorption by the basal node. The only effect of Cd-induced impairment on photosynthesis of B. decumbens was a reduction in instantaneous and intrinsic water use efficiency in leaf III (older), which presented higher Cd concentrations than leaves I and II (newer). In addition to the Cd effect, photosynthetic activity decreased in the regrowth period, probably in response to the lower ambient temperature in this period compared to the growth period. The nodes of B. decumbens keep Cd accumulated in the lower plant parts and avoid nutritional disorders and photosynthesis impairment in the plant leaves allowing for growth and biomass yield.