Nitrogen Distribution Pattern of African Yam Bean (Sphenostylis stenocarpa) exposed to Cadmium stress
In Nigeria, S. stenocarpa is an under-utilized leguminous crop grown in Edo State mainly for its tuberous root and less for the seeds. The purpose of this study was to determine the nitrogen assimilation and distribution pattern of S. stenocarpa exposed to cadmium stress by partitioning the plant accessions into root and leaf, and N-nitrate and N-ammonia analysis was carried out during the seedling and flowering stage. The results showed that cadmium stress increased percentage foliar total nitrogen in TSs-91 in the Cd-5ESV from 2.03% to 2.03% and 1.93% to 5.73% 6 and 18 weeks after sowing with increased cadmium concentration. However, there was a reduction in leaves Nitrate-N with increase in cadmium concentration. TSs-93 in Cd-5ESV had a Nitrate-N of 703.84 ppm as compared to 968.14 ppm in control while the root was significantly reduced from 771.71 to 516.36 ppm. Irrespective of leaves, roots and metal concentration, TSs-91 sow in control soils assimilated 6.29% nitrogen nitrate as compared to 0.16% in nitrogen ammonia. It was observed that the plants assimilated nitrogen more in the nitrate form than in the ammonia form and are stored in the leaves as compared to the roots except TSs-95 which stored more N-nitrate in the roots.
Keywords: legumes, nitrogen, ammonia, pollution, Nigeria, heavy metal, assimilation