02261naa a2200313 a 450000100080000000500110000800800410001910000140006024500530007426000090012752015450013665000180168165000130169965000190171265000130173165000120174465000180175665000160177465000230179065000090181365300080182265300160183065300130184665300110185965300090187065300100187970000170188977300410190614579051992-09-22       1992    bl ---       0--  u    #d1 aLYNCH, J.  aShoot nitrogen dynamics in tropical common bean.  c1992  aThe common bean (Phaseolus vulgaris L.) is an important food crop in the tropics, where its productivity is often limited by low soil N availability. An ideotype for efficient N-use in bean would distribute N in time and space so that leaf N (and therefore leaf photosynthetic capacity) is optimized with respect to reproductive N sinks. To define parameters and estimate genetic variability for N use, we examined shoot N dynamics in three tropical bean genotypes of similar phenology believed to differ in N acquisition and allocation. Seeds were sown in a high-N soil in two plantings separated by 20 d. Shoots of BAT 477 acquired considerably more N than porrillo sintetico, but both genotypes yielded well. G 5059 acquired an intermediate amount of N, partitioned more N to leaves, and matured slightly later, but had a lower final N harvest index (NHI) than the other two genotypes. Time of planting had a substantial effect on shoot N uptake and partitioning. After flowering, N was lost from leaves and stems, rose and fell in young pods and pod walls, and accumulated in seeds. Harvest index (HI) and NHI increased almost linearly from flowering to physiological maturity at the same rate in all three genotypes. Seed N duration dominated post-flowering shoot N during. Leaf N duration represented 25% of post-flowering shoot N during on average. Leaf CO2 exchange rate (CER) was highly correlated with leaf N content, and both declined during mid and late pod filling. Instantaneous leaf photosynthetic N-use efficienty (CER per u  aharvest index  anitrogen  aphotosynthesis  aColheita  aFeijão  aFotossíntese  aNitrogênio  aPhaseolus Vulgaris  aTaxa  aCO2  aCommon bean  aExchange  aIndice  aRati  aTroca1 aWHITE, J. W.  tCrop Sciencegv.32, p.392-397, 1992.