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- Author or Editor: Peter H. Graham x
Leaves at nodes 4 or 8 of greenhouse grown beans, Phaseolus vulgaris L., cv. Puelba 152, were briefly exposed to 14CO2 at 35, 48, 63, or 70 days after planting. Prior to flowering, over 85% of the recovered 14C-activity translocated in 24 hours from node 4 was in roots, nodules, and lower stem. At flowering, radioactivity translocated to the lower stem decreased but correspondingly increased in nodules. Roots sequestered 45% of translocated-14C throughout the life of the node-4 leaf. About 80% of the 14C-activity exported from node 8 at flowering was in middle and upper stem sections, but during pod-fill over 85% moved into the pods and less than 1% to the nodulated root system. Starch concentration in the lower stem increased continuously from flowering, but in other plant parts declined after early pod-fill. At mid pod-fill, the concentration of soluble sugars in nodules and roots declined and reached a common value in stem sections. Nitrogen (C2H2) fixation decreased rapidly after peaking at early pod-fill. This decline, which was accompanied by loss of lower leaves, occurred in the presence of a high concentration of starch in the stem.
Mulching ‘Puebla 152’ beans with rice hulls to a depth of 4 cm reduced afternoon soil temperature, soil temperature fluctuation, and slowed the loss of soil moisture. These effects were greatest prior to canopy closure. Fresh weight of nodules, roots, stems, leaves, and total plant increased 50%, 38%, 49%, 24%, and 38%, respectively, with mulching, but pod and final seed weight were unaffected. Mulching had little effect on the concentration of soluble and insoluble carbohydrates. N2 fixation rates (C2H2 reduction) were low (≤ 0.6 µmole/plant per hr) but were as much as 3 times higher in mulched than unmulched plants.