Gaseous Losses of Nitrogen from Green Plants. Ii. Studies with Excised Leaves in Nutrient Media.

In the previous paper (1) of this series, studies to determine whether gaseous losses of nitrogen occur from cultures of Chlorella and Lemna when grown on various sources of nitrogen, showed that no losses occurred except for one minor exception. In this one case slight losses of nitrogen from Chlorella cultures, grown on ammonium nitrate, did occur. The significance of this finding is somewhat in doubt, however, since these cultures were nearly dead when analyzed, due to increasing acidity during growth. The work, of course, with this exception, failed to corroborate the findings of PEARSALL and BILLIMORIA (9). Most of the work of PEARSALL and BILLIMORIA (9, 10) was with sterilized Narcissus leaves floated on nutrient solutions. This technique provides conditions that are far from normal for growth, but it offers one of the few practical means of obtaining quantitative data on nitrogen losses resulting from the metabolism of common flowering plants. Where inorganic sources of nitrogen were present, losses of more than 50 per cent. of the total nitrogen added were sometimes observed by these workers. The indications were that nitrogen was lost by interaction of nitrites with amino nitrogen, both being products of plant metabolic processes. Under conditions where protein formation was proceeding, the nitrogen losses were small. Where protein hydrolysis predominated the rate of nitrogen, loss was often large. Similar experiments conducted by MOTHES (8), using leaves of Phaseolus mulltifloruts, Hippeastrum, and Agapanthus, failed to confirm these findings. In view of the obvious practical and theoretical importance (5, 12) of these observations of PEARSALL and BILLIMORIA, further work of the same type was initiated. In these experiments, which are reported below, the floating leaf technique similar to that used by Pearsall and Billimoria was adopted, but the analytical procedures were very different.