ENERGY AND NITROGEN TRANSFORMATION 



515 



changed to ammonia. This tends to demonstrate that, with a sub- 

 stance that has a C:N ratio of 16 (alfalfa meal), fungi require all the 

 nitrogen for synthetic purposes while bacteria can liberate, as am- 

 monia, an amount of nitrogen equivalent to the amount of carbon 

 decomposed. Since fungi produced as great an amount of C0 2 as the 

 complex soil suspension, Neller suggested that the fungi can be looked 

 upon as organisms active in normal soil. However, if fungi were the 

 predominating or only organisms in the soil, this state of affairs could 

 hardly be considered beneficial to higher plants. The rapid decom- 

 position of the organic matter by the fungi with a lack of ammonia 



1 — Soil infusion 

 2 — Trlchoderma 6p. 

 3--Aspergill.ua nlg«r 

 gatherium 

 subtil le 



DAYS 



Fio. 32. Rate of decomposition of alfalfa meal by pure cultures of micro- 

 organisms and by the mixed soil flora, as indicated by the daily evolution of C0 2 

 (from Neller). 



accumulation is true only of substances with a relatively wide carbon- 

 nitrogen ratio, such as alfalfa meal; these substances are usually acted 

 upon first of all by fungi and only later by bacteria. The fungi rapidly 

 break down the complex carbohydrates and cause a narrowing of the 

 carbon-nitrogen ratio. This leads to an abundant liberation of C0 2 

 but not of ammonia, since the proteins are decomposed to a limited 

 extent and all the ammonia is reassimilated. The synthesized fun- 

 gus mycelium is richer in nitrogen than the alfalfa and the fungi are 

 efficient utilizers of the available energy. The bacteria first of all 

 break down the proteins and liberate large quantities of ammonia as a 

 waste product. Due to the limited utilization of the celluloses and to 



