EVOLVED STRATEGIES IN NITROGEN ACQUISITION BY PLANTS

Eleven features of nitrogen metabolism in the plant and in the ecosystem are delineated, each appearing to have negative survival value, especially negative effects on yield. These include apparent failures in controls over N2 fixation and over nitrate uptake; preventable energy losses in soil microbial metabolism and in root reduction in nitrate; preventable mass losses of nitrogen via denitrification and ammonia volatilization, and insufficient partitioning of photosynthetic energy to support N2 fixation in N-limited ecosystems. A quantitative examination of the energetics of metabolizing N2, NH3, and NO3 - reveals behind often high costs some energy inefficiencies required for sufficiently fast kinetics and some compromises with other metabolisms. Cost: benefit ratios can be defined for assimilation of the three forms of N, and each ratio may vary significantly according to other physiological demands, such as pH control at the rhizosphere or stomatal closure for efficient use of water. For the individ...