Relationships between nitrogen fixation and growth in Robinia pseudoacacia seedlings: A functional growth‐analysis approach using ¹⁵N

Abstract

1992. Relationships between nitrogen fbiation and growth in Robinia pseudoacacia seedhngs: A functional growth-analysis approach using "N. -Physiol. Plant, 85: 77-84.The effects of NOj fertilization on N^ fixation and growth of black locust {Robinia pseudoacacia L.) seedlings were examined by growth analyses. Seedlings were grown under low (0.25 mM) and high (2.00 mM) NC5j provided with each watering. In one experiment, seedlings were given NO^ with enriched levels of ^^N (11.03%) to identify N accumulation from soil and atmospheric sources. Curves describing accretion of total dry weight and N were fit as functions of accumulated photosynthetically active radiation (PAR), Relative growth rates (RGR) and nitrogen productivities (NP) were derived from these curves and examined as functions of seedling size and/or internal N concentraflon. Early in the experiments seedlings receiving the higher amount of NOJ grew faster, acquired more N, had greater internal nitrogen concentrations (Nj) and had higher NP than seedlings receiving the lower amounts. Seedlings receiving higher N also acquired most of their N from NOj, whereas those receiving the lower N acquired most from N, fixation. Later in the experiments, no differences in growth rate, N^ or NP were observed. Furthermore, midway through the experiments seedlings receiving the higher amounts of NOf began to acquire the majority of N from N, fixation. At the end of the two experiments, seedlings given higher NO7 were 16 and 78% larger in dry weight. Differences in size were due to growth differences that occurred only during the first half of the experiments. During this period, the faster growth of seedlings given higher NO^ was attributed to greater access to utilizable N and iower energy costs associated with the acquisition and/or utUizaiion of NOj, relative to N^. Unlike the situation in non-Ni-fixing plants, differences in available soil N had no influence on biomass allocation to roots, stems 01 leaves in black locust. When soil N became limiting, N, fixation capacity increased, ralber (han root mass. 10 acquire more N,