Patterns of Growth Costs and Nitrogen Acquisition in Cytisus striatus (Hill) Rothm. and Cytisus balansae (Boiss.) Ball are Mediated by Sources of Inorganic N.

María Pérez-Fernández,Irene Ramírez-Rojas,Laura Moreno-Gallardo,Valentine Alexander,Elena Calvo-Magro

doi:10.3390/plants5020020

María Pérez-Fernández, Irene Ramírez-Rojas + Show 3 more

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https://doi.org/10.3390/plants5020020

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Abstract

Nitrogen-fixing shrubby legumes in the Mediterranean area partly overcome nutrient limitations by making use of soil N and atmospheric N2 sources. Their ability to switch between different sources lets them adjust to the carbon costs pertaining to N acquisition throughout the year. We investigated the utilization of different inorganic N sources by Cytisus balansae and Cytisus striatus, shrubby legumes under low and a sufficient (5 and 500 µM P, respectively) levels of P. Plants grew in sterile sand, supplied with N-free nutrient solution and inoculated with effective Bradyrhizobium strains; other treatments consisted of plants treated with (i) 500 µM NH4NO3; and (ii) 500 µM NH4NO3 and inoculation with effective rhizobial strains. The application of NH4NO3 always resulted in greater dry biomass production. Carbon construction costs were higher in plants that were supplied with mineral and symbiotic N sources and always greater in the endemic C. striatus. Photosynthetic rates were similar in plants treated with different sources of N although differences were observed between the two species. Non-fertilized inoculated plants showed a neat dependence on N2 fixation and had more effective root nodules. Results accounted for the distribution of the two species with regards to their ability to use different N sources.

Highlights

In natural stands where trees are absent, shrubby leguminous species play an important role in sustaining stand productivity and environmental values by regulating water uptake, the root environment and nutrient cycling [1,2]
Legumes contribute to global fertility by introducing nitrogen to the soils via their nitrogen-fixing symbiosis with legume-nodulating bacteria
It has been proven that the Cape Fynbos legume, Virgilia divaricata (Adamson), is able to switch N sources for its growth, depending on the environmental cues [7]

Summary

Introduction

In natural stands where trees are absent, shrubby leguminous species play an important role in sustaining stand productivity and environmental values by regulating water uptake, the root environment and nutrient cycling [1,2]. This is of particular relevance in arid areas of the world, where nutrients are impoverished and plant growth is strongly hindered by limiting factors such as water, extreme temperatures and excessive solar radiation [3,4]. Neff et al [8] suggested that leguminous plants can absorb and assimilate nitrogenous compounds such as nitrate, ammonium, or amino acids directly from

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