Response of nitrogen-fixing plant symbioses to changing temperature

Symbiotic nitrogen fixation (SNF) is an effective strategy for legumes and actinorhizal plants to acquire atmospheric nitrogen (N₂) for their growth and development. Like other enzymatic processes in roots, the efficiency of SNF is highly dependent on soil temperature. Since global atmospheric temperature change also affects soil temperature, it is essential to know the temperature response of different types of plant-microbial symbioses capable of SNF at the molecular, physiological, and ecosystem levels on air and soil temperature changes. This is of particular significance, because the ability of nitrogen-fixing microbial symbionts to deal with temperature changes in the soil can affect growth and development of legumes and actinorhizal plants and, hence, the sustainability of ecosystems in a changing climate. However, temperature response may differ between different groups of nitrogen-fixing microbial symbionts (e.g., rhizobia vs. Frankia) and between different strains of the same microbial symbiont. In the present review, we summarize current knowledge on the temperature response of SNF, describe unexplored research topics, and propose future basic and applied research avenues under controlled conditions and in field studies. It provides a holistic view on the subject to encourage interdisciplinary research on this subject which has been largely neglected during the last decades, but of increasing significance due to global climate change.