Latitudinal constraints in responsiveness of plants to arbuscular mycorrhiza: The ‘sun-worshipper’ hypothesis

Most terrestrial plants depend strongly on associations with arbuscular mycorrhizal (AM) fungi (Subphylum: Glomeromycotina) to establish and survive (van der Heijden et al., 1998; Bever, 2002; Klironomos et al., 2011; Veresoglou et al., 2017), and have evolved a nutritional mutualism. In this mutualism, the plant provides carbon to the fungus, usually subject to the availability of light (Hayman, 1974; Heinemeyer et al., 2003; Shi et al., 2014; Konvalinkova & Jansa, 2016), and the fungus provides the plant with mineral nutrients acquired from soil. Because of light constraints, it is expected that latitude exerts a strong influence on reciprocal exchange of resources between mycorrhizal plants and fungi, and this could have consequences on the responsiveness of plants to mycorrhizal fungi. Latitude induces changes in the amount of solar energy and the timing when this is made available to primary producers during the year and in the day. At the same time, there is a strong negative relationship between latitude and temperature that may also impact the functioning of the mycorrhizal symbiosis, and in some cases (e.g. in north temperate systems), a general relationship between latitude and several edaphic factors (Read & Perez-Moreno, 2003).