Abstract
Southern South American Proteaceae thrive on young volcanic substrates, which are extremely low in plant-available phosphorus (P). Most Proteaceae exhibit a nutrient-acquisition strategy based on the release of carboxylates from specialized roots, named cluster roots (CR). Some Proteaceae colonize young volcanic substrates which has been related to CR functioning. However, physiological functioning of other Proteaceae on recent volcanic substrates is unknown. We conducted an experiment with seedlings of five Proteaceae (Gevuina avellana, Embothrium coccineum, Lomatia hirsuta, L. ferruginea, and L. dentata) grown in three volcanic materials. Two of them are substrates with very low nutrient concentrations, collected from the most recent deposits of the volcanoes Choshuenco and Calbuco (Chile). The other volcanic material corresponds to a developed soil that exhibits a high nutrient availability. We assessed morphological responses (i.e., height, biomass, and CR formation), seed and leaf macronutrient and micronutrient concentrations and carboxylates exuded by roots. The results show that G. avellana was less affected by nutrient availability of the volcanic substrate, probably because it had a greater nutrient content in its seeds and produced large CR exuding carboxylates that supported their initial growth. Embothrium coccineum exhibited greater total plant height and leaf P concentration than Lomatia species. In general, in all species leaf macronutrient concentrations were reduced on nutrient-poor volcanic substrates, while leaf micronutrient concentrations were highly variable depending on species and volcanic material. We conclude that Proteaceae from temperate rainforests differ in their capacity to grow and acquire nutrients from young and nutrient-poor volcanic substrates. The greater seed nutrient content, low nutrient requirements (only for G. avellana) and ability to mobilize nutrients help explain why G. avellana and E. coccineum are better colonizers of recent volcanic substrates than Lomatia species.
Highlights
Temperate forest ecosystems of southern South America are a unique biome that is biogeographically isolated with a highly endemic flora (Quintero et al, 2014)
G. avellana showed greater total dry biomass and E. coccineum presented greater height in all substrates compared with the other species (Figures 1A,B)
The reason why G. avellana, in its early stages, produced more biomass than the other Proteaceae species is its larger seeds (Delgado et al, 2014) and higher nutrient content compared with those of the other species (Table 2), favoring its initial growth (Supplementary Figure 4). This trend was maintained in E. coccineum, which is the species that has the secondlargest seed nutrient content (Table 2)
Summary
Temperate forest ecosystems of southern South America are a unique biome that is biogeographically isolated with a highly endemic flora (Quintero et al, 2014) These ecosystems are frequently affected by catastrophic disturbances such as volcanic eruptions and earthquakes that usually trigger orogenic uplift and landslides (Veblen and Ashton, 1978; Veblen et al, 1992, 1996), which lead to soil rejuvenation, leaving bare areas where the process of primary succession begins again. Carboxylates increase the availability of some micronutrients through their solubilizing and reducing capacity, for example, Mn4+ to Mn2+ and Fe3+ to Fe2+, which are the forms that are taken up by roots that use Strategy I (i.e., roots of dicots and non-graminaceous monocots that release reducing/chelating substances and increase the plasma membrane-bound reductase activity) (Marschner et al, 1986; Dinkelaker et al, 1995) These micronutrients, like others transition metal cations such as zinc (Zn2+), can be mobilized by carboxylates at the root surface, where they are taken up by plasma membrane transporters with a low specificity (Lambers et al, 2015b). Carboxylate exudation by CR (which occurs in large quantities compared with that of nonCR) is an adaptive trait allowing species to thrive in nutrientpoor soils
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