Phosphorus-mobilization ecosystem engineering: the roles of cluster roots and carboxylate exudation in young P-limited ecosystems

Abstract

† Background Carboxylate-releasing cluster roots of Proteaceae play a key role in acquiring phosphorus (P) from ancient nutrient-impoverished soils in Australia. However, cluster roots are also found in Proteaceae on young, P-rich soils in Chile where they allow P acquisition from soils that strongly sorb P. † Scope Unlike Proteaceae in Australia that tend to proficiently remobilize P from senescent leaves, Chilean Proteaceae produce leaf litter rich in P. Consequently, they may act as ecosystem engineers, providing P for plants without specialized roots to access sorbed P. We propose a similar ecosystem-engineering role for species that release large amounts of carboxylates in other relatively young, strongly P-sorbing substrates, e.g. young acidic volcanic deposits and calcareous dunes. Many of these species also fix atmospheric nitrogen and release nutrient-rich litter, but their role as ecosystem engineers is commonly ascribed only to their diazotrophic nature. † Conclusions We propose that the P-mobilizing capacity of Proteaceae on young soils, which contain an abundance of P, but where P is poorly available, in combination with inefficient nutrient remobilization from senescing leaves allows these species to function as ecosystem engineers. We suggest that diazotrophic species that colonize young soils with strong P-sorption potential should be considered for their positive effect on P availability, as well as their widely accepted role in nitrogen fixation. Their P-mobilizing activity possibly also enhances their nitrogen-fixing capacity. These diazotrophic species may therefore facilitate the establishment and growth of species with less-efficient P-uptake strategies on more-developed soils with low P availability through similar mechanisms. We argue that the significance of cluster roots and high carboxylate exudation in the development of young ecosystems is probably far more important than has been envisaged thus far.

Biodiversity hotspots and Ocbil theory

“…Forest vegetation may self-enrich soil nutrients on Ocbils (Coetsee et al 2014). while cluster roots of Proteaceae play a significant role in forming lateritic soils profiles (e.g., the mesa summit of Mt Lesueur), and Myrtaceae roots similarly create clays or silcretes (Pate and Verboom 2009;Lambers et al 2012;Pate 2013, 2015).…”

Plant adaptations to severely phosphorus-impoverished soils

“…2) [10]; Hakea prostrata (Proteaceae) releases carboxylates (organic anions) in an exudative burst [11]. In southern South America, Proteaceae occur on young acidic soils with very high total P concentrations, but with a low P availability, due to strong sorption of P to oxides and hydroxides of iron and aluminium [12]; Embothrium coccineum releases predominantly citrate [13]. In tropical rainforests in north-eastern Australia, a mycorrhizal species without cluster roots, Placospermum coriaceum, occurs, together with non-mycorrhizal species with cluster roots [14].…”

Development of Common Bean (Phaseolus Vulgaris L.) Production Under Low Soil Phosphorus and Drought in Sub-Saharan Africa: A Review

“…More so, root exudation of acid phosphatase is believed to free bound P from the soil and has been shown to hydrolyse organic P in the rhizosphere into plant-available P for uptake (Lambers et al, 2006;Richardson et al, 2011;Song, 2005). This increases the availability of P in cluster roots resulting in increased root surface area for P uptake (Lambers, Bishop, Hopper, Laliberte, & Zu´n˜iga-Feest, 2012). …”