Costs of acquiring phosphorus by vascular land plants: patterns and implications for plant coexistence

Abstract

Content Summary1420I.Introduction1421II.Root adaptations that influence P acquisition1422III.Costs of P acquisition: general1423IV.Costs of P acquisition that are independent of soil P concentrations1423V.Costs of P acquisition that increase as soil P concentrations decline1424VI.Discussion and conclusions1424Acknowledgements1425References1425 Summary We compare carbon (and hence energy) costs of the different modes of phosphorus (P) acquisition by vascular land plants. Phosphorus‐acquisition modes are considered to be mechanisms of plants together with their root symbionts and structures such as cluster roots involved in mobilising or absorbing P. Phosphorus sources considered are soluble and insoluble inorganic and organic pools. Costs include operating the P‐acquisition mechanisms, and resource requirements to construct and maintain them. For most modes, costs increase as the relevant soil P concentration declines. Costs can thus be divided into a component incurred irrespective of soil P concentration, and a component describing how quickly costs increase as the soil P concentration declines. Differences in sensitivity of costs to soil P concentration arise mainly from how economically mycorrhizal fungal hyphae or roots that explore the soil volume are constructed, and from costs of exudates that hydrolyse or mobilise insoluble P forms. In general, modes of acquisition requiring least carbon at high soil P concentrations experience a steeper increase in costs as soil P concentrations decline. The relationships between costs and concentrations suggest some reasons why different modes coexist, and why the mixture of acquisition modes differs between sites.

Tradeoffs among root morphology, exudation and mycorrhizal symbioses for phosphorus‐acquisition strategies of 16 crop species

“…This strategy is particularly effective when there is very little P in the soil solution and most P is strongly sorbed onto soil particles (Parfitt, ; Lambers et al ., ). Although all these adjustments contribute to enhance plant P acquisition, the cost of each adjustment may confine the ability of plants to express all strategies simultaneously (Lynch & Ho, ; Ryan et al ., ; Raven et al ., ). Supporting this idea, our results show that the species varied in their ability to assemble these multiple root functional traits, forming a range of trait combinations in response to the stress associated with limited P. Overall, species with thinner roots probably relied predominantly on more intensely branched fine roots and higher specific root length to explore soil P, whereas species with thicker roots were probably more reliant on mycorrhizal fungi to compensate for a low root absorptive surface and/or P‐mobilizing exudates to mine sparingly soluble P in the rhizosheath.…”

Towards a more physiological representation of vegetation phosphorus processes in land surface models

“…Unlike modification of root architecture, which has a relatively small C cost, symbiotic association and root exudation are both C‐expensive nutrient acquisition strategies, but have benefits beyond P acquisition, such as plant defence (Laliberté et al ., ). Plants trade C for N and P at different exchange rates (Raven et al ., ), leading to different symbiotic associations and possibly different trajectories of nutrient recycling (Zechmeister‐Boltenstern et al ., ). Furthermore, it has been shown that plants may need to maintain photosynthetic capacity to provide sufficient C for exudation and symbiotic association under P deficiency (Zavišić & Polle, ).…”

Does plant biomass partitioning reflect energetic investments in carbon and nutrient foraging?

“…This includes the respiratory demands of active ion transport in roots (up to half the below‐ground C budget; Lambers, Scheurwater, & Atkin, ), root exudates fuelling heterotrophic microbial activity (up to 17% of plant NPP; Nguyen, ; Pausch & Kuzyakov, ; Yin et al, ), the provision of C to extracellular structures of mycorrhizal fungi (up to 20% of NPP; Allen, ; Brzostek, Fisher, & Phillips, ; Peng, Eissenstat, Graham, Williams, & Hodge, ; van der Heijden, Martin, Selosse, & Sanders, ) and rapid root turnover (Stewart & Frank, ) – none of which are accounted for in harvested root biomass (Farrar & Jones, ). Any or all of these below‐ground C sinks may increase with nutrient shortage, with or without associated root mass changes (Nielsen, Eshel, & Lynch, ; Peng et al, ; Raven, Lambers, Smith, & Westoby, ; Wright, Read, & Scholes, ). To the extent gross primary productivity (GPP) increases from enhanced nutrient uptake as a result of below‐ground C investment, plants have larger energy pools to support reproduction or other activities such as defence that contribute to fitness (Litton, Raich, & Ryan, ).…”