First, plants may alter the morphology of their fine roots in such a way as to increase their total absorptive length per unit of biomass (i.e., high SRL) and to decrease their thickness ( Treseder and Vitousek, 2001 Santiago, 2015). For example, specific root length (SRL) and root branching are linked to soil space occupancy while root phosphatase activity and mycorrhizal colonization are critical determinants of P uptake ( Lee, 1988 McCormack et al., 2017 Freschet et al., 2021).īelowground, adjustments in morphology, architecture, association with arbuscular mycorrhizal fungi, and phosphatase activity expression may be all viable P-acquisition strategies. Fine-root and mycorrhizal fungal trait expression is closely related to root function, such as resource foraging and uptake. Belowground, plants optimize P acquisition by displaying multiple strategies commonly described by the expression of the traits of the narrowest, most absorptive roots (i.e., fine roots) and their mycorrhizal symbionts ( Bardgett et al., 2014 Kramer-Walter et al., 2016 Weemstra et al., 2016 McCormack and Iversen, 2019 Bergmann et al., 2020 Lugli et al., 2021).
Aboveground, plants may increase P-use efficiency, which in turn leads to higher retention time of P in the canopy and higher resorption efficiency of P as tissues senesce ( Paoli et al., 2005 Dalling et al., 2016). Tree species that are successful in tropical lowlands have multiple acquisition strategies to overcome P limitation ( Zalamea et al., 2016 Lugli et al., 2021). The availability of soil inorganic phosphorus (orthophosphate hereafter, available P) strongly limits plant growth in lowland tropical forests where climate conditions lead to high soil weathering rates ( Walker and Syers, 1976 Vitousek and Sanford, 1986 Reed et al., 2011 Lugli et al., 2021). Altogether, our results suggest a combination of structural and physiological root traits for soil P acquisition in P-poor tropical soils by common tropical tree species, and show stability on most of the root trait expression after hurricane disturbances. Additionally, we found that root trait expression did not change comparing 6 months before and after the hurricanes, with the exception of root phosphatase activity. Furthermore, the former strategy was adopted by pioneer species ( Spathodea campanulata and Cecropia schreberiana), whereas the latter was adopted by non-pioneer species (mostly Dacryodes excelsa and Prestoea montana). In addition, we revealed a trade-off between highly colonized fine roots with high phosphatase activity and fine roots that have a high degree of branching. We found that variations in root trait expression were driven mainly by the large interspecific differences across the three selected sites. We then described species-specific P-acquisition strategies and explored the changes in fine-root trait expression from 6 months before to 6 months after two consecutive hurricanes, Irma and María, passed over the island.
Here, we measured seven fine-root functional traits related to P acquisition of five common tree species in three sites of the Luquillo Experimental Forest in Puerto Rico. However, empirical evidence remains scarce which hinders our understanding of soil P-acquisition processes in tropical forests. Trade-offs among P-acquisition strategies are expected because of their respective carbon cost. Some of these strategies belowground include adjustments in fine-root traits, such as morphology, architecture, association with arbuscular mycorrhizal fungi, and phosphatase activity. Tree species that are successful in tropical lowlands have different acquisition strategies to overcome soil phosphorus (P) limitations.
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