Rapid responses of root traits and productivity to phosphorus and cation additions in a tropical lowland forest in Amazonia

Abstract

Summary Soil nutrient availability can strongly affect root traits. In tropical forests, phosphorus (P) is often considered the main limiting nutrient for plants. However, support for the P paradigm is limited, and N and cations might also control tropical forests functioning. We used a large‐scale experiment to determine how the factorial addition of nitrogen (N), P and cations affected root productivity and traits related to nutrient acquisition strategies (morphological traits, phosphatase activity, arbuscular mycorrhizal colonisation and nutrient contents) in a primary rainforest growing on low‐fertility soils in Central Amazonia after 1 yr of fertilisation. Multiple root traits and productivity were affected. Phosphorus additions increased annual root productivity and root diameter, but decreased root phosphatase activity. Cation additions increased root productivity at certain times of year, also increasing root diameter and mycorrhizal colonisation. P and cation additions increased their element concentrations in root tissues. No responses were detected with N addition. Here we showed that rock‐derived nutrients determined root functioning in low‐fertility Amazonian soils, demonstrating not only the hypothesised importance of P, but also highlighting the role of cations. The changes in fine root traits and productivity indicated that even slow‐growing tropical rainforests can respond rapidly to changes in resource availability.

Trade-Offs in Phosphorus Acquisition Strategies of Five Common Tree Species in a Tropical Forest of Puerto Rico

“…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). Tree species that are successful in tropical lowlands have multiple acquisition strategies to overcome P limitation (Zalamea et al, 2016;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).…”

“…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). 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). Fine-root and mycorrhizal fungal trait expression is closely related to root function, such as resource foraging and uptake.…”

“…Research on belowground P-acquisition strategies suggests that plants simultaneously adjust the expression of multiple fineroot traits related to P-acquisition to overcome soil P limitation (Lugli et al, 2019(Lugli et al, , 2021. Therefore, root morpho-architectural adjustments, association with AM fungi, and phosphatase activity may be complementary strategies as opposed to alternatives (Smith and Read, 2008;Turner, 2008;Nasto et al, 2019), but empirical evidence remains scarce in tropical ecosystems.…”

“…However, "hard" traits generally strongly relate to root function compared to the commonly measured "soft" traits, such as SRL and root nitrogen concentration (Freschet et al, 2015(Freschet et al, , 2021. To date, knowledge on the relationships among plant fineroot traits related to P acquisition in lowland tropical forests mostly comes from community or ecosystem level studies (Lugli et al, 2019(Lugli et al, , 2021Addo-Danso et al, 2020;Cabugao et al, 2021). Consequently, individual relationships between fine-root morphology, phosphatase activity, and mycorrhizal colonization at the species level are underexplored.…”

Greater morphological and primary metabolic adaptations in roots contribute to phosphate-deficiency tolerance in the bread wheat cultivar Kenong199

“…Among them, RSA is a crucial component for enhanced root exploration capacity and Pi uptake capacity due to low mobility and uneven distribution of Pi in soil [ 6 ]. Fine roots are shorter and more with high plasticity [ 7 ], and a rapid change in fine root production plays a major role in response to Pi deficiency [ 8 , 9 ]. The modification of root traits varies significantly across species and cultivars.…”