Abstract
Fine roots mediate plant nutrient acquisition and growth. Depending on soil nutrient availability, plants can regulate fine root biomass and morphological traits to optimise nutrient acquisition. Little is known, however, about the importance of these parameters influencing forest functioning. In this study, we measured root responses to nutrient additions to gain a mechanistic understanding of plant adaptations to nutrient limitation in two tropical forests in French Guiana, differing twofold in their soil nutrient statuses. We analysed the responses of root biomass, mean root diameter (RD), specific root length (SRL), specific root area (SRA), root tissue density (RTD) and carbon (C), nitrogen (N) and phosphorus (P) concentrations in roots down to 15 cm soil depth after three years of N and P additions. At the lower‐fertility site Paracou, no changes in root biomass or morphological traits were detected with either N or P addition, although P concentrations in roots increased with P addition. In the higher fertility site, Nouragues, root biomass and P concentrations in roots increased with P addition, with no changes in morphological traits. In contrast, N addition shifted root traits from acquisitive to more conservative by increasing RTD. A significant interaction between N and P in Nouragues pointed to stronger responses to P addition in the absence of N. Our results suggest that the magnitude and direction of root biomass and trait expression were regulated by soil fertility, corroborated by the response to N or P additions. At low fertility sites, we found lower plasticity in root trait expression compared to more fertile conditions, where N and P additions caused stronger and antagonistic responses. Identifying the exact role of mechanisms affecting root nutrient uptake in Amazon forests growing in different soils will be crucial to foresee if and how rapid global changes can affect their carbon allocation.
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Claims 7
Claim · model-written summary
At Paracou, nitrogen or phosphorus addition did not detectably change root biomass or morphology.
- Taxon
- plantsViridiplantaee0e1e2e3
Not reportedComparator
Verbatim
e0“At the lower‐fertility site Paracou, no changes in root biomass or morphological traits were detected with either N or P addition”
e1“plants can regulate fine root biomass”
e2“At the lower‐fertility site Paracou”
e3“In the higher fertility site, Nouragues, root biomass and P concentrations in roots increased with P addition”
Claim · model-written summary
At Paracou, phosphorus addition increased root phosphorus concentration.
- Taxon
- plantsViridiplantaee0e1e2e3
Not reportedComparator
Verbatim
e0“although P concentrations in roots increased with P addition.”
e1“plants can regulate fine root biomass”
e2“At the lower‐fertility site Paracou”
e3“In the higher fertility site, Nouragues, root biomass and P concentrations in roots increased with P addition”
Claim · model-written summary
At Nouragues, phosphorus addition increased root biomass and phosphorus concentration.
- Taxon
- plantsViridiplantaee0e1e2e3
Not reportedComparator
Verbatim
e0“In the higher fertility site, Nouragues, root biomass and P concentrations in roots increased with P addition”
e1“plants can regulate fine root biomass”
e2“At the lower‐fertility site Paracou”
e3“In the higher fertility site, Nouragues, root biomass and P concentrations in roots increased with P addition”
Claim · model-written summary
At Nouragues, phosphorus addition did not change root morphological traits.
- Taxon
- plantsViridiplantaee0e1e2e3
Not reportedComparator
Verbatim
e0“with no changes in morphological traits”
e1“plants can regulate fine root biomass”
e2“At the lower‐fertility site Paracou”
e3“In the higher fertility site, Nouragues, root biomass and P concentrations in roots increased with P addition”
Claim · model-written summary
At Nouragues, nitrogen addition increased root tissue density.
- Taxon
- plantsViridiplantaee0e1e2e3
Not reportedComparator
Verbatim
e0“N addition shifted root traits from acquisitive to more conservative by increasing RTD”
e1“plants can regulate fine root biomass”
e2“At the lower‐fertility site Paracou”
e3“In the higher fertility site, Nouragues, root biomass and P concentrations in roots increased with P addition”
Claim · model-written summary
At Nouragues, response to phosphorus was stronger without nitrogen.
- Taxon
- plantsViridiplantaee0e1e2e3
Verbatim
e0“A significant interaction between N and P in Nouragues pointed to stronger responses to P addition in the absence of N”
e1“plants can regulate fine root biomass”
e2“At the lower‐fertility site Paracou”
e3“In the higher fertility site, Nouragues, root biomass and P concentrations in roots increased with P addition”
Claim · model-written summary
Root trait plasticity was lower at low-fertility sites than at more fertile sites.
- Taxon
- plantsViridiplantaee0e1e2e3
Verbatim
e0“At low fertility sites, we found lower plasticity in root trait expression compared to more fertile conditions”
e1“plants can regulate fine root biomass”
e2“At the lower‐fertility site Paracou”
e3“In the higher fertility site, Nouragues, root biomass and P concentrations in roots increased with P addition”
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