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Radar plot showing the trait-space occupied when combining the response of fine root biomass and traits (0-15 cm) in this study per site and per treatment. Since all traits were in different units, they are scaled to normalise the data by subtracting from each value the sample mean (n = 24 per site) and dividing it by the sample standard deviation for each trait. 'RB' refers to fine root biomass (Mg ha −1 ); 'RD' refers to fine root diameter (mm); 'SRL' refers to specific root length (m g −1 ); 'SRA' refers to specific root area (cm 2 g −1 ); 'RTD' refers to root tissue density (g cm −3 ) and 'N:P' refers to the ratio of concentrations and N and P in fine roots. Top two panels show traits from Paracou (PAR) and bottom two panels show traits from Nouragues (NOU). Colours indicate the presence and absence of N and P, as described in the figure. Values above 0 are above the mean, and values below 0 are below the mean, with their magnitudes indicating the number of standard deviations away from the mean. Significant effects reported in previous tables and figures comparing the trait response with and without a specific nutrient addition are indicated by *, ** and ***, representing p-values < 0.05, 0.01 and 0.001, respectively (n = 12 per treatment and site).

Radar plot showing the trait-space occupied when combining the response of fine root biomass and traits (0-15 cm) in this study per site and per treatment. Since all traits were in different units, they are scaled to normalise the data by subtracting from each value the sample mean (n = 24 per site) and dividing it by the sample standard deviation for each trait. 'RB' refers to fine root biomass (Mg ha −1 ); 'RD' refers to fine root diameter (mm); 'SRL' refers to specific root length (m g −1 ); 'SRA' refers to specific root area (cm 2 g −1 ); 'RTD' refers to root tissue density (g cm −3 ) and 'N:P' refers to the ratio of concentrations and N and P in fine roots. Top two panels show traits from Paracou (PAR) and bottom two panels show traits from Nouragues (NOU). Colours indicate the presence and absence of N and P, as described in the figure. Values above 0 are above the mean, and values below 0 are below the mean, with their magnitudes indicating the number of standard deviations away from the mean. Significant effects reported in previous tables and figures comparing the trait response with and without a specific nutrient addition are indicated by *, ** and ***, representing p-values < 0.05, 0.01 and 0.001, respectively (n = 12 per treatment and site).

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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 a...

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... 0.012), also resulting in lower SRA in +N−P plots (Fig. 4b). For RTD, +N significantly increased RTD in Nouragues (F 1,19 = 5.76, p = 0.027; Table 5), with no effects of +P or the interaction NP. When data were normalised to account for background differences at each site, we found that both sites responded proportionally similarly to P addition (Fig. 5), mainly driven by changes in root tissue stoichiometry, followed by increasing root biomass, but little or no responses of root morphological traits. Since no changes in N content in roots were captured in our treatments, the strong responses of N:P ratios were solely driven by changes in P content in roots. Differently to patterns ...
Context 2
... no responses of root morphological traits. Since no changes in N content in roots were captured in our treatments, the strong responses of N:P ratios were solely driven by changes in P content in roots. Differently to patterns seen with P addition, N addition rather triggered changes in root morphological traits, that differed depending on site (Fig. 5) dominated by a tendency of reduction in root biomass in Paracou and changes in tissue construction (RTD) in ...

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... Second, nitrogen addition enhances the turnover rate of fine roots and alters root exudates, thus increasing soil fertility [25,26]. The output processes include plant root and soil respiration, with soil respiration being the most important, accounting for more than 70% of the total respiration [23,52,53]. Moreover, a recent meta-analysis confirmed that nitrogen addition reduced soil respiration [22]. ...
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... 61 and root growth is likely adapted to the site's nutrient supply. Moreover, the extent to which nutrient availability constrain different components of NPP (above-, and below-ground) and which single or multiple nutrients are responsible for these limitations remain largely unresolved 38,57 , partly due to the varied responses of NPP or its components to nutrient additions in different tropical forests (Table 1). As an example, several methods of estimating FRP are discussed in literature 40 , however, the lack of consensus for a single established approach for the tropics 40 and site-specific soil fertility 57,62 may contribute to the contrasting responses of FRP or FRB to nutrient additions 50 in different forests. ...
... Moreover, the extent to which nutrient availability constrain different components of NPP (above-, and below-ground) and which single or multiple nutrients are responsible for these limitations remain largely unresolved 38,57 , partly due to the varied responses of NPP or its components to nutrient additions in different tropical forests (Table 1). As an example, several methods of estimating FRP are discussed in literature 40 , however, the lack of consensus for a single established approach for the tropics 40 and site-specific soil fertility 57,62 may contribute to the contrasting responses of FRP or FRB to nutrient additions 50 in different forests. In our experiment, the response of FRB to nutrient additions was consistent between the two estimation methods (i.e., monolith-based FRB and SC-based FRB; Figs. ...
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Nutrient limitations play a key regulatory role in plant growth, thereby affecting ecosystem productivity and carbon uptake. Experimental observations identifying the most limiting nutrients are lacking, particularly in Afrotropical forests. We conducted an ecosystem-scale, full factorial nitrogen (N)-phosphorus (P)-potassium (K) addition experiment consisting 32 40 × 40 m plots (eight treatments × four replicates) in Uganda to investigate which (if any) nutrient limits fine root growth. After two years of observations, added N rapidly decreased fine root biomass by up to 36% in the first and second years of the experiment. Added K decreased fine root biomass by 27% and fine root production by 30% in the second year. These rapid reductions in fine root growth highlight a scaled-back carbon investment in the costly maintenance of large fine root network as N and K limitations become alleviated. No fine root growth response to P addition was observed. Fine root turnover rate was not significantly affected by nutrient additions but tended to be higher in N added than non-N added treatments. These results suggest that N and K availability may restrict the ecosystem’s capacity for CO2 assimilation, with implications for ecosystem productivity and resilience to climate change.