Plasticity in nitrogen uptake among plant species with contrasting nutrient acquisition strategies in a tropical forest

Abstract

Nitrogen (N) availability influences the productivity and distribution of plants in tropical montane forests. Strategies to acquire soil N, such as direct uptake of organic compounds or associations with root symbionts to enhance N acquisition in exchange for carbon (C), may facilitate plant species coexistence and ecosystem N retention. Alternatively, rapid microbial turnover of soil N forms in tropical soils might promote flexible plant N-uptake strategies and mediate species coexistence. We tested whether sympatric plant species with different root symbiont associations, and therefore potentially different nutrient acquisition strategies, partition chemical forms of N or show plasticity in N uptake in a tropical pre-montane forest in Panama. We traced the movement of three N forms into soil pools, microbes, and seedlings of eleven species differing in root traits. Seedlings were grown in a split-plot field transplant experiment, with plots receiving equimolar mixtures of ammonium, nitrate, and glycine, with one form isotopically labeled in each block. After 48 h, more N was recovered in microbes than in plants, while all pools (extractable organic and inorganic N, microbial biomass, and leaves) contained greater amounts of N from nitrate than from ammonium or glycine. Furthermore, C from dual-labeled glycine was not recovered in the leaves of any seedling, suggesting the studied species do not directly take up organic N or transform organic N prior to translocation to leaves. Nitrogen uptake differed by root symbiont group only for nitrate, with greater N recovery in plants with arbuscular mycorrhizal (AM) associations or proteoid roots compared to orchids. Some root trait groups differed in N recovery among N forms, with greater nitrate uptake than ammonium or glycine by AM-associated and N -fixing plants. However, only five of eleven species showed differences in uptake among N forms. These results indicate flexibility in uptake of N forms in tropical plants across root trait groups, with only a few species displaying weak preferences for a specific N form.

Soil microbes promote complementarity effects among co‐existing trees through soil nitrogen partitioning

“…AM fungi) that host different mycorrhizal types (Nasto et al., ; Steidinger et al., ). In contrast, another study on more fertile soil only provided weak evidence for N partitioning among tropical tree species with different mycorrhizal types (Andersen, Mayor, & Turner, ). It is possible that the N partitioning we observed is more common on soils with low overall N availability than on N‐rich soils.…”

Plant nitrogen and phosphorus utilization under invasive pressure in a montane ecosystem of tropical China

“…Tropical and subtropical ecosystems usually have higher N cycling rates compared with high‐latitude and high‐altitude ecosystems where N mineralization and nitrification are generally lower and plants rely more on organic N sources (Elser et al., ; Liu et al., ; Vitousek et al., ; von Felten et al., ). Until now, most studies on plant N uptake in tropical ecosystems have stressed inorganic N due to its much higher availability than organic N (Andersen, Mayor, & Turner, ; Craine et al., , ; Houlton et al., ). Moreover, plant dissolved organic nitrogen (DON) use was often demonstrated experimentally by the uptake of one or a few 15 N‐labelled amino acids, which cannot elucidate the real availability of the whole soil DON pool to plants (Kahmen, Livesley, & Arndt, ), so that substantial uncertainties existed in the source contributions estimated by using the δ 15 N of the whole DON pool (e.g.…”

“…Consequently, we assume NH 4 + and NO 3 − to be the dominant N sources for plants in tropical ecosystems (e.g. Andersen et al., ; Houlton et al., ), and use a δ 15 N mass balance between leaf N and source N (referred to Houlton et al., ; Equation ) to evaluate the fractional contributions of soil NH 4 + () and NO 3 − () to plant N by considering isotope effects during plant N uptake and assimilation (ε). where 1 = and ε = ε u + ε i × [L below /(L above + L below )]. The ε u denotes the isotope effects during root N uptake, ε i denotes the isotope effects between N sources of the whole plant and leaves due to differing N allocation/assimilation between above‐ and below‐ground tissues (Houlton et al., ).…”

Wet and Dry Nitrogen Depositions in the Pearl River Delta, South China: Observations at Three Typical Sites With an Emphasis on Water‐Soluble Organic Nitrogen

“…Cornell et al (2003) and Cornell (2011) collected available studies over the world and revealed that WSON/TDN ratio in precipitation exhibited a large range with the typical ratios ranging from 25% to 35%. There are increasing number of studies which revealed that plant uptake of organic N, particularly low molecular weight amino acids, occurs widely in low N ecosystems (Andersen et al, 2017;Kielland, 1994;Kielland et al, 2006). Kielland (1994) revealed that the uptake rates of glycine and ammonium by plants in arctic tundra are comparable.…”