Nitrogen use plasticity in response to light intensity in neotropical tree species of distinct functional groups

Abstract

Environmental conditions influence the use of different nitrogen (N) sources by plants. We hypothesized that an increase in light intensity favors the use of nitrate (NO 3 À ) relative to ammonium (NH 4 + ) by seedlings of neotropical tree species from different functional groups, that is, Cecropia pachystachya (a shade-intolerant species), Cariniana estrellensis (a shade-tolerant canopy species), and Guarea kunthiana (a shade-tolerant understory species). We analyzed the growth and N metabolism in seedlings simultaneously provided with NH 4 + and NO 3 À , under lower (LL) and higher (HL) light intensity. 15 N incorporation into amino acids was monitored after incubation with 15 N-labeled NH 4 + or NO 3 À . Under HL, all species showed decreased leaf area ratio, and increased growth, nitrate reductase activity and assimilated N content. Cecropia pachystachya increased the use of both N sources under HL, with substantial increases in 15 N-amino acids derived from 15 NO 3 À (12.5-and 4.0-fold in roots and leaves, respectively) and 15 NH 4 + (4.5-and 3.0-fold in roots and leaves, respectively). Guarea kunthiana showed the greatest plasticity in N use, as the assimilation of 15 NO 3 À in roots and leaves increased substantially under HL (11.2-and 17.0-fold, respectively). Cariniana estrellensis increased the assimilation of 15 NH 4 + in roots and 15 NO 3 À in leaves under HL. Therefore, the responses of N use strategies to light intensity varied with the species according to their ecological characteristics.

Effect of Nitrogen Addition to the Soil on Atlantic Forest Tree Seedlings

“…In C. floribundus, treatment N increased the nitrate content in the xylem sap and in the leaves, indicating translocation of this ion from the roots to the leaves, where N is preferentially assimilated in this pioneer, shade-intolerant species [24,[26][27][28]. Despite this, N addition to the soil did not increase the content of soluble proteins and total N in the leaves of C. floribundus, which may have occurred due to the use of these metabolites for the formation of new tissues and growth.…”

“…Tree species from different functional groups in tropical forests have different N use strategies, which are important adaptive responses to the environment where they live [6,[24][25][26][27][28]. Studies with tree seedlings native to the Brazilian Atlantic Forest indicate that shade-intolerant species have high N assimilation capacity in the shoots, associated with high activity of nitrate reductase (NR) in the leaves and high levels of nitrate translocated in the xylem sap.…”

Fire effect on bamboo-dominated forests in Southwestern Amazon: impacts on tree diversity and forest structure

“…This genus is among the most abundant genera of tree species in Neotropical forests, with rapid growth and propensity to colonize large gaps and habitats in the initial stage of succession (Zalamea et al, 2013). On the contrary, the tree species most associated with the unburned forests were species considered shade tolerant, such as Guarea kunthiana (Debiasi et al, 2021) and Trichilia indet. (Calzavara et al, 2019).…”

Nitrogen assimilation plays a role in balancing the chloroplastic glutathione redox state under high-light conditions

“…Nitrate and ammonium are the primary nitrogen forms absorbed by plant roots, and their relative availability varies in different ecosystems and environmental conditions (Reed and Hageman, 1980; Andrews, 1986). Under light-limiting conditions, ammonia assimilation can be an adaptive strategy to fulfill the heightened demand for photosynthetically derived reducing power when nitrate is assimilated (Debiasi et al, 2021). Yet, ammonium might be toxic to plant cells when it accumulates to high concentrations, limiting its utilization even under low light conditions.…”

“…Nitrate assimilation occurs both in roots and shoots, with high variation across plant species in their reliance on such activities in the root versus shoot, as explored by the differences in NR activity in the two plant parts and the relative abundance of nitrate and reduced nitrogen compounds in the xylem sap of various plant species (Crafts-Brandner and Harper, 1982; Sprent and Thomas, 1984; Smirnoff and Stewart, 1985; Andrews, 1986; Debiasi et al, 2021). Root assimilation, which relies on respiration-derived reductants, is more energetically costly than utilizing reducing equivalents directly from the photosynthetic light reaction, although the reliance on respiratory fixed sugar was suggested to be an advantage in certain conditions, such as low temperatures (Andrews, 1986).…”