Abstract
To investigate N metabolism of two contrasting Populus species in acclimation to low N availability, saplings of slow-growing species (Populus popularis, Pp) and a fast-growing species (Populus alba × Populus glandulosa, Pg) were exposed to 10, 100, or 1000 μM NH4NO3. Despite greater root biomass and fine root surface area in Pp, lower net influxes of NH4 + and NO3 – at the root surface were detected in Pp compared to those in Pg, corresponding well to lower NH4 + and NO3 – content and total N concentration in Pp roots. Meanwhile, higher stable N isotope composition (δ15N) in roots and stronger responsiveness of transcriptional regulation of 18 genes involved in N metabolism were found in roots and leaves of Pp compared to those of Pg. These results indicate that the N metabolism of Pp is more sensitive to decreasing N availability than that of Pg. In both species, low N treatments decreased net influxes of NH4 + and NO3 –, root NH4 + and foliar NO3 – content, root NR activities, total N concentration in roots and leaves, and transcript levels of most ammonium (AMTs) and nitrate (NRTs) transporter genes in leaves and genes involved in N assimilation in roots and leaves. Low N availability increased fine root surface area, foliar starch concentration, δ15N in roots and leaves, and transcript abundance of several AMTs (e.g. AMT1;2) and NRTs (e.g. NRT1;2 and NRT2;4B) in roots of both species. These data indicate that poplar species slow down processes of N acquisition and assimilation in acclimation to limiting N supply.
Highlights
As woody crops, forest plantations hold a great potential for the pulp and paper industry, carbon mitigation, and biomass production for biofuels (Luo et al, 2006; Luo and Polle, 2009; Novaes et al, 2009; Studer et al, 2011)
These results indicate that the N metabolism of Pp is more sensitive to decreasing N availability than that of Populus glandulosa (Pg)
The greater root biomass and larger fine root surface area of Pp compared with Pg suggest that root morphological features of Pp are more responsive to limiting N availability than those of Pg
Summary
Forest plantations hold a great potential for the pulp and paper industry, carbon mitigation, and biomass production for biofuels (Luo et al, 2006; Luo and Polle, 2009; Novaes et al, 2009; Studer et al, 2011). Due to the high demand of fertile soil for agriculture, poplar plantations have often been established on marginal lands where soil N is limiting (Rennenberg et al, 2010; Bilodeau-Gauthier et al, 2011) The growth and wood properties of this species are more responsive to different N levels than those of Populus trichocarpa which is adapted to fluctuating N supply (Euring et al, 2012) These results highlight that it is essential to better understand the distinctness of N metabolism in different poplar species in order to select poplars with tolerance to low N availability
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