Scientists Found the Nitrogen Uptake Strategy of Mature Conifers in Northeast China
Nitrogen (N) is one of the major nutrients limiting plant growth in terrestrial ecosystems. Soil N, including ammonium, nitrate and dissolved organic N, is particularly important in maintaining plant growth and regulating photosynthesis. However, different plants do not use different forms of soil N equally, which is the important mechanism promoting species coexistence and forest productivity.
Previous studies have suggested preferential ammonium uptake in conifers. Most of these studies, however, focused on N uptake by fine roots of seedlings or juvenile trees using hydroponic experiments, ignoring microbial competition for ammonium and adsorption of ammonium by soil minerals. Therefore, these results are difficult to reflect the realistic N uptake and acquisition by mature trees in the field.
Prof. Yunting Fang’s lab from the Institute of Applied Ecology of Chinese Academy of Sciences, therefore, first conducted an in situ whole tree 15N labelling experiment (15NH4+ vs. 15NO3-) (Fig 1) to investigate the N uptake strategy of four mature conifers (Pinus koraiensis, Pinus Sylvestris, Picea koraiensis, and Larix olgensis) in Northeast China.
They found that all four mature coniferous species assimilated nitrate efficiently, with 15NO3- contributing 39% to 90% to total 15N tracer uptake (Fig 2), in contrast to those from the hydroponic experiments by various coniferous species where ammonium was preferentially taken up (ammonium contributing 55% to 98% of total N uptake). The in situ whole tree 15N paired labelling experiment fully considers the competition and fixation of soil nitrogen by soil microorganisms and abiotic processes, which truly reflects the N uptake strategy of mature conifers. From the perspective of the supply and absorption of plant nutrients, efficient utilization of nitrate in conifers might constitute growth advantage and be positive for productivity and timber production for coniferous plantations under the context of increasing proportions of nitrate in N deposition, which efficiently promotes carbon sequestration and mitigates the global climate change.
This study entitled “Mature conifers assimilate nitrate as efficiently as ammonium from soils in four forest plantations” has recently been published in New Phytologist.
This work was financially supported by the National Key Research and Development Program of China, the Key Research Program of Frontier Sciences of Chinese Academy of Sciences, Liaoning Vitalization Talents Program, and the National Natural Science Foundation of China.
Fig 1. Schematic diagram of experimental design for in situ pairing 15N labelling (Image by WANG Ang).
Fig 2. Contribution of 15NH4+ and 15NO3- to total 15N tracer uptake by the whole plant in the four forest plantations of (a) Pinus koraiensis, (b) Picea koraiensis, (c) Pinus sylvestris, and (d) Larix olgensis (Image by WANG Ang).
