Spatial patterns nitrogen transfer models of ectomycorrhizal networks in a Mongolian scotch pine plantation

Ectomycorrhizal (EM) networks provide a variety of services to plants and ecosystems include nutrient uptake and transfer, seedling survival, internal cycling of nutrients, plant competition, and so on. To deeply their structure and function in ecosystems, we investigated the spatial patterns and nitrogen (N) transfer of EM networks using 15N labelling technique in a Mongolian scotch pine (Pinus sylvestris var. mongolica Litv.) plantation in Northeastern China. In August 2011, four plots (20 × 20 m) were set up in the plantation. 125 ml 5 at.% 0.15 mol/L 15NH 4 15 NO3 solution was injected into soil at the center of each plot. Before and 2, 6, 30 and 215 days after the 15N application, needles (current year) of each pine were sampled along four 12 m sampling lines. Needle total N and 15N concentrations were analyzed. We observed needle N and 15N concentrations increased significantly over time after 15N application, up to 31 and 0.42%, respectively. There was no correlation between needle N concentration and 15N/14N ratio (R2 = 0.40, n = 5, P = 0.156), while excess needle N concentration and excess needle 15N/14N ratio were positively correlated across different time intervals (R2 = 0.89, n = 4, P < 0.05), but deceased with time interval lengthening. Needle 15N/14N ratio increased with time, but it was not correlated with distance. Needle 15N/14N ratio was negative with distance before and 6th day and 30th day, positive with distance at 2nd day, but the trend was considerably weaker, their slop were close to zero. These results demonstrated that EM networks were ubiquitous and uniformly distributed in the Mongolian scotch pine plantation and a random network. We found N transfer efficiency was very high, absorbed N by EM network was transferred as wide as possible, we observed N uptake of plant had strong bias for 14N and 15N, namely N fractionation. Understanding the structure and function of EM networks in ecosystems may lead to a deeper understanding of ecological stability and evolution, and thus provide new theoretical approaches to improve conservation practices for the management of the Earth’s ecosystems.