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 ^(15)N 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 ^(15)NH_4 ^(15)NO_3solution was injected into soil at the center of each plot.Before and 2,6,30 and 215 days after the ^(15)N application,needles(current year)of each pine were sampled along four 12 m sampling lines.Needle total N and ^(15)N concentrations were analyzed.We observed needle N and^(15)N concentrations increased significantly over time after ^(15)N application,up to 31 and0.42%,respectively.There was no correlation between needle N concentration and ^(15)N/ ^(14)N ratio(R2=0.40,n=5,P=0.156),while excess needle N concentration and excess needle ^(15)N/^(14)N ratio were positively correlated across different time intervals(R^2=0.89,n=4,P\0.05),but deceased with time interval lengthening.Needle ^(15)N/^(14)N ratio increased with time,but it was not correlated with distance.Needle ^(15)N/ ^(14)N 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 ^(14)N and ^(15)N,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
