Fig. 4From: Alpine ecology, plant biodiversity and photosynthetic performance of marker plants in a nitrogen gradient induced by Alnus bushesNitrate concentration in soil (mg nitrate–N/kg dry soil, for the sampling sites see Fig. 2). Box plot with median value, 25th and 75th percentiles and minimum and maximum values (n = 5, control = sampling site b-5). For statistical treatment see text and Additional file 2: Table S2Back to article page