Growth and nutrient uptake by birch and maple seedlings on soil with patchy or homogeneous distribution of organic matter

We compare responses to soil heterogeneity of red maple (Acer rubrum L.) and gray birch (Betula populifolia Marsh.). Seedlings were grown with root systems split between two pots with soil: (i) without additional organic matter or nutrients ("no-addition" treatment), (ii) with additional organic matter and nutrients distributed evenly throughout the soil ("mixed" treatment), and (iii) with additional organic matter and nutrients concentrated in one pot ("patch" treatment). Compared with the no-addition treatment, mixed and patch treatments resulted in taller plants, and greater leaf and total plant dry masses for birch, while growth of maple was mostly unaffected. Birch root biomass was significantly increased in the organic patch. Specific root length of fine roots (<1 mm diameter) in the organic patch was twice as large for birch than for maple. Total plant biomass and N and P contents did not differ between mixed and patch treatments, possibly because the contrast between N and P concentrations between patch and non-patch soil was too small. In all treatments, birches took up more N than maples. In addition, the faster localized root growth and larger specific root length indicate a greater potential for birch than for maple to exploit heterogeneous soils.