The distribution of soil nutrients with depth: Global patterns and the imprint of plants

EG JOBBÁGY; RB JACKSON

BIOGEOCHEMISTRY

Springer

Lugar: Netherlands; Año: 2001 vol. 53 p. 51 - 77

0168-2563

To understand the importance of plants in structuring the vertical distributionsof soil nutrients, we explored nutrient distributions in the top meter of soil for more than10,000 profiles across a range of ecological conditions. Hypothesizing that vertical nutrientdistributions are dominated by plant cycling relative to leaching, weathering dissolution, andatmospheric deposition, we examined three predictions: (1) that the nutrients that are mostlimiting for plants would have the shallowest average distributions across ecosystems, (2)that the vertical distribution of a limiting nutrient would be shallower as the nutrient becamemore scarce, and (3) that along a gradient of soil types with increasing weathering-leachingintensity, limiting nutrients would be relatively more abundant due to preferential cyclingby plants. Globally, the ranking of vertical distributions among nutrients was shallowest todeepest in the following order: P > K > Ca > Mg > Na = Cl = SO4. Nutrients strongly cycledby plants, such as P and K, were more concentrated in the topsoil (upper 20 cm) than werenutrients usually less limiting for plants such as Na and Cl. The topsoil concentrations of allnutrients except Na were higher in the soil profiles where the elements were more scarce.Along a gradient of weathering-leaching intensity (Aridisols to Mollisols to Ultisols), totalbase saturation decreased but the relative contribution of exchangeable KC to base saturationincreased. These patterns are difficult to explain without considering the upward transportof nutrients by plant uptake and cycling. Shallower distributions for P and K, together withnegative associations between abundance and topsoil accumulation, support the idea that plantcycling exerts a dominant control on the vertical distribution of the most limiting elements forplants (those required in high amounts in relation to soil supply). Plant characteristics liketissue stoichiometry, biomass cycling rates, above- and belowground allocation, root distributions,and maximum rooting depth may all play an important role in shaping nutrient profiles.Such vertical patterns yield insight into the patterns and processes of nutrient cycling throughtime.