Stability of elemental content correlates with plant resistance to soil impoverishment

Aims We investigated whether plant resistance to soil impoverishment would depend on their flexibility in taking up nutrients and on maintaining elemental stoichiometry.

Methods We mixed sand with grassland soil in mass proportions of 0, 10, 30, 50 and 70% to simulate soil impoverishment as caused by a gradient of desertification intensity and examined how plant nitrogen (N) uptake (¹⁵NH₄NO₃ and NH₄¹⁵NO₃ labelling) and nutrient stoichiometry were associated with plant growth responses of a sedge (Carex duriuscula) and a forb (Potentilla chinensis).

Results With increasing intensity of soil impoverishment, plant biomass, cover and density decreased for C. duriuscula, but not for P. chinensis. Interestingly, uptake of both ¹⁵NO₃^- and ¹⁵NH₄⁺ increased for the sedge but not for the forb, with the former species showing stronger preference of NO₃^-. However, the sedge showed decreasing nutrient contents and concentrations of phosphorus (P) and magnesium (Mg), and thus increasing stoichiometric ratios of N:P and calcium (Ca):Mg. In contrast, the forb maintained its biomass by showing strong stability in nutrient content, concentration and stoichiometry.

Conclusions Stability of N uptake and nutrient stoichiometry were associated with higher resistance to soil impoverishment of the forb than the sedge. Our study highlights the importance of stability in nutrient uptake and stoichiometry for determining plant-species resistance to nutrient-poor conditions.