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.