Soil nutrient heterogeneity shifts functional group composition without altering total biomass in an alpine grassland

Abstract Soil nutrient heterogeneity is common in nature, but few studies have tested the effects of soil nutrient heterogeneity on plant productivity in natural communities. Such effects are of particular interest in habitats where heterogeneity may be increasing due to global warming, as in high-elevation grassland on the Qinghai-Tibetan Plateau. In a three-year study, we added N, P and K to 2 m × 2 m plots in grassland to establish five homogeneous and six heterogeneous treatments that varied in patch size, patch contrast (difference in nutrient levels between patches), and number of patch types (with different nutrient levels). We measured aboveground biomass of grasses, other graminoids, legumes and forbs. Biomass of grasses was higher (over 300 g m–2) and that of legumes was lower (about 25 g m–2) at higher nutrient availability in homogeneous treatments. Within heterogeneous plots, grasses similarly had about 25% higher biomass and legumes had about 60% lower biomass in patches with higher nutrients, mainly at the larger patch size and sometimes more so when patch contrast was greater. Accounting for 47%–61% of the total aboveground biomass, grasses showed a roughly similar pattern to that of the whole community. An increase in soil nutrient heterogeneity is unlikely to affect plant aboveground biomass in this grassland, although it can increase biomass of grasses and decrease that of legumes. Soil nutrient heterogeneity might partly mitigate these effects if large patches without elevated nutrients persist.