Foliar phosphorus content predicts species relative abundance in P-limited Tibetan alpine meadows

• Which traits can predict species relative abundance (SRA) remains largely unknown.
• We assessed the importance of traits predicting SRA in Tibetan alpine meadows.
• Species were differentiated along a trade-off in growth vs competition.
• A higher Leaf P was the most important trait predicting SRA in grazed community.
• Species with low LPC but higher LDMC held an advantage in ungrazed community.

Traits that favor rapid plant growth are expected to have an important influence on species relative abundance (SRA) in semi-natural grasslands where competitive exclusion is reduced by grazing. However, which traits are more strongly associated with variation in SRA remains largely unknown, especially in P-limited but species-rich grasslands. We assessed the relative importance of traits predicting SRA in P-limited Tibetan alpine meadows subject to long term grazing. We assessed abundance in terms of both aboveground biomass and ramet numbers in relation to seven traits (specific leaf area, LDMC: leaf dry matter content, leaf carbon concentration, leaf nitrogen concentration, LPC: leaf phosphorus concentration, mature height, and seed size) for all component species in grazed and ungrazed plots in each of three contrasting sites on the Tibetan Plateau. We used CATS regression (i.e. regression for Community Assembly through Trait Selection) to quantify the relative importance of different traits in predicting SRA, and tested dependence of trait importance values on both environmental context and alternative measures of abundance. Species were primarily differentiated along a trade-off axis involving traits promoting nutrient acquisition for fast growth vs resource conservation and competitive ability. A higher LPC consistently was the most important trait predicting species abundance in grazed plots, while species with low LPC but higher LDMC held an advantage in ungrazed plots. This suggests that in competition-released communities, species with a high ability to uptake soil available P tend to become abundant, while in competition-dominated communities, species using fixed P efficiently do better. The relative importance of traits in ungrazed plots did not change across sites, but in grazed plots species that have traits associated with nutrient conservation were favored in colder and drier conditions. The results highlight the importance of traits affecting acquisition of soil available P in these Tibetan alpine meadow communities. Species tradeoffs in nutrient acquisition versus conservation are a primary determinant of SRA, but the relative importance of traits depended on both environmental context and whether SRA was estimated as above-ground biomass or as number of ramets.