Measurements of plant biomass and functional traits
To quantify the effect of the shrub (A.ordosica ) on the herbaceous understory species, we selected two 1 × 1 m quadrats in each plot, with one quadrat positioned in a shrub patch and the other one positioned away from a shrub patch. The aboveground biomass of each species was sampled in all quadrats, at the end of August 2017, by cutting individual plants at ground level using scissors and weighing the samples after oven-drying at 75 °C for 48 h.
In order to assess functional divergence (i.e., the degree of functional dissimilarity in trait values within the community; de Bello et al. , 2010), from May to August 2017 (depending on species phenology), we measured two traits, known as good proxies of functional strategies of herbaceous plants (Díaz et al. , 2016): (i) height, measured as the shortest distance between the upper boundary of the main photosynthetic tissues (excluding inflorescences) of a plant individual and the ground level (m); leaf dry matter content, LDMC (g·kg−1), measured as the ratio between leaf dry mass and fully rehydrated fresh mass. For measuring traits, we chose at least 10 individuals per species in the community in areas outside our plots and patches where species had their best growth performances. We did not take samples in the control plots of the design because they did not include all species, and this would have affected our biomass measurement. For each selected individual, height was directly measured with band tape and leaves were sampled for area and dry mass measurements. Methods for measuring each trait followed standardized protocols proposed by Pérez-Harguindeguy et al. (2013).