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).