Figure 4 Relationships between average plot biomass (a), plant
abundance of plot (b) and network complexity are given, respectively.
The least square regression is used to fit the relationships. The blue
solid circle represent the mean, the blue line is the error bar, and the
red quadratic curve is regression linear. Relationship between geometric
average of plot biomass and plant abundance and complexity is also given
(c). Note: * * * is p<0.001.
N-addition
affected primary productivity of plants, but also network structure. The
relationship between biomass and complexity was a significant quadratic
curve with down bending direction (\(r^{2}=0.313,\ \ P<0.001\), Fig.
4a). Especially, under high nitrogen fertilization (N >= 2
g N·m-2·year-1) at high frequency
(once a month) and without mowing treatment, complexity will have a
great negative impact on biomass (in Fig. S3). On the contrary, there
was a significant quadratic curve, with an opposite direction, between
plant abundance and complexity (\(r^{2}=0.171,\ \ P<0.001\), Fig.
4b). There was a complementary relationship between biomass and plant
abundance, which the regression line of geometric average of the two
remained almost horizontal. In addition, biomass in short networks was
significantly more than that in nested networks
(\(T_{\text{test}}=2.416,\ \ P<0.05\)). The plants abundance was not
able to reflect competitivity of species to resources
(\(T_{\text{test}}=-0.784,\ P>0.05\)). However, biomass and plant
abundance both increased in the late stage of the experiment (in Fig.
S4).
3.3 Network structure affects ecological
function