Role of relative competitive intensity and plasticity index
Relative competition intensity (RCI) of WT and
WC indicated improved competition intensity under
interspecific competition due to decrease in plant height, leaf nitrogen
and increase in SLA and chlorophyll content
(Fig.4). Flooding and nitrogen
enrichment have great impact on the interspecific competition in the
water fluctuation habitat (Zhou et al.,
2017). Relative competition intensity is the trade-off among plants
between competition and facilitation, which means that under higher
resource availability plant shows competition and under stressful
condition plant exhibits facilitation
(Gratani, 2014). RCI of most functional
traits under additional nitrogen and combination of flooding (2N and
F.2N) were negative of WT that indicated the
WT was more competitive than WC,
especially when both plants grew in mixed
culture,
because of its survival and better
competition ability under flooding and nitrogen enrichment conditions.
WC might be repressed by two factors; one is competition
with WT and the other sensitivity to flooding with
higher nutrient availability. Mainly this type of outcome happens under
these conditions because every plant species have different tolerance
ability under adverse environments (Sun et
al., 2019). Here WT appears to be more dominant due to
greater tolerance of flooding and nitrogen enrichment. Furthermore, RCI
under
combination
of flooding and additional nitrogen (F.N and F.2N), LN and CHI of
WT had negative values, but WC had
positive values for these parameters, which indicated that
WT became competitor but WC behaved like
facilitator. Thus, the competition intensity of WTdecreased under combination of flooding and additional nitrogen (F.N and
F.2N), but WC increased (Fig. 4). This can be explained
by the flaring of the functional divergence between WTand WC under combination of nitrogen and flooding
treatments.
Functional traits observed in this study revealed phenotypic plasticity
to some extent (Fig. 3). Phenotypic plasticity is the traits mechanism
that make plant able to cope with biotic and abiotic environments
(Gratani, 2014) and main factor for the
success of different plant under different habitats
(Legay et al., 2014). According to the
results, it was obvious that phenotypic plasticity may play a vital part
to adapt to the adverse changes in the environments. However, it was
noted that the phenotypic plasticity in functional traits of
WT was higher than WC. Phenotypic
plasticity and relative competitive intensity are closely related to
each other because both make invasive plant species able to alter above
and below ground functional traits to cope with a wide range of
environmental changes (Lamarque et al.,
2013). Conflicting to prediction, phenotypic plasticity of LN and CHI
in WT were lower than in WC. These lower
ranges may indicate a fitness cost for plastic physiological traits
under complex environments. Leaf construction costs and plant growth
rate may be quiet due to lower phenotypic plasticity of LN and CHI
(Drenovsky et al., 2012).
WT compensated the negative effects of these adverse
environments due to the limited plasticity of functional traits
(Quan et al., 2015). Thus, this
facilitates invasion and the development of populations in new habitats
(Wang et al., 2017). However, plasticity
of other indices of WT was significantly different from
WC (Fig. 3). Although invasive species mostly did not
show higher range of plasticity compared with the natives, here
WT showed higher plasticity than WCbecause of availability of nitrogen and water. WT and
WC showed also higher plasticity in plant growth under
combination of W × N, which that enhanced their competitiveness
(Čuda et al., 2017,
Wan et al., 2019). Previous studies also
confirmed that invasive and native species could positive respond under
competition (Liu et al., 2018a).