4.3 Plants and soil act together to promote plant invasion
Previous studies have found that root hemiparasitic plants usually occur
in soils with poor nutrient levels (Press and Phoenix, 2005), and this
can be attributed to their root hemiparasitism. Their aboveground parts
are usually at a disadvantage when competing with their host plants for
light and space (Tӗšitel et al., 2011), but belowground, they obtain
nutrients from their host root via haustoria (Joel et al., 2013; Sui et
al., 2015). Plants will invest more nutrients into root growth when
nutrient conditions are poor (Yu et al., 2010) and increased numbers of
roots increase the initiation of haustoria. We expected to find that
soil nutrient levels were lower in P. kansuensis invasive areas,
but the results of a previous nutrient addition test showed that theP. kansuensis population hardly decreased when 9
m–2 of nitrogen was added. Furthermore, the nutrient
contents in the P. kansuensis invaded area were higher than in
the non-invaded area according to the in-situ soil sampling results,
although the difference was not significant. Our results showed that
there may be a certain threshold value for P. kansuensis nutrient
demand. When the nitrogen content in the soil exceeds a certain amount,
it is not conducive to P. kansuensis growth, but when it is below
a certain amount, it may favor its establishment and growth. Previous
studies confirmed that water loss can drastically reduce or even stop
photosynthesis and growth in plants, but excess water can also inhibit
soil respiration and affect the normal growth of plants (Fay and
Schultz, 2009; Ferrante et al., 2014). Other research has shown that the
abundance and occurrence of a species are mainly influenced by
interspecies interactions at small scales, but in large areas, it is
soil properties that are the major factors (Wiegand et al., 2012;
Driscoll and Strong, 2018). Furthermore, another reason for the better
growth in nutrient poor areas is that intraspecies competition is
greater under low N conditions. However, further studies are required to
confirm to what extent SOC in soil is conducive to P. kansuensisinvasion. It has also been reported that nutrient abundance is more
conducive to invasive plants than native plants when soil fertility is
high (Broadbent et al., 2017).
Overall, our results demonstrate that
both plant and soil factors drive P. kansuensis invasions in the
Bayanbulak Grassland, and that SW plays the decisive role. This explains
why there are more P. kansuensis distributed near the
sides of water flows in the Bayanbulak Grassland.
Author Contributions: Conceptualization,
Y.L. and Y.G.; methodology, Y.L. and
Y.G.; software, Y.G..; formal analysis,
Y.L., H.L., J.Z. and F.F.;
investigation, Y.L., Y.G. and H.L.; data curation, H.L. and F.F.;
writing-original draft preparation,
Y.L..; writing-review and editing,
Y.L., Y.G., J.Z., K.L. and F.F.;
visualization, Y.L., J.Z. and Y.G.; supervision, Y.L. and Y.G.; funding
acquisition, Y.L. and Y.G. All authors have read and agreed to the
published version of the manuscript.
Funding: This research was supported by the Nsfc (National
Natural Science Foundation of China) (grant numbers 32271747), ”Young
Scholars in Western China” Program of the Chinese Academy of Sciences
(grant no.2019-XBQNXZ-B-002), Nsfc (grant no. 31700460).
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: Not applicable.
Conflicts of Interest: The authors declare no conflict of
interest.