4.2 Nutrient effects on invasion by P. kansuensis
Some researchers have reported that it was nutrition that played a
decisive role in the success of alien species (Driscoll and Strong,
2018). For example, invasive plants often show a superior competitive
ability at acquiring and using nutrients than natives, even in nutrient
deficient areas (Funk and Vitousek, 2007). For example, it has been
reported that the established species were not easily attacked by
hemiparasitic plants in nutrient-rich habitats, even though the
established species were the superior hosts. However, the reverse was
true in nutrient-poor areas (Marvier and Smith, 1997). In our study,P. kansuensis was more prone to emerge in areas with high SWs and
organic matter contents. Therefore, our results confirmed the above
studies. Other studies have found that water stress can reduce
aboveground biomass and primary productivity (Knapp et al. 2002;
Yahdjian and Sala, 2006). Generally, root hemiparasitic plants obtain
nutrients, such as water and inorganic materials, from their host.
Therefore, regions with higher SWs are more favorable to P.
kansuensis growth. Other researchers think that nutrient allocation
strategies are used. They have suggested that invasive plants might
develop different biomass allocation strategies than native species in
order to ensure a successful invasion (Press and Phoenix, 2005; Demey et
al., 2013). For example, studies have found that under the interaction
of temperature increase and nitrogen addition treatment (W × N), an
invasive population of Plantago virginica (PV-In) and the native
population (PV-Na) had different biomass allocation strategies when in
competition with the local competitor P. asiatica (Luo et al.,
2020).
We found that there was a significant positive correlation between SK
and LK, and SP:SK and LP:LK. Soil water content was significantly
negatively correlated with LP:LK and extremely significant positively
and significantly positively correlated with LP and LN:LP, respectively.
This could be related to the fact that the N:P ratios in plant organs
can be regulated by internal nutrient transfer (Zhang et al., 2016). In
other words, the plant itself has stoichiometric plasticity and can
adjust its elemental balance under environmental pressure (Sterner and
Elser, 2002). Furthermore, soil nutrients are widely used to manipulate
resource availability to reduce invasion by exotic species in fragile
ecosystems because they play a key role in the success of invasive
species (Perry et al., 2004). Meanwhile, it has reported that increasing
nutrient supply modulated the dominant plant defensive tactics from
tolerance to induced resistance (Burghardt, 2016). For example,Bromus tectorum invasion was controlled by regulating the
nutrient ratio in California (Walker et al., 2017), but in the wetlands,
carbon addition combined with repeated biomass harvesting was used to
reduce invasion by Phalaris arundinacea (Perry et al., 2004). The
root hemiparasitic characteristics shown by P. kansuensis means
that it mainly obtains water and other inorganic materials from its
host, which is why sites with high SOC were used in this study. Our
results also agreed with previous research that showed that invasion by
root hemiparasitic plants was mainly affected by soil nutrient levels
(Borowicz and Armstrong, 2012).