Magnitude and timing of resource pulses interact to affect plant invasion

Abstract

Human activities can cause resource fluctuations through reducing uptake by the resident vegetation (e.g. disturbance) or through changing external resource supply (e.g. fertilization). Resource fluctuations often occur as pulses which are low frequency, large magnitude and short duration and now are recognized as an important driver of plant invasions. However, resource pulses often vary dramatically in a number of attributes, yet how these attributes mediate the impacts of resource pulses on plant invasions remains unclear. Erigeron canadensis is a serious invader of disturbed habitats and agricultural fields in China. Thus, it experiences nutrient pulses with different magnitudes and timings. Here, we grew E. canadensis and six co-occurring native plant species with three different magnitudes of nutrient enrichment (low, medium, or high).For each magnitude, we added equivalent amounts of nutrients with a constant supply as a control or one of three pulses with different timings (early, middle, or late stages). We found that pulse magnitude, timing and their interaction significantly affected E. canadensis growth (biomass production) and invasion (proportion of biomass in a pot). For each timing, E. candensis growth and invasion increased with nutrient magnitude. At low magnitude, middle and late pulses promoted E. canadensis growth and invasion. At medium magnitude, late pulses suppressed E. canadensis growth, but did not affect its invasion. At high magnitude, early and middle pulses strongly suppressed E. canadensis growth and invasion. In contrast, natives generally exhibited different responses to nutrient pulses. Our study shows that plant responses are not just dependent on the presence of a resource pulse but also on its attributes. In contrast to theory and many empirical studies, our results show that resource fluctuation does not always promote plant invasion. We highlight that the attributes of resource pulses are key to understanding the impact of resource fluctuations on plant invasion.

Effects of nutrient pulses on exotic species shift from positive to neutral with decreasing water availability

“…For multiple small pulses, we added Hoagland solution with the following sequence: 5, 75, 40, 80, 35, 5, 65, 20, 35, and 40 ml. The total amount of nutrients was 400 ml of 400% Hoagland solution for all treatments, which is consistent with previous studies (Liu & van Kleunen, 2017; Liu, Zhang, & van Kleunen, 2018; Tao et al, 2021). To eliminate a potential bias in water supply in nutrient treatments, we dissolved Hoagland solution in the water being added to pots to maintain the target volumetric water content.…”

Soil microbes mediate the effects of environmental variability on plant invasion

“…a temporal increase) in resource availability 6 . Although it has become a widely accepted theory in ecology, empirical studies that tested it [7][8][9][10][11][12] have found mixed results. For example, whereas Parepa et al 7 found that a nutrient pulse increased the dominance of an invasive plant, Liu et al 9 showed that a pulsed nutrient supply decreased the dominance of invasive alien plants.…”

Fluctuations in resource availability shape the competitive balance among non‐native plant species

“…The suppression of native plants by one nonnative species may thus result in an overall facilitative effect for another non-native species (Allen et al, 2021;Flory & Bauer, 2014). Therefore, considering the increasing number of non-natives accumulating in native communities (Kuebbing et al, 2013;van Kleunen et al, 2015), native species should be included in future studies to test how resource pulse impacts interactions among non-natives. Moreover, the impact of resource pulses on individual growth, population dynamics, and community structure can vary significantly depending on the characteristics of the nutrient inputs (Felton et al, 2020;Post & Knapp, 2020;Sher et al, 2004).…”

“…Moreover, the impact of resource pulses on individual growth, population dynamics, and community structure can vary significantly depending on the characteristics of the nutrient inputs (Felton et al, 2020; Post & Knapp, 2020; Sher et al, 2004). For example, Tao et al (2021) demonstrated that, compared with nutrients supplied at a constant rate, nutrients supplied as a single large pulse increased the proportion of aboveground biomass of non‐native C. canadensis under low nutrient addition magnitude in an artificial native community but decreased the proportion of C. canadensis in a community under high magnitude nutrient additions. Thus, to accurately predict the responses of interactions among non‐natives to resource pulses, it is essential to integrate attributes of resource pulses, such as magnitude and timing, in future studies.…”