Direct and higher-order interactions in plant communities under
increasing weather persistence
Abstract
Climate
change is increasing the weather persistence in the mid-latitudes,
prolonging both dry and wet spells compared to historic averages. These
newly emerging environmental conditions destabilize plant communities,
but the role of species interactions in this process is unknown. Here,
we tested how direct and higher-order interactions (HOIs) between
species may change in synthesized grassland communities along an
experimental gradient of increasing persistence in precipitation
regimes. Our results indicate that species interactions (including HOIs)
are an important determinant of plant performance under increasing
weather persistence. Out of the 12 most parsimonious models predicting
species productivity, 75 % contained significant direct interactions
and 92 % significant HOIs. Inclusion of direct interactions or HOIs
respectively tripled or quadrupled the explained variance of target
species biomass compared to null models only including the precipitation
treatment. Drought dominated the plant responses, with longer droughts
increasing direct competition but also HOI-driven facilitation. Despite
these counteracting changes, drought intensified net competition.
Grasses were generally more involved in competitive interactions whereas
legumes had a stronger affinity for facilitative interactions. Under
longer drought, species affinity for nutrient rich or wet environments
resulted in more negative direct interactions or HOIs, respectively. We
conclude that higher-order interactions, crucially depending on species
identity, only partially stabilize community dynamics under increasing
weather persistence.
Keywords: higher-order interactions, grasslands, facilitation
and competition, species interactions, increasing weather persistence,
drought
Introduction
Climate warming changes the inter- and intra-annual variability of
precipitation regimes in the mid-latitudes (Pendergrass et al., 2017),
including shifts towards more persistent summer weather with longer dry
and wet spells compared to historic averages (Pfleiderer et al., 2019).
With more extreme precipitation regimes (Fig. 1), we expect that
ecosystems will be subjected more often to prolonged plant
stress-inducing extreme conditions, due to the accompanying changes in
soil water and temperature (Felton et al., 2021; Knapp et al., 2008;
Reynaert et al., 2021; Zhao & Khalil, 1993), and potential changes in
nutrient cycling (Borken & Matzner, 2009). For example, when dry
periods become longer, or occur at higher temperatures (Collins et al.,
2013), soil water declines more, increasing the chance of crossing
mortality thresholds (De Boeck et al., 2018; Knapp et al., 2008).
Moreover, longer droughts can increase the risk of nutrient leaching
upon rewetting, potentially leading to nutrient shortages in the longer
term (Borken & Matzner, 2009; Klaus et al., 2020).