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).