Contrasting effects of producer and consumer resource use efficiency on trophic asynchrony and stability of food web under multiple stressors

The ongoing global biodiversity loss caused by multi-stressors has raised
concerns about the potential consequences of species extinctions on the
functionality and stability of ecosystems. It has been widely recognized
that biodiversity could stabilize the ecosystem by enhancing the
asynchronous dynamics among species within a single trophic level.
However, in natural multi-trophic ecosystems, asynchronous changes between
trophic levels (trophic asynchrony) are expected to increase trophic
mismatch and alter trophic interactions, which may consequently alter
ecosystem stability. Under changeable environments, it is currently
unclear how biodiversity in different trophic levels affects the stability
of food web by changing the trophic interactions (represented by resource
use efficiency, RUE) and trophic asynchrony, which is key to providing
further insights into the biodiversity effects on ecosystem stability.
Using a 6-month mesocosm experiment, we tested how
multi-stressors—microplastics, eutrophication, dissolved organic carbon,
and invasive fish—affected species richness and RUE of phytoplankton
(producer) and zooplankton (consumer), subsequently influencing temporal
stability of food web via altering the trophic asynchrony. Our results
demonstrated that multi-stressors could shape ecosystem temporal stability
through species richness-RUE-trophic asynchrony pathways, emphasizing the
cascading impacts of multi-stressors on ecosystem functions and stability.
Increasing species diversity of phytoplankton and zooplankton enhanced the
RUE within that trophic level. However, greater producer diversity
decreased RUE of consumers, probably due to an increase in inedible
producer species. This suggests that benefits of biodiversity of producer
could diminish functions at higher trophic levels. In addition,
zooplankton RUE increased trophic asynchrony, whereas phytoplankton RUE
decreased it. Crucially, trophic asynchrony stabilized phytoplankton and
food web but destabilized zooplankton community, highlighting contrasting
impacts of trophic asynchrony on stability across trophic levels. Our
study showed that producer diversity may indirectly decrease the functions
and stability of consumers under multiple stressors, which challenged the
simplistic expectation that more diversity universally stabilized
ecosystems. This study provided a new insight into the
biodiversity-ecosystem stability relationships by highlighting the
mediating roles of RUE and trophic asynchrony under realistic
environmental change scenarios.