PS 2-14 - Priority effects diminish over time whereas chemical recalcitrance constraint their strength during fungal necromass decomposition

Abstract: Understanding how communities assemble and change over time is relevant given that early-arriving species modify the resources and/or the environment in ways that influence the colonization of late-arriving species. Known as priority effects, these ecological processes have been crucial to explaining the dynamics and functioning of communities across varied realms of ecology. However, their impacts on ecosystem services such as carbon storage remain poorly understood. Here we use dead fungal mycelium (i.e., necromass) as a model system to study priority effects during decomposition. Theory suggests that priority effects become weakened as resource availability decreases due to growth limitations of early-arriving species. Therefore, we used the abundance of a recalcitrant compound found in necromass (i.e., melanin) as a proxy of environmental stress and hypothesize that this pigment will be a key factor driving the dynamics of the decomposer community and the accrual of necromass-associated carbon in the soil.



Melanized and non-melanized necromass was grown in the laboratory and incubated in 250 mL glass jars filled with sieved-, moistened-, sterilized soil. We used 52-µm nylon mesh bags to pack 100 mg of freeze-dried necromass and insert them into each jar. Next, we inoculated the jars with four fungal species. After two weeks of incubation in the laboratory, all bags were buried in a white pine forest at 5 cm depth and harvested after four, eight, and 12 weeks. At each harvest, necromass was collected in sterile conditions and freeze-dried to obtain its dry weight. Our experimental design consisted of two necromass types, three harvest times, and six assembly histories. Four single-species treatments and two controls were used as assembly histories. Controls consisted of one inoculum with the four species added at time zero and sterile water added instead of inoculum, respectively. Nine replicates were used per treatment for a total of 324 experimental units.



Our results to date have shown that the identity of the early-arriving species in conjunction with whether the necromass had melanin or not, modified necromass decomposition rates. Interestingly, although we detected that priority effects became attenuated over time, they remained significant in non-melanized necromass after twelve weeks of field incubations. Collectively, these results highlight the impact of abiotic constraints (here melanin abundance) on the prevalence of priority effects during necromass decomposition. These findings are important to understanding which ecological contexts are more prone to priority effects.