Quantifying Microbial Associations of Dissolved Organic Matter under
Global Change
Abstract
Microbes play a critical role in regulating the size, composition, and
turnover of dissolved organic matter (DOM), which is one of the largest
pools of carbon in aquatic ecosystems. Global change may alter
DOM-microbe associations with implications for biogeochemical cycles,
although disentangling these complex interactions remains a major
challenge. Here we develop a framework called Energy-Diversity-Trait
integrative Analysis (EDTiA) to examine the associations between DOM and
bacteria along temperature and nutrient gradients in a manipulative
field experiment on mountainsides in contrasting subarctic and
subtropical climates. In both study regions, the chemical composition of
DOM correlated with bacterial communities, and was primarily controlled
by nutrients and to a lesser degree by temperature. At a
molecular-level, DOM-bacteria associations depended strongly on the
molecular traits of DOM, with negative associations indicative of
decomposition as molecules are more biolabile. Using bipartite networks,
we further demonstrated that negative associations were more specialized
than positive associations indicative of DOM production. Nutrient
enrichment promoted specialization of positive associations, but
decreased specialization of negative associations particularly at warmer
temperatures in subtropical climate. These global change drivers
influenced specialization of negative associations most strongly via
molecular traits, while both molecular traits and bacterial diversity
similarly affected positive associations. Together, our framework
provides a quantitative approach to understand DOM-microbe associations
and wider carbon cycling across scales under global change.