Eukaryotes contribute more than bacteria to the recovery of freshwater ecosystem functions under different drought durations

Abstract

Global climate change mostly impacts river ecosystems by affecting microbial biodiversity and ecological functions. Considering the high functional redundancy of microorganisms, the unknown relationship between biodiversity and ecosystem functions obstructs river ecological research, especially under the influence of increasing weather extremes, such as in intermittent rivers and ephemeral streams (IRES). Herein, dry-wet alternation experiments were conducted in artificial stream channels for 25 and 90 days of drought, both followed by 20 days of rewetting. The dynamic recovery of microbial biodiversity and ecosystem functions (represented by ecosystem metabolism and denitrification rate) were determined to analyse biodiversity-ecosystem-function (BEF) relationships after different drought durations. There was a significant difference between bacterial and eukaryotic biodiversity recovery after drought. Eukaryotic biodiversity was more sensitive to drought duration than bacterial, and the eukaryotic network was more stable under dry-wet alternations. Based on the establishment of partial least squares path models, we found that eukaryotic biodiversity has a stronger effect on ecosystem functions than bacteria after long-term drought. Indeed, this work represents a significant step forward for further research on the ecosystem functions of IRES, especially emphasizing the importance of eukaryotic biodiversity in the BEF relationship.

Transformation of Biofilm to Carbon Sinks after Prolonged Droughts Linked with Algal Biodiversity Change

“…In line with previous studies, the interdomain network's response mechanism to short-term drought stress reflects a tight, complex, and stable network structure. 5 Simultaneously, the interdomain network exhibits high ecological adaptability, evident from its rapid stability recovery and the positive correlation ratio approaching control levels as drought duration increase (Figure 4 and Figure S5). Moreover, the similar response of the positive correlation ratio to the average degree and robustness indicates that a preference for cooperative relationships among microorganisms, rather than exclusion, in face of hydrological disturbances could explain the response mechanism 55 (Figure 4b).…”

“…Building on our previous study, biofilm colonization was conducted in the Qin Huai River (32°03′36.2’’ N; 118°44′38.1’’ E) located in Nanjing, Eastern China. , For this purpose, each device consisted of wire cages measuring 30 cm in diameter and 30 cm in height, consisting of cobbles (2–3 cm in diameter). The cultivation process lasted for 44 days under natural conditions to obtain mature biofilm growth on the cobbles .…”

“…Notably, fungal networks displayed the most stability and resilience to prolonged drought. 5 Additionally, the increasing prominence of stochastic processes becomes more pronounced with longer drought durations, particularly among algae and fungi. These shifts in microbial network stability and community assembly could significantly impact ecosystem functions, particularly the carbon metabolism in river ecosystems.…”

“…Shifts in hydrological regimes within aquatic systems might impact CO 2 fluxes by influencing carbon (C) loading or processing . Despite this, the role and contribution of intermittent rivers and ephemeral streams (IRES), which experience intermittent droughts multiple times a year, to riverine C fluxes have largely been overlooked. As ecological indicators connecting biodiversity structure and functions in river ecosystems, biofilms dominate ecosystem metabolism and contribute significantly to riverine CO 2 fluxes. , However, drought significantly inhibits the biofilm ecosystem metabolism and affects recovery during rewetting, − potentially exerting significant effects on global carbon cycling.…”

“…Moreover, Timoner et al discovered that distinct drought durations yield varying impacts on biofilm metabolism functions. As per prior research, eukaryotic biodiversity tends to be more sensitive to drought duration compared to bacterial, owing to their higher biological adaptability in response to external hydrological changes. , Given that biodiversity stands as a key factor driving ecosystem functions, including CO 2 emission, there exists a scarcity of studies exploring how the relationship of biodiversity and ecosystem functions (BEFs) evolves with increasing drought duration. , In addition, gaining an understanding of when drought conditions surpass the threshold biodiversity and ecosystem functions’ biological adaptability becomes imperative to formulate effective conservation plans and mitigation strategies for IRES …”