Global climate change has greatly increased the drought duration, frequency, and severity of intermittent river ephemeral stream (IRES), affecting the microbial-mediated biogeochemical process. While there is limited information about the responses of community structure and ecosystem functions of benthic biofilms in IRES, especially under the increased drought duration. Here, we focused on the increased drought duration and summarized their effects on the structure and functions of benthic biofilms in IRES. First, the increased dehydration duration led to distinct effects on the α-diversity or β-diversity of benthic microbial communities. The interaction network should be considered in future research as they are essential to maintain biofilm structure and play key roles in the resistance and resilience in biofilm community recovery under hydrological stress. In addition, inconsistent response patterns of the fundamental functions, such as gross primary production, ecosystem respiration, and functional enzymes activity of biofilms were discussed. Besides, the emissions of greenhouse gases (GHGs) of biofilms in IRES deserve more attention due to that their emission flux of biofilms could be significantly altered after prolong dehydration duration with a huge pulse when rewetting. More important, it is ecosystem multifunctionality rather than a single function that needs to be fully considered when studying the microbial functions and the biogeochemical process mediated by biofilms in IRES under increased dehydration duration. Also, more research is needed at larger spatial and longer temporal scales to evaluate the effects from a more macro perspective for better understanding the ecological impacts of increased dehydration duration in IRES ecosystems.

Global change has led to the increased duration and frequency of droughts and may affect the microbial-mediated biochemical processes of intermittent rivers and ephemeral streams (IRES). Effects of flow desiccation on the physical structure and community structure of benthic biofilms of IRES have been addressed, however the dynamic responses of biofilm functions related to ecosystem processes during the dry-wet transition remain poorly understood. Herein, dynamic changes in biofilm metabolic activities were investigated during short-term (25-day) and long-term (90-day) desiccation, both followed by a 20-day rewetting period. Distinct response patterns of biofilm metabolism were observed based on flow conditions. Specifically, biofilms were completely desiccated after 10 days of drying. Biofilm ecosystem metabolism, represented by the ratio of gross primary production (GPP) and community respiration (CR), was significantly inhibited during desiccation and gradually recovered back to autotrophic after rewetting due to the high resilience of GPP. Also, the potential metabolic activities of biofilms were maintained during desiccation and showed a tendency to recover after rewetting. While long-term desiccation caused irreparable damage to the total carbon metabolism of biofilms that could not be recovered to the control level even after 20 days of rewetting. Moreover, the metabolic activities of amine and amino acids showed an inconsistent pattern of recovery with total carbon metabolism, indicating the development of selective carbon metabolism. This research provides direct evidence that the increased non-flow periods affects biofilm-mediated carbon biogeochemical processes, which should be taken into consideration for the decision-making of the ecological and environmental flow of IRES.