Regulation of the Nutrient Cycle Pathway and the Microbial Loop Structure by Different Types of Dissolved Organic Matter Decomposition in Lakes

Abstract

To explore the effect of different types of dissolved organic matter (DOM) decomposition on nutrient cycling pathways and the microbial loop, four lakes with different DOM sources were investigated monthly. In Lake Tangxun, Dolichospermum decay released highly labile dissolved organic nitrogen into the water column. This induced bacterial organic nitrogen decomposition, as indicated by the increased abundance of gltB, gltD, gdh, and glnA as well as aminopeptidase activity. Genes associated with dissimilatory nitrate reduction to ammonium further fueled ammonium accumulation, driving Microcystis blooms in the summer. In Lake Zhiyin, fish bait deposits (high nitrogen, similar to Dolichospermum detritus) also caused Microcystis blooms. Detritus from Microcystis decomposition then produced high levels of labile dissolved organic phosphorus, inducing phosphatase activity and increasing soluble reactive phosphorus concentrations from September to April in Lakes Tangxun and Zhiyin. The high refractory DOM from macrophytes in Lake Houguan led to insufficient nutrient availability, leading to nutrient mutualism between algae and bacteria. The high levels of labile dissolved organic carbon from terrestrial detritus in Lake Yandong increased bacterial biomass and production, resulting in low chlorophyll content due to the competitive relationship between algal and bacterial nutrient requirements. Therefore, different DOM compositions induce unique connections among available nutrients, algae, and bacteria in the microbial loop.

Differential Adsorption of Dissolved Organic Matter and Phosphorus on Clay Mineral in Water-Sediment System

“…These findings highlighted the distinct roles of Ca/Fe−Mt in nutrient cycling and their potential impacts on water quality and ecosystem health. 7,20 The abundance and distribution of Fe−Mt in lake sediments might play a crucial role in controlling eutrophication in lakes, while Ca−Mt might be more involved in regulating the cycling of C and energy in aquatic food webs. 51,52 Furthermore, the effect of environmental factors, such as pH, temperature, and oxygen content, on the adsorption behavior of Ca/Fe−Mt for P and DOM highlighted the sensitivity of these interactions to changing conditions in the lake environment (Figures S3 and S7).…”

“…Conversely, DOM serves as a source of organic carbon (OC) and energy for microorganisms, impacting aquatic food web dynamics . The interactions between P and DOM in lakes are complex, modulated by various factors, including biogeochemical cycling, hydrodynamics, and microbial processes. − In eutrophic lakes, interactions involving P, DOM, and other chemical constituents significantly impact water quality and ecosystem functioning. , Therefore, understanding the fate and cycling of P and DOM in such eutrophic environments is crucial for effective management strategies to maintain water quality and ecosystem health.…”