Elucidating the dual effects of DOM from composted pig manure on Aliinostoc (Cyanobacteria): Convergence of positive and negative impacts

Abstract

The complex composition of dissolved organic matter (DOM) underlies its diverse biological effects on microorganisms. This study investigated the dual positive and negative effects of DOM derived from composted pig manure (CPM-DOM) on the diazotrophic cyanobacterium Aliinostoc sp. YYLX235. Physiological responses, including growth, photosynthesis, N₂-fixation, and antioxidative activity, were evaluated under CPM-DOM exposure (40–240 mg L⁻¹). After 2 days of exposure to CPM-DOM at concentrations ranging from 40 to 240 mg L⁻¹, the growth of Aliinostoc increased by 74.8 %–167.2 %, while its nitrogen-fixation activity was inhibited by 67.0 % and 87.4 % at CPM-DOM concentrations of 160 mg L⁻¹ and 240 mg L⁻¹, respectively. The temporal dynamics of phycobiliprotein content under CPM-DOM exposure exhibited an opposite trend to the electron transport efficiency of photosystem II (PS II). The combined effects of nutrient supplementation and allelopathy likely accounted for the complex physiological responses of Aliinostoc to CPM-DOM exposure. Certain toxic fractions in CPM-DOM, such as cysteinylglycine-containing substances, may bind to nitrogenase and PS II D1 protein, thereby interfering with their functions. CPM-DOM also reduced reactive oxygen species (ROS) and lipid peroxidation, indicating an absence of oxidative stress. These results reveal concentration-dependent trade-offs between growth stimulation and metabolic inhibition, with significant implications for optimizing the co-application of composted pig manure fertilizers and diazotrophic cyanobacteria-based biofertilizers in rice cultivation.