Decomposition-dependent biphasic regulatory effects and possible mechanisms of rice straw on Nostoc sphaeroides
摘要
Diazotrophic cyanobacteria play crucial roles in nitrogen (N) input in paddy fields. The potential effects of rice straw return and its decomposition on these cyanobacteria within soil ecosystems remain poorly understood and are often overlooked in current agricultural management practices. This study systematically investigated the physiological responses of Nostoc sphaeroides, an edible diazotrophic cyanobacterium in paddy ecosystems, to leachate from decomposed rice straw (LDRS), and explored potential mechanisms through integrated analysis of physiological responses and phytochemical composition. The results showed that LDRS from 10-30 days decomposing rice straw (RS, 1 g L-1) stimulated N. sphaeroides growth by 28.3-38.6%. However, LDRS from the 45-60 day stage at 5 g RS L⁻1 inhibited growth by 17.2-24.3%. Both effects were diminished when using LDRS from the 90-day decomposition stage. Nutrient supplementation likely explains the stimulation of algal growth, whereas phenolic compounds may conversely account for its inhibition. Mechanistic studies demonstrated that LDRS disturbed photosynthetic electron transfer in photosystem Ⅱ (PS II) through dual interference at both donor and acceptor sides of the reaction center. Furthermore, LDRS exposure induced intracellular ROS accumulation, potentially originating from non-photochemical exciton dissipation in photosynthetic apparatus and auto-oxidation of phenolic hydroxyl compounds, ultimately causing oxidative damage to plasma membranes. The results suggest that the rice straw incorporation rate should be limited to 3846.15 kg ha⁻1 to avoid adverse effects on N. sphaeroides during decomposition. Furthermore, the negative impact on this cyanobacterium can be mitigated by avoiding its inoculation into paddy fields during the first 60 d of straw decomposition.