Chaetomorpha linum exhibits a strong tolerance to fluctuations in salinity and temperature. To investigate its environmental adaptation strategies, a 12-day two-factor culture experiment was conducted at five salinities (0, 5, 10, 15, and 30) and two temperatures (15 and 25 ℃). Indicators related to growth, morphology, photosynthetic performance, osmotic regulation, key enzyme activity, and oxidative stress were systematically analyzed. The results showed that at 25 ℃ and salinities of 10 and 15, C. linum exhibited the highest relative growth rate, photosynthetic and respiratory activities, and ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) activity, leading to significantly enhanced carbon fixation and energy conversion efficiency. In contrast, under salinity 0 conditions, the alga died, while under salinity 5 and low temperature (15 ℃) conditions, its growth was significantly inhibited, exhibiting a combined stress effect. Low temperature induced cell wall thickening, a decline in maximum photochemical efficiency, and an increase in non-photochemical quenching, indicating the activation of photoprotective responses. Under optimal thermal conditions, cell volume expansion and reduced chlorophyll content reflected improved light energy utilization. Salinity reduction disturbed the osmotic homeostasis while the compatible solute synthesis gradually restored its stability. At combined low temperature and low salinity stress, nitrogen assimilation was restricted, which was accompanied by the accumulation of reactive oxygen species and malondialdehyde. Elevated catalase and glutathione peroxidase activities alleviated the oxidative damage. In conclusion, C. linum adapts to varying salinity and temperature through coordinated regulation of Rubisco activity, cellular morphology, pigment composition, osmotic balance, photoprotection, and antioxidant defense. Our findings revealed a multifaceted physiological response of the alga, provided an essential basis for evaluating the adaptive potential of C. linum in dynamic coastal environments and will support the future ecological management and resource utilization.

Organic carbon sources are essential nutrients for the growth and development of autotrophic microorganisms. To investigate the effects of different organic carbon sources on Nostoc sphaeroides, a 9-day cultivation experiment was conducted using four types of organic carbon sources (glucose, sucrose, sodium pyruvate, and sodium acetate) each at four concentrations (0.01, 0.1, 0.2, and 0.4 mol·L^-1). After the experiment, the relative growth rate (RGR) and the contents of four biochemical compositions (chlorophyll a, soluble sugars, soluble proteins, and phycocyanin) of N. sphaeroides were measured. The results showed that both the types and concentrations of organic carbon sources had significant influences on the growth and biochemical compositions of N. sphaeroides. Glucose and sucrose significantly promoted the growth of N. sphaeroides, with the highest RGR observed at a sucrose concentration of 0.2 mol·L^-1. The addition of glucose and sucrose also stimulated the accumulation of soluble sugar, and the contents increased with the increasing carbon source concentration. As sucrose concentration enhanced, the chlorophyll a content of N. sphaeroides initially rose and then declined, reaching its peak at 0.2 mol·L^-1. In contrast, high concentrations of sodium pyruvate and sodium acetate inhibited the growth of N. sphaeroides. Additionally, the highest content of soluble proteins was observed at 0.1 mol·L^-1 of sodium pyruvate while the highest phycocyanin content was detected at 0.2 mol·L^-1 of sodium acetate. These findings provided effective strategies and data for the appropriate organic carbon source supplementation of the artificial cultivation of N. sphaeroides.