(1) Objective: To investigate the chemical defense response mechanisms of two cotton (Gossypium hirsutum L., Malvaceae) varieties, Xinlu Zhong 57 and Xinlu Zhong 78, in response to feeding by the cotton aphid (Aphis gossypii Glover, 1877) (Hemiptera: Aphididae) in the Kashi region. (2) Methods: The artificial infestation method was adopted to determine the dynamic changes in the contents of secondary metabolites (tannins, total phenols), activities of protective enzymes (SOD, POD, PPO), and contents of nutrients (soluble sugars, amino acids) in cotton leaves at 0, 24, 48, 72, and 96 h after infestation with cotton aphids. (3) Results: The contents of secondary metabolites and the activities of protective enzymes in both varieties showed an initial increase followed by a decrease. The response of Xinlu Zhong 57 was earlier and stronger. Its tannin and total phenol contents reached a peak at 48 h, with values of 264.2 nmol/g and 5.973 mg/g, respectively, which were significantly higher than those of Xinlu Zhong 78 (p < 0.05). The activities of SOD, POD, and PPO were consistently higher in Xinlu Zhong 57. At 48 h post-inoculation, SOD activity in Xinlu Zhong 57 was 238.1 U/g, significantly higher than in Xinlu Zhong 78 (p < 0.05). POD activity was 49.0 U/g, and PPO activity was 94.5 U/g, both significantly higher than those of Xinlu Zhong 78 (p < 0.05). This suggests that Xinlu Zhong 57 has a stronger ability to scavenge reactive oxygen species. Regarding nutrients, soluble sugar content in Xinlu Zhong 57 was 6.99 mg/g at 96 h, significantly higher than that in Xinlu Zhong 78 (p < 0.05). The amino acid content at 96 h was 224.4 μg/g, also significantly higher than in Xinlu Zhong 78 (p < 0.05). (4) Conclusions: Xinlu Zhong 57 forms a more effective chemical defense system by rapidly activating the defense enzyme system, efficiently accumulating secondary metabolites, and optimizing nutrient allocation. This study provides a theoretical basis for elucidating the physiological mechanisms of cotton resistance induced by cotton aphids by analyzing the effects of cotton aphid stress on the contents of secondary metabolites, protective enzyme activities, and nutrient contents in cotton leaves.

A field experiment was conducted to explore how long-term integrated organic or inorganic fertilization influences soil bacterial communities in dryland farming systems. High-throughput amplicon sequencing was applied to profile bacterial composition and diversity under six treatments—no fertilizer (T0), chemical fertilizer alone (T1), and chemical fertilizer combined with cattle manure (T2), sheep manure (T3), bio-organic fertilizer (T4), or potassium fulvate (T5)—and to pinpoint the major environmental determinants. The results showed that combined fertilization markedly elevated soil nutrient levels, with cattle manure (T2) and sheep manure (T3) exhibiting the strongest effects. The bacterial community was dominated by Actinomycetota, Pseudomonadota, and Chloroflexota. Relative abundances of Pseudomonadota and Bacteroidota increased under combined fertilization, whereas Actinomycetota declined—particularly in T2 and T3. At the genus level, Nocardioides, KD4-96, and Subgroup 6 were predominant. Moreover, T2 and T3 significantly raised the Simpson index relative to T1. Redundancy analysis revealed that soil organic matter (p = 0.002) and pH (p = 0.03) were strongly associated with variation in bacterial community composition. Collectively, long-term combined organic-inorganic fertilization with different organic amendments effectively enhances soil fertility and bacterial community structure, offering a promising approach for nutrient management in the dryland farming regions of the Ningxia Hui Autonomous Region, northwestern China.