Critical factors in soil organic carbon mineralization induced by drying, wetting and wet-dry cycles in a typical watershed of Loess Plateau.

As global climate change progresses, soil will experience prolonged periods of both drought and heavy rainfall, leading to a more frequent drought-re-wetting process that may impact the ecosystem's carbon (C) cycle. However, understanding the extent to which different water conditions and wet-dry cycles alter the process of soil organic carbon (SOC) mineralization remains limited. Therefore, our study focused on the dammed land unique to the Loess Plateau, silted by check dams constructed for erosion control. We implemented three water gradients-drought (30% WHC), water stress (100% WHC), and wet-dry cycling (30-100%)-indoors to observe the SOC mineralization process five times. We identified a transient excitation effect of the wet-dry cycles on SOC mineralization. Soil mineralization decreased gradually with the alternation of wet-dry cycles. The wet-dry cycles not only significantly impacted the contents of SOC and TN but also stimulated the activities of enzymes related to C and N cycles. As the cycle frequency increased, the utilization of C sources by soil microorganisms gradually decreased, and the dominance of carbohydrates, amines, and acids evolved into a single acid, esters, or alcohols. Phosphatase and Chloroflexi were the main factors influencing SOC mineralization under drought stress, while TN and Ascomycota were the primary factors under water stress. SOC and Gemmatimonadetes were the main limiting factors for SOC mineralization under the wet-dry cycles. Additionally, we quantified the direct and interactive contributions of each factor to SOC mineralization. The direct contributions of drought stress, water stress, and the wet-dry cycles to SOC mineralization were 0.961, 0.736, and 0.942, respectively. This study contributes to a more comprehensive understanding of the mechanisms underlying SOC mineralization in the Loess Plateau under changing conditions.

The therapeutic effect of radiotherapy combined with systemic therapy compared to radiotherapy alone in patients with simple brain metastasis after first-line treatment of limited-stage small cell lung cancer: a retrospective study.

PURPOSE: We aimed to compare the therapeutic effect of radiotherapy (RT) plus systemic therapy (ST) with RT alone in patients with simple brain metastasis (BM) after first-line treatment of limited-stage small cell lung cancer (LS-SCLC). METHODS: The patients were treated at a single center from January 2011 to January 2022. BM only without metastases to other organs was defined as simple BM. The eligible patients were divided into RT alone (monotherapy arm) and RT plus ST (combined therapy arm). Univariate and multivariate Cox proportional hazards analyses were used to examine factors associated with increased risk of extracranial progression. After 1:1 propensity score matching analysis, two groups were compared for extracranial progression-free survival (ePFS), PFS, overall survival (OS), and intracranial PFS (iPFS). RESULTS: 133 patients were identified and 100 were analyzed (monotherapy arm: n = 50, combined therapy arm: n = 50). The ePFS of the combined therapy was significantly longer than that of the monotherapy, with a median ePFS of 13.2 months (95% CI, 6.6-19.8) in combined therapy and 8.2 months (95% CI, 5.7-10.7) in monotherapy (P = 0.04). There were no statistically significant differences in PFS (P = 0.057), OS (P = 0.309), or iPFS (P = 0.448). Multifactorial analysis showed that combined therapy was independently associated with better ePFS compared with monotherapy (HR = 0.617, P = 0.034); more than 5 BMs were associated with worse ePFS compared with 1-5 BMs (HR = 1.808, P = 0.012). CONCLUSIONS: Compared with RT alone, combined therapy improves ePFS in patients with simple BM after first-line treatment of LS-SCLC. Combined therapy and 1-5 BMs reduce the risk of extracranial recurrence.