Dynamics of the nitrogen cycle and paleoproductivity across the Guadalupian-Lopingian Boundary - Qiuping Chen; Hansheng Cao; Fajin Chen; Sheng Hu; Shiqi Li; Chao Huang; Zaiyun Wang; Hanli Huang; Chunqing Chen; Yuda Zeng (Palaeogeography, Palaeoclimatology, Palaeoecology, 2026)