ABSTRACT
The increasing nitrogen deposition due to human activities has impacted forest ecosystems to a large extent. The organic carbon and nitrogen released from decomposing litters play an important role in the formation, stability and transformation of soil organic carbon and nitrogen. We collected soil samples from a subtropical evergreen broadleaved forest experiment with nitrogen deposition [control (0), LN (75 kg·hm-2·a-1), HN (150 kg·hm-2·a-1)] and litter control (litter retained and litter removal) for eight years. After extracted by solution of K2SO4, Na2B4O7, Na4P2O7, NaOH, H2SO4, Na2S2O4 and HF step by step, carbon and nitrogen in each extraction was analyzed. The results showed that overall most of soil carbon and nitrogen existed in the Humin fraction, accounting for 33.5% of the total carbon and 33.3% of the total nitrogen. The soluble total carbon and nitrogen extracted by Na2B4O7 solution was the highest, followed by NaOH and Na4P2O7 solution. The soluble total carbon, soluble total nitrogen and soluble organic nitrogen of soil extracted by three reagents accounted for 46.2%, 47.9%, and 76.5% of the total extractions, respectively. In addition, nitrogen addition significantly increased carbon and nitrogen content in Na2S2O4 and Humin fractions. Litter removal reduced carbon content in Na2B4O7, H2SO4, Na2S2O4 and Humin fractions, and nitrogen content in NaOH, HF and Humin fractions. The nitrogen content in the K2SO4 extraction was significantly increased by both litter remained and nitrogen addition. Our results demonstrated that litter and nitrogen added could mutually affect carbon and nitrogen concentration of soil fractions with different chemical stability, with consequences on the process of soil carbon and nitrogen.
Subject(s)
Carbon , Forests , Nitrogen , China , Ecosystem , SoilABSTRACT
Seven coordination polymers, namely [Mn(4-cptpy)2]n (1), [Co(4-cptpy)2]n (2), [Mn3(4-cptpy)6(H2O)]n·2nH2O (3), [Co(4-cptpy)(HCOO)(H2O)]n·nDMF (4), [Zn2(4-Hcptpy)2Cl4]n·2nC2H5OH·nH2O (5), [Co4(3-cptpy)4(HCOO)4(H2O)2]n (6), and [Mn(3-cptpy)2]n (7) (4-Hcptpy = 4-(4-carboxyphenyl)-4,2':6',4''-terpyridine; 3-Hcptpy = 4-(4-carboxyphenyl)-3,2':6',3''-terpyridine), have been synthesized under hydro(solvo)thermal conditions and structurally characterized. A general solvothermal method is proposed for preparing carboxylate complexes in DMF solution without any basic additive. 1 and 2 possess isostructural 3D metal-organic frameworks containing nanosized cavities. 3 is a beautiful 2D coordination polymer assembled by flower-like Mn3(4-cptpy)6(H2O) subunits. 4 and 6 both display 2D polymeric networks constructed from 4/3-cptpy(-) ligands, in which the formate ligands originate from the hydrolysis of DMF. 5 is a 1D 2(1) helical chain polymer. 7 shows a 2D network with a (3.6) two-nodal kgd topology. 4/3-Hcptpy ligands display seven types of coordination modes. The zinc complex 5 emits strong violet luminescence. 1 and 2 are both thermally stable below 440 °C and exhibit antiferromagnetic interactions.
