https://nova.newcastle.edu.au/vital/access/ /manager/Index ${session.getAttribute("locale")} 5 https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:33596 Thu 22 Nov 2018 13:48:22 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:24869 13C-labeled Pinus massoniana leaf litter. An orthogonal experiment with three levels of N (0, 81, and 270 mg N kg^-1 soil) and S (0, 121, and 405 mg S kg^-1 soil) was conducted. We traced the incorporation of ¹³C-litter into carbon dioxide (CO₂), dissolved organic C (DOC), and microbial phospholipids. Over the 420-day incubation, litter decomposition did not respond to low N and S additions but increased under high levels and combined amendments (NS). However, litter-derived CO₂ emissions were enhanced during the first 56 days, with a positive interaction of N x S. N additions promoted fungal growth, while S stimulated growth of Gram-positive bacteria, fungi, and actinobacteria. Increased decomposition was related to higher litter-derived DOC and fungi/bacteria ratio. Inversely, N and/or S amendments inhibited decomposition (N > NS > S) from day 57 afterwards, possibly due to C limitation and decreased abundances of Gram-negative bacteria and actinobacteria. These results suggested that N deposition interacted with S to affect litter decomposition, and this effect depended on N and S deposition levels and litter decomposition stage.]]> Sat 24 Mar 2018 07:11:21 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:32293 Pinus massoniana needles were incubated in a subtropical plantation forest soil exposed to: no amendment (Control), N amendments of 81 (N1) and 270 (N2) mg kg⁻¹, S amendments of 121 (S1) and 405 (S2) mg kg⁻¹ and combined N and S amendments. Litter decomposition was measured as litter-derived carbon dioxide (CO₂) emissions and the litter C pools were partitioned using a two-pool model. Relationships between litter residue chemistry (assessed by ¹³C nuclear magnetic resonance spectroscopy analysis) and microbial community composition (probed by phospholipid fatty acid analysis, PLFA) and activity (the metabolic quotient, qCO₂) were investigated. Over the 420 days incubation period, N and S additions (except N and S addition alone at low rate) significantly increased litter decomposition by 7.2–18.9% compared to the Control. Decomposition was stimulated by 10.2–61.9% during the initial 56 days (stage 1) and in contrast, 8.3–42.1% inhibition was measured during 57–420 days (stage 2) across the addition treatments. Stimulation on litter-derived CO₂ emissions under the N and S additions was largely dependent on the loss of O-alkyl C, a dominant component of the litter active C pool. During the initial 7 days, N and S additions increased the ratio of fungal to bacterial PLFAs compared to the Control, which was accompanied by the increases in methoxyl C. The activity of microbes, particularly gram-negative bacteria, was also increased by N and S additions at stage 1, which was related to di-O-alkyl C. In contrast, fungal activity decreased under N and S additions at stage 2, accompanied by lowered C availability and increased methoxyl C. Alkyl C and aromatic C in the litter had positive relationships with the half-life of the slow C pool. Accordingly, the residue recalcitrance was increased under N and S additions compared with Control at stage 2, and was largely responsible for the inhibition of litter decomposition. Thus, N and S deposition is likely to increase the persistence of litter-derived recalcitrant C in subtropical forest soils in the long term.]]> Mon 21 May 2018 15:09:58 AEST ]]>