Nitrogen functional gene activity in soil profiles under progressive vegetative recovery after abandonment of agriculture at the Puding Karst Critical Zone Observatory, SW China. (October 2018)

• Record Type: Journal Article
• Authors: Li, Dandan; Zhang, Xinyu; Green, Sophie M.; Dungait, Jennifer A.J.; Wen, Xuefa; Tang, Yuqian; Guo, Zhiming; Yang, Yang; Sun, Xiaomin; Quine, Timothy A.
• Is Part Of: Soil biology and biochemistry. Volume 125(2018)
• Page Start: 93
• Page End: 102
• Publication Date: 2018-10
• Subjects: Nitrogen functional genes -- Soil profile -- Vegetation recovery -- Karst ecosystems -- Nitrate -- Phosphorus; Soil biochemistry -- Periodicals; Soil biology -- Periodicals; Sols -- Biochimie -- Périodiques; Sols -- Biologie -- Périodiques; Sols -- Microbiologie -- Périodiques; Bodembiologie; Biochemie; 631.46
• DOI: 10.1016/j.soilbio.2018.07.004
• Languages: English
• ISSNs: 0038-0717

Abstract

Abstract: At the end of the 20th century, China launched the 'Grain-for-Green' Project (GGP) that recommended the abandonment of low-yielding sloping farmland (>15°) prone to soil degradation by erosion, to allow recovery through natural vegetative regeneration. The effect of this policy on soil nitrogen (N) cycling, as fertilization applications are also withdrawn after abandonment, is poorly understood. A space-for-time approach was applied to investigate the responses of nitrogen functional genes (NFGs) in soil profiles (surface to bedrock) associated with progressive vegetative recovery (sloping farmland > recently abandoned sloping farmland > secondary forest > primary forest) at the Puding Karst Critical Zone Observatory in Guizhou province, southwest China. Coincident soil chemical properties (dissolved organic carbon (DOC), nitrate ( N O 3 - -N), ammonium ( N H 4 + -N), available inorganic phosphorus (AP), soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP)) were also quantified. We found that the absolute abundance of NFGs significantly varied according to the phase of vegetation recovery, and that concentrations of AP and N O 3 - -N were the best explanatory variables. The external N from fertilizer application promoted the absolute abundances of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in sloping farmland. The relative abundances of chiA (associated with decomposition) increased with soil depth across all vegetation recovery phases. The relative abundances of chiA and nifH (associated with N fixation) accounted for the largest proportion (58–72%) of the measured NFGs, indicating that active N-acquisition increased along the vegetation recovery gradient. The ratios of (chiA + nifH)/(AOA + AOB) and the sums of (nirK + nirS) were larger in the forest soil than those of sloping farmland and abandoned sloping farmland, implying a greater capacity for N storage potential, though accompanied by increased gas N emission potential, in the karst forest ecosystems. Our results provide a new and comprehensive understanding of soil N cycling potentials at the microscale in degraded and recovering karst ecosystems. Highlights: The abundances of total NFGs increased with vegetation recovery gradient. Soil nitrate and available phosphorus contributed to the variations in NFGs. The N resource acquisition genes (nifH + chiA) accounted for 58–72% of the NFGs. The absolute and relative abundances of nirK and nirS decreased with soil depth. The (chiA + nifH)/(AOA + AOB) ratios increased with vegetation recovery gradient.