Department of Soil and Physical Sciences
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The Department of Soil and Physical Sciences has responsibility for the delivery of all undergraduate and postgraduate soil-related subjects, and many physical science subjects.
The range of research being undertaken is extensive but in recent years has increasingly focused on environmental issues, especially soil's role and influence on water and air quality.
Recent Submissions
Item Contrasting response of comammox Nitrospira, ammonia oxidising bacteria, and archaea to soil pH and nitrogen inputs(Elsevier B.V., 2024-05-10) Chisholm, C; Di, Hong; Cameron, Keith; Podolyan, Andriy; Shen, J; Zhang, L; Sirisena, Kosala; Godsoe, WilliamThis study aimed to investigate the effect of soil pH change, and nitrogen amendment on ammonia oxidiser abundance and comammox Nitrospira community composition. The experimental design used soil mesocosms placed in a temperature-controlled incubator for 90 days. A Templeton silt loam was used as its physiochemical properties are typical of the region's dairy farms. The results showed that comammox Nitrospira clade B preferred the natural (pH 6.1–6.2) soil pH with no applied nitrogen. Furthermore, synthetic urine (N700) decreased the abundance of comammox Nitrospira clade B. This may have been because the large amounts of available ammonia in the N700 treatments inhibited the growth of comammox Nitrospira. These results suggest that while comammox Nitrospira clade B are present in New Zealand dairy farm soils, but their role in nitrification in the very high nitrogen environment under a urine patch in grazed pastures may be limited. Further research is needed to confirm this. In contrast to comammox, the AOB community (dominated by Nitrosospira) responded positively to the application of synthetic urine. The response was greatest in the high pH soil (7.1), followed by the natural and then the low pH (4.9) soils. This may be due to the difference in ammonia availability. At high pH, the ammonia/ammonium equilibrium favours ammonia production. Calculated ammonia availability in the N700 treatments accurately predicted the AOB amoA gene abundance. Interestingly, the AOA community abundance (which was predominantly made up of Thaumarchaeota group I.1b clade E) seemed to prefer the natural and high pH soils over the low pH. This may be due to the specific lineage of AOA present. AOA did not respond to the application of nitrogen.Item Thermal adaptation of soil microbial functional responses: Insights from a geothermal gradient in Aotearoa New Zealand(2023) Alster, Charlotte; van de Laar, A; Arcus, V; Prentice, E; Bååth, E; Schipper, LNatural soil temperature gradients provide an excellent proxy to study how soil microbial communities, and their associated activities, will adapt to global warming. The rate at which soil microbes adapt to warming has important implications for biogeochemical cycling and predictions of soil carbon loss. In Aotearoa New Zealand, we take advantage of a decades long geothermal gradient, ranging from 15-42°C mean annual soil temperature, to investigate thermal adaptation of soil microbial respiration (with unlimited substrate), bacterial growth, and extracellular enzyme activities (β-glucosidase, acid phosphatase, and N-acetyl-β-ᴅ-glucosaminidase). We sampled soils from across this gradient and constructed temperature response curves for each soil sample in the lab by incubating them at six or more different temperatures. Using these temperature response curves, we then estimated rates of thermal adaptation for each microbial function and compared how different microbial processes adapt differentially. Despite major changes in microbial community diversity and composition along the gradient, we found only modest shifts in thermal adaptation of the microbial functional responses. The temperature response curves for soil microbial respiration and bacterial growth increased at a rate of approximately 0.2°C per 1°C increase in mean annual temperature. In contrast, we did not find a significant relationship between mean soil temperature and the temperature response of extracellular enzyme activity, suggesting that temperature responses are highly conserved across a variety of soil microbial functions. Nonetheless, it is important to consider how these changes in microbial rates may affect predictions of soil carbon loss with global warming.Item Quantifying soil microbial thermal adaptation(2024-04) Alster, C; van de Laar, A; Goodrich, J; Arcus, V; Deslippe, J; Marshall, A; Schipper, LThermal adaptation of soil microbial respiration has the potential to greatly alter carbon cycle-climate feedbacks through acceleration or reduction of soil microbial respiration as the climate warms. However despite its importance, the relationship between warming and soil microbial activity remains poorly constrained. Part of this uncertainty stems from persistent methodological issues and difficulties isolating the interacting effects of changes in microbial community responses from changes in soil carbon availability. To address these challenges, we sampled nearly 50 soils from around New Zealand, including from a long-term geothermal gradient, with mean annual temperatures ranging from 11-35°C. For each of these soils we constructed temperature response curves of microbial respiration given unlimited substrate and estimated a temperature optima (Topt) and inflection point (Tinf). We found that thermal adaptation of microbial respiration occurred at a rate of 0.29°C ± 0.04 1SE for Topt and 0.27°C ± 0.05 1SE for Tinf per degree of warming, demonstrating that thermal adaptation is considerably offset from warming. These relatively small changes occurred despite large structural shifts in microbial community composition and diversity. We also quantitatively assessed how thermal adaptation may alter potential respiration rates under future warming scenarios by consolidating all of the temperature response curves. Depending on the specific mean and instantaneous soil temperatures, we found that thermal adaptation of microbial respiration could both limit and accelerate soil carbon losses. This work highlights the importance of considering the entire temperature response curve when making predictions about how thermal adaptation of soil microbial respiration will influence soil carbon losses.Item Nitrous oxide emission factors for fertiliser ammonium sulphate, diammonium phosphate, and urea(Taylor & Francis, 2023) Luo, J; van der Weerden, T; Saggar, S; Di, Hong; Podolyan, Andriy; Adhikari, K; Ding, K; Lindsey, S; Luo, D; Ouyang, L; Rutherford, AThis study determined the nitrous oxide emission factors (EF₁, the percentage of N₂O emitted as a proportion of fertiliser N applied) for fertilisers ammonium sulphate (AS), diammonium phosphate (DAP), and urea under the same field conditions. Trials were conducted on pasture soils across four sites (Waikato, Manawatu, Canterbury and Otago) in New Zealand during late autumn and spring of 2022. The average EF₁ values for urea across all four sites were 0.128% (95% C.I., 0.023% and 0.249%) in late autumn and 0.136% (95% C.I., 0.031% and 0.259%) in spring. The corresponding EF₁ values for AS were 0.125% (95% C.I., - 0.021% and 0.246%) in late autumn and 0.083% (95% C.I., 0.015% and 0.197%) in spring, while for DAP, they were 0.049% (95% C.I., - 0.044% and 0.157%) in late autumn and 0.090% (95% C.I., -0.009% and 0.205%) in spring. The mean EF₁ values across all four sites and two seasons were calculated as 0.132% (95% C.I., 0.016% and 0.269%) for urea, 0.104% (95% C.I., - 0.008% and 0.235%) for AS, and 0.069% (95% C.I., - 0.036 and 0.194) for DAP. No significant differences in EF₁ were observed between the three fertilisers (P > 0.05) at individual sites or when considering all four sites collectively.Item Comammox bacteria and ammonia oxidizing archaea are major drivers of nitrification in glacier forelands(Elsevier, 2023-12) Yu, H; Shen, J; Zeng, J; Hu, H-W; Pendall, E; Xiao, H; Liu, Z; Zhang, H; Di, Hong; Li, Z; He, J-ZThis study investigated the abundance of comammox bacteria and canonical ammonia-oxidizing bacteria (AOB) and archaea (AOA), and their relative contribution to nitrification along a chronosequence of deglaciated forelands. The results showed that nitrification related gene abundance tended to increase with glacier retreat, with comammox bacteria and AOA appearing to be the most critical drivers for soil nitrification rates. These findings provide new evidence for the presence of comammox bacteria in glacier forelands and enhance our understanding of the niche differentiation of canonical nitrifier and comammox bacteria.