Search

Understanding the temperature sensitivity (Q 10 ) of carbon (C) mineralization and priming of organic matter with different stabilities in a soil with aged biochar is required to enable better forecasting of biochar C sequestration potential under a warming climate. Here, we quantified the Q 10 and priming of C mineralization in a Vertisol from: (i) newly added labile organic matter (LOM) in the presence of “aged biochars”; and (ii) stable (“aged”) native soil organic matter in the presence of aged biochars or new LOM. We also quantified the Q 10 of aged biochar-C (BC) or aged soil organic carbon (SOC)+BC mineralization. Leaf litter from Eucalyptus saligna (a source of LOM) was applied at 4% w/w (δ 13 C −38‰) to a Vertisol (δ 13 C −14‰), containing either wood, leaf or poultry litter biochar (δ 13 C −25 to −28‰), and nil biochar (control soil), previously incubated for 4 years. These biochar−soil mixtures and the control soil, with or without LOM, were re-incubated at 10, 20, 30 and 40 °C for 252 days. The results showed that 22–39% of LOM-C, 0.10–2.81% of aged BC and 2.4–77.0% of “aged SOC” mineralized across all temperatures over 252 days. The Q 10 of C mineralization increased with decreasing quality of C substrates in the soil, that is, LOM (1.17–1.21) < SOC (1.23–1.66), SOC + BC (1.23–1.60) < aged BC (1.92–2.26). Positive priming of SOC mineralization was greater by LOM (cf. aged biochar), causing a significant decrease in the SOC Q 10 at all temperatures. The aged biochars resulted in negative priming of LOM-C mineralization, mainly at 10 °C, with no impact on the LOM Q 10 . The results suggest that global warming and tropical climates may lower the C sequestration potential of biochar, by reducing its capacity to slow the mineralization of LOM-C, while increasing the mineralization of native SOC. [ABSTRACT FROM AUTHOR]

• MLR and RF were used to estimate current SOC stocks in south-eastern Australia. • Rainfall and minimum temperature were major drivers in determining SOC stocks. • The multi-GCM ensemble means suggested an overall decrease in SOC stocks. • The largest mean decrease of SOC stocks occurs in the high-rainfall alpine regions. Soil organic carbon (SOC) plays a key role in the sequestration of carbon that could otherwise be warming the atmosphere. Climate change including increased temperature and changed rainfall will greatly impact the global SOC cycle. There are still significant gaps in our knowledge of the size of the global SOC pool and how future climate will affect SOC stocks and flows in many parts of the world, including Australia. In this study, we used SOC data in a Digital Soil Mapping framework to predict current and future SOC stocks across the state of New South Wales (NSW) in south-eastern Australia. In the first phase of the study we estimated the current SOC stock using multiple linear regression (MLR) and random forest (RF) modelling, and in the second phase we projected the change of SOC stocks in the near future (2050s) and far future (2090s) under two Shared Socio-economic Pathways (SSPs) scenarios based on 25 global climate models (GCMs) from the Coupled Model Inter-comparison Project Phase 6 (CMIP6). Our spatial modelling showed that estimated current SOC stocks in NSW decreased from east to west. Multi-GCM ensemble means suggested SOC stocks would decrease by 7.6–12.9% under SSP2-4.5 and 9.1–20.9% under SSP5-8.5 across NSW under future climate. The extent of change in SOC stocks varied spatially with the largest mean decrease of SOC stocks occurring in the North Coast and South East (alpine) regions of NSW. Our findings can support decision-making in land management and climate change mitigation strategies in NSW at the regional level. Furthermore, the modelling methods can be applied to other areas where edaphic and landscape properties, land use, and climate data are available. [ABSTRACT FROM AUTHOR]