{"type": "FeatureCollection", "features": [{"id": "10.1007/s10533-021-00838-z", "type": "Feature", "geometry": null, "properties": {"updated": "2026-06-23T16:15:20Z", "type": "Journal Article", "created": "2021-08-27", "title": "Soil organic matter turnover rates increase to match increased inputs in grazed grasslands", "description": "Abstract

Managed grasslands have the potential to store carbon (C) and partially mitigate climate change. However, it remains difficult to predict potential C storage under a given soil or management practice. To study C storage dynamics due to long-term (1952\uffe2\uff80\uff932009) phosphorus (P) fertilizer and irrigation treatments in New Zealand grasslands, we measured radiocarbon (14C) in archived soil along with observed changes in C stocks to constrain a compartmental soil model. Productivity increases from P application and irrigation in these trials resulted in very similar C accumulation rates between 1959 and 2009. The \uffe2\uff88\uff8614C changes over the same time period were similar in plots that were both irrigated and fertilized, and only differed in a non-irrigated fertilized plot. Model results indicated that decomposition rates of fast cycling C (0.1 to 0.2\uffc2\uffa0year\uffe2\uff88\uff921) increased to nearly offset increases in inputs. With increasing P fertilization, decomposition rates also increased in the slow pool (0.005 to 0.008\uffc2\uffa0year\uffe2\uff88\uff921). Our findings show sustained, significant (i.e. greater than 4 per mille) increases in C stocks regardless of treatment or inputs. As the majority of fresh inputs remain in the soil for less than 10\uffc2\uffa0years, these long term increases reflect dynamics of the slow pool. Additionally, frequent irrigation was associated with reduced stocks and increased decomposition of fresh plant material. Rates of C gain and decay highlight trade-offs between productivity, nutrient availability, and soil C sequestration as a climate change mitigation strategy.The radiocarbon signature of respired CO2 (\uffe2\uff88\uff8614C\uffe2\uff80\uff90CO2) measured in laboratory soil incubations integrates contributions from soil carbon pools with a wide range of ages, making it a powerful model constraint. Incubating archived soils enriched by \uffe2\uff80\uff9cbomb\uffe2\uff80\uff90C\uffe2\uff80\uff9d from mid\uffe2\uff80\uff9020th century nuclear weapons testing would be even more powerful as it would enable us to trace this pulse over time. However, air\uffe2\uff80\uff90drying and subsequent rewetting of archived soils, as well as storage duration, may alter the relative contribution to respiration from soil carbon pools with different cycling rates. We designed three experiments to assess air\uffe2\uff80\uff90drying and rewetting effects on \uffe2\uff88\uff8614C\uffe2\uff80\uff90CO2 with constant storage duration (Experiment 1), without storage (Experiment 2), and with variable storage duration (Experiment 3). We found that air\uffe2\uff80\uff90drying and rewetting led to small but significant (\uffce\uffb1\uffc2\uffa0<\uffc2\uffa00.05) shifts in \uffe2\uff88\uff8614C\uffe2\uff80\uff90CO2 relative to undried controls in all experiments, with grassland soils responding more strongly than forest soils. Storage duration (4\uffe2\uff80\uff9314\uffc2\uffa0y) did not have a substantial effect. Mean differences (95% CIs) for experiments 1, 2, and 3 were: 23.3\uffe2\uff80\uffb0 (\uffc2\uffb16.6), 19.6\uffe2\uff80\uffb0 (\uffc2\uffb110.3), and 29.3\uffe2\uff80\uffb0 (\uffc2\uffb129.1) for grassland soils, versus \uffe2\uff88\uff9211.6\uffe2\uff80\uffb0 (\uffc2\uffb14.1), 12.7\uffe2\uff80\uffb0 (\uffc2\uffb18.5), and \uffe2\uff88\uff9224.2\uffe2\uff80\uffb0 (\uffc2\uffb113.2) for forest soils. Our results indicate that air\uffe2\uff80\uff90drying and rewetting soils mobilizes a slightly older pool of carbon that would otherwise be inaccessible to microbes, an effect that persists throughout the incubation. However, as the bias in \uffe2\uff88\uff8614C\uffe2\uff80\uff90CO2 from air\uffe2\uff80\uff90drying and rewetting is small, measuring \uffe2\uff88\uff8614C\uffe2\uff80\uff90CO2 in incubations of archived soils appears to be a promising technique for constraining soil carbon models.Managed grasslands have the potential to store carbon (C) and partially mitigate climate change. However, it remains difficult to predict potential C storage under a given soil or management practice. To study C storage dynamics due to long-term (1952\uffe2\uff80\uff932009) phosphorus (P) fertilizer and irrigation treatments in New Zealand grasslands, we measured radiocarbon (14C) in archived soil along with observed changes in C stocks to constrain a compartmental soil model. Productivity increases from P application and irrigation in these trials resulted in very similar C accumulation rates between 1959 and 2009. The \uffe2\uff88\uff8614C changes over the same time period were similar in plots that were both irrigated and fertilized, and only differed in a non-irrigated fertilized plot. Model results indicated that decomposition rates of fast cycling C (0.1 to 0.2\uffc2\uffa0year\uffe2\uff88\uff921) increased to nearly offset increases in inputs. With increasing P fertilization, decomposition rates also increased in the slow pool (0.005 to 0.008\uffc2\uffa0year\uffe2\uff88\uff921). Our findings show sustained, significant (i.e. greater than 4 per mille) increases in C stocks regardless of treatment or inputs. As the majority of fresh inputs remain in the soil for less than 10\uffc2\uffa0years, these long term increases reflect dynamics of the slow pool. Additionally, frequent irrigation was associated with reduced stocks and increased decomposition of fresh plant material. Rates of C gain and decay highlight trade-offs between productivity, nutrient availability, and soil C sequestration as a climate change mitigation strategy.The radiocarbon signature of respired CO2 (\uffe2\uff88\uff8614C\uffe2\uff80\uff90CO2) measured in laboratory soil incubations integrates contributions from soil carbon pools with a wide range of ages, making it a powerful model constraint. Incubating archived soils enriched by \uffe2\uff80\uff9cbomb\uffe2\uff80\uff90C\uffe2\uff80\uff9d from mid\uffe2\uff80\uff9020th century nuclear weapons testing would be even more powerful as it would enable us to trace this pulse over time. However, air\uffe2\uff80\uff90drying and subsequent rewetting of archived soils, as well as storage duration, may alter the relative contribution to respiration from soil carbon pools with different cycling rates. We designed three experiments to assess air\uffe2\uff80\uff90drying and rewetting effects on \uffe2\uff88\uff8614C\uffe2\uff80\uff90CO2 with constant storage duration (Experiment 1), without storage (Experiment 2), and with variable storage duration (Experiment 3). We found that air\uffe2\uff80\uff90drying and rewetting led to small but significant (\uffce\uffb1\uffc2\uffa0<\uffc2\uffa00.05) shifts in \uffe2\uff88\uff8614C\uffe2\uff80\uff90CO2 relative to undried controls in all experiments, with grassland soils responding more strongly than forest soils. Storage duration (4\uffe2\uff80\uff9314\uffc2\uffa0y) did not have a substantial effect. Mean differences (95% CIs) for experiments 1, 2, and 3 were: 23.3\uffe2\uff80\uffb0 (\uffc2\uffb16.6), 19.6\uffe2\uff80\uffb0 (\uffc2\uffb110.3), and 29.3\uffe2\uff80\uffb0 (\uffc2\uffb129.1) for grassland soils, versus \uffe2\uff88\uff9211.6\uffe2\uff80\uffb0 (\uffc2\uffb14.1), 12.7\uffe2\uff80\uffb0 (\uffc2\uffb18.5), and \uffe2\uff88\uff9224.2\uffe2\uff80\uffb0 (\uffc2\uffb113.2) for forest soils. Our results indicate that air\uffe2\uff80\uff90drying and rewetting soils mobilizes a slightly older pool of carbon that would otherwise be inaccessible to microbes, an effect that persists throughout the incubation. However, as the bias in \uffe2\uff88\uff8614C\uffe2\uff80\uff90CO2 from air\uffe2\uff80\uff90drying and rewetting is small, measuring \uffe2\uff88\uff8614C\uffe2\uff80\uff90CO2 in incubations of archived soils appears to be a promising technique for constraining soil carbon models.