Assessing land-use changes and carbon storage: a case study of the Jialing River Basin, China.

Land-use change is the main driver of carbon storage change in terrestrial ecosystems. Currently, domestic and international studies mainly focus on the impact of carbon storage changes on climate, while studies on the impact of land-use changes on carbon storage in complex terrestrial ecosystems are few. The Jialing River Basin (JRB), with a total area of ~ 160,000 km2, diverse topography, and elevation differences exceeding 5 km, is an ideal case for understanding the complex interactions between land-use change and carbon storage dynamics. Taking the JRB as our study area, we analyzed land-use changes from 2000 to 2020. Subsequently, we simulated land-use patterns for business-as-usual (BAU), cropland protection (CP), and ecological priority (EP) scenarios in 2035 using the PLUS model. Additionally, we assessed carbon storage using the InVEST model. This approach helps us to accurately understand the carbon change processes in regional complex terrestrial ecosystems and to formulate scientifically informed land-use policies. The results revealed the following: (1) Cropland was the most dominant land-use type (LUT) in the region, and it was the only LUT experiencing net reduction, with 92.22% of newly designated construction land originating from cropland. (2) In the JRB, total carbon storage steadily decreased after 2005, with significant spatial heterogeneity. This pattern was marked by higher carbon storage levels in the north and lower levels in the south, with a distinct demarcation line. The conversion of cropland to construction land is the main factor driving the reduction in carbon storage. (3) Compared with the BAU and EP scenarios, the CP scenario demonstrated a smaller reduction in cropland area, a smaller addition to construction land area, and a lower depletion in the JRB total carbon storage from 2020 to 2035. This study demonstrates the effectiveness of the PLUS and InVEST models in analyzing complex ecosystems and offers data support for quantitatively assessing regional ecosystem services. Strict adherence to the cropland replenishment task mandated by the Chinese government is crucial to increase cropland areas in the JRB and consequently enhance the carbon sequestration capacity of its ecosystem. Such efforts are vital for ensuring the food and ecological security of the JRB, particularly in the pursuit of the "dual-carbon" objective.

Effect of tea plantation age on the distribution of glomalin-related soil protein in soil water-stable aggregates in southwestern China.

Glomalin-related soil protein (GRSP) is crucial for the accumulation of soil organic carbon (SOC), and contributes to the formation of soil aggregates. However, it remains unclear whether GRSP is involved in altering the stability of soil aggregates in the long-term tea planting process. The relationship between the distribution of GRSP and soil aggregates in tea plantations is poorly studied. We compared the distribution of SOC and GRSP in aggregates in tea plantations of different ages (18, 25, 33, and 55 years) and those in an abandoned land and investigated their potential contribution to the soil aggregate stability. Tea plantation was found to be beneficial for the accumulation of SOC and GRSP compared to the abandoned land. The content of SOC significantly increased after tea plantation, especially in surface soil (0-20 cm), and the increase range was 21.79%-46.51%, due to the centralized management of tea plantations. The content of total glomalin-related soil protein (T-GRSP) and easily extractable glomalin-related soil protein (EE-GRSP) varied with the increasing tea plantation age. The T-GRSP content was higher in 25-year-old tea plantation, while EE-GRSP was gradually decreased with the increasing age of the tea plantation, and T-GRSP had better correlation with SOC than EE-GRSP. Long-term tea plantation (after 33 years) was not conducive to the preservation of GRSP. The distribution of GRSP in the tea plantation soils differed greatly among the aggregates, with the 0.25-1-mm aggregate having less GRSP, which might be related to the distribution of soil fungi in the aggregates. There was a significant correlation between T-GRSP and mean weight diameter (MWD; P < 0.05) in the whole soil, whereas EE-GRSP had no correlation with the MWD of the aggregates. The T-GRSP content was correlated closely with the stability of soil aggregates in the tea plantations, and their relationship was dependent on the aggregate scale. Our results show that the T-GRSP content in the tea plantation soils has important effects on the formation and stability of aggregates in this region, which was one of the factors affecting the structure and quality of tea plantation soil. Improving GRSP is an effective way for the both SOC sequestration and soil health after long-term tea plantation.

Dynamics of soil organic carbon mineralization in tea plantations converted from farmland at Western Sichuan, China.

Climate warming and land use change are some of the drivers affecting soil organic carbon (SOC) dynamics. The Grain for Green Project, local natural resources, and geographical conditions have resulted in farmland conversion into tea plantations in the hilly region of Western Sichuan. However, the effect of such land conversion on SOC mineralization remains unknown. In order to understand the temperature sensitivity of SOC decomposition in tea plantations converted from farmland, this study considered the different years (i.e., 2-3, 9-10, and 16-17 years) of tea plantations converted from farmland as the study site, and soil was incubated for 28 days at 15°C, 25°C, and 35°C to measure the soil respiration rate, amount, and temperature coefficient (Q10). Temperature and land use type interactively affected the SOC mineralization rate, and the cumulative amount of SOC mineralization in all the plots was the largest at 35°C. SOC mineralization was greater and more sensitive to temperature changes in the farmland than in the tea plantations. Compared with the control, tea plantation soils showed lower SOC mineralization rate and cumulative mineralization amount. The 16-17-year-old tea plantation with a low SOC mineralization amount and high SOC content revealed the benefits of carbon sequestration enhancement obtained by converting farmland into tea plantations. The first-order kinetic equation described SOC mineralization dynamics well. Farmland conversion into tea plantations appeared to reduce the potentially mineralizable carbon pool, and the age of tea plantations also had an effect on the SOC mineralization and sequestration. The relatively weak SOC mineralization temperature sensitivity of the tea plantation soils suggested that the SOC pool of the tea plantation soils was less vulnerable to warming than that of the control soils.