Saline soils in coastal areas, such as reclaimed tideland (RTL), are commonly used for rice (Oryza sativa L.) cultivation as excessive salts can be removed through leaching by irrigation during rice growth though a high salinity still hampers rice growth. The coastal RTLs are also characterized by a low soil organic carbon (SOC) content, implying that the RTL soils can store large amounts of C additionally. In this context, rice cultivation with organic input (including rice residue) and fertilizer may be useful in meeting the food demand as well as enhancing SOC sequestration in coastal RTL soils. In this study, to understand the inter-correlations among rice cultivation year and change in salinity, rice biomass and yield, and SOC in coastal RTLs, the changes in salinity (measured as electrical conductivity of soil extracts, EC_e), SOC content, and rice biomass and yield at 10 RTLs sites that have different rice cultivation years (13-35 years) were investigated. In March of 2019, surface soil (0-20 cm) samples were collected from 72 selected fields (3 to 12 for each RTL site) of the RTLs sites and analyzed for chemical properties, and rice biomass and yield were determined at harvest season (October). Comparing among 10 RTLs, the mean EC_e decreased (r²=0.80, P=0.003) with cultivation year, but neither SOC contents nor rice biomass and yield was correlated with cultivation year. When all the data (n=72) were pooled across of RTLs, however, rice biomass (r²=0.44, P<0.001) and yield (r²=0.33, P<0.001) as well as SOC content (r²=0.25, P<0.001) were negatively correlated with EC_e. These results suggest that continuous rice cultivation in RTLs may be helpful in desalinization of coastal RTL soils, but rice growth and SOC content might be affected field-specific conditions including not only salinity but also nutrient managements. (Funding sources: BK21 and RDA)

Land-use types and thus farmers’ fertilization practices, particularly application of livestock manure and compost which are typically enriched with heavy isotopes of carbon (C) and nitrogen (N) as well as copper (Cu) and zinc (Zn), may change these chemical variables in agricultural soils. This study was conducted to investigate variations in the concentrations of C, N, Cu and Zn, and stable C (δ¹³C) and N (δ¹⁵N) isotope ratios of paddy, upland, and orchard soils that received different rate of manure and compost. Forest soils were additionally included as background soils. The elemental and isotopic compositions of agricultural inputs (including synthetic fertilizer, rice straw, and livestock feed, manure, and compost) and forest litter layer were also analyzed. There was no systematic variation in soil C and N concentrations among different land-use types. However, the δ¹³C, δ¹⁵N, and the concentrations of Cu and Zn of agricultural soils were higher than those of forest soils, possibly reflecting higher inputs such as synthetic fertilizers, manures, and composts in agricultural soils. Among agricultural soils, orchard soils which received higher rates of manure and compost had higher δ¹³C (‒24.2‰), δ¹⁵N (+10.6‰), and the concentrations of Cu (16.3 mg kg^-1) and Zn (61.7 mg kg^-1), compared to paddy (‒28.0‰, +4.9‰, 10.3 mg kg^-1, and 41.9 mg kg^-1 for δ¹³C, δ¹⁵N, and Cu and Zn concentrations, respectively) and upland soils (‒25.4‰, +9.6‰, 11.8 mg kg^-1, and 41.7 mg kg^-1, respectively). Such differences in the isotopic and metal compositions among agricultural soils were also found for soil solutions extracted with K₂SO₄. Our study suggests that agricultural land-use types and associated farmers’ fertilization practices such as repeated application of livestock manure and compost may change δ¹³C, δ¹⁵N, and Cu and Zn concentrations of agricultural soils. (Funding sources: BK21 project and RDA)

The large soil organic carbon (SOC) storage capacity of volcanic ash soils is attributed to physical and chemical stabilization of SOC. However, variability of SOC content in relation with the physico-chemical properties of soils under different land-uses is not fully understood. This study was conducted to understand the effects of physico-chemical properties of soils on the content of total SOC and humus fractions (including fulvic acid, humic acid, and humin) of volcanic ash soils under different land-uses (cropland, coniferous forest, and deciduous forest). Top mineral (0‒10 cm) soil as well as litter and organic (FH) layer (for forest soils only) samples were collected from seven sites of each land-use. Mineral soils were analyzed for physico-chemical properties associated with SOC content that include clay content, aggregate size distribution, pH, and active Al and Fe concentration as well as total SOC and humus. Cropland soils had lower SOC (by 5-fold) and humus (4-fold) than forest soils, and these were associated with lower Al and Fe concentrations (and higher pH) as well as lower content of clay and macro-aggregates of cropland soils, probably due to agricultural practices such as liming and tillage. Between coniferous and deciduous forest soils, no difference in SOC and humus concentration was found. Concentrations of SOC and humus increased with increasing clay content and metal (Al and Fe) concentrations, indicating that clay and active metals are drivers of SOC accumulation in the study forest Andisols. This study enlarges our understanding on the variations in SOC of volcanic ash soils with soil properties under different land-uses.

Natural stable carbon and nitrogen isotopes ratio (δ¹³C and δ¹⁵N) can be used to estimate the C and N dynamics in the plant-soil ecosystems. Vegetation changes affect soil C and N dynamics to contribute global and local environmental problems, including global warming. The purpose of this study was to investigate how different vegetation changes (including non-vegetation) on soil C and N dynamics by a concrete frames experiment. Nine concrete frames were filled with soil in the winter of 2016. The soil was collected from pasture in the farm of Yamagata University, where C3 plant, Reed canarygrass (Phalaris arundinacea L.) was cultivated. There are three treatments in the study as: 1) C4 plant, Japanese susuki (Miscanthus sinensis); 2) nitrogen-fixed C3 plant, white clover (Trifolium repens); 3) no vegetation, which soil surface was covered by black sheet and stone. The experiment was begun in April 2017 and soils and plants samples were taken from the treatments on every October. Then C and N contents of soil and plant samples, and their δ¹³C and δ¹⁵N values were measured. As the result until 2020, Soil N was not change, but soil C increased significantly in susuki treatment. The δ¹³C of surface soil in the susuki treatment rose from -25.24 ‰ to -19.86 ‰. Based on the mass balance method, 42.7 % of the total soil C was from new C4 plant-derived C. The both of soil C and N were increased in clover treatment, 26.0 % of the total N was from N fixation by legume clover. For no vegetation treatment, both soil C and N contents were decreased, while the δ¹³C value was increased and δ¹⁵N values was decreased lightly after 4 years without vegetation.

Elevation-related differences in tree growth-climate relationships are very important for understanding the influence of climate change on forest production and carbon sequestration. However, it is not clear how trees (both conifers and broadleaved) will respond to climate change in China's subtropical zone. Here, we present a tree ring study to reveal the dendroclimatological differences between Pinus massoniana and Castanopsis eyrei growing at two elevations (400m and 890m) at the northern Luoxiao Mountains in Central South China. Results show that the long-term drought caused by rapid warming and reduced precipitation after the 1990s led to a significant (p<0.05) decline in radial growth of trees at all sites except low elevation P. massoniana. Relationships of radial growth of two species differ with elevations. The radial growth of P. massoniana from high elevation was significantly and positively correlated with C. eyrei at both low and high elevation sites but weakly correlated with P. massonianaat thelow elevation site. The radial growth of P.massoniana at a high elevation site was significantly and positively correlated with relative humidity and negatively correlated with vapor pressure deficit (especially in the winter season). Temperatures in almost all seasons were significantly and negatively correlated with the radial growth of C. eyrei. The relationship between relative humidity and radial growth of P. massoniana at high elevation showed an increasing trend with time, while P. massoniana at low elevation showed the opposite. At the two elevations, the relationships between C. eyrei growth and precipitation gradually increased, and the relationships with the temperature gradually weakened. Overall, the two coniferous and broadleaved tree species in subtropical forests have shown different responses to recent climate change, which should be considered in future forest management, vegetation restoration and prediction model on vegetation dynamics and carbon cycle processes.