Nitrogen and Biochar Addition Affected Plant Traits and Nitrous Oxide Emission From Cinnamomum camphora.

Atmospheric nitrous oxide (N2O) increase contributes substantially to global climate change due to its large global warming potential. Soil N2O emissions have been widely studied, but plants have so far been ignored, even though they are known as an important source of N2O. The specific objectives of this study are to (1) reveal the effects of nitrogen and biochar addition on plant functional traits and N2O emission of Cinnamomum camphora seedlings; (2) find out the possible leaf traits affecting plant N2O emissions. The effects of nitrogen and biochar on plant functional traits and N2O emissions from plants using C. camphora seedlings were investigated. Plant N2O emissions, growth, each organ biomass, each organ nutrient allocation, gas exchange parameters, and chlorophyll fluorescence parameters of C. camphora seedlings were measured. Further investigation of the relationships between plant N2O emission and leaf traits was performed by simple linear regression analysis, principal component analysis (PCA), and structural equation model (SEM). It was found that nitrogen addition profoundly increased cumulative plant N2O emissions (+109.25%), which contributed substantially to the atmosphere's N2O budget in forest ecosystems. Plant N2O emissions had a strong correlation to leaf traits (leaf TN, P n , G s , C i , Tr, WUE L , α, ETR max, I k , Fv/Fm, Y(II), and SPAD). Structural equation modelling revealed that leaf TN, leaf TP, P n , C i , Tr, WUE L , α, ETR max, and I k were key traits regulating the effects of plants on N2O emissions. These results provide a direction for understanding the mechanism of N2O emission from plants and provide a theoretical basis for formulating corresponding emission reduction schemes.

Responses of microbial function, biomass and heterotrophic respiration, and organic carbon in fir plantation soil to successive nitrogen and phosphorus fertilization.

Carbon dioxide (CO2) emissions from forest ecosystems originate largely from soil respiration, and microbial heterotrophic respiration plays a critical role in determining organic carbon (C) stock. This study investigated the impacts of successive nitrogen (N) and phosphorus (P) fertilization after 9 years on soil organic C stock; CO2 emission; and microbial biomass, community, and function in a Chinese fir plantation. The annual fertilization rates were (1) CK, control without N or P fertilization; (2) N50, 50 kg N ha-1; (3) N100, 100 kg N ha-1; (4) P50, 50 kg P ha-1; (5) N50P50, 50 kg N ha-1 + 50 kg P ha-1; and (6) N100P50, 100 kg N ha-1 + 50 kg P ha-1. The N100P50 treatment had the highest cumulative soil CO2 emissions, but the CK treatment had the lowest cumulative soil CO2 emissions among all treatments. The declines of soil organic C (SOC) after successive 9-year fertilization were in the order of 100 kg N ha-1 year-1 > 50 kg N ha-1 year-1 > CK. Compared to the CK treatment, successive N fertilization significantly changed soil microbial communities at different application rates and increased the relative gene abundances of glycoside hydrolases, glycosyl transferases, carbohydrate-binding modules, and polysaccharide lyases at 100 kg N ha-1 year-1. Relative to P fertilization alone (50 kg P ha-1 year-1), combined N and P fertilization significantly altered the soil microbial community structure and favored more active soil microbial metabolism. Microbial community and metabolism changes caused by N fertilization could have enhanced CO2 emission from heterotrophic respiration and eventually led to the decrease in organic C stock in the forest plantation soil. KEY POINTS: • N fertilization, alone or with P, favored more active microbial metabolism genes. • 100 kg N ha-1 fertilization significantly changed microbial community and function. • N fertilization led to a "domino effect" on the decrease of soil C stock.

Successive mineral nitrogen or phosphorus fertilization alone significantly altered bacterial community rather than bacterial biomass in plantation soil.

Bacteria play determining roles in forest soil environment and contribute to essential functions in the cycling of nitrogen (N) and phosphorus (P). Understanding the effects of different fertilizer applications, especially successive fertilization, on soil properties and bacterial community could reveal the impacts of fertilization on forest soil ecology and shed light on the nutrient cycling in forest system. This study aimed to evaluate the impacts of successive mineral N (NH4NO3) and P (NaH2PO4) fertilization at different rates, alone or together, on soil bacterial biomass and communities at 0-5, 5-10, and 10-20 cm. Compared with the control, N fertilization decreased soil pH, but P alone or with N fertilization had negligibly negative impacts on soil pH. Different mineral fertilizer applications, alone or together, showed no significant effects on soil organic matter contents, relative to the control treatment. Bacterial biomass remained stable to different fertilizations but decreased with sampling depths. Sole N or P fertilization, rather than combined fertilizations, significantly changed soil bacterial community structures. Our results demonstrated that mineral N or P fertilization alone significantly affected bacterial community structures rather than biomass in the plantation soils. KEY POINTS: • Impacts of successive mineral fertilization on soil bacteria were determined. • Mineral fertilization showed negligible impacts on bacterial biomass. • N additions stimulated Chloroflexi relative abundances. • Mineral N or P fertilization significantly altered bacterial community structure.