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Aims: Replenishment of soils with carbon (C) produced during photosynthesis plays an important role in global C cycling. Nitrogen (N) fertilization is critical for rice production, but its effects on the deposition of photosynthesis-derived C into soil C pools is poorly understood. To address this, we used continuous C-labeling to quantify the deposition of photosynthesis-derived C into various soil organic pools in a rice-soil system. Methods: Rice ( Oryza sativa L.) was continuously supplied with C-labeled CO (C-CO) for 36 days, with increasing N fertilizer rates (0 [N], 10 [N], 20 [N], or 40 mg N kg soil [N], respectively). Results: Rice shoot and root biomass significantly increased following N fertilization. The amount of photosynthesis-derived C converted into soil organic carbon (C-SOC) was proportional to the soil N concentration, and accounted for 8.0-19.3 % of rice biomass C. The C-SOC content was positively correlated with the rice root biomass, suggesting that N increased root exudation of photosynthesis-derived C. The amounts of C-labeled C in the dissolved organic carbon (C-DOC) and in the microbial biomass carbon (C-MBC), as proportions of C-SOC, were 3.9-7.8 and 6.6-24.0 %, respectively. The C-DOC, C-MBC, and C-SOC as proportions of total DOC, MBC, and SOC were 9.7-11.6, 6.9-10.6, and 0.37-1.71 %, respectively. Conclusions: Nitrogen fertilization promotes deposition of photosynthesis-derived C into SOC pools in a rate-dependent manner. However, the C-MBC as a proportion of both C-SOC (C-MBC/C-SOC) and MBC (C-MBC/MBC) increase during rice growth at lower N concentrations. [ABSTRACT FROM AUTHOR]

Elucidating the biodiversity of CO-assimilating bacterial communities under different land uses is critical for establishing an integrated view of the carbon sequestration in agricultural systems. We therefore determined the abundance and diversity of CO assimilating bacteria using terminal restriction fragment length polymorphism and quantitative PCR of the cbbL gene (which encodes ribulose-1,5-biphosphate carboxylase/oxygenase). These analyses used agricultural soils collected from a long-term experiment (Pantang Agroecosystem) in subtropical China. Soils under three typical land uses, i.e., rice-rice (RR), upland crop (UC), and paddy rice-upland crop rotation (PU), were selected. The abundance of bacterial cbbL (0.04 to 1.25 × 10 copies g soil) and 16S rDNA genes (0.05-3.00 × 10 copies g soil) were determined in these soils. They generally followed the trend RR > PU > UC. The cbbL-containing bacterial communities were dominated by facultative autotrophic bacteria such as Mycobacterium sp., Rhodopseudomonas palustris, Bradyrhizobium japonicum, Ralstonia eutropha, and Alcaligenes eutrophus. Additionally, the cbbL-containing bacterial community composition in RR soil differed from that in upland crop and paddy rice-upland crop rotations soils. Soil organic matter was the most highly statistically significant factor which positively influenced the size of the cbbL-containing population. The RR management produced the greatest abundance and diversity of cbbL-containing bacteria. These results offer new insights into the importance of microbial autotrophic CO fixation in soil C cycling. [ABSTRACT FROM AUTHOR]

An obituary for soil scientist David Jenkinson is presented.

The article presents an obituary for soil scientist David Jenkinson.