[Response of Extracellular Enzyme Activities to Substrate Availability in Paddy Soil with Long-term Fertilizer Management].

The availability of carbon (C), nitrogen (N), and other substrates in soil determines the growth and metabolism of microorganisms and affects the activity of extracellular enzymes. To study the activities of -1,4-glucosidase (BG) and -1,4--acetylglucosaminidase (NAG) in response to C and N availability, samples that underwent four treatments-non-fertilization (CK), chemical fertilizer (NPK), combination of organic manure and chemical fertilizer (OM), and mixture of straw and chemical fertilizer (ST)-were collected from long-term fertilization paddy soil and incubated for 0, 4, 8, and 12 months to obtain soil with different C and N availability gradients. The results showed that the dissolved organic carbon(DOC) content of OM and ST treatment samples was 2-3 times higher than that of CK and NPK treatment samples.

[Characterization of Soil Organic Carbon Mineralization Under Different Gradient Carbon Loading in Paddy Soil].

Available carbon is the most active part of the soil carbon pool. It is also the main carbon source of soil microbes and plays an important role in the processes of soil organic carbon mineralization and accumulation. However, the mechanisms are still not clear how soil organic carbon mineralization and its priming effect (PE) are affected by different input levels of readily available carbon, based on the growth requirements of microbes in paddy soil.

[Allocation and Stabilization Responses of Rice Photosynthetic Carbon in the Plant-Soil System to Phosphorus Application].

This research studied the response of the input and allocation of photosynthetic carbon (C) to phosphorus (P) in paddy soils. Two treatments were conducted in this experiment:no P application (P) and the application of 80 mg·kg of P (P). The rice cultivar was the indica Zhongzao 39.

[Effect of CO Doubling and Different Plant Growth Stages on Rice Carbon, Nitrogen, and Phosphorus and Their Stoichiometric Ratios].

The variation characteristics of ecological stoichiometric ratios can reflect the nature of plant adaptation to environmental changes. The C, N, and P contetns, and their stoichiometric ratios in different organs of rice were studied using a CO continuous labeling system, by simulating the increase of atmospheric CO concentration (800×10). The results showed that CO doubling promoted the growth of rice organs and increased the root/shoot ratio.

[Dynamics of Rice Photosynthesized Carbon Input and Its Response to Nitrogen Fertilization at the Jointing Stage: C-CO Pulse-labeling].

Photosynthesized carbon (C) is an important source of soil organic C in paddy fields, and its input and distribution are affected by rice growth and soil fertility. Fertilizer application plays an important role in rice growth. The C pulse-labeling method was used to quantify the dynamics and distribution of input photosynthesized C in the rice-(rhizosphere-and bulk-) soil system and its response to nitrogen fertilizer (N) application.

[Characteristics and Influencing Factors of Biologically-based Phosphorus Fractions in the Farmland Soil].

A suitable fractionation method of phosphorus (P) is a key to effective assessment of soil P componential features. Here a new biologically-based P (BBP) method was used to evaluate the P fractions in the upland and paddy soils across large-scale area in China. The soil P was divided into four components:① soluble or rhizosphere-intercepted (CaCl-P), ② organic acid activated and inorganic weakly bound (Citrate-P), ③ enzyme mineralization of organic P (Enzyme-P), ④ potential activation of inorganic P (HCl-P).

[Characteristic of Abundances and Diversity of Carbon Dioxide Fixation Microbes in Paddy Soils].

To get a better understanding of the microbial autotrophic carbon sequestration potential of paddy fields and its mechanisms, soil incubation experiment was conducted for four representative paddy soils. The molecular biological methods[quantitative PCR (qPCR), clone library and terminal-restriction fragment length polymorphism (T-RFLP) technique] based on and genes encoding the key enzymes[ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO)] of Calvin cycle were used to determine the abundance and diversity of autotrophic microbes. The results showed that, after 45 days of incubation, carbon dioxide fixation autotrophic microbial abundances were generally increased compared with those before incubation, and gene abundances were approximately three magnitudes higher than those of .

[Effects of Soil Texture on Autotrophic CO Fixation Bacterial Communities and Their CO Assimilation Contents].

Autotrophic bacteria can assimilate atmospheric carbon dioxide (CO) and convert CO into organic carbon. The CO fixation by autotrophic bacteria is important for the improvement of carbon sequestration in agricultural soils. However, the effect of soil texture on autotrophic CO fixation bacteria and their CO fixation capacity is still unknown.

[Effects of Different Plantation Type on the Abundance and Diversity of Soil Microbes in Subtropical Red Soils].

Soil microbe plays an important role in carbon cycling, however, the effect of land use on soil microbe remain unclear. In present study, soil samples were collected from a long-term field experiment (Pantang Agroecosystem) in subtropical China (established in 1989), including paddy-rice (PR), upland-crop (UC), and paddy rice-upland crop rotation (PU) on soil bacterial (bacteria and Archaea) community structures. The effects of long-term different land uses were determined using terminal restriction fragment length polymorphism (T-RFLP) and quantitative PCR (RT-PCR) of the 16S rRNA gene.

[Effects of long-term fertilization on bacterial and archaeal diversity and community structure within subtropical red paddy soils].

Paddy soils not only function as an important sink for "missing carbon" but also play an important role in the production of greenhouse gases such as N2O and CH4. Dynamic changes in greenhouse gases in the atmosphere are closely related to microbially mediated carbon and nitrogen transformation processes occurring in soil. Using soil samples collected from a long-term fertilization experimental site in Taojiang County, subtropical China (established in 1986), we determined the effects of long-term (>25 years) non-fertilization (CK), chemical fertilization (NPK), and NPK combined with rice straw residues (NPKS) on soil bacterial and archaeal community structures.

[Characteristics of the mineralization and transformation of autotrophic microbes-assimilated carbon in upland and paddy soils].

In this study, the mineralization and decomposition of autotrophic microbe assimilated carbon (new carbon) and native organic carbon in three upland and three paddy soils in subtropical China were measured using the 14C-labelled tracer technique. The results showed that, during the 100-d incubation, the mineralization of the 'new carbon' displayed three stages: a rise in the first 10 days, a slowdown from 11-d to 50-d, and a stabilization stage after 50 d. The mineralization ratio of the 'new carbon' ranged between 8.

[Input and distribution of rice photosynthesized carbon in the tillering stage under different nitrogen application following continuous 13C labeling].

The input of rice-photosynthesized carbon (C) into soil plays an important role in soil C cycling. A 13C-labelled microcosm experiment was carried out to quantify the input of photosynthesized C into soil C pools in a rice-soil system during the tillering stage. Growing rice (Oryza sativa L.

[Carbon dioxide assimilation potential, functional gene amount and RubisCO activity of autotrophic microorganisms in agricultural soils].

Carbon dioxide (CO2) assimilation by autotrophic microorganisms plays a significant role in carbon sequestration in terrestrial ecosystems. Here, experiments were carried out to determine the contribution of autotrophic microorganisms to atmospheric CO2 fixation in 6 representative agricultural soils. Soils were incubated continuously in an atmosphere of 14CO2 and the distribution of labeled C into soil organic carbon (14C-SOC) was determined after 110 d.

[Quantifying soil autotrophic microbes-assimilated carbon input into soil organic carbon pools following continuous 14C labeling].

Soil autotrophic microbe has been found numerous and widespread. However, roles of microbial autotrophic processes and the mechanisms of that in the soil carbon sequestration remain poorly understood. Here, we used soils incubated for 110 days in a closed, continuously labeled 14C-CO2 atmosphere to measure the amount of labeled C incorporated into the microbial biomass.

[Microbial activity and community structure analysis under the different land use patterns in farmland soils: based on the methods PLFA and MicroResp].

Soil microbe plays an essential role in terrestrial ecosystem through its role in cycling mineral compounds and decomposing organic matter. The objective of this paper is to determine the influences of different land use patterns on soil microbial activity and community structure, which were analyzed by phospholipids fatty acid (PLFA) and MicroResp method, based on a long-term fertilization experiment in Taoyuan County, Hunan Province. There were three land use patterns included, i.