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Purpose: Soil fauna are potential regulators of plant pathogens and soil nutrient cycles. However, direct evidence demonstrating faunal controls over pathogens and plant diseases is still limited. Interactions between diverse faunal groups, soilborne pathogen, and microbial community remain elusive. Methods: The fungivorous nematode Aphelenchus avenae, two collembolan species (Hypogastrura perplexa and Sinella curviseta), and their combinations were introduced to test their suppression effects on the soilborne fungus Pythium ultimum in tomato, and impacts on microbial biomass and activities in soil. Results: The introduction of A. avenae, H. perplexa and combinations of three faunal species decreased tomato seedlings damping-off incidence, and nematode suppressed P. ultimum population in the microcosms. The damping-off disease suppression efficiency is different between faunal treatments, with A. avenae and diverse faunal treatments were more efficient, followed by H. perplexa. The disease suppression effects of S. curviseta were poor. This may be attributed to the non-specific feeding preference of collembolan, different spatial niches and body size of three species. Furthermore, A. avenae and H. perplexa inoculation increased the soil respiration. S. curviseta increased the microbial biomass carbon and nitrogen in microcosms compared with other faunal treatments. These suggest that activities of soil fauna may promote microbial turnover and nutrient cycling to alleviate plant disease. Conclusion: Fungivorous nematode A. avenae and collembola H. perplexa can promote the activities of soil microbes, and alleviate damping-off disease incidence caused by P. ultimum in tomato. Effective management of soil fauna is recommended to control root pathogens and maintain tomato health in organic farming systems. [ABSTRACT FROM AUTHOR]

Background and aims: Mineral cycling plays a critical role in wetland ecosystem functions and can be affected by environmental changes, such as CO enrichment. Learning the responses of mineral bioavailability in wetlands to elevated CO under field conditions will provide enormous benefits to the assessment of climate change impacts on wetland ecosystems. Methods: A free-air CO enrichment (FACE) experiment was conducted in a rice ecosystem in Jiangsu, China, with two nitrogen (N) application levels. Responses of K, Ca, Mg, Fe, Mn, Zn, and Si in this ecosystem were investigated in situ. Results: CO enrichment increased rice biomass Ca, Mg, Fe, Mn, Zn, and Si regardless of N application levels. Dissolved mineral contents in surface water and available mineral contents in the 0-15 cm soil layer were higher in the FACE plots than in the ambient under both N levels. Elevated CO reduced the pH values of the 0-15 cm soil layer and surface water, but increased the cation exchange capacity of the soil layer. The effects of N treatment and its interaction with CO enrichment were mostly insignificant on the above parameters. Conclusions: Our results indicate that CO enrichment can enhance mineral bioavailability in a rice ecosystem through accelerating mineral transformation from the bio-inactive reservoirs to the bioactive ones. [ABSTRACT FROM AUTHOR]

Background and aims: Through agriculture and industry, humans are increasing the deposition and availability of nitrogen (N) in ecosystems worldwide. Carbon (C) isotope tracers provide useful insights into soil C dynamics, as they allow to study soil C pools of different ages. We evaluated to what extent N enrichment affects soil C dynamics in experiments that applied C isotope tracers. Methods: Using meta-analysis, we synthesized data from 35 published papers. We made a distinction between "new C" and "old C" stocks, i.e., soil C derived from plant C input since the start of the isotopic enrichment, or unlabeled, pre-existing soil C. Results: Averaged across studies, N addition increased new soil C stocks (+30.3%), total soil C stocks (+6.1%) and soil C input proxies (+30.7%). Although N addition had no overall, average, effect on old soil C stocks and old soil C respiration, old soil C stocks increased with the amount of N added and respiration of old soil C declined. Nitrogen-induced effects on new soil C and soil C input both decreased with the amount of extraneous N added in control treatments. Conclusion: Although our findings require additional confirmation from long-term field experiments, our analysis provides isotopic evidence that N addition stimulates soil C storage both by increasing soil C input and (at high N rates) by decreasing decomposition of old soil C. Furthermore, we demonstrate that the widely reported saturating response of plant growth to N enrichment also applies to new soil C storage. [ABSTRACT FROM AUTHOR]

Aims: The stability of soil organic carbon (SOC) is of great importance in controlling long-term carbon (C) sequestration and feedbacks of soil C pools to climate change. It has been well documented that rice cropping and organic amendments could enhance SOC stocks, while the stability of the sequestered C has not been well understood yet. The objective of this study was to examine the difference in SOC content and stability between a paddy and an upland field under long-term fertilization and to explore the potential link between SOC chemical and biological stability. Methods: Soils were collected from two adjacent long-term paddy (annually double-rice cropping) and upland (annually double-corn cropping) experiments with the same soil parent material, where different fertilization regimes were initiated in 1981 and 1986, respectively. The chemical and biological stability of SOC were measured by acid hydrolysis and aerobic incubations, respectively. Results: The C concentration was significantly higher in the paddy soil than in the upland soil, regardless of fertilization regimes. As compared to the initial level, long-term rice cropping without any fertilization (CK) significantly enhanced SOC concentration, whereas corn cropping led to a slight decline. Manure amendments combined with inorganic NPK fertilizers (NPKM) significantly increased SOC content relative to the inorganic NPK application alone treatment (NPK) in both the upland and paddy fields. The paddy soil had significantly greater cumulative C released per gram of soil C (i.e., the biological stability of SOC) than the upland soil. Cumulative C released per gram of soil C was significantly higher in NPKM than in NPK in both the paddy and upland soils, whereas no significant difference was observed between the CK and NPK treatments. Acid hydrolysis could reveal the difference in C stability between the paddy and upland soils, but could not characterize the effect of fertilization. Conclusions: Rice cropping facilitates SOC accumulation relative to upland cropping, whereas the inherent SOC stability is lower under the former than the latter in the site. The lower SOC turnover in the paddy than in the upland is mainly due to anaerobic conditions. Organic amendments significantly enhance SOC, but reduce its stability in both the paddy and upland fields. The sensitivity of acid hydrolysis is relatively low in determining SOC stability. [ABSTRACT FROM AUTHOR]