Deciphering the Role of Soil Mesofauna in Altering Microbial Decomposition in a Model Lawn System

Turnover of nitrogen-rich root nodules follows the pruning of legume trees, forming a potentially important yet little studied way of N release to the soil. The effects of soil moisture, herbivory by soil mesofauna and microbial decomposition on the disappearance rate of woody legume nodules was studied in two tree/grass forage production associations. Litter bags containing nodules of Erythrina variegata L. (Papilionoideae: Phaseoleae) were incubated for four weeks in grass-covered alleys between Gliricidia sepium (Jacq.) Walp. (Papilionoideae: Robinieae) hedgerows, established on a deep alluvial Oxisol under a humid tropical climate and on a shallow Vertisol under a subhumid tropical climate in Guadeloupe, French Antilles. Soil moisture was regulated by irrigating or covering small plots from natural rainfall. Fine nylon mesh bags were used to study the rate of microbial decomposition, and open-ended perforated cylinders were used to estimate nodule herbivory. The chemical traits, especially the lignin: nitrogen ratio, of E. variegata and G. sepium nodules were similar (lignin: N 1.70 and 1.55, respectively), and suggest that the results are probably also applicable to the G. sepium nodules in the associations. Both soil moisture and decomposing agent (microbes or mesofauna) had a significant effect on the nodule disappearance rate, but soil type did not have any apparent effect. The nodule half-life varied from three to seven days under different treatments. The N release rate from the nodules was high, with N half-life varying from three to five days. Herbivory accounted for ca. 10% of total mass and N loss from nodules during the four-week field incubation period, but its importance increased towards the end of the incubation, especially in Vertisol, after the most easily decomposable part of the nodules had decayed. After pruning, the nodule N is released to soil more rapidly than from mulch.

Collembola (Isotomidae) and mowing management practices control distinct aspects of thatch decomposition in a lawn mesocosm experiment

The fate of the soil organic matter stored in arctic ecosystems in a future warmer climate is highly debated but remains quite uncertain, especially as most studies do not take into account the combined effect of climate change and simultaneous invasion by non-native fauna. For example, while the impact of climate change on carbon losses from the arctic might be limited due to the strong nutrient limitations restricting microbial activity and decomposition speed in these ecosystems, the current invasion by burrowing earthworms as a result of human activity might alleviate the nutrient limitations and modify the soil food web, which could significantly increase carbon losses. We investigated the effect of burrowing earthworm addition on soil mesofauna and microbial community composition and on associated carbon stability of the arctic tundra by the end of a 4-year-long mesocosm experiment in northern Sweden. The abundance of collembola and oribatid mites was positively affected by earthworm addition in a heath-type tundra ecosystem, while no changes were detectable in a meadow-type tundra. This is surprising as the meadow-type tundra was strongly affected by earthworms in terms of soil structure with a decrease in total carbon stock. We tested the stability of the residual carbon by measuring CO2 emissions during an incubation of the organic and mineral soil horizons at current and increased temperatures. We found that while carbon stability is not clearly affected by earthworm addition in the heath-type tundra, the stability of the leftover carbon is increased in the presence of earthworms in the meadow-type tundra in the first 10 soil centimeters in both incubation temperatures. This suggests that the ultimate effect on carbon dynamics of earthworm invasion cannot be simply estimated from the immediate carbon loss from the organic layer, as the changes in carbon forms and quality could modify the future organic matter availability to decomposers. 

ABSTRACT: Soil mesofauna consists of small invertebrates that live in the soil or litter and are sensitive to climatic conditions, management systems, plant cover and physical or chemical soil attributes. These organisms are active in the cycling of nutrients, since they fragment the organic matter hereby accelerating microbial decomposition. The aim of this study was to evaluate the invertebrate community in no-tillage, conventional tillage, minimum tillage and secondary forest in regeneration to determine the relationship of mesofauna to litter, soil attributes, management and seasonality. Therefore, ten soil samples in each system and eight litter samples in no-tillage and the forest were taken over four seasons. These samples remained in Berlese extractors for seven days for quantification and identification of mesofauna. For each fauna sample, soil samples were collected for chemical analysis. Next, diversity indices and richness were calculated and multivariate analyses were used to establish relationships between the mesofauna, soil attributes and management. In the soil, mites were more abundant in the agricultural systems than in the forest, but the springtails, sensitive to low moisture and high temperature, were more abundant in the forest. Diversity and richness were higher in soil from the forest than under other systems. In no-tillage, there was a lower density of soil mesofauna, however, under this system, many invertebrates live in litter, since litter is the main food resource for them. In forest litter, we found lower invertebrate density and higher diversity than in no-tillage. Carbon, basic cations, pH, Al and V% were the attributes that best explained fauna variability in the systems.