Popular Science: Soil macrofauna – help in carbon stabilization?
Photosynthesis involves the incorporation of part of the carbon received from the atmosphere into the plant body. After a biomass dies, it decomposes and partially releases carbon by respiration or in the form of soluble organic compounds.
The most important factors affecting leaf litter decomposition and mineralization are climatic factors, especially temperature and moisture, and the chemical composition of the material. Other factors are soil type, microbial life, and the soil macrofauna activity (large soil animals readily visible with the naked eye usually >0,5 mm), such as earthworms, millipedes, termites and woodlice. Phenolic compounds, which are present in plants as the chemical defense against herbivores and pathogens, also play an important role in the litter decomposition process. The total phenolic content in the plants differs depending on the plant age, ambient temperature and solar radiation. The amount of these compounds may affect the activity of the decomposers.
Soil macrofauna significantly affects leaf litter decomposition. In particular, they improve the conditions for microbial decomposition by aerating the soil, increasing the surface accessible to microbial activity, mixing the litter and transporting it to deeper and moister parts of the soil. On the other hand, their feces, which decompose more slowly than pure litter, can stabilize the amount of organic matter in the soil.
Scientists carried out an experiment lasting 50 weeks to examine the effects of various factors on the decomposition of organic matter. Three types of leaf litter with different C:N ratios and phenol content were used in the experiment - alder (Alnus glutinosa), willow (Salix caprea) and maple (Acer campestre). In addition, 120 individual terrestrial isopodes (Armadillidium vulgare) were collected and divided into three boxes with different substrates. Within three months, the feces of the isopoda were collected for the next experiment. The different types of substrate were separated and the experiment was performed at three constant temperatures (8 °C, 16 °C, 24 °C) and one fluctuating temperature (8 °C for the first week, 24 °C for the next week). The C:N ratio and the total soluble phenolics were measured in all substrates at the start and the end of the experiment.
The effect of macrofauna was particularly significant in litter with a lower C:N ratio (willow, alder), but was not observed in litter with a higher C:N ratio (maple). The results of the laboratory experiment were supported by field measurements. The litter respiration was positively influenced by the increasing temperature, but not in the feces. The fluctuating temperature caused lower or equal respiration compared to a constant temperature. The content of the phenolics after the decomposition process and in the feces of isopoda significantly decreased compared to the content in intact litter. The C:N ratio decrease in the isopod feces feeding on the maple and alder litter, and conversely the increase in the C:N ratio in the feces from the willow litter, was interesting.
Although many factors affect the decomposition process and the carbon loss from the soil, recent research shows the significant impact of the litter type. At the same time, there is an indisputable influence of macrofauna, which the authors have also devoted attention to in detail in previous research. In this case, it was the woodlice (Isopoda) that, like other macrofauna, promote the stabilization of organic matter in the soil and thus the retention of carbon in the soil environment.
Špaldoňová, A., Frouz, J. (2019): Decomposition of Forest Litter and Feces of Armadillidium vulgare (Isopoda: Oniscidea) Produced from the Same Litter Affected by Temperature and Litter Quality. Forests, 10, 939; doi:10.3390/f10110939.
Frouz, J., Roubíčková, A., Heděnec, P., Tajovský, K. (2015): Do soil fauna really hasten litter decomposition? A meta-analysis of enclosure studies. European Journal of Soil Biology 68, s. 18–24.
Frouz, J., Špaldoňová, A., Lhotáková, Z., Cajthaml, T. (2015): Major mechanisms contributing to the macrofauna-mediated slow down of litter decomposition.Soil Biology & Biochemistry 91, s. 23–31.