Soil-Moss-Relations: The path of water from dripping to infiltration

Nonvascular plants like mosses are often overseen; however, they are important players in the soil-atmosphere interface in regard to water exchange. Mosses are especially known for their influence on surface runoff, infiltration, soil water content as well as soil evaporation. Moreover, they can enhance soil moisture by water uptake from dew, vapor or fog. Due to their ability to colonize a variety of different environments, such as temperate, boreal, alpine, arctic and dryland ecosystems, mosses are found all over the world. According to their wide distribution, the impact of mosses on soil hydrology is thus assumed to be of great relevance globally. In particular, the specific influence of different moss species and according soil substrates on water movement has been largely disregarded in this context.

In this study, we examined infiltration, percolation and evaporation patterns in moss-covered soil substrates typical for Central European forests during and after rainfall simulations. Soil substrates were sampled at four sites in the Schönbuch Nature Park in South Germany with different kinds of bedrock with varying soil texture and pH. Additionally, one acrocarpous and four pleurocarpous moss species common in central European forests were examined, either collected in Schönbuch Nature Park or cultivated in the lab. Substrates were filled into metal infiltration boxes (30 x 40 cm) to a height of 6.5 cm and mosses were placed on top of the substrates half a year prior to the experiment for acclimatization and rootage. The experimental setup consisted of duplicates of 6 differently combined soil substrate-moss cover samples. Using biocrust wetness probes (BWP), water content values were calculated from measurements of electrical conductivity during one hour of artificial irrigation and subsequent dehydration for 71 hours. BWPs were located in three positions per sample: a) in 3 cm soil depth, b) at the soil surface, and c) in the moss layer. Electrical conductivity and temperature at each BWP position, as well as air temperature and air humidity, were measured in 10 s intervals during the experiment.

Expecting a relation between infiltration, percolation, evaporation and maximum water content of moss species and soil substrates, we furthermore measured their maximum water storage capacities. As we assumed a high relevance of moss surface area on water storage capacities as well as evaporation rates, we also determined surface and leaf area indices of the studied moss species.

First results show relations between air humidity and moss as well as soil moisture. In addition, we observed different water content trends during percolation, infiltration and evaporation between the studied samples. Maximum water storage capacities differed significantly between the moss species with the loosest and the moss species with the densest structure. Preliminary results indicate that moss surface areas and maximum water storage capacities are not correlated. Since the data analysis is currently still in progress, further results will be presented at vEGU21.