Mosses are often overlooked; however, they are important for soil-atmosphere interfaces with regard to water exchange. This study investigated the influence of moss structural traits on maximum water storage capacities (WSCmax) and evaporation rates, and species-specific effects on water absorption and evaporation patterns in moss layers, moss-soil-interfaces and soil substrates using biocrust wetness probes. Five moss species typical for Central European temperate forests were selected: field-collected Brachythecium rutabulum, Eurhynchium striatum, Oxyrrhynchium hians and Plagiomnium undulatum; and laboratory-cultivated Amblystegium serpens and Oxyrrhynchium hians. WSCmax ranged from 14.10 g g−1 for Amblystegium serpens (Lab) to 7.31 g g−1 for Plagiomnium undulatum when immersed in water, and 11.04 g g−1 for Oxyrrhynchium hians (Lab) to 7.90 g g−1 for Oxyrrhynchium hians when sprayed, due to different morphologies depending on the growing location. Structural traits such as high leaf frequencies and small leaf areas increased WSCmax. In terms of evaporation, leaf frequency displayed a positive correlation with evaporation, while leaf area index showed a negative correlation. Moisture alterations during watering and desiccation were largely controlled by species/substrate-specific patterns. Generally, moss cover prevented desiccation of soil surfaces and was not a barrier to infiltration. To understand water’s path from moss to soil, this study made a first contribution.

Raindrop impact on leaves is a common event which is of relevance for numerous processes, including the dispersal of pathogens and propagules, leaf wax erosion, gas exchange, leaf water absorption, and interception and storage of rainwater by canopies. The process of drop impact is complex and its outcome depends on many influential factors. The wettability of plants has been recognized as an important parameter which is itself complex and difficult to determine for leaf surfaces. Other important parameters include leaf inclination angle and the ability of leaves to respond elastically to drop impact. Different elastic motions are initiated by drop impact, including local deformation, flapping, torsion and bending, as well as “swinging” of the petiole. These elastic responses, which occur on different time scales, can affect drop impact directly or indirectly, by changing the leaf inclination. An important feature of drop impact is splashing, meaning the fragmentation of the drop with ejection of satellite droplets. This process is promoted by the kinetic energy of the drop and leaf traits. For instance, a dense trichome cover can suppress splashing. Basic drop impact patterns are presented and discussed for a number of different leaf types, as well as some exemplary mosses.

<p>Despite being small in size, mosses fulfill vital roles in ecosystem functioning, especially in temperate ecosystems. Due to their unique ecology and physiology, they affect water and nutrient cycles, even at larger scales. This study investigated water-related interactions between soil and moss from the site scale of skid trails in temperate forests to the microscopic scale of individual structural moss traits. First, the natural succession of mosses in skid trails was surveyed, together with their effect on soil erosion using a rainfall simulator. Second, different soil-moss combinations and their impact on runoff formation, percolation, and sediment discharge were investigated. In addition, the temporal dynamics of soil water content were recorded during erosion measurements as well as during watering and subsequent desiccation. Third, a detailed study on how structural traits affect maximum water storage capacity (WSC<sub>max</sub>) and its interactions with soil water content was conducted on the species level.</p> <p>Mosses appeared in our temperate forests as biocrusts during the first few weeks after disturbance and developed for four months until they formed a mature moss cover and biocrust characteristics steadily disappeared. Soil erosion was most reduced when moss-dominated biocrusts were abundant. In general, mosses made a major contribution to erosion control in skid trails after disturbance, showing stronger impacts than vascular plants. The different soil-moss combinations showed clear variations among bare & dry, bare & wet, moss & dry and moss & wet treatments in terms of surface runoff, percolated water volume and sediment discharge. Surface runoff and soil erosion were significantly decreased in the moss treatments, while the amount of percolated water was increased; however, these processes were superimposed by desiccation cracks and water repellency. Moss treatments exhibited lower water contents over time compared to bare treatments, highlighting the strong influence of moss covers and desiccation cracks on the soil water balance. During watering of soil-moss combinations, no clear relationships between water absorption and moss structural traits could be found, which suggests capillary spaces as important influencing factor. In general, mosses were no barrier for infiltration in case of high precipitation rates and they did not store much of the applied water themselves, but passed it on to the soil. During desiccation, mosses with high leaf area index had lower evaporation rates and they prevented desiccation of the substrate, although even dense moss covers did not completely seal the surface. WSC<sub>max</sub> of the studied moss species varied widely, which could not be explained by their total surface area or leaf area index, and higher WSC<sub>max </sub>values were correlated with low leaf area and high leaf frequency.</p> <p>Our results underlined the importance of mosses for the soil water balance and protection of soil against erosion in disturbed forest ecosystems. However, it became simultaneously apparent that the role of mosses in forest ecosystems is not yet fully understood and that there is still great potential for further research on soil-water relations and erosion control.</p>

<p>For decades, soil erosion has been a major environmental problem as it degrades the most productive soil layers, which threatens, among other things, food production worldwide. Although these effects have been known for a long time, there are still a variety of challenges to mitigating soil erosion in different ecosystems. As climate change progresses, the risk of soil loss increases, making the preparation of effective solutions very urgent. A current research focus is on the restoration of a protective soil cover following disturbances in the vegetation layer, e.g., through the reestablishment of biological soil crust communities. These are often dominated by bryophytes in humid climates. So far, several studies examined the general protective influence of bryophytes against soil erosion, however only few of them addressed how individual species affect specific erosion processes in detail.</p><p>To fill this research gap we investigated the impact of six moss species on soil erosion, percolation and carbon relocation by means of rainfall simulations. Therefore, we used topsoil substrate from four sites in the Schönbuch Nature Park in South Germany which covers different kinds of bedrock and varying soil texture and pH. Subsequently, they were sieved by 6.3 mm and filled into metal infiltration boxes (40 x 30 cm) up to a height of 6.5 cm. The moss species differ in origin (either collected in the field or cultivated in the lab) as well as growth form (pleurocarpous or acrocarpous). Rainfall simulations were performed for bare soil substrates, as well as for moss-covered soil substrates six months later and both in dry and wet conditions. Additionally, we conducted rainfall simulations with leaf and coniferous litter on bare soil substrates. During the simulations we monitored soil moisture in two position - 3 cm depth plus soil surface - with biocrust wetness probes (BWP) and quantified surface runoff, percolation and sediment discharge. Afterwards we determined carbon contents of the sediment and dissolved organic carbon in the liquid phase of runoff and percolated water.</p><p>While surface runoff was increased by 5% due to the litter cover compared to the bare soil substrate, sediment discharge decreased to 97%. Runoff rates could also be mitigated by 90 % as a result of the moss cover. Furthermore, due to the dense moss cover sediment rates were almost reduced to zero. Preliminary results show that there are differences between the moss species in terms of sediment discharge, but not in context with runoff. The analyses of carbon contents in surface runoff and the percolated water are still in progress, as is the evaluation of the BWP measurements. These outcomes will be presented at vEGU21.</p>

<p>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.</p><p>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.</p><p>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.</p><p>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.</p>