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.
Abstract. Soil erosion continues to be one of the most serious environmental problems of our time and is exacerbated by progressive climate change. Until now, forests have been considered an ideal erosion control. However, even minor disturbances of the forest floor, for example, from heavy vehicles used for timber harvesting, can cause substantial sediment transport. An important countermeasure is the quick restoration of the uncovered soil surface by vegetation. To date, very little attention has been paid to the development of nonvascular plants, such as bryophytes, in disturbed areas of temperate forests and their impact on soil erosion. This study examined the natural succession of pioneer vegetation in skid trails on four soil substrates in a central European temperate forest and investigated their influence on soil erosion. For this purpose, rainfall simulations were conducted on small-scale runoff plots, and vegetation was continuously surveyed during the same period, primarily to map the development of bryophytes and the occurrence of biological soil crusts (biocrusts). Biocrusts appeared immediately after disturbance, consisting primarily of bryophyte protonemata and cyanobacteria as well as coccoid and filamentous algae that lost their biocrust characteristics as succession progressed. They were present from April to July 2019, with a particular expression in the skid trail that was on shale clay (Psilonotenton Formation) and silty clay loam substrate. In general, skid trails on clayey substrates showed considerably higher bryophyte cover and species richness. Although bryophytes were subsequently overtopped by vascular plants, they managed to coexist until their growth was restricted due to leaf litter fall. Brachythecium rutabulum and Oxyrrhynchium hians were the most important and persistent pioneer bryophyte species, while Dicranella schreberiana and Pohlia lutescens were volatile and quickly disappeared after spreading in the summer. Sediment discharge was 22 times higher on disturbed bare soil compared with undisturbed forest soil and showed the largest sediment removal in the wheel tracks. Counteracting this, soil erosion decreased with the recovery of surface vegetation and was particularly reduced with growing pioneer biocrusts in summer, but it again increased in winter, when vascular vegetation became dominant. This leads to the conclusion that the role of bryophyte-dominated biocrusts in forests has been underestimated so far, and they can contribute more to soil conservation at specific times of succession than vascular plants.
Abstract. Soil erosion continues to be one of the most serious environmental problems of our time, which is exacerbated by progressive climate change. Until now, forests have been considered an ideal erosion control in this regard. However, even minor disturbances of the forest floor for example from heavy vehicle used for timber harvesting can cause substantial sediment transport. An important countermeasure is the quick restoration of the uncovered soil surface by vegetation. In this context, biological soil crusts (biocrusts) can play a vital role, as they are known for their soil-protective effect. This study examined the natural succession of pioneer vegetation in skid trails on four soil substrates in a central European temperate forest and investigated their influence on surface runoff and sediment discharge. We applied rainfall simulation experiments on small-scale runoff plots and continuously surveyed vegetation during the same period, primarily to map biocrust development. Skid trails on clayey substrates showed considerably higher biocrust cover and species richness. Biocrust cover was higher in center tracks than in wheel tracks, while there was no clear difference for biocrust species richness with regard to track position. Although biocrusts were quickly overtopped by vascular plants, they managed to coexist until their growth was restricted due to leaf litter fall. Brachythecium rutabulum and Oxyrrhynchium hians were the most important and persistent pioneer biocrust species, while Dicranella schreberiana and Pohlia lutescens were volatile and quickly disappeared after spreading in summer. Soil erosion was reduced with pioneer biocrust vegetation in summer, and again increased in winter. Total amount of sediment discharge was clearly site-dependent, indicating a high relevance of underlying substrates. Sediment discharge was 13.2 times higher in wheel tracks compared to undisturbed forest soil, and bare soil runoff plots produced 22-fold sediment discharge compared to undisturbed forest soil. Overall, bryophyte-dominated biocrusts contributed more to mitigating soil erosion than vascular plants. When soil coverage exceeded 50 %, biocrusts resulted in an average of 18 times less sediment loss compared to vascular plants.
Biological soil crusts, or “biocrusts”, are biogeochemical hotspots that can significantly influence ecosystem processes in arid environments. Although they can cover large areas, particularly in managed sites with frequent anthropogenic disturbance, their importance in mesic environments is not well understood. As in arid regions, biocrusts in mesic environments can significantly influence nutrient cycling, soil stabilization, and water balance; however, their persistence may differ. We call for interdisciplinary physical, biological, microbiological, chemical, and applied soil science research with a special focus on biocrusts of managed soils from mesic environments, to better understand their impact on overall ecosystem health and resilience, particularly with regard to climate change.
<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 Sch&#246;nbuch 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&#160;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 Sch&#246;nbuch 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 Sch&#246;nbuch 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>
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