While there are hints that biological soil crusts (BSCs) can constitute physical barriers for the emergence of vascular plants, a conceptual approach for the quantitative evaluation of these effects is still missing. Here we present an experimental design to test the emergence of seedlings in situ with (i) capping natural intact, (ii) destroyed and (iii) removed BSC. The selected field site is directly adjacent to the constructed Hühnerwasser catchment (Lusatia,
Germany). This site exists since the end of 2008 and consists of loamy sand. Serving as proxy for seedling thrust, we inserted pre-germinated seeds of three confamiliar plant species with different seed masses (members of the Fabaceae family: Lotus corniculatus
L., Ornithopus sativus Brot., and Glycine max
(L.) Merr.). In each treatment as well as in the control group planting depths were 10 mm. We took care that experimental plots had identical crust thickness, slightly less than 4 mm, serving as proxy for mechanical resistance.
A plot became established as follows: Firstly, the pristine crusted surface was vertically cut. To the windward side the BSC remained intact (i: “with BSC” stripe). To the downwind side soil material was temporarily excavated for laterally inserting the seeds beneath the surface of the first stripe. Then at the thereby disturbed second stripe pulverised BSC material became filled as a top layer (ii: “BSC mix” stripe). From the next stripe the BSC was removed (iii : “no BSC” stripe). Thus each plot had each experimental group in spatial contiguity (within 50 cm * 50 cm). The overall 50 plots were distributed across an area of 40 m * 12 m. When individuals of a species either emerged at all stripes, “XXX”, or at no stripe of a plot, “– – –“, there was no reason to suppose any effect of a crust. The “–XX” emergence pattern (depicting the appearance of seedlings in both stripes possessing manipulated surfaces) points towards hindrance more clearly than “–X–” or “– - X”. Altogether eight possible combinations exist. Combinatorial analysis turned out that seedling emergence had been notably impeded for light-weighted seeds but little for heavy seeds. Repeated recordings enable to account for adaptable emergence of seedlings according to varying crust conditions – in spatial as well as temporal terms. The proposed experimental procedure hence is highly recommended as a viable instrument to further investigate filter and facilitation processes between BSCs and vascular plants.
Als mehrjährige Bioenergiepflanze kann Sida hermaphrodita eine wichtige Rolle für den Anbau auf marginalen Standorten in der nahen Zukunft spielen. In einem kontrollierten Topfexperiment wurde der Einfluss von verschiedenen Kompostgehalten (10, 20, 30, 50%) und mineralischem Stickstoffdünger (100 kg N ha–1) auf Biomasse, Wuchshöhe und Kohlenstoffallokation während der Etablierungsphase untersucht. Weiterhin wurden ökophysiologische Parameter (Gaswechsel, Chlorophyllfluoreszenz, Chlorophyllgehalte) mit nicht-destruktiven Methoden bestimmt. Die Ergebnisse des Experimentes zeigen, dass sowohl die Stickstoffdüngung als auch die Kompostgabe positive Effekte für das Wachstumsverhalten hat. Während der Etablierungsphase erreichten die gedüngten Pflanzen eine mittlere Pflanzenhöhe von bis zu 127 cm (maximale Wuchshöhe 168 cm). Die Photosynthese wurde nicht durch die unterschiedlichen Behandlungen beeinflusst. Die mittlere CO2-Austauschrate variiert zwischen 5,8 und 9,9 μmol m–2 s–1 und die Elektronentransportrate zwischen 34,5 und 53,9 μmol m–2 s–1. Die Verwendung von Kompost und Stickstoff ist für eine bessere Biomasseproduktion von Sida in marginalen Böden möglich, auch wenn das Wachstum im ersten Jahr limitiert ist und es negative Rückwirkungen auf die Bestandesetablierung gibt.
Degradation of soils and the destruction of vegetation as a result of anthropogenic disturbances affect ecosystem functions and properties worldwide. In Brandenburg (NE Germany) various ecosystems were degraded by different human activities like surface mining and military activities on sand dunes. These resulted in degraded open landscapes with an initial soil development. These new ecosystems are characterized by a high vulnerability to erosion, low water holding capacity, lack of nutrients, or low pH. For rehabilitation of degraded soils and vegetation, these post-mining and mobile sand dunes need specific restoration measures, but beside inappropriate soil characteristics, insufficient water availability can limit plant growth. Even located in the temperate zone of Europe, Brandenburg belongs to the driest regions in Germany and faces long drought periods. In this context, the determination of the influence of biocrusts on carbon accumulation during initial ecosystem succession, small-scale investigations on photosynthetic capacity and active phase regarding biocrust formation and developmental stage, which vary from initial green algae-crusts to biocrusts dominated by soil lichens or mosses, are necessary. Hence, succession of biocrusts result in a spatiotemporal heterogeneity and distribution pattern. We could show that varying species abundance, composition, and crust succession affect photosynthetic capacity, and hence, carbon fixation capability. Different spatial hotspots could be analyzed under field conditions and monitored during the season. Long-term measurements of climatic parameters, which include radiation, temperature, precipitation, and desiccation of biocrusts, will be linked to photosynthetic performances under lab conditions. This spatial model can help to understand the impact of biocrusts on carbon accumulation in initial soils. Due to the potential to colonize soil surface under harsh conditions without human support, advantages of biocrusts can be used systematically as a supporting rehabilitation measure for physical stabilization, gain of organic carbon, and hence, facilitates the growth of indigenous vegetation during primary succession.
Investigations were done on two former open-cast lignite mining sites under reclamation, an artificial sand dune in Welzow Süd, and a forest plantation in Schlabendorf Süd (Brandenburg, Germany). The aim was to associate the topsoil hydrological characteristics of green algae dominated as well as moss and soil lichen dominated biological soil crusts during crustal succession with their water retention and the repellency index on sandy soils under temperate cli-mate and different reliefs.
The investigation of the repellency index showed on the one hand an increase due to the cross-linking of sand parti-cles by green algae which resulted in clogging of pores. On the other hand, the occurrence of moss plants led to a de-crease of the repellency index due to absorption caused by bryophytes. The determination of the water retention curves showed an increase of the water holding capacity, especially in conjunction with the growth of green algae layer. The pore-related van Genuchten parameter indicate a clay-like behaviour of the developed soil crusts. Because of the inho-mogeneous distribution of lichens and mosses as well as the varying thickness of green algae layers, the water retention differed between the study sites and between samples of similar developmental stages. However, similar tendencies of water retention and water repellency related to the soil crust formation were observed.
Biological soil crusts should be considered after disturbances in the context of reclamation measures, because the ini-tial development of green algae biocrusts lead to an increasing repellency index, while the occurrence of mosses and a gain in organic matter enhance the water holding capacity. Thus, the succession of biocrusts and their small-scale succes-sion promote the development of soil and ecosystem.
Following surface disturbance, quaternary sands are the basic substrate for soil development in the Lusatian reclamation area. These substrates mostly contain few organic matter and, hence, are nutrient poor. Accumulation of soil carbon is an important factor for ecosystem development, where biological soil crusts initially influence soil processes and promote ecosystem succession. The compositional structures of biological soil crusts at various developmental stages and their photosynthetic properties were investigated on two former open-cast lignite sites, currently under reclamation, an artificial sand dune in Welzow Süd, and a forest plantation in Schlabendorf Süd (Brandenburg, Germany). As development of biological soil crusts progressed, their contents of organic carbon and total chlorophyll increased. The ratio of these parameters, however, varied with the relative contribution of lichens and mosses in particular. Also maximum photochemical efficiency, net photosynthesis and respiration increased with crustal development. An additional evaluation of NDVI and chlorophyll fluorescence images showed that especially moss-dominated biocrusts had higher photosynthetic capacity compared to green algae-dominated biocrusts or soil lichens, so the photosynthetic capacity showed to be highly species-specific. The ratio of gross photosynthesis to respiration indicated a higher ecological efficiency of biocrusts dominated by green algae than of lichen-dominated biocrusts. The occurrence of soil lichens reduced net CO2 fixation and increased CO2 release due to the enhanced mycobiontic respiration. During crustal succession, the rise of photosynthesis-related parameters is not necessarily linear as a result of the highly heterogenic distribution of the different crustal organisms between biocrusts of similar developmental stages as well as between those growing at the two study sites. Therefore, the evaluation of relevant ecophysiological parameters highlighted that not all biocrust-forming organisms similarly contribute to the ecophysiological behavior of biological soil crusts. Nevertheless, the occurrence of the biological soil crusts promoted soil formation and accumulation of soil carbon in initial soils.
Biological soil crusts serve as a vanguard for improving the ecological environment in arid, semi-arid desertification areas.It is a good indicator of the level of improvement which the local ecological evironment is undertaking. In desert areas, water condition is a key factor of improving the ecological environment. As a first layer protection, biological crusts play an important role in local vegetation succession due to their abilities to conserve and maintain moisture. Using Maowusu desert in Yanchi of Ningxia province as an example, after three years of research, this paper chooses three kinds of biological crusts including lichen, moss and cyanobacterial which are under the cover of Artemisia ordosicaas research objects. The results of this study indicate that, the closer biological crusts are to Artemisia ordosica vegetation, the thicker they become. In the same position of Artemisia ordosica vegetation, the
thickness of moss crusts is the highest, followed by lichen crusts, and the thickness of cyanobacterial crusts is the lowest. Biological soil crusts coverage protects the natural water content of soil layers from 0 to 5cm. Also, it effects falling water to infiltrate deeper, and cannot prevent the surfacewater content from evaporating effectively. The effect of biological crusts blocking water infiltration decreases with the increase of rainfall. At the same rainfall level, moss crusts provide the strongest water infiltration blockage, followed by lichen crusts and cyanobacterial crusts. With the increase of rainfall, the depth of water infiltration increases.At the same rainfall level, the relationship of water infiltration depth is as follows: cyanobacterial crusts > lichen crusts > moss crusts. With the increase of biological crusts thickness, they blocking water infiltration capacity is stronger, and the depth of water infiltration is smaller. Analysis on the characteristic of simulated rainfall process on biological crusts shows that sandy land can be fixed by applying appropriate artificial biological crusts to build a sustainable forest protection system and to create a stable ecosystem in desertification area.
Mining activities can strongly affect ecosystem properties by destruction of naturally developed soils and removal of vegetation. The unstructured substrates show high bulk densities, compaction, low water infiltration rates, reduced water holding capacities and higher susceptibility to wind and water erosion. In the initial stage of the ecosystem development, the post-mining sites are open areas without or with a low cover of higher vegetation. It is well-known that biocrusts are able to colonize the soil surface under such extreme conditions without human support and affect soil hydrological processes such as water infiltration, run-off or re-distribution. Investigations were conducted on two former lignite open-cast mining sites, an artificial sand dune on the reclaimed watershedWelzow “Neuer Lugteich” and a reforestation area in Schlabendorf (Brandenburg, north-east Germany). The aim was to relate the hydrological characteristics of the topsoil to successional stages of biological soil crusts on reclaimed soils and their influence on repellency index and water holding capacity compared to pure mining substrate. Our study emphasized the influence of changing successional stages and species composition of biological soil crusts, forming a small-scale crust pattern, on water repellency and retention on sandy soils in temperate climate. Different successional stages of soil crusts were identified from initial scattered green algae crusts, dominated by Zygogonium spec. and Ulothrix spec., and more developed soil crusts containing mosses such as Ceratodon purpureus and Polytrichum piliferum. Lichens of the Genus Cladonia were more pronouncedly contributed to biocrusts at later and mature stages of development. The repellency index on the one hand increased due to the cross-linking of sand particles by the filamentous green algae Zygogonium spec. which resulted in clogging of pores, and on the other hand decreased with the occurrence of moss plants due to absorption caused by bryophytes. The determination of the water retention curves showed an increase of the water holding capacity, especially in conjunction with the growth of green algae layer. The absorption capacity of soil crust biota as well as a decreased pore diameter in the green algae layers positively affected the water retention of crusted soil compared to pure substrate. The occurrence of bryophytes with later succession weakened the repellent behavior of the biocrusts, increased infiltration, and might have affected the run-off at small-scale on biocrusts. Certainly, the biological soil crusts showed water repellent properties but no distinctive hydrophobic characteristics. On both locations, similar trends of water repellency and retention related to crustal formation were observed, in spite of different relief, reclamation time and inhomogeneous distribution of crustal organisms.
Der parallele Anbau von Ackerfrüchten und Agrarholz in Agroforstsystemen führt zu einer ökologischen Aufwertung der landwirtschaftlichen Nutzfläche und hat auch positive Auswirkungen auf das Mikroklima zwischen den Gehölzstreifen. Bei streifenförmigen Agroforstsystemen (Alley Cropping) in Brandenburg konnte eine deutliche Reduktion der Windgeschwindigkeit und von Temperaturextremen sowie ein Anstieg der relativen Luftfeuchtigkeit beobachtet werden (Böhm et al. 2014,
Kanzler et al. 2015). Eine Reduzierung der Windgeschwindigkeit führt zudem zu einer Minderung der potentiellen Evaporation. Dabei stellt sich die Frage, wie sich diese Veränderungen kleinräumig auf die gemessene Evaporation und auf die Produktivität der Ackerkulturen auswirken.