Establishment Of Vascular Plants Research Articles

Biological soil crusts as a major ecosystem component in sandization areas of the Brazilian Pampa

In the Brazilian Pampa, vegetation disturbance and soil degradation led to an expansion of sediment remobilization areas, a process locally termed as sandization. Transported sands generate severe environmental problems and hamper the growth of vegetation. However, parts of these sandization areas are quickly covered by biological soil crusts (biocrusts), which have not been investigated in this biome before.This study describes biocrust occurence in sandization areas of the Brazilian Pampa for the first time and analyses their distribution patterns related to the local topography. We studied biocrusts at two research sites where their presence appeared to be essential for soil protection. First, the occurrence of different biocrust types were assessed and a taxonomic survey was conducted. Second, UAV-based imagery was created and biocrusts were classified, using a random forest approach to understand the relation of their abundance to topography.We observed that biocrusts occurred widely in areas prone to sandization with an approx. 25% distribution on the land surface. They are mostly dominated by cyanobacteria and secondarily by bryophytes. Among the observed genera, the cyanobacterial genus Stigonema sp. was dominating in both study sites. Campylopus pilifer was the dominating moss species. The mapped biocrusts represented all major morphological types and were classified as rolling, pinnacled, rugose, and smooth crusts. Local topography was a major driver for biocrust distribution, but also the establishment of vascular plants. Slope and aspect had a strong influence on biocrust development, but the presence of protective topographic positions against atmospheric influences most prominently facilitated their occurrence.This pilot study proves that biocrusts can potentially play a key role as ecosystem engineers in the Brazilian Pampa with a positive effect on general vegetation growth and soil-stabilization. In this biome, however, they have been largely overlooked compared to other areas globally. Thus, biocrusts need to be further studied and their effects considered in land management to constrain further soil degradation.

Factors influencing the establishment of vascular plants at Sphagnum cultivation sites

Sphagnum cultivation is a type of paludiculture and a way to use formerly drained peatlands productively but under wet and therefore climate-friendly conditions. Where Sphagnum mosses are cultivated other plant species will also establish and possibly compete with the Sphagnum. The aim of this study was to determine which factors influence vascular plant cover as well as plant species numbers at Sphagnum cultivation sites and to derive recommendations for their management. Two cultivation sites were studied in northwest Germany. One of these was established directly after peat extraction while the other was rewetted seven years prior to establishment. Irrigation ditches for water management were installed at both sites. The cover of vascular plants and the number of plant species present were determined in systematically positioned plots. Six variables were tested for their influence on the assessed data by applying boosted regression tree models. The main factors influencing vascular plant cover at the two Sphagnum cultivation sites were the distance to an irrigation ditch (m), the site (location) and Sphagnum cover (%). The number of species per plot was influenced mainly by Sphagnum cover (%), the distance to an irrigation ditch (m) and the donor species used for initiating the cultivation sites. A sufficient supply of nutrient-poor water and optimal Sphagnum growth can reduce vascular plant cover and the number of plant species potentially present at a site. Insufficient water distribution and uneven Sphagnum establishment lead to inhomogeneous site conditions and thus to a higher number of plant species. The number and cover of plant species at a cultivation site are influenced by the vegetation of the sites’ surroundings and the selection of the donor site.

Consequences of an ecosystem state shift for nitrogen cycling in a desert stream

AbstractCessation of cattle grazing has resulted in the reestablishment of wetlands in some streams of the U.S. Southwest. Decades of cattle grazing prevented vascular plant growth in Sycamore Creek (Arizona, U.S.A.), resulting in stream reaches dominated by diatoms and filamentous green algae. Establishment of vascular plants can profoundly modify ecosystem processes; yet, the effects on nitrogen (N) cycling remain unexplored. We examined the consequences of this ecosystem state shift on N cycling in this N‐limited desert stream. We compared results from whole‐reach ammonium‐N stable isotope (15NH4+) tracer additions conducted before (pre‐wetland state) and 13 yr after (wetland state) free‐range cattle removal from the watershed. Water column estimations showed that in‐stream N uptake and storage were higher in the pre‐wetland than in the wetland state. N turnover was also higher in the pre‐wetland state, indicating that assimilated N was retained for shorter time in stream biomass. In addition, N uptake was mostly driven by assimilatory uptake regardless of the ecosystem state considered. Water column trends were mechanistically explained by the fact that the dominant primary uptake compartments in the pre‐wetland state (i.e., algae and diatoms) had higher assimilatory uptake and turnover rates than those in the wetland state (i.e., vascular plants). Overall, results show that the shift in the composition and dominance of primary producers induced by the cessation of cattle grazing within the stream‐riparian corridor changes in‐stream N processing from a dominance of intense and fast N recycling to a prevalence of N retention in biomass of primary producers.

The ecological importance of moss ground cover in dry shrubland restoration within an irrigated agricultural landscape matrix.

Kānuka (Kunzea serotina, Myrtaceae) dryland shrubland communities of the lowland plains of South Island (Te Wai Pounamu), New Zealand (Aoteoroa), contain a ground cover largely consisting of mosses, predominantly Hypnum cupressiforme. There has been no previous study of the role of mosses in this threatened habitat which is currently being restored within a contemporary irrigated and intensively farmed landscape that may be incompatible with this component of the ecosystem.The aim of the present study was to investigate the influence of moss ground cover on hydrology, nitrogen (N) availability and vascular plant interactions, and in relation to nutrient spillover from adjacent farmland. Experimental work was a combination of glasshouse experiments and field‐based studies.Extremes of soil temperature and moisture were found to be mediated by the moss carpet, which also influenced N speciation; available N declined with moss depth. The moss layer decreased the amount of germination and establishment of vascular plants but, in some cases, enhanced their growth. Spillover of mineral nitrogen and phosphate from farmland enhanced invasion of exotic grasses which may have benefited from conditions provided by the moss carpet. Synthesis: We found the moss layer to be crucial to ecosystem functioning in these dry habitats with low nutrient substrate. However, when the moss layer is accompanied by nutrient spillover, it has the potential to increase exotic weed encroachment. Our results not only emphasize the importance of non‐vascular plant inclusion in restoration schemes but also highlights the importance of mitigating for nutrient spillover.

Value of large Quercus robur fallen logs in enhancing the species diversity of vascular plants in an old-growth mesic broad-leaved forest in the Central Russian Upland

Large old trees and decaying logs are key-retained structures for the retention forestry approach, but quantitative estimations of the role of fallen logs in the overall diversity and composition of forest vascular species are few and controversial. Particularly for mesic deciduous forests only a small number of such estimates are known. Our study aimed to partly fill this gap using data collected in the Reserve Kaluzhskie Zaseki where large Quercus robur individuals of more than 300 years old and fallen logs are frequent. We found 44 fallen oak logs supporting vascular plants within a 200-ha forest tract. The vegetation in plots of 1 m2 located on the fallen logs and on the forest floor adjacent to the logs was surveyed together with vegetation in fifteen 10 × 10 m plots randomly placed in patches without large fallen logs. NMDS and PERMANOVA were applied to examine differences in composition between fallen logs and forest floor. Generalized linear models were used to examine the relationships between environmental variables and species richness. Additive diversity partitioning was performed to examine differences in species richness and to estimate the contribution of the fallen logs to the general diversity in vascular species. In total, 71 vascular plant species in 108 1 m2-plots were identified. Twenty-five and 16 species were detected only on fallen logs and on the forest floor, respectively. More than 60% of the studied logs were in early stages of decomposition; their mean diameter was 75.4 ± 25.6 cm. Fallen logs significantly affected species richness and composition in terms of both woody seedlings and herbaceous species. The diameter of logs significantly and positively affected species diversity and composition. Large logs with cracked bark at the first two stages of decay were places of successful vascular plant establishment and growth. The abundance and frequency of tree seedlings were higher on the logs than on the forest floor and seven out of ten tree species appeared to be significant indicator species for the log-plots. Illumination varied over the observed sites and directly influenced the richness of herbaceous species and the overall species composition, but had no effect on woody species richness. We conclude that retention of large fallen logs can be an effective tool for maintaining and restoring the vascular species richness and composition in mesic broad-leaved forests.

Effects of mosaic biological soil crusts on vascular plant establishment in a coastal saline land of the Yellow River Delta, China

Abstract Aims The effects of biocrusts on vascular plants are rarely evaluated in coastal saline lands. Our aim was to examine whether and how a mosaic of biocrusts affect seed germination of two typical herbaceous plants in a coastal saline land of the Yellow River Delta, to enhance our understanding by which substrate heterogeneity influences plant community dynamics. Methods We conducted growth chamber experiments to investigate the effects of biocrusts and uncrusted soil from bare patch-, Phragmites australis-, Suaeda glauca- and Tamarix chinensis-dominated habitats on seed germination percentage and mean germination time of two herbaceous plants: the perennial P. australis and the annual S. glauca. We also explored the mechanisms underlying the effects of substrate on seed germination. Important Findings Compared with uncrusted soil, biocrusts increased water content, nutrient accumulation and concentration of most salt ions, but they reduced soil pH value. Biocrusts with mosses directly decreased soil pH value and concentration of Mg2+, resulting in an indirect increase in seed germination percentage of S. glaucas. The low soil pH value also resulted in an indirect decrease in seed germination speed of P. australis in their own habitats. Bare patch directly increased accumulation of Cl−, resulting in an indirect decrease in seed germination speed of P. australis. These results suggest that biocrusts with mosses in P. australis habitats offer a window of opportunity for germination of S. glaucas. Biocrusts combined with habitat type have the potential to influence plant community structure through an effect on seed germination and establishment.

Ecosystem Birth Near Melting Glaciers: A Review on the Pioneer Role of Ground-Dwelling Arthropods.

Simple SummaryDue to climate change, glaciers are retreating. On newly deglaciated ground, ecosystems gradually evolve through the process of primary succession. This gives scientists a unique opportunity to study how a new ecosystem is born. During the first few years, before plants establish, the barren ground of sand, silt, and stones close to the ice edge is conquered by a rich variety of insects, spiders, and other small animals. Many of these are predators and their prey are either transported by air or produced in situ. The real pioneers are, however, wingless springtails that graze on biofilm containing algae or cyanobacteria. Studies of two pioneer food webs showed differences in structure and function. In the one case, beetles, spiders, and harvestmen exhibit preferences for locally produced springtails, while predators in the other example relied mainly upon midges hatching from young ponds. Pioneer communities contain a mixture of generalists and specialists. Species composition vary under different climatic and geographical conditions, depending on the available candidate species in the surrounding areas. This study illustrates flexibility in the early phase of primary succession. Certain cold loving beetles, spiders, and springtails may become extinct if glaciers disappear completely.As glaciers retreat, their forelands represent “natural laboratories” for the study of primary succession. This review describes how certain arthropods conquer pristine ground and develop food webs before the establishment of vascular plants. Based on soil samples, pitfall traps, fallout and sticky traps, gut content studies, and some unpublished data, we compare early arthropod succession on glacial forelands of northern Europe (Iceland, Norway including Svalbard, and Sweden) and of the Alps (Austria, Italy). While macroarthropod predators like ground beetles (Coleoptera: Carabidae), harvestmen (Arachnida: Opiliones), and spiders (Arachnida: Araneae) have usually been considered as pioneers, assumed to feed on airborne prey, this review explains a different pattern. Here, we highlight that springtails (Collembola), probably feeding on biofilm made up of algae or cyanobacteria, are super-pioneers, even at high altitudes and under arctic conditions. We also point out that macroarthropod predators can use locally available prey, such as springtails or non-biting midges (Diptera: Chironomidae). Pioneer arthropod communities vary under different biogeographical and climatic conditions. Two pioneer food webs, from northern Europe and the Alps, respectively, differed in structure and function. However, certain genera and orders were common to both. Generalists and specialists live together in a pioneer community. Cold-adapted specialists are threatened by glacier melting.

Hydrological response of biological soil crusts to global warming: A ten-year simulative study.

Biological soil crusts across the desert regions play a key role in regional ecological security and ecological health. They are vital biotic components of desert ecosystems that maintain soil stability, fix carbon and nitrogen, influence the establishment of vascular plants, and serve as habitats for a large number of arthropods and microorganisms, as well as influencing soil hydrological processes. Changes in temperature and precipitation are expected to influence the functioning of desert ecosystems by altering biotic components such as the species composition of biological soil crusts. However, it remains unclear how these important components will respond to the prolonged warming and reduced precipitation that is predicted to occur with climate change. To evaluate how the hydrological properties of these biological soil crusts respond to these alterations, we used open-top chambers over a 10-year period to simulate warming and reduced precipitation. Infiltration, dew entrapment, and evaporation were measured as surrogates of the hydrological functioning of biological soil crusts. It was found that the ongoing warming coupled with reduced precipitation will more strongly affect moss in crustal communities than lichens and cyanobacteria, which will lead to a direct alteration of the hydrological performance of biological soil crusts. Reductions in moss abundance, surface cover, and biomass resulted in a change in structure and function of crustal communities, decreased dew entrapment, and increased infiltration and evaporation of biological soil crusts in desert ecosystems, which further impacted on the desert soil water balance.

How do Cryptogams Affect Vascular Plant Establishment?

Abstract There are many conflicting reports regarding the effects of cryptogamic biological soil crusts on seed germination, seedling emergence and plant establishment. The current research investigated the effects of cryptogams (mosses and lichens) on seedling emergence and initial establishment of two vascular plants, namely Stipa barbata and S. capensis, under greenhouse conditions. For this purpose, 28 cylindrical pots were used to carefully transport field soil to the greenhouse, from two adjacent areas with similar conditions with and without cryptogams in the northeast of Golestan province of Iran. For S. barbata and S. capensis seeds planted in pots, seedling emergence, establishment and performance were evaluated over two months. The rate and percentage were higher for plants, particularly S. capensis, on soils with cryptogams than those on soils without cryptogams; such improvements could be related to the effects of cryptogams on moisture, temperature and nutrient increase in soil.

Interactions between soil phototrophs and vascular plants in Himalayan cold deserts

The high-elevation cold deserts in Tibet and Himalaya are rich in soil cyanobacterial communities, which facilitate an initial establishment of vascular plants. During the following succession, the increasing cover of vascular plants modifies light intensity and nutrient availability for soil cyanobacterial community and other soil phototrophs. Despite the importance of soil phototrophic community for ecosystem functioning, surprisingly little is known about the actual interactions between vascular plants and soil phototrophs and about their variation along environmental gradients in high-elevation cold deserts. In this study, we disentangle the direct impact of vascular plants on soil phototrophic community, mainly on cyanobacteria, from indirect ones mediated through modification of soil chemistry and temperature stress along an unprecedented elevational gradient (5200–6000 m a.s.l.) using a combination of conditional inference trees, co-correspondence analysis and variation partitioning. We found that vascular plants and cyanobacteria substantially differ in their response to increasing elevation. While species richness, diversity and abundance of vascular plants decreased with elevation, the species richness, diversity and abundance of cyanobacteria growing below vascular plants did not change with elevation and the richness, abundance and diversity of cyanobacteria from bare soil increased with elevation. Cyanobacteria were generally more abundant and diverse in bare soil than in vegetated soil. This difference was caused mainly by the substantially higher abundance of cyanobacteria from orders Chroococales and Nostocales in bare soils. The diversity of cyanobacteria from vegetated-soil was unrelated to vascular plant cover, but the diversity of cyanobacteria from bare soil strongly declines with increasing plant cover. In vegetated soils, the composition of soil cyanobacterial communities was affected mainly by the species composition of vascular plants. In bare soil, the composition of soil cyanobacterial communities was driven mainly by the soil chemistry and elevation. Cyanobacterial assemblages were also indirectly affected by vascular plants through changes in soil texture and fertility, with finer and more nutrient rich soils hosting less diverse cyanobacterial communities. Our results shed light on the interactions between soil cyanobacteria and vascular plants in the high-elevation cold deserts and disentangle the role of different ecological filters in structuring soil phototrophic communities in the rapidly-warming Himalayas.

Bryophyte traits explain climate‐warming effects on tree seedling establishment

SummaryAbove the alpine tree line, bryophytes cover much of the tundra soil surface in dense, often monospecific carpets. Therefore, when climate warming enables tree seedling establishment above the tree line, interaction with the bryophyte layer is inevitable. Bryophytes are known to modify their environment in various ways. However, little is known about to which extent and by which mechanisms bryophytes affect the response of tree seedlings to climate warming.We aimed to assess and understand the importance of bryophyte species identity and traits for tree seedling performance at tree line temperatures and their response to warmer conditions. Seedlings of two common, tree line‐forming tree species (Betula pubescensandPinus sylvestris) were planted into intact cushions of eight common tundra bryophyte species and bryophyte‐free soil and grown for 18 weeks at current (7·0 °C) and near‐future (30–50 years; 9·2 °C) tree line average growing‐season temperatures. Seedling performance (biomass increase and N‐uptake) was measured and related to bryophyte species identity and traits indicative of their impact on the environment.Tree seedlings performed equally well or better in the presence of bryophytes than in bryophyte‐free soil, which contrasts to their usually negative effects in milder climates. In addition, seedling performance and their response to higher temperatures depended on bryophyte species and seedlings of both species grew largest in the pan‐boreal and subarctic bryophyteHylocomium splendens. However,B. pubescensseedlings showed much stronger responses to higher temperatures when grown in bryophytes than in bryophyte‐free soil, while the opposite was true forP. sylvestrisseedlings. ForB. pubescens, but not forP. sylvestris, available organic nitrogen of the bryophyte species was the trait that best predicted seedling responses to higher temperatures, likely because these seedlings had increased N‐demands.Synthesis. Climatically driven changes in bryophyte species distribution may not only have knock‐on effects on vascular plant establishment, but temperature effects on seedling performance are themselves moderated by bryophytes in a species‐specific way. Bryophyte traits can serve as a useful tool for understanding and predicting these complex interactions.

Pssst…pass the algae: succession in lichen soil crusts

Pssst…pass the algae: succession in lichen soil crusts

Liverworts to the rescue: an investigation of their efficacy as mycorrhizal inoculum for vascular plants

Summary Pezoloma ericae (D.J. Read) Baral, a widespread mycorrhizal fungus of plants in the Ericales, is known to form intracellular associations with several families of leafy liverworts (Schistochilaceae, Lepidoziaceae, Cephaloziaceae, Cephaloziellaceae) in vitro. The ecological significance of this link between vascular and non‐vascular plants is unknown. Fungal symbionts were isolated from rhizoids of the leafy liverworts Cephalozia connivens (Dicks.) Lindb. and C. bicuspidata (L.) Dum. (Cephaloziaceae), as well as from the hair roots of two dominant ericoid mycorrhiza‐forming species of European heathlands, Erica tetralix (L.) and Calluna vulgaris (L.). Using pure cultures of P. ericae, we resynthesized liverwort–fungus associations to use colonized liverworts as inoculum which was applied to substrates supporting the growth of heather seedlings and cuttings. Effects were quantified using germination, rooting, plant colonization, plant survival under waterlogging stress and growth in height in experimental systems with and without liverworts and/or fungi. Fungal symbionts growing from liverwort rhizoids readily colonized the hair roots of ericaceous plants to form typical ericoid mycorrhizas. The presence of inoculum‐bearing liverworts led to significant increases in plant growth. Erica tetralix was more responsive to inoculation than C. vulgaris. Ericaceous cuttings rooted and survived more successfully when they were coplanted with previously colonized liverwort stems. We demonstrate, under realistic ecological circumstances, that liverworts can deliver mycorrhizal inoculum and improve the establishment of vascular plants. We propose that by providing sources of mycorrhizal inoculum, symbiotic non‐vascular plants can contribute to the restoration of plant communities dominated by Ericales plants. This research leads to broader knowledge about the function of ericoid mycorrhizas in ecosystems.

Effects of biological soil crust and water availability on seedlings of three perennial Patagonian species

Biological soil crusts are communities composed of mosses, lichens and cyanobacteria. They cover a large portion of the arid and semiarid regions of the world and play key roles in nutrient cycles and soil erosion diminution. Biological soil crust might affect germination, establishment and growth of vascular plants. In this study we examined the differential response to soil cover and water availability of grasses and shrubs. Our hypothesis was that seed germination and seedling survival are greater in soils with biological soil crust cover because crust have positive effects on vascular plant establishment. We evaluated the effect of biological soil crust cover on seed emergence, survival and seedling growth of Nassella tenuis, Senecio subulatus and Larrea divaricata. The experiment had four treatments combining biological soil crust (C) or bare soil (BS) with drought (D) or soil at field capacity (FC). Seeds of L. divaricata did not germinate and S. subulatus only germinated in BS-FC. Emergence and biomass of seedlings of N. tenuis were higher with C and at FC. There were no differences in seedling survival. Soil cover with biological soil crust and water availability influenced germination and seedling growth and their effects are different according to the species or plant functional groups. Germination of seeds varies with the composition and structure of the biological soil crust and the vascular plants, and the response may change with different species or plant functional groups.

Biological soil crust influence on germination and rooting of two key species in a Stipa tenacissima steppe

Background and aims In Mediterranean steppes, Stipa tenacissima tussocks facilitate the establishment of vascular plants. We hypothesized that this effect may partially reflect the indirect interaction between Stipa tenacissima, biological soil crusts (BSC), and seeds. Methods We explored the relationship between BSC composition and soil surface conditions (surface roughness and hydrophobicity by using the water drop penetration time test), and seed germination and seedling rooting in aS. tenacissima steppe in southeastern Spain. We explored the causal factors of seed germination at two spatial scales and used SADIE index to represents the soil surface heterogeneity. Results Microsites strongly differed in BSC compositionand soilsurface conditions. Germination of two key species, Pistacia lentiscus and Brachypodium retusum, was not affected by BSC type. In contrast, rooting was lower on soil from open areas covered by BSC than on soil from open areas dominated by bare soil and soil collected under the tussocks. The effect was similar in both species. Lichens were probably responsible for the decrease in rooting. Conclusions Our results suggest that lichen cover and the cover of bare soil and mosses may hamper and facilitate rooting, respectively. By affecting seedling rooting, BSC may contribute to the facilitative effect of Stipa tenacissima.

Influence of Different Bryophyte Carpets on Vascular Plant Establishment Around Pools in Restored Peatlands

AbstractVascular plants associated to natural peatland pools do not spontaneously colonize edges of man‐made pools in restored peatlands and have proven to be recalcitrant to the usual restoration techniques. The goal of this study was to evaluate the effect of the species used as a seedbed (Cladopodiella fluitans, Sphagnum cuspidatum, or Sphagnum magellanicum) and its developmental stage (established carpet or newly reintroduced fragments) on establishment success in the field of the seeds of four vascular species: Carex limosa, Carex magellanica, Carex oligosperma, and Scheuchzeria palustris. The germination rate was measured after one season and growth after two seasons. Seedbed composition and developmental stage had no effect on Carex, whereas the germination of S. palustris was higher on S. cuspidatum. Growth of vascular plants was slightly improved on S. magellanicum carpets and was lower on seedbeds of C. fluitans. Our results lead us to recommend seeding at the same time as bryophyte fragments are spread and fostering introduction of Sphagnum mosses, preferably to C. fluitans, around artificial pool edges. Copyright © 2013 John Wiley & Sons, Ltd.

Peatlands in a changing world

Peatlands in a changing world

Carbon exchange in biological soil crust communities under differential temperatures and soil water contents: implications for global change

AbstractBiological soil crusts (biocrusts) are an integral part of the soil system in arid regions worldwide, stabilizing soil surfaces, aiding vascular plant establishment, and are significant sources of ecosystem nitrogen and carbon. Hydration and temperature primarily control ecosystem CO2 flux in these systems. Using constructed mesocosms for incubations under controlled laboratory conditions, we examined the effect of temperature (5–35 °C) and water content (WC, 20–100%) on CO2 exchange in light (cyanobacterially dominated) and dark (cyanobacteria/lichen and moss dominated) biocrusts of the cool Colorado Plateau Desert in Utah and the hot Chihuahuan Desert in New Mexico. In light crusts from both Utah and New Mexico, net photosynthesis was highest at temperatures >30 °C. Net photosynthesis in light crusts from Utah was relatively insensitive to changes in soil moisture. In contrast, light crusts from New Mexico tended to exhibit higher rates of net photosynthesis at higher soil moisture. Dark crusts originating from both sites exhibited the greatest net photosynthesis at intermediate soil water content (40–60%). Declines in net photosynthesis were observed in dark crusts with crusts from Utah showing declines at temperatures >25 °C and those originating from New Mexico showing declines at temperatures >35 °C. Maximum net photosynthesis in all crust types from all locations were strongly influenced by offsets in the optimal temperature and water content for gross photosynthesis compared with dark respiration. Gross photosynthesis tended to be maximized at some intermediate value of temperature and water content and dark respiration tended to increase linearly. The results of this study suggest biocrusts are capable of CO2 exchange under a wide range of conditions. However, significant changes in the magnitude of this exchange should be expected for the temperature and precipitation changes suggested by current climate models.

Seed characteristics and soil surface patch type interact to affect germination of semi-arid woodland species

Biological soil crusts are common in many arid and semi-arid regions and they can alter microenvironments which are likely to directly and indirectly influence vascular plant establishment. The effect of biological soil crusts on germination is also influenced by the biological characteristics of the seeds themselves but rarely have the effects of both crust type and seed morphology on germination been examined in the same study. In this study, seed of five semi-arid woodland species with contrasting seed morphology were sown on top of patch types that commonly occur in natural woodlands (foliose lichen, short-turf moss, tree leaf litter, disturbed crust) and their emergence was followed. Percent germination varied between patch types and, for the largest-seeded species (Maireana excavata), final germination was significantly lower on the biological soil crust and litter patch types because they strongly acted as a physical barrier to seed penetration into the soil. The remaining four species showed no significant differences in final percent germination with patch type because most seeds either completely or partially penetrated the surface layer. Germination time courses, however, showed that biological soil crusts delayed the timing of germination of these species. Hence, soil crusts might differentially affect the spatial patterning of species in semi-arid woodlands by their subtle influence on seedling emergence that is determined by differences in seed morphology and subsequent positioning within crusts.

Disturbance of the biological soil crusts and performance of Stipa tenacissima in a semi-arid Mediterranean steppe

Biological soil crusts (BSC) play a major role in water and nutrient fluxes in semi-arid and arid areas, affecting the establishment of vascular plants and contributing to the spatial arrangement of vegetated and open areas. However, little is known regarding their effects on the performance of extant vegetation. By using experimental manipulations (surface soil cutting and herbiciding), we evaluated the effect of the physical structure and the biotic component of smooth biological soil crusts on soil moisture dynamics, and on the nutrient and water status, growth rate, and reproductive effort of Stipa tenacissima tussocks in a semi-arid steppe. Soil moisture content was weakly reduced after cutting the soil surface and was not affected by herbicide application. Cutting and herbiciding the biological soil crust had no effect on most morpho-functional and reproductive traits measured in S. tenacissima tussocks. The integrated water use efficiency of this species, as measured by 13C natural enrichment, decreased when the biotic community of biological soil crusts was killed with herbicide. In the S. tenacissima steppe studied, killing the BSC and breaking the continuity of the structural crust had a weak effect on the short-term performance of this species, but our results suggest that BSC exert a control on slope hydrology beyond that provided by physical soil crusts.