Cushion Shrubs Encroach Subhumid Rangelands: Fertility Islands in Fragile Soils Along a Grazing Gradient in Patagonia

PurposeThis work assesses changes in soil and vegetation structure associated with grazing intensity (GI) in subhumid grasslands. We conducted the study in the Subandean district of Patagonia, Argentina. Non-degraded Subandean grass steppes have extremely erodible volcanic soils and are valuable grazing ranges. However, nowadays vast portions exhibit a heterogeneous cover that is mostly of cushions shrubs, with big eroded soil patches.MethodsWe selected four study sites along a GI gradient and one grazed-excluded site. Soils, vegetation cover and patches structure were characterised. We took soil samples beneath grass and shrub patches and their interpatches and in undisturbed spots. ResultsSoils in undisturbed spots had the highest chemical fertility. Soils in grazing areas showed high heterogeneity associated with plant life-form and GI. Results also showed that medium and fine sand particles remobilised from bare soil to vegetated patches. Total nitrogen and organic matter increased in the same direction. Grass cover decreased as GI increases, while shrubs cover and total richness increased, until a collapse at the highest intensity. Relative cover of cushion shrubs and bare soil grow steadily with GI. ConclusionsThe fertility island effect was associated with cushion shrubs. Grazing caused cushion shrub encroachment regardless of its intensity. Notwithstanding this, the same disturbance -grazing- which promoted cushions prevalence also favoured the collapse of fertile islands when reached to maximum intensity. Ecosystem services provision from a range management standpoint decreased. However, the increases in richness under moderate GI could represent an enhancement in system functionality.

An updated checklist and quantitative analysis of the Marmarica Plateau flora, in the north-eastern part of Libya

The Marmarica Plateau, which is situated on both sides of the Libyan-Egyptian border, has significant historical and ecological importance. Nevertheless, its botanical components have not been updated or reviewed recently. This paper aims to study the floristic composition of the plateau on the Libyan side by a comprehensive review of the five most detailed studies conducted in the area during the period 1930−2008. The study area covers only 3.4% of the Libyan territory, while the plant inventory at the species level comprises 31% (642/2082) of the National flora. Plant life-form is dominated by therophytes (60.7%) and chamaephytes (23.7%). Seven taxa are new records for the Libyan flora, 14 are alien, 28 were cultivated, and 37 taxa are endemic or near-endemic to the Libyan flora and nearby countries. A total of 225 taxa have not been recorded since 1930, which revealed that they are scarce and may have gone locally extinct due to climatic and unsustainable anthropogenic stresses. Another possibility is that these taxa may be incorrectly identified in the original publications, and this data have never been updated. The present study highlighted the richness and importance of the flora in the Libyan part of the Marmarica Plateau, necessitating conservation intervention, particularly for protecting endemic and rare plants and the biodiversity hotspots.

Guest Essay Global hosts and global pathogens: a perspective

Plant species are assailed by a remarkable diversity of pathogens, and these and other pests pose a serious direct risk to collections in botanic gardens as well as a potential source of pathogen escape. The high diversity of species in gardens combined with low population numbers minimises the likelihood of disease spread of specialist pathogens, but importation of novel pathogens is a constant concern. In parallel with natural systems, there is little data on pathogen loads in botanic gardens, on what accession policies minimise these and if such loads are likely to differ by country of origin or plant life form. Nevertheless, commonsense measures such as prohibiting the importation of plants in soil, shifting to seed and in vitro propagation, and inspection and quarantine on receiving and transferring plants should be implemented.This edition of Sibbaldia explores a variety of directions for improving our ability to develop strategies for dealing not just with pathogen threats, but with a more rational approach to pests and to microbial interactions that are a natural part of a plant’s heritage.

Host identity and functional traits determine the community composition of the arbuscular mycorrhizal fungi in facultative epiphytic plant species

ABSTRACTThe epiphytic vascular flora is scarce and facultative in semiarid Mediterranean ecosystems, thus covering diverse taxonomic groups. However, differently to terrestrial conditions, little is known about the factors driving mycorrhizal communities in epiphytic environments. Here, we investigated the arbuscular mycorrhizal fungi (AMF) harboured by 31 plant species occurring in the trunks of Phoenix dactylifera. We wanted to ascertain if host identity and plant functional traits shape mycorrhizal communities. Specifically, we tested the plant life-cycle (perennial versus annual), the plant life-form (herbaceous versus woody), the plant origin (exotic versus native) and the plant species.The roots were examined by molecular and phylogenetic analysis of AMF community. The plant affiliation to species strongly influenced the AMF assemblages. Plant life-form and plant life-cycle also shaped AMF interactions. The AMF community differed between annual and perennial species and higher AMF richness was detected in perennial plants. The indicator species analysis revealed three Operational Taxonomic Units belonging to the Glomeraceae, associated with annual species. However, the epiphytic plants associated with AMF irrespective of whether they were native or not, probably because here no functional differences derive from plant origin.IMPORTANCEArbuscular mycorrhizal (AM) symbiosis has a decisive role in plant nutrient and water uptake by plants, with particular importance in stressful environments. Under semiarid conditions, the facultative epiphytic flora should cope with harsh conditions. While numerous studies have been conducted on factors driving terrestrial AM assemblages, the epiphytic environment remains unexplored. We offer new insights into composition of AM communities as shaped by epiphytic plant host identity and functional traits.