An arthropod community beyond the dry limit of plant life

Water availability,which enables plant growth and animal activity,regulates dryland ecosystem function.In hyper-arid ecosystems,rain cannot support vascular plant growth.Therefore,hyper-arid vegetation is restricted to the lower topography,where runoff accumulates.Typically,food resources originating from areas of dense vegetation are dispersed across the desert floor,enabling animal life in areas lacking vascular plant growth.However,certain regions,such as the hyper-arid upper topography,may be devoid of plant-derived food resources.The present study examined arthropod activity in the upper topography of a hyper-arid desert,in comparison with arthropod activity in the lower topography.Pitfall traps were utilized to compare arthropod activity along unvegetated ridges with activity in parallel,vegetated riverbeds.Surprisingly,the study revealed dense arthropod communities in the barren upper topography.Arthropods collected in the upper topography represented 26%of total arthropod abundance.In addition,the overlap between arthropod identity in the ridges and wadis(i.e.,riverbeds)was low,and certain arthropods were strongly affiliated with the ridges.The upper topographic communities included high numbers of silverfish(Zygentoma:Lepismatidae),malachite beetles(Psiloderes),and predatory mites(Acari:Anystidae),and these arthropods were present at various life stages.It remains unclear how arthropod communities can persist in the unvegetated upper topography of the hyper-arid study area.These results raise the possibility that other food sources,independent from vascular plants,may play a significant role in the life history of hyper-arid arthropods.

Unexpectedly low δ^(13)C in leaves,branches,stems and roots of three acacia species growing in hyper-arid environments

Aims In plant eco-physiology,less negative(enriched)carbon 13(^(13)C)in the leaves indicates conditions of reducing leaf gas exchange through stomata,e.g.under drought.In addition,^(13)C is expected to be less negative in non-photosynthetic tissues as compared with leaves.However,these relationships inδ^(13)C from leaves(photosynthetic organs)to branches,stems and roots(non-photosynthetic organs)are rarely tested across multiple closely related tree species,multiple compartments,or in trees growing under extreme heat and drought.Methods We measured leaf-to-root^(13)C in three closely related desert acacia species(Acacia tortilis,A.raddiana and A.pachyceras).We measuredδ^(13)C in leaf tissues from mature trees in southern Israel.In parallel,a 7-year irrigation experiment with 0.5,1.0 or 4.0 L day1 was conducted in an experimental orchard.At the end of the experiment,growth parameters andδ^(13)C were measured in leaves,branches,stems and roots.Important Findings Theδ^(13)C in leaf tissues sampled from mature trees was ca.-27‰,far more depleted than expected from a desert tree growing in one of the Earth's driest and hottest environments.Across acacia species and compartments,δ^(13)C was not enriched at all irrigation levels(-28‰to ca.-27‰),confirming our measurements in the mature trees.Among compartments,leafδ^(13)C was unexpectedly similar to branch and rootδ^(13)C,and surprisingly,even less negative than stemδ^(13)C.The highly depleted leafδ^(13)C suggests that these trees have high stomatai gas exchange,despite growing in extremely dry habitats.The lack ofδ^(13)C enrichment in nonphotosynthetic tissues might be related to the seasonal coupling of growth of leaves and heterotrophic tissues.