Abstract
Vegetation rings are a common pattern in water-limited environments and mostly occur in clonal plants. This study presents, for the first time, rings of the geophyte species Urginea maritima. The rings, typically 40–90 cm in diameter, are abundant in the sandy environment of Little Petra and Wadi Rum, in the southern Jordanian drylands. Soil properties were studied in the rings’ center, periphery, and matrix. Soil-water volumetric content was significantly higher in the rings’ periphery than in the center and matrix. The soil organic carbon was highest in the periphery, intermediate in the center, and lowest in the matrix. At the same time, the soil texture, hydraulic conductivity, and gravimetric moisture content at the hygroscopic level were similar in the three microenvironments. According to the results, a possible ring formation mechanism is the soil-water uptake mechanism, which results in competition between the plants at the periphery and those in the center and is generally attributed to plants with large lateral root zones. Numerical simulations of a mathematical model implemented in this study support the soil-water uptake mechanism. A second possible mechanism is negative plant-soil feedback due to the accumulation of dead biomass and its consequent decomposition, with the resultant release of autotoxic compounds. It is possible that several mechanisms occur simultaneously and synergistically affect the formation of U. maritima rings.
Highlights
We used the mathematical model introduced by Gilad et al [22,23], which has been used in the context of ring formation in drylands [1,9,10,11], and here, we briefly describe its main assumptions
This soil property was significantly higher in the periphery than in the center and matrix, whereas the soil-water content in the matrix and center was similar
This study suggests that the U. maritima rings in the drylands of southern Jordan are formed due to the water uptake mechanism, which is attributed to the extended lateral roots of this geophyte species
Summary
The first is the infiltration feedback that increases surface water flow towards the ring periphery This feedback can be further enhanced by aeolian processes and biocrust growth in the patch’s center and matrix [7,8,9]. Land 2022, 11, 285 flow towards the ring periphery The study’s hypothesis was that ring formation is related to intraspecific competition for water between the ramets at the periphery and those a the center, which causes a central dieback and an outwardly expanding rin3go.f 11. The results were divided by 1.724 to calculate soil organic carbon (SOC)
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