Size-class structure and growth traits of Anastatica hierochuntica L. populations as rainfall indicators in aridlands

Field data verified by green house experiment were used to evaluate the response of Anastatica hierochuntica L. to the amount of rainfall. Field study of the populations was carried out in the runnel and depression microhabitats of gravel and sand sites. Four water treatments, equivalent to 100, 200, 500 and 1000 mmrainfall, were used to simulate different levels of water availability. Under 500 and 1000 mm rainfall, the size-class structure of A. hierochuntica populations consists of a high proportion of large size-class individuals, while a higher proportion of small size-class individuals was obtained under 100 and 200 mm rainfall. The dry skeletons of A. hierochuntica can be used as a ‘‘rain gauge’’ to predict the amount of rain or water received. The dominance of small size-classes (from 1 to 8 cm^3) gives a prediction of less than 200 mm rainfall received. Intermediate size-classes(8–64 cm^3) characterize habitats with 200–500 mm rainfall, while habitats with 500 mm rainfall produce large size-classes ( 64 cm^3). Small size-class individuals produced under low amounts of rainfall allocated up to 60% of their phytomass to the reproductive organs. Allocation to reproductive organs decreased with the increase in the amount of rainfall, while allocation to the stem increased in large size-class individuals produced under the highest amount of rainfall (1000 mm) reaching 54%. Increased allocation to stem in large-sized individuals favours the hygrochastic seed dispersal role in the plant. The root/shoot ratio decreased with the increase of the individual sizeclass, i.e. under high rainfall treatments. Higher values of relative growth rate, net assimilation rate and leaf area index were obtained under high water treatments. Conversely, less expanded leaves, i.e. lower specific leaf area, were manifested in the lowest water treatments.