Annual biomass increment and biomass partitioning to leaves, roots and reproduction, and biomass storage in the below-ground bulb was measured in plants of two species of the geophytic genus Bellevalia grown outdoors at three levels of soil moisture. The differences between the species were in accordance with the hypothesis that plants of more arid environments should rely more on internal reserves than plants of more productive environments. In Bellevalia desertorum, a shallow rooted species of the most arid habitats in the Central Negev, leaf and root development during outgrowth at the beginning of winter was rather variable, and followed soil moisture availability to a certain degree. A small portion of its biomass budget was committed to seed production, which varied little among the irrigation regimes. The rest of the biomass was stored in the bulb. The amount of biomass devoted annually to reproduction was mainly determined by the amount of reserves already present in the bulb. In contrast, in B. eigii, which grows in the more productive wadis with its bulb at a depth of 15 to 30 cm, leaf and root growth was not only determined by water availability, but also by initial bulb mass. This resulted in a greater potential relative growth rate than in B. desertorum, but also in a greater risk of accumulating less biomass than it spent in root and leaf construction under poor soil moisture conditions. In this species, reproductive biomass and seed yield were proportional to current biomass gain and, in contrast to B. desertorum, independent of initial bulb mass, provided that the bulb was large enough to initiate flowering.
Keywords: Below-ground biomass storage; Biomass partitioning; Desert geophytes; Net biomass production; Reproductive biomass; Water availability.