Biomass partitioning in response to soil drought: A pot experiment with Prunus dulcis trees during four years

Growth and biomass partitioning of almond trees [Prunus dulcis (Miller) D.A .Webb] were investigated in a semi-controlled pot experiment under arid con ditions in the Negev Desert (Israel). Single trees of two varieties grafted on a local rootstock were grown for 1 to 4 years in pots of 3 in diameter and 1, 2 and 3 m depth, which resulted in 7, 14 and 21 m(3) soil volume. Th e pots were watered to field capacity once per year at the beginning of eac h growing season. Thus the plants received different amounts of water in re lation to their biomass and leaf area as a function of their age and pot vo lume. This procedure resulted in different rates of soil drying and differe nt stages of water deficit throughout the season, which allowed an investig ation of the interactive effect of both seasonally varying water status and atmospheric conditions for a woody species in large soil volumes. We prima rily tested whether a progressive reduction in the amount of water applied to the trees in relation to their leaf area would increase (1) biomass part itioning in favour of roots, especially fine roots, (2) the ratio of fine r oot length to leaf area. Neither biomass partitioning into leaves nor fine roots was significantly i nfluenced by the amount of water supplied. There was no effect of water sup ply on the relationship between fine root length and finch root biomass (sp ecific root length) either. Consequently, the relationship between length o f fine roots and leaf area was not dependent on the amount of available wat er. The constant relationship between most of the biomass partitioning para meters examined in spite of the great range in water availability and over several years of growth is discussed as the result of the seasonal variatio n in the interaction of water supply and demand on tree growth and biomass distribution.