Alternate Bearing in Pistachio as a Masting Phenomenon: Construction Cost of Reproduction versus Vegetative Growth and Storage

Abstract

Whole-tree effects of alternate bearing on the reproductive growth, vegetative growth, and carbohydrate storage in mature pistachio (scion Pistacia vera L., rootstock Pistacia atlantica Desf.) were examined. Although it is generally accepted that the “off” year in pistachio may be used to accumulate carbohydrate reserves, it was found that starch and sugars from the “off” year equaled only 8% of the construction cost of the “on” year's fruit load. The dry mass increase in perennial woody tissue of roots, trunk and branches in the “off” year (20.2 kg/tree), was 75% of the mass of fruit in “on” trees (26.4 kg/tree). When construction cost of wood and fruit is considered, “off” year woody tissue growth is 64% of “on” year fruit growth. Since previous studies have shown that leaf dry mass is generally 30% greater in “off” than “on” pistachio trees, we conclude that the overall production of biomass in “off” and “on” year pistachio is similar. Therefore, we suggest that the “off” year is not a period of substantial storage carbohydrate accumulation, but rather a switch in allocation from reproductive to vegetative growth. This is consistent with ecologically based theories of the adaptive advantage of masting behavior, and suggests that withholding water and fertilizer during the “off” year may not harm “on” year yield.