Measurement and Modeling of Carbon Balance of the Apple Tree

Received for publication 15 Oct. 1998. Accepted for publication 17 Nov. 1998. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact. Apple (Malus ×domestica Borkh.) trees can produce very large crops under optimal conditions. In New Zealand, record yields approaching 120 to 140 t·ha fresh weight (≈18–20 t·ha dry weight) have been sustained over several years (D.S. Tustin, personal communication). The high yields in New Zealand have been attributed to relatively cool but sunny growing conditions and a long postharvest season (Wünsche and Palmer, 1997). Thus, for a C3 crop, apple has high potential productivity. In a classic study, Monteith (1977) elucidated that dry-matter productivity of crops, including apple, is essentially a linear function of total radiant energy interception over the season. The slope of the relationship (i.e., the conversion of absorbed radiation to dry matter) is called the “dry matter : radiation quotient” (Russell et al., 1989). This relationship has been further verified for apple (Palmer, 1988, 1989). Many reports indicate that yields of apple orchards are correlated with light interception, although high light interception does not guarantee high yields because of detrimental effects of excessive shade within the canopies (see reviews by Jackson, 1980; Lakso, 1994; Palmer, 1989; and Wagenmakers, 1991, 1996). We will review the components of light interception, the conversion to dry matter, and the partitioning of dry matter to fruit that lead to the high productivity of apple.