Effects of irrigation deprivation during the harvest period on nonstructural carbohydrate and nitrogen contents of dormant, mature almond trees

Effect of irrigation deprivation during the harvest period on the nonstruct ural carbohydrate (NC) content of dormant, mature, field-grown almond (Prun us dulcis (NEU.) D.A. Webb cv. Nonpareil) trees was studied. Roots, trunk, branches, spurs and stems of 12 trees were subsampled in February 1997, acr oss a gradient of irrigation treatments (FI = fully irrigated, MS = moderat ely stressed and SS = severely stressed) to relate NC concentration to the degree of water stress experienced by individual trees during the previous (1996) harvest period. To assess the effect of water stress on whole-tree N C content, three dormant FI trees and three dormant SS trees were excavated on December 10, 1997, and dry weights and NC and N concentrations of the t ree components were determined. Whole-tree biomass did not differ significa ntly between FI and SS trees, although SS trees tended to have less total d ry weight. Although roots constituted just 13% of tree biomass, they stored 36 and 44% of tree NC and N contents, respectively. There were negative re lationships between the seasonal minimum values of both midday (psi (ms)) a nd predawn (psi (pd)) stem water potentials during the harvest period and r oot NC content of dormant trees. Severe water stress during the harvest per iod resulted in a 26% reduction in NC content and a 50% reduction in biomas s of current-year stems (> 5 cm in length) per tree. The reduction in NC co ntent is consistent with the previously reported late season reductions in leaf function and persistence. The SS trees exhibited a reduction in NC con tent but not in N content per tree, indicating that late season accumulatio n of NC and N were uncoupled in trees subjected to severe harvest-period wa ter stress.