Effects of regulated deficit irrigation during the pre-harvest period on gas exchange, leaf development and crop yield of mature almond trees

Abstract

We investigated the effects of regulated deficit irrigation (RDI) during the pre-harvest period (kernel-filling stage) on water relations, leaf development and crop yield in mature almond (Prunus dulcis (Mill.) D.A. Webb cv. Cartagenera) trees during a 2-year field experiment. Trees were either irrigated at full-crop evapotranspiration (ETc=100%) (well-irrigated control treatment) or subjected to an RDI treatment that consisted of full irrigation for the full season, except from early June to early August (kernel-filling stage), when 20% ETc was applied. The severity of water stress was characterized by measurements of soil water content, predawn leaf water potential (Psipd) and relative water content (RWC). Stomatal conductance (gs), net CO2 assimilation rate (A), transpiration rate (E), leaf abscission, leaf expansion rate and crop yield were also measured. In both years, Psipd and RWC of well-irrigated trees were maintained above -1.0 MPa and 92%, respectively, whereas the corresponding values for trees in the RDI treatment were -2.37 MPa and 82%. Long-term water stress led to a progressive decline in gs, A and E, with significant reductions after 21 days in the RDI treatment. At the time of maximum stress (48 days after commencement of RDI), A, gs and E were 64, 67 and 56% lower than control values, respectively. High correlations between A, E and gs were observed. Plant water status recovered within 15 days after the resumption of irrigation and was associated with recovery of soil water content. A relatively rapid and complete recovery of A and gs was also observed, although the recovery was slower than for Psipd and RWC. Severe water stress during the kernel-filling stage resulted in premature defoliation (caused by increased leaf abscission) and a reduction in leaf growth rate, which decreased tree leaf area. Although kernel yield was correlated with leaf water potential, RDI caused a nonsignificant 7% reduction in kernel yield and had no effect on kernel size. The RDI treatment also improved water-use efficiency because about 30% less irrigation water was applied in the RDI treatment than in the control treatment. We conclude that high-cropping almonds can be successfully grown in semiarid regions in an RDI regime provided that Psipd is maintained above a threshold value of -2 MPa.

Response to severe water stress of the almond(Prunus amygdalus)’Ferragnès’ grafted on eight rootstocks

“…^pd on 31 July 2002 was higher on the Drepanoto and GN-22 than on the remaining rootstocks. Common levels of ^pd of almond trees grown under irrigation were maintained above -1.0 MPa whereas ^pd was significantly lower in non-irrigated trees (<-2 MPa) than in irrigated ones (Romero et al 2003). ^pdOf almond trees maintained in a growth chamber at 90, 60, and 30% of available water decreased from -1.1 to -1.2 and -2 MPa respectively (Dettori 1987).…”

“…This tolerance is conferred from the rootstock to the scions (Massai & Gucci 1997) and therefore, where water for irrigation is not available, selection of rootstocks more tolerant to water stress than 'Ferragnès' is considered critical for tree survival and good performance. Adaptation of a rootstock to water stress may involve maintenance of high photosynthetic rate and stomatal conductance, a decrease of transpirational water loss, and a reduction of growth of the tree (Romero et al 2003).…”

Synergistic Effect of Selenium Addition and Water Stress on <i>Melilotus officinalis</i> L. Mineral Content

“…However, under the addition of 3 mg Se L -1 , Ca has followed the same pattern as the other macro-nutrients, while Mg had no significant difference in its concentration. Water treatment could affect the nutrient balance in plants (Romero et al, 2004). Its combination with Se addition at various levels could have contrasting effects on nutrient uptake.…”

Drought susceptibility and recovery of transplanted Quercus rubra seedlings in relation to root system morphology

“…Strong positive linear relationships were detected between g s , A, and E in our study as similarly observed for mature almond (Prunus dulcis (Mill.)) trees (Romero et al, 2004). In contrast, water deficits may decrease A directly by affecting the metabolic and photochemical process in the leaf or indirectly through stomatal closure leading to cessation of leaf growth and consequent decreased leaf area.…”