Influence of mechanical root restriction on gas-exchange of four papaya genotypes

Abstract

Four papaya genotypes, two from the ‘Solo’ group (Sunrise Solo TJ and Improved Sunrise Solo line 72/12) and two from the ‘Formosa’ group (Tainung 02 and Know You 01) grown in ultisol under field conditions in Macaé, RJ, Brazil, were used in this study. Two different effective depths (ED) were determined in the area using a penetrographer with average soil moisture of 11.2%. The area with ED of 0.35 m with a maximum pressure of 4.12 MPa for penetration was defined as an area with restriction (WR) to root growth, while, the area with minimum ED of 0.60 m and a pressure lower than 2.30 MPa as an area with no restriction (NR). The net CO2 assimilation rate (A), stomatal conductance (g s), leaf temperature (Tl), intercellular partial pressure of CO2 (c i) and intrinsic water use efficiency (IWUE) were evaluated for three consecutive days after irrigation. Mechanical root restriction affected gas exchange of the four papaya genotypes. All genotypes grown in the WR area had lower A, g s and c i and higher Tl than the same genotypes in the NR area. All genotypes grown in the WR area had high IWUE and Sunrise Solo TJ had the highest IWUE.

Ecophysiology of papaya: a review

“…The absence of margin cell formation in the vascular bundles of papaya leaves (Buisson and Lee, 1993) is a characteristic associated with C 3 metabolism. Maximum net carbon assimilation (A) rates of 25 to 30 µmol m -2 s -1 are achieved at 2000 µmol m -2 s -1 photosynthetic photo flux density (PPFD) (Marler and Mickelbart, 1998;Campostrini and Yamanishi, 2001;Reis, 2007). While photorespiration in C 3 plants can decrease the net efficiency of carbon assimilation by 25 to 30% (Lawlor, 1993), papaya can maintain high A rates under well-watered and PPFD saturating conditions suggesting minimal photorespiration losses and adaptation to high light intensities.…”

“…Chronic photoinhibition also decreases A rates at light levels above saturation, in this case through damage and replacement of the D1 protein in the reaction center of PSII by excess PPFD (Critchley, 1998). Sink strength will also limit A rates in papaya (Campostrini and Yamanishi, 2001).…”

“…In addition, naturally dense soil layers or fragipans, common in tropical and subtropical soils that represent a significant area for potential papaya production, May ultimately impede root growth (Unger and Kaspar, 1994). Soil compaction will reduce gas exchange, chlorophyll content, F v /F m , and growth Yamanishi et al, 1998;Campostrini e Yamanishi, 2001). In studies Campostrini and Yamanishi, 2001) evaluating cultivar adaptation to soil compaction and root restriction, all cultivars had reduced total leaf number, average leaf area, length of leaf central vein, total leaf area, trunk diameter and tree height compared to nonrestricted plants.…”

“…Soil compaction will reduce gas exchange, chlorophyll content, F v /F m , and growth Yamanishi et al, 1998;Campostrini e Yamanishi, 2001). In studies Campostrini and Yamanishi, 2001) evaluating cultivar adaptation to soil compaction and root restriction, all cultivars had reduced total leaf number, average leaf area, length of leaf central vein, total leaf area, trunk diameter and tree height compared to nonrestricted plants. Campostrini et al (1998) concluded that rooting volume restriction induced senescence as a general physiological response.…”

Gas Exchange and Photochemical Efficiency in Lima Bean Genotypes Grown in Compacted Soils

“…Reductions in the photosynthetic rate were also observed by Tu and Tan (1988) in common bean varieties grown in compacted soil (1.6 g cm -3 ), with reductions of up to 46%. Campostrini and Yamanishi (2001), observed reductions in the photosynthetic rates (28 to 51%) of papaya genotypes grown in compacted soil (4.12 MPa), and attributed this result to the reduction of stomatal conductance caused by the transport of abscisic acid from the root to the shoot.…”