Leaf expansion, photosynthesis, and water relations of sunflower plants grown on compacted soil

Abstract

Leaf expansion and growth response of sunflower (Helianthus annuus, L.) to soil compaction were investigated in relation to compaction effects on water relations, nitrogen nutrition, and photosynthesis. A series of field experiments were conducted with plants grown in 20 cm-diameter cylinders with soil bulk densities ranging from 1.2 to 1.7 g cm -3 at the 0-20 cm depth (equivalent to 0.8 to 2.4 MPa soil strength measured with a soil penetrometer). Relative leaf expansion rate (RLER) decreased linearly with increasing soil strength. Smaller plant size in compacted treatments was due not only to slower expansion rates, but also smaller maximum size of individual leaves. Sensitivity of leaf expansion to soil strength was best illustrated by a reduction in RLER and maximum size of the first leaf to emerge in a treatment with only the lower 10-20 cm of the profile compacted (bulk density of 1.7 g cm-3). Root growth was less affected than shoot growth by compaction and root:shoot ratios of compacted treatments were significantly higher than the control.Soil compaction had no significant effect on pre-dawn or midday leaf water potential, osmotic potential or leaf turgor. Specific leaf weight was usually higher in plants grown on compacted soil, and leaf nitrogen and photosynthesis per unit leaf area were either unaffected by treatment or significantly higher in compacted treatments. The results suggest that early growth reduction of sunflower plants grown on compacted soil was more sink-than source-limited with regard to water, nitrogen, and carbon supply. Further evaluation of this hypothesis will require verification that these whole-leaf measurements provided a sufficiently accurate approximation of treatment effects on the dynamic equilibria of expanding cells.

Interspecific differences in root architecture among maize and triticale genotypes grown under drought, waterlogging and soil compaction

“…Results obtained in this work confirm that severe levels of soil compaction led to reduction in shoot and root In columns (genotype) with similar letters do not differ significantly at 0.05 probability level according to Duncan's multiple range test * Total length of 2 or 3 seminal adventitious roots of maize and triticale genotypes, respectively growth. Several authors have pointed out effects of soil impedance on reduction of plant dry matter, size, and yield (Andrade et al 1993;Lipiec et al 1993;Whalley and Dexter 1994). Reduction in dry matter of maize shoots in compact soil conditions was mostly due to reduction in leaf area, stem diameter and plant height (Lipiec et al 1996) ( Tables 6, 7).…”

‘Soil conditions and plant growth’

“…However, there can also be a substantial feedforward response, i.e. a response to compaction that cannot be readily explained in terms of the supply of water and nutrients to the shoot (Masle & Passioura 1987;Andrade, Wolfe & Fereres 1993;Mulholland et al . 1996;Stirzaker, Passioura & Wilms 1996;Masle 1998) Figure 1 shows the leaf area of plants whose roots were growing in soil of various hardness.…”

Is coordination of leaf and root growth mediated by abscisic acid? Opinion

“…Leaf growth is reduced in dry and saline soil while leaf water status is maintained by either pressurising the soil to raise the xylem hydrostatic pressure to zero and consequently the shoot water status to its maximum (Passioura, 1988;Termaat et al, 1985) or by a splitroot design so that some roots obtain enough water to keep the shoot water status high (Gowing et al, 1990;Saab and Sharp, 1989). Leaf growth is reduced in compacted soil despite shoot water and nutrient status being maintained (Andrade et al, 1993;Masle and Passioura, 1987;Passioura and Gardner, 1990). Leaf growth is reduced in nitrogen-deficient soil before photosynthesis is affected .…”