Response of the components of sugar beet leaf water potential to a drying soil profile

Abstract

For many field-grown crops, including sugar beet, there is little information on the seasonal changes in leaf water potential and its components as the soil dries. Therefore, seasonal changes in leaf water, osmotic and turgor potentials of sugar beet were measured in two seasons, in crops that experienced differing degrees of soil moisture stress. In 1983 potentials of crops exposed to early and late droughts were compared with those of irrigated crops, and in 1984 measurements were made in a non-irrigated crop. In the irrigated crop the midday leaf water potential changed little during the season, except in response to fluctuating evaporative demand. In the drought and non-irrigated treatments there was a sharp fall in leaf water potential as soon as the soil water potential decreased. The size of the midday leaf water potential was primarily determined by soil dryness. However, the leaf water potential did not decrease below about -1-5 MPa in either year. The leaf osmotic potential declined at the same time as the leaf water potential, but the extent to which this happened differed in the two years. Only in the 1984 non-irrigated crop did the osmotic potential continue to decrease as the soil dried, suggesting that osmotic adjustment had taken place in 1984 but not in 1983. Thus higher turgor was maintained in the 1984 crop than in the 1983 drought-affected crops. Some turgors were recorded as apparently negative in 1983.Since the leaf water potential declined to a minimum of about -15 MPa, the soil water potential minima were also about -1-5 MPa. However, deeper soil was not dried to this extent, suggesting that the extra resistance for water uptake from deep soil was limiting or the rooting density was too low.The pattern of recovery of leaf water potential overnight suggested that the rhizosphere resistance to water movement was small, even as the soil dried. However, measurement of stem water potentials in 1984 indicated that a significant resistance to water flow existed within the aerial part of sugar beet plants. This shows that the use of the water potential in leaves as an estimate of that in stems or roots can be misleading.-a n d t h e t u r S o r P o t e n t i a l ' f v (Wallace, Clark & McGowan, 1983). Generally only f t and f, can be The flow of water from the soil to the atmosphere easily measured and \jr p is obtained by difference, via the plant is driven by a water potential gradient Turgor is considered to be a more appropriate between the leaf and the soil. The magnitude of the indicator of plant water status than i/r,, as many water potential gradient depends on the relative plant processes are turgor-dependent (Hsaio et al. rates of water absorption from the soil and water loss 1976). Use of i/r, alone ignores the possibility of from the leaf. Evaporation from the leaf lowers leaf osmotic adjustment which may allow positive turgor water potential and this change is transmitted via to be maintained even when i/r t becomes low. the xylem to the root, and hence to the soil.There is limited in...

Assessing water uptake in sugar beet ( Beta vulgaris ) under different watering regimes

“…Considering the total amount of water taken up (on average 5600 ml for all treatments), there was limited water uptake from 90 cm depth (Figure 1) before the shallow soil layers were depleted, as previously observed in the field (Brown et al 1987). Our findings suggest this is, at least in part, due to a lack of secondary xylem, as previously been seen by Mapfumo et al (1993).…”

Evaluation of Yield and Quality of Some Sugar Beet Varieties Under Salinity Conditions at Port-Said Governorate, Egypt

“…fresh weight) with substantial augmentation amounted to (1.03 and 1.08 mg/g) and (1.61 and 1.77 mg/g) in the case of the more saline type in the first and second seasons, respectively. The reason may be that some of these amino-N compounds and presumably glycine betaine and proline found as impurities in the storage roots of stressed plants, result from osmotic adjustment as suggested by Brown et al, (1987). Data in Table ( 4) revealed that saline soil yielded roots with excessive sucrose % by ( 0.84 and 0.91%) in the first and second seasons, respectively, as compared to the non-saline one.…”