No abstract

Understanding the physiological mechanisms of hypoxia tolerance is important for developing hypoxia‐tolerant genotypes. This experiment investigated whether differential responses to hypoxia and ethylene exist in root characteristics, hormonal activity, and shoot growth for two wheat (Triticum aestivum L.) cultivars, Bayles and Jackson, differing in waterlogging tolerance. Rooting characteristics, ethylene production, cellulase activity, and shoot growth were determined after application of hypoxia and various concentrations of ethylene to the rooting medium in a growth chamber. Hypoxia limited root elongation for both cultivars but enhanced production of crown roots for tolerant Jackson. Hypoxia induced root aerenchyma formation and enhanced root ethylene production for both cultivars, but the response was greater for Jackson than Bayles. Ethylene effects on root growth and aerenchyma formation were similar to those observed for hypoxia treatment. All concentrations of ethylene (0.1, 1.0, and 5.0 μL−1) hastened the production of crown roots for Jackson but inhibited root elongation at the highest ethylene concentration (5 μL L−1). For sensitive Bayles, crown root production was promoted by the lowest concentration of ethylene, whereas root elongation was restricted at all levels of ethylene. Ethylene also promoted formation of aerenchyma in crown roots by increasing cellulase activity. This effect occurred earlier and was more dramatic for Jackson. The promoting effect of ethylene on aerenchyma formation was also more pronounced for newly formed than pre‐existing roots. The results showed that the effects of ethylene on roots varied with cultivar and ethylene concentration.

Modern soil erosion prediction technology, such as the Water Erosion Prediction Project, requires detailed information about plant status in the interrill and rill erosion processes. The total amount of rain that reaches the soil and is available for erosion under vegetated surfaces is a function of rain throughfall and stemflow. The objective of our research was to determine the effects, including the production of stemflow of canopies, of corn (Zea mays L.) and sorghum (Sorghum bicolor [L.] Merr.) on interrill soil erosion. A series of rainfall simulations of similar intensity (6.35 cm h‐1) was performed in 1989 and 1990 on experimental plots of Cargill SX 383 corn and Garst 5503 sorghum grown on Cecil soil (clayey, kaolinitic, thermic Typic Kanhapludult). Runoff and sediment were collected at 5‐min intervals over a 1‐h period for two sets of treatments each under corn and sorghum: canopy and canopy minus stemflow. Stemflow, plant‐height, and leafarea data were collected from a total of 18 corn and 16 sorghum plants and used to estimate stemflow. Rain throughfall was estimated as the difference between total rainfall and calculated stemflow and was compared with observed runoff. Both corn and sorghum were observed to have high stemflow, the amount being highly correlated to total leaf area. Runoff under sorghum indicated that all the stemflow was potentially available for infiltration. Under corn, however, about one‐third of the stemflow may have contributed to runoff. The average sediment concentration was not sensitive to canopy type. Erosion due to stemflow appeared negligible compared with that caused by throughfall.

Estimation of plant root activities by the minirhizotron technique is a nondestructive approach for observing root responses to the soil environment, yet few such observations have been made. The purpose of this report is to compare methods for installing minirhizotron tubes in separate experiments located in two regions of the USA. Transparent plastic tubes were installed at acute angles of 0.8 and 1.2 rad to the surfaces of sandy loam (Typic Hapludult and Typic Hapludalf) soils located in Georgia and Michigan. Soil cores were removed from these low expansion‐contraction soils using Giddings hydraulic power samplers. Both ends of the minirhizotrons were stoppered and the aboveground portion of the tube surfaces were made opaque before inserting. The excellent soil to minirhizotron wall interfaces provided clear and high contrast root images that were observed and video recorded. These procedures provided information which indicate that short‐term drought results in root losses near the soil surface and large increases in deep root growth. Uninterrupted O2 stress substantially reduced growth of wheat (Triticum aestivum L.) roots throughout the rhizosphere.

A nondestructive, quick, and efficient root measurement technique that quantifies root dynamics is critical to understanding environmental effects on rooting. The objective of this study was to compare roots of three cultivars of soft red winter wheat (Triticum aestivum L.) observed in minirhizotrons with those washed from soil cores. Minirhizotron determinations were root count (Ca, count cm−2) and root length (La, cm cm−2) per unit area; soil core determinations were root length (Lv, cm cm−3) and root dry weight (Wv, mg cm−3) per unit volume. Growth stages studied were double ridge, early boot, milk, and soft dough. Analysis of variance showed that growth stage and soil depth were significant for Lv, Wv, Ca, and La. Cultivar was significant at early boot and milk growth stages for Ca. Linear regression of Lv, Wv or La as a function of Ca provided highly significant slope and, except for Wv, intercept values. Statistically, Ca was the most discriminating minirhizotron measurement parameter.