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Schematic representation of the effects of salinity on root structural traits. Namely; enlarged root diameter and periderm tissue while stele smaller with larger xylem vessels. • Roots modified their structural traits to enhance salt compartmentation and exclusion. • Salts accumulated in enlarged periderm tissue allowing greater compartmentation. • Two putative apoplastic barriers were identified: around the periderm and the stele. • Xylem vessel diameter distribution shifted to allow higher hydraulic conductivity. Roots are the first plant organ to encounter, sense, and respond to soil salinity. Like for many moderately salt tolerant species, roots of olive (Olea eurpaea) trees are the principal players in salt tolerance. We studied roots of mature olive trees in order to illuminate the yet vague mechanism(s) of root salt exclusion. Root structural traits were examined in olive trees grown in lysimeters and from a long-term salinity field trial. The distribution of salts was detected in root cross-sections using scanning electron microscopy combined with energy dispersive spectroscopy. Increased soil salinity caused a continuous decline in specific root length and an increase in root diameter, periderm thickness, and specific hydraulic conductivity. While periderm cell number was not modified, cell diameter increased linearly by a total of 50 % as root zone salinity increased nearly eight-fold. Strong compartmentation of Na within the periderm was found, with highest content in the outer periderm layer and lowest content in the stele. Increase in soil salinity was associated with decrease in stele area, yet, hydraulic conductivity was doubled due to higher fraction of large diameter xylem vessels. Our results indicate significant root structural plasticity, which underlies the salt resistance mechanisms. The dominant trait enabling salt tolerance of olive trees is the enlarged periderm serving as an apoplastic barrier that enhances salt compartmentation and exclusion from the vascular tissues. [ABSTRACT FROM AUTHOR]

Abstract: A 4-year trial was set up to test the feasibility of growing waxy corn (Zea mays L. var. ceratina Kulesh) in a highly saline wasteland with drip irrigation in the Ningxia plain, northwest China. The original soil salinity expressed as electrical conductivity of the saturation paste extract (EC e ) averaged 28dS/m in the 0–120cm depth. The experiment included five soil matric potential (SMP) treatments in which the SMP at 20cm depth below the drip emitters was controlled higher than −5, −10, −15, −20 and −25kPa after waxy corn establishment. The results showed that drip irrigation created a favorable soil condition for waxy corn growth through forming and maintaining a high moisture and low salinity region in the root zone when the SMP was maintained higher than −25kPa. Waxy corn growth and yield parameters increased with the increase of SMP from −25kPa to −5kPa, but their responses to SMP decreased with the prolonged period of cultivation. Irrigation frequency and irrigation amount decreased significantly as SMP decreased from −5kPa to −25kPa, and the highest irrigation water use efficiency (IWUE) was available when the SMP was around −15kPa in 2005, and was between −20kPa and −25kPa in successive years. After years of cultivation and drip leaching, the highly saline soil gradually changed to a moderately saline soil. This research suggests that drip irrigation can be successfully used in growing waxy corn in dry and highly saline conditions after appropriate management strategies are adopted. [Copyright &y& Elsevier]