The rare species Magnolia wufengensis frequently suffers from freezing injury in northern China. To investigate the influence of exogenous abscisic acid (ABA) application on the natural cold acclimation of M. wufengensis, physiological and biochemical changes in field-grown M. wufengensis seedlings subjected to foliar ABA treatments at four concentrations (0, 300, 600, and 900 mg·L−1) were evaluated from Sept. 2012 to Jan. 2013. The optimum foliar application concentrations of ABA for M. wufengensis were between 600 and 900 mg·L−1, which led to faster shoot growth cessation, leaf senescence, and development rates of bud endodormancy level and shoot freezing tolerance. The improved freezing tolerance under exogenous ABA application was associated with promoted dehydration and accumulation of proline, soluble protein, and certain soluble sugars such as glucose and fructose. Foliar ABA treatments initiated a cascade of steps for advancing the cold acclimation process of M. wufengensis. We suggest that exogenous ABA application may be used on M. wufengensis grown in northern China, where there are short growing seasons and early fall frost events.
Under field conditions, this study investigated the influence of the irrigation amount on olive root morphology and spatial distribution. Soil samples were taken with an auger at distances of 30, 60, and 90 cm from the tree trunks in four directions. The roots were analyzed using an Epson Twain Pro root scanning system. The results indicated that under different irrigation treatments, the indicators of root morphology of different varieties showed different responses to the irrigation amount. The root length density (RLD), root surface area (RSA), and root volume (RV) of Arbosana first increased with increasing irrigation amount but then decreased; however, those of Arbequina monotonically increased with increasing irrigation amount. The root average diameter of the two varieties was inversely proportional to the irrigation amount. In the vertical dimension, the RLD and RSA of each treatment decreased with increasing soil depth and were mainly distributed in the surface soil (0–20 cm in depth). The RLD and RSA in the vertical direction (VD) of the drip irrigation belt were higher than those of the belt in the parallel direction (PD), and the range was 12% to 86%. Compared with the roots of the 0- to 20-cm soil layer, the roots of the 20- to 40-cm and 40- to 60-cm soil layers were more influenced by the irrigation amount. Horizontally, the RLD and RSA decreased with increasing radial distance. The 30-cm radial area contained most roots, the proportion of roots in this region increased with increasing irrigation capacity. The influence of irrigation quantity in the PD of the drip irrigation belt was greater than that in the VD. The results suggest that irrigation does not change the root spatial distribution pattern but does promote root growth. The two varieties had different responses to irrigation. In terms of soil moisture levels after irrigation, 75% of field capacity is appropriate for ‘Arbosana’, whereas 100% is advisable for ‘Arbequina’. To improve water use efficiency, moisture should be irrigated within the 30-cm radial distance from the trunk, and irrigation depth is not easy to more than 20 cm. This study provides a scientific basis for the efficient water management of olive trees.