Impact of seedling age on the survival and productivity of Atriplex halimus shrubs in drought-affected rangelands of Jordan

Rangelands in Jordan are part of arid areas of the Mediterranean Basin. Stress-tolerant plants such as Atriplex halimus L. have been used to rehabilitate such degraded areas. Seeds of A. halimus were sown in plastic bags in mid-March, mid-August and mid-September of 2012 and placed on the ground in a nursery at Khaldiah Station. Seedlings that were 4, 5 and 10 months old were transplanted on 20 January 2013 to the Khanasri Range Reserve and monitored for their survival over the growing seasons of 2013, 2014 and 2015. At the time of transplanting, the height, weight, stem thickness and root length density of 10-month-old seedlings were greater than of 4- and 5-month-old seedlings. Analyses of leaf tissues indicated high crude protein content in seedlings of different ages (22-26%). The 10-month-old plants showed 15-40-fold higher stem dry weight and more convoluted roots than the 4- and 5-month-old seedlings. The average rate of survival of transplanted seedlings over the three growing seasons was 77.0%, 92.3% and 94.3% for 10-, 5- and 4-month-old seedlings, respectively. Thus, higher growth of the 10-month-old seedlings than of 4- and 5-month-old seedlings at transplanting was compromised by their lower survival percentage throughout the 2013, 2014 and 2015 growing seasons. The dry yield of fodder shrubs was comparable across different-aged seedlings after 2 years of growth in permanent pastures (380, 364 and 354kg dry yield ha(-1) for 10-, 5- and 4-month-old seedlings, respectively). Taken together, these data suggest that 4-5-month-old seedlings of A. halimus are more appropriate for transplanting than 10-month-old seedlings because of cost-effective establishment of seedlings in the nursery, because no significant differences in shrub productivity were observed among plants derived from seedlings of different ages in the permanent rangeland. The impact of the introduced shrubs on different native plants in the range can be addressed in future studies.