Kenneth B. Marcum

Growth Responses and Nitrogen-15 Absorption of Desert Saltgrass Under Salt Stress

Abstract Saltgrass [Distichlis spicata (L.) Greene var. stricta (Gray) Beetle], accession WA-12, collected from a salt playa in Wilcox, AZ, was studied in a greenhouse to evaluate its growth responses in terms of shoot and root lengths, shoot dry-matter yield, and nitrogen (N) (regular and 15N) absorption rates under control and salt (sodium chloride, NaCl) stress conditions. Plants were grown under a control (no salt) and three levels of salt stress (100, 200, and 400 mM NaCl, equivalent to 5850, 11700, and 23400 mg L− 1 sodium chloride, respectively), using Hoagland solution in a hydroponics system. Ammonium sulfate [(15NH4)2SO4], 53% 15N (atom percent 15N) was used to enrich the plants. Plant shoots were harvested weekly, oven-dried at 60°C, and the dry weights measured. At each harvest, both shoot and root lengths were also measured. During the last harvest, plant roots were also harvested and oven-dried, and dry weights were determined and recorded. All harvested plant materials were analyzed for total N and 15N. The results showed that shoot and root lengths decreased under increasing salinity levels. However, both shoot fresh and dry weights significantly increased at 200 mM NaCl salinity relative to the control or to the 400 mM NaCl level. Shoot succulence (fresh weight/dry weight) also increased from the control (no salt) to 200 mM NaCl, then declined. The root dry weights at both 200 mM and 400 mM NaCl salinity levels were significantly higher than under the control. Concentrations of both total-N and 15N in the shoots were higher in NaCl-treated plants relative to those under the control. Shoot total-N and 15N contents were highest in 200 mM NaCl-treated plants relative to those under the control and 400 mM salinity.

Saline Tolerance Physiology In Grasses

Salinization of agricultural lands is accelerating, with over 1 Mha of irrigated lands deteriorating to non-productivity each year (Hamdy, 1996; Choukr-Allah, 1996). Currently from 100 Mha to 1000 Mha of irrigated land is salt-affected due to human activity (Szabolcs, 1989; Oldeman et al., 1991). Though much of this land is currently too saline for conventional agriculture, it has the potential for growing salt tolerant forages, grasses (Poaceae) playing a dominant role (Ghassemi & Jakeman, 1995). With over 7,500 species, the Poaceae inhabit the earth in greater numbers, and have a greater range of Chlorideimatic adaptation than any other plant family (Hitchcock, 1971; Gould & Shaw, 1983). Therefore, it is not surprising that grasses show an extreme range in salinity tolerance, from salt-sensitive (ex. meadow foxtail Alopecurus pratensis L.), to salt-tolerant halophytic (ex. saltgrass Distichlis spicata L.) (Richards, 1954; Maas, 1986; Aronson, 1989). In this paper growth responses and physiological adaptations to salinity of eight C4 grass species studied in my lab will be discussed, representing an extreme range of tolerance. Physiological mechanisms of salt tolerance will be discussed, and crossreferenced to salinity studies involving other grass species. The grasses, listed in (Table 1), will be indicated in this paper by genus, except for Sporobolus, where genus abbreviation is followed by species names.

Genotypic variation in salinity tolerance of Distichlis spicata turf ecotypes

Water quantity and quality issues are accelerating the search for alternative xeriphytic and halophytic turf species. Growth and physiological responses to salinity of eight Distichlis spicata (L.) Greene genotypes were observed to elucidate salinity tolerance mechanisms operating in the species. Accession 1043 was superior in salinity tolerance to other genotypes, as indicated by percentage canopy green leaf area, relative (to control) shoot growth, relative root growth, and rooting depth, when exposed to increasing salinity up to 1.0 mol/L NaCl. Salinity tolerance was associated with complete, though minimal, shoot osmotic adjustment, maintenance of low shoot saline ion levels, and high shoot K+/Na+ ratios, all of which were facilitated by high leaf salt gland ion excretion rates.

World Halophyte Garden: Economic Dividends with Global Significance

Developing biosaline agriculture more intensively will result in seriously enhanced global food-security, especially in dry land countries. It will assist generating jobs and income. Certain successes have been achieved over the past five decades. However, much more attention is needed, including a full collection of wild halophytic plant species. This short communication suggests that the world needs a World Halophyte Garden.

Plant Response to Saline-Water Irrigation in a Sicilian Vineyard

This chapter presents results of a 3-year field investigation in a vineyard located in Sicily (Mazara del Vallo, Trapani) within the framework of the Project “Evolution of cropping systems as affected by climate change” (CLIMESCO). Soil-plant responses to two saline irrigation waters were determined by measuring soil hydrological characteristics, soil salinity, crop transpiration and stomatal conductance in field plots of a Sicilian vineyard. The results proved that crop transpiration (T r) and stomatal conductance (G s) were significantly affected by soil salinity conditions, expressed by electrical conductivity of soil saturation extract (ECe). Significant reductions in T r and G s were found in plants irrigated with water of ECw = 1.6 dS m−1 (L) compared to T r and G s values in plots irrigated with water ECw = 0.6 dS m−1 (R). Significantly higher crop water stress index (CWSI) values, indicating stronger stress conditions, were measured in the L treatment, relative to the R treatment. Validity of the linear relationship between relative yield and relative transpiration was confirmed. A value of 0.7 for the yield response factor (Ky) provided accurate prediction of yield reduction in years 2008 and 2009. Reductions due to soil salinity, calculated according to Maas and Hoffman equation, showed that under conditions of water and salinity stress, yield reduction due to salinity represented a percentage of the total yield reduction of up to 11% in the L plots and up to 3.5% in the R plots. The investigation also indicated that ECe (1.5 dS m−1) discriminated a different plant response to salinity, indirectly confirming the Maas threshold value for grapes. Under the irrigation conditions in the Sicilian vineyard, it is suggested to implement management strategies aimed at keeping soil salinity below this threshold value. This can be realized by using low-salinity irrigation water only or by alternating the two irrigation sources.

Relative Salinity Tolerance of 35 Lolium spp. Cultivars for Urban Landscape and Forage Use

Increasing population growth, particularly in urban centers, is resulting in critical freshwater shortages for both agriculture and urban use worldwide. To counteract existing water crises, many governments are restricting use of freshwater sources for irrigation. In the urban setting, governments are requiring use of reclaimed wastewater or other secondary saline water sources in lieu of freshwater for landscape irrigation. Lolium spp. (ryegrasses) is widely used for forage as well as in urban turf landscapes. Relative salinity tolerance of 35 Lolium spp. cultivars was determined in solution culture by measuring changes in shoot weight, root weight, rooting depth, and % green leaf canopy area, relative to control (non-salinized) plants. There was a wide range in salinity tolerance of the tested cultivars, ranging from salt tolerant (e.g., cv. Paragon) to salt sensitive (e.g., cv. Midway). All shoot parameters were highly correlated, being mutually effective predictors of salinity tolerance. Root dry weight, significantly correlated with all shoot quality and growth parameters, was also effective in predicting relative salinity tolerance. However, rooting depth was not correlated with other parameters, and therefore not effective in predicting relative salinity tolerance. Based on these results, it is concluded that salt-tolerant cultivars exist within Lolium spp. for agricultural forage and urban landscape use.

Prospects of Environmentally Friendly Farms for Food Security in Hot and Dry Coastal Areas Based on Seawater Irrigation and Wasteproducts – An Inspirational Proposal

Salt-water-irrigated projects have been set-up in the 1980s and 1990s, with varying degrees of success, especially in Abu Dhabi, Khor Kalba, and Dubai in the United Arab Emirates, Ras as Zawr in Saudi Arabia, but also in Eritrea, Mexico, the Netherlands, Pakistan, Sudan and elsewhere, with the rational to develop productive agro-systems for food production under marginal soil-water conditions. The human population in coastal dry lands has significantly increased in the last 20–30 years, or so, and with it, their dependency on food-important, even more limited freshwater resources, and the increase of waste products. This manuscript is not another proposal to establish seawater experimental farms – it is a call to continue the overall process of the sustainable utilization of halophytes in hyper-saline ecosystems. In order to achieve meaningful progress, these projects need to find long-term support, with targeted scientific research, capacity augmentation, education, and the utilization of waste-products from human settlements.

Salinity Tolerant Turfgrasses for Biosaline Urban Landscape Agriculture

Critical fresh water shortages are occurring in population centers worldwide. Overuse of fresh water resources, coupled with effects of global warming such as salt water intrusion and desertification, are resulting in salinization of water and soil resources. Rapid urban population growth has put enormous pressures on limited freshwater supplies, and many governments have responded by placing restrictions on the use of fresh water for irrigating turfgrass landscapes, instead requiring use of reclaimed, or other secondary saline water sources. Issues facing landscape managers using saline water sources are soil salinization, resulting in direct salt injury, and secondary problems of loss of soil structure ensuing from sodium and bicarbonate effects, resulting in loss of salt leaching potential and soil anaerobiosis. Long-term solutions to the salinity problem will require development of improved salinity tolerant turfgrasses. Progress has been made in understanding turfgrass salinity tolerance mechanisms, and in development of salinity tolerant turfgrass cultivars and alternate native species.

Distichlis Spicata – A Salt- and Drought-Tolerant Plant Species with Minimum Water Requirements for Sustainable Agriculture in Desert Regions and Biological Reclamation of Desert Saline Soils

Desertification of arable lands due to urbanization, global warming, and low rainfall mandates water conservation and using low-quality/saline waters for irrigation. Use of low-quality irrigation water imposes more stress on plants which are already under stress in these regions. Thus, there is an urgent need for finding salt/drought-tolerant plants to survive under stresses. Since the native plants are growing under such conditions and are adapted to these stresses, they are the most suitable candidates for use under arid regions. If stress-tolerant native species are identified, there would be a substantial savings in inputs in using them under stressful conditions. Present studies on saltgrass (Distichlis spicata L.), a euhalophyte, have shown it to have excellent drought/salinity tolerance, making it well adapted to harsh desert conditions, with great potential for use in urban landscape and agricultural settings to combat desertification and reclaim arid saline soils. The objectives of this study were to find the most drought-tolerant saltgrass genotypes for use in arid regions, where limited water supplies coupled with saline soils result in drought/salinity stresses, for use in sustainable desert agriculture, urban landscapes, and in biologically reclaiming desert saline soils. Various saltgrass genotypes were studied to evaluate their growth responses under progressive drought stress. Though all the grasses showed a high level of drought tolerance, there was a wide range of variations observed in their stress tolerance levels. Superior stress-tolerant genotypes were identified which could be recommended for sustainable production under arid regions and combating desertification.