Salinity Effects On Turfgrass And Its Rootzone Media Properties

Salinity is one of the major environmental stresses that detrimentally affect plant growth and development. As the salinization is increasing worldwide, more and more turf sites are under the threat of salinity. The potable water limits as the fast development of urbanaztion in turn aggravte this situation. Hence, the need of salt tolerant turfgrass species or cultivars is ever increasing. The appropriate management practises of turfgrass under salinity also need to be evaluated.This study systematically evaluated the relative salt tolerance of several grass species, such as creeping bentgrass (Agrostis stolonifera) and prairie junegrass (Koeleria macrantha). The study also simulated a salt water irrigation situation, and investigated the effects of irrigation management on turfgrass and its rootzone characteristics. The study mainly covered the following six aspects:①responses of 26 creeping bentgrass cultivars to salinity stress during germination;②the salinity effects on 9 representative creeping bentgrass cultivars during mature stage;③the effects of different growing media on salt tolerance of turfgrasses during germination;④the effects of salt water irrigation on creeping bentgrass greens of different rootzone media;⑤the effects of salt water irrigation on rootzone media properties of creeping bentgrass greens;⑥the evaluation of salt tolerance for prairie junegrass. And the main findings are as followings:(1) Final germination rate (FGR) and daily germination rate (DGR) decreased as salinity levels increased; however, DGR was more sensitive to salinity stress. Substantial differences in salt tolerance were observed in bentgrass cultivars, with'Declaration','SeasideⅡ','T-1', and'Bengal'being the most salt-tolerant(averaged predicted salinity level causing 50% reduction of DGR [PSLD]= 8.2 g L-1 NaCl) and'Tyee','Kingpin', and'SRI 150'being the most salt-sensitive (averaged PSLD= 6.5 g L-1 NaCl).(2) Turfgrass clippings yield (CY), leaf water content (LWC), chlorophyll content (Chl), root mass (RM) was measured to compare the relative salinity tolerance of the 9 representative cultivars. The results showed that salinity had significant detrimental effects on the entire index. However, CY and RM increased at the lower concentration before D22, and then decreased. Among all cultivars, 'Alpha' was the most tolerant cultivar,'Kingpin' was the most sensitive, other cultivars were moderate tolerant, indicating substantial variation in salinity tolerance exists among these cultivars.(3) The three germination methods showed similar trends in evaluating salinity tolerance of turfgrasses that salinity reduces germination and early seedling growth. A few grasses were consistently ranked either high or low in salinity tolerance across the three germination methods. However, some exceptions were also observed such as variation of salt tolerance of coated 'Turf Blue' Kentucky bluegrass. Similarly, 'Declaration' creeping bentgrass showed superior salt tolerance on the agar medium and germination paper tests but moderate tolerance in the hydroponic test. 'Marco Polo'sheep fescue was ranked salt-tolerant in the germination paper test but medium on the agar medium test and sensitive in the hydroponic test. Researchers and practitioners have to choose a proper germination method based on their facility and purpose with understanding of the influence of different germination methods on salinity tolerance.(4) Tissue DW and VQ were higher in soil-based than in sand-based putting greens in the first 9 weeks after treatment (WAT); however, the difference in DW and VQ among the rootzone meida diminished by 11 WAT. Salinity damage on DW and VQ decreased when the irrigation level increased from 60 to 100% ET. Irrigated with tap water, grasses showed the highest DW and the best VQ. Tissue DW appeared to be more sensitive to SARw than VQ.(5) In the surface layer (0-10 cm), the average soil saturated hydraulic conductivity (Ksat) was 72.8 cm h"1 in the sand-based media and only 0.66 cm h-1 in the soil-based putting greens. The influence of SARw on Ksat was only pronounced in the soil-based putting greens where Ksat decreased along with increasing SARw levels. Soil electrical conductivity (EC) was affected by rootzone media, SARW, and irrigation levels and their interactions in all depths (0-40 cm). In general, soil EC was the highest in clay loam, followed by clay and lowest in the two sand-based putting greens. Soil EC increased with increasing irrigation levels in the soil-based putting greens but not in the sand-based putting greens. In contrast, soil pH was more affected by the SARW than the irrigation level. Soil pH increased with an increase of SARW under saline irrigation, and such a pH increase was higher in the sand-based than in the soil-based putting greens. (6) All populations of prairie junegrass showed similar salt tolerance with an average of PSLF and PSLD being 7.1 and 5.3 g L-1 NaCl, respectively, comparable to Kentucky bluegrass and hard and sheep fescue but lower than tall fescue and perennial ryegrass. In junegrasses, larger variations were observed in visual quality (VQ) than in electrolyte leakage (EL) and dry weight (DW) at vegetative growth stage. 'Barleria' junegrass showed the highest VQ, following two salt-tolerant grasses, tall fescue and sheep fescue. Junegrass-Nebraska population was the least salt-tolerant within the species, but still exhibited similar or higher tolerance than Kentucky bluegrass and perennial ryegrass cv. Arctic Green. Overall, junegrass was more salt sensitive during germination but more tolerant to salinity when mature.