Buffalograss is native to the Great Plains of North America (Huff and Wu, 1987). This species is widely used as a low-maintenance turfgrass in parks, cemeteries, and rights of way due to its excellent cold, heat, and drought tolerance (Beard, 1985). Buffalograss is increasingly used on golf course fairways and other sports fields in arid and semiarid regions where water shortage is becoming an important concern (Frank et al., 2004; Pozarnsky, 1983). However, one of the weaknesses of buffalograss for use in golf fairways is poor ball-supporting ability due to low shoot density. Improving the traits related to shoot density has been proposed as one of the goals in buffalograss breeding programs (Johnson et al., 2000; Taliaferro and McMaugh, 1993). Buffalograss is considered a “guerilla”-type clonal species (Lovett Doust, 1981), meaning it can spread extensively. The opposite are “phalanx”-type plants [short nodes and compact growth (Lovett Doust, 1981)], which have higher potential for shoot density because of the intensive growth habit. Limited information is available on shoot density affected by the growth type, “guerilla” type versus “phalanx” type, although research has been conducted on the effects of nitrogen and mowing height (Frank et al., 2004). No research has yet been conducted to understand the effect of nutrient and carbohydrate translocation on the shoot density of buffalograss.
Reproduction and population density are often discussed in relation to population biology and ecology of clonal plants. Semiautonomous young ramets may import nutrients, water, hormones, etc., from the parent until they are established, and thereafter they may be independent of parental support (Pitelka and Ashmun, 1985). In ecological research, members of a clone are considered ramets before they become independent from the parent plant for study of photosynthate partition (Alpert, 1991). Another important characteristic of clonal plants is physiological integration, which is defined as a process of redistribution of assimilated resources among the interconnected ramets according to source-sink relationships (Forde, 1966; Kaitaniemi and Honkanen, 1996; Marshall, 1990). Physiological integration is an important means by which clonal plants adapt to heterogeneous environmental conditions (Kroon et al., 1996; Marshall, 1990). Because buffalograss has a “guerilla”-type growth habit, it may differentially exploit the environment, selecting favorable and avoiding unfavorable sites (Jackson, 1979). As a stoloniferous clonal species, buffalograss clones are often connected for an extended period of time after establishment.
Resource sharing in clonal plants is reflected in the ability of perennial grasses to change phenotypes in response to fluctuating environments and stresses (Bradshaw, 1965). For instance, the specialization of certain ramets in photosynthesis and nutrient-uptaking functions may be enhanced when essential nutrients and light are heterogeneously distributed (Stuefer et al., 1994). The consideration of phenotypic changes in turfgrass breeding was discussed by Casler and Duncan (2003) and Bradshaw (1965). An internal gradient was established when connected ramets were exposed to different nutrient availability (Marshall, 1990), and such a gradient may be the driving force for the nutrient redistribution (Marshall and Price, 1999). Water was transported from parent ramets to offspring ramets along the water potential gradient in Fragaria chiloensis (Alpert and Mooney, 1986). Photosynthate also was translocated among connected ramets in many grass species (Nyahoza et al., 1974; St. Pierre and Wright, 1972). However, the mechanisms of physiological integration in grasses are not well understood (Hellström et al., 2006).
Huang (1999) reported that buffalograss performed better than zoysiagrass (Zoysia japonica) under localized soil drying and attributed the difference to the more extensive root system in buffalograss. Qian et al. (2009) reported that buffalograss shoot number displayed water integration when connected ramets were grown in media with different soil water contents. The same authors also reported inter-ramet translocation of lipid peroxidation, antioxidants, and proline (Qian et al., 2009). High uniformity is a major quality component of turf. One of the purposes of topdressing and applying wetting agents, among many other turfgrass management practices, is to correct the heterogeneous conditions in the root zone media and to create uniform turf (Karnok and Tucker, 2001; Minner et al., 1997). This integration appears to deal with soil variability to provide more uniform growth in buffalograss—a highly desirable trait. Understanding this process may also help to make precise cultural practices and improve turf uniformity.
The role of plant hormones in response to drought stress has been discussed for endogenous (Abreu and Munne-Bosch, 2008) and exogenous (Liu and Huang, 2002; Zhang and Schmidt, 1999) sources. Abscisic acid was found to play a role in water stress-induced antioxidants (Jiang and Zhang, 2002) and morphological responses (Zhang and Davies, 1989). Increased contents of zeatin riboside (ZR) in shoot and root alleviated the heat stress in creeping bentgrass (Agrostis palustris) (Liu and Huang, 2002). Gibberellic acid treatment delayed senescence in bermudagrass (Cynodon dactylon) caused by chilling (DiPaola et al., 1981). Research also indicated that hormone allocation was modified in the process of resource sharing in clonal plants of F. chiloensis (Alpert et al., 2002).
The primary objective of this study was to assess the effects of differential water stress on water transport and photosynthate translocation and distribution. A secondary objective was to examine if endogenous hormone translocation and distribution display coordinated changes under differential water stress in buffalograss.
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