Effect of drought on morphological and functional traits of Poa ligularis and Pappostipa speciosa, native perennial grasses with wide distribution in Patagonian rangelands, Argentina

Abstract

Poa ligularis Nees. Ap. Steudel and Pappostipa speciosa (Trin. et Rupr.) Romaschenko are dominant perennial grasses in the arid Patagonian rangelands of Argentina. Both species are exposed to periods of water shortage during spring-summer and are grazed by domestic and native herbivores. Pappostipa speciosa displays xeromorphic adaptations and is less preferred by herbivores than P. ligularis. The knowledge of how drought affects morphological/functional traits in coexisting perennial grass species is useful to understanding the function of desert perennial grasses, and for the use and conservation of Patagonian arid rangelands. The hypothesis of this study was that co-existing perennial grasses contrasting in drought resistance mechanisms display different degrees of phenotypic plasticity in underlying and/or functional traits. Plants of both species were exposed to two levels of gravimetric soil moisture: 16% (~field capacity) and 4%. Plant vegetative and reproductive traits were measured weekly in individual plants and these were harvested at the end of the experiment. Aboveground and root biomass were separated in the harvested plants and the concentration of photosynthetic pigments was assessed in green leaves. The trait response range was also calculated through the plasticity index. In both species, drought stress led to significant reductions in plant height, total plant dry weight, number of total leaves, dry weight of green and senescent leaf, percentage of flowering plants, length of inflorescences, and number, length and dry weight of roots. The concentration of photosynthetic pigments increased under drought in both species. In conclusion, drought strongly affected reproductive and vegetative traits in both species and the greatest negative effect of drought was found in P. speciosa, the most conservative species. However, our findings might indicate that both species are able to maintain photosynthetic activity through the increase of photosynthetic pigments under drought conditions in Patagonian rangelands.

Do species' strategies and type of stress predict net positive effects in an arid ecosystem?

“…On the contrary, the lack of a positive influence of a canopy is more likely to occur in species that are relatively tolerant to high light and dry conditions (Holmgren et al 2012). Poa, the more xerophytic species, has been shown to increase chlorophyll content and photoprotective carotenoids concentration under drought (Cenzano et al 2013). Therefore, Poa could be more protected than Bromus against high irradiance stress and could even be photoinhibited in shade.…”

“…Poa, on the other side, displays mechanisms to maintain photosynthetic activity under drought conditions through the increase of photosynthetic pigments (Cenzano et al. ). In relative terms, Bromus exhibits an acquisitive resource‐use strategy compatible with Grime's “competitive” syndrome, whereas Poa fits into a stress tolerant strategy (Table ; Couso and Fernández ).…”

“…It is also the most sensitive grass to water stress within the steppe (Golluscio and Oesterheld 2007), and after a simulated drought, the number of dead plants was more than two fold higher in Bromus than in Poa (see Couso and Fernández 2012 for experimental test). Poa, on the other side, displays mechanisms to maintain photosynthetic activity under drought conditions through the increase of photosynthetic pigments (Cenzano et al 2013). In relative terms, Bromus exhibits an acquisitive resource-use strategy compatible with Grime's "competitive" syndrome, whereas Poa fits into a stress tolerant strategy (Table 2; Couso and Fernández 2012).…”

Drought weakens the positive effects of defoliation on native rhizomatous grasses but enhances the drought‐tolerance traits of native caespitose grasses

“…Drought can cause a series of reductions in morphologic and physiological functional traits, such as plant height, specific leaf area, leaf water potential, leaf tissue density, and length of roots. Then, these variations of plant traits may lead to a decline in yield and nutritive value (Cenzano, Varela, Bertiller, & Luna, ; del Glise et al., ; Wellstein et al., ). Therefore, an understanding of the quantitative relationship between drought and various plant traits is a key to the utilization of drought‐resistant species.…”

Small-Scale Habitat-Specific Variation and Adaptive Divergence of Photosynthetic Pigments in Different Alkali Soils in Reed Identified by Common Garden and Genetic Tests

“…The pigment concentration is strongly correlated with photosynthetic capacity and is an important indicator of growth status and photosynthetic properties (Cenzano et al, 2013). As a leaf functional trait, Chl content has been shown to be consistent with vegetative growth traits that are crucial individual fitness components (Bragato et al, 2009; Zhang et al, 2013).…”