Seasonal carbon isotope discrimination in a grassland community

Abstract

Grassland communities of arid western North America are often characterized by a seasonal increase in ambient temperature and evaporative demand and a corresponding decline in soil moisture availability. As the environment changes, particular species could respond differently, which should be reflected in a number of physiological processes. Carbon isotope discrimination varies during photosynthetic activity as a function of both stomatal aperture and the biochemistry of the fixation process, and provides an integrated measure of plant response to seasonal changes in the environment. We measured the seasonal course of carbon isotope discrimination in 42 grassland species to evaluate changes in gas exchange processes in response to these varying environmental factors. The seasonal courses were then used to identify community-wide patterns associated with life form, with phenology and with differences between grasses and forbs. Significant differences were detected in the following comparisons: (1) Carbon isotope discrimination decreased throughout the growing season; (2) perennial species discriminated less than annual species; (3) grasses discriminated less than forbs; and (4) early flowering species discriminated more than the later flowering ones. These comparisons suggested that (1) species active only during the initial, less stressful months of the growing season used water less efficiently, and (2) that physiological responses increasing the ratio of carbon fixed to water lost were common in these grassland species, and were correlated with the increase in evaporative demand and the decrease in soil moisture.

Seasonal variation in nitrogen pools and <sup>15</sup>N/<sup>13</sup>C natural abundances in different tissues of grassland plants

“…The δ 13 C variation pattern for ryegrass observed in the present study (Fig. 7a) indicates less discrimination against 13 C during reproductive compared to vegetative growth, but the seasonal pattern may vary between species (Smedley et al, 1991). During intensive N application (April-July of both years), the δ 13 C values were constant or slightly elevated in all tissues (Fig.…”

Differing Selection on Plant Physiological Traits in Response to Environmental Water Availability: A Test of Adaptive Hypotheses

“…Commonly plants show greater water-use efficiency in drier environments (e.g., Ehleringer and Cooper 1988;Donovan and Ehleringer 1994) though decreases in wateruse efficiency with seasonal increases in drought stress have been observed in some species (DePuit and Caldwell 1975;Smedley et al 1991). In this study, the functional arguments, the field-selection results, and the genetic differences between populations all suggest that Cakile exhibited a maladaptive plastic response to the environment.…”

A calf for all seasons? The potential of stable isotope analysis to investigate prehistoric husbandry practices

“…Of interest from Figure 7 is the range of If cattle were grazing in the same type of open environment throughout the year, the  13 C values of their food might be expected to be more positive in the summer than in the winter because of environmental factors such as decreased water availability (Mole et al, 1994;Schnyder et al, 2006;Smedley et al, 1991). Such a seasonal variation has been measured for grasses and herbs sampled from grazed meadowland in Somerset, UK (Dungait et al, 2010).…”