Crassulacean acid metabolism in Isoetes bolanderi in high elevation oligotrophic lakes

Abstract

Isoetes bolanderi dominates the littoral flora of Siesta (elevation 2,440 m) and Ellery (2,905 m) lakes in the Sierra Nevada Range of California, USA. Both lakes are sparesly vegetated and I. bolanderi maintained aboveground oven dry weight of 30-50 m through most of the 1981 summer growing season. Plants at the higher elevation Ellery Lake were half as large as plants at Siesta Lake and had substantially more biomass in corms. Titratable acidity levels in Isoetes leaves showed a diurnal fluctuation <50 μeq g fresh weight early in the season at the highest elevation site but this increased to ∼300 μeq g FW by mid-summer; starch and chlorophyll levels likewise increased in the leaves over this time. Throughout the season the magnitude of the diurnal acid change was comparable inIsoetes from both lakes but the dynamics of daytime deacidification were not. Averaged over the season, total daytime deacidification at Ellery Lake was 65% complete by noon whereas at Siesta Lake it was only 22% complete by noon. It is suggested that this may be related to the fact that Siesta Lake was more acidic and thus more carbon was in the form of free CO. In both lakes water chemistry showed no consistent diurnal fluctuation in pH or free CO though total inorganic carbon levels were at the extreme low end for aquatic habitats. The studies reported here suggest that under extremely low inorganic carbon levels there may be selection for nighttime CO assimilation. Consistent with this hypothesis is the observation that emergent I. bolanderi plants, resulting from fluctuating water levels, initiated leaves with stomata(unlike adjacent submerged plants) and, although these leaves had substantially higher chlorophyll levels, they showed an order of magnitude less acid fluctuation than submerged leaves.

Deleterious interaction of light impairment and organic matter enrichment on Isoetes lacustris (Lycopodiophyta, Isoetales)

“…lacustris carbohydrates concentrations detected at natural conditions are comparable to those of other freshwater macrophytes given that natural concentration of soluble and non-soluble carbohydrates is highly variable depending on species, organ and season (e.g. Muztar et al, 1979;Keeley et al, 1983;Owens & Madsen, 1998;Gao et al, 2014). Even if helophytes and hydrophytes show similar carbohydrate concentration ranges, the highest values correspond to hydrophytes (i.e.…”

“…The levels encountered here for Isoetes lacustris are in the upper range when compared to other hydrophytes (e.g. Ceratophyllum, Myriophyllum, Potamogeton, Isoetes bolanderii, among others; Muztar et al, 1979;Keeley et al, 1983;Vermaat & Verhagen, 1995;Xie et al, 2014).…”

“…Carbohydrate production and allocation have been studied for some aquatic plants (e.g. Vermaat & Verhagen, 1995;Keeley et al, 1983), but not for I. lacustris.…”

Crassulacean acid metabolism enhances underwater photosynthesis and diminishes photorespiration in the aquatic plant Isoetes australis

“…CAM activity in leaves of Isoetes has been shown to vary significantly depending on both season and environment. For example, Isoetes bolanderi had much lower CAM activity in the spring compared with late summer (Keeley et al. , 1983b), and Isoetes howellii showed lower diurnal changes in tissue acidity when sampled from an oligotrophic lake as compared with a seasonal pool (Fig.…”

Aquatic CAM photosynthesis: A brief history of its discovery

“…Isoetes has a global distribution and CAM was found in vernal pool species in southeastern USA, Australia, South Africa, Chile, and the Mediterranean basin (Keeley, 1998). This taxon is also widely distributed in lakes, but primarily under oligotrophic conditions such as lakes in the Sierra Nevada alpine, upper Mid-west, Scandinavia, Scotland and tropical alpine environments (Keeley et al, , 1983Boston and Adams, 1983;Madsen, 1985;Keeley, 1998). In these species CAM is not driven by diurnal cycles in CO 2 availability as in vernal pools, but rather by the extraordinarily low levels of CO 2 in the water.…”