Production of Inorganic Carbon From Aquatic Macrophytes by Solar Radiation

Abstract

Solar radiation causes considerable photochemical effects on dissolved organic matter (DOM) from both fresh and marine waters. Photooxidation of DOM to dissolved inorganic carbon (DIC) has been shown to be a quantitatively significant process in the turnover of DOM. Less is known about photodegradation of particulate organic matter, e.g., plant detritus. We have evaluated direct and indirect (via photooxidation of DOM released from plant detritus) photooxidative inorganic-carbon production from detritus of the emergent macrophytes Phragmites australis, Typha angustifolia, and Juncus sp. Macrophyte leaves were sterilized and incubated in quartz tubes under three radiation regimes: darkness, ultraviolet (UV)-A, and UV-A ϩ UV-B radiation, using fluorescent lamps with radiation intensities and spectral composition of UV-B and UV-A radiation similar to those of natural solar radiation. Inorganic carbon production was investigated with leaves both immersed in water and in the air.Photoproduction of DIC in both water and air was linear over time (72 h). Production of DIC ranged from 0.22 to 0.44 g C·(mg dry mass) Ϫ1 ·(24 h) Ϫ1 . Experiments with macrophyte leachate, excluding the particulate matter (POM), indicated that ϳ56% of the DIC accumulating in the water originated from DOM leached from the plant detritus, while 44% of DIC production originated directly from POM. Carbon dioxide released from leaves incubated in air and exposed to UV radiation was lower than for leaves immersed in water (values including DIC produced from leachate). In most cases, DIC production with only UV-A radiation ranged between 60% and 75% of the values found in the UV-A ϩ UV-B treatments, even though the artificial radiation was deficient in UV-A compared to solar radiation. Similar experiments, using natural solar radiation, indicated that PAR (photosynthetically active radiation) has a major effect on DIC production. This shows that wavelength bands other than UV-B can play a significant role in photodegradation of organic matter.

Widespread production of nonmicrobial greenhouse gases in soils

“…Water provides the hydrogen that can act as electron donors. For example, appropriate water can stimulate the photodegradation, as reported by Anesio et al (1999). How moisture and its interactions with oxygen affect the photodegradation needs further investigations.…”

“…The idea of NM-CO 2 production from terrestrial ecosystems originated from studies of litter decomposition in arid and semiarid regions at the end of 1980s, when researchers found abiotic processes rather than only biotic processes also play a significant role in litter mass loss (Montaña, Ezcurra, Carrillo, & Delhoume, 1988;Moorhead & Reynolds, 1989). Not until 1999, however, were there direct measurements of CO 2 production from photodegradation of particular organic matter (POM) from plant detritus (Anesio, Tranvik, & Gran eli, 1999). During this period, investigations into oceanic carbon cycling around 1990 to a great extent facilitated its finding.…”

The interaction between abiotic photodegradation and microbial decomposition under ultraviolet radiation

“…The increase in DOC concentration might accelerate litter mass loss in several ways. DOC itself easily undergoes photodegradation, which has been widely observed in aquatic ecosystems (Anesio et al, 1999;Macdonald & Minor, 2013). In addition, the loss DOC due to leaching during rainfall would be increased due to the increased amount of DOC in litter under higher UV radiation (Gallo et al, 2009).…”

Photochemically induced carbon dioxide production as a mechanism for carbon loss from plant litter in arid ecosystems

“…Little is known about the contribution of photodegradation to CO 2 production in terrestrial systems. Only one previous study, using leaf litter of three aquatic macrophyte species, has demonstrated that CO 2 can be produced via photodegradation of dried leaves in the air [Anesio et al, 1999a]. However, the factors controlling rates of photochemical CO 2 production remain unknown.…”

“…Therefore, one would expect that litter with a higher initial lignin concentration may produce photochemically derived CO 2 at a higher rate. Other evidence suggests that leaf surface area may be a more important driver than litter chemistry [Anesio et al, 1999a;Gallo, 2006], as photochemical reactions can only occur on surfaces exposed to radiation. To date, there is insufficient information to determine whether litter chemistry, surface area, or both are important in driving photochemical CO 2 production.…”