Effects of riparian leaf dynamics on periphyton photosynthesis and light utilisation efficiency

Abstract

1. Streambed light regimes change dramatically when riparian trees gain leaves in spring and lose them in autumn. This study examined the effect of these changes on periphyton photosynthetic characteristics, primary production, and light utilisation efficiency in two eastern Tennessee streams. 2. Photosynthesis–irradiance responses were measured at intervals covering leaf emergence and abscission in spring and autumn. Photosynthetic efficiency (αchl) increased with declining streambed irradiances during spring leaf emergence, but returned to pre‐emergence values after autumn leaf fall. The onset of photosaturation (Ik) displayed the opposite pattern, decreasing during leaf emergence and increasing after leaf fall. Both αchl and Ik were closely associated (P < 0.01) with daily integrated streambed irradiance, as were periphyton carotenoids. Internal shading by photoprotective carotenoids is hypothesised to account for lower αchl when streambed irradiances are high. 3. An in situ shading experiment confirmed that the temporal changes observed in periphyton photosynthetic characteristics and carotenoids were primarily the result of changing light levels and not other environmental factors (e.g. nutrients, temperature). 4. Daily chlorophyll‐specific primary production (PPchl) was calculated with P–I models and recorded streambed irradiances. In both streams, PPchl was the highest in early spring when trees were leafless, and then declined markedly as leaves emerged, reaching a minimum in summer. PPchl increased after leaf abscission, but was still lower than it was in early spring, when the sun was higher and daylength was longer. A hyperbolic tangent equation fit to PPchl and daily integrated irradiance (r2=0. 85) suggested that primary production was light saturated at 4–8 mol m–2 d–1. 5. Light utilisation efficiency (Ψ) increased 10‐fold during leaf emergence. Photosaturation at high irradiances and photoacclimation at lower irradiances were responsible for a negative hyperbolic relationship between Ψ and daily integrated irradiance.

Pine afforestation changes more strongly community structure than ecosystem functioning in grassland mountain streams

“…Ecological indicator Values of Chl a obtained in the primary production experiment were similar to those found in other canopied headwater streams (Kiffney and Bull, 2000;Hill and Dimick, 2002;Roberts et al, 2004). Although we expected primary production to be an appropriate environmental indicator of changes induced by sunlight reduction following afforestation, periphyton growth did not show the anticipated differences.…”

Shifts in allochthonous input and autochthonous production in streams along an agricultural land-use gradient

“…However, we did not see the sharp contrast we saw with allochthonous inputs. Chlorophyll a concentrations and periphyton biomass did not vary significantly along the agricultural land-use gradient and were similar to values typical of forested (Sponseller et al, 2001;Hill & Dimick, 2002), agricultural (McTammany et al, 2007. and reforested (McTammany et al, 2007) streams in the southern Appalachians.…”

“…where d is mean depth (m), 0.375 is the molar ratio of C to O 2 , 1.2 is the photosynthetic quotient (Hill & Dimick, 2002), and 365 is the number of days in a year. Daily R E rates were converted to g C m -2 y -1 as: Table 1 Characteristics of each stream site including riparian tree basal area (BA) and tree density (TD) within 3 and 10 m of each stream reach, stream canopy cover (SCC) along each 100-m stream reach, riparian canopy cover (RCC) within 10 m of each stream reach, grass groundcover (GGC) within 10 m of each stream reach, and agricultural influence …”

Primary consumers and resources: Annual variation in two contrasting reaches of a Patagonian mountain stream

“…Resources are variable in time, and this is well exemplified in temperate regions where the availability of leaf litter is seasonal with light inputs closely linked to litterfall (Hill and Dimick, 2002;Bernhardt and Likens, 2004;Roberts et al, 2004). In those streams, detritus and primary production dynamics are affected by terrestrial plant phenology (i.e.…”