Lichen Physiology Xiii. Effects of Rewetting Dry Lichens

S U M M A R YThe efiects of prolonged simulated acid rain on percentage cover of ground vegetation, and on growth and reproduction of two dominating dwarf shrubs {Empetrum nigrum and Vaccinium vitis-idaea) were examined in a field experiment in the Finnish Subarctic, in an area with low ambient levels of sulphur and nitrogen deposition. Acid rain treatments included moderate (pH 3'8) and high (pH 2-9) concentrations of either H,SO^, or HNO3, or a mixture of them, and were compared with irrigated (pH 6) and dry control plots.Long-term application of acid rain caused significant alteration in the cover and composition of ground vegetation. Effects of acid rain depended on the accompanying anion and on pH. Sub-plots under different canopy tree species differed in responses indicating that spatial heterogeneity is important in predicting the effect of acidifying pollution on this plant community.In the bottom layer, acid rain caused significant reduction in cover of the cyanobacterial lichens Aephroma arcticuw and Peltigera spp. Decrease in cover of fruticose lichens, mainly composed of Cladina spp., more likely resulted from additional watering.In the field layer, acid rain containing moderate concentrations of NO.," caused an increase in cover of graminoid species. There were only slight alterations in growth and cover of the two dominant evergreen dwarf shrubs, E. nigrum and V. vitis-idaea, indicating that these species are tolerant to acid rain of as low as pH 3. Even some positive responses of dwarf shrubs were observed, depending on canopy tree. Application of acid rain of pH 3 to plots under pine trees caused an increase in cover of V. vitis-idaea and, when the nitric acid only was applied, a short-term increase in the number of new shoots of E. nigrum.In contrast to vegetative growth, reproduction of the dwarf shrubs was more strongly affected by acid ram, but this also depended on local conditions and anion composition of acid rain. On 'pine' plots, rain of pH 3 reduced the number of berries and flower buds on terminal current shoot of E. nigrum, however, this was partially compensated by an increase in berr\' production at the ramet level. Simulated acid rain had mainly negati\-e effects on berry production by V. vitis-idaea.

Section: Effects On the Bottom Layer Vegetationmentioning

confidence: 99%

Responses of ground vegetation to prolonged simulated acid rain in sub‐arctic pine—birch forest

Shevtsova

Neuvonen

1997

“…Respiration can be particularly high when dry lichens are rehydrated, resulting in a burst of respiration (Brown et al, 1983). The underlying biochemical mechanisms for this so-called resaturation respiration is not known, although there have been several suggestions such as an increased energy demand for repair of damaged membranes (Smith & Molesworth, 1973) and\or a burst in respirable substrates related to damage of membranes caused by drought (Farrar & Smith, 1976). Both the amplitude of the burst and the time required to reach steady state are probably dependent on the time for which the thallus was active during its previous active period and also on the rate of drying, with fast drying resulting in a larger burst (Brown et al, 1983).…”

Section: Respirationmentioning

confidence: 99%

Tansley Review No. 117

Palmqvist

2000

221

Lichens are nutritionally specialized fungi (the mycobiont component) that derive carbon and in some cases nitrogen from algal or cyanobacterial photobionts. The mycobiont and photobiont live together in an integrated thallus, but they lack specific tissue for the transport of metabolites and resources between them. Carbon is acquired through photosynthesis in the photobiont, which is active when the lichen is wet and exposed to light. Lichen photosynthesis is limited primarily by water, light and nitrogen, but can also be constrained by slow diffusion of CO # within the wet thallus. The assimilated carbon is exported from photobiont to mycobiont, which also predominates in terms of biomass, and apparently regulates the size of the photobiont population. It has therefore generally been assumed that most of the carbon is used for growth and maintenance of the fungal hyphae. However, the extent of photobiont respiration in relation to mycobiont respiration has seldom been quantified ; neither do we know the pool sizes of various carbon sinks within lichens. Owing to this lack of fundamental data we do not know whether, or how, carbohydrate resources are regulated to maintain an optimal balance between energy input and expenditures in these symbiotic organisms. This review summarizes data on growth, carbon gain and carbon expenditures in lichens, with particular emphasis on factors determining the photosynthetic capacity of their photobionts. An attempt is made to introduce an economic analysis of lichen growth processes, a view that has often been adopted in studies of higher plants. Areas in which more data are needed for the construction of a model on ' lichen resource allocation patterns ' are discussed.

“…Present results suggest the opposite, with rates of DR in control replicates (week 1) showing half recovery to their asymptotic values in less than 30 min (compared to over 70 min for half recovery of NP uptake). In comparison with other species, the 3-5 h required for full recovery of NP activity in control replicates of C. mitis is greater than seen in Xanthoria aureola (2 h), although less than the 9 h required for full recovery in Peltigera polydactyla (Smith & Molesworth, 1973). This would suggest intermediate habitat requirements for C. mitis, if these results are interpreted in the context of the gradient from xerie to mesic conditions implied by increased time required for NP recovery following resaturation in many lichen species (Link & Nash, 1984;Brown, MacFarlane & Kershaw, 1983).…”

Section: Discussionmentioning

confidence: 72%

Recovery of net photosynthesis and dark respiration on rehydration of the lichen, Cladina mitis, and the influence of prior exposure to sulphur dioxide while desiccated

Coxson

1988

SUMMARY The pattern of resaturation respiration and of rehydration recovery of net photosynthesis has been examined after pretreatment of desiccated thalli of the mat‐forming lichen species Cladina mitis (Sandst.) Hale & Culb, with sulphur dioxide. The recovery of photosynthetic activity lagged behind that of dark respiration in all treatments, pointing to the necessity of monitoring both processes when investigating rehydration phenomena. The exposure of desiccated thalli to sulphur dioxide concentrations of 0·2 and 1·0 μ11−1 (v/v in air) for periods of 2 and 3 weeks prior to rehydration resulted in the enhancement of subsequent photosynthetic activity in all treatments. These effects were greatest in the 0·2 μ11−1 treatment where, after 2 weeks fumigation, rates of net photosynthesis on recovery were nearly 40% higher than that of control replicates receiving no SO2. These results point to the importance of considering the effects of dry deposition on physiological processes and suggest that in some cases limited SO2 exposure may result in short‐term enhancement of photosynthetic uptake.