Solar ultraviolet-B radiation affects plant-insect interactions in a natural ecosystem of Tierra del Fuego (southern Argentina)

We examined the effects of solar ultraviolet-B radiation (UVB) on plant-herbivore interactions in native ecosystems of the Tierra del Fuego National Park (southern Argentina), an area of the globe that is frequently under the Antarctic “ozone hole” in early spring. We found that filtering out solar UVB from the sunlight received by naturally-occurring plants of Gunnera magellanica, a creeping perennial herb, significantly increased the number of leaf lesions caused by chewing insects. Field surveys suggested that early-season herbivory was principally due to the activity of moth larvae (Lepidoptera: Noctuidae). Manipulative field experiments showed that exposure to solar UVB changes the attractiveness of G. magellanica leaf tissue to natural grazers. In a laboratory experiment, locally caught moth caterpillars tended to eat more tissue from leaves grown without UVB than from leaves exposed to natural UVB during development; however, the difference between treatments was not significant. Leaves grown under solar UVB had slightly higher N levels than leaves not exposed to UVB; no differences between UVB treatments in specific leaf mass, relative water content, and total methanol-soluble phenolics were detected. Our results show that insect herbivory in a natural ecosystem is influenced by solar UVB, and that this influence could not be predicted from crude measurements of leaf physical and chemical characteristics and a common laboratory bioassay. Received: 4 December 1997 / Accepted: 12 May 1998     

Responses to solar ultraviolet-B radiation in a shrub-dominated natural ecosystem of Tierra del Fuego (southern Argentina)

A study was made of the effects of solar ultraviolet‐B radiation (UV‐B) on the growth of the dominant plant species of a shrub‐dominated ecosystem in Tierra del Fuego. This part of southern Argentina can be under the direct influence of the Antarctic ‘ozone hole’ during the austral spring and lingering ozone‐depleted air during the summer. The plant community is dominated by an evergreen shrub (Chiliotrichum diffusum) with an herbaceous layer of Gunnera magellanica and Blechnum penna‐marina in the interspaces between the shrubs. Inspections of ozone trends indicate that the springtime and summertime ozone column over Tierra del Fuego has decreased by 10–13% from 1978/9 to 1998/9. In a set of well‐replicated field plots, solar UV‐B was reduced to approximately 15–20% of the ambient UV‐B using plastic films. Polyester films were used to attenuate UV‐B radiation and UV‐transparent films (～90% UV‐B transmission) were used as control. Treatments were imposed during the growing season beginning in 1996 and continued for three complete growing seasons. Stem elongation of the shrub C. diffusum was not affected by UV‐B attenuation in any of the three seasons studied. However, frond length of B. penna‐marina under attenuated UV‐B was significantly greater than that under near‐ambient UV‐B in all three seasons. Attenuation of solar UV‐B also promoted the expansion of G. magellanica leaves in two of the growing seasons. Differences between treatments in leaf or frond length in B. penna‐marina and G. magellanica did not exceed 12%. Another significant effect of UV‐B attenuation was a promotion of insect herbivory in G. magellanica, with a 25–75% increase in the leaf area consumed. Changes in plant phenology or relative species cover were not detected within the time frame of this study. The results suggest that the increase in UV‐B radiation associated with the erosion of the ozone layer might be affecting the functioning of this ecosystem to some degree, particularly by inhibiting the growth of some plant species and by altering plant–insect interactions.     

Solar UV-B radiation affects below-ground parameters in a fen ecosystem in Tierra del Fuego, Argentina: implications of stratospheric ozone depletion

Stratospheric ozone depletion caused by the release of chlorofluorocarbons is most pronounced at high latitudes, especially in the Southern Hemisphere (including the so‐called ‘ozone hole’). The consequent increase in solar ultraviolet‐B radiation (UV‐B, 280–315 nm) reaching the earth's surface may cause a variety of alterations in terrestrial ecosystems. Most effects might be expected to occur above‐ground since sunlight does not penetrate effectively below‐ground. Here, we demonstrate that solar UV‐B radiation in a fen in Tierra del Fuego (Argentina), where the ozone hole passes overhead several times during the Austral spring, is causing large changes of below‐ground processes of this ecosystem. During the third and fourth year of a manipulative field experiment, we investigated root systems in these plots and found that when the ambient solar UV‐B radiation was substantially reduced, there was a 30% increase in summer root length production and as much as a threefold decrease in already low symbiotic mycorrhizal colonization frequency of the roots compared with plots receiving near‐ambient solar UV‐B. There was also an apparent shift toward older age classes of roots under reduced solar UV‐B. Such large changes in root system behaviour may have decided effects on competition and other ecological interactions in this ecosystem.     

Solar UVB and warming affect decomposition and earthworms in a fen ecosystem in Tierra del Fuego, Argentina

Combined effects of co-occurring global climate changes on ecosystem responses are generally poorly understood. Here, we present results from a 2-year field experiment in a Carex fen ecosystem on the southernmost tip of South America, where we examined the effects of solar ultraviolet B (UVB, 280–315 nm) and warming on above- and belowground plant production, C : N ratios, decomposition rates and earthworm population sizes. Solar UVB radiation was manipulated using transparent plastic filter films to create a near-ambient (90% of ambient UVB) or a reduced solar UVB treatment (15% of ambient UVB). The warming treatment was imposed passively by wrapping the same filter material around the plots resulting in a mean air and soil temperature increase of about 1.2 °C. Aboveground plant production was not affected by warming, and marginally reduced at near-ambient UVB only in the second season. Aboveground plant biomass also tended to have a lower C : N ratio under near-ambient UVB and was differently affected at the two temperatures (marginal UVB × temperature interaction). Leaf decomposition of one dominant sedge species ( Carex curta ) tended to be faster at near-ambient UVB than at reduced UVB. Leaf decomposition of a codominant species ( Carex decidua ) was significantly faster at near-ambient UVB; root decomposition of this species tended to be lower at increased temperature and interacted with UVB. We found, for the first time in a field experiment that epigeic earthworm density and biomass was 36% decreased by warming but remained unaffected by UVB radiation. Our results show that present-day solar UVB radiation and modest warming can adversely affect ecosystem functioning and engineers of this fen. However, results on plant biomass production also showed that treatment manipulations of co-occurring global change factors can be overridden by the local climatic situation in a given study year.     

Solar ultraviolet-B radiation influence on Sphagnum bog and Carex fen ecosystems: first field season findings in Tierra del Fuego, Argentina

Stratospheric ozone depletion occurs over Tierra del Fuego, southern Argentina and Chile, in the austral spring and summer due to the precession of the Antarctic ‘ozone hole’ and the general erosion of the ozone layer. Plots receiving either near-ambient or reduced UV-B radiation were established using different louvered plastic film filters over Sphagnum bog and Carex fen ecosystems in October 1996. In the Sphagnum bog system, growth measurements during the late spring and summer showed no significant differences in the moss Sphagnum magellanicum, or the vascular plants (Empetrum rubrum, Nothofagus antarctica, and Tetroncium magellanicum) between near-ambient and attenuated UV-B radiation treatments. In the Carex fen system, leaf length and spike height did not differ in the two dominant species, Carex decidua and C. curta, between UV-B radiation treatments. The length of individual spikelets of C. curta under near-ambient UV-B radiation was less than under the reduced UV-B radiation treatment, but this was not evident in C. decidua. No differences in seed number, seed mass, or viability were seen in either Carex species between the UV-B treatments. Two important constituents of the microfauna that inhabit the Sphagnum bog are testate amoebae and rotifers. These both appeared to be more numerous under near-ambient UV-B radiation than under reduced UV-B radiation. The subtle responses of the Sphagnum and Carex ecosystems may become more apparent in subsequent years as the treatments are continued. Trophic-level changes, such as the differences in number of amoebae and rotifers, may be more sensitive to solar UV-B radiation than growth and productivity of the vegetation.     

Solar ultraviolet-B radiation can affect slug feeding preference for some plant species native to a fen ecosystem in Tierra del Fuego,Argentina

The objectives of this study were to test potential effects of solar ultraviolet-B (UV-B) radiation on (i) foliage nutritional quality and foliage decomposition rates of six plant species of this fen ecosystem (Nothofagus antarctica, Carex curta, C. decidua and C. magellanica; Acaena magellanica and Gunnera magellanica) and (ii) feeding preferences for these plant species of the slug Deroceras reticulatum prevalent in this ecosystem. In a mixed-diet selection slugs were offered leaves of the six species that had been grown for three years in experimental field plots under either near-ambient or reduced solar ultraviolet-B (UV-B) radiation. The chosen characteristics of leaf quality (nitrogen concentration, carbon:nitrogen ratio, specific leaf area) and leaf decomposition rates of the six species varied significantly among species but were not affected by the UV-B treatments. However, there were UV-B treatment effects on slug feeding preference for two plant species. For the tree species, Nothofagus, slugs had consumed only one-third as much foliage grown under near-ambient UV-B radiation as of foliage grown under reduced UV-B by the end of the feeding experiment. In contrast, leaves of the sedge C. decidua that had been grown under near-ambient UV-B were consumed twice as much as leaves grown under reduced UV-B radiation. Consumption of foliage for the other four species was similar for the two UV-B treatments. Additionally, diet selection of the slugs was also significantly affected by prior UV-B conditions under which foliage had been grown. Nothofagus leaves were consumed proportionately less and C. decidua proportionately more if the foliage had been grown under near-ambient UV-B radiation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Elevated UV-B radiation incident on Quercus robur leaf canopies enhances decomposition of resulting leaf litter in soil

We examined whether the exposure of Quercus robur L. to elevated UV-B radiation (280–315 nm) during growth would influence leaf decomposition rate through effects on litter quality. Saplings were exposed for eight months at an outdoor facility in the UK to a 30% elevation above the ambient level of erythemally weighted UV-B radiation under UV-B treatment arrays of fluorescent lamps filtered with cellulose diacetate, which transmitted both UV-B and UV-A (315–400 nm) radiation. Saplings were exposed to elevated UV-A alone under control arrays of lamps filtered with polyester and to ambient radiation under unenergised arrays of lamps. Abscised leaves from saplings were enclosed in 1 mm² mesh nylon bags, placed in a Quercus–Fraxinus woodland and were sampled at 0.11, 0.53, 1.10 and 1.33 years for dry weight loss, chemical composition and saprotrophic fungal colonization. At abscission, litters from UV-A control arrays had ≈ 7.5% higher lignin/nitrogen ratios than those from UV-B treatment and ambient arrays (P < 0.06). Dry weight loss of leaves treated with elevated UV-B radiation during growth was 2.5% and 5% greater than that of leaves from UV-A control arrays at 0.53 and 1.33 years, respectively. Litter samples from UV-B treatment arrays lost more nitrogen and phosphorus than samples from ambient arrays and more carbon than samples from UV-A control arrays. The annual fractional weight loss of litter from UV-B treatment arrays was 8% and 6% greater than that of litter from UV-A control and ambient arrays, respectively. Regression analyses indicated that the increased decomposition rate of UV-B treated litters was associated with enhanced colonization of leaves by basidiomycete fungi, the most active members of the soil fungal community, and that the frequency of these fungi was negatively associated with the initial lignin/nitrogen ratio of leaves.     

凋落物多样性及组成对凋落物分解及土壤微生物群落的影响——二氧化碳倍增条件下

受全球变化的影响生物多样性的丧失日益严重,及时了解凋落物物种多样性及其组成如何直接或者通过调节微生物群落来间接影响凋落物分解已经成为生态学领域的热点问题之一。在呼伦贝尔典型草原区,羊草（Leymus chinensis）为原生群落建群种,茵陈蒿（Artemisia capillaris）、麻花头（Serratula centauroides）、二裂委陵菜（Potentilla bifurca）在退化及恢复群落中的多度均较大,本研究以此4种植物的凋落物为研究对象,在两倍于当前大气CO₂浓度（800 μmol/mol）条件下,通过嵌套实验设计来研究凋落物多样性（凋落物组成）对凋落物质量、C、N残余率和残余C/N的影响,并深入分析凋落物初始性质以及土壤革兰氏阳性菌（G⁺）、革兰氏阴性菌（G^-）、细菌（B）、真菌（F）及土壤总微生物磷脂脂肪酸（Phospholipid Fatty Acid,PLFA）含量和F/B对凋落物分解的影响。结果表明：（1）凋落物多样性及组成对凋落物质量、C、N残余率以及残余C/N均具有显著影响;凋落物组成对G⁺ PLFAs含量具有显著影响;（2）冗余分析（Redundancy Analysis,RDA）结果表明凋落物组成对凋落物分解和土壤微生物群落相关指标的影响高于凋落物多样性;（3）结构方程模型（Structural Equation Model,SEM）结果表明凋落物初始木质素含量和初始C/N均对凋落物分解具有显著影响,其中凋落物初始木质素含量起主导作用,其还可通过对土壤真菌PLFAs含量的影响来间接影响凋落物N残余率和残余C/N。所得结果可为大气CO₂浓度升高条件下退化草原生态系统的物质循环特征的预测乃至草原生态系统功能的合理评估提供数据支持。     

Direct and indirect effects of solar ultraviolet-B radiation on long-term decomposition

As a result of stratospheric ozone depletion, more solar ultraviolet-B radiation (UV-B, 280–315 nm) is reaching the Earth's surface. Enhanced levels of UV-B may, in turn, alter ecosystem processes such as decomposition. Solar UV-B radiation could affect decomposition both indirectly, by changes in the chemical composition of leaves during growth, or directly by photochemical breakdown of litter and through changes in decomposer communities exposed to sunlight. In this experiment, we studied indirect and direct effects of solar UV-B radiation on decomposition of barley (Hordeum vulgare). We used barley straw and leaf litter grown under reduced UV-B (20% of ambient UV-B) or under near-ambient UV-B (90% of ambient UV-B) in Buenos Aires, Argentina, and decomposed the litter under reduced or near-ambient solar UV-B for 29 months in Tierra del Fuego, Argentina. We found that the UV-B treatment applied during growth decreased the decay rate. On the other hand, there was a marginally significant direct effect of elevated UV-B during the early stages of decomposition, suggesting increased mass loss. The effect of UV-B during growth on decomposition was likely the result of changes in plant litter chemical composition. Near-ambient UV-B received during plant growth decreased the concentrations of nitrogen, soluble carbohydrates, and N/P ratio, and increased the concentrations of phosphorus, cellulose, UV-B-absorbing compounds, and lignin/N ratio. Thus, solar UV-B radiation affects the decomposition of barley litter directly and indirectly, and indirect effects are persistent for the whole decomposition period.     

Elevated UV-B radiation has no effect on litter quality and decomposition of two dune grassland species: evidence from a long-term field experiment

From studies on living plant tissues it has been inferred that elevated UV‐B radiation could negatively affect litter quality and subsequent decomposition. However, in general, the effects of UV‐B radiation on litter chemistry and decomposition reported in the literature are variable and are often only marginally (if at all) significant. This might be due to the ecologically unrealistic conditions under which these experiments were performed. We investigated the effects of elevated UV‐B radiation on litter quality and subsequent decomposition on initial litter chemistry and long‐term (2 years) decomposition of freshly senesced Carex arenaria and Calamagrostis epigejos leaf litter under ecologically realistic conditions. This material was collected from a dune grassland that had received UV‐B radiation treatments for three growing seasons. It was then used in a 2‐year decomposition study using litter bags. We found no significant effects of elevated UV‐B radiation on any of the litter chemistry parameters in either of the two species, nor did we find significant effects on litter decomposition. However, we did find significant differences in litter decomposition between the species. These differences were related to the interspecific differences in litter chemistry, particularly the litter phenolics concentration. These results show that litter quality and decomposition in dune grasslands are, also under ecologically realistic conditions, not affected by UV‐B radiation. Instead, litter decomposition is determined by constitutive interspecific differences in litter chemistry. In conclusion, with our results added to the already existing literature, the preponderance of evidence now clearly suggests that elevated UV‐B radiation has very little, if any, impact on litter quality and subsequent decomposition in real ecosystems.     

Stratospheric ozone reduction and ecosystem processes: enhanced UV-B radiation affects chemical quality and decomposition of leaves of the dune grassland species Calamagrostis epigeios

This study reports changes in the plant's chemical composition and the decomposition of this plant material under enhanced solar UV-B radiation. Calamagrostis epigeios, a dominant grass species in the dune grassland in The Netherlands, was grown outdoor on an experimental field under ambient and enhanced solar UV-B (5 and 7.5 kJ m^-2 day^-1 UV-B_BE, respectively), corresponding to about 15% stratospheric ozone depletion. After one growing season aerial plant parts were harvested. The decomposition of this harvested leaf material was studied in a dune grassland and on the above mentioned experimental field under ambient (5 kJ m^-2 day^-1 UV-B_BE) and enhanced (7.5 kJ m^-2 day^-1 UV-B_BE) radiation, using litter bags. The chemical quality of the leaves grown under enhanced solar UV-B changed. There was an increase in the leaf content of lignin, while no significant changes occurred for the content of -cellulose, hemicellulose and tannins under enhanced UV-B. In the field, the rate of decomposition of leaf material grown under enhanced UV-B (with an increased content of lignin) was reduced. The content of lignin of the decomposing leaf material increased, but less under exposure to enhanced UV-B. The latter may be explained by photodegradation of the lignin. The consequences of enhanced UV-B radiation for carbon fluxes in the dune grassland ecosystem are discussed.     

Interactions among fungal community structure, litter decomposition and depth of water table in a cutover peatland

Peatlands are important reservoirs of carbon (C) but our understanding of C cycling on cutover peatlands is limited. We investigated the decomposition over 18 months of five types of plant litter (Calluna vulgaris, Eriophorum angustifolium, Eriophorum vaginatum, Picea sitchensis and Sphagnum auriculatum) at a cutover peatland in Scotland, at three water tables. We measured changes in C, nitrogen (N) and phosphorus (P) in the litter and used denaturing gradient gel electrophoresis to investigate changes in fungal community composition. The C content of S. auriculatum litter did not change throughout the incubation period whereas vascular plant litters lost 30-40% of their initial C. There were no differences in C losses between low and medium water tables, but losses were always significantly less at the high water table. Most litters accumulated N and E. angustifolium accumulated significant quantities of P. C, N and P were significant explanatory variables in determining changes in fungal community composition but explained <25% of the variation. Litter type was always a stronger factor than water table in determining either fungal community composition or turnover of C, N and P in litter. The results have implications for the ways restoration programmes and global climate change may impact upon nutrient cycling in cutover peatlands.     

土壤微生物群落结构对中亚热带三种典型阔叶树种凋落物分解过程的响应

通过小盆模拟试验研究了南方红壤丘陵区典型阔叶树种香樟、白栎和青冈的凋落物分解过程中土壤微生物群落结构的异同。结果表明:(1)凋落物含氮量:白栎>香樟>青冈;碳、木质素的含量以及碳/氮比、木质素/氮比:青冈>香樟>白栎;分解速率:白栎>香樟>青冈;(2)随着凋落物分解的进程,土壤微生物群落16 ∶ 0、15 ∶ 0、i16 ∶ 0、a17 ∶ 0、17 ∶ 0、18 ∶ 2ω6,9c和10Me18 ∶ 0的含量上升,18 ∶ 0、14 ∶ 0、16 ∶ 1ω7c、18 ∶ 1ω7c、cy19 ∶ 0、i19 ∶ 0和10Me19 ∶ 0的含量下降,饱和直链脂肪酸/单不饱和脂肪酸、革兰氏阳性菌/革兰氏阴性菌以及cy19 ∶ 0/18 ∶ 1ω7c的比值都显著上升。(3)两个时期白栎凋落物处理土壤16 ∶ 0、15 ∶ 0、a15 ∶ 0、i16 ∶ 0、a17 ∶ 0、 17 ∶ 0、cy19 ∶ 0、18 ∶ 2ω6,9c、18 ∶ 1ω9c和10Me18 ∶ 0的含量显著高于香樟和青冈凋落物处理的土壤,细菌、真菌的磷脂脂肪酸含量以及磷脂脂肪酸总量显著高于香樟和青冈凋落物处理的土壤。随着阔叶凋落物的分解,变化的土壤环境对土壤微生物群落的胁迫增强,土壤微生物群落结构发生显著变化。与香樟和青冈的凋落物相比,白栎凋落物碳/氮比和木质素/氮比低、分解快,能显著改善土壤微生物群落结构,更有利于土壤肥力提高和生态系统养分循环的改善。     

Disentangling direct and indirect effects of water table drawdown on above‐ and belowground plant litter decomposition: consequences for accumulation of organic matter in boreal peatlands

Pristine peatlands are carbon (C)‐accumulating wetland ecosystems sustained by a high water table (WT) and consequent anoxia that slows down decomposition. Persistent WT drawdown as a response to climate and/or land‐use change affects decomposition either directly through environmental factors such as increased oxygenation, or indirectly through changes in plant community composition. This study attempts to disentangle the direct and indirect effects of WT drawdown by measuring the relative importance of environmental parameters (WT depth, temperature, soil chemistry) and litter type and/or litter chemical quality on the 2‐year decomposition rates of above‐ and belowground litter (altogether 39 litter types). Consequences for organic matter accumulation were estimated based on the annual litter production. The study sites were chosen to form a three‐stage chronosequence from pristine (undrained) to short‐term (years) and long‐term (decades) WT drawdown conditions at three nutrient regimes. The direct effects of WT drawdown were overruled by the indirect effects through changes in litter type composition and production. Short‐term responses to WT drawdown were small. In long‐term, dramatically increased litter inputs resulted in large accumulation of organic matter in spite of increased decomposition rates. Furthermore, the quality of the accumulated matter greatly changed from that accumulated in pristine conditions. Our results show that the shift in vegetation composition as a response to climate and/or land‐use change is the main factor affecting peatland ecosystem C cycle, and thus dynamic vegetation is a necessity in any model applied for estimating responses of C fluxes to changing environment. We provide possible grouping of litter types into plant functional types that the models could utilize. Furthermore, our results clearly show a drop in soil summer temperature as a response to WT drawdown when an initially open peatland converts into a forest ecosystem, which has not yet been considered in the existing models.     

Non‐symbiotic nitrogen fixation during leaf litter decomposition in an old‐growth temperate rain forest of Chiloé Island,southern Chile: Effects of single versus mixed species litter

Heterotrophic nitrogen fixation is a key ecosystem process in unpolluted, temperate old‐growth forests of southern South America as a source of new nitrogen to ecosystems. Decomposing leaf litter is an energy‐rich substrate that favours the occurrence of this energy demanding process. Following the niche ‘complementarity hypothesis’, we expected that decomposing leaf litter of a single tree species would support lower rates of non‐symbiotic N fixation than mixed species litter taken from the forest floor. To test this hypothesis we measured acetylene reduction activity in the decomposing monospecific litter of three evergreen tree species (litter C/N ratios, 50–79) in an old‐growth rain forest of Chiloé Island, southern Chile. Results showed a significant effect of species and month (anova , Tukey's test, P < 0.05) on decomposition and acetylene reduction rates (ARR), and a species effect on C/N ratios and initial % N of decomposing leaf litter. The lowest litter quality was that of Nothofagus nitida (C/N ratio = 78.7, lignin % = 59.27 ± 4.09), which resulted in higher rates of acetylene reduction activity (mean = 34.09 ± SE = 10.34 nmol h^?1 g^?1) and a higher decomposition rate (k = 0.47) than Podocarpus nubigena (C/N = 54.4, lignin % = 40.31 ± 6.86, Mean ARR = 4.11 ± 0.71 nmol h^?1 g^?1, k = 0.29), and Drimys winteri (C/N = 50.6, lignin % = 45.49 ± 6.28, ARR = 10.2 ± 4.01 nmol h^?1 g^?1, k = 0.29), and mixed species litter (C/N = 60.7, ARR = 8.89 ± 2.13 nmol h^?1g^?1). We interpret these results as follows: in N‐poor litter and high lignin content of leaves (e.g. N. nitida) free‐living N fixers would be at competitive advantage over non‐fixers, thereby becoming more active. Lower ARR in mixed litter can be a consequence of a lower litter C/N ratio compared with single species litter. We also found a strong coupling between in situ acetylene reduction and net N mineralization in surface soils, suggesting that as soon N is fixed by diazotroph bacteria it may be immediately incorporated into mineral soil by N mineralizers, thus reducing N immobilization.     

Ecological role of reindeer summer browsing in the mountain birch (<Emphasis Type="Italic">Betula pubescens</Emphasis> ssp. <Emphasis Type="Italic">czerepanovii</Emphasis>) forests: effects on plant defense,litter decomposition,and soil nutrient cycling

Mammalian herbivores commonly alter the concentrations of secondary compounds in plants and, by this mechanism, have indirect effects on litter decomposition and soil carbon and nutrient cycling. In northernmost Fennoscandia, the subarctic mountain birch (Betula pubescens ssp. czerepanovii) forests are important pasture for the semidomestic reindeer (Rangifer tarandus). In the summer ranges, mountain birches are intensively browsed, whereas in the winter ranges, reindeer feed on ground lichens, and the mountain birches remain intact. We analyzed the effect of summer browsing on the concentrations of secondary substances, litter decomposition, and soil nutrient pools in areas that had been separated as summer or winter ranges for at least 20 years, and we predicted that summer browsing may reduce levels of secondary compounds in the mountain birch and, by this mechanism, have an indirect effect on the decomposition of mountain birch leaf litter and soil nutrient cycling. The effect of browsing on the concentration of secondary substances in the mountain birch leaves varied between different years and management districts, but in some cases, the concentration of condensed tannins was lower in the summer than in the winter ranges. In a reciprocal litter decomposition trial, both litter origin and emplacement significantly affected the litter decomposition rate. Decomposition rates were faster for the litter originating from and placed into the summer range. Soil inorganic nitrogen (N) concentrations were higher in the summer than in the winter ranges, which indicates that reindeer summer browsing may enhance the soil nutrient cycling. There was a tight inverse relationship between soil N and foliar tannin concentrations in the winter range but not in the summer range. This suggests that in these strongly nutrient-limited ecosystems, soil N availability regulates the patterns of resource allocation to condensed tannins in the absence but not in the presence of browsing.