Species-specific Growth Responses Research Articles

Declining Radial Growth in Major Western Carpathian Tree Species: Insights from Three Decades of Temperate Forest Monitoring.

This study investigates the radial growth response of five key European forest tree species, i.e., Fagus sylvatica, Picea abies, Abies alba, Quercus petraea, and Pinus sylvestris, to dry years in the West Carpathians, Slovakia. Utilizing data from ICP Forests Level I plots, we identified species-specific growth declines, particularly in Pinus sylvestris and Fagus sylvatica, with milder radial growth declines for Quercus petraea and Picea abies. Abies alba exhibited a growth peak in the mid-2000s, followed by a decline in the end of the observed period. Elevation emerged as the only significant environmental predictor, explaining 3.5% of growth variability during dry periods, suggesting a potential mitigating effect. The scope of this study was limited by the complex interplay of ecological factors that influence tree growth, which vary across the ICP Forests Level I monitoring sites. Nonetheless, our findings enhance the understanding of species-specific growth responses and offer insights for the climate-smart management of temperate forests under changing conditions.

Species-specific growth responses to local and regional climate variability indicate the presence of a diversity portfolio effect in mediterranean tree assemblages

Understanding the role of tree biodiversity in stabilizing ecosystem processes is of paramount importance in forest ecology, especially because of increasing temperatures and droughts. The portfolio effect is one of the main hypotheses explaining the biodiversity-stability relationship that has been defined as a variance reduction effect of biodiversity in an ecosystem process, so that fluctuations over time in highly diverse communities become significantly smaller in low-diversity communities. In this work, two main objectives were established: to analyze a potential portfolio effect in a tree assemblage through functional mechanisms of compensation, and to identify the local climatic factors and teleconnections responsible for the interannual variations in the growth of tree species. The study was carried out in a region of the Iberian Peninsula with transitional climatic characteristics that allow the coexistence of needleleaf and broadleaf tree species with a wide variety of strategies and functional traits allowing them to respond differentially to climatic conditions. A dendrochronological approach was followed to analyze tree growth in relation to climate factors. We found that the magnitude and sensitivity of the response to both local climatic elements and teleconnections were species-dependent and that during climatically extreme years, the species exhibited marked differences in tree growth and compensatory responses that contributed to an increase in temporal stability. These results point to the existence of a portfolio effect in Mediterranean woodlands that supports tree diversity as an effective driver of ecosystem stability. Although the combination of dry and hot years always has a negative effect on tree growth, the association of coniferous and broadleaved (evergreen and marcescent) species at our study site could have a significantly positive influence by increasing temporal stability at landscape level through complementary functional responses.

Species-specific growth, morphological and physiological responses ofAbies faxonianaandPicea purpureaunder elevated temperature and CO2

AbstractAlthough many studies have evaluated plant ecophysiological responses to increasing atmospheric carbon dioxide concentration (CO2) and increasing temperature, few studies have addressed the interactive effects of these two factors, especially on high-altitude trees that are more sensitive. To address this issue, we used Abies faxoniana and Picea purpurea seedlings to evaluate the effects of elevated CO2 (CeTa, 700 ppm), elevated temperature (CaTe, 2 °C above ambient temperature) and elevated CO2 combined with elevated temperature (CeTe) on plant growth, morphology and physiological responses. We found that CaTe increased conifer total dry mass, specific root length, net photosynthesis rate and translocation rates of 15NH4+ and 15NO3−, but CeTe had stronger responses (except net photosynthesis rate of A. faxoniana). These results indicate that the effect of elevated temperature on the growth and physiological responses is enhanced by elevated CO2. Furthermore, effect of CeTe on physiological traits was higher in P. purpurea, which possessed a higher total dry mass, specific leaf area, water use efficiency (δ 13C), δ 15NO3−-N level, translocation rates of 15NH4+ and 15NO3− and total nonstructural carbohydrates than A. faxoniana. Overall, these findings suggest that the interactive effects of CO2 × temperature should be considered when assessing conifer responses to future climates.

Tree growth responses to extreme drought after mechanical thinning and prescribed fire in a Sierra Nevada mixed-conifer forest, USA

An estimated 128 M trees died during the 2012–2016 California drought, largely in the southern Sierra Nevada Range. Prescribed burning and mechanical thinning are widely used to reduce fuels and restore ecosystem properties, but it is unclear if these treatments improve tree growth and vigor during extreme drought. This study examined tree growth responses after thinning, prescribed burning, and extreme drought at the Teakettle Experimental Forest, a historically frequent fire mixed-conifer forest in the southern Sierra Nevada of California, USA. Mechanical thinning (no thin, understory thin, and overstory thin) and prescribed burning (unburned, fall burning) were implemented in 2000–2001. Using annual growth data from increment cores, over 10,000 mapped and measured trees, and lidar-derived metrics of solar radiation and topographic wetness, we had two primary questions. First, what were the growth responses to thinning and prescribed burning treatments, and did these responses persist during the 2012–2016 drought? Second, what tree-level attributes and environmental conditions influenced growth responses to treatments and drought?Thinning increased residual tree growth and that response persisted through extreme drought 10–15 years after treatments. Growth responses were higher in overstory versus understory thinning, with differences between thinning types more pronounced during drought. Species-specific growth responses were strongest with overstory thinning, with sugar pine (Pinus lambertiana) and incense-cedar (Calocedrus decurrens) having higher growth responses compared to white fir (Abies concolor) and Jeffery pine (Pinus jeffreyi). For individual trees, factors associated with higher growth responses were declining pretreatment growth trend, smaller tree size, and post-treatment low neighborhood basal area. Growth responses were initially not influenced by topography, but topographic wetness became important during extreme drought. Mechanical thinning resulted in durable increases in residual tree growth rates during extreme drought over a decade after thinning occurred, indicating treatment longevity in mitigating drought stress. In contrast, tree growth did not improve after prescribed burning, likely due to fire effects that reduced surface fuels, but had little effect on reducing tree density. Thinning treatments promoted durable growth responses, but focusing on stand-level metrics may ignore important tree-level attributes such as localized competition and topography associated with higher water availability. Mechanical thinning was effective at improving growth in trees that had been experiencing declining growth trends, but was less effective in improving growth responses in large old trees of higher ecological importance.

Traits of tidal marsh plants determine survival and growth response to hydrodynamic forcing: implications for nature-based shoreline protection

Tidal marshes are increasingly valued for their nature-based shoreline protection function, as they reduce waves, currents and erosion. The effectiveness of this function depends on the ability of tidal marsh plants to grow and survive under pressure from waves and currents. However, how this varies with species-dependent plant traits is poorly understood. We performed a field transplantation experiment to quantify species-specific growth responses to different levels of hydrodynamic exposure and tidal inundation for 3 NW European marsh species: Schoenoplectus tabernaemontani, Bolboschoenus maritimus and Phragmites australis. In this order, these species showed increasing shoot stiffness, length and biomass, which are traits that increase hydrodynamic drag forces experienced by plants. Increased exposure to tidal inundation and hydrodynamics reduced the growth of all 3 species, but species with lower biomass and shorter, thinner and more flexible shoots could better cope with higher hydrodynamic exposure and tidal inundation. Furthermore, transplants of S. tabernaemontani (i.e. the species with the lowest shoot stiffness, length and biomass that survived under all tested conditions) developed smaller, thinner and more flexible shoots in response to higher hydrodynamic exposure and inundation. Hence our study indicates that similar inter- and intra-specific plant traits drive plant growth in response to hydrodynamics and inundation. This suggests that the spatial distribution of species typically observed in tidal marshes results not only from species-specific tolerance to tidal inundation gradients but also from hydrodynamic gradients. Allowing enough space for development of species zonation may be important to increase the efficiency of nature-based shoreline protection by tidal marshes.

Microfabrication and its use in investigating fungal biology.

Advances in microfabrication technology, and its increasing accessibility, allow us to explore fungal biology as never before. By coupling molecular genetics with fluorescence live-cell imaging in custom-designed chambers, we can now probe single yeast cell responses to changing conditions over a lifetime, characterise population heterogeneity and investigate its underlying causes. By growing filamentous fungi in complex physical environments, we can identify cross-species commonalities, reveal species-specific growth responses and examine physiological differences relevant to diverse fungal lifestyles. As affordability and expertise broadens, microfluidic platforms will become a standard technique for examining the role of fungi in cross-kingdom interactions, ranging from rhizosphere to microbiome to interconnected human organ systems. This review brings together the perspectives already gained from studying fungal biology in microfabricated systems and outlines their potential in understanding the role of fungi in the environment, health and disease.

Seedling Response to Simulated Browsing and Reduced Water Availability: Insights for Assisted Migration Plantations

To facilitate forest transition to future climate conditions, managers can use adaptive silvicultural tools, for example the assisted translocation of tree species and genotypes to areas with suitable future climate conditions (i.e., assisted migration). Like traditional plantations, however, assisted migration plantations are at risk of failure because of browsing by ungulate herbivores. The ability of seedlings to tolerate browsing could also be hampered by low water availability, as is expected under climate change. Using a greenhouse experiment with five eastern North American tree species, we evaluated the effects of simulated winter browsing and reduced water availability on the growth (total biomass, shoot:root ratio), survival, and chemical composition (nitrogen, total phenolics, flavonoids) of seedlings. We compared seedlings from three geographic provenances representing three climate analogues, i.e., locations with a current climate similar to the climate predicted at the plantation site at a specific time (here: current, mid-century and end of the century). We hypothesized that seedlings would allocate resources to the system (shoots or roots) affected by the most limiting treatment (simulated browsing or reduced water availability). Additionally, we evaluated whether the combination of treatments would have an additive or non-additive effect on the growth, survival and chemical composition of the seedlings. Quercus rubra seedlings reacted only to the water reduction treatment (changes in biomass and N concentration, dependent on geographic provenance) while Pinus strobus reacted only to the simulated browsing treatment (biomass and chemical composition). We also observed non-additive effects of reduced water availability and simulated browsing on Prunus serotina, Acer saccharum and Thuja occidentalis. In general, shoot:root ratio and investment in chemical defense did not vary in response to treatments. The regrowth response observed in Q. rubra and A. saccharum suggests that these species could tolerate periodic browsing events, even when water availability is reduced. More information is required to understand their long-term tolerance to repeated browsing events and to harsher and more frequent water stress. We highlight the importance of species-specific growth and allocation responses that vary with geographic provenance, which should be considered by managers when planning climate-adapted strategies, such as assisted migration.

Growth responses of Abies spectabilis to climate variations along an elevational gradient in Langtang National Park in the central Himalaya, Nepal

ABSTRACTStudies on tree-growth responses to climatic variations in a subalpine ecoregion of the central Himalaya are limited. The Himalayan silver fir (Abies spectabilis (D. Don) Spach), a dominant tree species in subalpine forest on mesic north-facing slopes, was used to analyse the tree-growth‒climate relationship along an elevational gradient. Tree growth shows sensitive responses to both growing-season and non-growing season temperature and precipitation variability at all elevations. Temperature has a strong influence at the boundaries (highest and lowest elevation) of the forest range. The uppermost tree-limit boundary is strongly associated with summer temperature, and the lowest forest boundary with winter temperature. Autumn temperatures (November, prior to growth year) influence tree growth regardless of elevation. Premonsoon precipitation has a significant influence on growth only at intermediate elevations. As the study describes the response pattern from only a mesic area, more studies covering a range of climate regimes are required to see whether there is a clear pattern of species-specific growth responses to climate variables along an elevational gradient.

Different responses of multispecies tree ring growth to various drought indices across Europe

Increasing frequency and intensity of drought extremes associated with global change are a key challenge for forest ecosystems. Consequently, the quantification of drought effects on tree growth as a measure of vitality is of highest concern from the perspectives of both science and management. To date, a multitude of drought indices have been used to accompany or replace primary climatic variables in the analysis of drought-related growth responses. However, it remains unclear how individual drought metrics compare to each other in terms of their ability to capture drought signals in tree growth.In our study, we employ a European multispecies tree ring network at the continental scale and a set of four commonly used drought indices (De Martonne Aridity Index, self-calibrating Palmer Drought Severity Index, Standardized Precipitation Index and Standardized Precipitation Evapotranspiration Index, the latter two on varying temporal scales) to derive species-specific growth responses to drought conditions. For nine common European tree species, we demonstrate spatio-temporal matches and mismatches of tree growth with drought indices subject to species, elevation and bioclimatic zone. Forests located in the temperate and Mediterranean climate were drought sensitive and tended to respond to short- and intermediate-term drought (<1year). In continental climates, forests were comparably more drought resistant and responded to long-term drought. For the same species, stands were less drought sensitive at higher elevations compared to lower elevations. We provide detailed information on the month-wise performance of the four drought indices in different climate zones allowing users the selection of the most appropriate index according to their objective criteria. Our results show that species-specific differences in responses to multiple stressors result in complex, yet coherent patterns of tree growth.

Quantifying the effects of drought on abrupt growth decreases of major tree species in Switzerland.

Drought entails important effects on tree physiology, which may result in short‐ to long‐term radial growth decreases. While the majority of studies have focused on annual drought‐related variability of growth, relatively little is known about sustained growth decreases following drought years. We apply a statistical framework to identify climatic factors that induce abrupt growth decreases and may eventually result in tree mortality. We used tree‐ring data from almost 500 standing dead trees and 200 living trees in eight sites of the Swiss network of strict forest reserves, including four of the most important Central European tree species (Abies alba, Picea abies, Fagus sylvatica and Quercus spp.). First, to assess short‐term growth responses to drought under various climate and site conditions, we calculated correlations and linear mixed‐effects models between ring‐width indices (RWIs) and drought based on the Standardized Precipitation Evapotranspiration Index (SPEI). Second, to quantify drought effects on abrupt growth decreases, we applied distributed lag nonlinear models (DLNMs), which account for both delayed effects and the nonlinear relationship between the SPEI and the occurrence of abrupt growth decreases. Positive correlations between RWIs and the SPEI indicated short‐term growth responses of all species, particularly at arid sites. Results of the DLNMs revealed species‐specific growth responses to drought. For Quercus spp., abrupt growth decreases were more likely to occur several years following severe drought, whereas for P. abies, A. alba, and F. sylvatica abrupt growth decreases started frequently immediately in the drought year. We conclude that the statistical framework allows for quantifying the effects of drought intensity on the probability of abrupt growth decreases, which ultimately contributes to an improved understanding of climate impacts on forest community dynamics.

Species-specific growth and photosynthetic responses of first-year seedlingsof four coniferous species to open-field experimental warming

Temperature increase due to climate change may affect the growth and physiological traits of trees. To cope with climate change, it is important to understand the responses of trees to these changes, as well as how these responses vary among species, functional groups, and biomes. In this study, we aimed to examine the species-specific growth and photosynthetic responses of first-year seedlings of 4 coniferous species to future temperature increase by conducting an open-field experimental warming study. The air temperature in the warmed plots was maintained at 3.02 °C higher than that in the control plots with an open-field experimental warming system. The seeds of Pinus densiflora, Pinus koraiensis, Abies holophylla, and Abies koreana were planted in 2012, and the effects on growth, biomass allocation, leaf area, net photosynthetic rate, and chlorophyll contents of first-year seedlings were measured. Compared to the other species, P. densiflora showed pronounced responses to warming after the growing period, including increase in root collar diameter (RCD) and seedling height respectively by 10% and 6%, total biomass by 45%, net photosynthetic rate by 61%, and total chlorophyll content by 45%. For P. koraiensis, RCD, seedling height, and total chlorophyll contents increased by 7%, 5%, and 20% in warmed plots, respectively. A. holophylla showed an increase in RCD by 7%, whereas A. koreana responded inconsistently to warming. Changes in the seedling height to diameter ratio, organ-specific biomass, leaf area, and specific leaf area were also species-dependent. In addition, altered growth throughout the observation period was due to acclimation and phenological change. This suggests that species-specific growth responses to warming are affected by altered net photosynthetic rate, chlorophyll contents, and leaf area. Species-specific responses of first-year seedlings of 4 coniferous species to warming and the relationship between growth and photosynthesis might be applied to estimate the growth and distribution of coniferous species after future temperature rises.

거제수나무, 물푸레나무, 굴참나무 묘목의 실외 인위적 온난화에 대한 수종 특이적 생장 반응

기후변화 대응 산림 관리 방법을 개발하기 위해서는 온난화에 따른 수목의 반응을 예측하는 것이 중요하다. 본 연구는 우리나라 주요 활엽수종인 거제수나무(Betula costata), 물푸레나무(Fraxinus rhynchophylla), 굴참나무(Quercus variabilis) 묘목의 실외 인위적 온난화에 대한 생장 반응을 알아보기 위하여 수행되었다. 이를 위해 적외선등을 이용하여 지속적으로 기온을 <TEX>$3^{\circ}C$</TEX> 증가시킬 수 있는 실외 인위적 온난화 시스템을 구축하고, 활엽수 3개 수종을 파종한 후, 온도 증가에 대한 발아 당년 묘목의 생장, 생물량 분배 및 순광합성률의 반응을 분석하였다. 연구 결과, 거제수나무, 물푸레나무, 굴참나무 묘목의 생장은 실외 인위적 온난화 처리에 대하여 수종과 시기에 따라 서로 다른 반응을 나타냈다. 즉 거제수나무는 온난화 처리에 따라 근원경 대비 묘고 비율, 총 생물량, 지상부 대비 뿌리 중량 비율, 순광합성률 등이 감소한 반면, 굴참나무는 근원경, 묘고, 총 생물량, 순광합성률 등이 증가하였으며, 물푸레나무는 다른 수종에 비하여 생장 반응이 뚜렷하지 않았다. 시기별 반응으로는, 7월에는 모든 수종에 대하여 온난화 처리에 따른 변화가 나타나지 않았으나 11월에는 굴참나무의 근원경, 묘고, H/D율이 증가한 반면 거제수나무의 H/D율이 감소하였다. 온난화에 대한 수종별 생장 반응의 차이는 순광합성률 및 생물량 분배의 수종별 반응과 유사하게 나타나, 온도 증가에 의한 순광합성률과 생물량 분배의 수종별 차이가 생장에 영향을 미친 것으로 생각된다. 한편, 여름에 비하여 가을에 더 두드러지게 나타난 생장 반응은 온난화에 의한 식물 계절 특성의 변화에 의한 것으로 보인다. 활엽수 3개 수종에 대하여 온난화에 의한 수종 특이적 생장 반응을 밝힌 본 연구 결과는 기후변화에 대응한 산림 관리 정책 개발에 활용될 수 있을 것으로 사료된다. Evaluation of tree responses to temperature elevation is critical for a development of forest management techniques coping with climate change. We conducted a study on the growth responses of Betula costata, Fraxinus rhynchophylla, and Quercus variabilis seedlings to open-field artificial warming. Artificial warming set-up using infra-red heater was built in 2012 and the temperature in warmed plots was regulated to be consistently <TEX>$3^{\circ}C$</TEX> higher than that of control plots. The seeds of three species were sown, and the responses of growth, biomass allocation, and net photosynthetic rate of newly-germinated seedlings on the open-field artificial warming were determined. As a result, the growth responses of the seedlings differed with the species. B. costata showed decreases in the height to diameter ratio (H/D ratio), biomass, root weight to shoot weight ratio, and net photosynthetic rate. However, root collar diameter (RCD), height, biomass, and net photosynthetic rate of Q. variabilis were increased, while the response of F. rhynchophylla was rather obscure. There was no significant difference between warmed and control plots in seedling growth for 3 species in July, whereas, RCD, height, and H/D ratio of Q. variabilis were increased and H/D ratio of B. costata was decreased in November under warming. Species-specific growth responses to warming were similar to the species-specific responses of net photosynthetic rate and biomass allocation; therefore, net photosynthetic rate and biomass allocation might attribute to growth responses to warming. Besides, a relatively obvious response in autumn compared to summer might be affected by the phenological change following artificial warming. Species-specific responses of three deciduous species to warming in this study could be applied to the development of adaptive forest management policies to climate change.

Competitive balance among tree species altered by forest tent caterpillar defoliation

In northern hardwood forests with a closed canopy, tree growth is largely driven by tree size and competition with neighboring trees. Canopy defoliation during insect outbreaks temporarily increases light availability and may decrease light competition among neighboring trees. Defoliation typically reduces tree growth, but canopy defoliation could also stimulate growth of trees that maintain some leaf area. We compared the growth responses of mature trees of non-host species Acer rubrum, and the three host species Acer saccharum, Quercus rubra and Tilia americana, to defoliation by forest tent caterpillar (Malacosoma disstria, Lasiocampidae), a native forest insect with a ∼10-year outbreak periodicity, in a northern hardwood forest in northern lower Michigan.We compared tree growth during the forest tent caterpillar outbreak in 2009, and in the following year, to the average growth before the outbreak in relation to the defoliation level of both the focal tree and its neighbors. Growth responses were related to focal tree defoliation, but we found little direct evidence for effects of neighborhood defoliation; relatively uniform defoliation within sites may have obscured detection of neighborhood effects. Growth of T.americana increased substantially in the year following defoliation, despite the growth reduction during the outbreak in 2009. T.americana rapidly produced new leaves after peak defoliation in 2009, which could explain increased growth in 2010. A.rubrum, which was not defoliated, decreased growth slightly during the outbreak. In 2010, however, one year after peak defoliation, A. rubrum growth was similar to pre-outbreak growth. The two other defoliated species, A. saccharum and Q. rubra, decreased growth in both 2009 and 2010. These strongly species-specific growth responses to canopy defoliation might result in changes in tree species’ interactions and shifts in species advantages over time.

Stand recovery and self-organization following large-scale mountain pine beetle induced canopy mortality in northern forests

A mountain pine beetle (MPB) epidemic is currently ravaging large areas of interior British Columbia (BC) with significant implications for ecosystem services including future timber supply and community economic stability. Information is needed on future stand dynamics in areas of impacted forests that are unlikely to be salvaged logged. Of greatest concern are stands dominated by lodgepole pine (>50% timber volume). Predicting how surviving trees in these areas respond and grow and the timing and species composition of natural regeneration ingress is of critical importance for multiple forest values. We undertook a retrospective study in the Flathead Valley of southeastern British Columbia where an intense MPB epidemic peaked in 1979–1980. Our objective was to gain insight into stand recovery and stand self-organization as influenced by species-specific growth responses of different sized secondary structure trees (individual seedling, sapling, sub-canopy and canopy trees surviving the epidemic) and post-beetle regeneration dynamics. MPB mortality rates, the percent of basal area killed by beetles, varied from 42% to 100% with most stands between 60% and 80%. In general, all surviving secondary structure released but the extent of growth release exhibited species variability. Release of surviving canopy lodgepole pine trees was often dramatic and greatest in stands with high total stand MPB mortality rates. Ingress of natural regeneration was slow in the first few years after MPB attack but there was a strong pulse of recruitment 10–20years post disturbance which then slowed considerably. Nearly 30years after the MPB attack, the stocking and composition of the understories have changed dramatically. Overall, the occurrence of the MPB epidemic resulted in more structurally and compositionally diverse stands leading to multiple successional pathways different from those of even-age pine dominated stands. The recovery and self-organization of unsalvaged natural stands in the Flathead Valley was a complicated process. It has provided insights for future forest management in areas impacted by the current massive MPB epidemic ongoing for the past decade in western North America.

Optimal Growing Substrate pH for Five Sedum Species

To determine the optimal growing substrate pH values for Sedum plants, Sedum album, Sedum reflexum ‘Blue Spruce’, Sedum spurium ‘Dragon’s Blood’, Sedum hybridum ‘Immergrunchen’, and Sedum sexangulare were grown in containers using peatmoss and perlite-based substrates at five target pH levels (i.e., 4.5, 5.5, 6.5, 7.5, and 8.5). Optimal pH levels, calculated from dry weight regression models, were 6.32, 6.43, 5.71, 6.25, and 5.91 for S. album, S. reflexum, S. spurium, S. hybridum, and S. sexangulare, respectively, and 5.95 overall. Sedum spurium dry weight varied the most among pH treatments (i.e., 9.5 times greater at pH 6.3 vs. 8.3), whereas S. reflexum varied the least (i.e., 1.3 times greater at pH 6.3 vs. 4.4), indicating species-specific growth responses to growing substrate pH. These findings identified a narrow range of optimal growing substrate pH levels within a wider pH range tolerated by five Sedum spp. Therefore, by adjusting substrate pH to optimal levels, Sedum growth can be maximized.

Changes in forest soil organic matter pools after a decade of elevated CO2 and O3

The impact of rising atmospheric carbon dioxide (CO2) may be mitigated, in part, by enhanced rates of net primary production and greater C storage in plant biomass and soil organic matter (SOM). However, C sequestration in forest soils may be offset by other environmental changes such as increasing tropospheric ozone (O3) or vary based on species-specific growth responses to elevated CO2. To understand how projected increases in atmospheric CO2 and O3 alter SOM formation, we used physical fractionation to characterize soil C and N at the Rhinelander Free Air CO2–O3 Enrichment (FACE) experiment. Tracer amounts of 15NH4+ were applied to the forest floor of Populus tremuloides, P. tremuloides–Betula papyrifera and P. tremuloides–Acer saccharum communities exposed to factorial CO2 and O3 treatments. The 15N tracer and strongly depleted 13C–CO2 were traced into SOM fractions over four years. Over time, C and N increased in coarse particulate organic matter (cPOM) and decreased in mineral-associated organic matter (MAOM) under elevated CO2 relative to ambient CO2. As main effects, neither CO2 nor O3 significantly altered 15N recovery in SOM. Elevated CO2 significantly increased new C in all SOM fractions, and significantly decreased old C in fine POM (fPOM) and MAOM over the duration of our study. Overall, our observations indicate that elevated CO2 has altered SOM cycling at this site to favor C and N accumulation in less stable pools, with more rapid turnover. Elevated O3 had the opposite effect, significantly reducing cPOM N by 15% and significantly increasing the C:N ratio by 7%. Our results demonstrate that CO2 can enhance SOM turnover, potentially limiting long-term C sequestration in terrestrial ecosystems; plant community composition is an important determinant of the magnitude of this response.

Radial Growth Responses of Three Co-Occurring Species to Small Canopy Disturbances in a Secondary Hardwood Forest on the Cumberland Plateau, Tennessee

We analyzed the radial growth patterns of Liriodendron tulipifera, Acer rubrum, and Acer saccharum growing in 39 canopy gaps in a mature secondary hardwood forest on the Cumberland Plateau in Tennessee to compare species-specific growth responses to small canopy disturbances. We tested for differences between mean radial growth increases during the year of release initiation (i.e., first year of discernible growth increase) over the year prior, mean percent growth increases during the year of release initiation over the year prior, mean release durations, and mean lag times between canopy gap formation and radial growth response. At each level of analysis (i.e., by species, canopy position, and gap position) only the radial growth increase during the year of release initiation over the year prior revealed significant differences. In each case where a systematic difference was noted, the growth increase of L. tulipifera was greater than one or both of the Acer species. However, field observation indicated accelerated growth of L. tulipifera was largely negated in the relatively small and short-lived gaps. Our findings provide information on the successional pathway of the forest, the physiological responses of these species to small canopy openings, and the applicability of these species to reconstruct canopy gap formation in secondary stands from tree-ring records.

Responses of Common Pot Grown Flower Species To Commercial Plant Growth Media Substituted With Vermicomposts

Waste management is an increasingly important problem in many developed countries and much effort is currently being expended into identifying novel uses for waste products. We consider the effects of substituting proportions of earthworm-digested composted green waste (vermicompost) into commercial peat based growing media on the germination, growth, and productivity of Helianthus annuus, Cosmos bipinnatus and Eschscholzia californica. The percentage germination, time to flowering, seed production, overall heights and biomass were measured for all three species in treatments of commercial peat based growing media where the growth medium was substituted with vermicompost at rates of 0%, 20%, 40%, 60% and 100%. In addition, the total numbers of inflorescences was recorded in multiple flowering species. Results for Helianthus suggest that while vermicompost additions induced small species specific growth responses in germination rate, growth rate, overall height and total biomass, none were statistically significant. For Cosmos there was a significant increase in early plant growth rate and in the final flower numbers at substitution rates of 20% and 40% vermicompost. The total biomass and numbers of flowers produced by Eschscholzia was decreased significantly by substitution of 20% and 40% vermicompost. We conclude that the plant growth enhancement properties of this vermicompost seem more species specific than previously reported. Further, in order to preserve consumer confidence in waste-derived horticulture products, vermicompost marketing strategies should acknowledge these findings.

Species-specific responses of freshwater diatoms to solar ultraviolet radiation

We studied species-specific growth responses of freshwater algae to solar ultraviolet radiation (UVR) by measuring growth-irradiance curves (G-E curves) of 17 algal diatoms (isolated from a periphyton community in a lotic system) in a solar simulator under photosynthetically available radiation plus UVR and minus UVR radiation condition. Algal growth responses to UVR were highly species-specific, and the photoinhibition parameter (β) of the +UVR condition differed greatly among species. We compared the degree of UVR effect on algal growth (UVR inhibition index: difference in between +UVR and -UVR conditions) with parameters derived from the G-E curve and with algal cell morphology. UVR inhibition indexes significantly correlated with the initial slope of light-limited portion of G-E curve (a) and with the irradiance at which the growth rate starts to saturate (E k ), but not with the cell surface to volume ratios. Low-light-adapted algae tended to be more susceptible to growth inhibition by UVR than high-light-adapted ones. Algae that formed dense colonies in the growth medium were relatively tolerant of UVR irrespective of E k values. Although past studies have emphasized that UVR effects on algae are algal-size dependent, the growth strategies dealing with solar radiation and algal growth forms appear to be more valid in correctly interpreting species-specific responses of algae to solar UVR.

Inhibition and Stimulation Effects in Communities of Wood Decay Fungi: Exudates from Colonized Wood Influence Growth by Other Species

The effects of exudates from uncolonized and from partly decayed beech wood on the extension rates of 16 later stage decay fungi were investigated. The partly decayed wood had been colonized by the pyrenomycete Eutypa spinosa, or the basidiomycetes Fomes fomentarius, Stereum hirsutum, and Trametes versicolor, all known as common early decay agents in European beech forests. Sterilized wood pieces were placed onto 0.5% malt agar, opposite to small agar plugs containing the test fungi. The latter showed very variable and species-specific growth responses to the various wood types. The presence of uncolonized wood stimulated extension rates in many species, whereas the four previously decayed wood types had variable stimulatory or inhibitory effects. Wood decayed by S. hirsutum resulted in reduced extension rate, delayed growth, or total inhibition in the majority of species, thus it is suggested that this species uses secondary metabolites in a defensive strategy. A single species was, however, stimulated in the presence of S. hirsutum-decayed wood. In contrast, the presence of wood decayed by F. fomentarius was stimulatory to 45% of the species. The other previously decayed wood types generally resulted in more variable responses, depending upon species. The results are discussed in an ecological context and it is suggested that the exudates from the partly decayed wood that are responsible for the reported effects may function as infochemicals, structuring microbial communities in wood.