Dark microbial CO2 fixation in temperate forest soils increases with CO2 concentration

Dark, that is, nonphototrophic, microbial CO₂ fixation occurs in a large range of soils. However, it is still not known whether dark microbial CO₂ fixation substantially contributes to the C balance of soils and what factors control this process. Therefore, the objective of this study was to quantitate dark microbial CO₂ fixation in temperate forest soils, to determine the relationship between the soil CO₂ concentration and dark microbial CO₂ fixation, and to estimate the relative contribution of different microbial groups to dark CO₂ fixation. For this purpose, we conducted a ¹³C‐CO₂ labeling experiment. We found that the rates of dark microbial CO₂ fixation were positively correlated with the CO₂ concentration in all soils. Dark microbial CO₂ fixation amounted to up to 320 µg C kg^?1 soil day^?1 in the Ah horizon. The fixation rates were 2.8–8.9 times higher in the Ah horizon than in the Bw1 horizon. Although the rates of dark microbial fixation were small compared to the respiration rate (1.2%–3.9% of the respiration rate), our findings suggest that organic matter formed by microorganisms from CO₂ contributes to the soil organic matter pool, especially given that microbial detritus is more stable in soil than plant detritus. Phospholipid fatty acid analyses indicated that CO₂ was mostly fixed by gram‐positive bacteria, and not by fungi. In conclusion, our study shows that the dark microbial CO₂ fixation rate in temperate forest soils increases in periods of high CO₂ concentrations, that dark microbial CO₂ fixation is mostly accomplished by gram‐positive bacteria, and that dark microbial CO₂ fixation contributes to the formation of soil organic matter.     

The canopy beetle faunas of Gondwanan element trees in Chilean temperate rain forests

Aim To describe the coleopteran fauna occurring in canopies of temperate Gondwanan tree species in terms of their diversity and guild and taxonomic structures, and to test the proposition that this structuring reflects the Gondwanan origins of this fauna. Location The Andes and the coastal cordillera of temperate Chile. Methods Canopy fogging was used to sample beetles from 29 trees. The samples were statistically described using S_chao and the Simpson diversity index D. Cluster analyses and multi‐dimensional scaling (MDS) were performed. The taxonomic and guild structures of the Chilean coleopteran fauna were compared quantitatively with those found in other parts of the world using homogeneity chi‐square and t‐tests. Results A collection of 25,497 beetle specimens was obtained primarily from Nothofagus dombeyi, Nothofagus obliqua and Araucaria araucana. The specimens collected were distributed between 485 morphospecies and included 107 putative, new generic‐level taxa and 223 apparently undescribed species. Estimates of the size of the canopy beetle fauna showed that 600+ species were likely to be present. The communities found on a tree species differed markedly between years. MDS plots showed less community divergence between tree species for predators than for phytophages and xylophages. The guild structure was similar to that found on Australian ‘Gondwanan’ trees but differed significantly from the community structures found on ‘Laurasian’ tropical and temperate trees in supporting fewer phytophages and saprophages, but more xylophages. The predator guild showed a different pattern, with tropical faunas differing from those of more temperate regions, irrespective of hemisphere, as did the distribution of superfamilies. Main conclusions The beetle fauna found in the canopies of N. dombeyi, N. obliqua and A. araucana was large (600+ species), with about half of the species undescribed. S_chao was found to vary with sample size and to give lower estimates of S than species attenuation curves, raising the possibility that the two methods are estimating the sizes of different statistical communities. It is possible that the attenuation curve is estimating the number of species to be found on a particular tree species, while S_chao is estimating the ‘carrying capacity’ for beetle species of individual trees, and this varies from tree to tree. Care also needs to be taken in experimental design when monitoring temporal changes in forest insect communities given the difference in communities found between years in this study. The proportions of phytophages, saprophages and xylophages resemble those of a ‘Gondwanan’ rain forest from Australia and differ significantly from those of tropical and temperate ‘Laurasian’ forests.     

Stem CO2 efflux of ten species in temperate forests in Northeastern China

Stem CO₂ efflux (E _S) is an important component of forest ecosystem carbon budgets and net ecosystem CO₂ exchange, but little is known about E _S in temperate forests in Northeastern China, an area with a large extent of forest. We measured E _S along with stem temperature at 1?cm depth (Ts) over a 9?month period in 2007 on ten dominant tree species of secondary forests of the region. Other measurements included the autotrophic component of soil CO₂ efflux (E _A) and stem diameter at breast height (DBH). Our objectives were to (1) examine the seasonal patterns and species differences in E _S, and (2) determine the correlations between E _S and Ts, DBH and E _A. Mean E _S for the measurement period ranged from 1.09 to 1.74?μmol?CO₂?m^?2?s^?1 among the ten species. The sensitivity of E _S to Ts (Q ₁₀ ) ranged from 1.87 to 2.61. Across the ten species 57–89% of variation in E _S was explained by T _S and DBH. There was also a linear relationship between mean E _S and E _A. E _S was better predicted by Ts in the dormant season than the growing season, indicating that additional factors such as growth respiration and internal transport of CO₂ in the xylem became more important contributors to E _S during the growing season. Stem CO₂ efflux increased, and Q ₁₀ decreased, with increasing DBH in all species. Although temperature exerts strong control on the rate of cellular respiration, we conclude that in tree stems in situ, T _S, DBH and many other factors affect the relationship between CO₂ evolution by respiring cells and the diffusion of CO₂ to the stem surface.     

Wood ants prefer conifers to broadleaved trees in mixed temperate forests

1. Wood ants, species of the subgenus Formica s. str., are one of the most important groups of insects in forest ecosystems due to their high abundance and activity.
2. We assessed the foraging pressure of Formica polyctena and Formica rufa, two dominant wood ant species in the Białowieża Forest. In addition, we compared coniferous and mixed stands in these respects.
3. In mixed stands F. polyctena visited more trees per plot than F. rufa. F. polyctena might forage a larger area due to higher population sizes, which further confirms higher foraging pressure of F. polyctena in comparison with F. rufa.
4. In our study area, host trees of the ant–aphid mutualism were larger in diameter than nonhost trees. The ants also preferred trees situated closer to their nests. In both mixed and coniferous stands, the most visited tree species was Norway spruce. Thus, we can conclude that Norway spruce seems to be preferred by the ant. The decline of living spruce in the Białowieża Forest may endanger their food source and impact the vitality of ant colonies.

     

Taxonomic identity determines N2 fixation by canopy trees across lowland tropical forests

Legumes capable of fixing atmospheric N₂ are abundant and diverse in many tropical forests, but the factors determining ecological patterns in fixation are unresolved. A long‐standing idea is that fixation depends on soil nutrients (N, P or Mo), but recent evidence shows that fixation may also differ among N₂‐fixing species. We sampled canopy‐height trees across five species and one species group of N₂‐fixers along a landscape P gradient, and manipulated P and Mo to seedlings in a shadehouse. Our results identify taxonomy as the major determinant of fixation, with P (and possibly Mo) only influencing fixation following tree‐fall disturbances. While 44% of trees did not fix N₂, other trees fixed at high rates, with two species functioning as superfixers across the landscape. Our results raise the possibility that fixation is determined by biodiversity, evolutionary history and species–specific traits (tree growth rate, canopy stature and response to disturbance) in the tropical biome.     

Rodent seed predation promotes differential recruitment among bird-dispersed trees in temperate secondary forests

We investigated the role of seed predation by rodents in the recruitment of the fleshy-fruited trees Taxus baccata, Ilex aquifolium and Crataegus monogyna in temperate secondary forests in NW Spain. We measured the densities of dispersed seeds, early emerged seedlings, established recruits and adults, at four sites over a period of 2 years. Seed predation among species was compared by seed removal experiments and analysis of rodent larder-hoards. The three species differed markedly in local regeneration patterns. The rank order in the seed rain following decreasing seed density was Ilex, Taxus and Crataegus. However, Crataegus established 3.3 times more seedlings than Taxus. For all species, there was a positive linear relationship between the density of emerged seedlings and seed density, suggesting that recruitment was seed- rather than microsite-limited. A consistent pattern of seed selection among species was exerted by rodents, which preferred Taxus and, secondarily, Ilex seeds to Crataegus seeds. Predation ranking was the inverse of that of seed protection against predators, measured as the mass of woody coat per mass unit of the edible fraction. Recruitment potential, evaluated as the ratio of seedlings to seeds, was negatively related to seed predation, with the rank order Crataegus > Ilex > Taxus. The selective early recruitment limitation exerted by predation may have a demographic effect in the long term, as judged by the positive relationship between early seedling emergence and the density of established recruits. By modulating the pre-emptive competition for seed safe sites, rodents may preclude the progressive exclusion of species that produce low numbers of seeds (i.e. Crataegus) by those dominant in seed number (i.e. Ilex, Taxus), or at least foster the evenness for site occupation among seedlings of different species.     

Rapid turnover of DOC in temperate forests accounts for increased CO2 production at elevated temperatures

The evidence for the contribution of soil warming to changes in atmospheric CO₂ concentrations and carbon stocks of temperate forest ecosystems is equivocal. Here, we use data from a beech/oak forest on concentrations and stable isotope ratios of dissolved organic carbon (DOC), phosphate buffer-extractable organic carbon, soil organic carbon (SOC), respiration and microbial gross assimilation of N to show that respired soil carbon originated from DOC. However, the respiration was not dependent on the DOC concentration but exceeded the daily DOC pool three to four times, suggesting that DOC was turned over several times per day. A mass flow model helped to calculate that a maximum of 40% of the daily DOC production was derived from SOC and to demonstrate that degradation of SOC is limiting respiration of DOC. The carbon flow model on SOC, DOC, microbial C mobilization/immobilization and respiration is linked by temperature-dependent microbial and enzyme activity to global warming effects of CO₂ emitted to the atmosphere.     

Forgotten underwater forests: The key role of fucoids on Australian temperate reefs

Kelp forests dominated by species of Laminariales are globally recognized as key habitats on subtidal temperate rocky reefs. Forests characterized by fucalean seaweed, in contrast, receive relatively less attention despite being abundant, ubiquitous, and ecologically important. Here, we review information on subtidal fucalean taxa of Australia's Great Southern Reef, with a focus on the three most abundant and widely distributed genera (Phyllospora, Scytothalia, and Sargassum) to reveal the functionally unique role of fucoids in temperate reef ecology. Fucalean species span the entire temperate coastline of Australia (~71,000 km²) and play an important role in supporting subtidal temperate biodiversity and economic values on rocky reefs as well as in adjacent habitats. Climatic and anthropogenic stressors have precipitated significant range retractions and declines in many fucoids, with critical implications for associated assemblages. Such losses are persistent and unlikely to be reversed naturally due to the life history of these species and colonization of competitors and grazers following loss. Active restoration is proving successful in bringing back some fucoid species (Phyllospora comosa) lost from urban shores and will complement other passive and active forms of conservation. Fucalean forests play a unique role on subtidal temperate reefs globally, especially in Australia, but are comparatively understudied. Addressing this knowledge gap will be critical for understanding, predicting, and mitigating extant and future loss of these underwater forests and the valuable ecosystem services they support.     

Tree and stand level variables influencing diversity of lichens on temperate broad-leaved trees in boreo-nemoral floodplain forests

Tree and stand level variables affecting the species richness, cover and composition of epiphytic lichens on temperate broad-leaved trees (Fraxinus excelsior, Quercus robur, Tilia cordata, Ulmus glabra, and U. laevis) were analysed in floodplain forest stands in Estonia. The effect of tree species, substrate characteristics, and stand and regional variables were tested by partial canonical correspondence analysis (pCCA) and by general linear mixed models (GLMM). The most pronounced factors affecting the species richness, cover and composition of epiphytic lichens are acidity of tree bark, bryophyte cover and circumference of tree stems. Stand level characteristics have less effects on the species richness of epiphytic lichens, however, lichen cover and composition was influenced by stand age and light availability. The boreo-nemoral floodplain forests represent valuable habitats for epiphytic lichens. As substrate-related factors influence the species diversity of lichens on temperate broad-leaved trees differently, it is important to consider the effect of each tree species in biodiversity and conservation studies of lichens. Nomenclature Randlane et al. (2007) for lichens; Leht (2007) for vascular plants.     

CO2 fixation in halobacteria

Seven strains of extremely halophilic bacteria (Halobacterium spp., Halococcus spp., and Haloarcula sp.) fixed CO₂ under light and dark conditions. Light enhanced CO₂ fixation in Halobacterium halobium but inhibited it in Halobacterium volcanii and Haloarcula strain GN-1. Propionate stimulated ¹⁴CO₂ incorporation in some strains, but inhibited it in others. Semi-starvation in basal salts plus glycerol induced enhanced CO₂ fixation rates. ¹⁴CO₂ fixation in semi-starved cells was stimulated by NH ₄ ⁺ or pyruvate and inhibited by succinate and acetate in most strains. No possible reductant was found. In cell-free extracts of H. halobium, NH ₄ ⁺ but not propionate stimulated ¹⁴CO₂ fixation. No RuBP carboxylase activity was detected. The main ¹⁴C-labeled -keto acid detected after a 2-min incubation with ¹⁴CO₂ and pyruvate was pyruvate. Little or no -ketobutyrate was detected among the early products of propionate-stimulated CO₂ fixation. Glycine was the major amino acid synthesized during a 2-min incubation with NH ₄ ⁺ , propionate, and ¹⁴CO₂. Propionate-stimulated CO₂ fixation was sensitive to trimethoprim and insensitive to avidin. A novel pathway for non-reductive CO₂ fixation involving a glycine synthase reaction with CO₂, NH ₄ ⁺ , and a methyl carbon derived from the -carbon cleavage of propionate is tentatively proposed.Abbreviations used BBS buffered basal salts - HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid - MOPS 3-(N-morpholino)propanesulfonic acid - DNPH 2,4-dinitrophenylhydrazine - DNP dinitrophenyl - TLC thin-layer chromatography - FH₄ tetrahydrofolate This work was supported by National Science Foundation grant PCM-8116330 and Petroleum Research Fund grant PRF 13704-AC2     

Subcanopy gaps in temperate and tropical forests

Abstract We present a model of gaps in the vertical structure of forest vegetation. The traditional model of a forest gap assumes the existence of a ‘hole’ in the uppermost canopy layer, often extending down to near the ground. The present model extends the concept to gaps at any level, including those in lower layers below an intact canopy or subcanopy. It assumes that gaps at any level represent spaces with unused resources, especially favourable for plant growth and survival. Evidence from temperate and tropical forests indicates that gaps in the subcanopy and understorey layers below intact canopies are common, and that plants have higher growth rates in them than in non-gap sites. We also extend this model to below-ground gaps in the root zone.     

Structure and pattern in temperate seasonal forests

Demography, spatial pattern, and diversity of canopy and subcanopy trees, shrubs, and lianas were compared in two cool and two warm temperate North American forests, paired at 30° and 40° north latitudes. All woody stems 1 cm dbh in 16 randomly located, non-contiguous plots totalling 1 ha at each of the four sites were measured, mapped, and identified. Basal area and overall density did not differ between latitudes. Demographic and spatial analyses revealed remarkable similarity in spatial dispersion, irrespective of density or species composition. At all sites, dispersion of canopy trees was random but all understory stems were uniformly distributed relative to all canopy trees. Species diversity and vertical structure differed between the warm and cool temperate sites, especially in species composition of individual strata. Associations of understory species relative to canopy species were more random at 30° than at 40° north, where a higher degree of association between canopy and understory species' patterns, coupled with their size class distributions, suggested more lengthy regeneration cycles and an alternation of species assemblages. The forests at 30°, those subject to periodic canopy disturbance by hurricanes, had more vertical mixing of species (i.e., canopy species represented in all size classes), more tree saplings, and significantly more shrub and liana species.     

Evaluating the role of fire disturbance in structuring small reptile communities in temperate forests

Fire is an integral disturbance shaping forest community dynamics over large scales. However, understanding the relationship between fire induced habitat disturbance and biodiversity remain equivocal. Ecological theories including the intermediate disturbance hypothesis (IDH) and the habitat accommodation model (HAM) offer predictive frameworks that could explain faunal responses to fire disturbances. We used an 80 year post-fire chronosequence to investigate small reptile community responses to fires in temperate forests across 74 sites. First, we evaluated if changes in species richness, abundance and evenness post-fire followed trends of prior predictions, including the IDH. Second, using competing models of fine scale habitat elements we evaluated the specific ways which fire influenced small reptiles. Third, we evaluated support for the HAM by examining compositional changes of reptile community post-fire. Relative abundance was positively correlated to age post-fire while richness and evenness showed no associations. The abundance trend was as expected based on the prior prediction of sustained population increase post-disturbance, but the trend for richness contradicted the prediction of highest diversity at intermediate levels of disturbance (according to IDH). Abundance changes were driven mainly by changes in overstorey, ground layer, and shelter, while richness and evenness did not associate with any vegetation parameter. Community composition was not strongly correlated to age since fire, thus support for the HAM was weak. Overall, in this ecosystem, frequent fire disturbances can be detrimental to small reptiles. Future studies utilizing approaches based on species traits could enhance our understanding of biodiversity patterns post-disturbance.     

温带森林展叶物候学

物候学是研究自然事件的周期性变化的科学,是一门古老的传统学科.在全球温带地区,春季开始时问已经显著提前.随着气候变化日益得到关注,物候学也重新引起了人们的重视.植物在春季的展叶对温度特别敏感,展叶时间决定着许多基本的生态系统过程,因此,近年来生态学家们对展叶物候学表现出极大兴趣.本文综述了最新文献,介绍了展叶物候的不同研究方法、温带木本植物展叶的控制因子,以及气候变化对展叶物候的影响.除了传统的地面监测方法之外,一些使用遥感和专用相机的新方法已经被用来在更大尺度上监测春季开始时间.未来的研究工作应聚焦于植物的展叶物候如何应对气候变化,及其对不同营养级物种问相互作用的影响.     

The carbon balance of tropical, temperate and boreal forests

Forest biomes are major reserves for terrestrial carbon, and major components of global primary productivity. The carbon balance of forests is determined by a number of component processes of carbon acquisition and carbon loss, and a small shift in the magnitude of these processes would have a large impact on the global carbon cycle. In this paper, we discuss the climatic influences on the carbon dynamics of boreal, temperate and tropical forests by presenting a new synthesis of micrometeorological, ecophysiological and forestry data, concentrating on three case-study sites. Historical changes in the carbon balance of each biome are also reviewed, and the evidence for a carbon sink in each forest biome and its likely behaviour under future global change are discussed. We conclude that there have been significant advances in determining the carbon balance of forests, but there are still critical uncertainties remaining, particularly in the behaviour of soil carbon stocks.