Wood growth patterns of <Emphasis Type="Italic">Macrolobium acaciifolium</Emphasis> (Benth.) Benth. (Fabaceae) in Amazonian black-water and white-water floodplain forests

Macrolobium acaciifolium (Benth.) Benth. (Fabaceae) is a dominant legume tree species occurring at low elevations of nutrient-poor black-water (igapó) and nutrient-rich white-water floodplain forests (várzea) of Amazonia. As a consequence of the annual long-term flooding this species forms distinct annual tree rings allowing dendrochronological analyses. From both floodplain types in Central Amazonia we sampled cores from 20 large canopy trees growing at identical elevations with a flood-height up to 7 m. We determined tree age, wood density (WD) and mean radial increment (MRI) and synchronized ring-width patterns of single trees to construct tree-ring chronologies for every study site. Maximum tree age found in the igapó was more than 500 years, contrary to the várzea with ages not older than 200 years. MRI and WD were significantly lower in the igapó (MRI=1.52±0.38 mm year^?1, WD=0.39±0.05 g cm^?3) than in the várzea (MRI=2.66±0.67 mm year^?1, WD=0.45±0.03 g cm^?3). In both floodplain forests we developed tree-ring chronologies comprising the period 1857–2003 (n=7 trees) in the várzea and 1606–2003 (n=13 trees) in the igapó. The ring-width in both floodplain forests was significantly correlated with the length of the terrestrial phase (vegetation period) derived from the daily recorded water level in the port of Manaus since 1903. In both chronologies we found increased wood growth during El Niño events causing negative precipitation anomalies and a lower water discharge in Amazonian rivers, which leads to an extension of the terrestrial phase. The climate signal of La Niña was not evident in the dendroclimatic proxies.     

Above-ground biomass changes over an 11-year period in an Amazon monodominant forest and two other lowland forests

Tropical rain forest dominated by Peltogyne gracilipes (Fabaceae) occurs on Maracá Island, Roraima, Brazil, on a range of soil types. Three forest types were stratified for sampling, according to the occurrence of Peltogyne trees: (1) Peltogyne-rich forest (PRF), (2) Peltogyne-poor forest (PPF), and (3) forest without Peltogyne (FWP). Biomass increment and change in total stand biomass were calculated from mortality, recruitment, and growth data for trees in the three forest types. Data were derived from permanent plots established in 1991, where all trees (≥10 cm diameter at breast height), including palms and vines (lianas), were tagged and measured in three plots, each of 0.25 ha, in each of the three forest types. Field surveys were carried out in October 1991 and March 2003. Over a period of 11 years, the above-ground biomass in all forest types declined slightly (<5%), associated with the death of large trees, especially in the monodominant forests (PRF and PPF). Within the study period, the forest on Maracá experienced two heavy droughts, related to El Niño events (1997–1998 and 2002–2003) and most mortality and loss of biomass probably occurred during these events. Therefore, as the Maracá forests appear not be increasing in above-ground biomass overall, they may not be acting as a sink for atmospheric CO₂. The trees of the five most abundant species (Ecclinusa, Lecythis, Licania, Peltogyne, and Pradosia) accounted for about 55% of the total biomass in both FWP and PPF and for 74% in PRF. Peltogyne gracilipes had a stable, regenerating population in PRF, and is clearly a persistent dominant in a monodominant forest.     

Tree-growth responses across environmental gradients in subtropical Argentinean forests

Subtropical forests in montane ecosystems grow under a wide range of environmental conditions. However, little is known about the growth responses of subtropical trees to climate along ecological gradients. To assess how, and to what extent climate controls tree growth, we analyzed tree responses to climate for 15 chronologies from 4 different species (Schinopsis lorentzii, Juglans australis, Cedrela lilloi, Alnus acuminata) across a variety of environments in subtropical forests from northwestern Argentina (22–28°S, 64–66°W). Using correlation and principal component analysis, site and species differences in tree-growth responses to precipitation and temperature were determined along the elevation gradient from the dry-warm Chaco lowlands to the wet-cool montane Yungas. Our results show that species responses differ according to the severity in climate conditions along the elevation gradient. At sites with unfavorable conditions, mainly located at the extremes of the environmental gradient, responses of different species to climate variations are similar; in contrast, at sites with relatively mild conditions, tree growth displays a large variety of responses reflecting differences in both local environmental conditions and species physiology. Our research suggests that individualistic responses to environmental variability would determine differences in the type and timing of the responses of dominant trees to climate, which ultimately may shift species’ assemblages in montane subtropical regions of South America under future climate changes.     

Tree selection by the endangered beetle <Emphasis Type="Italic">Rosalia alpina</Emphasis> in a lapsed pollard beech forest

Abandoned pollard beech forests are particular habitats that may require special conservation efforts to preserve the endangered beetle Rosalia alpina, a model species whose protection may perpetuate the habitat of many other saproxylic species. Forest use can determine the tree selection and population size of R. alpina, variables previously not researched in pollard forests. Selected tree traits and population size, indicated by presence of adult specimens and recent exit holes, were determined in a pollard beech forest before the implementation of habitat manipulations targeted to preserve the species. Multivariate analysis showed tree condition (living, snag, fallen) and clearing size and aspect as influential variables, with the former explaining more variance than the latter. R. alpina positively selected pollard snags and trees located in big and dry clearings, avoiding those in small clearings or shaded areas. Snags showed most adults (90 %) and recent emergence holes (84 %). Distance to the nearest occupied tree, trunk diameter, bark thickness and presence of sap leaks had no effect on the occurrence of R. alpina. Population size was estimated in 0.1 individuals day^?1 ha^?1, and 38 % of available habitat trees showed exit holes, values lower than those observed in other European countries. These results show the need to start re-pollardings in the forest to extend pollard standing life and enhance exposure to sunlight. Pinpointing pollard snags and clearing the surrounding vegetation are recommended as the first measures to be taken in order to favor R. alpina populations on pollard stands with closed canopies.     

Endophytic aquatic hyphomycetes in roots of riparian tree species of two Western Ghat streams

Bubble chamber incubation of surface sterilized segments of root bark and xylem of 10 riparian tree species of the Sampaje (475–500 m asl) and V?Badaga (765–800 m asl) stream reaches of the Western Ghats yielded 20 species of endophytic aquatic hyphomycetes. Anguillospora crassa, A. longissima and Cylindrocarpon sp. were among the top five species in streams. A two-way ANOVA showed significantly higher species richness and counts of conidium in the tree species of Sampaje compared to V?Badaga (p < 0.001), while two variables were not significantly different between bark and xylem. The total number of species recovered was slightly higher in bark than in xylem (14–19 vs. 13–17 spp.) and the average species richness between tissues did not differ significantly except for one tree species (Madhuca neriifolia: p < 0.05). The release of conidia from bark of only three tree species was significantly higher than from xylem (M. neriifolia and Canarium strictum: p < 0.05; Vateria indica: p < 0.01). Sørensen’s similarity index for bark as well as xylem between tree species was higher in Sampaje stream than in V?Badaga stream (0.45–0.78 vs. 0.25–0.61). The diversity of aquatic hyphomycetes in bark and xylem was higher in the trees of Sampaje than V?Badaga (3.1–3.3 vs. 2.7). A cluster analysis of aquatic hyphomycetes in bark and xylem resulted in two groups coinciding with the two streams. The results of this study revealed that assemblage and diversity of endophytic aquatic hyphomycetes in riparian tree roots are high in the mid-altitude Sampaje stream as previously documented for saprotrophic aquatic hyphomycetes.     

Soil spore banks of ectomycorrhizal fungi in endangered Japanese Douglas-fir forests

Interactions between trees and ectomycorrhizal fungi are critical to the growth and survival of both partners. However, ectomycorrhizal symbiosis has barely been explored in endangered trees, and no information is available regarding soil spore banks of ectomycorrhizal fungi from forests of threatened trees. Here, we evaluated soil spore banks of ectomycorrhizal fungi from endangered Japanese Douglas-fir (Pseudotsuga japonica) forests using bioassay approaches with congeneric P. menziesii and Pinus densiflora seedlings in combination with molecular identification techniques. Rhizopogon togasawariana was predominant in soil propagule banks and was found in all remaining P. japonica forests when assayed with P. menziesii, while no colonization of this fungus was observed on Pinus seedlings. Given the observed specificity of R. togasawariana for P. menziesii and its phylogenetic position within the Pseudotsuga-specific Rhizopogon lineage, its geographical distribution is likely restricted to the remaining Japanese Douglas-fir forests, indicating a high extinction risk for this fungus as well as its endangered host. Spore banks of R. togasawariana remained highly infective after preservation for 1 year or heat treatment at 70 °C, suggesting an ecological strategy of establishing ectomycorrhizal associations on regenerating Japanese Douglas-fir seedlings after disturbance, as observed in other Rhizopogon–Pinaceae combinations. Therefore, the regeneration of Japanese Douglas-fir seedlings may depend largely on the soil spore banks dominated by R. togasawariana, which has co-evolved with the Japanese Douglas-fir for over 30 million years. More attention must be paid to underground ectomycorrhizal fungi for the conservation of endangered tree species, especially in the era of human-induced mass extinction.     

Effects of converting natural forests to coniferous plantations on fruit and seed production and mating patterns in wild cherry trees

Landscape disturbances can affect reproductive performance of animal-pollinated trees. We verified the effects of the loss and fragmentation of natural forests caused by the creation of coniferous plantations on fruit and seed production as well as mating patterns of animal-pollinated trees. We investigated 146 and 134 individual flowering trees of Prunus verecunda (Koidz.) Koehne in 2012 and 2013, respectively, at 12 sites. These sites were at least 1.2 km apart from each other in an 8 × 15-km forestry region, and the composition and configuration of natural forests varied in the study area. The mean outcrossing rate was >0.99 across the sites. Among trees within the sites, the number of fruits per inflorescence was positively correlated with the basal stem area and leaf chlorophyll density of the trees. Among the sites, the mean number of fruits per inflorescence was positively correlated with the site elevation, and the correlated paternity was positively correlated with the mean distance between trees. The sound-seed rate was positively correlated with the natural-forest area among the sites. These results suggest that environments and resources of trees influence their fruit production, that a loss of natural forests increases in embryo mortality, and that a reduction in tree density decreases pollen donor diversity in P. verecunda. Thus, a landscape disturbance may decrease seed production, whereas outbreeding is maintained, and fruit production is not likely to be dependent on the landscape disturbance in this species.     

Influence of climatic factors on tree growth in riparian forests in the humid and dry savannas of the Volta basin,Ghana

Key message

The paper demonstrates the prospects and applications of dendrochronology for understanding climate change effects on riparian forests in the savanna landscape. 

Abstract

Riparian trees in savannas have a potential for dendro-climatic studies, but have been neglected hitherto. We examined ring-width series of Afzelia africana (evergreen) and Anogeissus leiocarpus (deciduous) to study the influence of climatic factors on the growth of riparian trees in the humid (HS) and dry (DS) savanna zones of the Volta basin in Ghana. A total of 31 stem discs belonging to A. africana and A. leiocarpus were selected from HS and DS to establish species-specific local chronologies of tree growth. Each individual of A. africana and A. leiocarpus from the two savanna sites showed distinct growth rings. Cross-dating of individual tree-ring patterns was successful using standard dendrochronological techniques. The mean annual growth rates of A. africana in the HS (1.38 ± 0.09) and DS (1.34 ± 0.08) were not statistically different. Furthermore, mean annual growth rate of A. leiocarpus in the DS (3.75 ± 0.27) was higher than in the HS (2.83 ± 0.16) suggesting that species in drier environment can have higher growth rates when sufficient soil moisture is available. The growth rates of both species at the same sites were different, which might indicate different water use strategies. High correlations of individual tree-ring series of A. africana and A. leiocarpus trees at HS and DS suggest a strong climatic forcing controlled by the seasonal movement of the inter-tropical convergence zone. The annual growth of A. africana and A. leiocarpus at both the HS and DS was significantly correlated with local temperature and precipitation. The negative correlations of the growth of the two tree species to global sea surface temperatures were however, indications that the growth of riparian forests can be impacted during El Niño-Southern Oscillation years. The result of our study shows that riparian trees in the humid and dry savanna zones of West Africa can be successfully used for dendrochronological studies.

     

Shade tolerance of <Emphasis Type="Italic">Ailanthus altissima</Emphasis> revisited: novel insights from southern Switzerland

The tree of heaven (Ailanthus altissima (Mill.) Swingle) is considered to be an early-successional, gap-obligate pioneer species with vigorous height growth, low shade tolerance, early fecundity and large seed production. It is a highly invasive species in many temperate and Mediterranean ecosystems outside its natural range, especially after disturbance. Due to its low shade tolerance, the potential of A. altissima to colonise undisturbed forests is thought to be low. In this study we analysed the potential of juvenile A. altissima to grow and survive in sweet chestnut (Castanea sativa Mill.) forests in southern Switzerland. We used hemispherical photography to assess the light conditions of 204 individuals of A. altissima (31 % generative, 69 % vegetative) aged between 1 and 7 years (median: 3 years) in six sites. Generative (seed-borne) and vegetative (clonal ramet) offspring of A. altissima are able to grow in light conditions well below the requirements of shade-intolerant tree species such as European larch (Larix decidua Mill.) and Scots pine (Pinus sylvestris L.). The relatively low light conditions found to be sufficient for the growth and survival of generative regeneration of A. altissima suggest a higher shade tolerance for this species than previously stated, at least for early regeneration. Consequently, the colonisation frontier of A. altissima should be intensively monitored in both forest openings but also in closed canopy forests in the vicinity of seed-bearing A. altissima.     

Comprehensive dataset of mangrove tree weights in Southeast Asia

We assembled a dataset tabulating the weights of Thai and Indonesian mangrove trees that we measured between 1982 and 2001. We selected four Thai study sites in Phang Nga, Ranong, Satun, and Trat Provinces and one site in eastern Indonesia on Halmahera Island in Maluku Province. The stands in Ranong Province and on Halmahera Island were in primary forests with data collected in the 1980s and the remaining stands were in secondary forests with data collected later. We collected 124 tree samples from ten species (Avicennia alba, Bruguiera cylindrica, B. gymnorrhiza, Ceriops tagal, Rhizophora apiculata, R. mucronata, Sonneratia alba, S. caseolaris, Xylocarpus granatum, and X. moluccensis) and measured the root weights of 32 individuals of nine species (A. alba, B. cylindrica, B. gymnorrhiza, C. tagal, R. apiculata, R. mucronata, S. alba, S. caseolaris, and X. granatum). All sampled trees were subjected to a standardized protocol to obtain aboveground weights. The trunks were divided into horizontal segments from which the leaves and branches were collected separately. Roots were collected by winching them out of the ground, by trench digging, or by complete excavation. Thus, we were able to compile the weights of the trunk, branches, leaves, and roots of each tree sampled. Aerial roots were included in root weight measurements, although they were collected above ground. We compiled separate lists of trunk diameters, trunk heights, heights of the lowest living branches, and the heights of aerial roots on the trunks of trees in different size categories. Our dataset includes a wide range of tree sizes (maximum trunk diameter 48.9 cm), geographical locations (1°10′N–12°24′N, 98°32′E–123°49′E) and organ weights (trunks, branches, leaves, and roots), and therefore should prove useful in future biomass studies of mangrove forests.     

Linking above- and belowground phenology of hybrid walnut growing along a climatic gradient in temperate agroforestry systems

Background and aims

Plant phenology is a sensitive indicator of plant response to climate change. Observations of phenological events belowground for most ecosystems are difficult to obtain and very little is known about the relationship between tree shoot and root phenology. We examined the influence of environmental factors on fine root production and mortality in relation with shoot phenology in hybrid walnut trees (Juglans sp.) growing in three different climates (oceanic, continental and Mediterranean) along a latitudinal gradient in France.

Methods

Eight rhizotrons were installed at each site for 21 months to monitor tree root dynamics. Root elongation rate (RER), root initiation quantity (RIQ) and root mortality quantity (RMQ) were recorded frequently using a scanner and time-lapse camera. Leaf phenology and stem radial growth were also measured. Fine roots were classified by topological order and 0–1 mm, 1–2 mm and 2–5 mm diameter classes and fine root longevity and risk of mortality were calculated during different periods over the year.

Results

Root growth was not synchronous with leaf phenology in any climate or either year, but was synchronous with stem growth during the late growing season. A distinct bimodal pattern of root growth was observed during the aerial growing season. Mean RER was driven by soil temperature measured in the month preceding root growth in the oceanic climate site only. However, mean RER was significantly correlated with mean soil water potential measured in the month preceding root growth at both Mediterranean (positive relationship) and oceanic (negative relationship) sites. Mean RIQ was significantly higher at both continental and Mediterranean sites compared to the oceanic site. Soil temperature was a driver of mean RIQ during the late growing season at continental and Mediterranean sites only. Mean RMQ increased significantly with decreasing soil water potential during the late aerial growing season at the continental site only. Mean root longevity at the continental site was significantly greater than for roots at the oceanic and Mediterranean sites. Roots in the 0–1 mm and 1–2 mm diameter classes lived for significantly shorter periods compared to those in the 2–5 mm diameter class. First order roots (i.e. the primary or parents roots) lived longer than lateral branch roots at the Mediterranean site only and first order roots in the 0–1 mm diameter class had 44.5% less risk of mortality than that of lateral roots for the same class of diameter.

Conclusions

We conclude that factors driving root RER were not the same between climates. Soil temperature was the best predictor of root initiation at continental and Mediterranean sites only, but drivers of root mortality remained largely undetermined.

     

Water relations of ponderosa pines in Patagonia Argentina: implications for local water resources and individual growth

Replacement of grasslands by forests may result in increased water consumption, and the magnitude of this will depend on stand density. To test this hypotheses and evaluate the impact of pine plantations on hydric resources in Patagonia Argentina, we measured over two seasons (1999–2000 and 2000–2001) and at two densities of ponderosa pine plantations (350 and 500 trees ha^?1) the following variables: soil water content, leaf water potential (ψ), individual tree growth, individual sap flow, and response of sap flow density (u) to vapor pressure deficit (VPD). Stand transpiration (T) and whole-plant liquid-phase hydraulic conductance (L) were also estimated. Pre-dawn ψ varied from about –0.5 to –1.0 MPa. No differences were found in midday maximum u (1100–1800 hours) on clear days between the 2 measurement years, throughout each season, or between different densities of plantation. Sapflow density was also not correlated with soil water storage up to 1.4 m soil depth. Sapflow increased until VPD of about 2.3 kPa, and decreased at VPD >4 kPa, describing a hysteresis in the afternoon. Values of L in Patagonian trees were similar to those recalculated from published data for pines of the same height in the USA. Average stand transpiration increased with increased density (2.07 and 3.08 mm day^-1 for 350 and 500 pines ha^-1, respectively) and size of the trees. We conclude that ponderosa pines in Patagonia Argentina use more water, in a magnitude depending on the density of the trees, than native grasslands. Accordingly, ponderosa pines use deep water to maintain high water potential and transpiration rates even during the dry season.     

Antipredation Sleeping Behavior of Skywalker Hoolock Gibbons (<Emphasis Type="Italic">Hoolock tianxing</Emphasis>) in Mt. Gaoligong,Yunnan, China

Studying sleeping behavior can provide key information for understanding the ecology of a species. Antipredation is an important factor that affects primate sleeping behavior. We studied antipredation sleeping behavior in skywalker hoolock gibbons (Hoolock tianxing). We studied one group (NA) and a solitary female (NB) at Nankang from July 2010 to September 2011, and another group (BB) at Banchang from May 2013 to December 2014 in Mt. Gaoligong, Yunnan, China. Over the study period, we recorded 67 sleeping trees for members of group NA over 92 days, 17 trees for the solitary female NB over 22 days, and 159 trees for members of group BB over 186 days. Skywalker hoolock gibbons at both sites rarely used the same tree on consecutive days (N = 3 at both sites). They traveled fast to enter sleeping tree a mean of 160 ± SD 43 min before sunset at Nankang, and a mean of 192 ± SD 40 min before sunset at Banchang. They seldom (Nankang: 14%, N = 183 observations; Banchang: 25%, N = 548 observations) defecated in sleeping trees. They slept at sites with more tall and large trees and preferred to sleep on tall trees in the site. They slept on branches of small diameter and closer to tree tops. Our study suggests that antipredation plays an important role in skywalker hoolock gibbons’ sleeping tree selection and sleeping behavior. In addition, our data suggest potential effects of habitat degradation on gibbons’ sleeping behavior. Tall trees are especially important for gibbons in degraded forest and should be protected.     

Modeling individual tree height to diameter ratio for Norway spruce and European beech in Czech Republic

Key message

The purposed spatially explicit and spatially non-explicit height to diameter ratio models can be useful to evaluate the stability of trees and stands for Norway spruce and European beech forests.

Abstract

Height to diameter ratio (HDR) is an individual tree index, also known as slenderness coefficient, and commonly used to evaluate stability of trees and stands. We developed both spatially explicit and spatially non-explicit HDR models for Norway spruce (Picea abies (L.) Karst.) and European beech (Fagus sylvatica L.) using a large dataset collected from fully stem-mapped permanent research plots in various parts of the Czech Republic. Various tree and stand characteristics were evaluated for their potential contributions to the the HDR models. In addition to diameter at breast height (DBH), other highly significant predictor variables identified are dominant height (HDOM) (site quality measure), dominant diameter (DDOM) and quadratic mean diameter (QMD) (spatially non-explicit competition measures), and Hegyi’s index (spatially explicit competition index, CI). A simple exponential decay function was chosen as a base function to include these predictor variables. Both spatially explicit and spatially non-explicit models described large parts of the HDR variations [R _adj ²  = 0.66 (Norway spruce), 0.72 (European beech)] without any systematic deviation of the residuals across the observed data range. Unlike for European beech, spatially explicit model for Norway spruce better described HDR variations than its spatially non-explicit counterpart. After DBH, HDOM provided the largest contribution to each model type, followed by DDOM and QMD or CI for both species. The HDR increased with increasing HDOM and CI, but it decreased with increasing DDOM and QMD, suggesting there were significantly large effects of site quality and stand density on HDR. Because of a little difference between the fit statistics and graphical displays of the two model types, spatially non-explicit model is recommended for prediction of HDR for both species as this model does not require spatially explicit CI, which is computationally much more complex than spatially non-explicit competition measures. The proposed HDR models may be applicable to assess stability of trees and stands, and to regulate stand densities.

     

Fine-root trait plasticity of beech (<Emphasis Type="Italic">Fagus sylvatica</Emphasis>) and spruce (<Emphasis Type="Italic">Picea abies</Emphasis>) forests on two contrasting soils

Aim

The fine roots of trees may show plastic responses to their resource environment. Several, contrasting hypotheses exist on this plasticity, but empirical evidence for these hypotheses is scattered. This study aims to enhance our understanding of tree root plasticity by examining intra-specific variation in fine-root mass and morphology, fine-root growth and decomposition, and associated mycorrhizal interactions in beech (Fagus sylvatica L.) and spruce (Picea abies (L.) Karst.) forests on soils that differ in resource availability.

Methods

We measured the mass and morphological traits of fine roots (i.e. ≤ 2 mm diameter) sampled to 50 cm depth. Fine-root growth was measured with ingrowth cores, and fine-root decomposition with litter bags. Mycorrhizal fungal biomass was determined using ingrowth mesh bags.

Results

Both tree species showed more than three times higher fine-root mass, and a ten-fold higher fine-root growth rate on sand than on clay, but no or marginal differences in overall fine-root morphology. Within the fine-root category however, beech stands had relatively more root length of their finest roots on clay than on sand. In the spruce stands, ectomycorrhizal mycelium biomass was larger on sand than on clay.

Conclusions

In temperate beech and spruce forests, fine-root mass and mycorrhizal fungal biomass, rather than fine-root morphology, are changed to ensure uptake under different soil resource conditions. Yet enhancing our mechanistic understanding of fine-root trait plasticity and how it affects tree growth requires more attention to fine-root dynamics, the functional diversity within the fine-roots, and mycorrhizal symbiosis as an important belowground uptake strategy.

     

Tree species mixture inhibits soil organic carbon mineralization accompanied by decreased r-selected bacteria

Background and aims

Fine-root functioning is a major driver of plant growth and strongly influences the global carbon cycle. While fine-root over-yielding has been shown in the upper soil layers of mixed-species forests relative to monospecific stands, the consequences of tree diversity on fine-root growth in very deep soil layers is still unknown. Our study aimed to assess the consequences of mixing Acacia mangium and Eucalyptus grandis trees on soil exploration by roots down to the water table at 17 m depth in a tropical planted forest.

Method

Fine roots (diameter < 2 mm) were sampled in a randomized block design with three treatments: monospecific stands of Acacia mangium (100A), Eucalyptus grandis (100E), and mixed stands with 50% of each species (50A50E). Root ingrowth bags were installed at 4 depths (from 0.1 m to 6 m) in the three treatments within three different blocks, to study the fine-root production over 2 periods of 3 months.

Results

Down to 17 m depth, total fine-root biomass was 1127 g m^?2 in 50A50E, 780 g m^?2 in 100A and 714 g m^?2 in 100E. Specific root length and specific root area were 110–150% higher in 50A50E than in 100A for Acacia mangium trees and 34% higher in 50A50E than in 100E for Eucalyptus grandis trees. Ingrowth bags showed that the capacity of fine roots to explore soil patches did not decrease down to a depth of 6 m for the two species.

Conclusions

Belowground interactions between Acacia mangium and Eucalyptus grandis trees greatly increased the exploration of very deep soil layers by fine roots, which is likely to enhance the uptake of soil resources. Mixing tree species might therefore increase the resilience of tropical planted forests through a better exploration of deep soils.

     

Effects of phosphorus addition with and without nitrogen addition on biological nitrogen fixation in tropical legume and non-legume tree plantations

It is well documented that phosphorus (P) input stimulates biological nitrogen (N) fixation (BNF) in tropical forests with non-legume trees. However, in tropical legume forests with soil N enrichment and P deficiency, the effects of P availability and its combination with N on BNF remain poorly understood. In this study, we measured BNF rate in different compartments, i.e., bulk soil, forest floor, rhizosphere, and nodules, in two tropical plantations with legume trees Acacia auriculiformis (AA) versus non-legume trees Eucalyptus urophylla, (EU) in southern China after 4 years of P addition and combined N and P additions. The objective was to investigate how P addition and its combination with N addition regulate BNF in a tropical legume plantation, and to compare the effects with those in a non-legume plantation. Our results showed that total BNF rates were significantly higher in the P-addition plots than in the control plots by 27.4 ± 4.3 and 23.3 ± 1.7 % in the EU and AA plantations, respectively. Total BNF rates were significantly higher in the NP-addition plots than in the control plots by 27.7  ± 5.0 and 8.5 ± 1.4 % in the EU and AA plantations, respectively, which contrasted to our previous result that total BNF rates were significantly lower in N-addition plots than in the control plots in the AA plantation. These findings suggest that P input can stimulate BNF in tropical forest biome dominated by legume trees, even in consideration of elevated atmospheric N deposition. Thus, our study revealed the important role of P in regulating biological N input, which should be taken into account in the modeling of biogeochemical cycles in the future.     

Influence of moss and lichen spatial mosaics on radial growth of Gmelin larch (Central Evenkia)

The results of research studies on the influence of high moss-and-lichen mosaicity typical for the northern taiga in Central Evenkia on the dynamics of radial growth of Gmelin larch trees (Larix gmelinii (Rupr.) Rupr.) are reported. Three sample plots were laid out in the larch ledum–cowberry–green moss forest on the northwest facing slope (8°–10°) in close proximity to each other; they differed in the proportions of area occupied by the principal components of a moss–lichen cover (Aulacomnium turgidum, Pleurozium schreberi, Cladonia rangiferina, and Hylocomium splendens), spatial distribution, and thermal properties of seasonally thawed soil layers. The worst thermal soil properties under the current climatic conditions have determined the comparatively low radial growth of trees in the sampling area, reduced response to air-temperature variations in the period of preseason cambium activity and at the beginning of the radial growth period, and heightened the response to this factor at the end of a season.     

Forest decline after a 15-year “perfect storm” of invasion by hemlock woolly adelgid,drought, and hurricanes

Invasions by introduced pests can interact with other disturbances to alter forests and their functions, particularly when a dominant tree species declines. To identify changes after invasion by the insect hemlock woolly adelgid (Adelges tsugae; HWA), coinciding with severe droughts and hurricanes, this study compared tree species composition of eastern hemlock (Tsuga canadensis) forests on 11 plots before (2001) and 15 years after (2016) invasion in the southern Appalachian Mountains, USA. Losses of hemlock trees after HWA invasion were among the highest reported, with a 90% decline in density, 86% decline in basal area, and 100% mortality for individuals ≥ 60 cm in diameter. In contrast to predictions of theoretical models, deciduous tree density declined after HWA invasion, while basal area changed little, at least during the initial 15 years after invasion. Overall, forest density declined by 58%, basal area by 25%, and tree species richness by 8%. Factors additional to HWA likely exacerbating forest decline included: droughts before (1999–2001) and after HWA invasion (2006–2008); tree uprooting from hurricane-stimulated winds in 2004; pest-related declines of deciduous tree species otherwise likely benefitting from hemlock’s demise; death of deciduous trees when large hemlocks fell; and competition from aggressive understory plants including doghobble (Leucothoe fontanesiana), rosebay rhododendron (Rhododendron maximum), and Rubus spp. Models of forest change and ecosystem function should not assume that deciduous trees always increase during the first decades after HWA invasion.     

Prebiotic effects of bovine lactoferrin on specific probiotic bacteria

Bovine lactoferrin (bLf) is a natural iron-binding protein and it has been suggested to be a prebiotic agent, but this finding remains inconclusive. This study explores the prebiotic potential of bLf in 14 probiotics. Initially, bLf (1–32 mg/mL) treatment showed occasional and slight prebiotic activity in several probiotics only during the late experimental period (48, 78 h) at 37 °C. We subsequently supposed that bLf exerts stronger prebiotic effects when probiotic growth has been temperately retarded. Therefore, we incubated the probiotics at different temperatures, namely 37 °C, 28 °C, room temperature (approximately 22–24 °C), and 22 °C, to retard or inhibit their growth. As expected, bLf showed more favorable prebiotic activity in several probiotics when their growth was partially retarded at room temperature. Furthermore, at 22 °C, the growth of Bifidobacterium breve, Lactobacillus coryniformis, L. delbrueckii, L. acidophilus, B. angulatum, B. catenulatum, and L. paraplantarum were completely blocked. Notably, these probiotics started regrowing in the presence of bLf (1–32 mg/mL) in a significant and dose-dependent manner. Accordingly, bLf significantly increased the growth of Pediococcus pentosaceus, L. rhamnosus, and L. paracasei (BCRC 17483; a locally isolated strain) when their growth was retarded by incubation at 22 °C. In conclusion, bLf showed inconsistent prebiotic activity in the 14 probiotics at 37 °C, but revealed strong prebiotic activity in 10 probiotic strains at 22 °C. Therefore, this study enables determining additional roles of Lf in probiotic strains, which can facilitate developing novel combinational approaches by simultaneously using Lf and specific probiotics.