What happens to the mycorrhizal communities of native and exotic seedlings when Pseudotsuga menziesii invades Nothofagaceae forests in Patagonia,Argentina?

Pseudotsuga menziesii is one of the most widely planted conifers in the Patagonian Andes of Argentina, having invading characteristics that are broadly reported. We studied the mycorrhizal status of seedlings along six Nothofagaceae + P. menziesii invasion matrices to investigate their role in the invasive process, according to these hypothesis: a) The abundance and richness of EM will be higher in seedlings grown in their own soil; b) In the presence of native EM inoculum, the invasive plant will be associated with generalist mycorrhizae (EM and/or AM), c) AM associations will be more abundant in P. menziesii seedlings grown in Interface or native forest soils, d) Mycorrhizal community differences between treatments will alter host fitness (growth and nutritional parameters). Seedlings from Nothofagus dombeyi, N. antarctica, Lophozonia alpina, L. obliqua and Pseudotsuga menziesii were set up in a soil-bioassay that included soils from non-invaded Nothofagaceae forests, pure P. menziesii plantations, and the interface between both. Pseudotsuga menziesii seedlings showed a decreasing, although never null, ectomycorrhizal (EM) colonization pattern from plantations to non-invaded forests, mainly with exotic EM species. Hebeloma mesophaeum and Wilcoxina sp. 1, two EM species with cosmopolitan distribution, were found to be shared by both tree species. Hebeloma hiemale and Wilcoxina sp. 1, common mycorrhizal partners of P. menziesii in Patagonia although not registered from Nothofagaceae forest, were found to be associated with N. antarctica, being the first report for both fungal species. Pseudotsuga menziesii seedlings showed the ability to form different arbuscular mycorrhiza (AM) colonization types (Paris-, Arum-, Both- and Intermediate-types) depending on the treatments, with significantly higher presence of Intermediate-type in the Interface treatment, where colonization was low. The shared EM species and the presence of different AM colonization types imply enhanced possibilities for invasive P. menziesii seedlings establishment and development. Seedling features and EM colonization rates evidenced that P. menziesii invasion could produce maladaptation (defined as a relative decline in host fitness due to altered mycorrhizal communities from native settings) of mycorrhizal communities, seriously injuring native ecosystem.     

The experimental verification of natural hybridization between two taxa of Hawaiian Bidens (Asteraceae)

Bidens ctenophylla andB. menziesii var.filiformis are two heterozygous, self-fertile but outcrossing, interfertile taxa. A relatively fertile intermediate population occurs on the “hybridized habitat” of a recent lava flow. This population contains some indi viduals which are similar toB. ctenophylla, some which are similar toB. menziesii var.filiformis, and many individuals of various intermediate forms. Variation studies of greenhouse populations of the two species, the F₁ hybrid, the F₂ hybrid, and the progeny of three wild intermediates confirm the field observation that the wild intermediate population is a product of natural hybridization betweenB. ctenophylla andB. menziesii var.filiformis. The analysis of two interspecific characters, stem anthocyanin and achene awns, indicates that each is polygenic and is regulated by relatively few genes.     

Mycorrhiza-like interaction by Morchella with species of the Pinaceae in pure culture synthesis

 Isolates from two species of Morchella were tested for ability to form mycorrhizae in pure culture synthesis with Arbutus menziesii, Larix occidentalis, Pinus contorta, Pinus ponderosa, andPseudotsuga menziesii. Ectomycorrhizal structures (mantle and Hartig net) formed with the four species of the Pinaceae but not with A. menziesii. Results are compared to previous studies on morel mycorrhizae and discussed in an ecological context. Accepted: 23 October 1999     

Resin duct size and density as ecophysiological traits in fire scars of Pseudotsuga menziesii and Larix occidentalis

Background and Aims

Resin ducts (RDs) are features present in most conifer species as defence structures against pests and pathogens; however, little is known about RD expression in trees following fire injury. This study investigates changes in RD size and density in fire scars of Douglas fir (Pseudotsuga menziesii) and western larch (Larix occidentalis) as a means to evaluate the ecophysiological significance of traumatic resinosis for tree defence and survival.

Methods

Transverse and tangential microsections were prepared for light microscopy and image analysis in order to analyse axial and radial RDs, respectively. Epithelial cells of RDs and fusiform rays associated with radial RDs were also examined. RDs were compared between normal xylem and wound xylem at four different section heights along the fire-injured stem.

Key Results

Following fire injury, P. menziesii axial RDs narrowed by 38–43 % in the first year after injury, and the magnitude of this change increased with stem height. Larix occidentalis axial RDs widened by 46–50 % in the second year after injury. Radial RDs were of equivalent size in P. menziesii, but widened by 162–214 % in L. occidentalis. Fusiform rays were larger following fire injury, by 4–14 % in P. menziesii and by 23–38 % in L. occidentalis. Furthermore, axial RD density increased in both species due to the formation of tangential rows of traumatic RDs, especially in the first and second years after injury. However, radial RD density did not change significantly.

Conclusions

These results highlight traumatic resinosis as a species-specific response. Pseudotsuga menziesii produce RDs of equivalent or reduced size, whereas L. occidentalis produce wider RDs in both the axial and radial duct system, thereby increasing resin biosynthesis and accumulation within the whole tree. Larix occidentalis thus appears to allocate more energy to defence than P. menziesii.     

Downregulation of net phosphorus-uptake capacity is inversely related to leaf phosphorus-resorption proficiency in four species from a phosphorus-impoverished environment

Background and Aims

Previous research has suggested a trade-off between the capacity of plants to downregulate their phosphorus (P) uptake capacity and their efficiency of P resorption from senescent leaves in species from P-impoverished environments.

Methods

To investigate this further, four Australian native species (Banksia attenuata, B. menziesii, Acacia truncata and A. xanthina) were grown in a greenhouse in nutrient solutions at a range of P concentrations [P]. Acacia plants received between 0 and 500 µm P; Banksia plants received between 0 and 10 µm P, to avoid major P-toxicity symptoms in these highly P-sensitive species.

Key Results

For both Acacia species, the net P-uptake rates measured at 10 µm P decreased steadily with increasing P supply during growth. In contrast, in B. attenuata, the net rate of P uptake from a solution with 10 µm P increased linearly with increasing P supply during growth. The P-uptake rate of B. menziesii showed no significant response to P supply in the growing medium. Leaf [P] of the four species supported this finding, with A. truncata and A. xanthina showing an increase up to a saturation value of 19 and 21 mg P g⁻¹ leaf dry mass, respectively (at 500 µm P), whereas B. attenuata and B. menziesii both exhibited a linear increase in leaf [P], reaching 10 and 13 mg P g⁻¹ leaf dry mass, respectively, without approaching a saturation point. The Banksia plants grown at 10 µm P showed mild symptoms of P toxicity, i.e. yellow spots on some leaves and drying and curling of the tips of the leaves. Leaf P-resorption efficiency was 69 % (B. attenuata), 73 % (B. menziesii), 34 % (A. truncata) and 36 % (A. xanthina). The P-resorption proficiency values were 0·08 mg P g⁻¹ leaf dry mass (B. attenuata and B. menziesii), 0·32 mg P g⁻¹ leaf dry mass (A. truncata) and 0·36 mg P g⁻¹ leaf dry mass (A. xanthina). Combining the present results with additional information on P-remobilization efficiency and the capacity to downregulate P-uptake capacity for two other Australian woody species, we found a strong negative correlation between these traits.

Conclusions

It is concluded that species that are adapted to extremely P-impoverished soils, such as many south-western Australian Proteaceae species, have developed extremely high P-resorption efficiencies, but lost their capacity to downregulate their P-uptake mechanisms. The results support the hypothesis that the ability to resorb P from senescing leaves is inversely related to the capacity to downregulate net P uptake, possibly because constitutive synthesis of P transporters is a prerequisite for proficient P remobilization from senescing tissues.     

Mono- and sesqui-terpenoid differentiation of Pseudotsuga of the United States and Canada

Nineteen composite samples of cortical oleoresin from Pseudotsuga menziesii and P. macorcarpa of different geographic origin were analyzed for the content of their essential oils. A dendrogram derived from this analysis revealed that the populations of P. menziesii from the Sierra Nevada are chemically closer to the inland var. glauca than to the coastal var. menziesii. Sesquiterpenoid hydrocarbons included in the essential oils proved to be chemosystematically as valuable as monoterpenoids in classifying the races.     

Pseudotsuga menziesii invasion in native forests of Patagonia,Argentina: What about mycorrhizas?

Pseudotsuga menziesii is one of the most widely planted conifers in the Patagonian Andes of Argentina, with invading characteristics that are widely reported. Nevertheless, little is known about the role of its obligate mycorrhizal associations in limiting or fostering the establishment of invading seedlings. We studied the richness and abundance of endo- (AM) and ectomycorrhizae (EM) present in P. menziesii seedlings growing in six Nothofagus forests invaded by P. menziesii seedlings (Nothofagus + P. menziesii) matrices. One transect along the maximum effective recruitment distance (ERA) was established at each site in order to wrench seedlings and sample soils. P. menziesii showed effective associations with a wide range of mycorrhizal symbionts: AM (ranging between 13.21 and 37.11%), EM (ranging between 79.91 and 89.14%) and Dark Septate Endophytes (DSE). Seedlings' mycorrhization percentages were always high, suggesting a good nursery effect provided by neighboring plantations. Mycorrhizal abundance (AM% and EM%), EM morphotypes richness and evenness showed significant differences between sites, indicating that P. menziesii displays a high plasticity being capable to select the more convenient mycorrhizal arrangement at each invaded site.     

The Importance of Large-Diameter Trees to Forest Structural Heterogeneity

Large-diameter trees dominate the structure, dynamics and function of many temperate and tropical forests. However, their attendant contributions to forest heterogeneity are rarely addressed. We established the Wind River Forest Dynamics Plot, a 25.6 ha permanent plot within which we tagged and mapped all 30,973 woody stems ≥1 cm dbh, all 1,966 snags ≥10 cm dbh, and all shrub patches ≥2 m². Basal area of the 26 woody species was 62.18 m²/ha, of which 61.60 m²/ha was trees and 0.58 m²/ha was tall shrubs. Large-diameter trees (≥100 cm dbh) comprised 1.5% of stems, 31.8% of basal area, and 17.6% of the heterogeneity of basal area, with basal area dominated by Tsuga heterophylla and Pseudotsuga menziesii. Small-diameter subpopulations of Pseudotsuga menziesii, Tsuga heterophylla and Thuja plicata, as well as all tree species combined, exhibited significant aggregation relative to the null model of complete spatial randomness (CSR) up to 9 m (P≤0.001). Patterns of large-diameter trees were either not different from CSR (Tsuga heterophylla), or exhibited slight aggregation (Pseudotsuga menziesii and Thuja plicata). Significant spatial repulsion between large-diameter and small-diameter Tsuga heterophylla suggests that large-diameter Tsuga heterophylla function as organizers of tree demography over decadal timescales through competitive interactions. Comparison among two forest dynamics plots suggests that forest structural diversity responds to intermediate-scale environmental heterogeneity and disturbances, similar to hypotheses about patterns of species richness, and richness- ecosystem function. Large mapped plots with detailed within-plot environmental spatial covariates will be required to test these hypotheses.     

Persistence of<Emphasis Type="Italic">Pseudotsuga menziesii</Emphasis> (Douglas-fir) in temperate coniferous forests of the Pacific Northwest Coast,USA

Old-growthPseudotsuga-Tsuga forests of the Pacific Northwest Coast of North America are characterized by the presence of large, old trees ofPseudotsuga menziesii var.menziesii (Douglas-fir). Colonizing soon after a stand-replacing disturbance,P. menziesii persists in these forests, coexisting for centuries with the late-successional species.P. menziesii survives by maintaining emergent status in the uppermost part of the forest canopy, above the crowns of competing late-successional species. After reaching maximum tree height and crown size,P. menziesii maintains shoots and foliage of the established crown by epicormic shoot production. In this review, we propose that attaining emergent status in the upper canopy combined with the process of crown maintenance contributes to the persistence ofP. menziesii into later stages of succession, making this species a long-lived pioneer that between infrequent disturbances can coexist with late-successional species for centuries.     

Species-mediated soil moisture availability and patchy establishment of Pseudotsuga menziesii in chaparral

The occurrence of mature individuals of Pseudotsuga menziesii in stands of Arctostaphylos species mark the initial stages of mixed evergreen forest invasion into chaparral in central coastal California. We planted two cohorts of P. menziesii seeds at three sites under stands of two Arctostaphylos species and Adenostoma fasciculatum in order to determine whether first-year seedling emergence and survival, particularly during the regular summer drought, underlie the spatial distribution of mature trees observed in chaparral. Regardless of the chaparral species they were planted under, P. menziesii seeds that were not protected from vertebrate predation displayed very little emergence and no survival. In contrast, emergence of P. menziesii that were protected from vertebrate predators was much higher but still did not significantly differ among the three chaparral species. However, survival of protected seedlings under Arctostaphylos glandulosa was much greater than under A. fasciculatum, with intermediate survival under Arctostaphylos montana. While mortality of protected seedlings due to insect herbivory, fungal infection, and disturbance displayed no consistent patterns, summer drought mortality appeared to drive the patterns of survival of P. menziesii under the different chaparral species. These emergence, mortality, and survival data suggest that spatial patterns of P. menziesii recruitment in chaparral are driven by first-year summer drought seedling mortality, but only in years when seeds and seedlings are released from vertebrate predation pressure. Because the first-year drought mortality and survival patterns of P. menziesii seedlings differed strongly depending on the chaparral species, we examined the additional hypothesis that these patterns are associated with differences in the availability of soil moisture under different chaparral species. Both higher survival and lower drought mortality of P. menziesii seedlings were associated with higher soil water potential under Arctostaphylos stands during the summer drought, especially in the subsurface soil. The data suggest that Arctostaphylos stands, particularly stands of A. glandulosa, ameliorate xeric summer conditions to a degree that facilitates first-year establishment of P. menziesii and strongly influences spatial distribution of mature trees. Received: 18 September 1998 / Accepted: 23 December 1998     

Bacterial Activity Associated with the Decomposition of Woody Substrates in a Stream Sediment

Ground bark and heartwood from Alnus rubra and Pseudotsuga menziesii were added to a muddy sediment from a small Oregon stream and incubated in situ. Carbon dioxide and methane production rates were increased by all amendments, the biggest increase being shown with A. rubra wood. Except for sediment amended with A. rubra wood, nitrogen fixation rates from all treatments (including the control) were approximately 0.1 nmol/g per h throughout the 6-month study period. Contrary to expectations, neither bark had a noticeable adverse effect on microbial activity, but the A. rubra wood promoted nitrogen fixation. These results help to explain the faster rate of decomposition of A. rubra wood in water compared with that of P. menziesii described in the literature. The uptake kinetics of glucose (V_max) did not follow the same pattern as gas evolution.     

Water flux and canopy conductance of natural versus planted forests in Patagonia, South America

In NW Patagonia, South America, natural shrublands and mixed forests of short Nothofagus antarctica (G. Forst.) Oerst. trees are currently being replaced by plantations with Pseudotsuga menziesii (Mirb) Franco. This land use change is controversial because the region is prone to drought, and replacement of native vegetation by planted forests may increase vegetation water use. The goal of this study was to examine the physiological differences, especially the response of water flux and canopy conductance to microclimate, that lead to greater water use by exotic trees compared to native trees. Meteorological variables and sapflow density of P. menziesii and four native woody species were measured in the growing season 2005–2006. Canopy conductance (gc) was estimated for both the exotic (monoculture) and native (multi-species) systems, including the individual contributions of each species of the native forest. Sapflow density, stand-level transpiration and gc were related to leaf-to-air vapor pressure difference (VPD). All native species had different magnitudes and diurnal patterns of sapflow density compared to P. menziesii, which could be explained by the different gc responses to VPD. Stomatal sensitivity to VPD suggested that all native species have a stronger stomatal control of leaf water potential and transpiration due to hydraulic limitations compared to P. menziesii. In conclusion, differences in water use between a P. menziesii plantation and a contiguous native mixed forest of similar basal area could be explained by different gc responses to VPD between species (higher sensitivity in the native species), in addition to particular characteristics of the native forest structure.     

The significance of life history strategies in the developmental history of mixed beech (Nothofagus) forests,New Zealand

Size and age structure analysis, dated past disturbances, treefall replacement patterns, and spatial pattern analysis were used to reconstruct the developmental history of two old-growth Nothofagus fusca/N. menziesii stands, South Island, New Zealand. Diameter and height class distributions suggested that N. menziesii was replacing N. fusca, however, stand history reconstruction analysis showed that both species had regenerated intermittently after small-scale disturbances. Although large-scale disturbances such as blowdowns may occasionally generate even-aged stands, gap-phase regeneration maintains the forests in compositional equilibrium. In the absence of other competing tree species and understorey plants the two species appear to coexist by way of different life history strategies, where one species (N. menziesii) has low juvenile mortality and the other (N. fusca) has faster height growth rates and greater longevity and adult survivorship.     

Geographic differentiation of cortical monoterpenoids of Pseudotsuga macrocarpa

Cortical essential oil from Pseudotsuga macrocarpa was analyzed for monoterpenoid compounds. Only minor differences were apparent between samples collected in different locations. Pseudotsuga macrocarpa and P. menziesii appeared to be quite distinct chemically. No evidence was obtained of any gene exchange between the two species in the southern California coastal region, where they grow a short distance from each other.     

Effectiveness of green-tree retention in the conservation of ectomycorrhizal fungi

Habitat fragmentation stresses may reduce the long-term effectiveness of green-tree retention as refugia for ectomycorrhizal fungal (EMF) species. We tested for a minimum retention patch size where EMF species abundance (morphotyping with molecular analysis), richness and reproduction (epigeous sporocarps) aligned with interior Pseudotsuga menziesii habitat on Vancouver Island (Canada). Ten years after logging, species richness was altered along the entire gradient of patch sizes (single trees to 0.12 ha), while % abundance and fruiting had significantly declined for some prevalent EMF species. Retention patches 20 m in diameter, on average, were therefore insufficient in size to ensure the continuity of mature-forest dependent EMF species. Refugia effectiveness would also correspond with habitat extent, and α and γ diversity estimates indicated retention patches approximately 0.2 ha in size, and culminating in at least 3 % of the cutblock area, would capture much of the spatial heterogeneity and species diversity of this EMF community.     

Lack of Physiological Depth Patterns in Conspecifics of Endemic Antarctic Brown Algae: A Trade-Off between UV Stress Tolerance and Shade Adaptation?

A striking characteristic of endemic Antarctic brown algae is their broad vertical distribution. This feature is largely determined by the shade adaptation in order to cope with the seasonal variation in light availability. However, during spring-summer months, when light penetrates deep in the water column these organisms have to withstand high levels of solar radiation, including UV. In the present study we examine the light use characteristics in parallel to a potential for UV tolerance (measured as content of phenolic compounds, antioxidant activity and maximum quantum yield of fluorescence) in conspecific populations of four Antarctic brown algae (Ascoseira mirabilis, Desmarestia menziesii, D. anceps and Himantothallus grandifolius) distributed over a depth gradient between 5 and 30 m. The main results indicated that a) photosynthetic efficiency was uniform along the depth gradient in all the studied species, and b) short-term (6 h) exposure to UV radiation revealed a high tolerance measured as chlorophyll fluorescence, phlorotannin content and antioxidant capacity. Multivariate analysis of similarity indicated that light requirements for photosynthesis, soluble phlorotannins and antioxidant capacity are the variables determining the responses along the depth gradient in all the studied species. The suite of physiological responses of algae with a shallower distribution (A. mirabilis and D. menziesii) differed from those with deeper vertical range (D. anceps and H. grandifolius). These patterns are consistent with the underwater light penetration that defines two zones: 0–15 m, with influence of UV radiation (1% of UV-B and UV-A at 9 m and 15 m respectively) and a zone below 15 m marked by PAR incidence (1% up to 30 m). These results support the prediction that algae show a UV stress tolerance capacity along a broad depth range according to their marked shade adaptation. The high contents of phlorotannins and antioxidant potential appear to be strongly responsible for the lack of clear depth patterns in light demand characteristics and UV tolerance.     

Determination of Indole-3-acetic Acid in Douglas Fir Using a Deuterated Analog and Selected Ion Monitoring: Comparison of Microquantities in Seedling and Adult Tree

Indole-3-acetic acid (IAA) content in shoot tips of Douglas fir (Pseudotsuga menziesii [Mirb.] Franco) trees and seedlings was determined by combined gas chromatography-mass spectrometry using a deuterated analog (d₂-IAA) as an internal standard and the technique of selected ion monitoring. Ratios of the peak heights of the deuterated analog internal standard to endogenous IAA revealed a slightly higher content of IAA in seedlings compared with the shoot tips collected in June. The relatively high level of IAA (2.9 micrograms per gram fresh weight) in seedlings is discussed in relation to in vitro propagation of this species.     

Photosynthetic characteristics and UV stress tolerance of Antarctic seaweeds along the depth gradient

The photosynthetic characteristics through P-E curves and the effect of UV radiation on photosynthesis (measured as rapid adjustment of photochemistry, F _v/F _m) and DNA damage (as formation of CPDs) were studied in field specimens of green, red and brown algae collected from the eulittoral and sublittoral zone of Fildes Peninsula (King George Island, Antarctic). The content of phenolic compounds (phlorotannins) and the antioxidant activity were also studied in seven brown algae from 0 to 40 m depth. The results indicated that photosynthetic efficiency (α) was high and did not vary between different species and depths, while irradiances for saturation (E _k) averaged 55 μmol m^?2 s^?1 in subtidal and 120 μmol m^?2 s^?1 in eulittoral species. The studied species exhibited notable short-term UV tolerance along the vertical zonation. In intertidal and shallow water species, decreases in F _v/F _m by UV radiation were between 0 and 18 %, while in sublittoral algae, decreases in F _v/F _m varied between 3 and 35 % relative to PAR treatment. In all species, recovery was high averaging 84–100 %. The formation of CPDs increased (15–150 %) under UV exposure, with the highest DNA damage found in some subtidal species. Phlorotannin content varied between 29 mg g^?1 DW in Ascoseira mirabilis from 8 m depth and 156 mg g^?1 DW in Desmarestia menziesii from 17 m depth. In general, phlorotannin concentrations were constitutively high in deeper sublittoral brown algae, which were correlated with higher antioxidant activities of algal extracts and low decreases in photosynthesis. UV radiation caused a strong decrease in phlorotannin content in the deep-water Himantothallus grandifolius, whereas in D. menziesii and Desmarestia anceps, induction of the synthesis of phlorotannins by UV radiation was observed. The antioxidant activity was in general less affected by UV radiation.     

Facilitation and Inhibition of Seedlings of an Invasive Tree (Acer platanoides) by Different Tree Species in a Mountain Ecosystem

Facilitation is known to be an important process structuring natural plant communities. However, much less is known about its role in facilitating the invasion of ecosystems by non-native plant species. In this study we evaluated the effects of invasive (Acer platanoides) and native (Pseudotsuga menziesii) forest types on the performance of A. platanoides seedlings, and related these effects to structural and functional properties associated with the two forest types, in a native P. menziesii forest that is being invaded by A. platanoides. Acer platanoidesseedlings had higher densities, recruitment, and survival, and experienced less photoinhibition and water stress when beneath conspecific canopies than in the adjacent P. menziesii forest. Soil moisture and canopy cover were greater in the invaded patch than the native forest. There was no difference in soil fertility or understory light levels between locations. These demographic (i.e. seedling survival), physiological, and environmental differences appeared to be due to the effects of A. platanoides and P. menziesii trees. Thus, Acer trees appear to produce a more mesic environment by modifying the structure and phenology of the forest canopy and by altering the timing of transpirational water loss relative to P. menziesii. Environmental modification by invaders that lead to positive effects on conspecifics may help us to understand the dramatic success and lag periods of some invasive species     

Crown closure affects endophytic leaf mycobiome compositional dynamics over time in Pseudotsuga menziesii var. menziesii

Old-growth Pseudotsuga menziesii var. menziesii forests produce complex environmental and spatial gradients along which biota assemble. Given this, it has been proposed that changes in the crown microenvironment are associated with different community assembly outcomes for needle fungi. Using high-throughput sequencing, the endophytic mycobiomes of needles were characterized for increasing ages of needles sampled along the boles of eight coastal Douglas-fir trees. Leveraging airborne light detection and ranging (LiDAR) data to create three-dimensional “point cloud” representations of tree crowns revealed that crown closure accounted for more fungal compositional variation than height in crown, and fungal richness and diversity were positively correlated with increasing crown closure. Supplementing the point clouds of each climbed tree with clouds from >5,000 randomly selected trees in the study area showed that fungal communities from closed portions of the crown were increasingly structured with needle age. These findings highlight the importance of the crown microenvironment in the development of foliar fungal communities for a foundation tree species.