Quercus Emoryi Research Articles

Synergistic Interactions between Tocol and Phenolic Extracts from Different Tree Nut Species against Human Cancer Cell Lines.

Tree nuts are rich in polar (phenolic compounds) and non-polar (tocols) antioxidants, with recognized effects in the prevention of diseases such as cancer. These biomolecules possess antiproliferative activity on cancer cells; however, the combined effect of both types of compounds has been scarcely studied, and this approach could give valuable information on the real anticancer potential of tree nuts. In the present study, the antiproliferative activity of pure tocols and phenolic compounds, tocol- and phenolic-rich extracts (TRE and PRE, respectively) from tree nuts and the extracts combinations, was evaluated in four cancer (HeLa, MCF7, PC3, A549) and one control (ARPE) cell lines. The most sensible cell lines were HeLa and MCF7. TRE and PRE from nuts were chemically characterized; γ and δ tocopherols, total tocols, total tocopherols and total phenolic compounds were negatively correlated with cell viability in MCF7 cells. In HeLa cells, only δ and total tocopherols were negatively correlated with cell viability. TRE and PRE had a low effect in reducing cell viability of the cancer cell lines, the most effective extracts were those of emory oak acorn (EOA), pecan nut (PEC) and walnut (WAL), and these were further studied for their pharmacological interactions, using the combination index and the isobologram methods. Combinations of both extracts showed a synergistic and strongly synergistic behavior in the three nuts (EOA, PEC and WAL), with combination indexes between 0.12 and 0.55. These results highlight the need to understand the interactions among components found in complex natural extracts or food products in order to fully understand their bioactivities.

First Report of Biscogniauxia mediterranea on Quercus emoryi in Southern Arizona.

In 2019, a decline of Quercus emoryi (Emory oak) was observed on the Coronado National Forest located in southeastern Arizona. Symptoms associated with oak mortality included crown die-back and large cankers revealing charcoal-like stromal growth. Trunks and root collars showed girdling and many affected trees also displayed evidence of gold-spotted oak borer activity. Initial surveys in stands identified clusters of severe infections. Samples with black perithecia and stromal tissue were collected from symptomatic hosts. Morphological characterization of the fungus was completed on fresh perithecial tissue. Stromata were pulvinate and black showing embedded perithecial bumps, with ostioles visible from the surface of the stroma. Asci were short stipitate and cylindrical with visible oil drops, 6.6 to 9.4 (mean: 8.8) × 139.8 to 179.9 μm (mean: 166.4). Ascospores were smooth ovoid, brown to dark brown, with narrowed and round ends, 6.9 to 9.1 (mean: 7.7) × 13.8 to 25.9 μm (mean: 16.5). Colonies grown on ½ strength potato dextrose agar (½ PDA) (Korhonen 1980) at 25°C for 14 days were whitish-grey when viewed from the top and darkened embedded spheres were visible from the bottom. Single-spored cultures were isolated by dissecting the hymenium and placing in distilled water. The suspension was streaked onto ½ PDA plates and incubated for 12 hours, and pure cultures were grown on ½ PDA. DNA was isolated from a mycelial scrape and extracted using a 10% Chelex solution (Safaee 2017). The internal transcribed spacer region was amplified with the ITS1/ITS4 primers (White et al. 1990) and PCR products were sequenced at Eurofins Scientific (Lewisville, KY). Isolates (BSS1, BSS2, BSS3, BSS4) were compared to other Biscogniauxia mediterranea sequences in the NCBI database (MG098274, EF026134) and had 100% sequence identity. Pathogenicity assays were conducted using 8-year-old Emory oaks in a greenhouse. The oaks were drought stressed and watered at 50% pot capacity for two months prior to inoculation. Each tree received approximately 2400 ml of water every two weeks for the remainder of the experiment. Eight trees were wounded three times with a 5mm corer. A 5mm plug of mycelium of isolate BSS2 was used to inoculate wounds. Four trees were used as controls and inoculated with ½ PDA plugs. Wounded and inoculated areas were assessed after three months. All eight trees exhibited dark necrotic tissue in the vascular cambium and lesions ranged from 11.4 - 25.8 mm in length and were 3.9 - 13.3 mm wide. The controls exhibited no fungal sign, lesions, or necrotic tissues. The pathogen B. mediterranea was recovered from 13 of the 24 total inoculations and its identity was confirmed with ITS sequencing. Mortality and die-back caused by Biscogniauxia spp. are commonly associated with drought-stressed trees, with increasingly hot and dry conditions routinely noted as inciting factors (Desprez Loustau et al.). Emory oaks are among the dominant tree species in much of the Madrean oak woodlands of the southwestern US and Mexico and provide vital ecological and cultural services. As southwestern states continue to experience hotter and drier, conditions, it is likely Emory oak will become increasingly susceptible to die-back and mortality due to this Biscogniauxia species (Southern et al.).

Insights into the restoration and sustainable management of Emory oak: A southwestern cultural keystone species

Emory oak acorns are a critically important commodity for Western Apache Tribal Nations, both as a food source and also for cultural and ceremonial uses. The Apache people historically inhabited much of Emory oak's range, but these lands are now divided among many entities, with the majority of trees occurring off-reservation in public domains. Based on observations of diminished acorn production and seedling recruitment, Apache Elders called for restoration and improved management of Emory oaks on public lands to ensure the long-term availability of acorns for Western Apache Tribes. Ecological information is critical to effectively design restoration efforts and successfully manage Emory oak, but little is known about Emory oak’s current ecological status on the landscape. Here, we use Forest Inventory and Analysis (FIA) data to examine factors that influence Emory oak distribution, abundance, and demography, and relate findings to observations made by Tribal Elders. We found that Emory oak distribution was constrained by metrics related to water availability. Drought and fire occurred frequently in Emory oak habitats, highlighting the likely importance of these disturbance events in determining oak population dynamics. Emory oak growth was predicted by environmental variables related to water availability, like physiographic class and elevation, and population characteristics, like stand age and size, but not by land ownership classifications. Interestingly, no environmental variables explained patterns of seedling recruitment and mortality perhaps owing to the stochastic nature of these events and the coarse temporal scale of FIA data in AZ. Drier, warmer conditions projected by climate models was shown to reduce future suitable Emory oak habitat, particularly in central AZ. Restoration efforts should focus on increasing water availability for Emory oaks and reducing the likelihood of high intensity fires. This could be accomplished, in part, by thinning competing vegetation at Emory oaks stands and restoring historical fire regimes. Given projections that suggest drier regional climatic patterns, strategic seed augmentation aimed at enhancing population resilience through selection of drought-adapted genotypes may also be warranted. Data were insufficient to confirm Apache Elders’ observations of diminished acorn production and seedling recruitment, highlighting the need for comprehensive demographic analyses of Emory oaks in the Southwest.

Fire regimes and structural changes in oak-pine forests of the Mogollon Highlands ecoregion: Implications for ecological restoration

Ponderosa pine (Pinus ponderosa) forests occur at their warmer, drier environmental limits in the Mogollon Highlands ecoregion (MHE) of the Southwestern United States, and are commonly found in stringers or discrete stands that form ecotones with interior chaparral. These “rear edge” forests are likely to be highly vulnerable to rapid changes in structure and composition with climate warming, drought, and wildfire. There is increasing interest in understanding historical conditions, ecosystem changes, and restoration needs for MHE forests. However, comprehensive reconstruction analysis of fire regimes and stand structure has not been done for these systems, which differ from many montane ponderosa pine forests by having an abundance of understory shrubs. In this study we used demographic data from field plots, fire scar samples, and dendroecology to reconstruct historical fire regimes and landscape structure at ponderosa pine-dominated sites that spanned a range of environmental conditions on the Prescott and Tonto National Forests. We found strong evidence of historical surface fire regimes with mean fire intervals ranging 1.3–15.6 years across the five MHE sites during the period 1700–1879. We found very little evidence of historical high-severity fire at any study site. Historical forest structure was open with tree densities ranging 84.7–136.4 trees ha−1 and stand basal area (BA) ranging 4.5–8.4 m2 ha−1. Historical composition showed codominance of ponderosa pine, Arizona white oak (Quercus arizonica), Emory oak (Q. emoryi), and Gambel oak (Q. gambelii). Thus, oak species and likely other hardwoods were important historical components of these ecosystems. Contemporary forests are greater in stand density and BA by 359–703% and 285–502%, respectively, compared to historical estimates. In addition, we observed contemporary shifts in species composition. Changes related to disruption of historical fire regimes have increased susceptibility of ponderosa pine forests in the MHE to rapid shifts in structure and composition that may come about with climate change and high-intensity wildfire. Meeting fuels reduction and ecological restoration goals will be challenging for land managers due to vigorous regeneration responses of shrubs to tree thinning, prescribed burning, or other management activities. Managers will be required to balance attention to historical reference conditions, conservation of biological diversity, and needs for fuels management.

Chemical Composition and In Vitro Bioaccessibility of Antioxidant Phytochemicals from Selected Edible Nuts.

The ultimate health benefits of peanuts and tree nuts partially depend on the effective gastrointestinal delivery of their phytochemicals. The chemical composition and in vitro bioaccessibility of tocopherols, tocotrienols and phenolic compounds from peanuts and seven tree nuts were evaluated by analytical and chemometric methods. Total fat and dietary fiber (g 100 g−1) ranged from 34.2 (Emory oak acorn) to 72.5 (pink pine nut; PPN) and from 1.2 (PPN) to 22.5 (pistachio). Samples were rich in oleic and linoleic acids (56–87 g 100 g−1 oil). Tocopherols and tocotrienols (mg·kg−1) ranged from 48.1 (peanut) to 156.3 (almond) and 0 (almond, pecan) to 22.1 (PPN) and hydrophilic phenolics from 533 (PPN) to 12,896 (Emory oak acorn); flavonoids and condensed tannins (mg CE.100 g−1) ranged from 142 (white pine nut) to 1833 (Emory oak acorn) and 14 (PPN) to 460 (Emory oak acorn). Three principal components explained 90% of the variance associated with the diversity of antioxidant phytochemicals in samples. In vitro bioaccessibility of tocopherols, tocotrienols, hydrophilic phenolics, flavonoids, and condensed tannins ranged from 11–51%, 16–79%, 25–55%, 0–100%, and 0–94%, respectively. Multiple regression analyses revealed a potential influence of dietary fiber, fats and/or unsaturated fatty acids on phytochemical bioaccessibility, in a structure-specific manner.

Tree mortality from a short-duration freezing event and global-change-type drought in a Southwestern piñon-juniper woodland, USA.

This study documents tree mortality in Big Bend National Park in Texas in response to the most acute one-year drought on record, which occurred following a five-day winter freeze. I estimated changes in forest stand structure and species composition due to freezing and drought in the Chisos Mountains of Big Bend National Park using permanent monitoring plot data. The drought killed over half (63%) of the sampled trees over the entire elevation gradient. Significant mortality occurred in trees up to 20 cm diameter (P < 0.05). Pinus cembroides Zucc. experienced the highest seedling and tree mortality (P < 0.0001) (55% of piñon pines died), and over five times as many standing dead pines were observed in 2012 than in 2009. Juniperus deppeana vonSteudal and Quercus emoryi Leibmann also experienced significant declines in tree density (P < 0.02) (30.9% and 20.7%, respectively). Subsequent droughts under climate change will likely cause even greater damage to trees that survived this record drought, especially if such events follow freezes. The results from this study highlight the vulnerability of trees in the Southwest to climatic change and that future shifts in forest structure can have large-scale community consequences.

Oak bark allometry and fire survival strategies in the Chihuahuan desert Sky Islands, Texas, USA.

Trees may survive fire through persistence of above or below ground structures. Investment in bark aids in above-ground survival while investment in carbohydrate storage aids in recovery through resprouting and is especially important following above-ground tissue loss. We investigated bark allocation and carbohydrate investment in eight common oak (Quercus) species of Sky Island mountain ranges in west Texas. We hypothesized that relative investment in bark and carbohydrates changes with tree age and with fire regime: We predicted delayed investment in bark (positive allometry) and early investment in carbohydrates (negative allometry) under lower frequency, high severity fire regimes found in wetter microclimates. Common oaks of the Texas Trans-Pecos region (Quercus emoryi, Q. gambelii, Q. gravesii, Q. grisea, Q. hypoleucoides, Q. muehlenbergii, and Q. pungens) were sampled in three mountain ranges with historically mixed fire regimes: the Chisos Mountains, the Davis Mountains and the Guadalupe Mountains. Bark thickness was measured on individuals representing the full span of sizes found. Carbohydrate concentration in taproots was measured after initial leaf flush. Bark thickness was compared to bole diameter and allometries were analyzed using major axis regression on log-transformed measurements. We found that bark allocation strategies varied among species that can co-occur but have different habitat preferences. Investment patterns in bark were related to soil moisture preference and drought tolerance and, by proxy, to expected fire regime. Dry site species had shallower allometries with allometric coefficients ranging from less than one (negative allometry) to near one (isometric investment). Wet site species, on the other hand, had larger allometric coefficients, indicating delayed investment to defense. Contrary to our expectation, root carbohydrate concentrations were similar across all species and sizes, suggesting that any differences in below ground storage are likely to be in total volume of storage tissue rather than in carbohydrate concentration.

Potential influence of plant chemicals on infectivity of Batrachochytrium dendrobatidis

We explored whether extracts of trees frequently found associated with amphibian habitats in Australia and Arizona, USA, may be inhibitory to the fungal pathogen Batrachochytrium dendrobatidis (Bd), which has been associated with global amphibian declines. We used salamanders Ambystoma tigrinum as the model system. Salamanders acquired significantly lower loads of Bd when exposed on leaves and extracts from the river red gum Eucalyptus camaldulensis, and loads were also low in some animals exposed on extracts of 2 oak species, Quercus emoryi and Q. turbinella. Some previously infected salamanders had their pathogen loads reduced, and some were fully cured, by placing them in leaf extracts, although some animals also self cured when housed in water alone. A significant number of animals cured of Bd infections 6 mo earlier were found to be resistant to reinfection. These results suggest that plants associated with amphibian habitats should be taken into consideration when explaining the prevalence of Bd in these habitats and that some amphibians may acquire resistance to the fungus if previously cured.

Collection History and Comparison of the Interactions of the Goldspotted Oak Borer,Agrilus auroguttatusSchaeffer (Coleoptera: Buprestidae), with Host Oaks in Southern California and Southeastern Arizona, U.S.A.

An invasive population of the goldspotted oak borer, Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), is colonizing and killing three species of oaks in San Diego Co., California. However, the interactions of A. auroguttatus with oaks in its native range in southeastern Arizona have not been recorded. We present a complete inventory of the North and Central American collection records of A. auroguttatus and Agrilus coxalis Waterhouse from the literature and from a survey of the holdings of 27 museum and personal collections. We also discuss the relationship between this collection history and the behavior of A. auroguttatus as an intracontinental invasive species. Surveys of native populations of A. auroguttatus in oak forest stands from four mountain ranges in southeastern Arizona revealed injury patterns on Emory oak, Quercus emoryi Torrey, and silverleaf oak, Quercus hypoleucoides A. Camus, similar to those observed on other “red” oaks in California. No damage was observed on “white” oaks in Arizona, and observed only rarely on a white oak, Quercus engelmannii Greene, in California. In Arizona, adult emergence was confirmed from bark removed from Q. emoryi, representing the first developmental record of A. auroguttatus from a native host. Late instars of Agrilus sp. were also recovered from Q. hypoleucoides, but they were not reared to the adult stage for species identification. Nonetheless, our observations of damage and the presence of larvae in the same configuration and location in the outer bark as we would expect for A. auroguttatus suggest that Q. hypoleucoides is also likely a host. Two hymenopteran parasitoids, Calosota elongata Gibson (Eupelmidae) and Atanycolus simplex Cresson (Braconidae), and two likely coleopteran predators (Trogossitidae and Elateridae) emerged from, or were collected in southeastern Arizona from, Q. emoryi bark infested with A. auroguttatus. Based on the museum survey results, the morphological similarity of individuals from the California and Arizona populations, the spatial dynamics of the pattern of infestation in California, the geographic isolation of hosts in California from native populations of the beetle, and the proximity of San Diego Co. to southeastern Arizona, we hypothesize that A. auroguttatus was introduced to California from Arizona or less likely from the Mexican states of Baja California, Chihuahua, or Sonora, and that the introduction most likely occurred on oak firewood. Further, we hypothesize that the oak mortality in southern California is occurring from this intracontinental invasive species because the beetle is filling a vacant niche by colonizing and developing in non-coevolved trees with low host resistance in the absence of a diverse and coevolved insect natural enemy complex.

The remarkably low leaf-selectivity prior to oviposition in the moth-pest Cameraria ohridella is not unique to this species within the genus Cameraria

Summary. — Cameraria ohridella, a recent leaf-mining invader of the horse-chestnut tree Aesculus hippocastanum, likely persists as a strong pest with unusually high levels of incidence. For example, among Cameraria moths, C. ohridella ordinarily features more than hundred times denser upon Aesculus leaflets than C. gr. guttifinitella is upon leaves of Quercus emoryi. There is general agreement to consider that the singular success of C. ohridella in mining Aesculus leaves mainly results from deficient top-down control, especially extremely low level of parasitoids efficiency. Another remarkable aspect of C. ohridella outbreaks however is the very high level of leaves acceptance (low selectivity) of females prior to egg-laying, which may often rise up near to 100 %. Would this low bottom-up control also feature (or not) as a specificity of this species within the genus Cameraria ? Using an appropriate indirect method, it is shown that the proportions of “ acceptable” leaves by ovipositing females are substantially similar (and high) in both Cameraria species (96 % and 78 % for Cameraria ohridella and C. gr. guttifinitella respectively), in spite of the dramatically different proportions of “ accepted” (= actually oviposited) leaves (89 % and 2 % respectively). In turn, this would contribute to make still more relevant the currently oriented focus upon top-down regulation as one of the major lever for a better control of Cameraria ohridella.

Description of Komagataella phaffii sp. nov. and the transfer of Pichia pseudopastoris to the methylotrophic yeast genus Komagataella

The new methanol-assimilating yeast species Komagataella phaffii Kurtzman sp. nov. (type strain NRRL Y-7556(T)=CBS 2612(T)) is described. Of the four known strains of this species, two were isolated from black oak trees in California, USA, one from an Emory oak in Arizona, USA, and one from an unidentified source in Mexico. The species forms hat-shaped ascospores in deliquescent asci and appears to be homothallic. Analysis of nucleotide sequences from domains D1/D2 of large-subunit (26S) rDNA separates the new species from Komagataella pastoris, the type species of the genus, and from Pichia pseudopastoris, which is here renamed Komagataella pseudopastoris (Dlauchy, Tornai-Lehoczki, Fulop & Peter) Kurtzman comb. nov. (type strain NRRL Y-27603(T)=CBS 9187(T)=NCAIM Y 01541(T)). On the basis of D1/D2 26S rDNA sequence analysis, the three species now assigned to the genus Komagataella represent a clade that is phylogenetically isolated from other ascomycetous yeast genera.

Growth and Volume of Emory Oak Coppice 10 Years After Thinning: A Case Study in Southeastern Arizona

Abstract Effects of stump diameter and thinning treatments at different ages of Emory oak (Quercus emoryi) coppice (stump-sprouts) are described in terms of growth and volume of the stump-sprouts 10 yr after the thinning treatments were applied. Growth and volume of the residual stump sprouts depend largely on the number of sprouts left after thinning; the effects of stump diameter were inconsistent. Harvesting cycles for fuelwood and other wood products obtained from stump-sprouts can be shortened through coppice thinning. Structural diversity following earlier harvesting and future wood production in oak woodlands dominated by Emory oak are “optimized” by retaining three stump-sprouts after thinning. West. J. Appl. For. 18(2):77–80.

DO FUNGAL ENDOPHYTES RESULT IN SELECTION FOR LEAFMINER OVIPOSITIONAL PREFERENCE?

Microorganisms can alter the direction and magnitude of plant–herbivore interactions. However, how they affect the susceptibility of the host plant and their impact on the herbivore may vary depending on the scale of the interaction such as among locations, individual plants, and parts of the plant. Positive preference–performance relationships for insects in general, and for sedentary insects such as leafminers in particular, would predict that there would be negative selection pressure against females ovipositing in low-performance sites. Thus, where the presence of microorganisms causes reduced performance, selection would favor oviposition in sites where the microbes are absent. However, this assumes that ovipositing females can detect the microbes and respond by avoidance, or that females can use cues that predict the future presence of microbes and use these predictors to respond by avoidance. We used the Cameraria sp. leafminer–Quercus emoryi system and the associated fungal endophyte species that ...

Do Fungal Endophytes Result in Selection for Leafminer Ovipositional Preference?

Microorganisms can alter the direction and magnitude of plant–herbivore interactions. However, how they affect the susceptibility of the host plant and their impact on the herbivore may vary depending on the scale of the interaction such as among locations, individual plants, and parts of the plant. Positive preference–performance relationships for insects in general, and for sedentary insects such as leafminers in particular, would predict that there would be negative selection pressure against females ovipositing in low-performance sites. Thus, where the presence of microorganisms causes reduced performance, selection would favor oviposition in sites where the microbes are absent. However, this assumes that ovipositing females can detect the microbes and respond by avoidance, or that females can use cues that predict the future presence of microbes and use these predictors to respond by avoidance. We used the Cameraria sp. leafminer–Quercus emoryi system and the associated fungal endophyte species that share the leaves of the host to test the hypothesis that leafminer ovipositional preference and therefore distribution are negatively associated with endophyte distribution at scales where endophytes mediate insect antagonism and where endophyte distribution is predictable. We censused fungal endophyte distribution and abundance on >20 trees over three growing seasons at the following scales: among trees, among positions within trees, among leaves, and between and within seasons. In addition, we censused leafminer distribution and abundance and used data on leafminer distributions at different spatial scales collected over the past decade from other studies in this system to determine how they are associated with endophytes. We found that leafminers and fungal endophytes were negatively associated at two spatial scales where endophytes have been shown to affect leafminer performance negatively and where endophyte distribution and abundance were predictable. Endophytes and leafminers were not associated at one spatial scale where endophytes do not affect leafminers, and distribution and abundance was not predictable. Leafminer growth and endophyte infection were positively associated over time as both increase over the season. The results demonstrate that leafminer ovipositional preference may have been selected by avoidance of fungal endophytes and associated endophyte-mediated antagonism, but that avoidance is reliant on predictable patterns of infection.

Nest-Site Characteristics and Nesting Success of the Greater Pewee in Arizona

Nest-Site Characteristics and Nesting Success of the Greater Pewee in Arizona

A microtiter plate procedure for evaluating fungal functional diversity

A method (FungiLog) was developed that allows a quantitative approach to examining aspects of fungal functional diversity. The BIOLOG microtiter plate method for measuring bacterial functional diversity was modified for use with fungal assemblages. Each BIOLOG plate contains 95 different carbon substrates. Eight different tetrazolium dyes were evaluated and dimethylthiazolyl-diphenyltetrazolium bromide (MTT) was chosen as the most suitable indicator of fungal growth. Procedures for inoculum preparation from a variety of substrates and inoculation into modified BIOLOG SF-N microplates were devised. By also plating out inoculum used to inoculate the FungiLog plates, taxonomic data can be obtained in conjunction with functional diversity. The FungiLog method was subsequently evaluated for detecting landscape patterns of fungal functional diversity using decaying lechuguilla (Agave lechuguilla) leaves placed along an elevational gradient in Big Bend National Park, Texas, in 5 vegetation zones. Sites ranged from a high elevation (2098 m) zone dominated by live oak (Quercus emoryi) and pinyon pine (Pinus cembroides) to a low land Chihuahuan Desert scrub (973 m). Ten, preweighed, 10-cm pieces of lechuguilla leaves were collected from each vegetation zone, 5 per transect, after 6 mo decomposition. FungiLog data were used to calculate two measures of fungal functional diversity, substrate richness and total activity. FungiLog patterns distinguished differences in total activity and substrate richness among the low elevational and the high elevational sites at this stage in the decomposition of lechuguilla leaves. Furthermore, litter decomposition was greater for sites with high fungal functional diversity.

A Microtiter Plate Procedure for Evaluating Fungal Functional Diversity

A method (FungiLog) was developed that allows a quantitative approach to examining aspects of fungal functional diversity. The BIOLOG microti- ter plate method for measuring bacterial functional diversity was modified for use with fungal assemblag- es. Each BIOLOG plate contains 95 different carbon substrates. Eight different tetrazolium dyes were eval- uated and dimethylthiazolyl-diphenyltetrazolium bro- mide (MTT) was chosen as the most suitable indi- cator of fungal growth. Procedures for inoculum preparation from a variety of substrates and inocu- lation into modified BIOLOG SF-N microplates were devised. By also plating out inoculum used to inoc- ulate the FungiLog plates, taxonomic data can be ob- tained in conjunction with functional diversity. The FungiLog method was subsequently evaluated for de- tecting landscape patterns of fungal functional diver- sity using decaying lechuguilla (Agave lechuguilla) leaves placed along an elevational gradient in Big Bend National Park, Texas, in 5 vegetation zones. Sites ranged from a high elevation (2098 m) zone dominated by live oak (Quercus emoryi) and pinyon pine (Pinus cembroides) to a low land Chihuahuan Desert scrub (973 m). Ten, preweighed, 10-cm pieces of lechuguilla leaves were collected from each vege- tation zone, 5 per transect, after 6 mo decomposi- tion. FungiLog data were used to calculate two mea- sures of fungal functional diversity, substrate richness and total activity. FungiLog patterns distinguished differences in total activity and substrate richness among the low elevational and the high elevational sites at this stage in the decomposition of lechuguilla leaves. Furthermore, litter decomposition was greater

Effects of biotic factors on emergence and survival of Quercus emoryi at lower treeline,Arizona, U.S.A.

Woody plants have increased in abundance in many of the world’s grasslands during the last three centuries. In contrast, Quercus emoryi Torr. has not encroached into adjacent grasslands for several centuries. The objective of this study was to identify potential constraints on emergence and survival of Quercus emoryi at the boundary between oak woodland and semi-desert grassland. We established a large-scale field experiment at this boundary in southern Arizona, U.S.A. Emergence of Q. emoryi seedlings occurred only during years in which supplemental water was added to experimental plots (1993, 1995), and emergence was lower in grassland than within adjacent intact woodland or cleared woodland. Seedling survival of both cohorts was reduced by herbaceous interference; survival of the 1993 cohort was greater in cleared woodland than in intact woodland or grassland, and survival of the 1995 cohort was reduced by vertebrate herbivory. Seedling mortality was almost always attributed to desiccation. Biotic factors (e.g., herbaceous interference, vertebrate herbivory) can reduce seedling emergence and survival; however, their effects become important only after abiotic constraints are overcome. Thus, we conclude that abiotic factors exert primary control in structuring the boundary of these communities. In addition, our research supports the interpretation that the lower treeline in this system is currently static.

Effects of timing of precipitation and acorn harvest date on emergence of Quercus emoryi

Abstract. Germination of semi‐arid Quercus is strongly correlated with the rainy season. However, the timing and amount of summer precipitation in the southwestern United States is extremely variable. Ongoing and impending changes in global and regional climates are likely to increase this variability. Specifically, anthropogenically induced changes in general circulation patterns may alter the seasonal distribution of precipitation in a directional manner. In addition to climatic variability, the inter‐ and intra‐annual variability of Quercus emoryi Torr. (Emory oak) acorn maturation also is high. Therefore, in light of existing climatic variability and potential future climate change, we conducted a greenhouse experiment to investigate the effects of acorn maturation date and the timing of the onset of the ‘monsoon’ on emergence of Q. emoryi seedlings.Acorns were collected at weekly intervals in July of 1995 and 1996, planted in a greenhouse, and subjected to different watering treatments. Watering treatments were (1) acorns watered the same day as planting; (2) acorns watered two weeks after planting; (3) acorns watered four weeks after planting. Emergence in 1995 was significantly greater in the last week of acorn maturation and decreased significantly as time to the onset of the ‘monsoon’ increased. Emergence in 1996 was very low, presumably because of soil moisture contents that were lower than those observed in 1995. The dependence of Q. emoryi on water for emergence has profound implications for Q. emoryi recruitment in the face of current climatic variability and future climate change. Summers with a delayed ‘monsoon’ and decreased soil moisture may severely constrain recruitment of this woody plant.

Spatial and temporal soil moisture resource partitioning by trees and grasses in a temperate savanna, Arizona, USA.

Stable isotope analysis was used to determine sources of water used by coexisting trees and grasses in a temperate savanna dominated by Quercus emoryi Torr. We predicted that (1) tree seedlings and bunchgrasses utilize shallow sources of soil water, (2) mature savanna trees use deeper sources of water, and (3) trees switch from shallow to deep water sources within 1 year of germination. We found that Q. emoryi trees, saplings, and seedlings (about 2 months, 1 year, and 2 years old), and the dominant bunchgrass [Trachypogon montufari (H.B.K.) Nees.] utilized seasonally available moisture from different depths within the soil profile depending on size/age relationships. Sapling and mature Q. emoryi acquired water from >50 cm deep, 2-month-old seedlings utilized water from <15 cm, and 1- and 2-year-old seedlings and grasses used water from between 20 cm and 35 cm. This suggests that very young seedlings are decoupled from grasses in this system, which may facilitate germination and early establishment of Q. emoryi within extant stands of native grasses. The potential for subsequent interaction between Q. emoryi and native grasses was evidenced by similar patterns of soil water use by 1- and 2-year-old seedlings and grasses. Q. emoryi seedlings did not switch from shallow to deep sources of soil water within 2 years of germination: water use by these seedlings apparently becomes independent of water use by grasses after 2 years of age. Finally, older trees (saplings, mature trees) use water from deeper soil layers than grasses, which may facilitate the stable coexistence of mature trees and grasses. Potential shifts in the seasonality of precipitation may alter interactions between woody plants and grasses within temperate savannas characterized by bimodal precipitation regimes: reductions in summer precipitation or soil moisture may be particularly detrimental to warm-season grasses and seedlings of Q. emoryi.