Quercus Lobata Research Articles

Landscape position mediates drought vulnerability in California valley oak (Quercus lobata)

Future climate change will exacerbate drought stress in water-limited ecosystems. However, topography can alter the fine-scale climatic and hydrologic conditions that mediate plant response to meteorological drought. Here, with six new valley oak (Quercus lobata) tree-ring width chronologies, we assess how topography acts as a mediating factor on tree growth and drought sensitivity. Because valley oaks are known to be highly dependent on subsurface water, we predicted that trees growing in riparian sites would be less sensitive to precipitation variability due to greater access to groundwater. Trees were sampled in the Tehachapi Mountains of California across a landscape gradient of sites ranging from 375–1650 m elevation and across upland (55–69 m mean height above nearest drainage) and riparian (2–6 m mean height above the nearest drainage) hillslope positions. Interannual tree growth patterns and drought sensitivity varied substantially in association with hillslope position and elevation. Valley oak radial growth showed a consistently weaker response to precipitation at riparian sites. The influence of hillslope position on drought sensitivity varied with elevation, such that the riparian buffering effect was weakest at sites higher in the watershed and strengthened, progressively, toward the lower elevation sites with greater climatic water deficit. Upland tree growth exhibited a strong response to high-frequency interannual precipitation variability at the high elevation site, whereas trees at lower elevation upland sites responded more to low-frequency decadal trends in precipitation, possibly reflecting hydrogeological processes by which precipitation feeds groundwater lower in the watershed. Our results are consistent with groundwater-dependence of valley oak and indicate that riparian habitats are the most likely refugia for the species during prolonged drought.

Cynipid wasps systematically reprogram host metabolism and restructure cell walls in developing galls.

Many insects have evolved the ability to manipulate plant growth to generate extraordinary structures called galls, in which insect larva can develop while being sheltered and feeding on the plant. In particular, cynipid (Hymenoptera: Cynipidae) wasps have evolved to form morphologically complex galls and generate an astonishing array of gall shapes, colors, and sizes. However, the biochemical basis underlying these remarkable cellular and developmental transformations remains poorly understood. A key determinant in plant cellular development is cell wall deposition that dictates the physical form and physiological function of newly developing cells, tissues, and organs. However, it is unclear to what degree cell walls are restructured to initiate and support the formation of new gall tissue. Here, we characterize the molecular alterations underlying gall development using a combination of metabolomic, histological, and biochemical techniques to elucidate how valley oak (Quercus lobata) leaf cells are reprogrammed to form galls. Strikingly, gall development involves an exceptionally coordinated spatial deposition of lignin and xylan to form de novo gall vasculature. Our results highlight how cynipid wasps can radically change the metabolite profile and restructure the cell wall to enable the formation of galls, providing insights into the mechanism of gall induction and the extent to which plants can be entirely reprogrammed to form unique structures and organs.

A first draft genome of holm oak (Quercus ilex subsp. ballota), the most representative species of the Mediterranean forest and the Spanish agrosylvopastoral ecosystem "dehesa".

The holm oak (Quercus ilex subsp. ballota) is the most representative species of the Mediterranean Basin and the agrosylvopastoral Spanish "dehesa" ecosystem. Being part of our life, culture, and subsistence since ancient times, it has significant environmental and economic importance. More recently, there has been a renewed interest in using the Q. ilex acorn as a functional food due to its nutritional and nutraceutical properties. However, the holm oak and its related ecosystems are threatened by different factors, with oak decline syndrome and climate change being the most worrying in the short and medium term. Breeding programs informed by the selection of elite genotypes seem to be the most plausible biotechnological solution to rescue populations under threat. To achieve this and other downstream analyses, we need a high-quality and well-annotated Q. ilex reference genome. Here, we introduce the first draft genome assembly of Q. ilex using long-read sequencing (PacBio). The assembled nuclear haploid genome had 530 contigs totaling 842.2Mbp (N50 = 3.3Mbp), of which 448.7Mb (53%) were repetitive sequences. We annotated 39,443 protein-coding genes of which 94.80% were complete and single-copy genes. Phylogenetic analyses showed no evidence of a recent whole-genome duplication, and high synteny of the 12 chromosomes between Q. ilex and Quercus lobata and between Q. ilex and Quercus robur. The chloroplast genome size was 142.3Kbp with 149 protein-coding genes successfully annotated. This first draft should allow for the validation of omics data as well as the identification and functional annotation of genes related to phenotypes of interest such as those associated with resilience against oak decline syndrome and climate change and higher acorn productivity and nutraceutical value.

Vehicle pollution is associated with elevated insect damage to street trees

Abstract Vehicle pollution is a pervasive aspect of anthropogenic change across rural and urban habitats. The most common emissions are carbon‐ or nitrogen‐based pollutants that may impact diverse interactions between plants and insect herbivores. However, the effects of vehicle pollution on plant‐insect interactions are poorly understood. Here, we combine a city‐wide experiment across the Sacramento Metropolitan Area and a laboratory experiment to determine how vehicle emissions affect insect herbivory and leaf nutritional quality. We demonstrate that leaf damage to a native oak species (Quercus lobata) commonly planted across the western US is substantially elevated on trees exposed to vehicle emissions. In the laboratory, caterpillars preferred leaves from highway‐adjacent trees and performed better on leaves from those same trees. Synthesis and applications. Together, our studies demonstrate that the heterogeneity in vehicle emissions across cities may explain highly variable patterns of insect herbivory on street trees. Our results also indicate that trees next to highways are particularly vulnerable to multiple stressors, including insect damage. To combat these effects, urban foresters may consider planting trees that are less susceptible to insect herbivory along heavily travelled roadways.

Fungal communities associated with acorn woodpeckers and their excavations

Wood-decay fungi soften wood, putatively providing opportunities for woodpeckers to excavate an otherwise hard substrate, yet the fungal community composition in tree cavities and the specificity of these relationships is largely unknown. We used high-throughput amplicon sequencing of the fungal ITS2 region to examine the fungal communities associated with acorn woodpeckers ( Melanerpes formicivorus ) and their cavities in mature valley oak ( Quercus lobata ) and blue oak ( Q. douglasii ) trees in an oak savannah of central coastal California, USA. Acorn woodpeckers and their excavations harbored over 1500 fungal taxa, including more than 100 putative wood-decay fungi. The fungal communities found on the birds were more similar to those found in excavated cavities than those found in trees without excavated holes. These results suggest that symbiotic associations between acorn woodpeckers and fungi are highly diverse, with low specificity. Symbiotic associations between cavity-excavators and fungi are likely more common and widespread than previously thought.

High-quality genome and methylomes illustrate features underlying evolutionary success of oaks

The genus Quercus, which emerged ∼55 million years ago during globally warm temperatures, diversified into ∼450 extant species. We present a high-quality de novo genome assembly of a California endemic oak, Quercus lobata, revealing features consistent with oak evolutionary success. Effective population size remained large throughout history despite declining since early Miocene. Analysis of 39,373 mapped protein-coding genes outlined copious duplications consistent with genetic and phenotypic diversity, both by retention of genes created during the ancient γ whole genome hexaploid duplication event and by tandem duplication within families, including numerous resistance genes and a very large block of duplicated DUF247 genes, which have been found to be associated with self-incompatibility in grasses. An additional surprising finding is that subcontext-specific patterns of DNA methylation associated with transposable elements reveal broadly-distributed heterochromatin in intergenic regions, similar to grasses. Collectively, these features promote genetic and phenotypic variation that would facilitate adaptability to changing environments.

THE ROLE OF WINTER PRECIPITATION AS A CLIMATIC DRIVER OF THE SPRING PHENOLOGY OF FIVE CALIFORNIA QUERCUS SPECIES (FAGACEAE)

Understanding the phenological sensitivity of keystone plant species, such as oaks, to climate variables provides a foundation for assessing the impacts of changing climate on ecosystem resilience, biodiversity, and carbon sequestration. This study assessed the responsiveness of bud burst, flowering, and fruiting phenophases of five native California oaks to climate variables using 2012–2019 USA National Phenology Network data, which are contributed by scientists and trained volunteers. Climate data included seasonal measurements of precipitation and maximum and minimum temperatures. Phenophase data for five oak species: Quercus agrifolia Née and Quercus kelloggii Newb. from Quercus section Lobatae (red oaks), Quercus douglasii Hook. & Arn., Quercus garryana Douglas ex Hook., and Quercus lobata Née from Quercus section Quercus (white oaks) were analyzed. The majority of the trees in the study were located in California, although a small number of sites were beyond their normal distribution ranges. No significant differences were found among species for bud burst and fruiting onsets using ANOVA and Tukey HSD tests. However, significant differences were identified between the flowering onsets of the white oaks Quercus lobata and Quercus douglasii and between Quercus lobata and the red oak Quercus agrifolia. Multiple regression models identified the strongest climate predictors of oak phenophase onset as: (1) winter precipitation, (2) mean accumulated precipitation, and (3) maximum winter temperature, so that winter precipitation and temperature have been found to be the main climate drivers of vegetative growth and reproductive potential for these native California oaks.

BUDBURST TIMING OF VALLEY OAKS AT HASTINGS RESERVATION, CENTRAL COASTAL CALIFORNIA

We studied the timing of budburst of valley oak (Quercus lobata Née) at Hastings Reservation, central coastal California. Similar to other taxa, budburst was advanced by warmer temperatures. Over the 30-year study period, however, there were no significant trends in either air temperature or the timing of budburst, except during the 2014–2016 drought, during which the earliest budburst dates were advanced. Several individual tree characteristics correlated with budburst timing, including access to ground water, soil available phosphorus, and elevation, the effects of which were in turn correlated with winter microclimatic conditions of individual trees. Budburst timing was significantly related to both subsequent acorn production and radial growth; trees leafing out on or near the population mean for the year experienced greater radial growth and produced larger acorn crops than trees leafing out earlier or later than the mean. Differences in acorn production were due to both differences in phenology among trees and plasticity in the phenology of individual trees across years, while differences in radial growth were primarily due to plasticity in individual tree phenology. Valley oak phenology exhibits considerable variability; the extent to which this plasticity will help this keystone California species adapt to future climate change remains to be seen.

TIMING OF BUD BURST IS ASSOCIATED WITH CLIMATE OF MATERNAL ORIGIN IN QUERCUS LOBATA PROGENY IN A COMMON GARDEN

Deciduous trees leaf out in the spring beginning with bud burst. Proximally, the timing of that process is triggered by temperature, but natural selection on bud burst timing may have acted in local populations through additional factors, such as frost damage, insect herbivores and fungal pathogens. Valley Oak, Quercus lobata Née, is a deciduous California endemic tree species that shapes the ecosystems where it is found. We examined the phenology of spring bud burst in trees collected from 674 maternal families across the species range, grown in two replicate common gardens. We found significant differences among the families for timing of bud burst, and also found that onset of bud burst differed between gardens, presumably due to climate. The differences among families were associated with the climate of origin where the trees were collected suggesting that some extent of genetic differentiation in bud burst is due to local adaptation. Given predicted changes in climate in California for the future, understanding patterns of bud burst will help inform the selection of seed sources for reforestation efforts.

The complex trophic community of Disholcaspis eldoradensis, a sucrose‐secreting cynipid gall wasp of Quercus lobata

1. Galls of some species of cynipid wasps produce a sugary secretion that attracts ants, which are thought to defend gall‐inducers against natural enemies, although evidence in support of this hypothesis is mixed. Some discrepancies may be explained by the complexity of the multitrophic interactions, which involve multiple ant and parasitoid species, and which are influenced by gall size and aggregation. The gall exudate also affects these relationships, although secretion patterns and possible host plant impacts appear to be unstudied.2. We studied Disholcaspis eldoradensis Beutenmuller (Hymenoptera:Cynipidae) galls on Quercus lobata Née (Fagaceae) and its interactions with ants and parasitoids. We used exclusion experiments to test the defensive benefits of ants and timing of parasitoid oviposition, and we measured how gall size, aggregation, and ant visitation influence these interactions. In addition, we measured variation in sucrose secreted by galls during larval development.3. Ants benefited gall inducers in 2018, but not 2019. Over 80% of visits observed were from invasive ants. Gall aggregation was not associated with parasitism, gall inducer success, or visitation by ants. During 2018, gall size was inversely correlated with the chance of parasitism and positively correlated with gall inducer biomass, whereas in 2019, parasitoid community composition varied with gall size. Sucrose secretion varied widely among galls and through time.4. Facultative mutualisms between ants and sugar‐secreting galls are complex and likely vary through time depending on local ecological circumstances. Gall secretions warrant increased attention and may impose a substantial burden on some host plant photosynthetic budgets.

The EpiDiverse Plant Epigenome-Wide Association Studies (EWAS) Pipeline.

Bisulfite sequencing is a widely used technique for determining DNA methylation and its relationship with epigenetics, genetics, and environmental parameters. Various techniques were implemented for epigenome-wide association studies (EWAS) to reveal meaningful associations; however, there are only very few plant studies available to date. Here, we developed the EpiDiverse EWAS pipeline and tested it using two plant datasets, from P. abies (Norway spruce) and Q. lobata (valley oak). Hence, we present an EWAS implementation tested for non-model plant species and describe its use.

Genome-Wide Variation in DNA Methylation Predicts Variation in Leaf Traits in an Ecosystem-Foundational Oak Species

Epigenetic modifications such as DNA methylation are a potential mechanism for trees to respond to changing environments. However, it remains controversial the extent to which DNA methylation impacts ecologically important traits that influence fitness. In this study, we used reduced-representation bisulfite sequencing to associate genomic and epigenomic variation with seven phenotypic traits related to growth, leaf function, and disease susceptibility in 160 valley oak (Quercus lobata) saplings planted across two common gardens in California. We found that DNA methylation was associated with a significant fraction of phenotypic variance in plant height, leaf lobedness, powdery mildew infection, and trichome density. Two of the seven traits were significantly associated with DNA methylation in the CG context, three traits were significantly associated with CHG methylation, and two traits were significantly associated with CHH methylation. Notably, controlling for genomic variation in SNPs generally reduced the amount of trait variation explained by DNA methylation. Our results suggest that DNA methylation may serve as a useful biomarker to predict phenotypic variation in trees, though it remains unclear the degree to which DNA methylation is a causal mechanism driving phenotypic variation in forest tree species.

Retention of green leaves not brown leaves increases spring cynipid diversity on large valley oaks

Plants can retain either physiologically active green leaves or inactive brown leaves over winter. Research has suggested that leaf retention incurs a cost due to higher herbivore load in the following year; however, no distinction has, thus, far been made between retention of green and brown leaves. We surveyed the over-winter retention of physiologically active green and inactive brown leaves of valley oaks (Quercus lobata) and examined their relationship with the diversity and density of 15 gall-making cynipid wasp species. Cynipid diversity in the spring was 8.2-fold greater on larger trees with more green leaf retention. Brown leaf retention was not associated with spring cynipid diversity, but was related to a substantial 20-fold reduction in spring cynipid densities on large trees. Retention of either leaf type was generally a poor predictor of summer cynipid diversity and density. Overall, green leaf retention better explained cynipid diversity, but brown leaf retention better explained cynipid densities. These differing effects may be explained by the fact that green leaves provide a common cue used by herbivores to find a suitable host. Retained brown leaves, however, may be an ecological trap for over-winter gall wasps that normally drop to the ground.

Victoria L. Sork—Recipient of the 2020 Molecular Ecology Prize

Victoria L. Sork—Recipient of the 2020 Molecular Ecology Prize

Landscape genomics of Quercus lobata reveals genes involved in local climate adaptation at multiple spatial scales.

Understanding how the environment shapes genetic variation provides critical insight about the evolution of local adaptation in natural populations. At multiple spatial scales and multiple geographic contexts within a single species, such information could address a number of fundamental questions about the scale of local adaptation and whether or not the same loci are involved at different spatial scales or geographic contexts. We used landscape genomic approaches from three local elevational transects and rangewide sampling to (a) identify genetic variation underlying local adaptation to environmental gradients in the California endemic oak, Quercus lobata; (b) examine whether putatively adaptive SNPs show signatures of selection at multiple spatial scales; and (c) map putatively adaptive variation to assess the scale and pattern of local adaptation. Of over 10k single-nucleotide polymorphisms (SNPs) generated with genotyping-by-sequencing, we found signatures of natural selection by climate or local environment at over 600 SNPs (536 loci), some at multiple spatial scales across multiple analyses. Candidate SNPs identified with gene-environment tests (LFMM) at the rangewide scale also showed elevated associations with climate variables compared to the background at both rangewide and elevational transect scales with gradient forest analysis. Some loci overlap with those detected in other oak species, raising the question of whether the same loci might be involved in local climate adaptation in different congeneric species that inhabit different geographic contexts. Mapping landscape patterns of adaptive versus background genetic variation identified regions of marked local adaptation and suggests nonlinear association of candidate SNPs and environmental variables. Taken together, our results offer robust evidence for novel candidate genes for local climate adaptation at multiple spatial scales.

Matching species traits and microsites improves regeneration in mixed oak woodlands

AbstractQuestionWorldwide, mixed oak woodlands regenerate poorly due to different anthropogenic impacts. Our question is whether spatial distribution (regeneration microsite) of oak recruits is determined by different biotic and abiotic stress agents and whether recruits of co‐occurring oak species may respond differently to each source of stress.LocationMediterranean California mixed oak woodlands.MethodsWe recorded the main regeneration microsites of four co‐occurring oak species (Quercus lobata, Q. douglasii, Q. kelloggii and Q. agrifolia) in 25 belt transects in a nature reserve and identified the main stress agent for each species and microsite. We also analyzed their response to stress through physiological parameters (chlorophyll, flavonol, anthocyanin and nitrogen).ResultsQ. agrifolia and Q. lobata seedlings mostly established under shrubs and trees, respectively. The other species did not have a prime regeneration microsite. Biotic stress occurred more frequently than abiotic (drought) stress for all species. Regarding biotic sources of stress, the deciduous Q. lobata, Q. douglasii and Q. kellogii showed high browsing damage; insect damage was light and occurred mostly in the evergreen Q. agrifolia whereas fungal damage was significantly lower in Q. douglasii. Physiologically, all oak species responded similarly to stress agents although Q. douglasii and Q. kelloggii showed higher chlorophyll content than Q. agrifolia and Q. lobata, which might be related to differences in resilience.ConclusionsDeciduous oaks are particularly vulnerable to overgrazing whereas the evergreen Q. agrifolia seems more affected by fungal and insect damage. Management aimed at the co‐existence of deciduous and evergreen oaks should consider the enhancement of microsites that best ameliorate the impact of predicted stress agents but also the oak physiological responses (i.e. resilience) to each stress agent. We suggest keeping low ungulate densities and carefully consider the species selection in assisted regeneration projects depending on the predominant stress agent and microsite.

VARIATION IN LEAF SHAPE IN A QUERCUS LOBATA COMMON GARDEN: TESTS FOR ADAPTATION TO CLIMATE AND PHYSIOLOGICAL CONSEQUENCES

Oak leaf morphology is highly variable. Leaf shape in oaks has been shown to covary with climate, and leaf dissection is negatively correlated with hydraulic resistance. Such patterns may reflect local adaptation of genotypes or plastic responses to local environments. We tested two hypotheses regarding variation in leaf shape in Quercus lobata Nee, a widely distributed oak tree endemic to California, using subsamples of trees from a large provenance trial involving source populations throughout the species range. First, we tested the hypothesis that variation in leaf dissection (perimeter · area–1) and specific leaf area could be explained by adaptation to climate. If so, we predicted that the progeny of trees originating from contrasting climates would also contrast in leaf dissection or specific leaf area when grown in a common environment. Second, we tested the hypothesis that variation in leaf dissection is associated with photosynthetic rate. Because dissection affects hydraulic resistance and heat transfer, more dissected leaves are thought to experience lower water stress. If so, we predicted that individuals with more dissected leaves would maintain higher rates of photosynthesis than those with less dissected leaves, especially during hot and dry conditions. We found no association of leaf traits with maternal climate, but we observed a positive relationship between leaf dissection and photosynthetic rates. This result suggests variation in leaf shape may have functional consequences and influence how valley oaks cope with environmental stress in California's Mediterranean climate.

Plant Communities of Economically Valuable Forest-Forming Species of the Orenburg Region

The article provides an analysis of their sinusial structure, the species composition of vascular plants of the Ural River floodplain within the steppe zone is studied in detail. For the first time, a classification has been carried out for the study area and a phytocenological characteristic of all tree-shrub vegetation has been compiled; patterns of ecological-dynamic changes in the types of floodplain forests are revealed. It has been established that the Tilia cordata and Quercus robur formations are quite rare for the territory of the Orenburg region. The growth class of oak forests is assessed in grades II – IV, and linden forests in grades III. Two groups of types of oak forests are characteristic of the floodplain of the study area: blackberry oak and lily of the valley oak. Linden associations are represented by two-tier plantations. Tilia cordata dominates in the first tier, Ulmus laevis and Quercus robur form the second tier. A decrease in the floodplain area under Quercus robur and Tilia cordata on the territory of the Ilek and Tashlinsky forestries was noted. Phytocenoses are transformed by replacing Quercus robur formations with Ulmus laevis formations.

Identification of starch granules from oak and grass species in the central coast of California

Starch granule analysis is commonly used to describe the incorporation of plants into past human diets. However, assigning starch granules to particular plant taxa can be problematic. Here we take a statistical approach to analyzing multiple diagnostic characteristics of starch granules from three species of oak, Quercus agrifolia (coast live oak), Q. douglasii (blue oak), Q. lobata (valley oak) and one species of wild rye (Elymus elymoides) that were collected and consumed by hunter-gatherers in California. Results show significant differences in maximum length and the presence of morphological features (e.g., lamellae, extinction cross, mesial longitudinal clefts, fissures, shape, hilum position, etc.), suggesting that taxonomic assignment of archaeological starch granules can be made with measurable degrees of confidence.

Walnut twig beetle landing rates differ between host and nonhost hardwood trees under the influence of aggregation pheromone in a northern California riparian forest

Abstract Host selection behaviour of the walnut twig beetle (WTB) among hardwood trees was investigated in a riparian forest in northern California by monitoring the landing rate of the beetle with sticky traps on branches baited with 3‐methyl‐2‐buten‐1‐ol, the male‐produced aggregation pheromone. The assay was conducted over 7 days (22 May to 29 May 2017) and compared landing rates on branches of six nonhost species paired with northern California black walnut, Juglans hindsii (the host). A total of 2242/1192 WTB were collected on branches of host/nonhost pairs, and more WTB landed on J. hindsii than on nonhosts in 42 of 58 instances. Female landing rate generally exceeded male landing rate, which underscores the influence of the male‐produced synthetic pheromone in this system. Landing rates of WTB males, females, and the combined sexes on boxelder, Acer negundo, and valley oak, Quercus lobata, did not differ significantly from the landing rates on J. hindsii, suggesting that these two nonhost riparian hardwoods do not repel WTB (in the context of the aggregation pheromone). Significantly fewer WTB landed on Oregon ash, Fraxinus latifolia, river red gum, Eucalyptus camaldulensis, Fremont cottonwood, Populus fremontii, and red willow, Salix laevigata, than on J. hindsii, which suggests that these four nonhosts may repel one or both sexes of WTB in the context of the aggregation pheromone. Future analysis of the volatiles from these four hardwood species may lead to the discovery of semiochemical repellents for WTB.