Native Shrub Species Research Articles

SEASONAL CHANGE OF CHLOROPHYLL CONTENT (SPAD VALUE) IN SOME TREE AND SHRUB SPECIES

Chlorophyll, which is of vital importance for living things, is the main active ingredient of photosynthesis, and the amount of chlorophyll in the plant can show very sensitive responses to various environmental factors, especially site conditions and plant species. In this study, it was aimed to determine the change of chlorophyll content (SPAD value) at the beginning (20 May) and the end (15 October) of growth period in some native and exotic tree and shrub species in Kanuni campus of Karadeniz Technical University and to reveal the differences between the species. Within the scope of the study, measurements were made on a total of 20 species including five native (Quercus hartwissiana Steven, Fagus orientalis Lipsky, Ulmus minör Mill., Liquidambar orientalis Mill., Quercus pubescens Willd.) and seven exotic (Eucalyptus camadulensis Dehnh., Ginkgo biloba L., Quercus castaneifolia C.A.Mey., Cinnamomum camphora (L.) Sieb., Acer negundo L., Quercus rubra L., Aesculus hippocastanum L.) tree species and seven native (Cercis siliquastrum L., Laurus nobilis L., Osmanthus decorus (Boiss.&Balansa) Kasapligil, Laurocerasus officinalis M.Roem., Ostrya carpinifolia Scop., Corylus avellana L., Arbutus unedo L.) and one exotic (Weigela coraensis Thunb.) shrub species. Chlorophyll content was determined with four replications by portable chlorophyll meter (Minolta SPAD-502, Osaka, Japan) which indirectly measures the amount of chlorophyll in the leaf. The data obtained were subjected to Wilcoxon test, variance analysis (one-way ANOVA) and Duncan’s test by using SPSS 23.0 statistical program. As a result of the study, it was determined that there are statistically significant differences (p

Antibacterial, Mutagenic Properties and Chemical Characterisation of Sugar Bush (Protea caffra Meisn.): A South African Native Shrub Species.

Protea caffra is used as a diarrhoeal remedy in South African herbal medicine, however, its pharmacological properties remain largely unknown. In the present study, extracts from different Protea caffra organs were screened against drug-sensitive and -resistant diarrhoeagenic pathogens using the microdilution assay (minimum inhibitory concentration, MIC). Twig extracts (70% methanol, MeOH) of the plant were purified and the resultant fractions screened for antibacterial properties (MIC). The chemical profiles of the fractions were determined by Gas Chromatography-Mass Spectrometry (GC-MS), while ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) was used to quantify the phenolic acids in the plant. The mutagenic properties of bioactive extracts were assessed using the Ames test. The extracts demonstrated weak-moderate antibacterial properties (MIC: 0.3–0.6 mg/mL). A cold ethyl acetate fraction of MeOH twig extract exhibited significant antibacterial properties (MIC = 0.078 mg/mL) against Enterococcus faecalis. The presence of antibacterial compounds (1-adamantane carboxylic acid, heptacosanol, levoglucosan, nonadecanol) in the plant was putatively confirmed based on GC-MS analysis. Furthermore, UHPLC-MS/MS analysis revealed varying concentrations of phenolic acids (0.08–374.55 µg/g DW). Based on the Ames test, the extracts were non-mutagenic thereby suggesting their safety. To a certain degree, the current study supports the traditional use of Protea caffra to manage diarrhoea among local communities in South Africa.

Optimal water and fertilizer applications improve growth of Tamarix chinensis in a coal mine degraded area under arid conditions.

Coal-mined areas are often associated with hostile environmental conditions where the scarcity of water and key nutrient resources negatively affect plant growth and development. In this study we specifically addressed how different combinations of water (W), nitrogen (N) and phosphorus (P) might affect morpho-physiological and biochemical attributes of a native shrub species, Tamarix chinensis, grown on coal mine spoils. Our results show that under greenhouse conditions the application of moderate-to-high doses of W, N and P considerably improved growth-associated parameters (i.e. plant height, stem diameter, dry weight), as well as gas-exchange parameters, photosynthetic pigment contents and leaf water status of T. chinensis. Under field conditions high W and low N, P doses led to significant increases in plant growth-associated traits, gas-exchange parameters and leaf water status. Plant growth was generally higher under greenhouse conditions mainly because seedlings faced multiple stress when growing under field conditions. Low W-regime, regardless of N-P additions, improved osmotic adjustments in leaf tissues and also boosted the activity of several antioxidant enzymes to reduce the oxidative stress associated with W scarcity under greenhouse conditions. Importantly, our study shows how maximum growth performance of T. chinensis under field conditions was achieved at W, N and P doses of 150 mm year-1 , 80 kg ha-1 and 40 kg ha-1 , respectively. Our findings suggest that achieving optimal rates of W, N and P application is crucial for promoting the ecological restoration of coal-mined areas with T. chinensis under arid environmental conditions.

A comparative analysis of the community of carabid beetles associated with two native xerophytic shrub species (Atriplex halimus L. and Artemisia herba alba L.) in the semi-arid zone of Algeria

The distribution of carabid beetles in two xerophytic native shrub species was studied by pitfall trapping during four years, in a semi-arid zone of Algeria. A total of 51 beetle species were recorded; 38 and 23 species were encountered in the Atriplex halimus and the Artemisia herba alba L. shrub habitats, respectively. Differences were found in the beetle species richness and abundance among the sampled shrubs and the years of study. The data of the species traits as habitat affinity, food preference and flying ability show that xerophilic, carnivorous and macropterous species dominate in both shrub habitats. In the Atriplex halimus habitat, which has a dense vegetation cover and high humidity conditions, granivorous and hygrophilous species were more numerous. Analysis revealed a significant correlation between beetle abundance and inter-annual rainfall change and a low affinity between the species assemblages of both shrub habitats. Our results suggest that shrub size and species identity play an important role in structuring ground beetle communities.

Plant-Soil Feedback Effects on Germination and Growth of Native and Non-Native Species Common across Southern California

Changes in plant assemblages can influence biotic and abiotic soil conditions. These changes can cause plant–soil feedbacks that can inhibit or facilitate plant germination and growth. Here, we contribute to a growing literature examining plant–soil feedbacks in the endangered sage scrub ecosystem by examining the germination and growth of Artemisia californica, the dominant native shrub species in the ecosystem, in soil conditioned by two widespread plant invaders (Brassica nigra, Bromus madritensis ssp. rubens), and the germination and growth of these invasive species in conspecific and heterospecific soils. Our findings suggest that: (i) A. californica soils can limit establishment of some species (B. nigra) but not others (B. madritensis), (ii) A. californica soil conditions reduce growth of all plant species, and (iii) non-natives are negatively impacted by soil microbes, but in some contexts can do better in heterospecific soil. As our findings were often incongruent with other studies that examined interactions among similar species at other sites, we suggest that we are at our infancy of understanding these complex interactions, and that developing a predictive framework for understanding plant soil feedbacks in the sage scrub ecosystem involves understanding how various plant species respond in different soil contexts within the ecosystem.

Functional traits indicate faster resource acquisition for alien herbs than native shrubs in an urban Mediterranean shrubland

In urban Mediterranean ecosystems, invasive alien plants should have characteristics that enable faster resource acquisition and utilization than native species. We tested this hypothesis by comparing stem and leaf functional traits from five abundant native woody shrubs and five of the most abundant alien species within an urban coastal scrub community in Ensenada, Baja California, Mexico. Twelve anatomical and ecophysiological traits were studied: light-saturated CO2 assimilation rate, stomatal conductance, stem and leaf water potentials during transpiration, % stem allocation to bark, xylem and pith, stem xylem vessel diameter and density, leaf size, and % allocation to spongy and palisade mesophyll. Alien species varied more in these traits, and their trait combinations reflected less investment in long-lived tissues; they had higher CO2 assimilation and stomatal conductance rates, higher values of leaf and stem water potential, and higher allocation to pith, larger stem xylem vessels, and larger leaf areas. In contrast, native woody shrub species were relatively convergent in leaf and stem traits reflecting more conservative resource use. Within disturbed urban environments, alien species may outcompete the native stress-tolerant species through rapid resource acquisition, enhanced by a broader set of functional trait combinations across species.

Topsoil Transfer from Natural Renosterveld to Degraded Old Fields Facilitates Native Vegetation Recovery

The transfer of soils from intact vegetation communities to degraded ecosystems is seen as a promising restoration tool aimed at facilitating vegetation recovery. This study examined how topsoil transfer from intact renosterveld to degraded old fields improves vegetation diversity, cover, and composition. Transferred topsoil were overlaid on 30 quadrats, each measuring 1 m2, in May 2009. Eight years following the initial soil transfer, vegetation diversity in the soil transfer site showed an increase towards the natural site compared to the old field site where no soil transfer was administered. Both species richness and cover for trees and shrubs in the soil transfer site increased towards the natural site, though this was not the case for herbs and grasses. One-way analysis of similarity (ANOSIM) showed significant (R = 0.55) separation in community composition between sites. The study concludes that soil transfer from intact renosterveld to degraded old fields is a promising restoration technique because it increases species diversity and cover and facilitates vegetation recovery. A significant restoration implication of this study is that soil transfer introduces key renosterveld native tree and shrub species that can facilitate successful restoration and act as restoration foci or nurse plants.

Leaf chlorophyll estimates of temperate deciduous shrubs during autumn senescence using a SPAD-502 meter and calibration with extracted chlorophyll

The soil plant analysis development (SPAD) meter proved effective at estimating leaf Chl content of native and non-native temperate deciduous shrubs. However, due to the change in the relationship between SPAD values and Chl content during the course of autumn senescence, it may be necessary to establish separate calibration equations to cover a range of leaf Chl concentrations. Non-destructive estimates of leaf chlorophyll (Chl) content by hand-held chlorophyll meters such as the Minolta SPAD-502 provide an effective time-efficient method of collecting field data on senescence. To establish useable species-specific calibration equations of relationships between chlorophyll meter readings and leaf Chl content. During autumn, we collected SPAD values and quantum yield of photosystem-II (ΦPSII) over a 10-week period from 1044 leaf samples representing native and non-native temperate deciduous shrub species growing in the wild. Subsequently, Chl was extracted from leaf discs (1 cm diameter), incubated at 65 °C for 2 h in dimethyl sulfoxide, and quantified by spectroscopy. Relationships between extracted Chl and SPAD values were established using linear, quadratic, and exponential equations. Quadratic functions proved the most reliable fit for the data. Interestingly, non-native species tended to have higher leaf Chl content and SPAD values but also exhibited higher variability than native species. The strength (r2) of the SPAD-Chl relationships was weaker than those reported for agricultural or greenhouse-grown plants, but strengthened over time as Chl, ΦPSII, and SPAD values declined. The SPAD meter proved effective at estimating leaf Chl content of native and non-native temperate deciduous shrubs. These estimates may be used in future to validate remote sensing (satellite and near-surface) vegetation indices in late autumn when trees are leafless.

Vegetative functional traits guide plant species selection for initial mineland rehabilitation

Functional ecology provides useful tools for selecting native species for rehabilitation purposes. Here, we evaluated a list of native tree and shrub species as candidates for use in waste pile rehabilitation in the Carajás National Forest, eastern Amazon, Brazil, to increase the diversity and stability of the reinstated communities. Native species lists were compiled from vegetation inventories performed in two different ecosystems in the region, i.e., dense evergreen Amazonian forests and ferriferous savannah formations, locally known as cangas. For prospection, we evaluated the functional differences among the forest, canga and waste pile communities and computed the functional space defined by wood density and 14 leaf traits of species that had already established during former rehabilitation efforts targeting the waste piles. Native species falling within this trait space were selected for further initial rehabilitation activities, while species outside this space were considered unsuitable for this purpose. As a proof of concept, we compared the survival of seedlings of selected and nonselected tree species to evaluate their potential for initial rehabilitation activities. We found functional differences in the communities between the rehabilitating waste piles and natural environments but higher functional congruence with forest than with canga ecosystems, making the conversion of waste piles into forests more likely. The assessment of functional differences enabled the identification of additional species for initial waste pile rehabilitation; we present a list of 76 candidates for future waste pile rehabilitation activities in Carajás National Forest. Our approach was validated by the seedling survival experiment, where selected species showed higher survival than nonselected species, highlighting the suitability of the selected species for initial waste pile rehabilitation in the region to increase the species richness and functional redundancy of the reinstated communities. The validation via the seedling survival experiment furthermore encourages the replication of the proposed functional prospection procedure for other environments to be rehabilitated, with different species sets being sought for different regions.

Drivers of Functional Composition of Bird Assemblages in Green Spaces of a Neotropical City: A Case Study From Merida, Mexico

Given current urbanization trends, understanding the factors that affect local biodiversity is paramount for designing sound management practices. Existing evidence suggests that the assembly of urban communities is influenced by the environmental filtering of organisms based on their traits. Here, we investigate how environmental characteristics including isolation measurements affect the functional composition of avian assemblages in green spaces of Merida, Mexico, a Neotropical city. We sampled 22 sites, analyzed point-count data collected during fall migration, and characterized the habitat with regard to floristic and structural vegetation attributes, vegetation cover within green spaces, urban infrastructure, and isolation. We assessed the relationship between habitat descriptors and bird functional traits using RLQ and fourth-corner tests and compared trait–environment associations between resident and wintering species. Our results showed that functional composition of resident bird assemblages was linked to the environmental characteristics of the site, while the functional composition of wintering species was not. In particular, the degree of isolation revealed to be an important determinant of trait composition. Plant species richness, particularly native tree and shrub species, were critical for the functional composition of resident birds in green spaces. Our findings suggested shifts in body mass from less to more isolated green spaces. Specifically, we observed that large-bodied species predominated in isolated green spaces. This information is useful given the predicted increases in habitat isolation and transformation of green spaces due to urbanization.

Browsing and fire decreases dominance of a resprouting shrub in woody encroached grassland

North American grasslands have experienced increased relative abundance of shrubs and trees over the last 150yr. Alterations in herbivore composition, abundance, and grazing pressure along with changes in fire frequency are drivers that can regulate the transition from grassland to shrubland or woodland (a process known as woody encroachment). Historically, North American grasslands had a suite of large herbivores that grazed and/or browsed (i.e., bison, elk, pronghorn, deer), as well as frequent and intense fires. In the tallgrass prairie, many large native ungulates were extirpated by the 1860s, corresponding with increased homesteading (which led to decreased fire frequencies and intensities). Changes in the frequency and intensity of these two drivers (browsing and fire) have coincided with woody encroachment in tallgrass prairie. Within tallgrass prairie, woody encroachment can be categorized in to two groups: non-resprouting species that can be killed with fire and resprouting species that cannot be killed with fire. Resprouting species require additional active management strategies to decrease abundance and eventually be removed from the ecosystem. In this study, we investigated plant cover, ramet density, and physiological effects of continuous simulated browsing and prescribed fire on Cornus drummondii C.A. Mey, a resprouting clonal native shrub species. Browsing reduced C.drummondii canopy cover and increased grass cover. We also observed decreased ramet density, which allowed for more infilling of grasses. Photosynthetic rates between browsed and unbrowsed control shrubs did not increase in 2015 or 2016. In 2017, photosynthetic rates for browsed shrubs were higher in the unburned site than the unbrowsed control shrubs at the end of the growing season. Additionally, after the prescribed fire, browsed shrubs had ~90% decreased cover, ~50% reduced ramet density, and grass cover increased by ~80%. In the roots of browsed shrubs after the prescribed fire, nonstructural carbohydrates (NSC) experienced a twofold reduction in glucose and a threefold reduction in both sucrose and starch. The combined effects of browsing and fire show strong potential as a successful management tool to decrease the abundance of clonal-resprouting woody plants in mesic grasslands and illustrate the potential significance of browsers as a key driver in this ecosystem.

Comparing Insect Pollinator Visitation for Six Native Shrub Species and Their Cultivars

Interest in native landscape plants to support pollinators has increased. Most native plants sold by nurseries are cultivars, and some consumer and conservation groups question the suitability of native cultivars to support pollinators. In 2017 and 2018, insect pollinator visitation was quantified for six native shrub species and one or more cultivars of each species (Aronia melanocarpa, A. melanocarpa ‘UCONNAM012’ Ground Hog®, A. melanocarpa ‘UCONNAM165’ Low Scape Mound®, Clethra alnifolia, C. alnifolia ‘Hummingbird’, C. alnifolia ‘Ruby Spice’, Dasiphora fruticosa, D. fruticosa ‘Goldfinger’, D. fruticosa ‘Pink Beauty’, Hydrangea arborescens, H. arborescens ‘Annabelle’, Kalmia latifolia, K. latifolia ‘Sarah’, Physocarpus opulifolius, and P. opulifolius ‘Monlo’ Diabolo®). Insects were identified into 12 categories (Apis mellifera, Bombus spp., Andrenidae, Halictidae, Megachilidae, other bees, Lepidoptera, Syrphidae, other flies, wasps, Coleoptera, and other insects). The number of inflorescences and insect visitation was similar for C. alnifolia and its cultivars, and the compact cultivar Hummingbird had the greatest floral density. A. melanocarpa had more total visitors of Andrenidae than both of its compact cultivars because it was larger and produced more inflorescences. Compact Aronia cultivars and the straight species were mostly similar for Andrenidae visitation when compared on a per-inflorescence basis. D. fruticosa had more visitors of Bombus spp. and Megachilidae than both of its cultivars. These insects may have been less attracted to ‘Pink Beauty’ because of its pink flower color and ‘Goldfinger’ because of its wider flowers, which result from it being a tetraploid. H. arborescens ‘Annabelle’ had one-third the number of Bombus spp. visitors as H. arborescens because ‘Annabelle’ produces >50% fewer fertile florets. P. opulifolius ‘Monlo’ attracted more syrphids than P. opulifolius possibly because flowers contrasted more strongly with the reddish purple foliage of ‘Monlo’ than with the green foliage of the straight species. Insect visitation was similar for K. latifolia and K. latifolia ‘Sarah’. Based on this work, we determined that native shrub cultivars are not universally less or more attractive to pollinators and must be evaluated on a case-by-case basis.

Chemical composition of essential oil from Varronia curassavica Jacq. accessions in different seasons of the year

Varronia curassavica Jacq. is a native shrub species of the Atlantic Forest and is used as a phytomedicine in Brazilian folk medicine against inflammations, ulcers and arthritis and in commercial products as an anti-inflammatory drug. In this study, for the first time, the chemical profiles of the essential oils from three accessions of V. curassavica from different geographic origins in Brazil, namely, Bahia (BA), São Paulo (SP) and Rio de Janeiro (RJ), were evaluated according to their origin and season of the year. The yield of essential oil between accessions ranged from 0.44 to 2.74% (v/w) which the highest amount was found to BA and the lowest to SP. The substances with the highest relative proportions were α-pinene (RJ – 49.2% and SP – 32.6%) and (E)-caryophyllene (SP – 16.1% and RJ – 11.1%). For BA, the substance with the highest content was amorpha-4,7(11)-diene (14.5%), followed by eudesm-7 (11)-en-4-ol (7.00%). Principal component analysis (PCA) revealed that the accession from Rio de Janeiro showed the most similarity to composition of its essential oil, whereas the accession from Bahia presented the most dissimilarity. Regardless of the differences within each population, the grouping of the samples occurred according to their origins, and no mixing occurred between the samples from the accessions. The difference in the chemical profiles found by the PCA analysis was corroborated by the hierarchical cluster analysis (HCA), which the samples from São Paulo were similar to those from Bahia, and those from Rio de Janeiro were the ones that differed most from the other accessions. Among the evaluated accessions, those from Rio de Janeiro (RJ) showed the highest content of α-humulene, with a higher production during the spring (2.89%), while SP had the highest (E)-caryophyllene content (16,12%) in all evaluated seasons, showing the potential of these accessions for cultivation of V. curassavica and consequently production of its essential oil for a phytomedicine application.

Invasive Japanese Barberry, Berberis thunbergii (Ranunculales: Berberidaceae) Is Associated With Simplified Branch-Dwelling and Leaf-Litter Arthropod Communities in a New York Forest.

Arthropod food webs can be indirectly impacted by woody plant invasions, with cascading consequences for higher trophic levels. There are multiple bottom-up pathways by which invasive plants can alter food webs: above-ground interactions based on plant-herbivore associations and below-ground at the interface of leaf-litter and soil food webs. We compared arthropod community composition in these two food web dimensions in a New York forest that has been heavily invaded by nonnative Japanese barberry. Using two sampling protocols, we compared arthropod community composition on Japanese barberry shrubs to multiple species of native host shrubs and then compared leaf-litter arthropod assemblages between forest patches with exceptionally high Japanese barberry densities and those with relatively little to no Japanese barberry present. Fitting with trends in other woody shrub invasions, arthropod species richness was significantly lower in the leaf litter around Japanese barberry and on Japanese barberry plants themselves. Although overall arthropod abundance was also significantly lower on and in the leaf litter around Japanese barberry than on and around native shrubs, total biomass did not differ due to the taxa associated with Japanese barberry tending to be larger-bodied. We observed a dramatic reduction in predatory arthropods in response to both bottom-up pathways, particularly among ants and spiders. Our results show that Japanese barberry-invaded habitats may be experiencing trophic downgrading as result of lower numbers of generalist predators like spiders and ants, which may have rippling effects up the food web to insectivorous animals and their predators.

Detection of Colletotrichum gloeosporioides in native cashew species in Brazil.

The savanna cashew (Anacardium humile A. St. Hil.) nut is a native shrub species distributed in the savanna biome of Central Western Brazil. This species is similar to the cashew (Anacardium occidentale L.) nut, and its edible pseudo-fruits have been used for various purposes. However, A. humile is at risk of extinction. One reason for this is the phytosanitary issues. Therefore, phytosanitary studies of the serious plant diseases caused by fungal pathogens are necessary. The aim of this study was to survey the savanna cashew nut (Anacardium humile) in Central Western Brazil from August 2013 to October 2014. Serious damage caused by anthracnose to the plant's leaves and fruits was consistently detected. The pathogen fungal species was Colletotrichum gloeosporioides. It was identified by morphological characteristics and molecular analyses. Additional experiments showed evidence that C. gloeosporioides can be transmitted by cashew seeds. We observed anthracnose symptoms on the surfaces of the floral peduncle, leaves, and peduncle of the A. humile cashew nuts. The genomic DNA sequences of the selected strains for molecular characterization have had 99% identity with the analogous sequences of C. gloeosporioides. Naturally occurring C. gloeosporioides infection of the leaves of A. humile was low (20.3%) compared with that of the nuts (79.7%). Our results can be used to design strategies to prevent the introduction and establishment of C. gloeosporioides in new areas. They can also be helpful in monitoring programs in areas with a current occurrence of C. gloeosporioides. Finally, these results can be used in future research plans of C. gloeosporioides infection management.

Altered leaf elemental composition with climate change is linked to reductions in photosynthesis, growth and survival in a semi‐arid shrubland

Abstract Climate change will increase heat and drought stress in many dryland areas, which could reduce soil nutrient availability for plants and aggravate nutrient limitation of primary productivity. Any negative impacts of climate change on foliar nutrient contents would be expected to negatively affect the photosynthetic capacity, water use efficiency and overall fitness of dryland vegetation. We conducted a 4‐year manipulative experiment using open top chambers and rainout shelters to assess the impacts of warming (~2°C, W), rainfall reduction (~30%, RR) and their combination (W + RR) on the nutrient status and ecophysiological performance of six native shrub species of contrasting phylogeny in a semi‐arid ecosystem. Leaf nutrient status and gas exchange were assessed yearly, whereas biomass production and survival were measured at the end of the study. Warming (W and W + RR) advanced shoot growth phenology and reduced foliar macro‐ (N, P, K) and micronutrient (Cu, Fe, Zn) concentrations (by 8%–18% and 14%–56% respectively), net photosynthetic rate (32%), above‐ground biomass production (28%–39%) and survival (23%–46%). Decreased photosynthesis and growth in W and W + RR plants were primarily linked to enhanced nutritional constraints on carbon fixation. Poor leaf nutrient status in W and W + RR plants partly decoupled carbon assimilation from water flux and led to drastic reductions in water use efficiency (WUEi; ~41%) across species. The RR treatment moderately decreased foliar macro‐ and micronutrients (6%–17%, except for Zn) and biomass production (22%). The interactive impacts of warming and rainfall reduction (W + RR treatment) on plant performance were generally smaller than expected from additive single‐factor effects. Synthesis. Large decreases in plant nutrient pool size and productivity combined with increased mortality during hotter droughts will reduce vegetation cover and nutrient retention capacity, thereby disrupting biogeochemical processes and accelerating dryland degradation with impending climate change. Increased macro‐ and micronutrient co‐limitation of photosynthesis with forecasted climate change conditions may offset any gains in WUEi and productivity derived from anthropogenic CO2 elevation, thereby increasing dryland vegetation vulnerability to drought stress in a warmer and drier climate. The generalized reduction in leaf nutrient contents with warming compromises plant nutritional quality for herbivores, with potential cascading negative effects across trophic levels.

Functional shifts in leaves of woody invaders of deciduous forests between their home and away ranges.

Temperate forests are widely invaded by shade-tolerant shrubs and trees, including those of Eastern North America (ENA). However, it remains unknown whether these invaders are 'preadapted' for success in their new ranges due to unique aspects of their evolutionary history or whether selection due to enemy release or other postintroduction processes have driven rapid evolution in the invaded range. We sampled leaf traits of populations of woody understory invaders across light gradients in their native range in Japan and in their invaded ENA range to examine potential phenotypic shifts related to carbon gain and nitrogen use between ranges. We also measured leaf traits in three co-occurring ENA native shrub species. In their invaded range, invaders invested significantly less in leaf chlorophyll content (both per unit leaf mass and area) compared with native range populations of the same species, yet maintained similar rates of photosynthesis in low light. In addition, compared with ENA natives, ENA invaders displayed greater trait variation in response to increasing light availability (forest edges, gaps), giving them a potential advantage over ENA natives in a variety of light conditions. We conclude that, for this group of species, newly evolved phenotypes in the invaded range are more important than preadaptation for their success as shade-tolerant forest invaders.

Invasion of Euryops floribundus in degraded South African communal grassland: Unpacking the invasion relationship with elevation, soil properties, the quality and quantity of the herbaceous layer

AbstractShrub invasion is a recent occurrence in African grassland ecosystems. This study assessed the distribution of Euryops floribundus (a native shrub species) along an elevation and invasion intensity gradients, and its relationship with soil and herbaceous vegetation in a South African grassland. Shrub density increased (p < 0.05) from the uplands (2,301 plants/ha) to the bottomlands (4,888 plants/ha). Themeda triandra (a highly palatable grass) was dominant at the uplands and sloping sites, whereas Eragrostis plana and Sporobolus africanus (poorly palatable grasses) dominated the bottomlands. Upland soils had the highest organic carbon (OC), phosphorous (P), calcium and nitrogen (N) contents, but the lowest shrub density and herbaceous biomass. Canonical correspondence analysis indicated that elevation, soil OC and N contents determine important vegetation variables along the elevation gradient. In the shrub density gradient, soil P, OC and N responded positively to E. floribundus density. Grass biomass in the moderate and heavily invaded sites was high, but the abundance of palatable grasses declined, suggesting that E. floribundus invasion may be concomitant with a decrease in rangeland condition in terms of quality forage provision.

Water Stress Patterns of Xerophytic Plants in an Urban Landscape

Efficient water use in urban landscapes is a common objective throughout the western United States. Vegetative species promoted for their drought tolerance characteristics are often included in landscapes designed for resource conservation. However, water requirements of most common landscape species have not been quantified. This is especially true for xerophytic species. This lack of landscape plant water requirement data is a significant constraint on the design of efficient irrigation systems and management practices affecting urban landscape water use. Current irrigation practices often fail to consider the unique physiology of xerophytic species, and irrigation scheduling models may not be appropriate for xeric landscapes using xerophytic vegetation as the primary method of reducing water use. This work describes the seasonal patterns of growth and xylem water status for four regionally native xeric shrub species planted in an unirrigated urban landscape in the semi-arid environment of central Oregon. The four species (Artemisia tridentata, Holodiscus microphyllus, Ericameria nauseosa, and Ribes cereum) exhibited substantial growth over the course of 18 months without irrigation in a heavily modified urban soil profile. Water potential of the four species was strongly correlated with surface (10 cm) soil moisture (r ≥ 0.90), less so with reference monthly evapotranspiration (r ≤ 0.55), and only weakly with water vapor deficit (r ≤ 0.22). In A. tridentata and H. microphyllus, xylem water potential became more negative during the growing season and tracked the seasonal decline in soil moisture. In contrast, the xylem water potential of E. nauseosa and R. cereum tracked soil moisture early in the season but became less responsive to soil moisture in the driest months, suggesting different drought adaptation strategies in these species. Three of the four species showed no visual signs of drought stress and maintained acceptable aesthetics even as soil moisture decreased to less than 10%. However, R. cereum exhibited a drought dormancy strategy that made it less aesthetically desirable. These results suggest that extreme xerophytic shrubs provide an opportunity for significant reductions in water use in urban landscapes.

Water use characteristics of native and exotic shrub species in the semi-arid Loess Plateau using an isotope technique

Knowledge of the processes underlying plant water use characteristics is critical for understanding soil–plant interactions and evaluating plant adaptability in water-limited ecosystems. The vegetation on the Loess Plateau has -dramatically changed due to the implementation of the Grain-for-Green Project from 1999. Despite this, water use characteristics of native and exotic shrub species remain poorly understood in this region. In this study, seasonal variations of water use characteristics of Spiraea pubescens (a native shrub) and Hippophae rhamnoides (an exotic shrub) in the Loess Plateau were investigated by examining the δ2H and δ18O of xylem and soil water from different soil layers within 300 cm of the surface, as well as the δ13C in plant leaves. Results revealed that H. rhamnoides and S. pubescens derived ˜80% of their water sources from the 0–120 cm soil layer during the growing seasons. However, H. rhamnoides absorbed higher proportions of deep soil water (120–300 cm) as the growing season progressed. H. rhamnoides flexibly converted its water source between shallow (0–40 cm) and deep soil layers. Moreover, H. rhamnoides had higher leaf-level water use efficiency than that of S. pubescens. These results suggest that H. rhamnoides has a greater degree of ecological plasticity in water use. Flexible water use characteristics are relevant to functionally dimorphic root systems as an adaptation strategy for the plants in water-limited environments. These findings indicate that water use characteristics of these plants should be considered when exotic species are introduced for revegetation in semiarid regions.