Ecosystem legacy of the introduced N2-fixing tree Robinia pseudoacacia in a coastal forest

Habitat invasibility has been found to increase dramatically following the alteration of ecosystem properties by a nonnative species. Robinia pseudoacacia, black locust, is a nitrogen-fixing, clonal tree species that aggressively invades open habitats and expands outside of plantations worldwide. Robinia pseudoacacia stands in Cape Cod National Seashore were particularly susceptible to a hurricane in 1991 that caused widespread blowdown and a dramatic reduction in Robinia in some stands. We used this change to investigate the lasting ecological effects of this nonnative species on this upland coastal ecosystem. We established replicate clusters of 20 × 20 m field plots within 50 m of each other that contained native pitch pine (Pinus rigida) and oak (Quercus velutina, Q. alba) forest, living Robinia stands, and stands in which Robinia was eliminated or reduced to less than 5 % cover by the hurricane. Net nitrification and extractable soil nitrate concentration differed significantly between stand types, in the order Robinia > former Robinia > pine-oak. Nonnative species cover differed significantly between each stand type, in the order Robinia > former Robinia > pine-oak. Invasion of Robinia pseudoacacia increased soil net nitrification and nitrogen availability and precipitated a change in forest species composition that favored nonnative species. The presence of elevated soil nitrogen and nonnative species persisted at least 14 years after the removal of the original invading tree species, suggesting that the invasion of a tree species left a legacy of altered soil biogeochemistry, a higher number of nonnative species, and greater nonnative species cover.     

Impacts of the exotic,nitrogen-fixing black locust (Robinia pseudoacacia) on nitrogen-cycling in a pine–oak ecosystem

We investigated the influence of the exotic nitrogen-fixing black locust (Robinia pseudoacacia) on nitrogen cycling in a pitch pine (Pinus rigida) −scrub oak (Quercus ilicifolia, Q. prinoides) ecosystem. Within paired pine-oak and adjacent black locust stands that were the result of a 20-35 year-old invasion, we evaluated soil nutrient contents, soil nitrogen transformation rates, and annual litterfall biomass and nitrogen concentrations. In the A horizon, black locust soils had 1.3-3.2 times greater nitrogen concentration relative to soils within pine-oak stands. Black locust soils also had elevated levels of P and Ca, net nitrification rates and total net N-mineralization rates. Net nitrification rates were 25-120 times greater in black locust than in pine-oak stands. Elevated net N-mineralization rates in black locust stands were associated with an abundance of high nitrogen, low lignin leaf litter, with 86 kg N ha^–1 yr^–1 in leaf litter returned compared with 19 kg N ha^–1 yr^–1 in pine-oak stands. This difference resulted from a two-fold greater litterfall mass combined with increased litter nitrogen concentration in black locust stands (1.1% and 2.6% N for scrub oak and black locust litter, respectively). Thus, black locust supplements soil nitrogen pools, increases nitrogen return in litterfall, and enhances soil nitrogen mineralization rates when it invades nutrient poor, pine-oak ecosystems. This revised version was published online in June 2006 with corrections to the Cover Date.     

Host‐associated divergence in the activity of digestive enzymes in two populations of the gypsy moth Lymantria dispar (Lepidoptera: Erebidae)

The gypsy moth is a generalist insect pest with an extremely wide host range. Adaptive responses of digestive enzymes are important for the successful utilization of plant hosts that differ in the contents and ratios of constituent nutrients and allelochemicals. In the present study, we examined the responses of α‐amylase, trypsin, and leucine aminopeptidase to two tree hosts (suitable oak, Quercus cerris, and unsuitable locust tree, Robinia pseudoacacia) in the fourth, fifth, and sixth instars of gypsy moth larvae originating from oak and locust tree forest populations (hereafter assigned as Quercus and Robinia populations, respectively). Gypsy moths from the Robinia forest had been adapting to this unsuitable host for more than 40 generations. To test for population‐level host plant specialization, we applied a two‐population × two‐host experimental design. We compared the levels, developmental patterns, and plasticities of the activities of enzymes. The locust tree diet increased enzyme activity in the fourth instar and reduced activity in advanced instars of the Quercus larvae in comparison to the oak diet. These larvae also exhibited opposite developmental trajectories on the two hosts, i.e. activity increased on the oak diet and decreased on the locust tree diet with the progress of instar. Larvae of the Robinia population were characterized by reduced plasticity of enzyme activity and its developmental trajectories. In addition, elevated trypsin activity in response to an unsuitable host was observed in all instar larvae of the Robinia population, which demonstrated that Robinia larvae had an improved digestive performance than did Quercus larvae.     

Arthropod diversity of exotic vs. native Robinia species in northern Arizona

1 Arthropods were collected on native locust, Robinia neomexicana A. Gray, and exotic Robinia pseudoacacia L. in northern Arizona over a 2‐year period to determine the number of arthropod species and number of individuals present. 2 More arthropod species were found on the native (251) than on the exotic Robinia (174). 3 Greater species diversity was likewise found on the native than the exotic. The five most numerous insects collected each year accounted for 81% to 91% of the total number collected on the exotic and native Robinia in 1997 and 1998. Only 12 species occurred on both the native and exotic Robinia in both years. 4 These findings are discussed in the context of using exotic trees in plantations and ecological theory regarding rates of arthropod species accumulation on exotic hosts.     

Adaptation of the gypsy moth to an unsuitable host plant

The pattern of adaptation with regard to life history traits and traits thought to be important in feeding habits of caterpillars in two populations of the gypsy moth (Lymantria dispar L.; Lepidoptera: Lymantriidae) originating from the locust tree (Robinia pseudoacacia; Fabaceae) and oak (Quercus petrea; Fagaceae) forests were investigated in the laboratory. The Robinia population has experienced unsuitable locust tree leaves as an exclusive food resource for more than 40 years. Since Quercus species are the principal host plants of the gypsy moth, the specific objectives of this study have been to measure the extent of differentiation between ancestral and derived populations in several life history traits (egg-to-adult viability, duration of larval and pupal stages, and pupal weight) and nutritional indices – relative growth rate (RGR), relative consumption rate (RCR), assimilation efficiency (AD), gross growth efficiency (ECI), and net growth efficiency (ECD). Significant differences between the Quercus and Robinia populations were detected in pupal duration, RGR, RCR, and AD. The presence of a significant population × host interaction in traits such as preadult viability, duration of pupal stage, RGR, and ECI suggests that adaptation of the gypsy moth to the unsuitable host might be ongoing. Using a full-sib design, we screened for genetic variation in life history traits within both populations, and examined the genetic correlations of performance across oak and locust leaves within both populations. The genetic variances for analyzed life history traits were lower under conditions that are commonly encountered in nature. Our data show that positive cross-host genetic correlations preponderate within both populations.     

Insight into the evolutionary history of symbiotic genes of Robinia pseudoacacia rhizobia deriving from Poland and Japan

The phylogeny of symbiotic genes of Robinia pseudoacacia (black locust) rhizobia derived from Poland and Japan was studied by comparative sequence analysis of nodA, nodC, nodH, and nifH loci. In phylogenetic trees, black locust symbionts formed a branch of their own suggesting that the spread and maintenance of symbiotic genes within Robinia pseudoacacia rhizobia occurred through vertical transmission. There was 99–100% sequence similarity for nodA genes of Robinia pseudoacacia nodulators, 97–98% for nodC, and 97–100% for nodH and nifH loci. A considerable sequence conservation of sym genes shows that the symbiotic apparatus of Robinia pseudoacacia rhizobia might have evolved under strong host plant constraints. In the nodA and nodC gene phylograms, Robinia pseudoacacia rhizobia grouped with Phaseolus sp. symbionts, although they were not closely related to our isolates based on 16S rRNA genes, and with Mesorhizobium amorphae. nifH gene phylogeny of our isolates followed the evolutionary history of 16S rDNA and Robinia pseudoacacia rhizobia grouped with Mesorhizobium genus species. Nodulation assays revealed that Robinia pseudoacacia rhizobia effectively nodulated their native host and also Amorpha fruticosa and Amorpha californica resulting in a significant enhancement of plant growth. The black locust root nodules are shown to be of indeterminate type.     

我国新发现一种外来蚜虫——刺槐附毛斑蚜Appendiseta robiniae

记述了采自北京刺槐上的1种中国的记录外来蚜虫——刺槐附毛斑蚜,它原产于北美,寄主为刺槐,在当地一些地区较为常见,并已扩散到欧洲等地。描述了有翅孤雌蚜、无翅雌性蚜和有翅雄性蚜的鉴别特征,并提供了生态图片。最后讨论了它的潜在危害性及蚜虫寄主植物、蚜群生活状及生态照片在蚜虫识别上的重要性。     

Human impact on the forest vegetation in the western part of the Pannonic Plain (Yugoslavia)

A comparative phytosociological study was made out on two types of forest on the southern slopes of Moslavaka gora in the western part of the Pannonic Plain, Yugoslavia: acidophilic oak forest of Festuco-Quercetum petraeae Hruka 1975 and areas where Robinia pseudoacacia has been introduced by man. After cutting, the oakforest reestablishes spontaneously. Reafforestation with Robinia leads to changes irreversible in species composition and vegetational structure and prevents reestablishment of oak forest. The introduction of this allochthonous species prevents the primary wood from being restored. Forestry planting projects with a view to reducing the Robinia have so far proved ineffective.     

Soil Nitrogen Conditions Approach Preinvasion Levels following Restoration of Nitrogen-Fixing Black Locust (Robinia pseudoacacia) Stands in a Pine–Oak Ecosystem

Restoring native plant communities on sites formerly occupied by invasive nitrogen‐fixing species poses unique problems due to elevated soil nitrogen availability. Mitigation practices that reduce available nitrogen may ameliorate this problem. We evaluated the effects of tree removal followed by soil preparation or mulching on native plant growth and soil nitrogen transformations in a pine–oak system formerly occupied by exotic nitrogen‐fixing Black locust (Robinia pseudoacacia) trees. Greenhouse growth experiments with native grasses, Andropogon gerardii and Sorghastrum nutans, showed elevated relative growth rates in soils from Black locust compared with pine–oak stands. Field soil nutrient concentrations and rates of net nitrification and total net N‐mineralization were compared 2 and 4 years since Black locust removal and in control sites. Although soil nitrogen concentrations and total net N‐mineralization rates in the restored sites were reduced to levels that were similar to paired pine–oak stands after only 2 years, net nitrification rates remained 3–34 times higher in the restored sites. Other nutrient ion concentrations (Ca, Mg) and organic matter content were reduced, whereas phosphorus levels remained elevated in restored sites. Thus, 2–4 years following Black locust tree removal and soil horizon mixing achieved through site preparation, the concentrations of many soil nutrients returned to preinvasion levels. However, net nitrification rates remained elevated; cover cropping or carbon addition during restoration of sites invaded by nitrogen fixers could increase nitrogen immobilization and/or reduce nitrate availability, making sites more amenable to native plant establishment.     

The seed lectins of black locust (robinia pseudoacacia) are encoded by two genes which differ from the bark lectin genes

Two lectins were isolated from Robinia pseudoacacia (black locust) seeds using affinity chromatography on fetuin-agarose, and ion exchange chromatography on a Neobar CS column. The first lectin, R. pseudoacacia seed agglutinin I, referred to as RPsAI, is a homotetramer of four 34 kDa subunits whereas the second lectin, referred to as RPsAII, is composed of four 29 kDa polypeptides. cDNA clones encoding the polypeptides of RPsAI and RPsAII were isolated and their sequences were determined. Both polypeptides are translated from mRNAs of ca. 1.2 kb encoding a precursor carrying a signal peptide. Alignment of the deduced amino acid sequences of the different clones indicates that the 34 and 29 kDa seed lectin polypeptides show 95% sequence identity. In spite of this striking homology, the 29 kDa polypeptide has only one putative glycosylation site whereas the 34 kDa subunit has four of these sites. Carbohydrate analysis revealed that the 34 kDa possesses three carbohydrate chains whereas the 29 kDa polypeptide is only partially glycosylated at one site. A comparison of the deduced amino acid sequences of the two seed and three bark lectin polypeptides demonstrated unambiguously that they are encoded by different genes. This implies that five different genes are involved in the control of the expression of the lectins in black locust.Abbreviations LECRPAs cDNA clone encoding Robinia pseudoacacia seed lectin - LoLI Lathyrus ochrus isolectin I - PsA Pisum sativum agglutinin - RPbAI Robinia pseudoacacia bark agglutinin I - RPbAII Robinia pseudoacacia bark agglutinin II - RPsAI Robinia pseudoacacia seed agglutinin I - RPsAII Robinia pseudoacacia seed agglutinin II     

Neighborhood effects on soil properties,mycorrhizal attributes,tree growth,and nutrient status in afforested zones

A harmonious interspecies relationship is the key to the success of mixed afforestation. This study was conducted to assess the responses of afforestation species to their neighboring trees. We examined five types of stands—monocultures of Chinese pine (Pinus tabuliformis), black locust (Robinia pseudoacacia), sea‐buckthorn (Hippophae rhamnoides), and two mixtures (Chinese pine × black locust mixture and Chinese pine × sea‐buckthorn mixture)—in the Loess Plateau, northwestern China. The height and diameter at breast height of each tree species were measured, and rhizosphere soil, shoot, and root were sampled. In monocultures, black locust was taller than Chinese pine and sea‐buckthorn, while the height of Chinese pine and sea‐buckthorn was similar. In mixtures, Chinese pine grew better with sea‐buckthorn than alone as a result of modified soil properties and plant nutrition, but not with black locust. When Chinese pine was used as neighbors, it affected the level of arbuscular mycorrhizal (AM) colonization of black locust, soil properties and AM fungal spore density of black locust and sea‐buckthorn, but did not significantly affect their growth. Our results suggest that the reciprocal effects between tree species in mixture are not symmetric, and thus planning for efficient mixed afforestation requires knowledge of species‐specific growth rate, nutrient requirements, and species interactions.     

Natural Regeneration of Trees in Three Types of Afforested Stands in the Taihang Mountains,China

Natural regeneration is the natural process by which plants replace themselves. It is a cost-effective way to re-establish vegetation, and it helps to preserve genetic identity and diversity. In this study, we investigated the natural regeneration of trees in three types of afforested stands in the Taihang Mountains, China, which were dominated by Robinia pseudoacacia (black locust), Quercus variabilis (Chinese cork oak) and Platycladus orientalis (Chinese arborvitae) respectively. A consistent pattern was found among the three types of stands, being that the density of seedlings was positively correlated with the overstory canopy cover and negatively correlated with the covers of shrub, herb and litter layers. While a positive correlation between the density of seedlings and stand age was found for the conifer stands, negative correlations were found for the two types of broadleaf stands. Correlations between the density of saplings and the stand attributes were not consistent among the three types of stands. The two types of broadleaf stands had higher densities of seedlings and saplings than the conifer stands. While the broadleaf stands had adequate recruits for regeneration, the conifer stands did not have enough recruits. Our findings suggest that the overstory canopy should be prevented from being disturbed, any reduction of the canopy cover will decrease the recruits and affect the regeneration.     

Patterns of β-diversity and similarity reveal biotic homogenization of epiphytic lichen communities associated with the spread of black locust forests

We compared epiphytic lichen communities of native broadleaved and secondary black locust (Robinia pseudoacacia) forests to detect possible differences in community structure that could be indicative of biological homogenization enhanced by the replacement of native by black locust forests. The study was carried out in two areas of Italy with different bioclimatic conditions using a balanced stratified random sampling. Results reveal a different pattern of community structure between native and black locust forests across the two regions that may reflect a process of biological homogenization. In particular, lichen communities of black locust forests share several species between the two study regions. This pattern of floristic homogenization parallels with a functional homogenization related to the spread of highly competitive species. This research provides early evidence that the decrease of native forests associated with the spread of black locust is a mechanism triggering biological homogenization of the epiphytic lichen biota.     

Strophiole of seeds of the black locust acts as a water gap

In Japan the black locust (Robinia pseudoacacia L.) is undergoing rapid habitat expansion, which has an adverse effect on native vegetation. It is therefore a priority to clarify the regeneration characteristics of the black locust and establish adequate management of this invasive species in Japan. To determine the germination characteristics of physically dormant black locust seeds, we observed anatomical features of the seed coat and identified the water gap that acts as a signal detector. Our microscopic observations showed that seed coats of this species had hilum, micropyle and strophiole. The anatomical features of these regions correspond to the general characteristics of papilionoid legume seeds. Based on our microscopic observations, water absorption blocking experiments and a dye tracking experiment, we identified the strophiole as a water gap in black locust seeds. Our results suggest that the opening of the strophiole is important for water uptake to the embryo and subsequent germination of black locust seeds under natural conditions.     

Characterization of Phages Virulent for <Emphasis Type="Italic">Robinia pseudoacacia</Emphasis> Rhizobia

Three lytic phages (ΦRP1, ΦRP2, and ΦRP3) specific for Robinia pseudoacacia rhizobia were isolated from the soil under black locust. They were characterized by their morphology, host range, and some other properties including DNA molecular weights. Studied phages have been found to belong to Siphoviridae family that comprises viruses with long, and noncontractile tails. They had broad host ranges and effectively lysed not only Robinia pseudoacacia microsymbionts but also different Mesorhizobium species. The phages were homogenous in latent periods (300 min) but heterogeneous in burst sizes (100–200 phage particles per one infected cell) and rise periods (90–120 min). They showed a distinct adsorption rate to Robinia pseudoacacia rhizobia (70.4–93.94%). The molecular weights of phage DNAs estimated from restriction enzyme digests were in the range from ca. 82 kb to ca. 105 kb.     

Effects of black locust (Robinia pseudoacacia) on soil properties in the loessial gully region of the Loess Plateau, China

Black locust (Robinia pseudoacacia) has been widely planted in the Loess Plateau for soil and water conservation. The effects of black locust on soil properties has significant role in land use and ecosystem management. However, this beneficial effect has been little studied in the Loess Plateau. The soil properties below black locust and native grass growing in Nanxiaohe and Wangdonggou watersheds, located in the loessial gully region of the Loess Plateau, were studied for changes in soil properties after establishment of black locust. The black locust significantly increased soil cation exchange capacity, organic carbon, total nitrogen, nitrate, and carbon:nitrogen and carbon:phosphorus (P) ratios, as well as some enzymes like alkaline phosphatase and invertase in 0–20 cm or 0–80 cm depths of soil compared to the native grassland in Nanxiaohe and Wangdonggou watersheds. However, the effects on ammonium, total P, and extractable P and potassium were not consistent in both watersheds. There were more obvious differences in soil properties between black locust land and grassland for Nanxiaohe watershed than for Wangdonggou watershed, suggesting that the effects of black locust on most soil properties increase with black locust age. The results indicate that black locust has potential to improve soil properties in the loessial gully region of the Loess Plateau and the improvements were greater in long-term than middle-term black locust stands.     

Elevated Cd and Zn uptake by aspen limits the phytostabilization potential compared to five other tree species

Phytostabilization of metals using trees is often promoted, although the influence of different tree species on the mobilization of metals is not yet clear. This study examined effects of six tree species on the soil characteristics pH, organic carbon (OC) content and cation exchange capacity (CEC) and on the redistribution of cadmium (Cd) and zinc (Zn) on a polluted sandy soil. Soil and biomass were sampled in 10-year-old stands growing on former agricultural land. The tree species included were silver birch (Betula pendula), oak (Quercus robur and Quercus petraea), black locust (Robinia pseudoacacia), aspen (Populus tremula), Scots pine (Pinus sylvestris) and Douglas fir (Pseudotsuga menziesii). In the short period of 10 years, only aspen caused significant changes in the soil characteristics. Due to accumulation of Cd and Zn in its leaf litter, aspen increased the total as well as the NH₄OAc-EDTA-extractable Cd and Zn concentrations in the topsoil compared to deeper soil layers and to other tree species. Also, topsoil pH, OC content and CEC were significantly higher than under most of the other species. This caused rather low ‘bioavailable’ CaCl₂-extractable concentrations under aspen. Nevertheless, given the risks of aboveground metal dispersion and topsoil accumulation, it is recommended that aspen should be avoided when afforesting Cd and Zn contaminated lands.     

Fossil Robinia wood from the western United States

A collection of petrified wood from the Lower Pliocene Ogallala Formation in western Oklahoma was examined. All specimens appear to be of the same taxon and exhibit features of extant Robinia species. To date, four fossil wood species of Robinia have been described. The relationship of Robinioxylon zuriensis Falqui to Robinia is doubtful because of the lack of diagnostic critical features. The remaining three, Robinia alexanderi Webber, Robinia breweri Prakash, Barghoorn and Scott, and Robinioxylon zirkelii (Platen) Müller-Stoll and Mädel do show affinity to Robinia and all have been noted as structurally similar to R. pseudoacacia. The Oklahoma woods and these three fossil species show considerable overlap in quantitative features and are identical in qualitative features. Examination of different sections (and specimens) of extant Robinia pseudoacacia wood reveals quantitative and qualitative variation similar to that found amongst the petrified woods. Robinia alexanderi, Webber, R. breweri Prakash, Barghoorn and Scott, R. zirkelii (Platen) Müller-Stoll and Mädel, and the Oklahoma specimens are considered to be conspecific as the differences between these fossil wood species are no different from those accounted for by variation within a single living species, R. pseudoacacia.     

Genetic relatedness in open-pollinated families of two leguminous tree species,Robinia pseudoacacia L. and Gleditsia triacanthos L.

Summary When conducting tree breeding experiments, geneticists often assume that individuals from open-pollinated families are halfsibs. The reliability of this assumption was tested using data from enzyme electrophoresis to estimate the genetic relatedness among progeny within 22 open-pollinated families of Robinia pseudoacacia L. (black locust) and 34 open-pollinated families of Gleditsia triacanthos L. (honey locust) from natural stands. An algorithm employing population estimates of fixation indices, pollen allele frequencies, and selfing rates was used to calculate the mean expected number of alleles in common across loci under assumptions of either full-sib (i.e., a single pollen parent) or half-sib (i.e., random mating) relationships. For each open-pollinated family, the average coefficient of relationship among progeny was calculated by linear interpolation from the observed number of alleles in common. For most families of both species, coefficients were significantly higher than 0.25 (half-sib relation), but were significantly lower than 0.50 (full-sib relation). These results suggest that the assumption of a half-sib relationship among progeny of open-pollinated families is violated for these tree species. More critical to the estimation of heritabilities and the prediction of genetic gains was the observation that estimates of the coefficient of relationship varied widely among open-pollinated families (for R. pseudoacacia r ₀=0.20–0.43, mean=0.34; for G. triacanthos r ₀=0.29–0.55, mean=0.36).