Soil‐mediated effects on germination and seedling growth of coastal wattle (Acacia sophorae) by the environmental weed,bitou bush (Chrysanthemoides monilifera ssp. rotundata)

Bitou bush (Chrysanthemoides monilifera ssp. rotundata; Asteraceae) is a major woody weed that competes with the native legume Acacia sophorae in coastal ecosystems of eastern Australia. Three glasshouse experiments examined whether litter or soil from beneath bitou bush or Acacia plants could influence seed germination and seedling growth of A. sophorae. The presence of litter decreased seed germinability and this effect was greater for bitou bush litter than for Acacia litter. Shoot growth was increased by the addition of Rhizobium after 40 days, irrespective of soil type. After 78 days, shoot and root biomass were significantly lower for seedlings grown in bitou bush soil than for those grown in Acacia soil. There was a non‐significant trend towards a lower median population of Rhizobium in the soil beneath bitou bush than in that beneath Acacia. The results demonstrated a slight effect of bitou bush on the growth of A. sophorae, which could, however, be overshadowed by the judicious use of herbicides or fire for weed control and revegetation.     

Integrating revegetation with management methods to rehabilitate coastal vegetation invaded by Bitou bush (Chrysanthemoides monilifera ssp. rotundata) in Australia

Two multi‐year field experiments investigated the effects of integrating revegetation with invasive plant management methods to rehabilitate coastal dune and woodland vegetation invaded by Bitou bush (Chrysanthemoides monilifera (L.) Norl. ssp. rotundata (DC.) Norl.) in New South Wales, Australia. The revegetation technique used was to sow directly seeds of three native species common to coastal habitats. Management treatments involved combinations of prescribed fire, manual removal of Bitou bush and an application of herbicide. Addition of native seeds significantly increased density of native species in both habitats. The benefits of manually removing Bitou bush were observed only where densities of native species were at their lowest. Fire increased densities of some native species in the woodland, but decreased those of others in the dune. Densities of Acacia longifolia ssp. sophorae (Labill.) Court (woodland) and of Banksia integrifolia L.f. (woodland and dune) were significantly reduced within 4 months of herbicide application, alone or in combination with other treatments. The majority of these effects, however, did not persist. Manual removal in both habitats and addition of seed in the woodland were most effective in reducing Bitou bush densities when applied post‐fire. Herbicide treatment on its own or in combination with other treatments did not significantly reduce Bitou bush densities by the end of the experiments. We conclude that restoration of coastal ecosystems invaded by a major invasive plant species requires a whole‐of‐system approach involving revegetation in combination with known management methods to assist recovery of native species in the longer term.     

Unsuccessful introduced biocontrol agents can act as pollinators of invasive weeds: Bitou Bush (Chrysanthemoides monilifera ssp. rotundata) as an example

The extent of self‐compatibility and reliance on pollinators for seed set are critical determinants of reproductive success in invasive plant species. Seed herbivores are commonly used as biocontrol agents but may also act as flower visitors, potentially resulting in pollination. However, such contrasting or potentially counterproductive interaction effects are rarely considered or evaluated for biological control programs. We investigated the breeding system and pollinators of Bitou Bush (Chrysanthemoides monilifera ssp. rotundata), an invasive species in Australia that has been the subject of biocontrol programs since 1987. We found the species to be obligate outcrossing in all six populations tested. From 150 video hours, we found 21 species of potential pollinators, including Mesoclanis polana, the Bitou Seedfly, native to South Africa and released in Australia as a biocontrol agent in 1996. Mesoclanis polana transferred pollen to stigmas and was the most common pollinator (52% of pollinator visits), followed by the syrphid fly Simosyrphus grandicornis (9%) and introduced honeybee, Apis mellifera (6.5%). Fruit‐to‐flower ratios ranged from 0.12 to 0.45 and were highest in the population with the greatest proportion of Mesoclanis polana visits. In an experimental trial, outside the naturalized range, the native bee Homalictus sphecodoides and the native syrphid Melangyna viridiceps were the primary pollinators, and fruit‐to‐flower ratios were 0.35, indicating that Bitou Bush would have ready pollinators if its range expanded inland. Synthesis. Invasive Bitou Bush requires pollinators, and this is effected by a range of generalist pollinators in eastern Australia including the Bitou Seedfly, introduced as a biocontrol agent, and the major pollinator detected in this study. Fruit‐to‐flower ratios were highest when the Bitou Seedfly was in high abundance. This study underscores the importance of evaluating the pollination biology of invasive species in their native ranges and prior to the introduction of biocontrol agents.     

Preliminary host specificity testing of Endophyllum osteospermi (Uredinales, Pucciniaceae), a biological control agent against Chrysanthemoides monilifera ssp. monilifera

Chrysanthemoides monilifera ssp. monilifera, indigenous to the Western Cape Province of South Africa, is a serious invader of native vegetation in south-eastern Australia. The rust fungus Endophyllum osteospermi causes witches' brooms on C. monilifera ssp. monilifera in South Africa, and is associated with a reduction in growth and seed production of its host under natural conditions, as well as mortality of severely infected bushes. This rust fungus is considered to be a potential biological control agent for use against C. monilifera ssp. monilifera in Australia. Endophyllum osteospermi has a long latent period, typically between 6 and 24 months between infection and the initiation of witches' brooms. This long latent period makes the logistics of doing traditional host specificity testing, in which all test plant species are inoculated and observed for symptom development, unfeasible for this rust fungus. Germination of aecidioid teliospores and penetration by basidiospores were observed on the surface of excised leaves of 32 test plant species at 4 days after inoculation, and compared to that on C. monilifera ssp. monilifera. Germinating aecidioid teliospores aborted on 14 test plant species, whilst no penetration was attempted on a further 12 test plant species. Penetration only occurred on nine of the 32 test plant species, in addition to C. monilifera ssp. monilifera. Inoculating whole plants of nine selected test plant species confirmed the above results. Therefore, only the test plant species in which penetration occurred, or at least was attempted, need to undergo comprehensive host specificity testing. Pending these results, E. osteospermi may be suitable for release in Australia for the biological control of C. monilifera ssp. monilifera.     

Long-Term Effects of Frequent Low-Intensity Burning on the Abundance of Litter-Dwelling Invertebrates in Coastal Blackbutt Forests of Southeastern Australia

Low-intensity fire is extensively used in Australian dry eucalypt forests to reduce fuel levels. The long-term impact of this management practice on terrestrial invertebrates is, however, unknown and is of concern given their contribution to ecosystem function and forest biodiversity. This study found that areas subjected to frequent low-intensity fire had significantly lower numbers of spiders, ticks and mites, pseudoscorpions, woodlice, springtails, bugs, beetles, ants and insect larvae in the leaf litter compared with adjacent unburnt areas. Taxa numbers were between 41 and 82% lower and these reductions in abundance have led to an overall decline in taxon richness. This decrease was attributed to a reduction in the amount of litter and associated moisture levels, and a simplification of habitat structure. The extent of local and regional extinctions will depend upon the scale of this disturbance, with future studies investigating the impact on individual species within these communities. A comparison of two sampling techniques, pitfall-trapping and litter extraction, highlighted important considerations for spatial components of invertebrate sampling designs.     

Impact of the biological control agent Mesoclanis polana (Tephritidae) on bitou bush (Chrysanthemoides monilifera subsp. rotundata) in eastern Australia

The seed fly Mesoclanis polana (Diptera: Tephritidae) was released in Australia in 1996. Its impact on seed production of bitou bush (Chrysanthemoides monilifera subsp. rotundata) was monitored at eight sites along the New South Wales coast from 1996 to 2004. Peak flowerhead production occurred in autumn (March to May); therefore, samples collected in May of each year were used to compare abundance and impact of M. polana across sites and between years. Latitude had a significant effect on abundance and impact of M. polana. By May 2004, 99.6% of flowerheads at the five most northern sites contained at least one egg, while 64% of flowerheads from the two most southern sites contained at least one egg. In May 2004, mean numbers of M. polana eggs per flowerhead were between 13 and 17 at four of the six northern sites and below two at the two southern sites. In May 2004, average seed destruction by M. polana was 58% at the four most northern sites and 11% at the two most southern sites. The highest level of seed destruction recorded was 86% at Kingscliff in May 2003. Percentage seed destruction in May provided a reasonable estimate of seed destruction for the whole year. Parasitoids were found throughout the range of M. polana in Australia. Their attack rate on M. polana was less than 10% at all sites, except at the two most northern sites where parasitism of up to 27% was recorded. Parasitism results are compared with predictions made following an earlier study. The release of Mesoclanis magnipalpis, a species suited to cooler environments, is recommended for the southern range of C. monilifera subsp. rotundata.     

The Short-term Impact of Forest Fire on Soil Invertebrates in the Miombo

A study was conducted in eastern Zambia to assess the impact of fire on soil invertebrate communities between December 2003 and November 2004. Soil samples were collected 4 times from secondary miombo forest patches that were burnt in July–September 2003 and 2004 and patches not affected by fire. Macro-invertebrates were hand-sorted from soil samples and their population densities computed. The total number of orders per sample and the population density of Annelida, Chilopoda, Arachnida and some Hexapoda were lower under burnt forest patches compared to unburnt ones throughout the study period. Although the difference between burnt and unburnt patches in populations of other taxa such as Lepidoptera and Diptera remained below the threshold of statistical significance, fire appeared to have reduced their densities. It is concluded that fire can alter the structure of soil invertebrate communities through direct mortality or by its effect on availability of food resources. Further studies are needed to establish the linkage between fire, invertebrate community structure, ecosystem processes and floristic composition of the miombo.     

核桃凋落叶分解对萝卜生长和生理的影响

为考察核桃(Juglans regia L.)与冬性作物复合种植模式中凋落叶分解对作物生长的影响,该试验采用盆栽法,以冬性作物萝卜(Raphanus sativus L.)为受体,种入混有0、60、120和180g/pot核桃凋落叶的土壤中,并在萝卜生长过程中测定其形态、生理及生殖相关指标。结果表明:(1)萝卜地上部分的生长在凋落叶分解初期受到显著抑制,而在后期得到明显恢复。(2)在核桃凋落叶分解的影响下萝卜出现了明显的胁迫响应,特别是在分解初期和较高凋落叶量(120、180g/pot)处理下,光合色素含量受到明显抑制,叶片内活性氧含量增加,并在一定程度上受到渗透胁迫。(3)在测定时期内,萝卜叶片内MDA含量并未显著增加,即萝卜可通过自身调节抵御胁迫造成的危害。(4)萝卜在较高凋落叶剂量处理下,产出的种子颜色较深,且在180g/pot处理下产出的种子萌发率较低,种子质量受到明显影响。研究认为,土壤中核桃凋落叶分解初期能对萝卜造成化感胁迫,但长久来看不会降低萝卜产量;将两者复合种植时,可保留地面凋落叶,且最好在叶片分解一段时间后种植作物。     

Studies on Detritus Energy During the Decomposition of Kandelia candel Leaf Litter

Changes of caloric values and energy-rich organic compounds were studied in the detritus derived from mangrove Kandelia candel (L.) Druce leaf litter during the various in situ seasonal decomposition in Jiulong River Estuary, Fujian, China. The results showed that the caloric values varied little among the seasonal fallen leaves being a mean of 19.63 kJ/g dry wt or 21.55 kJ/g AF dry wt, the caloric values of detritus increased remarkably after decomposition but they more rapidly in summer and autumn than in winter and spring. The change was well in agreement with the degree of decomposition, being increased in the early decomposition period and slightly decreased in the later, with a peak at about the half-time of decomposition (50% weight loss). The maximum was averagely 17.67% of dry weight and 14.35 % of ash-free dry; weight basis over the initial values. The dissipation of total energy was somewhat slower than the loss of dry matter. As decomposition proceeds the energy of detritus was more and more contributed by raw protein, raw fat, raw fibers rather than by N-free extract. Therefore it is suggested that detritus at half-time of decomposition should be more important to marine detritivores from the viewpoint of energy supplement.     

The Effects of Exotic Grasses on Litter Decomposition in a Hawaiian Woodland: The Importance of Indirect Effects

Exotic grasses and grass-fueled fires have altered plant species composition in the seasonal submontane woodlands of Hawaii Volcanoes National Park. These changes have altered both structural and functional aspects of the plant community, which could, in turn, have consequences for litter decomposition and nitrogen (N) dynamics. In grass-invaded unburned woodland, grass removal plots within the woodland, and woodland converted to grassland by fire, we compared whole-system fluxes and the contributions of individual species to annual aboveground fine litterfall and litterfall N, and litter mass and net N loss. We assessed the direct contribution of grass biomass to decomposition and N dynamics, and we determined how grasses affected decomposition processes indirectly via effects on native species and alteration of the litter layer microenvironment. Grasses contributed 35% of the total annual aboveground fine litterfall in the invaded woodland. However, total litterfall mass and N were not different between the invaded woodland and the grass removal treatment because of compensation by the native tree Metrosideros polymorpha, which increased litter production by 37% ± 5% when grasses were removed. The 0.3 g N m^–2/y^–1 contained in this production increase was equal to the N contained in grass litter. Litter production and litterfall N was lowest in the grassland due to the loss of native litter inputs. Decomposition of litterfall on an area basis was highest in the grass-invaded woodland. We attributed this effect to increased inherent decomposability of native litter in the presence of grasses because (a) the microenvironment of the three vegetation treatments had little effect on decomposition of common litter types and (b) M. polymorpha litter produced in the invaded woodland decomposed faster than that produced in the grass removal plots due to higher lignin concentrations in the latter than in the former. Area-weighted decomposition was lowest in the grassland due to the absence of native litter inputs. Across all treatments, most litter types immobilized N throughout the incubation, and litter net N loss on an area basis was not different among treatments. Our results support the idea that the effects of a plant species or growth form on decomposition cannot be determined in isolation from the rest of the community or from the direct effects of litter quality and quantity alone. In this dry woodland, exotic grasses significantly altered decomposition processes through indirect effects on the quantity and quality of litter produced by native species.     

The Impact of Fungal Extracts on Leaf Litter on the Food Preference of Gammarus roeselii

We investigated the effect of methanol and methanol/methylene chloride extracts of the oomycete Pythium sp. JN 1‐b and of the fungi Ascomycete sp. PVSo8, Fusarium sporotrichoides, and Cylindrocarpon sp. 94‐2057 on the food preference of Gammarus roeselii. The preference for leaf discs coated with these extracts compared to uncoated leaf discs was tested in food‐choice assays. Methanol extracts of all strains repelled G. roeselii, and the effect of the extract concentration on relative consumption was strain specific. The repellent effect of these extracts, especially of extracts of Cylindrocarpon sp., decreased when the fungi were grown on leaf extract medium as opposed to synthetic medium containing sucrose. None of the methanol/methylene chloride extracts affected the food preference of the gammarid. We conclude that biologically active compounds were extracted from fungi and an oomycete were soluble in methanol but not in methanol/methylene chloride. Only repellent activity was observed with the extracts, and relative ratios of repellents and attractants might determine the consumption of fungi by G. roeselii. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Comparison of Leaf Litter Decomposition Rates in Restored and Mature Riparian Forests on the Sacramento River, California

One of the largest riparian restoration projects in the United States is currently taking place in California on the Sacramento River. Nearly 2,000 ha of land adjacent to the river channel have been revegetated with native riparian species in an effort to reestablish riparian forests. The objective of this study was to compare leaf litter decomposition rates in restored riparian forests to those in mature, naturally established riparian forests, in order to monitor the development of this ecosystem function in restored forests. Leaf litter decomposition rates were measured over 1 year in six restored riparian forests (4, 7, and 9 years old) and two mature remnant riparian forests (>50 years old), in order to test two hypotheses: (1) decomposition rates of restored and mature forests are significantly different and (2) decomposition rates in the chronosequence of restored forests are moving along a trajectory, approaching the decomposition rates characteristic of mature forests as they age. Statistical analyses revealed no significant differences in annual decay rates among the four different forest ages and no trajectory among leaf litter decomposition rates in restored forests. These results suggest that a functionally equivalent process of leaf litter decomposition occurs in both restored and naturally established forests and show promise for the efficiency of nutrient cycling processes in these restored forests.     

Effects of the Tropical Freshwater Shrimp Caridina weberi (Atyidae) on Leaf Litter Decomposition1

Effects of feeding by atyid shrimp, Caridina weberi, on the rate of decomposition of leaf litter were studied in the Opunohu River, Moorea, French Polynesia. In a laboratory feeding experiment shrimp consumed microbially conditioned Hibiscus leaves, but in a field study shrimp did not affect the rate of decomposition of leaf litter. In this system, the rate of decomposition was influenced more by water discharge or by microbial activity than by shrimp.     

Studies on Available Caloric Content of Detritus During the Decomposition of Mangrove Kandelia candel Leaf Litter

The absolute and relative contents of hydrolysis available calories (HAC), tanninfree HAC (TFHAC) and chemical available calories (CAC) of the detritus during the seasonal decomposition of mangrove (Kandelia candel (L.) Druce) leaf litter in Fujian, China was determined. Defined arbitrarily as the portion of total caloric content in detritus hydrolized with 1 mol/L HC1 for 6 h at 20 ℃, HAC is presumed to be a rough index of potential energy readily utilized by marine detritivores. TFHAC is the remaining calories of HAC devoid of tannin-attributed calories and CAC is defined as the total caloric content derived from raw protein, raw fat and soluble sugar. The results showed that in leaf litter, the seasonal mean caloric contents were 4.06 kJ/g DW or 20.85% of the total caloric content for HAC and 3.23 kJ/g DW or 16.68% of the total caloric content for TFHAC, which decreased to 1.75 kJ/g DW or 9.25% for HAC, and 1. 64 kJ/g DW or 8.20% for TFHAC in the detritus at half-life of decomposition. The difference in contents between HAC and TFHAC diminished as decomposition was progressed. The contents of CAC generally increased during decomposition, always higher than those of HAC and TFHAC, suggesting that some protein and fat in detritus are nonavailable to detritivores since they are hydrolyzed by week acid. The value of detritus HAC per unit ash-free dry weight (AFDW), as determined at the time when the detritus lost 23% of its initial weight, ranged from 16. 16 to 17.41 kJ/g AFDW and increased rapidly to a maximum of 24.00 kJ/g AFDW at 49% dry weight loss of detritus during decomposition. The detritus derived from mangrove fallen leaves had a low available caloric content and an moderate caloric value of HAC as compared with detritus of other marine plants. Finally, the relationship between HAC, TFHAC and CAC was discussed and some points of attention relevant to the application of those indices were given in relation     

Identifying the Relative Importance of Leaf versus Shredder Species Loss on Litter Decomposition in Streams

Understanding how species loss influences ecosystem function is a contemporary issue in ecology. However, most research has focused on species loss at one trophic‐level. We explored the relationship between functional diversity (FD) and species richness separately for trees and aquatic leaf‐shredding detritivores. For trees, we collected information on species‐specific leaf tissue chemistry and species co‐occurrences in the mid‐Atlantic region (USA). For shredders, we used a published trait database with information on communities from 38 streams in the same region. We used a clustering algorithm to estimate FD for each community and for randomly assembled communities. If FD was high, we concluded that species loss was important to change in function; if low, species were functionally redundant and insensitive to species loss. We found tree FD to be significantly different than expected, but shredders exhibited FD levels similar to patterns based on random assembly. Furthermore, there were more leaf species exclusively associated with very high or very low levels of functional diversity compared to shredders. This approach revealed greater implications for leaf than shredder species loss for litter breakdown. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The effects on terrestrial arthropod communities of invasion of a coastal heath ecosystem by the exotic weed bitou bush (<Emphasis Type="Italic">Chrysanthemoides monilifera</Emphasis> ssp. <Emphasis Type="Italic">rotundata</Emphasis> L.)

Bitou bush (Chrysanthemoides monilifera ssp. rotundata) is a major environmental weed of littoral habitats on the southeastern coast of Australia. This study investigates the impacts upon selected arthropod assemblages of habitat invasion by this weed. Sixteen sites were placed at four geographic localities within nature reserves between Forster and Budgewoi on the coast of New South Wales. The sampling design included two spatial scales (between and within localities) and eight repeat samples (taken at two scales of temporal separation). Arthropods were collected from both arboreal and epigaeic micro-habitats. Specimens of ants (Hymenoptera: Formicidae), beetles (Coleoptera), true bugs (Heteroptera) and spiders (Araneae) were identified to species level. Differences in α diversity and species abundance distributions between the taxonomic assemblages are described, along with comparisons of data contrasts between bitou bush-free (“control”) and bitou bush-invaded (“impact”) habitats and between geographic localities. A subsidiary impact associated with herbicide application for control of the weed is also examined. Analysis of environmental differences indicates that bitou bush acts as a dampening agent, reducing the degree of seasonal fluctuation in factors such as leaf litter cover. Arboreal Heteroptera were the only group to show consistent evidence of significant differences in taxon richness or abundance between control and impact treatments within a locality, seen as a disruption of normal seasonal variation in diversity in bitou bush-impacted sites. Significant differences between geographic localities were more common, suggesting an effect at broader spatial scales. Evidence for arthropod assemblages characteristic of specific vegetation types was detected for several groups, as were changes in arthropod assemblage composition following application of herbicide for bitou bush control.     

降水强度变化对天山云杉地表凋落物和细根分解的影响

为了探明不同降水条件下干旱区山地森林主要优势树种凋落物分解特征,采用野外模拟试验,通过设计3种降水强度处理[ZP（去除降水）、CK（自然降水,对照）、DP（双倍降水）],研究了降水强度变化对天山云杉地表凋落物（叶和枝）和细根分解的影响。研究结果表明：分解24个月后对照凋落叶、凋落枝和细根干重损失率比去除降水损失率分别高24.79%、2.54%和23.09%,比双倍降水损失率低7.04%、0.68%和10.70%,去除降水对凋落叶和细根分解的抑制作用显著,对凋落枝抑制作用较微弱,双倍降水对分解具有促进作用,但仅对细根分解的促进作用显著。对照和双倍降水处理下凋落叶和细根月平均分解率均表现为双峰型曲线,凋落枝为单峰曲线,去除降水处理下地表凋落物和细根月平均分解率相对平缓。木质素和纤维素残留率也表现为去除降水 > 对照 > 双倍降水。不同降水处理下分解过程中N元素释放模式不同,但C释放模式基本一致。相关分析表明,凋落物月分解率与0~10 cm土层温度的相关性不显著（P>0.05）,但与土壤含水量间为线性极显著正相关（P<0.05）。我们研究结果发现云杉凋落物与根系分解对降水强度变化存在明显差异,未来气候变化对土壤碳周转影响应该充分考虑这种器官间差异。     

Impacts of the invasive Argentine ant on native ants and other invertebrates in coastal scrub in south‐eastern Australia

Invasive ants threaten native biodiversity and ecosystem function worldwide. Although their principal direct impact is usually the displacement of native ants, they may also affect other invertebrates. The Argentine ant, Linepithema humile (Dolichoderinae), one of the most widespread invasive ant species, has invaded native habitat where it abuts peri‐urban development in coastal Victoria in south‐eastern Australia. Here we infer impacts of the Argentine ant on native ants and other litter and ground‐dwelling invertebrates by comparing their abundance and taxonomic composition in coastal scrub forest either invaded or uninvaded by the Argentine ant. Species composition of native ants at bait stations and extracted from litter differed significantly between Argentine ant‐invaded and uninvaded sites and this was consistent across years. Argentine ants had a strong effect on epigeic ants, which were either displaced or reduced in abundance. The native ant Rhytidoponera victoriae (Ponerinae), numerically dominant at uninvaded sites, was completely absent from sites invaded by the Argentine ant. However, small hypogeic ants, including Solenopsis sp. (Myrmicinae) and Heteroponera imbellis (Heteroponerinae), were little affected. Linepithema humile had no detectable effect upon the abundance and richness of other litter invertebrates. However, invertebrate group composition differed significantly between invaded and uninvaded sites, owing to the varied response of several influential groups (e.g. Collembola and Acarina). Floristics, habitat structure and measured environmental factors did not differ significantly between sites either invaded or uninvaded by Argentine ants, supporting the contention that differences in native ant abundance and species composition are related to invasion. Changes in the native ant community wrought by Argentine ant invasion have important implications for invertebrate communities in southern Australia and may affect key processes, including seed dispersal.