鹤山马占相思人工林的生物量和净初级生产力

通过对鹤山马占相思（Ａｃａｃｉａ ｍａｎｇｉｕｍ）人工林的群落结构,生物量、净初级生产力的研究表明,１５龄的马占相思人工林乔木层总生物量为１９６．９４ｔ．ｈｍ＾－２,其中树干为８０．７５ｔ．ｈｍ＾－２,树枝为５５．１４ｔ．ｈｍ＾－２,树叶为１９．６９ｔ．ｈｍ＾－２,根为４１．３６ｔ．ｈｍ＾－２,该人工林１－７龄生物量增长迅速,而７－１１龄的生物量增则相对较慢,１１龄后生物量趋。１１龄马占相思林的净     

Humidity-regulated dormancy onset in the Fabaceae: a conceptual model and its ecological implications for the Australian wattle Acacia saligna

Background and aims

Seed dormancy enhances fitness by preventing seeds from germinating when the probability of seedling survival and recruitment is low. The onset of physical dormancy is sensitive to humidity during ripening; however, the implications of this mechanism for seed bank dynamics have not been quantified. This study proposes a model that describes how humidity-regulated dormancy onset may control the accumulation of a dormant seed bank, and seed experiments are conducted to calibrate the model for an Australian Fabaceae, Acacia saligna. The model is used to investigate the impact of climate on seed dormancy and to forecast the ecological implications of human-induced climate change.

Methods

The relationship between relative humidity and dormancy onset was quantified under laboratory conditions by exposing freshly matured non-dormant seeds to constant humidity levels for fixed durations. The model was field-calibrated by measuring the response of seeds exposed to naturally fluctuating humidity. The model was applied to 3-hourly records of humidity spanning the period 1972–2007 in order to estimate both temporal variability in dormancy and spatial variability attributable to climatic differences among populations. Climate change models were used to project future changes in dormancy onset.

Key Results

A sigmoidal relationship exists between dormancy and humidity under both laboratory and field conditions. Seeds ripened under field conditions became dormant following very short exposure to low humidity (<20 %). Prolonged exposure at higher humidity did not increase dormancy significantly. It is predicted that populations growing in a temperate climate produce 33–55 % fewer dormant seeds than those in a Mediterranean climate; however, dormancy in temperate populations is predicted to increase as a result of climate change.

Conclusions

Humidity-regulated dormancy onset may explain observed variation in physical dormancy. The model offers a systematic approach to modelling this variation in population studies. Forecast changes in climate have the potential to alter the seed bank dynamics of species with physical dormancy regulated by this mechanism, with implications for their capacity to delay germination and exploit windows for recruitment.     

温州地区黑荆树入侵群落的竞争与动态

黑荆树作为一种入侵植物在国外已经引起了相当的重视,被作为经济植物引入我国以后,目前在很多地区也形成了黑荆树天然更新林.但至今其对于我国生态系统的入侵风险的研究仍然很少.以温州地区6个黑荆树群落为样本,对黑荆树和其它树种的竞争强度、空间关系和群落中物种的相互替代进行了分析,结果表明:(1)黑荆树在群落竞争中并没有体现出优势;(2)黑荆树与其它物种在空间上基本是独立的,这可能是由于竞争强度比较弱,并不能造成明显的竞争性死亡;(3)除马尾松外各群落中物种都维持较高的自我替代,但是在PY04、CN02和RN01群落未来黑荆树仍可能替代其它物种变成主要优势种,而由于其存在幼苗更新困难这种优势不会长久;(4)黑荆树的入侵风险不高,保持群落的生物多样性能够有效地防止黑荆树成为优势物种,因此今后要尽力维持本地群落的生物多样性.     

Volatiles associated with different flower stages and leaves of Acacia cyclops and their potential role as host attractants for Dasineura dielsi (Diptera: Cecidomyiidae)

Acacia cyclops (Fabaceae) is an Australian species which was introduced into South Africa in the nineteenth century. Because of its invasive status in South Africa, a gall midge, Dasineura dielsi (Diptera: Cecidomyiidae), was released in 2001 in order to impact its reproduction by inducing galls on the flowers and thereby preventing seed set. Nothing is known about the cues used by D. dielsi for locating its host flowers. As part of an initial investigation into whether or not chemical cues might play a role in host finding, we analysed headspace samples of Acacia cyclops volatiles from leaves and reproductive parts at different stages (early bud, late bud, early flowering, and senescing flowering stages) using gas chromatography–mass spectrometry (GC–MS). In total, 72 different compounds were detected of which 62 were identified. The analyses showed that open flowers, the stage used by D. dielsi for oviposition, and yellow buds had similar odour compositions with (Z)-3-hexen-1-ol acetate, 4-oxoisophorone, (Z)-β-ocimene, an unknown aliphatic compound, heptadecane, and nonadecane dominating in open flowers. Leaf volatiles were distinct from those in the reproductive plant parts by their high relative amount of (Z)-β-ocimene. (Z)-3-Hexen-1-ol acetate had its maximum relative amount in the green bud samples and was much lower in the later floral stages. In contrast, 4-oxoisophorone peaked in yellow buds and open flowers with little or none of it found in younger or older stages. The volatile compounds of the different flower stages and leaves are discussed in relation to their potential role as attractants used by the biocontrol agent D. dielsi to locate its host plant.     

Guards and thieves: antagonistic interactions between two ant species coexisting on the same ant-plant

Abstract.  1. The simultaneous occupation of a rare understorey ant-acacia Acacia mayana by its guarding ant Pseudomyrmex ferrugineus , and an apparent opportunist parasite of the mutualism, the generalist ant Camponotus planatus is described. The two ant species occur together in 30.7% of the 26 mature A. mayana plants [23.5% of all trees ( n  = 34)] surveyed, but C. planatus is absent from saplings below 1 m in height ( n  = 8).
2. While P. ferrugineus shows behaviour compatible with effective host-tree defence, C. planatus does not attack phytophagous insects and appears ineffective as an ant-guard. Camponotus planatus does, however, occupy swollen thorns (pseudogalls) on the host tree, and harvests nectar from extrafloral leaf nectaries. It is proposed that C. planatus is a parasite of the Acacia–Pseudomyrmex mutualism.
3. Camponotus planatus does not harvest the second trophic reward produced by the tree for its Pseudomyrmex ant-guards, protein-rich food (Beltian) bodies. Camponotus planatus lack the specialised larval adaptations needed to use Beltian bodies as brood food, suggesting that this resource is potentially more resistant to exploitation by generalists than extrafloral nectar.
4. In competition for access to nectaries, C. planatus effectively displaced P. ferrugineus in 99.8% of encounters. These results suggest not only that C. planatus is a parasite of this mutualism, but also that it is able to effectively counteract the aggression shown to other insects by the resident ant-guards.     

The role of canopy gaps in the regeneration of coastal dune forest

In regenerating coastal dune forest, the canopy consists almost exclusively of a single species, Acacia karroo. When these trees die, they create large canopy gaps. If this promotes the persistence of pioneer species to the detriment of other forest species, then the end goal of a restored coastal dune forest may be unobtainable. We wished to ascertain whether tree species composition and richness differed significantly between canopy gaps and intact canopy, and across a gradient of gap sizes. In three known‐age regenerating coastal dune forest sites, we measured 146 gaps, the species responsible for gap creation, the species most likely to reach the canopy and the composition of adults, seedlings and saplings. We paired each gap with an adjacent plot of the same area that was entirely under intact canopy and sampled in the same way. Most species (15 of 23) had higher abundance in canopy gaps. The probability of self‐replacement was low for A. karroo even in the largest gaps. Despite this predominance of shade‐intolerant species, regenerating dune forest appears to be in the first phase of succession with ‘forest pioneers’ replacing the dominant canopy species. The nature of these species should lead to successful regeneration of dune forest.     

Effect of salinity on growth of four strains of Rhizobium and their infectivity and effectiveness on two species of Acacia

Two Rhizobium strains (WU1001 and WU1008) were isolated from nodules of Acacia redolens growing in saline areas of south-west Australia, and two strains selected from the University of Western Australia's culture collection (WU429 isolated from A. saligna and WU433 from A. cyclops). The growth of each in buffered, yeast extract mannitol broth culture was largely unaffected by salt up to 300 mM NaCl. A slight increase in lag time occurred at concentrations of 120 mM NaCl and above, but cell number at the static phase was not affected. Each of the four Rhizobium strains tested accumulated Na⁺ but showed decreasing levels of sugar with increasing salt in the external medium. Amino acid levels also increased, in some cases by more than tenfold. However, the relative proportion of each remained fairly constant in the bacteria, irrespective of salt treatment. Only trace quantities of proline were detected and there was no increase in this amino acid with salt. Acidic amino acids (glutamate and aspartate) remained as a constant proportion.Rhizobium strains WU429, WU1001 and WU1008 produced effective nodules on both A. cyclops and A. redolens grown in sand with up to 80 mM NaCl (added in nutrient solutions free of nitrogen). Strain WU433 was highly infective on both Acacia species tested at low salt concentrations (2–40 mM NaCl), but infection was sensitive to salt levels at 120 mM NaCl and above. Nodules formed with strain WU433 were, however, ineffective on both A. redolens and on A. cyclops and showed nil or negligible rates of acetylene reduction at all salt concentrations. Strains WU429, WU1001 and WU1008 in combination with a highly salt-tolerant provenance of A. redolens formed symbioses which did not vary significantly in nodule number and mass, specific nodule activity or total N content irrespective of salt level up to 160 mM NaCl. On a more salt sensitive provenance of A. redolens and on A. cyclops the infectivity and effectivity of the Rhizobium strains tested usually decreased as the external salt concentration increased. These data are interpreted to indicate that tolerance of the legume host was the most important factor determining the success of compatible Rhizobium strains in forming effective symbioses under conditions of high soil salinity.     

Effects of Acacia (Acacia auriculaeformis A. Cunn)‐associated fungi on mustard (Brassica juncea (L.) Coss. var. foliosa Bailey) growth in Cd‐ and Ni‐contaminated soils

Aims: To evaluate the effect of Acacia auriculaeformis‐associated fungi on the growth of mustard [Brassica juncea (L.) Coss. var. foliosa Bailey] in Cd‐ and Ni‐contaminated soils and design novel plant–fungi associations for bioremediation purpose. Methods and Results: Endophytic Trichoderma H8 and rhizosphere Aspergillus G16 were applied for rhizoremediation of Cd‐, Ni‐, and Cd–Ni combination‐contaminated soils through association with B. juncea (L.) Coss. var. foliosa. Compared with the noninoculated control plants, inoculation with Trichoderma H8 produced 109%, 41% and 167% more fresh weight (FW) plant yields in the Cd‐, Ni‐, and Cd–Ni‐contaminated soils, respectively (P < 0·05). Similarly, plants inoculated with Aspergillus G16 produced 109%, 47% and 44% more FW plant yields in these contaminated soils, respectively. Plants co‐inoculated with these two strains produced 118%, 100% and 178% more FW plant yields, respectively. The inoculations also increased the translocation factors and metal bioconcentration factors. Conclusions: The efficiency of phytoextraction for B. juncea (L.) Coss. var. foliosa was enhanced after inoculating with Acacia‐associated fungi. Significance and Impact of the study: The use of plant–fungi association may be a promising strategy to remediate metal‐contaminated soils.     

厚荚相思树根瘤菌HJ06菌株的16S rDNA全序列和nifA基因片段分析

对厚荚相思(Acaciacrassicarpa)根瘤菌HJ06菌株的16SrDNA全序列和nifA基因片段进行了测定。结果表明,HJ06菌株在以16SrDNA序列构建的系统发育树状图中位于根瘤菌属(Rhizobium)分支中,与根瘤菌属各个种的相似性达95%以上;从HJ06菌株克隆出的585bpnifA基因片段与Klebsiellapneumoniae的同源性达到99.3%,与Klebsiellaoxytoca的NifF,NifL,NifA,NifB蛋白基因的同源性为97.8%。     

Assessment of genetic variability for N2 fixation between and within provenances of Leucaena leucocephala and Acacia albida estimated by 15N labelling techniques

Nitrogen fixed in 13 provenances of Acacia albida and 11 isolines of Leucaena leucocephala inoculated with effective Rhizobium strains was measured by ¹⁵N techniques and the total N difference method. In the test soil, on the average, L. leucocephala derived about 65% of its total N from atmospheric N₂ fixation compared to about 20% by A. albida. Significant differences in the percentage of N derived from atmospheric N₂ (% Ndfa) occurred, between provenances or isolines within species. The % Ndfa ranged from 37 to 74% within L. leucocephala and from 6 to 37 within A. albida; (equivalent to 20–50 mg N plant^–1 and 4–37 mg N plant^–1 for the two species over three months, respectively) and was correlated with the nodule mass (r=0.91). The time course of N₂ fixation of three selected provenances (low, intermediate and good fixers) was followed at 12 weekly intervals over a 36 week period. The % Ndfa of all provenances and isolines increased with time; and except for one of the L. leucocephala provenances, % Ndfa was similar within species at the 36 weeks harvest. There was a significant correlation between % Ndfa and the amount of N₂ fixed (r=0.96). Significant interactions occurred between provenances and N treatments and often growth of uninoculated but N fertilized plants was less variable than for inoculated unfertilized plants.