Formation of filopodia in earthworm (Lumbricus terrestris) coelomocytes in response to osmotic stress

Coelomocytes, the immunodefense cells of the earthworm Lumbricus terrestris, are exposed to changing osmotic pressures as the worm's coelomic fluid responds to fluctuating wet-dry conditions of the surrounding soil. Using light and fluorescence microscopy combined with actin and tubulin disrupting drugs, we determined the effects of changing osmotic pressure on coelomocyte morphology. The coelomocytes from L. terrestris respond to an increase in environmental osmotic pressure from isotonic conditions (170 mOsm) to hypertonic conditions (715 mOsm) by changing from a round/petalloid morphology to a filopodial morphology. Cytoskeletal fluorescent staining studies indicate that for filopodia to form, the actin cortical ring, present in most coelomocytes in isotonic conditions, must be disrupted. Breakdown of the actin ring by exposure to a hypertonic environment or actin disrupting drugs allows the formation of actin or tubulin-based filopodia. The filopodia, or podial-like extensions formed by earthworm coelomocytes, may enable the cells to better explore their environment.     

宁夏河东沙地生物土壤结皮对土壤性质及入渗过程的影响

为了揭示沙漠化治理过程中生物土壤结皮覆盖对土壤入渗过程的影响规律,以宁夏河东沙地人工沙漠治理区4种典型地表覆盖类型：裸沙(BS)、藻类结皮(AC)、藓类结皮(MC)、草本-藓类结皮(H-MC)为研究对象,基于野外双环入渗试验与室内模拟,分析了3种生物土壤结皮覆盖下土壤性质的变化与土壤入渗特征。结果表明：(1)与BS相比,3种结皮覆盖下表层土壤砂粒含量减少2.0%-5.1%,粉粒含量增加3.6%-5.8%,有机质含量增加了5-6倍,AC和MC覆盖下土壤总孔隙度与饱和含水量降低,而H-MC与之相反;(2)平均入渗速率表现为BS>H-MC>AC>MC,1h累计入渗量表现为H-MC>BS>AC>MC,与BS相比,AC、MC和H-MC的初渗速率依次减少了14.3%、37.2%、11.8%,AC、MC的稳渗速率分别降低了14.4%和18.3%,H-MC的稳渗速率增加了4.5%;(3)三种模型中,Kostiakov模型最适用于模拟生物土壤结皮覆盖下土壤水分入渗过程。综上,研究区内不同发育程度生物土壤结皮改变了下层土壤的性质以及土壤的入渗特征,MC与AC阻碍水分入渗,H-MC促进水分入渗。     

Ancestral origins and invasion pathways in a globally invasive bird correlate with climate and influences from bird trade

Invasive species present a major threat to global biodiversity. Understanding genetic patterns and evolutionary processes that reinforce successful establishment is paramount for elucidating mechanisms underlying biological invasions. Among birds, the ring‐necked parakeet (Psittacula krameri) is one of the most successful invasive species, established in over 35 countries. However, little is known about the evolutionary genetic origins of this species and what population genetic signatures tell us about patterns of invasion. We reveal the ancestral origins of populations across the invasive range and explore the potential influence of climate and propagule pressure from the pet trade on observed genetic patterns. Ring‐necked parakeet samples representing the ancestral native range (n = 96) were collected from museum specimens, and modern samples from the invasive range (n = 855) were gathered from across Europe, Mauritius and Seychelles, and sequenced for two mitochondrial DNA markers comprising 868 bp of cytochrome b and control region, and genotyped at 10 microsatellite loci. Invasive populations comprise birds that originate predominantly from Pakistan and northern areas of India. Haplotypes associated with more northerly distribution limits in the ancestral native range were more prevalent in invasive populations in Europe, and the predominance of Asian haplotypes in Europe is consistent with the higher number of Asian birds transported by the pet trade outside the native range. Successful establishment of invasive species is likely to be underpinned by a combination of environmental and anthropogenic influences.     

Climate‐driven speedup of alpine treeline forest growth in the Tianshan Mountains,Northwestern China

Forest growth is sensitive to interannual climatic change in the alpine treeline ecotone (ATE). Whether the alpine treeline ecotone shares a similar pattern of forest growth with lower elevational closed forest belt (CFB) under changing climate remains unclear. Here, we reported an unprecedented acceleration of Picea schrenkiana forest growth since 1960s in the ATE of Tianshan Mountains, northwestern China by a stand‐total sampling along six altitudinal transects with three plots in each transect: one from the ATE between the treeline and the forest line, and the other two from the CFB. All the sampled P. schrenkiana forest patches show a higher growth speed after 1960 and, comparatively, forest growth in the CFB has sped up much slower than that in the ATE. The speedup of forest growth at the ATE is mainly accounted for by climate factors, with increasing temperature suggested to be the primary driver. Stronger water deficit as well as more competition within the CFB might have restricted forest growth there more than that within the ATE, implying biotic factors were also significant for the accelerated forest growth in the ATE, which should be excluded from simulations and predictions of warming‐induced treeline dynamics.     

No evidence for consistent long‐term growth stimulation of 13 tropical tree species: results from tree‐ring analysis

The important role of tropical forests in the global carbon cycle makes it imperative to assess changes in their carbon dynamics for accurate projections of future climate–vegetation feedbacks. Forest monitoring studies conducted over the past decades have found evidence for both increasing and decreasing growth rates of tropical forest trees. The limited duration of these studies restrained analyses to decadal scales, and it is still unclear whether growth changes occurred over longer time scales, as would be expected if CO₂‐fertilization stimulated tree growth. Furthermore, studies have so far dealt with changes in biomass gain at forest‐stand level, but insights into species‐specific growth changes – that ultimately determine community‐level responses – are lacking. Here, we analyse species‐specific growth changes on a centennial scale, using growth data from tree‐ring analysis for 13 tree species (~1300 trees), from three sites distributed across the tropics. We used an established (regional curve standardization) and a new (size‐class isolation) growth‐trend detection method and explicitly assessed the influence of biases on the trend detection. In addition, we assessed whether aggregated trends were present within and across study sites. We found evidence for decreasing growth rates over time for 8–10 species, whereas increases were noted for two species and one showed no trend. Additionally, we found evidence for weak aggregated growth decreases at the site in Thailand and when analysing all sites simultaneously. The observed growth reductions suggest deteriorating growth conditions, perhaps due to warming. However, other causes cannot be excluded, such as recovery from large‐scale disturbances or changing forest dynamics. Our findings contrast growth patterns that would be expected if elevated CO₂ would stimulate tree growth. These results suggest that commonly assumed growth increases of tropical forests may not occur, which could lead to erroneous predictions of carbon dynamics of tropical forest under climate change.     

Tree growth variation in the tropical forest: understanding effects of temperature,rainfall and CO2

Tropical forest responses to climatic variability have important consequences for global carbon cycling, but are poorly understood. As empirical, correlative studies cannot disentangle the interactive effects of climatic variables on tree growth, we used a tree growth model (IBTREE) to unravel the climate effects on different physiological pathways and in turn on stem growth variation. We parameterized the model for canopy trees of Toona ciliata (Meliaceae) from a Thai monsoon forest and compared predicted and measured variation from a tree‐ring study over a 30‐year period. We used historical climatic variation of minimum and maximum day temperature, precipitation and carbon dioxide (CO₂) in different combinations to estimate the contribution of each climate factor in explaining the inter‐annual variation in stem growth. Running the model with only variation in maximum temperature and rainfall yielded stem growth patterns that explained almost 70% of the observed inter‐annual variation in stem growth. Our results show that maximum temperature had a strong negative effect on the stem growth by increasing respiration, reducing stomatal conductance and thus mitigating a higher transpiration demand, and – to a lesser extent – by directly reducing photosynthesis. Although stem growth was rather weakly sensitive to rain, stem growth variation responded strongly and positively to rainfall variation owing to the strong inter‐annual fluctuations in rainfall. Minimum temperature and atmospheric CO₂ concentration did not significantly contribute to explaining the inter‐annual variation in stem growth. Our innovative approach – combining a simulation model with historical data on tree‐ring growth and climate – allowed disentangling the effects of strongly correlated climate variables on growth through different physiological pathways. Similar studies on different species and in different forest types are needed to further improve our understanding of the sensitivity of tropical tree growth to climatic variability and change.     

A novel transition state analog inhibitor of guanase based on azepinomycin ring structure: Synthesis and biochemical assessment of enzyme inhibition

Synthesis and biochemical inhibition studies of a novel transition state analog inhibitor of guanase bearing the ring structure of azepinomycin have been reported. The compound was synthesized in five-steps from a known compound and biochemically screened against the rabbit liver guanase. The compound exhibited competitive inhibition profile with a K_i of 16.7 ± 0.5 μM.