Nutrient cycling and distribution in different-aged plantations of Chinese fir in southern China

The distribution in tree biomass and understorey vegetation and annual biological and geochemical cycling of total nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) were measured in young, middle-aged and mature plantations (8-, 14- and 24-years old) of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) in southern China. Although >98% of nutrients occurred in the soil, soil nutrient content decreased with plantation age. Nutrient outputs from the soil exceeded inputs in stands of all ages but the net soil nutrient loss increased significantly for N, P and Ca with plantation age. Comparison of nutrient fluxes showed that the smallest (and hence limiting for nutrient cycling) fluxes were litter decomposition in the young plantation in contrast to canopy fluxes (apart from for Mg) in the middle-aged and mature plantations. Nutrient use efficiency, release of nutrients from litter decomposition and nutrient return, particularly in litterfall, increased significantly with plantation age. These results suggest that, as stand age increases, nutrient cycling in Chinese fir plantations is increasingly dominated by biological processes and becomes less dependent on external nutrient sources in rainfall and the soil. It therefore appears that prolonging the rotation length of Chinese fir plantations by approximately 5 years could be beneficial for maintaining the soil nutrient status for successive plantings.     

Private native forest policies in New South Wales,Queensland, Victoria and Tasmania

Private native forests in Australia perform a dual production and conservation role, providing an important source of timber, and complementing formal conservation reserves. A comparison of policies for private native forests in New South Wales, Queensland, Victoria and Tasmania illustrates the scope for timber harvesting, the provision for environmental values, and initiatives for responsible and sustainable forest management. The sustainable management of Australia’s forests requires initiatives by both government and landowners to accommodate changes in community attitudes, new management strategies, integrated catchment management principles and both commercial and non-commercial opportunities for forest use. Of all of the Australian states, New South Wales has the most restrictive laws in terms of forest management and harvesting. Queensland and Victorian legislation have a more commercial focus, while Tasmania has a balance of both environmental and commercial objectives. The duty of care for private native forests is a responsibility that falls to the landholder, and while this should be enforced by legislation, the private provision of community benefits requires both recognition and reward. The presence or absence of incentives potentially determines the effectiveness of forest codes of practice.     

Variation in seedling hydraulic architecture as a function of species and environment

Northern red oak (Quercus rubra L.) and yellow-poplar (Liriodendron tulipifera L.) were grown for two years in full sunlight (unshaded) or 20% of full sunlight (shaded) under either well-watered or drought conditions. There was a close association between evaporative flux (in situ) and leaf-specific conductivity (LSC) in stem segments of both species. Shaded, drought-stressed seedlings of both species had significantly reduced leaf area, evaporative flux, volume flow rate in xylem, flow velocity, potentially functional xylem area, and LSC than unshaded, well-watered seedlings. Reductions in LSC associated with drought or shade were similar for both species; and within a treatment, both species had similar LSC. Species differed in the manner of LSC adjustment to drought and shade. Reductions in leaf area associated with drought or shade were accompanied primarily by reductions in potentially functional xylem area for L. tulipifera, and by reductions in flow velocity for Q. rubra. These results suggest (1) the existence of a homeostatic balance between evaporative flux and LSC, (2) that species with widely different growth patterns and xylem anatomies may develop similar LSC within the same environment, and (3) a possible hydraulic basis for differences in habitat between ring- and diffuse-porous species.     

A comparison of the programme coverage of two therapeutic feeding interventions implemented in neighbouring districts of Malawi

OBJECTIVE: To compare therapeutic feeding programme coverage for severely malnourished children achieved by a community-based therapeutic care (CTC) programme and a therapeutic feeding centre (TFC) programme operating in neighbouring districts in Malawi. DESIGN: Two surveys were implemented simultaneously one in each of the two programme areas. Each survey used a stratified design with strata defined using the centric systematic area sample method. Thirty 100 km2 quadrats were sampled. The community or communities located closest to the centre of each quadrat were sampled using a case-finding approach. Cases were defined as children aged under 5 years with 相似文献   

RNA recognition and cleavage by a splicing endonuclease

The RNA splicing endonuclease cleaves two phosphodiester bonds within folded precursor RNAs during intron removal, producing the functional RNAs required for protein synthesis. Here we describe at a resolution of 2.85 angstroms the structure of a splicing endonuclease from Archaeglobus fulgidus bound with a bulge-helix-bulge RNA containing a noncleaved and a cleaved splice site. The endonuclease dimer cooperatively recognized a flipped-out bulge base and stabilizes sharply bent bulge backbones that are poised for an in-line RNA cleavage reaction. Cooperativity arises because an arginine pair from one catalytic domain sandwiches a nucleobase within the bulge cleaved by the other catalytic domain.     

Secretion of sex hormones in dogs with adrenal dysfunction

OBJECTIVE: To evaluate adrenal sex hormone concentrations in response to ACTH stimulation in healthy dogs, dogs with adrenal tumors, and dogs with pituitary-dependent hyperadrenocorticism (PDH). DESIGN: Prospective study. ANIMALS: 11 healthy control dogs, 9 dogs with adrenal-dependent hyperadrenocorticism (adenocarcinoma [ACA] or other tumor); 11 dogs with PDH, and 6 dogs with noncortisol-secreting adrenal tumors (ATs). PROCEDURE: Hyperadrenocorticism was diagnosed on the basis of clinical signs; physical examination findings; and results of ACTH stimulation test, low-dose dexamethasone suppression test, or both. Dogs with noncortisol-secreting ATs did not have hyperadrenocorticism but had ultrasonographic evidence of an AT. Concentrations of cortisol, androstenedione, estradiol, progesterone, testosterone, and 17-hydroxyprogesterone were measured before and 1 hour after i.m. administration of 0.25 mg of synthetic ACTH. RESULTS: All dogs with ACA, 10 dogs with PDH, and 4 dogs with ATs had 1 or more sex hormone concentrations greater than the reference range after ACTH stimulation. The absolute difference for progesterone, 17-hydroxyprogesterone, and testosterone concentrations (value obtained after ACTH administration minus value obtained before ACTH administration) was significantly greater for dogs with ACA, compared with the other 3 groups. The absolute difference for androstenedione was significantly greater for dogs with ACA, compared with dogs with AT and healthy control dogs. CONCLUSIONS AND CLINICAL RELEVANCE: Dogs with ACA secrete increased concentrations of adrenal sex hormones, compared with dogs with PDH, noncortisol-secreting ATs, and healthy dogs. Dogs with noncortisol-secreting ATs also have increased concentrations of sex hormones. There is great interdog variability in sex hormone concentrations in dogs with ACA after stimulation with ACTH.