Termite damage to maize grown in agroforestry systems, traditional fallows and monoculture on nitrogen-limited soils in eastern Zambia

Abstract 1 Termites cause significant damage to maize and other crops in southern Africa. Several studies were conducted with the objective of determining the difference in termite damage to maize in various land use systems between monoculture maize, maize grown using traditional fallows and improved fallows. 2 In an experiment conducted at four sites on noncoppicing fallows, maize planted after Tephrosia candida 02971 fallows had lower termite damage compared with fully fertilized monoculture maize. However, the termite suppression was not low enough to warrant rotation of noncoppicing fallows for termite management.. 3 In four experiments comparing termite damage to maize grown in monoculture and in coppicing fallows, fully fertilized monoculture maize had a higher percentage of lodged plants compared with maize grown in pure Leucaena leucocephala, Gliricidia sepium and Acacia anguistissima fallows or in a mixture of A. anguistissima + Sesbania sesban or Tephrosia vogelii + S. sesban. 4 More than 50–75% of the variance in maize yield was explained by preseason inorganic nitrogen and termite damage. However, termite damage to maize was not influenced by inorganic nitrogen, which represents nitrogen readily available to maize. The decomposition rate of biomass (related to lignin + polyphenol to nitrogen ratio) and water retention under fallows also appeared to influence termite damage. 5 It is concluded that maize grown in L. leucocephala, G. sepium, A. anguistissima and S. sesban fallows suffers less termite damage and produces maize yields comparable with conventionally tilled and fully fertilized monoculture maize.     

Nutrient stocks in managed and natural humid tropical fallows

Managed fallows which recover nutrients more rapidly than natural secondary vegetation may improve the performance of shifting agriculture systems operating under inadequately long fallow cycles. Our objective was to construct nutrient balances for the soil, vegetation, and litter compartments of six planted leguminous fallows and natural secondary vegetation during 53 months. The fallows were planted on a previously cultivated Ultisol (Acrisol) in the Peruvian Amazon and included:Centrosema macrocarpum (Centrosema),Pueraria phaseoloides (Pueraria),Stylosanthes guianensis (Stylosanthes),Desmodium ovalifolium (Desmodium),Cajanus cajan (Cajanus), andInga edulis (Inga). In addition, in the natural fallow treatment secondary vegetation was allowed to establish and grow naturally. Quantities of extractable P, K, Ca, and Mg, total N, and organic C in soil to a 45 cm depth, and macrouttrients in aboveground biomass, roots, and litter were estimated at fallow planting, at 8, 17, and 29 months afterward, and at fallow clearing (53 months). Total N stocks increased by 10% in the Stylosanthes, Desmodium, Pueraria, and Inga treatments, but changed little in the Cajanus, Centrosema and natural fallows. This difference was largely due to greater net increases in both soil and vegetation compartments in the former group of treatments. In the Inga, Desmodium, and natural fallows, total stocks of P and K at 53 months were about 40% to 80% greater and 12% greater, respectively, than initial values, but Ca and Mg stocks were reduced by 25% to 40%. In the other treatments, there was generally little change in P stocks, but large (30% to 60%) reductions in K, Ca, and Mg during the course of the fallow. Although there were net decreases of stocks of P, K, Ca, and Mg in soil in all treatments during the fallow, storage of P and K in vegetation and litter in the Inga, Desmodium, and natural fallows offset losses of these nutrients from soil. These treatments also tended to accumulate more Ca and Mg in biomass and litter than the other treatments. These results suggest that leguminous fallow vegetation that accumulates large amounts of biomass may increase N, P, and K stocks, but that incomplete recuperation of Ca and Mg may limit the sustainability of short-rotation fallow-based systems on acidic, infertile soils. ei]Section editor: G R Stewart     

Permafrost collapse alters soil carbon stocks,respiration, CH4, and N2O in upland tundra

Release of greenhouse gases from thawing permafrost is potentially the largest terrestrial feedback to climate change and one of the most likely to occur; however, estimates of its strength vary by a factor of thirty. Some of this uncertainty stems from abrupt thaw processes known as thermokarst (permafrost collapse due to ground ice melt), which alter controls on carbon and nitrogen cycling and expose organic matter from meters below the surface. Thermokarst may affect 20–50% of tundra uplands by the end of the century; however, little is known about the effect of different thermokarst morphologies on carbon and nitrogen release. We measured soil organic matter displacement, ecosystem respiration, and soil gas concentrations at 26 upland thermokarst features on the North Slope of Alaska. Features included the three most common upland thermokarst morphologies: active‐layer detachment slides, thermo‐erosion gullies, and retrogressive thaw slumps. We found that thermokarst morphology interacted with landscape parameters to determine both the initial displacement of organic matter and subsequent carbon and nitrogen cycling. The large proportion of ecosystem carbon exported off‐site by slumps and slides resulted in decreased ecosystem respiration postfailure, while gullies removed a smaller portion of ecosystem carbon but strongly increased respiration and N₂O concentration. Elevated N₂O in gully soils persisted through most of the growing season, indicating sustained nitrification and denitrification in disturbed soils, representing a potential noncarbon permafrost climate feedback. While upland thermokarst formation did not substantially alter redox conditions within features, it redistributed organic matter into both oxic and anoxic environments. Across morphologies, residual organic matter cover, and predisturbance respiration explained 83% of the variation in respiration response. Consistent differences between upland thermokarst types may contribute to the incorporation of this nonlinear process into projections of carbon and nitrogen release from degrading permafrost.     

Carbon stocks,sequestration, and emissions of wetlands in south eastern Australia

Nontidal wetlands are estimated to contribute significantly to the soil carbon pool across the globe. However, our understanding of the occurrence and variability of carbon storage between wetland types and across regions represents a major impediment to the ability of nations to include wetlands in greenhouse gas inventories and carbon offset initiatives. We performed a large‐scale survey of nontidal wetland soil carbon stocks and accretion rates from the state of Victoria in south‐eastern Australia—a region spanning 237,000 km² and containing >35,000 temperate, alpine, and semi‐arid wetlands. From an analysis of >1,600 samples across 103 wetlands, we found that alpine wetlands had the highest carbon stocks (290 ± 180 Mg C_org ha^?1), while permanent open freshwater wetlands and saline wetlands had the lowest carbon stocks (110 ± 120 and 60 ± 50 Mg C_org ha^?1, respectively). Permanent open freshwater sites sequestered on average three times more carbon per year over the last century than shallow freshwater marshes (2.50 ± 0.44 and 0.79 ± 0.45 Mg C_org ha^?1 year^?1, respectively). Using this data, we estimate that wetlands in Victoria have a soil carbon stock in the upper 1 m of 68 million tons of C_org, with an annual soil carbon sequestration rate of 3 million tons of CO₂ eq. year^?1—equivalent to the annual emissions of about 3% of the state's population. Since European settlement (~1834), drainage and loss of 260,530 ha of wetlands may have released between 20 and 75 million tons CO₂ equivalents (based on 27%–90% of soil carbon converted to CO₂). Overall, we show that despite substantial spatial variability within wetland types, some wetland types differ in their carbon stocks and sequestration rates. The duration of water inundation, plant community composition, and allochthonous carbon inputs likely play an important role in influencing variation in carbon storage.     

Mineral N dynamics,leaching and nitrous oxide losses under maize following two-year improved fallows on a sandy loam soil in Zimbabwe

Plant and Soil - The fate of the added N on a sandy loam soil was determined in an improved fallow - maize sequence field experiment in Zimbabwe. Pre-season mineral N was determined in...     

An improved synthesis of 2- and 4-bromoestradiols.

Bromination of estradiol-17beta by 2,4,4,6-tetrabromocyclohexa-2,5-dienone gives 2- and 4-bromoestradiols in good yields.     

青海省森林土壤磷储量及其分布格局

磷(P)是地球生态系统中重要的生命元素。全球变化背景下, 科学地探究森林土壤磷储量现状及其影响因子, 对陆地生态系统的稳定以及磷的可持续利用具有重要意义。因此, 该研究利用青海省240个森林标准样地土壤实测数据, 并结合青海省森林资源清查资料估算出了青海省森林土壤磷储量, 揭示了其分布格局, 并讨论了土壤磷储量与环境因子的关系。结果表明: (1)青海省森林土壤磷储量为1.74 Tg, 全省1 m深土壤平均磷密度为4.65 Mg·hm ^-2, 土壤磷密度总体上呈地带性分布。(2)土壤磷密度在中低海拔(2 200-3 000 m)区域随海拔的升高显著减小, 在高海拔(3 300-3 900 m)区域随海拔高度的增加而显著变大。山地灰褐色森林土的磷密度最大且显著大于山地棕色暗针叶林土和山地暗褐土。(3)土壤磷含量随海拔升高显著减小, 山地棕色暗针叶林土各土层磷含量相对较大, 山地暗褐土的磷含量最小, 且土壤磷含量随着土层的加深而减小。(4)海拔、温度、土壤类型以及土壤含水量均对土壤磷含量有直接影响, 且影响较大, 其中海拔和温度是影响土壤磷含量变化的关键因子; 土壤磷密度对土壤容重、土壤磷含量、土壤含水量、海拔、土壤类型的变化响应较为明显, 而土壤容重可能是限制土壤磷密度变化的主导因素。     

Trypanosoma brucei rhodesiense: characterisation of stocks from Zambia, Kenya, and Uganda using repetitive DNA probes

We have previously described a system for characterising the relationships between trypanosome stocks of the T.brucei group based on Southern blotting with repetitive DNA probes followed by cluster analysis of resultant banding patterns (G. Hide et al. Molec. Bioch. Parasitol. 39, 213-226, 1990). In this study, we extend this analysis to examine the relationships between trypanosome stocks isolated from major sleeping sickness foci in Zambia, Kenya, and Uganda. We show that the trypanosome strains responsible for disease in Zambia are quite distinct from those sampled from the Kenya/Uganda foci. Furthermore, the human serum resistant stocks isolated from the Kenya/Uganda foci which were isolated from man (or from animals) were found to form a tight group in the cluster analysis, while stocks isolated from nonhuman sources in the same area or stocks from elsewhere were found in separate groups. Thus, the human infective trypanosome strains found in these foci may have common origins and have, perhaps, arisen by clonal selection from a common source.     

Centrally administered N-terminal fragments of ACTH (1-10, 4-10, 4-9) display convulsant properties in rabbits

Electroencephalographic and behavioral effects of the following ACTH fragments: 1-4, 4-9, 4-11, 1-10, 4-10, 1-13, 1-17 and 1-24 were studied in rabbits. Sequences 4-9, 1-10 and 4-10 displayed some epileptic properties, i.e., they induced epileptic seizures (only electrographic or also behavioral) or increased hippocampal spiking. The 4-9 sequence seemed to be the common sequence responsible for these proconvulsant effects. The possible involvement of the enkephalinergic system is discussed.     

Effects of planted tree fallows on soil nitrogen dynamics,above-ground and root biomass,N2-fixation and subsequent maize crop productivity in Kenya

The effects of planted fallows of Sesbania sesban (L.) Merr. and Calliandra calothyrsus (Meissner) on soil inorganic nitrogen dynamics and two subsequent maize crops were evaluated under field conditions in the highlands of eastern Kenya. Continuous unfertilised maize, maize/bean rotation and natural regrowth of vegetation (weed fallow) were used as control treatments. The proportion of symbiotic N₂-fixation was estimated by measuring both leaf ¹⁵N enrichment and whole-plant ¹⁵N enrichment by the ¹⁵N dilution technique for Sesbania and Calliandra, using Eucalyptus saligna (Sm.) and Grevillea robusta (A. Cunn) as reference species. Above- and below-ground biomass and N contents were examined in Sesbania, Calliandra, Eucalyptus and Grevillea 22 months after planting. Both the content of inorganic N in the topsoil and the quantity of N mineralised during rainy seasons were higher after the Sesbania fallows than after the other treatments. Compared to the continuous unfertilised maize treatment, both residual crop yields were significantly higher when mineral N (one application of 60 kg N ha^–1) was added. Furthermore, the second crop following the Sesbania fallow was significantly higher than the continuous maize crop. The above-ground biomass of the trees at final harvest were 31.5, 24.5, 32.5 and 43.5 Mg ha^–1 for the Sesbania, Calliandra, Grevillea and Eucalyptus, respectively. For the total below-ground biomass the values for these same tree species were 11.1, 15.5, 17.7, and 19.1 Mg ha^–1, respectively, of which coarse roots (>2 mm), including tap roots, amounted to 70–90%. About 70–90% of the N in Sesbania, and 50–70% in Calliandra, was derived from N₂-fixation. Estimates based on leaf ¹⁵N enrichment and whole-plant ¹⁵N enrichment were strongly correlated. The N added by N₂-fixation amounted to 280–360 kg N ha^–1 for Sesbania and 120–170 kg N ha^–1 for Calliandra, resulting in a positive N balance after two maize cropping seasons of 170–250 kg N ha^–1 and 90–140 kg N ha^–1, for Sesbania and Calliandra, respectively. All the other treatments gave negative N balances after two cropping seasons. We conclude that Sesbania sesban is a tree species well suited for short duration fallows due to its fast growth, high nutrient content, high litter quality and its ability to fix large amounts of N₂ from the atmosphere.     

High-sorgoleone producing sorghum genetic stocks suppress soil nitrification and N2O emissions better than low-sorgoleone producing genetic stocks

Plant and Soil - Rapid nitrification leads to loss of nitrogen (N) fertilizer in agricultural systems. Plant produced/derived biological nitrification inhibitors (BNIs) are an effective...     

Soil macrofauna order diversity and abundance under improved fallows and organic matter transfer system in Zimbabwe

Sustainable crop production is dependent on improvement of soil health using different management strategies. A study was conducted in the 2008/09 cropping season to investigate soil macrofauna order diversity and abundance under organic matter transfer system and improved fallows in a high rainfall (>800 mm year^?1) area of Zimbabwe. Macrofauna were sampled using monoliths to a depth of 25 cm and Shannon‐Wiener diversity was used for diversity testing. Order diversity varied significantly with treatment under both systems. Under improved fallows, Leucaena trichandra had the highest fauna orders (6) followed by Calliandra colorthysus (5), then Acacia anguistissima (4) while Leucaena pallida and miombo forest had the least orders. Crotalaria juncea had the highest faunal orders (5), among organic material transfer system while other treatments had ≥3 orders. Unfertilized maize had one order. Calliandra colorthysus had the highest order diversity followed by maize stover > cattle manure > Cr. juncea > fully fertilized maize > unfertilized maize. Major groups identified were termites, earthworms, beetles, millipedes and ants. All taxa combined, cattle manure and miombo forest had the highest macrofauna abundance. This study showed that application of organic nutrient resources and use of improved fallows significantly influenced soil macrofauna order diversity and abundance.     

1，2，4－三氯苯在土壤中的降解

在好氧和厌氧两种条件下研究了１,２,４－三氯苯的降解,结果表明,１,２,４－三氯苯的好氧降解和厌氧降解均遵循一级反应动力学在同样水分、温度及初始浓度条件下,１,２,４－三氯苯的好氧降解比厌氧降解迅速,其半衰期分别为１．８９～５．８６和５．０７～１９．０８ｄ土壤中１,２,４－三氯苯的初始浓度对于其降解也有显著影响,在０～１００μｇ·ｇ－１的范围内,浓度增高时,其降解加快,说明污染物浓度对降解的影响;在１０～３０℃范围内,温度增高导致降解过程加快,归因于温度升高对微生物酶活性的激活作用．     

Immunolocalization of BMP-2/-4, FGF-4, and WNT10b in the developing mouse first lower molar.

Intercellular signaling controls all steps of odontogenesis. The purpose of this work was to immunolocalize in the developing mouse molar four molecules that play major roles during odontogenesis: BMP-2, -4, FGF-4, and WNT10b. BMP-2 and BMP-4 were detected in the epithelium and mesenchyme at the bud stage. Staining for BMP-2 markedly increased at the cap stage. The relative amount of BMP-4 strongly increased from E14 to E15. At E15, BMP-4 was detected in the internal part of the enamel knot where apoptosis was intense. In contrast to TGFbeta1, BMP-2 and -4 did not show accumulation at the epithelial-mesenchymal junction where the odontoblast started differentiation. When odontoblasts became functional, BMP-2 and BMP-4 were detected at the apical and basal poles of preameloblasts. BMP-2, which induces ameloblast differentiation in vitro, may also be involved physiologically. The decrease in FGF-4 from E14 to E15 supports a possible role for the growth factor in the control of mesenchymal cell proliferation. The relative amount of FGF-4 was maximal at E17. The subsequent decrease at E19 showed correlation with the withdrawal of odontoblasts and ameloblasts from the cell cycle. WNT10b might also stimulate cell proliferation. At E14-15, WNT10b was present in the mesenchyme and epithelium except for the enamel knot, where the mitotic activity was very low. At E19 there was a decreasing gradient of staining from the cervical loop where cells divide to the tip of the cusp in the inner dental epithelium where cells become postmitotic. The target cells for FGF-4 and WNT10b appeared different.     

The role of remnant trees in carbon sequestration,vegetation structure and tree diversity of early succession regrowing fallows in eastern Sierra Leone

Remnant tree presence affects forest recovery after slash‐and‐burn agriculture. However, little is known about its effect on above‐ground carbon stocks, especially in Africa. We focused our study on Sierra Leone, part of the Upper Guinean forests, an important centre of endemism threatened by encroachment and forest degradation. We studied 99 (20‐m‐radius) plots aged 2–10 years with and without remnant trees and compared their above‐ground carbon stocks, vegetation structure (stem density, basal area) and tree diversity. Above‐ground carbon stocks, stem density, basal area, species richness and tree diversity increased significantly with fallow age. Remnant tree presence affected significantly tree diversity, species dominance and above‐ground carbon stocks, but not vegetation structure (stem density, basal area). Number of remnant trees and number of species of remnant trees were also important explanatory variables. Although other factors should be considered in future studies, such as the size and dispersal modes of remnant trees, our results highlight that more strategic inclusion of remnant trees is likely to favour carbon stock and forest recovery in old fallows. To our knowledge, this is the first study on early succession regrowing fallows in West Africa.     

Differential Interactions of Thrombospondin-1, -2, and -4 with CD47 and Effects on cGMP Signaling and Ischemic Injury Responses

Thrombospondin-1 regulates nitric oxide (NO) signaling in vascular cells via CD47. Because CD47 binding motifs are conserved in the C-terminal signature domains of all five thrombospondins and indirect evidence has implied CD47 interactions with other family members, we compared activities of recombinant signature domains of thrombospondin-1, -2, and -4 to interact with CD47 and modulate cGMP signaling. Signature domains of thrombospondin-2 and -4 were less active than that of thrombospondin-1 for inhibiting binding of radiolabeled signature domain of thrombospondin-1 or SIRPα (signal-regulatory protein) to cells expressing CD47. Consistent with this binding selectivity, the signature domain of thrombospondin-1 was more potent than those of thrombospondin-2 or -4 for inhibiting NO-stimulated cGMP synthesis in vascular smooth muscle cells and downstream effects on cell adhesion. In contrast to thrombospondin-1- and CD47-null cells, primary vascular cells from thrombospondin-2-null mice lack enhanced basal and NO-stimulated cGMP signaling. Effects of endogenous thrombospondin-2 on NO/cGMP signaling could be detected only in thrombospondin-1-null cells. Furthermore, tissue survival of ischemic injury and acute recovery of blood flow in thrombospondin-2-nulls resembles that of wild type mice. Therefore, thrombospondin-1 is the dominant regulator of NO/cGMP signaling via CD47, and its limiting role in acute ischemic injury responses is not shared by thrombospondin-2.Nitric oxide (NO) is a major mediator of intracellular and paracellular signal transduction. NO preserves vascular health by minimizing the adhesion of inflammatory cells to the vessel wall, limiting platelet activation, and increasing blood vessel diameter and blood flow by relaxing vascular smooth muscle cells (VSMC).³ These actions of NO are mediated by activating soluble isoforms of guanylate cyclase (sGC) to increase cGMP levels, resulting in downstream activation of cGMP-dependent protein kinases and ion channels (1).Physiological NO/cGMP signaling is limited by several phosphodiesterases that degrade cGMP and by thrombospondin-1 (TSP). TSP1 is a secreted protein that is produced by vascular and inflammatory cells that regulates cellular behavior by engaging several cell surface receptors. Recently we reported that TSP1 potently blocks NO-stimulated prosurvival responses in endothelial and VSMC (2, 3). TSP1 also plays a role in promoting platelet thrombus formation and hemostasis by antagonizing the antithrombotic activity of NO (4). In all of these vascular cells, picomolar concentrations of TSP1 are sufficient to block NO-stimulated fluxes in cGMP by engaging its receptor CD47 (5). Nanomolar concentrations of TSP1 further inhibit the same signaling pathway by inhibiting CD36-mediated uptake of myristate into vascular cells (6). In vivo, mice lacking TSP1 demonstrate elevated basal tissue cGMP levels and greater increases in regional blood flow in response to a NO challenge than wild type controls (4). After an ischemic insult, the absence of TSP1 or CD47 in transgenic mice is associated with better maintenance of tissue perfusion and enhanced tissue survival. Similarly, targeting TSP1 or CD47 using function blocking antibodies enhances ischemic tissue perfusion and survival in wild type mice and pigs (7, 8).TSP1 belongs to a family of five secreted glycoproteins that share an evolutionarily conserved C-terminal signature domain (9). TSP1 and TSP2 form a distinct subfamily of trimeric proteins that exhibit similar anti-angiogenic activities for endothelial cells in vitro and activities in vivo to block tumor growth. Despite their similarities in structure, TSP1 and TSP2 have markedly different expression patterns after tissue injury, with TSP1 being immediately expressed and maximal at day 3, whereas TSP2 was not expressed until day 7 and was maximal 10 days after injury (10). In addition, large amounts of TSP1 but not TSP2 are stored in platelet α-granules and released into the wound environment. Polymorphisms in TSP1 and TSP2 have been linked to altered risk of premature myocardial infarction (11, 12). A 3′-untranslated region polymorphism in TSP2 is also associated with type 2 diabetes in men (13). The molecular basis for these associations is unclear.Less is known about the roles of the pentameric TSP3–5 in vascular cells. TSP3 and TSP5 (also known as cartilage oligomeric matrix protein) appear to serve their primary functions in bone development (14, 15). However, a polymorphism in TSP4 is associated with premature myocardial infarcts in certain populations (11, 16, 17). A proatherogenic activity for the A387P variant of TSP4 was proposed based on its differential ability to modulate proliferation of endothelial and VSMC (18). Cardiovascular functions of TSP4 may also be linked to the high expression of TSP4 in heart (19) and its altered expression in that tissue during hypertensive heart failure (20).The C-terminal domain of TSP1 is sufficient to mediate CD47-dependent inhibition of cGMP signaling (5). Of the two CD47 binding VVM motifs identified in this domain of TSP1, the first is conserved among all five TSPs, suggesting that CD47 binding could be a universal attribute of this family (21). Based on structural evidence that the VVM motifs may not be accessible (22, 23), however, conservation of VVM motifs may not be sufficient to predict CD47 binding. Uncertainty regarding the location of the CD47 binding site in the G domain of TSP1 therefore limits interpretation of the known sequence homology to predict CD47 binding to other TSP family members.Although CD47 recognition of other TSPs has not been demonstrated experimentally, a local deficiency of inflammation-associated T cell apoptosis shared by TSP1-, CD47-, and TSP2-null mice is consistent with this hypothesis (24). Furthermore, a 21-residue peptide from the C-terminal domain of TSP4 was found to decrease human umbilical vein endothelial cell proliferation similar to the CD47 binding peptides from TSP1, although it lacks the VVM motif and no interaction with CD47 was demonstrated (25).To directly address whether other TSP family members can inhibit NO responses and signaling in vascular cells, we now compare binding of recombinant signature domains of TSP1, TSP2, and TSP4 to cell surface CD47 and inhibition of NO-stimulated cell responses and cGMP signaling by these domains. We also compared acute tissue blood flow and perfusion responses to ischemic challenge in TSP1 and TSP2-null mice and cGMP responses in primary cultures of vascular cells isolated from these mice. These studies clearly demonstrate that CD47 selectively interacts with TSP1 and that the signature domains of TSP2 and TSP4 are less potent inhibitors of NO signaling in vascular cells in vitro. Furthermore, we show that the role of TSP1 to acutely limit recovery from ischemic injury in vivo is not shared by TSP2.