Uncertainties of snow cover extraction caused by the nature of topography and underlying surface

Manas River,the largest inland river to the north of the Tianshan Mountains,provides important water resources for human production and living.The seasonal snow cover and snowmelt play essential roles in the regulation of spring runoff in the Manas River Basin(MRB).Snow cover is one of the most significant input parameters for obtaining accurate simulations and predictions of spring runoff.Therefore,it is especially important to extract snow-covered area correctly in the MRB.In this study,we qualitatively and quantitatively analyzed the uncertainties of snow cover extraction caused by the terrain factors and land cover types using TM and DEM data,along with the Per(the ratio of the difference between snow-covered area extracted by the Normalized Difference Snow Index(NDSI) method and visual interpretation method to the actual snow-covered area) and roughness.The results indicated that the difference of snow-covered area extracted by the two methods was primarily reflected in the snow boundary and shadowy areas.The value of Per varied significantly in different elevation zones.That is,the value generally presented a normal distribution with the increase of elevation.The peak value of Per occurred in the elevation zone of 3,700–4,200 m.Aspects caused the uncertainties of snow cover extraction with the order of sunny slopesemi-shady and semi-sunny slopeshady slope,due to the differences in solar radiation received by each aspect.Regarding the influences of various land cover types on snow cover extraction in the study area,bare rock was more influential on snow cover extraction than grassland.Moreover,shrub had the weakest impact on snow cover extraction.     

Spatial patterns of encroaching shrub species under different grazing regimes in a semi-arid savanna,eastern Karoo,South Africa

Woody plant encroachment is increasing in arid and semi-arid regions of the world. We investigated the structure and fine-scale spatial pattern of encroaching species and how these patterns vary with different grazing regimes in semi-arid regions. In this study, we investigated how four encroaching shrub species (Searsia erosa, S. burchellii, Diospyros lycioides and Eriocephalus ericoides) in Middelburg (Eastern Cape, South Africa) coexist and partition space under different grazing regimes (viz. continuous rest, and continuous, summer and winter grazing). We used point-pattern analysis to assess the spatial ecology of these species. We also used an index of integration (mingling index), where low values indicate that they are surrounded by conspecifics and high values indicate that they are surrounded by heterospecifics. The three shrub species were highly mingled except in the winter-grazing plot, where S. burchellii and D. lycioides clustered. We found that the shrub species were generally aggregated in most of the grazing plots. These findings indicate that (1) at a fine spatial scale, grazing in the wet season promotes shrub encroachment, and (2) there is a tendency to aggregation among encroaching shrub species in the grazing plots.     

根际微生态系统理论在我国农业高产高效中的作用——间套种作物种间的根际微生态效应的发现及应用前景

近年来我们通过田间、盆栽、根箱试验对间作套种种间根际相互作用进行了系列研究,并对根际微生态理论在间套作中的应用进行了初步探讨.结果表明,根际效应对间作作物产量优势具有重要贡献,边行增产的84.4%(小麦-玉米)和53.6%(小麦-大豆)中,根际交换作用的贡献分别为37.8和23.2个百分点.     

Inheritance of Seed Shattering in Lolium temulentum and L. persicum Hybrids

Lolium temulentum and L. persicum are non-crop species found in wheat and barley fields. L. temulentum has non-shattering seeds like the associated grain crops, whereas L. persicum seeds shatter after maturity. We analyzed the inheritance mode of shattering tendency by comparing the F₂ of L. temulentum and L. persicum hybrids. The selfed progeny of L. temulentum and L. persicum exhibited typical non-shattering (1.6% shattering) and shattering phenotypes (70.8%), respectively. F₁ hybrids of L. temulentum×L. persicum and its reciprocals were of the shattering phenotype (71.4% and 63.8%, respectively), indicating that shattering is dominant to non-shattering. When the phenotype ratio was assumed to be 15 shattering: 1 non-shattering, the χ² value for F₂ segregation was not significant at the 5% level, and the reciprocal effect was not detected. This indicates that the non-shattering tendency is controlled by two recessive genes. The two-gene inheritance model of shattering tendency suggests that harvest is the selector for seed shattering in cultivated fields, thus the alternative tendency for non-shattering seeds of L. temulentum or shattering of L. persicum would be better adapted to cultivated fields.     

春季休牧后放牧强度变化对短花针茅草原植物种群种间关系的影响

为探讨春季休牧后放牧对短花针茅(Stipa breviflora)草原植物种群种间关系的影响,于2013年8月对苏尼特右旗荒漠草原进行调查研究,试验设2种放牧方式,分别为春季休牧+夏季重牧+秋季适牧(SA1)和春季休牧+夏季适牧+秋季重牧(SA2),分析物种数、物种频度差异,种对关联及群落总体关联性,得到如下结果:春季休牧较对照(全年禁牧)能够显著增加单位面积的物种数,且SA1>SA2;不同植物种群出现频率对春季休牧后不同放牧方式的响应存在显著差异(P < 0.05)。春季休牧后,主要植物种群短花针茅和无芒隐子草(Cleistogenes songorica)主要表现为无关联性,短花针茅与碱韭(Allium polyrhizum)主要表现为负关联性。无芒隐子草和碱韭受春季休牧影响,种间关联由对照处理的正关联转为负关联,且负关联程度SA1较SA2强。春季休牧后,无论放牧强度变化如何,正关联种总数较对照均减少,但物种总体种间亲和作用增加。     

豆禾草种种间竞争关系的研究

将沙漠王子 红三叶、爱森特 红三叶按100% 0%、75% 25%、50% 50%、25% 75%、0% 100%比例混播,400株/m2同比例定苗,用替代试验研究2组禾豆草种种间竞争关系。结果表明:沙漠王子 红三叶按75% 25%的比例混播时,沙漠王子的竞争力超过红三叶,而按50% 50%、25% 75%的比例混播,沙漠王子的竞争力小于红三叶;在爱森特 红三叶的3种混播草地中,爱森特的竞争力一直超过红三叶。     

人工促进天然更新培育菇木林效果调查

对造林后４年林分调查表明，在具有天然更新能力的阔叶林采伐迹地中开展人工促进天然更新培育菇木林比同期在相同条件下开展的人工造林具有保存率高、生长快、投资省的良好效果，是恢复阔叶林资源的有效途径。同时提出了在类似条件下通过人工促进天然更新培育阔叶林和针阔混交林的设想。     

生物质醋液在2种林木播种育苗上的应用

利用以芦苇为原料生产的生物质醋液,经过在西部沙樱、腺齿蔷薇2种林木播种育苗上的应用,确定醋液对其生长作用效果。结果表明：醋液对西部沙樱、腺齿蔷薇2种林木播种幼苗生长具有促进作用,以400、800倍液在种子出苗后4～6叶一心期开始灌根使用,每隔5天一次,共灌施6次,灌根处理为每穴20～30 mL,可显著促进供试幼苗高生长和根系的萌发和生长。     

How to Outgrow Your Native Neighbour? Belowground Changes under Native Shrubs at an Early Stage of Invasion

While it is acknowledged that invasive species are a global driver of land degradation, their effects are often only noticed when the invasion has been going on for a while. However, early stage processes must play a fundamental role in plant establishment until invasive plants are able to outgrow the native vegetation. In ten plots of 100 m² each, we tested the hypothesis that belowground properties are associated with early invasion processes aboveground. We examined the early stage of invasion by a woody legume (Acacia longifolia ), growing in the canopy of native dune shrubs (Corema album ) as a model system in oligotrophic primary dunes in southern Portugal. Biomass under canopies of invaded and non‐invaded C. album shrubs as well as organic matter (OM) distribution in various soil fractions was measured. In accordance with our hypothesis, A. longifolia presence was related to increased C. album foliar δ¹⁵N, a proxy for nitrogen derived from the invasive legume. Under invaded canopies, root and rhizosphere biomass were higher, as was OM in the silt‐clay fraction. Also, δ¹⁵N of the OM in the silt‐clay fraction under invaded canopies was enriched, while δ¹³C was depleted. Finally, we found that the ratio between OM in the biotic versus soil compartment could be a good early indicator for invasion. These findings suggest that even when aboveground invasion pressure on the system is low, it is imperative for ecosystem conservation to remove young plants, as they might alter soil functioning already at an early stage of invasion. Copyright © 2017 John Wiley & Sons, Ltd.     

Freshwater mussels increase survival of largemouth bass (Micropterus salmoides) in drying pools

Between global climate change and anthropogenic water needs, freshwater systems are becoming more intermittent, stressing organisms adapted to perennial waters. Drought-induced intermittency concentrates aquatic organisms into drying pools. These pools represent refugia from desiccation but apply other stressors, such as extreme temperatures and increased competition for dwindling resources. In the Southern United States, fishes and freshwater mussels are often concentrated together in drying pools during seasonal, summer droughts. This can result in increased competition for food among invertivorous fish, but also increased food abundance for these fish because mussels increase macroinvertebrate abundance. Further, since mussels require fish as hosts for their ectoparasitic larval phase, glochidia, competition with their host during this biologically active time is detrimental to mussels. We conducted an experiment to examine the effects of freshwater mussels on trophic resources and fish survival in drying pools. We stocked mesocosms with juvenile largemouth bass that were infected or uninfected with glochidia and tracked abiotic conditions, trophic resources and fish survival for 10 days. We found that fish survived longer in the presence of adult mussels, regardless of their infection status. We suspect that prey items supplemented by adult freshwater mussels increased the survival of fish. Thus, the presence of adult mussels and the resources that increase in their presence potentially mitigate stress to fish in “ecological crunch times.” By conserving mussels, fish populations might withstand droughts more easily.