农产品生产价格波动与农地利用的关系——以甘肃省为例

农产品生产价格波动与农村耕地利用关系密切,事关中国粮食安全和农业可持续发展问题。以甘肃省为例,通过实地调查和统计数据分析,对主要农产品生产价格波动对农地利用影响的状况进行实证研究,从而为政府相关部门针对影响的不同状况采取相应的对策和政策措施提供参考。     

The effects of light and temperature on the photosynthesis of the Asparagopsis armata tetrasporophyte (Falkenbergia rufolanosa), cultivated in tanks

The integrated aquaculture of the tetrasporophyte of Asparagopsis armata Harvey (Falkenbergia rufolanosa) using fish farm effluents may be viable due to the species high capacity of removing nutrients and its content of halogenated organic compounds with applications on the pharmaceutical and chemical industries. In order to optimize the integrated aquaculture of F. rufolanosa, we followed the daily variation of the potential quantum yield (F_v/F_m) of PSII on plants cultivated at different biomass densities and different total ammonia nitrogen (TAN) fluxes to check if they are photoinhibited at any time of the day. Moreover, the photoinhibition under continuous exposure to highly saturating irradiance and its potential for subsequent recovery in the shade was assessed. The potential for year round cultivation was evaluated by measuring rates of O₂ evolution of plants acclimated at temperatures ranging from 15 to 29 °C, the temperature range of a fish farm effluent in southern Portugal where an integrated aquaculture system of F. rufolanosa was constructed.Photoinhibition does not seem to be a major constrain for the integrated aquaculture of F. rufolanosa. Only when cultivated at a very low density of 1.5 g fresh weight (FW) l^− 1 that there was a midday decrease in maximal quantum yield (F_v/F_m). At densities higher than 4 g FW l^− 1, no photoinhibition was observed. When exposed to full solar irradiance for 1 h, F. rufolanosa showed a 33% decrease in F_v/F_m, recovering to 86% of the initial value after 2 h in the shade. A midday decline of the F. rufolanosa F_v/F_m was also observed under the lowest TAN flux tested (∼6 μM h^− 1), suggesting that this fast and easy measurement of fluorescence may be used as a convenient diagnostic tool to detect nutrient-starved unbalance conditions of the cultures. Maximum net photosynthesis peaked at 15 °C with 9.7 mg O₂ g dry weight (DW)^− 1 h^− 1 and remained high until 24 °C. At 29 °C, the net oxygen production was significantly reduced due to a dramatic increase of respiration, suggesting this to be the species' lethal temperature threshold.Results indicate that F. rufolanosa has a considerable photosynthetic plasticity and confirm it as a good candidate for integrated aquaculture at temperatures up to 24° C and cultivation densities of at least 5 g FW l^− 1. When cultivated at these densities, light does not penetrate below the first few centimetres of the surface zone. Plants circulate within the tanks, spending around 10% of the time in the first few centimetres where they are able to use efficiently the saturating light levels without damaging their photosynthetic apparatus.     

水肥组合对日光温室黄瓜叶片生长和产量的影响

在陕北黄土高原具隔水小区的日光温室内,设计完全随机区组试验,研究了不同水肥组合对结瓜期黄瓜叶片生长和产量的影响。结果表明,在结瓜期,所有处理黄瓜叶面积逐渐增加,而叶片扩展速率、叶片组织含水率、叶片中游离脯氨酸（PRO）和丙二醛（MDA）含量、黄瓜产量和水分利用效率（WUE）均先增加后降低;当土壤含水率一致时,高肥处理（N：600 kg/hm2,P2O5：420 kg/hm2）叶面积、叶片扩展速率、产量和WUE显著高于低肥处理（N：420 kg/hm2,P2O5：294 kg/hm2）;低肥处理产量随土壤含水率增加而增加,高肥处理随土壤含水率增加先增加后降低,WUE随土壤含水率增加而降低。中水高肥处理（WmFh）的叶片净光合速率（Pn）和蒸腾速率（Tr）日变化均高于其他处理。表明,中水高肥处理（田间持水率＞75%～90%,施用N：600 kg/hm2,P2O5：420 kg/hm2）黄瓜在结瓜期叶片生长健壮、光合作用强、产量较高,节约了水资源。     

面向对象的土地利用/覆盖遥感分类方法与流程应用

为了进一步提高干旱/半干旱地区土地利用/覆盖分类精度,该文以新疆石河子垦区为研究区,利用NDVI时间序列分析的方法确定了土地利用/覆盖遥感分类最佳时相组合;采用最佳指数因子OIF对参与图像分割的谱段进行选择;选择不同分割参数建立4级分割层次,构建了不同尺度的分类对象;针对其不同特点,分别选择基于知识的模糊分类和基于样本的监督分类方法;建立了面向对象的土地利用/覆盖遥感分类流程。采用地面实测数据对分类效果进行评估,与基于像元的分类方法相比,该文方法能够获取更高的分类精度,可为同类的研究与应用提供借鉴。     

喀斯特山区坡面土壤水分变异特征及其与环境因子的关系

为探明土地利用方式、地形、微地貌等环境因子对喀斯特山区土壤水分空间变异的影响,应用植被数量生态学中的去趋势典范对应分析方法（DCCA）在一典型坡面上研究了表层（0～15 cm）土壤水分变异特征及其与环境因子的数量关系。研究结果表明,在取样时段内坡面土壤质量含水率均值介于21.36%～32.58%之间,季节变化明显,均呈现中等变异特征。不同土地利用方式下土壤水分随时间的变化趋势一致,均呈明显的“四峰型”波动,土壤平均含水率以自然植被最高,撂荒地和坡耕地次之,人工林最低。DCCA的排序结果显示,土层深度、有机碳含量、土地利用方式和裸岩率对坡地土壤水分变异及其季节变化的影响最为显著,土壤体积质量和坡度的影响次之,坡位和海拔的影响最小。鉴于喀斯特坡面地形及微地貌的复杂性,后续研究还需要加大采样间隔和密度,并综合考虑坡向、坡面曲率、汇水分布面积等因素对土壤水分变异的影响,并结合各土地利用方式下土壤养分状况,探讨适应喀斯特坡地退化生态系统修复的农业工程措施和生态重建模式。     

北京市怀柔区生态用水计算研究

根据生态平衡理论,依据北京市怀柔区的实际情况,划分了北京市怀柔区生态用水类型,并将怀柔区划分为相互独立的二级生态区;计算出怀柔区各项生态用水量。结果为:全区现状生态用水总量为7.19亿m3/a。其中,森林植被生态用水量为4.65亿m3/a,水土保持生态用水量为0.83亿m3/a,城镇绿化生态用水量为0.02亿m3/a,草地生态用水量为1.29亿m3/a,河流生态系统生态用水为0.4亿m3/a。     

European Bison habitat in the Carpathian Mountains

European Bison (Bison bonasus) barely escaped extinction in the early 20th century and now only occur in small isolated herds scattered across Central and Eastern Europe. The species’ survival in the wild depends on identifying suitable habitat for establishing bison metapopulations via reintroductions of new herds. We assessed European Bison habitat across the Carpathian Mountains, a stronghold of European Bison and one of the only places where a viable bison metapopulation may be possible. We used maximum entropy models to analyze herd range maps and habitat use data from radio-collared bison to identify key habitat variables and map European Bison habitat across the entire Carpathian ecoregion (210,000 km²). Forest cover (primarily core and perforated forests) and variables linked to human disturbance best predict bison habitat suitability. Bison show no clear preference for particular forest types but prefer managed grasslands over fallow and abandoned fields. Several large, suitable, but currently unoccupied habitat patches exist, particularly in the eastern Carpathians. This available suitable habitat suggests that European Bison have an opportunity to establish a viable Carpathian metapopulation, especially if recent trends of declining human pressure and reforestation of abandoned farmland continue. Our results also confirm the suitability of a proposed Romanian reintroduction site. Establishing the first European Bison metapopulation would be a milestone in efforts to conserve this species in the wild and demonstrate a significant and hopeful step towards conserving large grazers and their ecological roles in human-dominated landscapes across the globe.     

Saiga antelope calving site selection is increasingly driven by human disturbance

Many terrestrial mammalian species aggregate to give birth. Such aggregations are likely to be a response to changing resource and water availability, for predator swamping and avoidance of disturbance. The critically endangered saiga antelope (Saiga tatarica) is one such species. We analysed spatio-temporal locations of saiga calving aggregations in Kazakhstan over the last four decades obtained from aerial and ground surveys, to identify the factors determining the selection of calving sites within the species’ range as well as any changes in these locations over time. Generalized mixed models were employed in a use - availability framework to assess the factors distinguishing calving from random sites and predict suitable areas for calving. Saigas selected sites, with lower than average productivity and low year to year variability in productivity, at an intermediate distance from water sources, and away from human settlements. A significant change in calving locations was observed during the last decade, with calving areas occurring further north and further away from settlements than previously. The results demonstrate that the choice of calving areas is largely driven by environmental factors. However, disturbance also has a significant impact on calving site selection and in recent decades, its influence overrides that of environmental factors. This increase in the influence of disturbance coincides with a precipitous decline in saiga numbers due to poaching, as well as substantial reductions in the intensity of land use for livestock grazing following the breakup of the Soviet Union. Predictive models based on such studies can improve species conservation by guiding the stratification of sampling for effective monitoring and deployment of rangers to protect the females at this critical time.     

Population demography and fecundity do not decline with habitat fragmentation in the rainforest tree Macadamia integrifolia (Proteaceae)

Habitat fragmentation is often associated with reduced levels of fitness and local extinction of plant species, and consequently poses a major threat to the persistence of species worldwide. The majority of demography-based fragmentation studies to date have focussed primarily on fragmentation impacts on individual plant fecundity. Here we investigate the impact of habitat fragmentation on the demography (plant height classes and density) and key population dynamic processes for the rainforest tree species Macadamia integrifolia (Proteaceae). Raceme and fruit production and seedling emergence across fragmented sites exceeded that in more intact sites with no apparent difference in short-term mortality rates. Fecundity of flowering trees did not appear to be affected by fragmentation. Instead, overall reproductive output in fragmented sites was enhanced relative to undisturbed sites due to a higher proportion of reproductively active individuals. The probability of flowering and fruiting was negatively correlated with the projected foliage cover (PFC) surrounding individual trees, and average PFC was significantly lower in small and medium fragments, suggesting light availability as a potential contributor to the trends observed here.This study demonstrates that the short-term effects of habitat fragmentation on population viability may not necessarily be detrimental for some species, and highlights the importance of assessing not only the fecundity of flowering individuals but also the proportion of individuals reproducing within fragments.     

Impact of litter quality on mineralization processes in managed and abandoned pasture soils in Southern Ecuador

Tropical regions are currently undergoing remarkable rates of land use change accompanied by altered litter inputs to soil. In vast areas of Southern Ecuador forests are clear cut and converted for use as cattle pastures. Frequently these pasture sites are invaded by bracken fern, when bracken becomes dominant pasture productivity decreases and the sites are abandoned. In the present study implications of invasive bracken on soil biogeochemical properties were investigated. Soil samples (0-5 cm) were taken from an active pasture with Setaria sphacelata as predominant grass and from an abandoned pasture overgrown by bracken. Grass (C₄ plant) and bracken (C₃ plant) litter, differing in C:N ratio (33 and 77, respectively) and lignin content (Klason-lignin: 18% and 45%, respectively), were incubated in soils of their corresponding sites and vice versa for 28 days at 22 °C. Unamended microcosms containing only the respective soil or litter were taken as controls. During incubation the amount of CO₂ and its δ¹³C-signature were determined at different time intervals. Additionally, the soil microbial community structure (PLFA-analysis) as well as the concentrations of KCl-extractable C and N were monitored. The comparison between the control soils of active and abandoned pasture sites showed that the massive displacement of Setaria-grass by bracken after pasture abandonment was characterized by decreased pH values accompanied by decreased amounts of readily available organic carbon and nitrogen, a lower microbial biomass and decreased activity as well as a higher relative abundance of actinomycetes. The δ¹³C-signature of CO₂ indicated a preferential mineralization of grass-derived organic carbon in pasture control soils. In soils amended with grass litter the mineralization of soil organic matter was retarded (negative priming effect) and also a preferential utilization of easily available organic substances derived from the grass litter was evident. Compared to the other treatments, the pasture soil amended with grass litter showed an opposite shift in the microbial community structure towards a lower relative abundance of fungi. After addition of bracken litter to the abandoned pasture soil a positive priming effect seemed to be supported by an N limitation at the end of incubation. This was accompanied by an increase in the ratio of Gram-positive to Gram-negative bacterial PLFA marker. The differences in litter quality between grass and bracken are important triggers of changes in soil biogeochemical and soil microbial properties after land use conversion.