开路与闭路涡度相关系统对森林生态系统甲烷通量观测的比较

作为涡度相关技术观测的两种主要技术手段,开路（OPEC）和闭路（CPEC）两种涡度相关系统在观测森林生态系统CH4通量过程中存在较大的不确定性,本研究利用OPEC和CPEC两种涡度相关系统,对黄河小浪底人工混交林CH4通量进行连续观测,选取生长旺季2016年7月24日-8月5日连续14d数据,对比两种观测系统的功率谱和协谱,估算闭路涡度相关系统的延迟时间,并分析其在连续晴天和连续雨天的通量观测结果。结果表明：CPEC系统的功率谱和协谱在所有频率上与OPEC系统基本一致,在惯性副区功率谱符合-5/3相似规律,协谱符合-4/3相似规律;以OPEC系统为“准”标准,CPEC系统观测CH4通量的延迟时间合适流速范围内的5个不同流速（40、37.5、35.5、33.5、31.5L·min-1）分别为4.6、7.7、5.3、10.8和14.3s,平均延迟时间为8～9s;与OPEC观测系统测定的CH4通量相比,CPEC系统观测结果晴天偏低12%;雨天高出32%。OPEC观测系统适用于晴天CH4通量观测。经校正,消除延迟影响后的CPEC观测系统可用于测定雨天CH4通量,以弥补OPEC观测系统缺测的值。两种系统并行观测、相互弥补,可望获得更完整、更高质量的CH4通量数据。     

Carabid beetle (Coleoptera: Carabidae) diversity in the black spruce succession of eastern Canada

This study provides the first assessment of carabid beetle diversity in a natural forest context that encompasses a complete black spruce (Picea mariana) natural succession. Boreal forest conservation has been based on several assumptions about forest age that only consider species richness without accounting for species composition. It has also been guided by studies of incomplete chronologies that do not include naturally burned or old-growth stages. Twenty-one forest stands of different ages following fire - from recently burned to old-growth stages (0-340 years of age) - were sampled, revealing a strong relationship between age of forest and diversity of Carabidae. Over time, species richness followed a parabolic U-shaped pattern both with observed (Obs) and predicted richness (ACE). Chronological clustering identified four groups of species in the succession: the ‘burned’ group characterized 0-2-year-old forests, ‘regenerating’ (21-58 year), ‘mature’ (70-170 year) and ‘old-growth’ (177-340 year). The time spans corresponding to each of these assemblages lengthen with age of forest at an exponential rate. Ward’s and K-means (clustering without constraint) provided support for the four assemblages but showed variation between individual successions, particularly for the ‘regenerating’ assemblage, identified as the most heterogeneous. The IndVal method identified characteristic species in every stage of the succession, particularly Sericoda spp. in the burned stage and Dromius piceus and Platynus mannerheimii associated with old-growth stands. The results obtained here show that diversity of Carabidae varies in primeval conditions according to age of forest and such variation should be taken into account when conservation issues are involved.     

The response of an elephant population to conservation area expansion: Phinda Private Game Reserve, South Africa

Continuous human population expansion pressure on conservation ecosystems restricts wildlife areas, and necessitates active management. In areas of changing land-use and increasing human-animal conflict, responses of wildlife to direct human interventions can inform managers and planners. During August 2004, the boundary fences between Phinda Private Game Reserve and two neighbouring reserves were removed. This study examined behavioural responses of the resident elephants. Older, recently introduced bulls moved into the new area during the first month after fence removal, while younger resident bulls and family groups took between five and eight months. Initially family groups only moved into the new area at night and spent minimal time there, while older bulls spent longer periods of time, regardless of time of day. One year after fence removal, most of the elephants had only expanded their home ranges slightly into the new area. One of the findings of this study is that elephants appear to act cautiously in exploring new areas and responded by moving into the area slowly and over a relatively long time period. This cautious behaviour reduced through time as animals became more familiar with the area. The spatial scale of response of the elephants was relatively small, while the temporal scale of response was relatively large.     

Non-stationary thermal time accumulation reduces the predictability of climate change effects on agriculture

Current modeling studies on the impacts of climate change on agriculture widely assume that thermal time accumulation of crops during the growing season remains constant under various climate conditions. However, in this study, a 20-year single rice variety, experimental dataset indicates that the thermal time accumulation for the entire growing season is not constant. As a result, a crop model based on constant thermal time accumulation significantly underestimates the observed phenological trend exhibited over the two decades of research—despite comparably accurate simulations of short periods. This deviation can result in misleading yield simulations, whereas the model simulations, using observed phenology data, show a similar yield trend as the observation. This study casts serious doubt on the assumptions of constant thermal time accumulation made in previous modeling studies, and, moreover, it highlights the critical requirements needed to improve phenology simulations on a larger scale so that predictions of the eventual yield trends due to climate change can more accurately reflect the results of yield trends in reality.     

氮素形态、用量及施用时期对小青菜产量和硝酸盐含量的影响

采用田间试验研究了氮素形态、用量及施用时期对小青菜产量和硝酸盐含量的影响。结果表明,等氮量施肥下,产量最高的是硝酸钙,尿素+微量元素处理;尿素,有机无机复混肥和碳酸氢铵处理间无显著差异,DMPP处理产量最低;追施微量元素能提高小青菜的产量。硝酸盐含量随着收获时期的延后而降低,有机无机复混肥处理则略有升高,但未达到显著水平;收获期取样时,不同氮肥对硝酸盐的积累是:硝酸钙＞DMPP＞尿素＞有机无机复混肥＞尿素+微量元素＞碳酸氢铵。配施微量元素及氮磷钾的协同吸收均能降低硝酸盐含量。综合考虑产量和品质指标,以有机无机复混肥处理效果较好。小青菜产量和Vc含量随着施氮量的提高而提高,但硝酸盐含量也随之提高;小青菜产量和Vc含量随着施氮时期的延后而降低,硝酸盐含量高峰出现在追肥后20d左右。     

几种不同类型土壤有机碳库容大小及周转研究

通过土壤样品的室内培养,运用三库一级动力学理论,分析了沼泽土、草甸土、普通黄棕壤和棕色石灰土4种土壤有机碳库容大小、各碳库平均周转时间及分解动态。结果表明,4种土壤剖面表层和中层有机碳含量分别为8.48~24.53 g/kg,4.02~16.77 g/kg;活性碳占总有机碳含量的0.99%~5.01%,1.31%~1.91%,平均周转时间分别为8.8~14.3 d,10.4~16.5 d;缓效性碳占总有机碳含量的15.88%~59.04%,20.43%~48.36%,平均周转时间分别为1.3~29.1 a,3.6~21.3 a;惰性碳占总有机碳含量的39.97%~79.11%,50.31%~77.66%。不同类型土壤三库有机碳含量均是上层明显大于中层,培养3个月,表层和中层土壤有机碳累计分解量分别达到了165.99~2 429.57 mg/kg,108.04~743.02 mg/kg,4种土壤有机碳分解速率大小顺序:沼泽土>草甸土>棕色石灰土>普通黄棕壤,与活性碳的百分比含量成正相关关系。对培养期间土壤有机碳累计释放量进行拟合,发现三次方程(Y=b0 b1x b2x2 b3x3)能很好地描述其变化趋势,相关性均达到极显著水平(P<0.01)。     

基于可见/近红外光谱的柑橘糖度在线检测分选系统的设计与试验

在6GF–4型林果无损检测与分选成套设备中,设计了基于可见/近红外光谱的柑橘糖度在线检测分选系统,系统主要包括传输装置、光谱采集装置、控制系统以及分选装置。系统在柑橘果实运动状态中采集其光谱信息,并通过所建立的果实糖度模型进行同步计算,根据所得糖度值对柑橘果实实现在线分选。在光谱采集装置中设计了双透镜式光路,可改变投射于柑橘果实上的光斑大小,通过研究比较试验参数积分时间和光斑尺寸大小,得出系统的最佳采集参数为积分时间100 ms,光斑尺寸设置为小,样本移动速率为5个/s。建立的SPXY–CARS–PLSR柑橘糖度在线检测模型校准集和预测集的决定系数分别为0.938和0.836,校准集和预测集的均方根误差分别为0.273°Brix和0.418°Brix。使用未参与建模的25个柑橘果实样本进行外部验证集的在线检测和分选,结果在1°Brix的误差范围内,检测糖度的准确率为92%;当样本分为4个等级时,系统分选正确率为92%;当样本分为3个等级时,系统分选正确率可达100%。     

烟株砍收遮光水养对东北烤烟低温减灾的成效

为破解东北烟区烤烟生长后期低温影响烟叶采收的障碍,提高烟叶质量,尝试将低温灾害风险预警等级划分成正常、低风险、中风险、高风险,在中风险和高风险临近时(前2 d),采取对烟株砍收遮光水养采烤的措施,分析其对烤后烟叶的经济性状、外观质量、化学成分含量及感官质量的影响。结果表明：当预警等级为中风险以下时,烟株砍收遮光水养采烤处理,烤坏烟损失率较常规采烤降低8.5%,总损失率降低12.6%,烟叶外观质量评价总分可提高0.06分,但外观和感官质量改善不明显;当预警等级为高风险时,烟株砍收遮光水养采烤处理,烤坏烟损失率降低55.1%,总损失率降低70.2%,上等烟和中等烟比例显著提高78.7%、57.2%,外观质量评价总分显著提高了0.58分,两糖比、糖碱比较高,改善了化学成分的协调性及感官质量。建议当低温灾害风险预警等级为中风险及以下时,对田间未达成熟标准的烟叶,采用常规采烤方法;当高风险临近时,则采用烟株砍收遮光水养采烤方法,以达到减灾保收的目的。     

The role of time preferences in contract breach: Evidence from Chinese poultry farmers participating in contract farming

Farmers’ contract breach behavior is cited as one of the major stumbling blocks in the sustainable expansion of contract farming in many developing countries. This paper examines farmers’ contract breach decisions from the perspective of time preferences. The empirical analysis is based on a household survey and economic field experiments of poultry households participating in contract farming conducted in Jiangsu Province, China. A discounted utility model and a maximum likelihood technique are applied to estimate farmers’ time preferences and the effect of time preferences on contract breach in the production and sales phases are explored with a bivariate probit model. The results show that, on average, the poultry farmers in the sample are generally present biased and impatient regarding future utility. The regression results show that farmers with a higher preference for the present and a higher discount rate are more likely to breach contracts, and time preferences play a greater role in the production phase than in the sales phase. When considering heterogeneity, specific investments and transaction costs promote contract stability only for farmers with a low degree of impatience. Moreover, compared with large-scale farmers, small-scale farmers’ contract breach decisions are more significantly affected by their time preferences. These results have implications for contract stability policies and other issues that are impacted by the linking of behavioral preferences to agricultural decisions.     

Influence of two-stage harvesting on the properties of cold-pressed rapeseed (Brassica napus L.) oils

Rapeseed (Brassica napus L.) harvesting method is critical since it significantly determines the seed yield, oil quality, and industrial efficiency. This study investigated the influences of harvesting methods on the quality of cold-pressed rapeseed oil of two varieties. Oil color, peroxide value (POV), tocopherol content, fatty acid composition, and polarity of total polyphenols (PTP) contents of two rapeseed varieties in Huanggang and Xiangyang were compared through artificially simulated combined harvesting and two-stage harvesting. Results showed significant differences in the quality of rapeseed oil between the two harvesting methods. The red value (R-value), POV, total tocopherol contents, linoleic and linolenic acid content, and PTP content of the pressed rapeseed oil prepared by the combined harvesting method were about 27.6, 5.7, 15.8, 2.0, 0.5, and 28.6% lower than those of the oil produced from the two-stage harvesting method, respectively. Xiangyang and Huayouza62 performed better in the two regions and two varieties, respectively. To sum up, the rapeseed oil obtained 41–44 days after final flowering of combined harvesting, 35 days after final flowering, and six days of post-ripening of the two-stage harvesting had the best quality.