Impact of harvesting and logging slash on nitrogen and carbon dynamics in soils from upland spruce forests in northeastern Ontario

The potential impact of timber harvesting in the boreal forest on aquatic ecosystem water quality and productivity depends in part on the production of nutrients within the soil of the harvested catchment. Nitrogen supplied by organic matter decomposition is of particular interest because of the important role that N plays in biotic processes in surface waters, and in forest nutrition in general. Logging slash quality and input to the forest floor has the potential to influence N availability after harvest on clearcut sites. Net production of organic and inorganic-N and microbial biomass C and N concentrations were determined during a 90-day laboratory incubation at constant temperature and moisture. Incubated soils included F horizon and shallow mineral soil horizons (0-5 cm) from unharvested and full-tree harvested (2 and 12 growing seasons since harvest) boreal forest sites at the Esker Lakes Research Area (ELRA), in northeastern Ontario, Canada. In an ancillary experiment, black spruce foliage was added to unharvested forest floor material after 30 days during a 90-day laboratory incubation to simulate the influence of logging slash from full-tree harvesting on C and N dynamics. Twelve-year old clearcut F horizon material released on average 75 and 5 times more -N and 3 and 2 times as much inorganic-N than soil collected from unharvested and 2-year-old clearcuts, respectively. This increase in -N accumulation during the incubation was accompanied by decreases in both exchangeable -N and microbial biomass C and N levels. Net daily changes in microbial biomass N were significantly related to organic and inorganic-N accumulation or loss within the F horizon. Mineral soil release of inorganic-N was lower than release from the forest floor. Nitrate-nitrogen accumulation was lower, and -N accumulation was higher in mineral soil from unharvested sites when compared to 12-year-old clearcuts. Calculated harvest response ratios indicated that incubated mineral soil from the 12-year-old clearcut sites released significantly greater amounts of -N than 2-year-old clearcuts. Incorporation of black spruce needles into F horizon material reduced the production of organic and inorganic-N and increased microbial biomass N. Laboratory incubations of F horizon and shallow mineral soil from 12-year-old clearcuts suggested that these boreal soils have the capacity for increased inorganic-N production compared to uncut stands several years after harvesting. This has the potential to increase N availability to growing boreal forest plantations and increase N leaching due to greater -N levels in the forest soil.     

倒株栽培对网室木瓜生长特性的影响研究

木瓜网室栽培是目前防止木瓜轮点毒素病最有效的方法。广东雷州半岛气温较高,网室因日照通风不良,且温度高于网外,导致植株易徒长、茎细、结果部位高。为探讨网室木瓜倒株栽培利弊,评估找出倒株适期及最佳倒株方法,开展本项技术研究。结果表明,冬植网室木瓜倒株适期为定植后2个月平均株高39.50 cm效果最好,株高及结果部位降低约20 cm,茎增粗0.37 cm,但结果数减少34个/株,采收期延迟18.5 d,开张度、叶片数、单果质量、肉质、糖度及肉色则与对照相比无显著差异;倒株方法以用塑胶绳固定拉倒法效果最好。秋植网室木瓜倒株适期为定植后1个月平均株高36.03 cm效果最好;倒株方法利弊与冬植相同,亦以塑胶绳固定拉倒法为佳。     

山东省群众渔业变水层绳拖网研究↑（*）

近几年，山东省群众渔业绳拖网发展很快，进入９０年代以来，先后在蓬莱、荣成和环翠等地的１３６－１４７Ｋｗ渔船上试验了目大０８ｍ、１ｍ、２２ｍ、３５ｍ、４ｍ、５ｍ、６ｍ、７ｍ、８ｍ、１０８ｍ的绳拖网，取得显著效果。本文对山东省各种绳拖网的试验情况，网型特点，网线配置和其他方面的性能进行了综合分析，并提出改进意见。     

不同栽培条件下枣树幼果期光合作用日变化规律的研究

笔者以10年生壶瓶枣为试材,研究了枣树在灌溉、未灌溉、遮阴、雾化栽培和喷施亚硒酸钠5个处理下光合作用的日变化规律。结果表明:干旱条件降低了树体的光合作用,通过遮阴、雾化栽培和喷施亚硒酸钠可以提高树体的气孔导度,调节叶片的蒸腾,提高树体的光合速率,保证光合作用的进行。亚硒酸钠处理显著提高了叶片上午的净光合速率,气孔导度和蒸腾速率都比其他处理高。     

Accuracy of a machine-vision pellet detection system

Video cameras are employed on net pen fish farms for monitoring food pellet levels near the cage bottom. Herein, the accuracy of a new machine-vision system for the identification of a feed-wastage event and its response time are reported. Research involved novel tests and definitions, video footage recorded under different stocking and environmental conditions, and numerical filters to reduce the effects of misclassifications and patchiness of the pellet wastage record on overall system accuracy. Single-frame food pellet detection accuracy was based on the difference between computer-generated and actual frame counts of pellets greater than 30 pixels in size. A pellet wastage event was defined as a median of three or more visible pellets per frame. During tests on still video frames from different feeding events, the system missed 0.1±0.1 to 1.3±0.4 pellets frame⁻¹, and miss-classified as pellets 0±0.1 to 2.3±0.5 objects frame⁻¹ (n=264). Most missed pellet images were on top of fish images. Waste matter accounted for 65% of the misclassifications, while particles associated with poor camera maintenance accounted for approximately 24%. The average response time to a pellet wastage event was 5.1 and 11.4 s for sampling rates of 2 frames s⁻¹ and 0.5 frames s⁻¹, respectively (n=20 different pellet wastage events). The longest response time (26 s) occurred when fish were amassed against the camera and/or covering pellets. Using appropriate camera lens, camera positioning and/or ‘warning’ software can address fish-interference problems.     

两种施肥情景对温室气体排放和经济成本的影响——以山东滕州和兖州为例

本研究对山东滕州和兖州的施肥状况进行入户调查,借鉴农田管理措施的固碳速率和温室气体(GHG)排放的计算方法,根据农业部的施肥建议设定不同推荐情景,估算施肥现状和推荐情景对GHG净排放和经济成本的影响。结果表明,小麦和玉米都采用推荐用肥能明显减少GHG排放和经济成本,特别是玉米采用基追结合,滕州和兖州的排放分别减少300 kgCe/(hm2·a),成本减少2 700元/hm2,化肥碳效率增加超过30%。总之,农业部施肥建议的推广应用具有重要的环境和经济价值。     

Tree species affect atmospheric CH4 oxidation without altering community composition of soil methanotrophs

Plant species exert strong effects on ecosystem functions and one of the emerging, and difficult to test hypotheses, is that plants alter soil functions through changing the community structure of soil microorganisms. We tested the hypothesis for atmospheric CH₄ oxidation by using soil samples from a Siberian afforestation experiment and exposing them to ¹³C-CH₄. We determined the activity of the soil methanotrophs under different tree species at three levels of initial CH₄ concentration (30, 200 and 1000 ppm) thus distinguishing the activities of low- and high-affinity methanotrophs. Half of the samples were incubated with ¹³C-enriched CH₄ (99.9%) and half with ¹²C-CH₄. This allowed an estimation of the amount of ¹³C incorporated into individual PLFAs and determination of PLFAs of methanotrophs involved in CH₄ oxidation at the different CH₄ concentrations. Tree species strongly altered the activity of atmospheric CH₄ oxidation without appearing to change the composition of high-affinity methanotrophs as evidenced by PLFA ¹³C labeling. The low diversity of atmospheric CH₄ oxidizers, presumably belonging to the UCSα group, may explain the lack of tree species effects on the composition of soil methanotrophs. We submit that the observed tree species effects on atmospheric CH₄ oxidation indicate an effect on biomass or cell-specific activities rather than by a community change and this may be related to the impact of the tree species on soil N cycling.     

Land Equivalent Ratio of Groundnut-Fingermillet Intercrops as Affected by Plant Combination Ratio,and Nitrogen and Water Availability

Abstract

Field experiments were conducted to characterize intercropping advantages in groundnut-fingermillet intercrop in relation to crop combination ratios, soil moisture and nitrogen (N) availability. Three intercrops in 1 : 2, 1 : 1 and 2 : 1 alternating rows of groundnut and fingermillet were examined for their growth and yield in comparison with their respective sole crops in 1996. The effect of well watered (W) and water stressed (D) conditions on the intercropping advantage was also examined for 1 : 1 intercrops in 1995 and 1996. Fertilizer N was applied at the rate of 20 kg ha^?1 in 1995 and 50 kg ha^?1 in 1996. The total above-ground biomass (DM) and its land equivalent ratio (LER) were highest in the 1 : 1 combination ratio. The DM production of intercropped fingermillet was higher in 1996 with higher N than in 1995 with low N application, while those of groundnut were similar in both years. The intercropped groundnut exhibited significantly higher DM production after the fingermillet harvest. The LERs in grain yield were higher in 1996 (1.43 under W and 1.45 under D), than in 1995 (0.87 under W and 1.22 under D). Also, LERs were consistently higher under D than W conditions. Water stress severely reduced the leaf area index (LAI) of fingermillet at a low N, especially in the later stages, whereas higher N alleviated the water stress effect. A close linear relationship was observed between LAI and leaf area (LA) per unit leaf N both for groundnut and fingermillet, with intercrops producing larger LA per unit leaf N than sole crops. Intercropping maintained higher ability in leaf net photosynthesis and transpiration of groundnut up to later stages, and significantly reduced water evaporation from the soil surface under the canopy than sole cropping of fingermillet. These results suggest that three processes associated with the intercropping yield advantages in the groundnut-fingermillet intercrop; 1) higher leaf photosynthesis and vigorous growth of groundnut after the fingermillet harvest, 2) higher LA production per unit N and 3) efficient water use. In conclusion, interspecific shading was considered to be the key mechanism associated with these processes, leading to the intercropping advantages. The degree of the interspecific shade and its effect on growth and yield depended on the available soil N and water.     

Impact analysis of climate data aggregation at different spatial scales on simulated net primary productivity for croplands

For spatial crop and agro-systems modelling, there is often a discrepancy between the scale of measured driving data and the target resolution. Spatial data aggregation is often necessary, which can introduce additional uncertainty into the simulation results. Previous studies have shown that climate data aggregation has little effect on simulation of phenological stages, but effects on net primary production (NPP) might still be expected through changing the length of the growing season and the period of grain filling. This study investigates the impact of spatial climate data aggregation on NPP simulation results, applying eleven different models for the same study region (∼34,000 km²), situated in Western Germany. To isolate effects of climate, soil data and management were assumed to be constant over the entire study area and over the entire study period of 29 years. Two crops, winter wheat and silage maize, were tested as monocultures. Compared to the impact of climate data aggregation on yield, the effect on NPP is in a similar range, but is slightly lower, with only small impacts on averages over the entire simulation period and study region. Maximum differences between the five scales in the range of 1–100 km grid cells show changes of 0.4–7.8% and 0.0–4.8% for wheat and maize, respectively, whereas the simulated potential NPP averages of the models show a wide range (1.9–4.2 g C m⁻² d⁻¹ and 2.7–6.1 g C m⁻² d⁻¹ for wheat and maize, respectively). The impact of the spatial aggregation was also tested for shorter time periods, to see if impacts over shorter periods attenuate over longer periods. The results show larger impacts for single years (up to 9.4% for wheat and up to 13.6% for maize). An analysis of extreme weather conditions shows an aggregation effect in vulnerability up to 12.8% and 15.5% between the different resolutions for wheat and maize, respectively. Simulations of NPP averages over larger areas (e.g. regional scale) and longer time periods (several years) are relatively insensitive to climate data aggregation. However, the scale of climate data is more relevant for impacts on annual averages of NPP or if the period is strongly affected or dominated by drought stress. There should be an awareness of the greater uncertainty for the NPP values in these situations if data are not available at high resolution. On the other hand, the results suggest that there is no need to simulate at high resolution for long term regional NPP averages based on the simplified assumptions (soil and management constant in time and space) used in this study.     

猕猴桃幼树光合特性的研究

猕猴桃幼树净光合速率日变化，一是在强光、高温土壤缺水时呈双峰曲线型，１４时左右出现剧降，光合速率午间锐减与光照、气温、蒸腾增同期发生：二是当光照、气温适中 ，或虽有强光、高温，但土壤水分状况良好时，呈单峰曲线。叶片光合能力旦盛盛时，净光全率在ＣＯ２１５～２０ｍｇ．ｄｍ＾－２．ｈ＾－１之间。气孔因素对光合作用的抑制在１２时前呈上升趋势，１２时以后变化很少。净光合率年变化呈双峰曲线型，５月中旬达峰值后