Diving behaviour of dugongs, Dugong dugon

The diving behaviour of 15 dugongs (Dugong dugon) was documented using time-depth recorders (TDRs), which logged a total of 39,507 dives. The TDRs were deployed on dugongs caught at three study sites in northern Australia: Shark Bay, the Gulf of Carpentaria and Shoalwater Bay. The average time for which the dive data were collected per dugong was 10.4±1.1 (S.E.) days. Overall, these dugongs spent 47% of their daily activities within 1.5 m of the sea surface and 72% less than 3 m from the sea surface. Their mean maximum dive depth was 4.8±0.4 m (S.E.), mean dive duration was 2.7±0.17 min and the number of dives per hour averaged 11.8±1.2. The maximum dive depth recorded was 20.5 m; the maximum dive time in water >1.5 m deep was 12.3 min. The effects of dugong sex, location (study site), time of day and tidal cycle on diving rates (dives per hour), mean maximum dive depths, durations of dives, and time spent ≤1.5 m from the surface were investigated using weighted split-plot analysis of variance. The dugongs exhibited substantial interindividual variation in all dive parameters. The interaction between location and time of day was significant for diving rates, mean maximum dive depths and time spent within 1.5 m of the surface. In all these cases, there was substantial variation among individuals within locations among times of day. Thus, it was the variation among individuals that dominated all other effects. Dives were categorised into five types based on the shape of the time-depth profile. Of these, 67% of dives were interpreted as feeding dives (square and U-shaped), 8% as exploratory dives (V-shaped), 22% as travelling dives (shallow-erratic) and 3% as shallow resting dives. There was systematic variation in the distribution of dive types among the factors examined. Most of this variation was among individuals, but this differed across both time of day and tidal state. Not surprisingly, there was a positive relationship between dive duration and depth and a negative relationship between the number of dives per hour and the time spent within 1.5 m of the surface after a dive.     

Vegetative growth response of young olive trees (Olea europaea L., cv. Arbequina) to soil salinity and waterlogging

High-density olive orchards are increasing around the world, many of which may be potentially affected by salinity and waterlogging (hypoxia), two important stresses common in irrigated fields in arid and semi-arid climates. However, the response of olive to these stresses under field conditions is not well established. Therefore, our objective was to evaluate the vegetative growth response of young olive trees (Olea europaea L., cv. Arbequina) grown in a spatially variable waterlogged, saline-sodic field. We monitored the growth in trunk diameter of 341, 3-year-old olives between September 1999 and September 2000. Field contour maps were developed delineating soil salinity (ECa), relative ground elevation (RGE) and water table depth (WTD). Soil samples were also collected and analyzed for ECe and SARe in order to characterize the salinity and sodicity profiles and develop the ECa-ECe calibration equation. The infiltration rate (IR) of the crusted and uncrusted soil and the penetration resistance (PR) were also measured. The field was characterized by spatially variable ECe (2–15 dS m^–1), SARe (3–40), RGE (–4 to +4 cm) and WTD (0.5–1.9 m, with corresponding ground water EC values between 12 and 6 dS m^–1). Steady-state IR of crusted soil was only 7% of the uncrusted soil. Since the field was heavily irrigated by flooding, waterlogging conditions were related to low RGE values. Soil salinity was negatively correlated (R ² = 0.83, P<0.001) with RGE (ponded water) and WTD (upward flux), due to the evapo-concentration of water and salts at the soil surface. Thus, inverted salinity profiles developed in high salinity areas. Fifty-five percent of the olives were dead 3.5 years after planted, and most of them were located in areas of high ECe (> 10 dS m^–1), low RGE (< – 1.5 cm) and low WTD (< 1.2 m). The surviving trees had vegetative salinity tolerance values of ECe threshold = 4 dS m^–1 and slope = –12% (i.e., percent decline per unit increase in ECe above the treshold), indicating that the Arbequina olive is moderately tolerant to salinity. The RGE and WTD thresholds for olive's survival were > 0.1 cm and > 1.6 m, respectively. Thus, very small changes in ground elevation had a significant effect on olive's survival or death. The coupled effects of salinity and waterlogging (hypoxia) stresses were most detrimental for olive's growth.     

Experimental evidence for the attenuating effect of SOM protection on temperature sensitivity of SOM decomposition

The ability to predict C cycle responses to temperature changes depends on the accurate representation of temperature sensitivity (Q₁₀) of soil organic matter (SOM) decomposition in C models for different C pools and soil depths. Theoretically, Q₁₀ of SOM decomposition is determined by SOM quality and availability (referred to here as SOM protection). Here, we focus on the role of SOM protection in attenuating the intrinsic, SOM quality dependent Q₁₀. To assess the separate effects of SOM quality and protection, we incubated topsoil and subsoil samples characterized by differences in SOM protection under optimum moisture conditions at 25 °C and 35 °C. Although lower SOM quality in the subsoil should lead to a higher Q₁₀ according to kinetic theory, we observed a much lower overall temperature response in subsoil compared with the topsoil. Q₁₀ values determined for respired SOM fractions of decreasing lability within the topsoil increased from 1.9 for the most labile to 3.8 for the least labile respired SOM, whereas corresponding Q₁₀ values for the subsoil did not show this trend (Q₁₀ between 1.4 and 0.9). These results indicate the existence of a limiting factor that attenuates the intrinsic effect of SOM quality on Q₁₀ in the subsoil. A parallel incubation experiment of ¹³C‐labeled plant material added to top‐ and subsoil showed that decomposition of an unprotected C substrate of equal quality responds similarly to temperature changes in top‐ and subsoil. This further confirms that the attenuating effect on Q₁₀ in the subsoil originates from SOM protection rather than from microbial properties or other nutrient limitations. In conclusion, we found experimental evidence that SOM protection can attenuate the intrinsic Q₁₀ of SOM decomposition.     

两种生境条件下差不嘎蒿细根寿命

细根寿命对细根周转具有重要影响, 是生态系统C分配格局和养分循环研究的重要内容。该文利用微管法研究了流动沙地和固定沙地生长的差不嘎蒿(Artemisia halodendron)灌丛细根生长的动态过程, 通过Kaplan-Meier方法估计了细根存活率和中位值寿命, 并做存活曲线, 用对数轶检验比较了不同生境、不同土壤层次和不同月出生细根寿命的差异程度, 同时分析了不同样地细根寿命同土壤全氮、有机质、体积含水量和容重的相关关系。结果表明, 流动沙地和固定沙地差不嘎蒿细根具有相似的存活曲线, 但在各观测点, 流动沙地的细根累积存活率均高于固定沙地, 流动沙地细根中位值寿命(47 d)显著高于固定沙地(35 d)。细根寿命同各样地的土壤全氮和土壤容重呈显著的负相关关系, 同土壤水分呈显著的正相关关系, 但多元回归分析表明, 土壤水分是引起细根寿命变异的关键因素。土层深度对流动沙地细根寿命没有显著影响, 但两生境深层30~50 cm的细根寿命均显著高于上层(10~30 cm)。不同出生月的细根寿命显著不同, 流动沙地和固定沙地细根寿命具有相似的季节变化规律, 春季(4、5月)细根的寿命最长(71 d), 秋季(8、9月)次之(61 d), 夏季(6、7月)最短(39 d)。     

Does hydrological fluctuation alter impacts of species richness on biomass in wetland plant communities?

Aims The diversity–productivity relationship is one of the most critical questions in ecology and can be altered by environmental factors. Hydrological fluctuation affects growth of wetland plants, and such effects vary with plant species. Therefore, we hypothesized that hydrological fluctuation changes effects of species richness on productivity of wetland plant communities.Methods We constructed wetland plant communities consisting of three or six wetland plant species and subjected them to hydrological fluctuation (i.e. gradually changing water level) of two frequencies and two ranges, with unchanged water level as the control. We measured height, root and shoot dry mass of each plant at harvest.Important findings Hydrological fluctuation significantly decreased biomass of wetland plant communities, which was due to impacts of fluctuation range, but not those of fluctuation frequency. Community biomass was significantly higher when species richness was higher, and such an effect did not depend on hydrological fluctuation. Therefore, hydrological fluctuation can decrease the productivity of wetland plant communities but may not alter the diversity–productivity relationship.     

Tracking and data–logging devices attached to elephant seals do not affect individual mass gain or survival

Understanding the cryptic lives of wide–ranging wild animals such as seals can be challenging, but with the advent of miniaturised telemetry and data–logging devices this is now possible and relatively straightforward. However, because marine animals have streamline bodies to reduce drag in their aquatic habitats, attaching external devices to their back or head may affect swimming performance, prey capture efficiency and ultimately, fitness. Given this, and allied welfare concerns, we assessed the short- and long-term consequences of external devices attached to southern elephant seal juveniles and adults under varying environmental conditions. We also assessed the effects of multiple deployments on individuals. There was no evidence for short-term differences in at-sea mass gain (measured as mass on arrival from a foraging trip) or long-term survival rate. The number of times that a seal carried a tracking device (ranging from 1 to 8 times) did not affect mass or estimated survival. Further, there were no tracking device effects in years of contrasting environmental conditions measured as ENSO anomalies. Consequently, we conclude that the current tracking devices available to researchers are valuable conservation tools that do not adversely affect the performance of a large marine mammal in terms of mass gain or survival probability over short (seasonal) or long (years) temporal scales.     

Bayesian inference of genetic parameters for ultrasound scanning traits of Kivircik lambs

Ultrasound scanning traits have been adapted in selection programs in many countries to improve carcass traits for lean meat production. As the genetic parameters of the traits interested are important for breeding programs, the estimation of these parameters was aimed at the present investigation. The estimated parameters were direct and maternal heritability as well as genetic correlations between the studied traits. The traits were backfat thickness (BFT), skin+backfat thickness (SBFT), eye muscle depth (MD) and live weights at the day of scanning (LW). The breed investigated was Kivircik, which has a high quality of meat. Six different multi-trait animal models were fitted to determine the most suitable model for the data using Bayesian approach. Based on deviance information criterion, a model that includes direct additive genetic effects, maternal additive genetic effects, direct maternal genetic covariance and maternal permanent environmental effects revealed to be the most appropriate for the data, and therefore, inferences were built on the results of that model. The direct heritability estimates for BFT, SBFT, MD and LW were 0.26, 0.26, 0.23 and 0.09, whereas the maternal heritability estimates were 0.27, 0.27, 0.24 and 0.20, respectively. Negative genetic correlations were obtained between direct and maternal effects for BFT, SBFT and MD. Both direct and maternal genetic correlations between traits were favorable, whereas BFT–MD and SBFT–MD had negligible direct genetic correlation. The highest direct and maternal genetic correlations were between BFT and SBFT (0.39) and between MD and LW (0.48), respectively. Our results, in general, indicated that maternal effects should be accounted for in estimation of genetic parameters of ultrasound scanning traits in Kivircik lambs, and SBFT can be used as a selection criterion to improve BFT.     

北京东灵山3种温带森林土壤呼吸及其20年的变化

土壤呼吸是陆地生态系统最主要的碳释放过程。为了探讨温带森林土壤呼吸在长时间尺度的变化, 利用北京东灵山地区的白桦(Betula platyphylla)林、辽东栎(Quercus wutaishanica)林和油松(Pinus tabuliformis)林3种温带森林永久样地, 于2012-2015年对其土壤呼吸进行测定, 并与1994-1995年的测定结果进行了比较。结果显示: 2012-2015年, 白桦林的平均年土壤呼吸量为(574 ± 21) g C·m^-2·a^-1, 显著高于辽东栎林(455 ± 31) g C·m^-2·a^-1和油松林(414 ± 35) g C·m^-2·a^-1, 比20年前(1994-1995年)的估测值分别增加了85%、17%和73%。这些结果表明, 近20年来这3种生态系统的碳周转速率明显加快。     

东北地区玉米生长发育特征及其对热量的响应

在大田条件下,以3个玉米品种（丹玉39、原单29和龙单13）为试验材料,设置早、中、晚3个播种期,分析了2007-2008年不同播期3个玉米品种关键生育阶段特征及其对温度的响应.结果表明： 从播种到出苗所需天数依次为早播(平均值为13 d)>中播(平均值为11 d)>晚播(平均值为8 d);出苗阶段平均气温在18 ℃左右时的出苗速率最快,气温偏高或偏低都会降低出苗速率.3个玉米品种在苗期营养阶段生育期天数的差异不大且受温度影响较小;从穗期阶段开始,晚熟品种龙单13的生长速率提高,成熟天数明显缩短;3个品种在穗期和花粒期阶段生长天数均随温度的增加呈减少趋势.全生育期地上干物质积累速率、产量、百粒重均表现为丹玉39>原单29>龙单13.