Seasonality affects leaf nutrient and condensed tannin concentration in southern African savannah browse

Trees that maintain some leaves throughout dry seasons become important ruminant browse depending on nutritive and antinutritive values. Leaves from seven tree species that maintained some leaves during the dry season were collected during dry and wet seasons and analysed for nutritive and antinutritive values. Neutral detergent fibre of leaves was either not different or less (P ≤ 0.05) during the dry season as compared to the wet season depending on species. Acid detergent fibre was either not different or greater (P ≤ 0.05) during the dry season as compared to the wet season. Crude protein and condensed tannins (CT) were either not different or less (P ≤ 0.05) during the dry season than during the wet season for the seven species. The biological activity (protein‐binding ability; PB) of the CT was highly species specific and was either not different between seasons, more bioactive during the wet season, or more bioactive during the dry season depending on the species. Based on combinations of low fibre, high protein and potentially beneficial levels of bioactive CT, Senegalia caffra, Vachellia karoo and Searsia lancea may be the most promising dry‐season browse of the species studied.     

不同径级马占相思(Acacia mangium)整树蒸腾的湿、干季变化

利用Granier树干液流测定系统对广东鹤山丘陵地马占相思(Acacia mangium)林进行长期监测,并同步监测环境因子(空气温度、相对湿度、光合有效辐射、土壤体积含水量),选择胸径具有代表性的样树,结合马占相思的形态学参数,计算马占相思的整树蒸腾.通过对光合有效辐射(PAR)分级,建立不同辐射强度等级的湿季(土壤水分θ≥33%)整树蒸腾与水汽压亏缺(VPD)的相关方程,以干季(θ≤24%)的VPD代入对应PAR等级的湿季的拟合方程,求出干季的潜在蒸腾,以潜在蒸腾和干季实际蒸腾之差分析不同径级整树蒸腾在不同季节的实际变化.在所有的PAR分级内,干季整树蒸腾显著低于湿季,仅占湿季蒸腾的10%～20%,就蒸腾减少的绝对量而言,优势木>中间木>劣势木.土壤水分下降缩小了不同径级树木之间液流密度的差异,土壤水分亏缺限制了树木的蒸腾,对马占相思的生长造成一定程度的水分胁迫.     

Seasonality,habitat type and locality influenced bird assemblage structure in Nigeria

This is the first report of the avian assemblage in the study area of Dutse, Nigeria. In addition to recording bird species, the effects of season, dominant vegetation structure, locality and anthropogenic activities on bird abundance, species richness and diversity were investigated. Using the point transect method, 264 points on 48 km of transect were used to count birds between 06:30 and 11:00 from August 2015 to February 2016. A total of 122 bird species of 41 families were recorded. Highest bird species richness was recorded in Warwade, highest abundance in Model, and highest diversity in Malamawa. The dry season and woodland habitat showed higher bird species richness, abundance and diversity than the wet season and shrubland habitat. Tree density was more important in increasing bird abundance than shrub density. Small-scale anthropogenic activities and habitat modification, such as farming, grazing, wood removal and human interference did not appear to have impacted the birds; however, loss of high tree-density woodland habitats may pose a major threat to the bird community in Dutse. The presence of birds of concern in the area suggests the need for conservation efforts of avifauna and as well as the forested habitats in Dutse.     

Seasonal variation in exposure frequency and concentration levels of aflatoxins and ochratoxins in urine samples of boys and girls

Urine samples from children in Sierra Leone (134 boys and 110 girls), were collected during the dry season. During the rainy season samples were collected from 97 boys and 93 girls. Analysis of the dry season samples, revealed that, with the exception of one boy, all children had detectable amounts of aflatoxins and/or ochratoxins in their urine. Similarly, with the exception of four children (two from each sex), rainy season urine samples also contained these two mycotoxins. There were significant differences in the frequency of exposure to some mycotoxins: ochratoxin A (OTA), p < 0.01;4-hydroxyochratoxin A (4R-OTA), p < 0.002; aflatoxin M1 (AFM₁), p < 0.04;aflatoxicol (AFL), p < 0.03; aflatoxin B₂ (AFB₂), p < 0.04 . There were also significant differences in the levels of aflatoxin B₁ (AFB₁), (p < 0.05) and AFB₂, (p < 0.02) detected in dry season samples. Stratification of these results according to season and sex, has indicated significant differences with respect to 4R-OTA (p < 0.04) and AFB₁ (p < 0.02). The results of this study show that in Sierra Leone, children are frequently and constantly exposed to both aflatoxins and ochratoxins. This revised version was published online in August 2006 with corrections to the Cover Date.     

非生长季降水对青藏高原高寒草甸优势种生物量稳定性的影响

受全球气候变化的影响,青藏高原在过去的几十年间整体上呈现暖湿化的趋势,相比于年际之间温度和降水的变化外,生长季和非生长季气候变化模式的差异可能会对生态系统产生更重要的影响,但相关的研究尚不充分。以青藏高原东部的高寒草甸为研究对象,基于2001年至2017年17年的野外观测数据,包括优势植物紫花针茅的高度、多度以及生物量、次优势物种洽草的生物量,结合生长季和非生长季平均温度和降水量的变化,通过线性回归以及结构方程模型,探究生长季/非生长季不对称气候变化对于青藏高原高寒草甸优势物种生物量稳定性的影响。研究结果表明：1)青藏高原东部年均温和年降水在过去的17年间显著增加,呈现暖湿化的趋势,但是非生长的降水却变化不明显;2)紫花针茅的高度、多度以及生物量在过去17年没有显著的趋势,但是洽草的生物量稳定性显著减少;3)非生长降水结合紫花针茅的高度、多度以及洽草的生物量稳定性促进了紫花针茅的生物量稳定性。研究结果可以为青藏高原高寒草甸在未来气候变化的背景下合理保护与利用提供科学依据。     

Seasonal differences in the hormonal control of territorial aggression in free-living European stonechats

In birds, territorial aggression during the breeding season is regulated by testosterone (T). However, many bird species also express aggressive behavior during the nonbreeding season, when plasma levels of T are low. It has been suggested that during this period estrogens might play a major role in regulating territorial aggression. In the present study we compared the effects of simultaneous blockage of androgenic and estrogenic actions on territorial aggression during the breeding and nonbreeding seasons in free-living male European stonechats (Saxicola torquata rubicola). European stonechats are of particular interest since they establish territories and form pairs during both the breeding and the nonbreeding seasons. Thus territorial aggression and its endocrine control can be compared between reproductive and non-reproductive contexts. Inhibition of androgenic and estrogenic actions by simultaneous application of Flutamide and ATD reduced territorial aggression during the breeding season, but not during the nonbreeding season. Our results show that androgens and/or estrogens are involved in the endocrine control of territorial aggression in stonechats only in a reproductive context, but not in a non-reproductive one.     

Phenology and climate relationships in aspen (Populus tremuloides Michx.) forest and woodland communities of southwestern Colorado

Trembling aspen (Populus tremuloides Michx.) occurs over wide geographical, latitudinal, elevational, and environmental gradients, making it a favorable candidate for a study of phenology and climate relationships. Aspen forests and woodlands provide numerous ecosystem services, such as high primary productivity and biodiversity, retention and storage of environmental variables (precipitation, temperature, snow–water equivalent) that affect the spring and fall phenology of the aspen woodland communities of southwestern Colorado. We assessed the land surface phenology of aspen woodlands using two phenology indices, start of season time (SOST) and end of season time (EOST), from the U.S. Geological Survey (USGS) database of conterminous U.S. phenological indicators over an 11-year time period (2001–2011). These indicators were developed with 250 m resolution remotely sensed data from the Moderate Resolution Imaging Spectroradiometer processed to highlight vegetation response. We compiled data on SOST, EOST, elevation, precipitation, air temperature, and snow water equivalent (SWE) for selected sites having more than 80% cover by aspen woodland communities. In the 11-year time frame of our study, EOST had significant positive correlation with minimum fall temperature and significant negative correlation with fall precipitation. SOST had a significant positive correlation with spring SWE and spring maximum temperature.     

青藏高原草地植物叶解剖特征

运用常规石蜡制片技术对我国青藏高原66种草地植物优势种的叶解剖特征进行研究,并分析了叶解剖特征与海拔、生长季降水及生长季均温之间的关系.结果表明:青藏高原草地植物叶片具有很多适应高寒环境的结构特征,如表皮层厚且表皮细胞大小差异显著,表皮毛等表皮附属物发达,异细胞丰富,通气组织普遍发达等;叶片各组成部分厚度的变异程度不同,其中海绵组织厚度变异最大,其次为上角质层、下表皮层、下角质层、上表皮层、栅栏组织,叶片厚度的变异最小;青藏高原草地植物叶片各组成部分的厚度存在协同进化,上下角质层厚度呈强烈正相关,海绵组织厚度与叶片厚度相关性最强;青藏高原草地植物叶片各组成部分的厚度与海拔、生长季降水、生长季均温3个重要环境变量呈较弱的相关性,总体表现为随海拔升高叶片各组成部分的厚度减小,而随生长季降水和生长季均温的增加叶片厚度增加.     

Spatial and temporal variability of the phenological seasons in Germany from 1951 to 1996

Various indications for shifts in plant and animal phenology resulting from climate change have been observed in Europe. This analysis of phenological seasons in Germany of more than four decades (1951–96) has several major advantages: (i) a wide and dense geographical coverage of data from the phenological network of the German Weather Service, (ii) the 16 phenophases analysed cover the whole annual cycle and, moreover, give a direct estimate of the length of the growing season for four deciduous tree species. After intensive data quality checks, two different methods – linear trend analyses and comparison of averages of subintervals – were applied in order to determine shifts in phenological seasons in the last 46 years. Results from both methods were similar and reveal a strong seasonal variation. There are clear advances in the key indicators of earliest and early spring (?0.18 to ?0.23 d y^?1) and notable advances in the succeeding spring phenophases such as leaf unfolding of deciduous trees (?0.16 to ?0.08 d y^?1). However, phenological changes are less strong during autumn (delayed by + 0.03 to + 0.10 d y^?1 on average). In general, the growing season has been lengthened by up to ?0.2 d y^?1 (mean linear trends) and the mean 1974–96 growing season was up to 5 days longer than in the 1951–73 period. The spatial variability of trends was analysed by statistical means and shown in maps, but these did not reveal any substantial regional differences. Although there is a high spatial variability, trends of phenological phases at single locations are mirrored by subsequent phases, but they are not necessarily identical. Results for changes in the biosphere with such a high resolution with respect to time and space can rarely be obtained by other methods such as analyses of satellite data.     

川西亚高山不同海拔森林土壤活性氮库及净氮矿化的季节动态

研究了川西理县毕棚沟不同海拔梯度(3600 m、3300 m和3000 m)森林群落土壤活性氮库及土壤净氮矿化速率的季节动态.结果表明: 研究区森林土壤活性氮库(铵态氮、硝态氮、微生物生物量氮和可溶性有机氮)及净氮矿化速率存在明显的季节变化,但不同形态土壤活性氮库的季节动态有一定差异.4个采样时期(非生长季与生长季初期、中期及末期)各海拔土壤硝态氮浓度(8.38～89.60 mg·kg^-1)均显著高于铵态氮浓度(0.44～8.43 mg·kg^-1).生长季初期各海拔梯度的土壤净氮矿化速率均表现为负值(-0.77～-0.56 mg·kg^-1·d^-1),而非生长季、生长季中期和末期均为正值.除硝态氮外,不同海拔的土壤铵态氮、微生物生物量氮和可溶性有机氮浓度的差异极显著,海拔对它们的影响与季节变化有关.该区土壤净氮矿化以硝化为主,且氮矿化过程不受海拔梯度的影响.冬季土壤净氮矿化明显(0.42～099 mg·kg^-1·d^-1),早春高的土壤无机氮可能为植物生长提供基础养分,也可能通过淋溶方式从系统中丢失.     

Prediction of the beginning of the olive full pollen season in south-west Spain

Given the clinical and agricultural importance of the olive in SW Spain, we have carried out a study to predict the starting date of its full pollen season. The study covers 6 years of meteorological and palynological observations — the latter using a Cour sampler installed in Huelva (SW Spain). The results obtained show that olive full pollination begins when the plant has accumulated 731C of daily temperature above 5C from the end of its dormant period. The mean duration of this accumulation was 83 days. A positive relationship has been found between mean temperature of the months before the pollen season (February and March) and the date when the season starts (April). From the data available, rainfall registered between 1 September and 31 March (both before pollination), does not affect the starting date of the full pollen season, but can affect total pollen production, particularly in years with prolonged drought.     

Prediction of the beginning of the olive full pollen season in south-west Spain

Given the clinical and agricultural importance of the olive in SW Spain, we have carried out a study to predict the starting date of its full pollen season. The study covers 6 years of meteorological and palynological observations — the latter using a Cour sampler installed in Huelva (SW Spain). The results obtained show that olive full pollination begins when the plant has accumulated 731°C of daily temperature above 5°C from the end of its dormant period. The mean duration of this accumulation was 83 days. A positive relationship has been found between mean temperature of the months before the pollen season (February and March) and the date when the season starts (April). From the data available, rainfall registered between 1 September and 31 March (both before pollination), does not affect the starting date of the full pollen season, but can affect total pollen production, particularly in years with prolonged drought.     

Seasonality of vegetation fires as modified by human action: observing the deviation from eco‐climatic fire regimes

Aim In any region affected, fires exhibit a strong seasonal cycle driven by the dynamic of fuel moisture and ignition sources throughout the year. In this paper we investigate the global patterns of fire seasonality, which we relate to climatic, anthropogenic, land‐cover and land‐use variables. Location Global, with detailed analyses from single 1°× 1° grid cells. Methods We use a fire risk index, the Chandler burning index (CBI), as an indicator of the ‘natural’, eco‐climatic fire seasonality, across all types of ecosystems. A simple metric, the middle of the fire season, is computed from both gridded CBI data and satellite‐derived fire detections. We then interpret the difference between the eco‐climatic and observed metrics as an indicator of the human footprint on fire seasonality. Results Deforestation, shifting cultivation, cropland production or tropical savanna fires are associated with specific timings due to land‐use practices, sometimes largely decoupled from the CBI dynamics. Detailed time series from relevant locations provide comprehensive information about these practices and how they are adapted to eco‐climatic conditions. Main conclusions We find a great influence of anthropogenic activities on global patterns of fire seasonality. The specificity of the main fire practices and their easy identification from global observation is a potential tool to support land‐use monitoring efforts. Our results should also prove valuable in the development of a methodological approach for improving the representation of anthropogenic fire practices in dynamic global vegetation models.     

Dynamics in foliar litter decomposition for Pinus koraiensis and Quercus mongolica in a snow-depth manipulation experiment

气候变化导致的冬季雪被格局变化将改变地表水热环境及分解者活性, 从而显著影响高寒地区森林凋落物分解过程。2014-2016年采用凋落物分解袋法, 研究了帽儿山森林生态站人工林控雪模拟试验下红松(Pinus koraiensis)和蒙古栎(Quercus mongolica)的凋落叶于雪被期和无雪期不同阶段的分解动态。控雪试验包括增雪、除雪和对照3个处理。结果发现: 树种、控雪处理、分解阶段以及环境因子(凋落物层平均温度、冻融循环次数、有机层全氮、全磷含量等)均影响着凋落叶分解率。分解试验的两年内, 不同控雪处理下红松凋落叶的分解率为52.1%-54.5%, 蒙古栎为53.9%-59.1%。两种凋落叶的分解系数均以增雪处理最大, 除雪处理最小。此外, 控雪处理改变了两种凋落叶雪被期或无雪期对分解总量的贡献率。与对照相比, 增雪处理使红松和蒙古栎凋落叶雪被期的分解贡献率分别提高9.1%和10.4%; 而除雪处理使两种凋落叶无雪期的分解贡献率分别提高10.4%和12.7%。因此, 由气候变化带来的冬季雪被改变不但会显著影响温带森林凋落叶的分解过程, 而且会改变雪被期和无雪期的分解量对年分解总量的贡献率。     

控雪处理下红松和蒙古栎凋落叶分解动态

气候变化导致的冬季雪被格局变化将改变地表水热环境及分解者活性, 从而显著影响高寒地区森林凋落物分解过程。2014-2016年采用凋落物分解袋法, 研究了帽儿山森林生态站人工林控雪模拟试验下红松(Pinus koraiensis)和蒙古栎(Quercus mongolica)的凋落叶于雪被期和无雪期不同阶段的分解动态。控雪试验包括增雪、除雪和对照3个处理。结果发现: 树种、控雪处理、分解阶段以及环境因子(凋落物层平均温度、冻融循环次数、有机层全氮、全磷含量等)均影响着凋落叶分解率。分解试验的两年内, 不同控雪处理下红松凋落叶的分解率为52.1%-54.5%, 蒙古栎为53.9%-59.1%。两种凋落叶的分解系数均以增雪处理最大, 除雪处理最小。此外, 控雪处理改变了两种凋落叶雪被期或无雪期对分解总量的贡献率。与对照相比, 增雪处理使红松和蒙古栎凋落叶雪被期的分解贡献率分别提高9.1%和10.4%; 而除雪处理使两种凋落叶无雪期的分解贡献率分别提高10.4%和12.7%。因此, 由气候变化带来的冬季雪被改变不但会显著影响温带森林凋落叶的分解过程, 而且会改变雪被期和无雪期的分解量对年分解总量的贡献率。     

Divergent response of seasonally dry tropical vegetation to climatic variations in dry and wet seasons

Interannual variations of photosynthesis in tropical seasonally dry vegetation are one of the dominant drivers to interannual variations of atmospheric CO₂ growth rate. Yet, the seasonal differences in the response of photosynthesis to climate variations in these ecosystems remain poorly understood. Here using Normalized Difference Vegetation Index (NDVI), we explored the response of photosynthesis of seasonally dry tropical vegetation to climatic variations in the dry and the wet seasons during the past three decades. We found significant (p < 0.01) differences between dry and wet seasons in the interannual response of photosynthesis to temperature (γ^int) and to precipitation (δ^int). γ^int is ~1% °C^?1 more negative and δ^int is ~8% 100 mm^?1 more positive in the dry season than in the wet season. Further analyses show that the seasonal difference in γ^int can be explained by background moisture and temperature conditions. Positive γ^int occurred in wet season where mean temperature is lower than 27°C and precipitation is at least 60 mm larger than potential evapotranspiration. Two widely used Gross Primary Productivity (GPP) estimates (empirical modeling by machine‐learning algorithm applied to flux tower measurements, and nine process‐based carbon cycle models) were examined for the GPP–climate relationship over wet and dry seasons. The GPP derived from empirical modeling can partly reproduce the divergence of γ^int, while most process models cannot. The overestimate by process models on negative impacts by warmer temperature during the wet season highlights the shortcomings of current carbon cycle models in representing interactive impacts of temperature and moisture on photosynthesis. Improving representations on soil water uptake, leaf temperature, nitrogen cycling, and soil moisture may help improve modeling skills in reproducing seasonal differences of photosynthesis–climate relationship and thus the projection for impacts of climate change on tropical carbon cycle.     

Ecophysiological and species‐specific responses to seasonal variations in halophytic species of the chenopodiaceae in a Mediterranean salt marsh

Plants adopt different strategies in response to seasonal variations in their natural biotype. In this study, the responses of seasonal changes on the organic osmolyte contents, ionic homoeostasis, osmotic potential and succulence of native chenopods in a salt marsh of Egypt were studied. Five halophytic species of the chenopodiaceae were collected during the rainy and dry season: Atriplex halimus L., Halocnemum strobilaceum (Pall.), Salicornia fruticosa (L.), Suaeda pruinosa (Lange) and Arthrocnemum macrostachyum (Moric). Results showed that plants employ an osmoconformer strategy via species specificity of response to seasonal variations. The total ions accumulation in all species was higher during the rainy season compared with the dry season. In particular, during rainy season, A. halimus resulted the higher accumulator species, followed by H. strobilaceum. Conversely, S. fruticosa, S. pruinosa and A. macrostachyum were defined as low‐accumulator species. In each studied species, the effective salinity, biological absorption coefficient as well as leaf succulence were higher during the rainy season. In conclusion, the present study have pointed out the importance that should be accorded with the development of research directed towards agronomic aspects for the uses of halophytic chenopodiaceae in salt marsh. Further, data obtained indicate that the ions accumulator species should be considered for use in phytoremediation of degraded saline lands.     

我国暖季型草坪草锈病的研究进展

锈病是暖季型草坪草上的一种重要病害,可明显降低暖季型草坪草的观赏价值和使用价值.综述了目前我国暖季型草坪草锈病的病原物、症状及发生情况、发病规律以及防治方面的研究进展,对目前我国暖季型草坪草锈病研究中存在的问题加以分析,并对暖季型草坪草锈病研究前景加以展望.     

Patterns of Seed Size,Germination and Seed Viability of Tropical Tree Species in Southern India1

Seed weight, days to germination and seed viability were observed for 99 species growing in the Western Ghats of Karnataka, India. Seed size was strongly correlated with days to germination; smaller seeds germinated faster than larger seeds. Species which flowered during the rainy season had lighter seeds than species which flowered during the dry season. It was also found that seed size and viability of seeds were related to the season of fruiting. Species which fruit during the rainy season had heavier seeds and shorter viability than species which fruit during the dry season. These flowering and fruiting patterns and varying seed sizes are argued to be adaptations to the time of dispersal, time of moisture availability in the habitat and seedling survival.