Soil seedbanks in slash‐and‐burn rice fields of northern Laos

Crops in shifting cultivation fields often suffer from severe weed infestation when long fallow periods are replaced by short fallow periods. The soil seedbank as a source of weed infestation was studied in four fields that differed in their last fallow duration. The effect of burning was analysed by comparing adjacent pre‐burn and post‐burn samples (two sites). Surface vegetation was monitored from burning to harvest in the plots from which soil samples were taken to determine the fraction of the seedbank germinating (three sites). Seedbank size (1700–4000 seedlings m^?2) varied depending on a single species, Mimosa diplotricha. Burning reduced emergence of most species, but stimulated emergence in others. Densities in the seedbank were not correlated with above‐ground abundances in the field, except for some species. Most species emerging after 50 days from the soil samples (40% of seedlings) were absent from the field after 190 days. Whilst the data from this study are derived from only four fields, the weed problems after short‐term fallowing appeared to be due to a larger fraction of the seedbank emerging, possibly due to shallow burial, and to a floristic shift towards adaption to burning, rather than the size of the seedbank per se.     

人工绿洲防护林林下植物多样性研究

采用"标准地+样方"法,对克拉玛依农业综合开发区防护林林下植物群落进行调查,统计并计算林下植物的丰富度、物种多样性及均匀度。结果表明:(1)研究区防护林林下植物共有33种,主要以农田杂草为主;(2)研究区防护林林下植物物种多样性以紫穗槐林为最高,沙棘、沙枣林和柽柳林次之,杨树林和榆树林最小;(3)高郁闭度的乔木防护林对林下植物的生长有较强的抑制作用,林下植物多样性低,中等郁闭度的乔木防护林林下植物多样性最高,而灌木防护林林下植物多样性和均匀性都比较高,多样性在不同郁闭度下差异不大。文中旨在了解干旱区不同防护林林下植物群落的现状,为该地区防护林建设和经营提供科学依据。     

三江平原典型湿地不同林型昆虫物种多样性研究

利用扫网,黄盘和巴氏罐诱法对三江平原典型环形湿地周围三个不同类型树林(岛状林,杨树林,松树林)的昆虫进行采集,经初步整理和鉴定,共采集标本24212号,其中昆虫20948号,分属于14目。其他的属于蛛形纲和多足纲。昆虫中种类最多的是双翅目和膜翅目,其次是弹尾目,同翅目,鞘翅目和缨翅目。在高的分类阶元(目)Shannon-wiener指数在松树林最高,杨树林最低。昆虫数量在各个林型中没有明显的不同。在这三个林型里面发现了长翅目蝎蛉,丰富了我国对于蝎蛉分布北限的记录,表明三江平原湿地区是我们昆虫多样性保护的一个重要区域。     

Impact of crop management on weed species diversity and community composition of winter wheat fields in Iran

The aim of this study was to assess the effects of crop management practices on the diversity, structure, and composition of weed communities. A total of 30 fields (15 fields each) in low‐input and conventional farming systems were surveyed in north‐eastern Iran. In the conventional cropping system, both mineral fertilizers and herbicides were applied, while in the low‐input cropping system, the fertilizer was mainly manure and herbicides were avoided. The results showed that the pool of species, species richness, number of unique species, and Shannon's diversity index were greater in the low‐input system than in the conventional system. Both cropping systems had more broad‐leaved species than grasses and more annual species than perennial species. All the multivariate methods of analysis that were applied revealed that the weed community composition was significantly different between the two management types. The low‐input cropping favored herbicide‐susceptible broad‐leaved weeds, legumes, and weeds with biodiversity value, whereas a high proportion of herbicide‐tolerant grasses was found in the conventional fields. The results suggest that low‐input cropping can sustain high weed diversity and abundance.     

黄土丘陵沟壑区退耕地植被自然演替系列及其植物物种多样性特征

根据吴起县20块样地和60个样方的退耕地植被调查数据,采用时空互代的方法,探讨退耕地植被自然演替系列及其物种多样性的变化规律。结果表明:研究区退耕地植被自然恢复的过程大致可划分为迅速恢复期(1~4年)、初级更替期(5~13年)、高级更替期(13~20年)和缓慢恢复期(20年以后)4个阶段。在25年的退耕地植被自然演替过程中,调查样方内共出现草本植物39种,分属于11科31属。其中,禾本科(Gramineae)、豆科(Legu-minosae)和菊科(Compositae)的物种占属种总数的61.29%和69.23%。群落的优势物种由藜科杂草开始,依次演替为一年生草本和多年生草本,大约20年后演替为地带性多年生草本,形成了依次包括猪毛菜(Salsola collina)、猪毛蒿(Artemisia scoparia)、达乌里胡枝子(Lespedeza davurica)、铁杆蒿(Artemisa vestita)和白羊草(Bothriochloa ischae-mum)5种群落类型的演替系列。整个演替过程中,Margalef指数和Shannon-Wiener指数总体上呈波动式增大,但增长的趋势并不明显,大约20年后各项多样性指数基本趋于稳定。在每一次更高级的群落取代前期群落的过程中,Margalef指数和Shannon-Wiener指数大致表现为先增大后减小,均匀度指数(Jsw,Ea)则表现为先减小后增大。     

Characteristics of soil seed banks at different geomorphic positions within the longitudinal sand dunes of the Gurbantunggut Desert,China

Understanding the characteristics of soil seed banks in sand dunes is crucial to stabilize the dune systems and maintain the plant populations in deserts. In this study, we conducted a survey investigation in the field and a seed germination experiment in the laboratory to explore the characteristics of soil seed banks at various geomorphic positions of longitudinal sand dunes in the Gurbantunggut Desert, China. Totally, 17 plant species belonging to 17 genera and 9 families were identified in soil seed banks, and 35 plant species belonging to 34 genera and 17 families were identified in aboveground vegetation. Plant species richness in soil seed banks decreased with increasing soil depth. The highest species richness was presented in the upper slope of the windward slope and the lowest species richness was presented in the base of the windward slope. There was no significant difference in seed density of soil seed banks among the examined seven geomorphic positions. The highest seed density occurred in the lower slope of the leeward slope while the lowest occurred in the crest. Moreover, seed density decreased with increasing soil depth, being the highest in the upper soil layer(0–2 cm). For both soil seed banks and aboveground vegetation, there was no significant difference in Simpson's diversity index among the seven geomorphic positions; however, Shannon-Wiener diversity index and Pielou's evenness index showed significant differences among the seven geomorphic positions. Those results showed that although there was no significant difference in seed density of soil seed banks among the seven geomorphic positions, the geomorphic positions significantly affected the species richness, diversity and distribution of soil seed banks. Therefore, understanding the characteristics of soil seed banks at different geomorphic positions of sand dunes is essential to vegetation restoration or reestablishment. Furthermore, the Jaccard's similarity coefficients of plant species between soil seed banks and aboveground vegetation at the seven geomorphic positions were low, suggesting that vegetation restoration or reestablishment processes should be promoted through adding seeds to surface layers.     

Origin of and resulting floristic composition from seedbanks in agroforestry systems of Tomé‐Açu,Eastern Amazon

The objective of this study was to verify the origin of and resulting floristic composition from seedbanks in different agroforestry systems in Tomé‐Açu, Brazil. The seedbanks were sampled in three smallholder farmers (Demonstration Units = DU), each with three agroforestry treatments and secondary forest as control. Seedling emergence in a glasshouse was used to quantify and identify the seeds collected in 2008. The floristic composition of the above‐ground community was characterised with annual floristic surveys from 2008 to 2011. The total densities and diversity of the seedbanks were not different among the treatments within a given DU, but differences occurred among DU. The most abundant woody species had higher seed densities in the secondary forests than in DU. Conversely, among the herbaceous species, two groups were differentiated: species with similar densities between the DU and the secondary forest and species with higher density in the DU. In the DU, the similarity between the floristic composition of the seedbank and the flora surveyed in 2008 was high, but decreased in subsequent years. The species present in the seedbank of agroforestry systems are highly influenced by the secondary forest, but provide little information about the floristic composition that will arise in the future.     

北方农牧交错带生态恢复与重建的原则及对策

对我国北方农牧交错带生态退化的现状和原因进行了分析 ,提出了生态恢复与重建的 5个指导思想与原则 :物种本地化原则、物种多样化及其合理配置原则、保护为主重建为辅的原则、以防为主防治结合的原则和生态与经济相协调的原则 ,并提出了生态恢复与重建策略。     

Development of arable weed seedbanks during the 6 years after the change from conventional to organic farming

All of the arable land of a farm in southern Germany was investigated during an 8-year period, starting 2 years before and ending 6 years after the change to organic farming. The first 3 years after the conversion, the total seed number in the soil increased from 4050 to 17 320 m⁻². From the fourth to the sixth year, it dropped back to 10 220 m⁻². The number of seeds increased particularly at sites with a low crop cover and a high density of weed plants at the soil surface. The increase predominantly occurring on the more fertile soils may have been caused by the rotation commencing with less competitive crops. Crops which increased the seedbank by 30–40% were winter cereals, sunflowers and lupins. Potatoes and sown fallow caused no significant change and grass–clover mixtures even reduced the number of seeds by 39%. Among 44 species occurring frequently enough for statistical analysis, 31 increased and only 3 decreased. The change of management particularly increased summer annual, perennial and dicotyledonous weeds. This can be attributed to both operations which are characteristic of organic farming (e.g. replacing herbicide applications by mechanical weed control) and to general modifications of the management practice which may also occur in non-organic farming systems (increasing the percentage of broad leaved and spring sown crops in crop rotation). The present study confirms investigations into the aboveground vegetation that indicate that arable organic farming favours plant species diversity and provides evidence that the conversion need not encourage the dominance of a few noxious weeds.     

新疆鄯善种子植物物种多样性及区系分析

文中在形态分类学研究的基础上,对鄯善野生种子植物物种多样性与区系地理进行了分析。鄯善共有种子植物48科177属,296种2亚种1变种。科的组成中,就属水平而言,寡属科与多属科构成科结构的主体,所含属数占74.01%,而就种水平而言,则大科和寡种科为主体,所含种数占81.94%;属的组成中,单种属和寡种属构成属结构的主体,所含种数占88.63%。该区新疆特有种与中国新疆仅分布种占26.09%,比例较高。生活型以地面芽植物与一、二年生植物为主;生态型以旱生植物与中生植物占较大优势,占种数的77.92%,与其区系的温带干旱性质相吻合。属的分布区类型表明,该区系地理成分多样,有11个分布类型和10个变型,温带性质明显,约占72.3%,以北温带为主。     

Effect of competition on spatial patterns of oak forests on the Chinese Loess Plateau

Reforestation or natural forest regeneration is an alternative measure for controlling soil erosion in degraded land on the Chinese Loess Plateau(CLP). However, our understanding of the temporal dynamics and the spatial patterns of forest regeneration remains inadequate. Two oak forests at different development stages were investigated to determine the spatial patterns of competitions(intraspecies and interspecies) during different successional stages. The intraspecies and interspecies spatial relationships among different tree diameters at breast height were analyzed at multiple scales by Kriging interpolation method and univariate and bivariate O-ring statistics. Our analytical results indicated that self-correlation and competition intensity were relatively high between oak and pine trees in the early development stage of oak forests due to their clumped distributions of heavy seeds. Birch trees had a lower competition in comparison to oak trees although birch was the dominant species. Therefore, asymmetric competition of oak trees was most likely to have led to their edge dispersal and their success in replacing the pioneer species. Asymmetric competition means that larger individuals obtained a disproportionately large share of the resources and suppressed the growth of smaller individuals. Kriging interpolation analysis showed a tendency towards homogenization caused by interspecies competition during the succession of oak forests. Our results demonstrated that the competition was the driving factor in the spatial distribution of oak forests on the CLP.     

Diversity of soil bacteria and fungi communities in artificial forests of the sandy-hilly region of Northwest China

Soil erosion is a serious issue in the sandy-hilly region of Shanxi Province, Northwest China. There has been gradual improvement due to vegetation restoration, but soil microbial community characteristics in different vegetation plantation types have not been widely investigated. To address this, we analyzed soil bacterial and fungal community structures, diversity, and microbial and soil environmental factors in Caragana korshinskii Kom., Populus tomentosa Carr., Populus simonii Carr., Salix matsudana Koidz, and Pinus tabulaeformis Carr. forests. There were no significant differences in the dominant bacterial community compositions among the five forest types. The alpha diversity of the bacteria and fungi communities showed that ACE (abundance-based coverage estimator), Chao1, and Shannon indices in C. korshinskii forest were significantly higher than those in the other four forest types (P<0.05). Soil organic matter, total nitrogen, and urease had a greater impact on bacterial community composition, while total nitrogen, β-glucosidase, and urease had a greater impact on fungal community composition. The relative abundance of beneficial and pathogenic microorganisms was similar across all forest types. Based on microbial community composition, diversity, and soil fertility, we ranked the plantations from most to least suitable as follows: C. korshinskii, S. matsudana, P. tabulaeformis, P. tomentosa, and P. simonii.     

Weed community responses to soil type during transition to no-till practice on smallholder farms in Zimbabwe

Understanding drivers of weed density and diversity is essential for the development of weed management strategies. Here, we compared temporal changes in weed density and diversity under no-till (NT) and conventional (CONV) tillage systems in cotton–maize rotations on loam, clay loam and sandy loam soils immediately after transition to NT in Kadoma, Zimbabwe. The effect of tillage system on weed density varied through the growth season and was dependent upon soil type and species composition of the weed community. Although weed responses to tillage system varied amongst species, we identified general trend effects on weed density on specific soils. At 3 weeks after crop emergence (WACE), weed density on loam soils was 76% and 96% higher in NT than in CONV during the 2009/2010 and 2010/2011 seasons, respectively, and on clay loam soils it was 37% and 33% higher in NT than CONV, respectively. Weed densities in NT and CONV were similar across all soil types at 6 WACE during the 2009/2010 and 2010/2011 seasons and at 9 WACE in 2009/2010. Tillage system did not affect weed density during the growth season on sandy loam soils. Weed diversity (Shannon index) was at least 75% higher in NT than CONV on loam and clay loam soils at 3 WACE during both seasons. It is likely these increases in weed densities following conversion to NT will exacerbate already prevalent weed management problems in the smallholder sector. Earlier weeding is recommended to suppress weed emergence and reduce likely associated crop yield losses.     

干旱区矿区不同立地类型土壤种子库特征

矿区的自然或人工植被恢复是维持生物多样性及生态系统稳定的重要途径。通过室外萌发法对金昌镍铜矿区7种不同立地生境土壤种子库的研究表明:该区域土壤中物种丰富度较高,包括16科47属,共56种植物,分别为:藜科(Chenopodiaceae)、禾本科(Gramineae)、菊科(Compositae)、柽柳科(Tamaricaceae)、苋科(Amaranthaceae)、马齿苋科(Portulacaceae)、豆科(Leguminosae)、十字花科(Cruciferae)、车前科(Plantaginaceae)、胡颓子科(Elaeagnaceae)、蒺藜科(Zygophyllaceae)、莎草科(Cyperaceae)、大戟科(Euphorbiaceae)、紫草科(Boraginaceae)、蔷薇科(Rosaceae)、茄科(Solanaceae);植物组成以一年生草本植物占绝对优势(89.3%),多年生草本植物次之(7.54%),灌木种最少(2.59%)。土壤种子平均储量412粒·m~(-2),不同立地类型土壤种子库储量差异显著,与其他荒漠地区比较,土壤种子库储量偏低;土壤种子库物种Simpson多样性指数为:新尾矿周边自然植被区龙首矿自然植被区龙首矿开采废弃地供暖公司柽柳林地。     

Altitudinal patterns of stand structure and herb layer diversity of Picea schrenkiana forests in the central Tianshan Mountains,Northwest China

Altitude is a useful indicator to examine patterns of forest structure and species diversity in relation to environmental factors.In this study,the altitude patterns of forest stand structure and species diversity were analyzed across 20 plots in the Tianchi Nature Reserve,Northwest China.The results showed that mean stem height(Hm),maximum stem height(Hmax) and mean stem diameter at breast height(Dm) of Picea schrenkiana trees all decreased significantly with increasing altitude.Potential tree height(H*) decreased while stem taper increased significantly as altitude increased,suggesting remarkable altitudinal changes in biomass allocation between the diameter and height growth of Picea schrenkiana.Understory herbaceous richness increased significantly with increasing altitude,or with decreasing total basal area(TBA),Hm and stand volume(Volume).High light availability for understory herbs might account for the higher species richness at high altitude.Sorensen Index decreased significantly with the increase in altitude intervals,while the Cody Index demonstrated a converse pattern,suggesting greater differences in species composition with larger distances.     

Impact of site conditions and farming practices on the occurrence of rare and endangered weeds on arable land in the Czech Republic

This article documents the impact of site conditions and farming practices on the occurrence of rare and endangered weeds on arable land in the Czech Republic. A survey was conducted between 2006 and 2008 in winter cereals, spring cereals and wide‐row crops. The relationship between the occurrence of plants and explanatory factors was analysed using a multivariate analysis to calculate species frequencies in different types of farming, crops and altitudes. In total, 290 relevés were recorded, with a total number of 172 weed species. Nineteen weeds, classified as rare and endangered species according to the national Czech list, were identified in 106 relevés. The highest effect on the occurrence of rare and endangered weed species was observed for altitude. Almost half of the recorded endangered and rare species belonged to the thermophilous weed vegetation typical for cereals on basic soils. A higher occurrence of endangered species has been confirmed for organic farming, where the sum of frequencies was 4.5 times higher than in conventional farming. Field size was not included in our analyses, but could be a factor affecting weed assemblages. The highest frequency of rare species was recorded in spring cereals, followed by winter cereals and wide‐row crops. Higher numbers were identified within fields with higher weed coverage. Lower farming intensity and diversified farming systems at higher altitudes provided better conditions for the occurrence of rare species than intensively farmed lowlands.     

我国北方土地荒漠化成因与草业发展研究

土地荒漠化是当今世界重要的生态环境问题 ,也是脆弱生态系统失去平衡而急需治理的国土整治问题。笔者认为 ,土地荒漠化的发生虽然是自然因素和人类活动共同作用的结果 ,但非可持续性的人类活动是加剧土地荒漠化的主导因素。从分析荒漠化发生的社会经济原因入手 ,阐述发展草业在保护生态与环境、发展西部经济中的重要地位。以此为突破口 ,提出完善软环境体系、创新草业发展机制、加强管理和强化目标责任制对策措施。     

短花针茅荒漠草原土壤种子库对不同放牧强度的响应

在内蒙古短花针茅荒漠草原,采用野外随机定点取样与室内萌发相结合的方法,对不同放牧强度下围封草地土壤种子库的密度、垂直结构、多样性、丰富度、均匀度、以及种子库与地上植被的相似性进行了研究。结果表明,在各试验区土壤种子库主要分布在0～20cm土层,占种子库总密度的87%～96%;随着放牧强度的增加,土壤种子库总密度减少,同时地上植被与土壤种子库的相似物种数减少,种子库组成的相异性增加;轻度放牧对土壤种子库中一二年生草本所占比例影响较小,而中度和重度放牧使土壤种子库中一二年生草本所占比例增加;土壤种子库的物种丰富度、多样性、均匀度均随放牧强度的增加而减小。