Seasonal changes in the relationship between species richness and community biomass in grassland under grazing and exclosure, Horqin Sandy Land, northern China

How species diversityroductivity relationships respond to temporal dynamics and land use is still not clear in semi-arid grassland ecosystems. We analyzed seasonal changes of the relationships between vegetation cover, plant density, species richness, and above- ground biomass in grasslands under grazing and exclosure in the Horqin Sandy Land of northem China. Our results showed that in grazed and fenced grassland, vegetation cover, richness, and biomass were lower in April than in August, whereas plant density showed a reverse trend. Vegetation cover during the growing season and biomass in June and August were higher in fenced grassland than in grazed grassland, whereas plant density in April and June was lower in fenced grassland than in grazed grassland. A negative relationship between species richness and biomass was found in August in fenced grassland, and in grazed grassland the relationship between plant density and biomass changed from positive in April to negative in August. The relationship between the density of the dominant plant species and the total biomass also varied with seasonal changes and land use （grazing and exclosure）. These results suggest that long-term grazing, seasonal changes, and their interaction significantly influence vegetation cover, plant density, and bio- mass in grasslands. Plant species competition in fenced grassland results in seasonal changes of the relationship between species rich- ness and biomass. Long-term grazing also affects seasonal changes of the density and biomass of dominant plant species, which fur- tiler affects the seasonal relationship between plant density and biomass in grasslands. Our study demonstrates the importance of tem- poral dynamics and land use in understanding the relationship between species richness and ecosystem fianction.

Species Richness, Diversity and Density of Understory Vegetation along Disturbance Gradients in the Himalayan Conifer Forest

We investigated whether species richness, diversity and density of understory herbaceous plants differed along logging(gap) and grazing(primarily by cattle) disturbance gradients, and sought to identify drivers of richness, diversity and density of understory vegetation of logged sites. A factorial experiment was conducted in the mixed conifer forest of Gidakom in Western Bhutan. Levels of the logging treatment included small(0.15 – 0.24 ha), medium(0.25 – 0.35 ha) and large(0.36 – 1.31 ha) gaps. The grazing treatment included grazed(primarily by cattle) and ungrazed(where herbivores were excluded by a fence) plots nested within each gap. Data were collected from 12 gaps(4 replicates at each level of logging) using the point intercept method. Shannon Weaver Diversity and Margalef's indices were used to estimate species diversity and describe species richness, respectively. Soil samples were analyzed for pH and nutrients. The interaction effect of logging and grazing was significant(p≤0.001) only on species diversity. Relative to ungrazed areas, species diversity was significantly higher(0.01≤p≤0.05) in medium grazed gaps. Under grazed conditions, soil P was negatively correlated with gap size and species diversity. While species diversity was positivelycorrelated(0.01≤p≤0.05) with soil N in grazed plots species richness was positively correlated(0.001≤p≤0.01) with soil N in ungrazed plots. Relative density of Yushania microphylla and Carex nubigena were higher under ungrazed conditions. Our study suggests that the combined effect of cattle grazing and logging results in higher species diversity of understory vegetation in medium and grazed gaps in mixed conifer forests of Bhutan,whereas increase or decrease in relative density of major species is determined primarily by the independent effects of grazing and logging. From management perspective, forest managers must refrain from creating large gaps to avoid loss of nutrients(mainly P and N), which may eventually affect tree regeneration. Managers intending to maintain understory vegetation diversity must consider the combined effects of grazing and logging, ensuring low to moderate grazing pressure.

Molecular evidence of introgressive hybridization between related species Jankowski's Bunting(Emberiza jankowskii)and Meadow Bunting(Emberiza cioides)(Aves:Passeriformes)

Natural hybridization,which often occurs between closely related species exhibiting sympatric or parapatric distributions,is an important source of genetic variation within populations.The closely related Jankowski’s Bunting(Emberiza jankowskii)and Meadow Bunting(E.cioides)are similar in morphology and genetics,occupy overlapping niches,and are sympatric in eastern Inner Mongolia.Previous studies have reported trans-species polymorphisms of alleles between the two species,as well as an unexpectedly high genetic diversity of the endangered E.jankowskii.We speculate that introgressive hybridization has occurred between the two species and contributed to the additional unexpected variation to E.jankowskii.We used mitochondrial NADH dehydrogenase subunit 2(ND2)gene and 15 nuclear microsatellite markers to compare the genetic diversity of E.jankowskii and E.cioides,and inferred the origin of trans-species polymorphisms between the two species by phylogenetic reconstruction and Bayesian cluster analysis.The two species could be clearly distinguished by population cluster analysis.Despite the large number of mutational differences,we still detected sharing of major haplotypes and the presence of hybrids between the two species.Our study confirmed that weak introgressive hybridization has occurred between sympatric E.jankowskii and E.cioides,which may be mediated by female E.cioides individuals,and that interspecific introgression has contributed to the maintenance of high genetic diversity in E.jankowskii.While being wary of the potential negative effects of introgressive hybridization,we suggest that expanding the habitat of E.jankowskii remains the most effective conservation strategy at present.

The Influence of Plant Diversity and Functional Composition on Ecosystem Stability of Four Stipa Communities in the Inner Mongolia Plateau

The main purpose of this study was to examine the effects of plant species diversity and functional composition (the identity of the plant functional groups) on ecosystem stability of Stipa, communities in the Inner Mongolia Plateau. The research work was based on a 12-year study (from 1984 to 1995) of species abundance, diversity, and primary productivity of four Stipa communities, i.e. S. baicalensis Roshev., S. grandis P. Smirn., S, krylovii Roshev., and S. klemenzii Roshev. respectively. The Shnnon-Wiener index was used as a measurement of plant diversity, while functional composition was used to differentiate the functional groups that were included in the communities. The plant species of four Stipa communities were classified into functional groups based on the differences in life forms and ecological groups, which influence their performance in resource requirements, seasonality of growth, tolerance to water stress, and life history. Plant species were classified into five functional groups based on their differences in life form, shrubs and half shrubs, perennial bunch grasses, perennial rhizome grasses, forbs, annuals and biennials. Based on their differences in water requirement these species were classified into four functional groups: xerads, intermediate xerads, intermediate mesophytes, and mesophytes. The results showed: 1) Plant species diversity stabilized ecosystem processes. Shannon-Wiener index were 2.401 4, 2.172 0, 1.624 8, 0.354 3 from S. baicalensis community to S. grandis, S. krylovii and S. klemenzii community, respectively. The dynamics of the aboveground net primary productivity (ANPP) for a 12-year's period showed a reverse pattern, the coefficients of variation of the four communities were 21.94%, 20.63%, 29.21% and 39.72% respectively. 2) The Life form functional group component of diversity was a greater determinant of the ecosystem processes than the species component of diversity. The effects of perennial bunch grasses, perennial rhizome grasses and forbs on community stability were highly significant. 3) The ecological group component of diversity was also a great determinant of the ecosystem processes. The effects of xerads, intermediate xerads, and mesophytes on community stability were also very strong.

Forest structure,productivity and soil properties in a subtropical ever-green broad-leaved forest in Okinawa,Japan

Structure, species composition, and soil properties of a subtropical evergreen broad-leaved forest in Okinawa, Japan, were examined by establishment of plots at thirty sites. The forest was characterized by a relatively low canopy and a large number of small-diameter trees. Mean canopy height for this forest was 10 m and stands contained an average of 5400 stems-ha^-1 （ -〉 3.0 cm DBH）; 64% of those stems were smaller than 10 cm DBH. The total basal area was 54.4 m^2-ha^-1, of which Castanopsis sieboldii contributed 48%. The forest showed high species diversity of trees. 80 tree species （≥ 3.0 cm DBH） from 31 families was identified in the thirty sampling plots. C. sieboldii and Schima wallichii were the dominant and subdominant species in terms of importance value. The mean tree species diversity indices for the plots were, 3.36 for Diversity index （H＇）, 0.71 for Equitability index （J＇） and 4.72 for Species richness index （S＇）, all of which strongly declined with the increase of importance value of the dominant, C. sieboldii. Measures of soil nutrients indicated low fertility, extreme heterogeneity and possible A1 toxicity. Regression analysis showed that stem density and the dominant tree height were significantly correlated with soil pH. There was a significant positive relationship between species diversity index and soil exchangeable K^＋, Ca^2＋, and Ca^2＋/Al^3- ratio （all p values 〈0.001） and a negative relationship with N, C and P. The results suggest that soil property is a major factor influencing forest composition and structure within the subtropical forest in Okinawa.

Species Composition, Richness and Aboveground Biomass of Natural Grassland in Hilly-Gully Regions of the Loess Plateau, China

In order to study the characteristics of species composition, richness and aboveground biomass of natural grasslands, and then ifnd out the relations between species richness and aboveground productivity of the communities and possible mechanisms to form the relations, four typical grassland communities （Artemisia capillaries （AC）, Thymus quinquecostatus （TQ）, Stipa bungeana （SB） and Stipa grandis （SG）） along with a succession sequence in hilly-gully regions of the Loess Plateau, China, were investigated by ifeld survey and laboratory analysis. The results were summarized as follows：Different succession stages had different species compositions as well as different proportions of plant life forms and photosynthetic types, and Asteraceae, Poaceae and Leguminosae were their dominant species as well as their dominant perennial herb species;and different succession stages had signiifcantly different species richness and aboveground biomasses. There were many relation patterns （linear positive correlation, unrelated relations and unimodal relations） between the species richness and aboveground biomass in different succession stages and a signiifcant unimodal relation between the species richness and aboveground biomass in all the grassland communities and the highest species diversity appeared at a moderate level of productivity. The results suggest the unimodal relations in all the grassland communities are accumulative results of the relations in each succession stage.

Distribution and Productivity of Naturalized Alfalfa in Mixed-Grass Prairie

Alfalfa (Medicago sativa L.) is an important forage and conservation crop in North America but occurrences of naturalized alfalfa in rangelands are rare. A naturalized population of yellow-flowered alfalfa in mixed-grass prairie on the Grand River National Grassland in South Dakota has potential agricultural value for the region. Despite this value, the distribution pattern of this alfalfa among and within native plant communities in the northern Great Plains is unknown. Field studies were conducted from 2003 through 2006 along topographic positions at two sites where yellow-flowered alfalfa was naturalized to evaluate the relationships of yellow-flowered alfalfa on biomass production, cover, species diversity, and alfalfa seedbank distribution characteristics. High yellow-flowered alfalfa cover (>50%) was associated with increased total biomass and occurred exclusively in swales and toeslopes that had silty loam soils. However, species diversity and non-alfalfa biomass were reduced when yellow-flowered alfalfa cover was high. Yellow-flowered alfalfa cover was lower and species richness was higher on backslopes and shoulder areas where sandy loam soils were present. A strong positive linear association existed between yellow-flowered alfalfa cover and alfalfa seedbank density (r values ranged from 0.76 to 0.82, P < 0.0001). Greater than 99% of the seeds were viable but germination rate was only 4%, indicating a high percentage of hard seed in this alfalfa population. Naturalized yellow-flowered alfalfa was a dominant component of a stable, low diversity plant community composed of mainly introduced species in rich soils of swales/toeslopes that contributed to forage production and quality in mixed-grass prairie in the northern Great Plains.

The relationship between species diversity and ecosystem function (productivity) of the late Middle Permian brachiopods community at the region of Hechuan,Chongqing,China

The relationship between species diversity and ecosystem function is a hot topic in ecology and environics. This paper investi- gates the evolution of diversity of the late Middle Permian brachiopods community in Hechuan, Chongqing, China, and dis- cusses the relationship between species diversity and community productivity in terms of the geohistorical development. This paper shows that the species diversity is externalized by several indexes, and the relationship between diversity and productiv- ity is too complex to be described by a single assumption. The relationship between species diversity and community produc- tivity is restricted by environment and community evolution. When the community succeeds normally, the relationship be- tween species richness index, species diversity index, and species evenness index to productivity is in linear dependence rela- tion to each other, which is met with the third assumption. But, when the environment interference surpasses the beating capa- bility of the community, not only the community succession will be terminated and be replaced by another one, but also the relationship between species richness index, species diversity index, and species evenness index to productivity is also in- versed to negative correlation by the interference from environment. Only the relationship between ecological dominance and productivity is in linear dependence relation to each other and approximately met with the third assumption. It is illustrated that the assumption that the productivity is in linear dependence relation with diversity should be established on the presupposition that the community succession is normal.

Assessment of Tree Diversity and Abundance in Rashad Natural Reserved Forest, South Kordofan, Sudan

This study aims to estimate the tree diversity status of Rashad Forest Reserves in the Rashad locality of the South Kordofan State of Sudan. For data collection, eight sample plots (20 × 20 m) were taken randomly, and parameters were determined: trees species diversity, composition, relative density, dominance, important value index, and species richness in the Rashad forest reserve. The results show that a total of 237 and 56 tree species, including 22 families, have been identified in the study area. Fabaceae family and species numbers have the highest number of 13 species in 8 genera, followed by Combretaceae with 8 species belonging to 3 different genera, Malvaceae with 5 species belonging to 4 different genera, Apocynaceae with 3 species belonging to 3 different genera. The Arecaceae, Burseraceae, Capparaceae, Euphorbiaceae, Meliaceae, and Rubiaceae families each had two species, and all the other 11 families had one species each. Among the 56 different tree species found within the reserve. The results also indicated that Tamarindus indica L. and Ziziphus spina-christi (L.) Desf. had the highest relative density and dominance of 4.64% and 11% respectively. Adansonia digitata L., Grewia villosa Willd, Vepris nobilis (Delile) Mziray had density and dominance of 4.80% and 9%. Followed by Anogeissus leiocarpa (DC.) Guill. & Perr, Adansonia digitata L., Catunaregam nilotica (Stapf) Tirveng. (Syn: Xeromphis nilotica (Stapf) Keay, Vangueria madagascariensis J. F. Gmel. with 3.38% and 8%, respectively. Eleven species recorded the least relative dominance of 0.42%. Shannon-Weiner diversity index (H’) value stood at 3.82. And as diversity indices varied with location depending on the species available within an ecological zone, Rashad forest reserve is blessed with a moderate diversity index.

The coordinated impact of forest internal structural complexity and tree species diversity on forest productivity across forest biomes

Forest structural complexity can mediate the light and water distribution within forest canopies,and has a direct impact on forest biodiversity and carbon storage capability.It is believed that increases in forest structural complexity can enhance tree species diversity and forest productivity,but inconsistent relationships among them have been reported.Here,we quantified forest structural complexity in three aspects(i.e.,horizontal,vertical,and internal structural complexity)from unmanned aerial vehicle light detection and ranging data,and investigated their correlations with tree species diversity and forest productivity by incorporating field measurements in three forest biomes with large latitude gradients in China.Our results show that internal structural complexity had a stronger correlation(correlation coefficient=0.85)with tree species richness than horizontal structural complexity(correlation coefficient=-0.16)and vertical structural complexity(correlation coefficient=0.61),and it was the only forest structural complexity attribute having significant correlations with both tree species richness and tree species evenness.A strong scale effect was observed in the correlations among forest structural complexity,tree species diversity,and forest productivity.Moreover,forest internal structural complexity had a tight positive coordinated contribution with tree species diversity to forest productivity through structure equation model analysis,while horizontal and vertical structural complexity attributes have insignificant or weaker coordinated effects than internal structural complexity,which indicated that the neglect of forest internal structural complexity might partially lead to the current inconsistent observations among forest structural complexity,tree species diversity,and forest productivity.The results of this study can provide a new angle to understand the observed inconsistent correlations among forest structural complexity,tree species diversity,and forest productivity.

Functional Diversity: An Important Measure of Ecosystem Functioning

Functional diversity is a component of biodiversity that generally covers the range of functional traits of microorganisms prevailing in an ecosystem. Functional diversity is of high ecological importance because it is capable of influencing several aspects of ecosystem functioning like ecosystem dynamics, stability, nutrient availability, etc. Functional diversity of a community can be measured by functional richness and evenness. Functional richness refers to the number of species inhabiting a particular niche and functional evenness reveals how evenly the species are being distributed. Increase or decrease in functional richness and evenness simultaneously increases and decreases the functional diversity respectively. Decrease in functional richness and evenness decreases the ecosystem productivity and stability which ultimately decreases functional diversity of the same ecosystem. The effects of functional diversity on the productivity of an ecosystem can be quantitatively explained by the sampling effect model and the niche differentiation model. There are other proposed mechanisms like Niche complementarity and species redundancy relating functional diversity with ecosystem functioning. Rivets and idiosyncratic models relate functional diversity and species richness with ecosystem functioning. By considering the above proposed models on ecosystem functioning, it can be considered that functional diversity is a principal component of ecosystem functioning. So it can be assumed that, knowledge about a particular ecosystem reveals its richness and evenness which enable an individual knowing about the diversity of functional traits prevailing in the ecosystem. Thus, it opens up a new way in understanding and carrying out ecology related studies more efficiently and precisely in ecosystem.

Evaluation on Genetic Quality and Traits of Rice Landraces in the Taihu Lake Area

In this paper,with 511 rice landraces in the Taihu Lake area as test materials,we select 19 starch synthesis-related intragenic molecular markers to detect the genetic quality of starch,and compare them with 86 bred varieties. The results show that the average polymorphic information content( PIC) of japonica landraces is 0. 1726,slightly higher than the average PIC( 0. 1101) of the bred japonica rice varieties.Based on Nei's genetic distance between materials,UPGMA method is used for clustering,and all study materials are divided into 6 groups.Group I mainly includes indica rice,the bred japonica rice varieties are mainly concentrated in the first half of Group II and Group III,and the japonica landraces are mainly concentrated in the second half of Group III,and Group Ⅳ,Ⅴ,Ⅵ. Both of them are in different regions,and there has been genetic differentiation. According to the national standard of high quality rice,it is found that many rice landraces in the Taihu Lake area have good quality and traits,and these varieties can be used for future high quality breeding.

长期降水变化和氮添加对青藏高原高寒草原物种多样性和生产力的影响

在全球气候变化背景下,降水变化和氮添加草地物种多样性和生产力,但高寒草原研究较少,尤其是长期水氮控制试验。为此,本试验于青海省三角城种羊场紫花针茅高寒草原开展降水变化和氮(N)添加野外控制试验,从植被盖度、物种多样性指数及地上生物量进行测定,研究高寒草原长期降水变化和N添加对其物种多样性及生产力的影响。降水增加处理使群落盖度显著增加,而降水减少使群落盖度显著降低;N添加使高寒草原物种多样性指数均显著降低;N添加与降水增加处理对地上生物量有显著的促进作用,但降水减少对地上生物量的影响则相反;地上生物量与物种多样性指数呈极显著的负相关关系(P<0.01)。本研究将为我国草原生态系统的保护及草原管理提供科学依据,同时也为后续的生态模型的建立和科学的预测提供理论依据。

西藏高寒草地物种多样性和生产力的环境驱动机制

全球变暖影响物种多样性和生产力及其关系。关于全球和区域的物种多样性与生产力关系已有许多研究,但气候变暖背景下西藏高寒草地物种多样性与生产力的关系及其环境驱动机制研究仍然很少。基于西藏高寒草地实测的35个样点调查数据,利用回归分析、Pearson相关性分析、方差分解和结构方程模型等方法,探究了物种多样性和生产力的关系及其影响机制。研究发现:(1)高寒草地的物种丰富度指数和香农-威纳指数与地上植被净初级生产力(ANPP)呈显著正相关关系,且ANPP对物种丰富度指数的变化更为敏感;(2)物种丰富度指数与经度、土壤有效氮、土壤有效磷、年降水量呈显著正相关;Shannon-Wiener指数与海拔和纬度呈显著负相关,与年均温度呈显著正相关;ANPP与经度、土壤有效氮、年降水量和年均温度呈显著正相关,与海拔、纬度和土壤有效钾呈显著负相关;(3)地理因子、土壤养分和气候因子的交互作用对物种丰富度指数和ANPP的贡献率最大,分别为10.99%和32.91%,地理因子和气候因子的交互作用对Shannon-Wiener指数的贡献率最大,为13.61%;(4)地理因子通过调控土壤养分和气候因子间接影响物种多样性和ANPP,土壤养分和气候因子均直接影响物种多样性和ANPP。研究结果揭示了环境因子对物种多样性和生产力的综合调控机制,为西藏高寒草地生态系统科学应对气候变化提供了依据。

青海海北金露梅灌丛草甸植物群落生产力时间稳性及其驱动因素

明确高寒金露梅(Potentilla fruticosa)灌丛草甸群落生产力时间稳定性的动态变化及驱动因素,对金露梅灌丛草甸生态系统功能维持以及适应性管理具有重要意义。因此,本研究以青海海北祁连山南麓金露梅灌丛草甸植物群落为研究对象,重点分析了2020-2023年间高寒金露梅灌丛草甸植物群落生产力季节和年际动态变化,并探讨了物种多样性和土壤因子对植物群落稳定性的影响。结果表明:1)季节尺度上,植物群落地上生产力呈现“单峰”曲线,在7月底达到峰值;年际尺度上禾本科与豆科的地上生物量在不同年份间无显著差异(P>0.05),而莎草科地上生物量在2022年达到最大值,杂类草地上生物量在2023年达到最大值;地下总生物量与0-10 cm、20-30 cm的生物量在年际间有明显变化。2)地上群落生产力时间稳定性和地下群落生产力时间稳定性没有显著差异,杂类草功能群生产力时间稳定性显著高于其他功能群(P<0.05),不同土层深度地下生产力时间稳定性没有显著差异(P>0.05)。3)莎草类功能群生产力时间稳定性、Shannon-Wiener指数、Simpson指数以及土壤速效钾与金露梅灌丛草甸植物地上生产力时间稳定性之间存在显著正相关关系(P<0.05),而表层(0-10 cm)土壤速效磷和pH与金露梅灌丛草甸植物地下生产力时间稳定性之间存在显著正相关关系(P<0.05)。综上所述,不同功能群植物、物种多样性以及土壤速效养分是影响金露梅灌丛草甸植物群落生产力时间稳定性的关键因素。

赣北山区草地植物群落及其影响因子

为研究江西省草地资源状况并探讨其影响因素,在赣北山区鄱阳湖流域设置了61个2 m×2 m的草地群落样地,包含废弃农田、山坡草地和杂草地3种样地类型。分析不同类型样地之间物种组成差异,并在物种和群落水平上分别探究了植物生态化学计量特征及其环境影响因素。结果表明:1)赣北山区鄱阳湖流域内草地植物41科93属111种。草地植物群落组成相对简单,不同生境条件下群落物种组成差异明显。2)3种样地的土壤总碳、总氮和总磷含量差异不显著(P>0.05),但山坡草地土壤总碳和土壤总氮含量较低,而废弃农田土壤总磷含量较高。3)植物物种和群落两个水平上,3种样地的植物N、P元素含量差异不显著(P>0.05),但山坡草地植物碳含量在个体和群落水平都显著高于杂草地,而废弃农田植物碳含量则在个体水平显著高于杂草地。4)在物种和群落水平上,土壤总氮和总磷含量均是植物生态化学计量特征的主要影响因子。综上,本研究对江西北部草地资源状况的调查,为该区域草地资源保护及恢复提供了数据支持和理论依据。

天目山常绿落叶阔叶林生产力及其影响因素

在浙江省杭州市临安区的天目山国家级自然保护区内,以分布在海拔850~1100 m的常绿落叶阔叶林为研究对象,2017年在海拔1000 m的常绿落叶阔叶林内设置1个100 m×100 m的监测样地,对胸径1 cm及以上的树木,记录种名、测定生长指标(胸径、树高、冠幅等),2022年采用与2017年相同方法测定样木相关指标;采用网格取样和随机取样相结合的方法,在样地土层深度0~20 cm采集土壤样品,参照相关标准和方法测定土壤理化性质指标;以树种重要值、森林生产力(树木生物量)、物种多样性(皮卢(Pielou)均匀度指数、马格利夫(Margalef)物种丰富度指数、香农-维纳(Shannon-Wiener)多样性指数、辛普森(Simpson)多样性指数)、结构多样性(胸径香农-维纳多样性指数、胸径辛普森多样性指数、胸径标准偏差、胸径基尼系数)为评价指标,以2次调查和测定的数据为基础,采用回归分析法、层次分割法,分析天目山常绿落叶阔叶林组成变化、各因素对森林生产力的影响。结果表明:①天目山常绿落叶阔叶林在5 a间,有24种退出、16种进入,有33.90%物种发生了变化,变化物种均为偶见种和稀有种;落叶树种减少,常绿树种占比增加,有向常绿阔叶林演替的趋势。②天目山常绿落叶阔叶林,生物量为147.90 t·hm^(-2),生产力为5.90 t·hm^(-2)·a^(-1);常绿树种占总生产力63.04%、落叶树种占总生产力39.96%,常绿树种是生产力的主要贡献者。③天目山常绿落叶阔叶林生产力主要受结构多样性的影响,土壤因子中碱解氮为主要影响因素。各影响因子中,结构多样性贡献率最高(为20.79%);结构多样性中,胸径香农-维纳多样性指数的贡献率最高(为9.11%),与生产力呈极显著正相关(P<0.01);碱解氮对生产力的贡献率为6.68%,与生产力呈极显著正相关(P<0.01)。

长白山阔叶红松林林层群落结构与生产力的关系

【目的】探究长白山阔叶红松林不同林层群落结构与林分生产力的关系,分析林分生产力的影响因素,为温带森林的恢复与可持续经营提供科学依据。【方法】基于长白山自然保护区阔叶红松林40 hm^(2)固定监测样地2年(2014和2019年)植被调查数据,以样地内胸径(DBH)≥5 cm的木本植物为对象,根据胸径将阔叶红松林群落划分为优势木层、亚优势木层、中等木层和被压木层,运用R4.0.3软件计算各林层物种多样性、结构多样性和林分密度,与生产力进行相关性分析并构建结构方程模型,探讨不同林层物种多样性、结构多样性和林分密度对生产力的影响。【结果】1)林分密度与生产力显著正相关(P<0.05),且相关关系随林层上升而下降。2)Pearson相关性分析结果显示,生产力与代表物种组成α多样性的香农威纳指数显著正相关(P<0.05),且随林层上升相关关系减弱;反之,代表物种组成β多样性的香农熵指数与生产力存在显著负相关(P<0.05),但该相关关系在中等木层和亚优势木层不显著。此外,物种均匀度指数与生产力显著负相关(P<0.05),相关系数随林层上升先增大后减小;胸高断面积基尼系数和胸径均匀度指数与生产力显著负相关(P<0.05),且该相关关系随林层上移而减弱,在优势木层与生产力无显著相关性。胸径香农威纳指数与生产力呈显著正相关(P<0.05),且随林层上移相关关系降低,相关系数由0.44降至0.31。3)不同林层林分密度对生产力均有显著影响(P<0.001),且随林层上升其作用强度逐渐降低,路径系数由0.59降至0.27;物种多样性在被压木层和中等木层对生产力有显著正向作用(P<0.05),在优势木层和亚优势木层对生产力无显著影响;结构多样性在被压木层和中等木层通过作用于物种多样性和林分密度间接影响林分生产力,在优势木层和亚优势木层则直接作用于林分生产力。【结论】各林层林分密度对生产力均有显著影响(P<0.05),且随林层上升对生产力的作用强度逐渐降低,群落物种多样性和结构多样性对生产力的作用方向和强弱在不同林层表现各异。深入探讨不同林层物种多样性和结构多样性以及其如何影响森林生产力,在现代森林经营管理中尤为重要。

模拟降水年际和年内变化对黑沙蒿群落物种多样性和生产力的影响

在全球气候变化影响下,中国西北部干旱半干旱荒漠区降水格局发生显著变化,表现为极端降水和干旱事件增多,对荒漠植物群落结构和功能的影响引发广泛关注。以毛乌素沙地典型荒漠灌草植被黑沙蒿群落为研究对象,利用人工遮雨装置进行小区降水控制,设置降水量(W-:减水30%,对照组W:自然降水,W+:增水30%)和降水间隔(对照组T:降水间隔5d,T++:降水间隔15d)的双因素完全随机控制实验,监测各降水处理下黑沙蒿群落物种组成和生产力。结果表明:(1)与降水间隔5d的对照组相比,降水间隔期的延长显著提高了灌木和杂草的重要值,而降低了禾草的重要值。(2)与对照组自然降水相比,降水量的增加提高了黑沙蒿植物群落的多样性。(3)降水量的增加或降水间隔的延长均可以提高黑沙蒿的地上初级生产力。延长降水间隔会增加深层土壤的含水量,这有助于黑沙蒿对土壤水分的利用进而促进其生产力积累并增强了其在群落中的优势度。

放牧强度对高寒草甸物种多样性和生产力关系的影响

放牧对草地植物群落结构和功能的影响深远而复杂,为了探讨高寒草甸植物物种多样性和生产力受长期不同放牧强度的影响,在高寒草甸草地群落设置不同放牧强度试验,分析不同放牧强度下植物群落物种多样性和生产力及其关系的变化,以期为高寒草甸生态系统的可持续利用和管理提供理论依据。结果表明,随着放牧强度的增大,草地植物群落的Shannon-Wiener指数和Margalef丰富度指数先增大后减小,高寒草甸植物群落的优势物种由禾本科向莎草科和杂类草转变,其中禾本科植物的优势度从70%降到12%,杂类草植物的优势度由13%增大到82%,植物群落的地上净初级生产力(ANPP)逐渐减小,轻度放牧处理减少了61.56%,中度放牧处理减少了76.75%,重度放牧处理减少了78.72%,重度放牧处理地下净初级生产力(BNPP)比禁牧处理降低了90.06%,轻度放牧、中度放牧处理地下净初级生产力与禁牧处理无明显差异,3个处理下的地下净初级生产力(NPP)总体保持稳定。放牧强度增大会导致植物群落高度下降,中度放牧处理会增加植物群落中莎草科植物的分蘖数。高寒草甸上植物群落的Pielou指数和NPP负相关,Margalef指数和BNPP正相关。研究结果表明,中度放牧强度有利于高寒草甸维持较高的物种多样性,过度放牧不利于高寒草甸维持较高的物种多样性和草地生产力。