Spatial models of foraging in clonal plant species

Ramets of some clonal plant species alter their internode lengths or their frequency of lateral branching in response to their immediate microenvironment. Such “plant foraging” responses are thought to allow clones to concentrate in favorable portions of their environment. Despite widespread interest among ecologists in plant foraging, few realistic models have been developed to examine conditions under which plant foraging responses are likely to provide clones with ecological benefit. In this paper, we develop spatially explicit, stochastic simulation models to examine consequences of both empirical and hypothetical plant foraging responses. We construct a hierarchical series of models in which we incorporate effects of resource heterogeneity on spacer lengths, angles of growth, and lateral branch production. We also vary the number, size, and arrangement of patches, and the presence or absence of ramet mortality. Simulations based on hypothetical data demonstrated the potential importance of shortening spacer lengths in favorable habitat. In these simulations, ramet crowding increased significantly, implying a potential cost to plant foraging responses whose magnitude is large enough to cause ramets to concentrate in favorable patches. Models calibrated with empirical data suggest that when clonal plants were able to concentrate in favorable habitat, this was usually caused by increased daughter ramet production in the favorable habitat. Variation in clonal growth angles had little impact on the ability of ramets or clones to locate favorable patches, but did increase the ability of clones to remain in favorable patches once found. Alterations in the number and size of patches strongly influenced the effectiveness of the foraging response. The spatial arrangement of patches also was important: clumped distributions of patches decreased the success with which plants located favorable patches, especially at the genet level and when the number of patches was low. Finally, when ramet mortality varied with patch quality, there was an increase in the percentage of ramets located in favorable patches; differential ramet mortality also lessened the impact of other effects, such as the decreased success of clones when patches are clumped. Overall, our models indicate that the effectiveness of plant foraging responses is variable and is likely to depend on a suite of environmental conditions.     

资源交互斑块性生境中两种不同分枝型匍匐茎植物的克隆内分工

以青藏高原和四川盆地过渡带两种不同分枝型匍匐茎植物野草莓 (Fragaria vesca)和过路黄 (Lysimachia christinae)为对象 ,研究它们在高光照低养分斑块和低光照高养分斑块组成的资源交互斑块性生境中的克隆内分工。结果显示 ,与资源的空间同质性处理 (I)和 (II)相比 ,资源的空间异质性处理 (III)和 (IV)中野草莓和过落黄的近端、远端和整个克隆片段的生物量和分株数均获得显著增加。生长在低光高养条件下的远端分株 ,若与高光低养的近端分株相连 ,相比连接到低光高养的近端分株 ,它们分配更多的生物量到地下部分 ;生长在高光低养条件下的远端分株 ,若与低光高养的近端分株相连 ,相比连接到高光低养的近端分株 ,它们分配更多的生物量到地上部分 ;生长在高光低养条件下的近端分株 ,若与低光高养的远端分株相连 ,相比连接到高光低养的远端分株 ,它们分配更多的生物量到地上部分。实验结果表明 ,资源交互斑块性生境中野草莓和过路黄均发生了克隆内分工。通过克隆内分工 ,克隆植物能有效的利用异质性分布的资源 ,缓解资源交互斑块性分布对克隆植物生长的不利影响     

克隆整合和石油污染对芦苇湿地土壤理化性质的影响

克隆整合是克隆植物重要的性状之一。它不仅能够提高分株对环境胁迫的耐受能力,而且可能影响分株周围的土壤属性。为检验克隆整合对土壤属性的影响,在黄河三角洲芦苇湿地开展克隆整合和石油污染的两因子的野外实验。每年将0、5或10 mm厚的原油添加到直径为60 cm的圆形芦苇群落样方内来模拟无污染、轻度或重度石油污染,并通过保留或切断样方内外芦苇根状茎的连接来实现克隆整合的有或无。实验开始于2014年,并于2016年10月采集样方内土壤样品,测定土壤团聚体组成、pH值、电导率、总碳、总氮、总磷和有机碳含量。石油污染显著增加了土壤粗大团聚体(粒径:2 mm)、pH值、总氮和有机碳含量,降低了土壤微团聚体(粒径:0.053—0.25 mm)占比以及电导率。克隆整合显著降低了土壤pH值,提高了土壤电导率和氮磷比。克隆整合和石油污染的交互作用仅对电导率有显著效应。因此,石油污染和克隆整合都可以影响湿地土壤的理化性质,而克隆整合对分株周围土壤理化性质的影响可能进一步影响克隆植物的优势度。     

Importance of clonal plants and plant species diversity in the Northeast China Transect

In plant communities, the internal (genet-level) control mechanisms on a spatio-temporal scale of clonal plants impose strong constraints on spatial pattern as well as on competitive relations and, thus, species coexistence. Therefore, the presence of clonal species within a plant community affects spatio-temporal dynamics and plant species diversity. We examined the distribution of plants with different clonal growth forms in the Northeast China Transect (NECT) and correlated plant species diversity with the importance of clonal plants, and the importance of phalanx and guerilla clonal plants. Phalanx clonal plants were more abundant in western communities where the altitude was higher and both the soil nitrogen contents and precipitation were relatively low. Whereas guerilla clonal plants were more abundant in the middle of the NECT where the precipitation, mean annual temperature and photosynthetically active radiation were relatively high. In the relatively productive temperate typical steppe, plant species diversity was negatively correlated with the importance of phalanx clonal plants and positively correlated with the importance of guerilla clonal plants. In relatively unproductive temperate desert steppe, plant species diversity was positively correlated with the importance of both phalanx and guerilla clonal plants.     

Differences in physiological integration between invasive and noninvasive introduced clonal species of Carpobrotus

AimsClonal growth is associated with invasiveness in introduced plant species, but few studies have compared invasive and noninvasive introduced clonal species to investigate which clonal traits may underlie invasiveness. To test the hypothesis that greater capacity to increase clonal growthviaphysiological integration of connected ramets increases invasiveness in clonal plants, we compared the effects of severing connections on accumulation of mass in the two species of the creeping, succulent, perennial, herbaceous genusCarpobrotusthat have been introduced on sand dunes along the Pacific Coast of northern California, the highly invasive speciesCarpobrotus edulisand the co-occurring, noninvasive speciesCarpobrotus chilensis.     

水分胁迫条件下草莓克隆分株间水分调控及其对光合功能的影响

以盆栽草莓(Fragaria×ananassa)为材料研究了水分胁迫下克隆植物草莓母株和子株间的水分调控机制及其与碳同化、光系统Ⅱ激发能分配的关系.实验材料分为匍匐茎连接和剪断两个大组,进行两步实验.第1步实验,对连接组和剪断组的所有母株控水,子株充分供水;4d后进入第2步实验,把连接组分为两小组,对其中一组充分供水子株开始控水,另一组保持不变.结果表明,土壤干旱引起母株叶片失水,并使其净光合速率和气孔导度显著降低.但是连接组中供水良好的子株能有效缓解缺水母株的水分胁迫.当供水良好的子株也开始受到干旱处理的时候,则会加剧与之相连母株的水分胁迫.受胁迫母株可以通过加强渗透调节能力和降低水势从相连子株获取水分.虽然土壤干旱会造成受胁迫母株叶片脱落酸(abscisic acid, ABA)含量的大幅度增加,但是与之相连子株的叶片ABA含量并没有增加;并且气孔导度与ABA变化趋势一致.(1)草莓母株和子株间的水分运输是由二者的水势差驱动的;(2)ABA不会通过匍匐茎在母株和子株间传递并影响相邻子株气孔导度;(3)在水分异质性较大情况下,生理整合可明显提高克隆系统的碳同化能力和光系统Ⅱ激发能利用效率.     

Geographic patterns of clonal diversity in the earth mite species Penthaleus major with particular emphasis on species margins

Patterns of clonal diversity in parthenogenetic species can be influenced by occasional sexual reproduction, selection due to environmental heterogeneity, and genetic drift. Here we investigate geographic patterns of clonal diversity in the obligate parthenogenetic earth mite species, Penthaleus major, in southeastern Australia. Spatial autocorrelation analysis indicated a relationship between geographic distance and clonal diversity at the sites. However, there was no evidence for an association between distance and clonal composition or the frequency of the two most common clones. Regression analyses indicated that clonal diversity and the frequency of one of the common clonal groups were associated with latitude and/or climatic variables, whereas the other common group was not associated with any of those variables. In four transects (each 250-400 km in length) extending from the center of the distribution of P. major to its margins, there was a consistent and continuous decline in clonal diversity as the margin was approached but no evidence that one clonal group predominated at the margin. This argues against the importance of a general-purpose genotype being favored at margins and suggests that either selection acts to decrease local diversity at sites near the margin or that diversity declines due to drift at these sites.     

鄂尔多斯高原沙地植被和两种优势克隆半灌木的空间格局

群落优势种重要值的变化可以表征植被的演替状况。研究了鄂尔多斯高原飞播后不同演替阶段的沙地植被 ,以及两种优势克隆植物羊柴 (H edysarum laeve)和油蒿 (Artemisia ordosica)种群的空间格局。结果表明 :在调查的尺度内 ,群落水平上 ,演替前期和演替中期的植被盖度空间自相关发生的尺度远小于演替后期。随着植被的演替和发育 ,小于抽样尺度 (<1m)的随机变异逐渐增加。暗示着植被盖度空间格局的变化与羊柴种群和油蒿种群在群落中的地位的变化有关。种群水平上 ,小尺度的空间自相关控制着羊柴种群在 3个演替阶段的空间格局 ;处于前 2个演替阶段的油蒿种群 ,空间格局受更大尺度的过程控制 ,并在自身为建群种的群落随机分布。对于 3个演替阶段的油蒿种群而言 ,发生在小于抽样尺度 (<1m)的随机变异都高于相应的羊柴种群。这两种克隆半灌木的种群空间格局的差异可能与二者克隆构型和克隆性的不同有关。本文还根据这两种植物的生物学特性探讨了二者对鄂尔多斯高原沙地植被恢复的不同作用     

平茬处理对小叶锦鸡儿灌丛邻居植物群落空间格局的影响

近几十年来,内蒙古典型草原小叶锦鸡儿(Caragana microphylla)灌丛化现象普遍发生,严重影响了草地生产力。平茬作为灌丛化草地主要管理方式之一,已受到广泛关注;然而平茬如何影响灌丛邻居植物群落的格局动态及其下土壤理化性质变化,仍缺少相应研究。以内蒙古草原小叶锦鸡儿灌丛化草地为研究对象,进行平茬处理,并依据距离小叶锦鸡儿灌丛的远近位置(远—2.5 m,近—0.5 m)设置样方进行植物群落调查和土壤样品的采集,经分析发现:(1)平茬处理显著提高了灌丛邻居植物群落均匀度及邻居植物群落下土壤全碳、全氮含量。(2)借助零模型(Null-model)分析,得出未平茬处理条件下,距离灌丛远近两种位置群落均表现为竞争性格局;而平茬处理条件下,群落竞争性格局作用弱化,且距离灌丛2.5 m位置处群落表现为促进性格局。(3)调查群落中物种间的关系多为中性作用;仅有少数物种对表现为显著正(或负)相互作用关系,且多由群落中优势物种组成;平茬处理条件下群落中显著负相互作用关系物种对比例下降,支持群落整体竞争性格局弱化这一结论。所得结果不仅为小叶锦鸡儿灌丛平茬处理条件下邻居植物群落及土壤环境的动态变化的探讨提供了实验依据,而且对灌丛化草地的恢复具有一定的实践指导意义。     

Spatial and temporal patterns of species richness in a riparian landscape

Aim To test for control of vascular plant species richness in the riparian corridor by exploring three contrasting (although not mutually exclusive) hypotheses: (1) longitudinal patterns in riparian plant species richness are governed by local, river‐related processes independent of the regional species richness, (2) riparian plant species richness is controlled by dispersal along the river (longitudinal control), and (3) the variation in riparian plant species richness mirrors variation in regional richness (lateral control). Location The riparian zones of the free‐flowing Vindel River and its surrounding river valley, northern Sweden. Methods We used data from three surveys, undertaken at 10‐year intervals, of riparian reaches (200‐m stretches of riverbank) spanning the entire river. In addition, we surveyed species richness of vascular plants in the uplands adjacent to the river in 3.75‐km² large plots along the same regional gradient. We explored the relationship between riparian and upland flora, and various environmental variables. We also evaluated temporal variation in downstream patterns of the riparian flora. Results Our results suggest that local species richness in boreal rivers is mainly a result of local, river‐related processes and dispersal along the corridor. The strongest correlation between species richness and the environment was a negative one between species number and soil pH, but pH varied within a narrow range. We did not find evidence for a correlation between species richness on regional and local scales. We found that the local patterns of species richness for naturally occurring vascular plants were temporally variable, probably in response to large‐scale disturbance caused by extreme floods. Most previous studies have found a unimodal pattern of species richness with peaks in the middle reaches of a river. In contrast, on two of three occasions corresponding to major flooding events, we found that the distribution of species richness of naturally occurring vascular plants resembled that of regional diversity: a monotonic decrease from headwater to coast. We also found high floristic similarity between the riparian corridor and the surrounding landscape. Main conclusions These results suggest that local processes control patterns of riparian species richness, but that species composition is also highly dependent on the regional species pool. We argue that inter‐annual variation in flood disturbance is probably the most important factor producing temporal variability of longitudinal species richness patterns.     

芦苇克隆整合对石油污染湿地土壤微生物群落结构和生物量的影响

克隆植物形体相连的无性个体(分株)之间可以进行水分、养分和光合产物的传递和共享,并且这种克隆整合可以显著提高分株对环境胁迫的耐受能力,从而可能进一步影响分株周围的土壤微生物群落结构和生物量。尽管国内外已经开展了大量有关克隆整合对分株耐受胁迫能力影响的研究,但克隆整合对土壤微生物群落结构和生物量影响的研究却十分缺乏。以黄河三角洲芦苇(Phragmites australis)湿地生态系统为研究对象,将直径60 cm的圆形样方进行三个水平的石油添加处理(不添加石油或每年添加5 mm或10 mm厚的石油),同时通过切断或不切断样方内外芦苇根状茎的连接来控制克隆整合的有无。实验连续开展了两年(2014—2015年),每年8月份在样方内进行土壤样品取样,在实验室内采用磷酸脂肪酸(PLFA)法测定土壤微生物总量及主要微生物类群含量,并测定土壤微生物生物量碳和氮含量。取样时间显著影响土壤微生物PLFA总量、微生物碳和氮含量,这3个变量在2015年均显著高于2014年。石油添加在2015年显著增加了土壤微生物PLFA总量,但在2014年却无显著效应;同时,石油添加在2014年降低了土壤微生物碳和氮含量,而在2015年却增加了其含量。然而,无论在2014年还是2015年,芦苇的克隆整合对土壤微生物PLFA含量、微生物碳和氮含量均没有显著影响。土壤微生物PLFA总量与土壤微生物碳和氮含量呈正相关关系。这些结果表明,石油污染可以显著影响湿地土壤微生物动态,但克隆整合却无显著效应。     

Exogenous disturbances and endogenous self-organized processes are not mutually exclusive drivers of spatial patterns in macroalgal assemblages

Complex spatial patterns are common in coastal marine systems, but mechanisms underlying their formation are disputed. Most empirical work has focused on exogenous spatially structured disturbances as the leading cause of pattern formation in species assemblages. However, theoretical and observational studies suggest that complex spatial patterns, such as power laws in gap-size distribution, may result from endogenous self-organized processes involving local-scale interactions. The lack of studies simultaneously assessing the influence of spatially variable disturbances and local-scale interactions has fuelled the idea that exogenous and endogenous processes are mutually exclusive explanations of spatial patterns in marine ecosystems. To assess the relative contribution of endogenous and exogenous processes in the emergence of spatial patterns, an intertidal assemblage of algae was exposed for two years to various combinations of intensity and spatial patterns of disturbance. Localized disturbances impinging at the margins of previously disturbed clearings and homogenous disturbances without any spatial pattern generated heterogeneous distributions of disturbed gaps and macroalgal patches, characterized by a power-law scaling. Spatially varying disturbances produced a spatial gradient in the distribution of algal patches and, to a lesser extent, also a power-law scaling in both patch- and gap-size distributions. These results suggest that exogenous and endogenous processes are not mutually exclusive forces that can lead to the formation of similar spatial patterns in species assemblages.     

土壤氮素异质性分布和马先蒿寄生对长芒棒头草生长发育及根系分布的影响

无论在农田还是自然生态系统中,土壤养分异质性普遍存在。植物具有感知土壤养分异质性的能力,并通过调节根系生物量分配及空间分布以获取更多资源。了解寄生胁迫在不同养分条件下对寄主生长发育及根系空间分布的影响,对解析寄主应对寄生胁迫和养分胁迫的适应策略,进而指导寄生性杂草防控具有重要的指导意义。该文采用分根试验,通过对寄主分根,并控制根室两侧氮供应水平及寄生胁迫程度,考察了氮胁迫及两种寄主依赖程度不同的马先蒿的寄生对寄主长芒棒头草生长发育及根系空间分布的影响。结果表明:(1)土壤氮水平与马先蒿寄生均可显著影响长芒棒头草生物量及根冠比,并且两者之间存在显著交互作用,其中土壤氮水平为主要影响因子。(2)两种马先蒿对长芒棒头草的危害程度不同。在NPK和2NPK处理时,三色马先蒿的寄生显著降低长芒棒头草生物量(茎叶:37. 1%、51. 5%;根系:35. 6%、63.6%);在NPK处理时,大王马先蒿的寄生显著增加长芒棒头草生物量(茎叶:29.9%,根系:61.2%)。(3)长芒棒头草的根系生长和空间分布受氮营养的异质分布和寄生的影响,具有明显的感知养分空间分布及调节根系生长能力。     

Experimental evidence for root competition effects on community evenness in one of two phytometer species

AimsPlant–plant interactions, being positive or negative, are recognized to be key factors in structuring plant communities. However, it is thought that root competition may be less important than shoot competition due to greater size symmetry belowground. Because direct experimental tests on the importance of root competition are scarce, we aim at elucidating whether root competition may have direct or indirect effects on community structure. Indirect effects may occur by altering the overall size asymmetry of competition through root–shoot competitive interactions.     

毛乌素沙地克隆植物沙鞭生长对AM真菌生态分布的影响

从毛乌素沙地沙鞭群落间隔空地沙鞭根状茎延伸方向设置样地,2007年5月、7月和10月在0-10、10-20、20-30、30-40和40-50 cm共5个土层分别采集土壤样品,研究了AM真菌时空分布及沙鞭侵入间隔空地前后对AM真菌分布的影响。结果表明,沙鞭能与AM真菌形成良好共生关系,菌根结构为中间型(I-型),AM真菌定殖率和孢子密度有明显的时空分布规律,并与土壤因子密切相关。随采样时间后延AM真菌定殖率先增后降,最大值出现在7月份;孢子密度先降后增,最大值出现在10月份。土壤采样深度对AM真菌定殖和孢子密度有显著影响,AM真菌最高定殖率和最大孢子密度均出现在0-20 cm浅土层。孢子密度仅与泡囊定殖率显著正相关。土壤速效N与菌丝和总定殖率极显著负相关;土壤温度与泡囊、丛枝、菌丝和总定殖率显著和极显著正相关,与孢子密度显著负相关;土壤湿度与丛枝、菌丝和总定殖率显著正相关,与孢子密度显著负相关。克隆植物沙鞭的生长对土壤AM真菌活动和分布有很大影响,沙鞭入侵前后样地中AM真菌孢子密度和定殖率变化显著。     

Effects of plant species richness on stand structure and productivity

Aims Aboveground biomass production commonly increases with species richness in plant biodiversity experiments. Little is known about the direct mechanisms that cause this result. We tested if by occupying different heights and depths above and below ground, and by optimizing the vertical distribution of leaf nitrogen, species in mixtures can contribute to increased resource uptake and, thus, increased productivity of the community in comparison with monocultures.Methods We grew 24 grassland plant species, grouped into four nonoverlapping species pools, in monoculture and 3- and 6-species mixture in spatially heterogeneous and uniform soil nutrient conditions. Layered harvests of above- and belowground biomass, as well as leaf nitrogen and light measurements, were taken to assess vertical canopy and root space structure.Important findings The distribution of leaf mass was shifted toward greater heights and light absorption was correspondingly enhanced in mixtures. However, only some mixtures had leaf nitrogen concentration profiles predicted to optimize whole-community carbon gain, whereas in other mixtures species seemed to behave more 'selfish'. Nevertheless, even in these communities, biomass production increased with species richness. The distribution of root biomass below ground did not change from monocultures to three- and six-species mixtures and there was also no indication that mixtures were better than monocultures at extracting heterogeneously as compared to homogeneously distributed soil resources. We conclude that positive biodiversity effect on aboveground biomass production cannot easily be explained by a single or few common mechanisms of differential space use. Rather, it seems that mechanisms vary with the particular set of species combined in a community.     

毛乌素沙地克隆植物生长对AM真菌多样性和菌根形成的影响

克隆植物的生态功能在沙地植被恢复过程中占据着重要位置。在毛乌素沙地由北向南选择两个典型样地,以根茎克隆植物沙鞭和羊柴为试验材料,连续2a系统地研究了克隆植物生长对AM真菌物种多样性和菌根形成的影响。结果表明:克隆植物生长对AM真菌物种多样性和丛枝菌根形成的影响因植物种类和样地不同而异。沙鞭通过克隆生长侵入灌丛空地后,AM真菌多样性指数在中国科学院植物研究所鄂尔多斯沙地草地生态研究站(简称OSES)和陕西榆林珍稀沙生植物保护基地(简称RSCF)样地均上升;孢子密度、菌丝、丛枝和总定殖率均显著提高;泡囊定殖率也有所增加,在OSES样地达显著水平,在RSCF样地未达显著水平。羊柴通过克隆生长侵入灌丛空地后,AM(Arbuscular mycorrhizal)真菌多样性指数在OSES样地上升,而在RSCF样地下降;孢子密度和丛枝定殖率在OSES和RSCF样地均显著增加,而泡囊定殖率均显著降低;菌丝和总定殖率也降低,在OSES样地未达显著水平,在RSCF样地达显著水平。     

异质光环境下克隆整合对白夹竹光合氮分配格局的影响

采用盆栽试验,以单轴散生型竹类植物——白夹竹(Phyllostachys bissetii)克隆片段为对象,使近端分株处于自然光照环境,远端分株处于遮荫环境中,对根状茎作切断或不切断处理,研究克隆整合对远端分株和近端分株光合氮分配格局的影响。结果表明:(1)根状茎保持连接的远端分株较根状茎切断的远端分株具有更高的最大净光合速率、叶片氮含量、光合色素含量、叶片光合氮分配系数。(2)相对根状茎切断处理,根状茎保持连接的远端分株将更多的氮分配到光合系统的羧化系统、生物力能学组分,而分配至捕光系统组分的比例较小。(3)比较处于自然光照条件的近端分株,比叶重、叶片氮含量等并没有因根状茎切断与否表现出显著性差异,根状茎连接的近端分株部分指标甚至高于根状茎切断的近端分株。研究认为,克隆整合作用影响处于遮荫环境的白夹竹远端分株的光合氮分配格局,使得处于遮荫生境中的克隆分株依旧维持较高的光合能力,保证了处于逆境条件下克隆分株的生存与生长。