Clonal Transgenerational Effects Transmit for Multiple Generations in a Floating Plant

Environmental conditions of a parent plant can influence the performance of their clonal offspring,and such clonal transgenerational effects may help offspring adapt to different environments.However,it is still unclear how many vegetative generations clonal transgenerational effects can transmit for and whether it depends on the environmental conditions of the offspring.We grew the ancestor ramets of the floating clonal plant Spirodela polyrhiza under a high and a low nutrient level and obtained the so-called 1^(st)-generation offspring ramets of two types(from these two environments).Then we grew the 1^(st)-generation offspring ramets of each type under the high and the low nutrient level and obtained the so-called 2^(nd)-generation offspring ramets of four types.We repeated this procedure for another five times and analyzed clonal transgenerational effects on growth,morphology and biomass allocation of the 1^(st)-to the 6^(th)-generation offspring ramets.We found positive,negative or neutral(no)transgenerational effects of the ancestor nutrient condition on the offspring of S.polyrhiza,depending on the number of vegetative generations,the nutrient condition of the offspring environment and the traits considered.We observed significant clonal transgenerational effects on the 6^(th)-generation offspring;such effects occurred for all three types of traits(growth,morphology and allocation),but varied depending on the nutrient condition of the offspring environment and the traits considered.Our results suggest that clonal transgenerational effects can transmit for multiple vegetative generations and such impacts can vary depending on the environmental conditions of offspring.

Emergent plant presence and richness alter competitive interactions between two foating plants

Interactions between two plant species can be infuenced by the presence of other plant species and such an effect may change as the diversity of the other species increases.To test these hypotheses,we frst constructed aquatic communities consisting of 1,2 and 4 emergent plant species and then grew ramets of Lemna minor only,ramets of Spirodela polyrhiza only or ramets of both L.minor and S.polyrhiza within these aquatic communities.We also included controls with ramets of L.minor,S.polyrhiza or both but without any emergent plants.Biomass and number of ramets of L.minor and S.polyrhiza were signifcantly smaller with than without the emergent plants,but they did not differ among the three richness levels.The presence of S.polyrhiza did not signifcantly affect the growth of L.minor,and such an effect was not dependent on the richness of the emergent plant species.Without the emergent plant species,the presence of L.minor markedly reduced biomass(-92%)and number of ramets(-88%)of S.polyrhiza.However,such a competitive effect of L.minor on S.polyrhiza became much weaker in the presence of one emergent plant species(-46%biomass and-39%number of ramets)and completely disappeared in the presence of two or four emergent plant species.Therefore,both the presence and richness of emergent plant species can alter competitive interactions between the two duckweed species.These fndings highlight the importance of species diversity in regulating plant-plant interactions.

地下芽植物芽库密度响应环境干扰的Meta分析

地下芽库是地下芽植物地下储存器官产生的无性繁殖体的集合,是地下芽植物繁殖的主要方式。地下芽库密度反映了地下芽植物群落的潜在更新能力。然而,不同的扰动和生境类型对地下芽库密度的影响尚缺乏全面的了解;此外,不同类型地下芽库对不同扰动类型的响应是否存在差异也不明确。本研究通过Meta分析系统收集了环境扰动对地下芽库密度影响的相关文献,计算了不同扰动和生境类型对各地下芽库类型密度影响的累计效应值。结果发现,由于地下芽库对扰动的响应存在相反或波动的特征,整体上环境扰动对地下芽库密度的影响较小,而干旱对芽库密度具有负效应。总体而言,环境扰动降低了根状茎芽的密度,但增加了分蘖芽的密度。环境扰动降低了湿地中的地下芽库密度,但在其它生境类型中并未发现显著影响。因此,地下芽植物的芽库对扰动有着很强的抗性和弹性,地下芽库的密度变化取决于扰动的类型、分布的生境和受扰动的芽库类型。

Interaction mechanism between BaZrO_(3)/Y_(2)O_(3) refractory and Ti_(2)Ni alloy melts

The titanium alloys with highly chemical activity require stable crucible refractories that can withstand the erosion of alloy melts.The phase composition and microstructure are crucial factors that affect the stability of the refractory crucible.The effect of Y_(2)O_(3) on the composition and microstructure of BaZrO_(3) crucible was systematically investigated,and the improved mechanism of the stability of BaZrO_(3)/Y_(2)O_(3) crucible was clarified in comparison with the BaZrO_(3) crucible.The results showed that the erosion layer thickness of the BaZrO_(3)/Y_(2)O_(3) crucible was only 63μm,which was far less than that in the BaZrO_(3) crucible(485μm),and the erosion layer in the BaZrO_(3)/Y_(2)O_(3) crucible also exhibited a higher density than that in the BaZrO_(3) crucible.During the sintering,Y_(2)O_(3) could improve the densification of the BaZrO_(3) crucible due to the solid solution effect between Y_(2)O_(3) and ZrO_(2),which also caused the evaporation of BaO,resulting in the generation of a Y_(2)O_(3)(ZrO_(2))film on the surface of the crucible.Furthermore,the Y_(2)O_(3)(ZrO_(2))had higher thermodynamic stability than Y_(2)O_(3),confirming that the BaZrO_(3)/Y_(2)O_(3) crucible with high density exhibited a superior erosion resistance to titanium alloys.This dual-phase structure provides a strategy to design a long-life and stable refractory for melting titanium alloys.

黄河三角洲溶解有机质的光谱特征及其驱动因素

河口三角洲是生物地球化学循环的热点地区。了解该区域溶解有机质(DOM)的来源及其驱动因素对于评估其在调节全球碳通量中的作用具有重要意义。本研究分析了黄河三角洲淡水和潮汐区域中土壤DOM的光谱特征。通过平行因子分析(PAFARAC),以及与在线数据库(http://www.openfluor.org)的对比最终确定了5种荧光组分(包括2种类腐殖酸、2种类蛋白质和1种可能的污染物)。淡水和潮汐区域中土壤DOM及各荧光组分的浓度、光谱性质和来源均不同。潮汐区DOM的浓度较低,而相对分子质量较高。在淡水地区,土壤DOM主要来源于浮游植物和微生物;而在潮汐地区,土壤DOM主要来源于微生物和人类活动。这两个地区土壤DOM的差异主要由环境因素驱动,尤其是土壤碳(C)、氮(N)及其化学计量比C/N,能够解释DOM和CDOM变化的80.7%和69.6%。此外,浮游植物也对该地区土壤中的DOM、CDOM和荧光组分(C1–C4)有重要的影响,结果发现它们之间存在显著的正相关关系。研究结果表明,黄河三角洲土壤DOM的浓度和组成受土壤性质和浮游植物密度的强烈驱动。

Effects of physiological integration on defense strategies against herbivory by the clonal plant Alternanthera philoxeroides

Aims The plant-herbivore interaction is one of the most fundamental inter-actions in nature.Plants are sessile organisms,and consequently rely on particular strategies to avoid or reduce the negative impact of herbivory.Here,we aimed to determine the defense strategies against insect herbivores in the creeping invasive plant Alternanthera philoxeroides.Methods We tested the defense response of A.philoxeroides to herbivory by a leaf-feeding specialist insect Agasicles hygrophila and a pol-yphagous sap-feeding insect Planococcus minor.We also tested the mechanisms triggering defense responses of A.philoxeroides by including treatments of artificial leaf removal and jasmonic acid application.Furthermore,we examined the effect of physiological integration on these defense strategies.Important Findings The combination of artificial leaf removal and jasmonic acid appli-cation produced a similar effect to that of leaf-feeding by the real herbivore.Physiological integration influenced the defense strat-egies of A.philoxeroides against herbivores,and increased biomass allocation to aboveground parts in its apical ramets damaged by real herbivores.Our study highlights the importance of physio-logical integration and modular plasticity for understanding the consequences of herbivory in clonal plants.

Effects of clonal integration and nitrogen supply on responses of a clonal plant to short-term herbivory

Aims Clonal integration,i.e.resource sharing between interconnected ramets,can help clonal plants tolerate abiotic stress.However,few studies have directly examined the ecological significance of clonal integration in the ability of clonal plants to tolerate biotic stress such as herbivory.Methods We grew clonal fragments of an invasive clonal plant Alternanthera philoxeroides,each consisting of an apical part(relatively young)and a basal part(relatively old),at two levels(low and high)of soil nitrogen(N).For each fragment,the apical part was subjected to either no herbivory or herbivory for 2 weeks by a specialist insect,Agasicles hygrophila,and was either connected with or discon-nected from the basal part not subjected to herbivory.Important Findings Herbivory in the apical part severely reduced leaf growth(leaf mass,leaf number or leaf area)and ramet production of both apical and basal parts,and increased root to shoot ratio of the apical part.Irrespective of herbivory and soil N,stem connection between the apical and the basal part decreased root to shoot ratio of the ap-ical part,but did not change its growth measures.Meanwhile,con-nection increased stem N concentration of the apical part growing under high-N supply and decreased stem carbon(C)concentration of the apical part under low-N supply.By contrast,connection in-creased root to shoot ratio of the basal part,but reduced its leaf and ramet production.Connection also increased leaf and stem C concentrations of the basal part under low-N supply.Thus,clonal integration can be beneficial for the early development of young A.philoxeroides ramets,but not for their local adaptation to herbivory damage by A.hygrophila.

Soil heterogeneity affects ramet placement of Hydrocotyle vulgaris

Aims Soil heterogeneity is common in natural habitats.It may trigger for-aging responses(placing more ramets and/or roots in nutrient-rich patches than in nutrient-poor patches)and further affect the growth of plants.However,the impact of soil heterogeneity on competitive interactions has been little tested.Methods We conducted a greenhouse experiment to investigate the effects of soil heterogeneity on intraspecific competition with a stolonif-erous herb Hydrocotyle vulgaris.We grew one(without com-petition)or nine ramets(with competition)of H.vulgaris under a homogeneous environment and two heterogeneous environ-ments differing in patch size(large or small patches).In the het-erogeneous treatment,the soil consisted of the same number of nutrient-rich and nutrient-poor patches arranged in a chessboard manner,and in the homogeneous treatment,the soil was an even mixture of the same amount of the nutrient-rich and the nutrient-poor soil.Important Findings Irrespective of intraspecific competition,H.vulgaris showed for-aging responses to soil heterogeneity in the large patch treatment,e.g.it produced significantly more biomass,ramets,aboveground mass and root mass in the nutrient-rich patches than in the nutrient-poor patches.In the small patch treatment,foraging responses were observed when intraspecific competition was present,but responses were not observed when there was no competition.However,we find a significant effect of soil heterogeneity on neither overall growth nor competitive intensity of H.vulgaris.Our results suggest that foraging responses to soil heterogeneity may not necessarily be adaptive and intraspecific competition may not be influenced by soil heterogeneity.

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.

Trans-generational effects in the clonal invader Alternanthera philoxeroides

Aims Recent studies have revealed heritable phenotypic plasticity through vegetative generations.In this sense,changes in gene regulation induced by the environment,such as DNA methylation(i.e.epigenetic changes),can result in reversible plastic responses being transferred to the offspring generations.This trans-generational plasticity is expected to be especially relevant in clonal plants,since reduction of sexual reproduction can decrease the potential for adaptation through genetic variation.Many of the most aggressive plant invaders are clonal,and clonality has been suggested as key to explain plant invasiveness.Here we aim to determine whether trans-generational effects occur in the clonal invader Alternanthera philoxeroides,and whether such effects differ between populations from native and non-native ranges.Methods In a common garden experiment,parent plants of A.philoxeroides from populations collected in Brazil(native range)and Iberian Peninsula(non-native range)were grown in high and low soil nutrient conditions,and offspring plants were transplanted to control conditions with high nutrients.To test the potential role of DNA methylation on trans-generational plasticity,half of the parent plants were treated with the demethylating agent,5-azacytidine.Important Findings Trans-generational effects were observed both in populations from the native and the non-native ranges.Interestingly,trans-generational effects occurred on growth variables(number of ramets,stem mass,root mass and total mass)in the population from the native range,but on biomass partitioning in the population from the non-native range.Trans-generational effects of the population from the native range may be explained by a‘silver-spoon’effect,whereas those of the population from the non-native range could be explained by epigenetic transmission due to DNA methylation.Our study highlights the importance of trans-generational effects on the growth of a clonal plant,which could help to understand the mechanisms underlying expansion success of many clonal plants.

Importance of starting points in heterogeneous environments: interactions between two clonal plants with contrasting spatial architectures

Aims Plants can benefit from heterogeneous environments via disproportionately increasing resource harvesting in resource-rich patches.Their initial growing positions with respect to resource patches may thus have important influences on their performance and relative competitive ability.Such impacts may differ between species with contrasting spatial architectures.However,the potential influence of initial growing positions in heterogeneous environment on plant growth and competition has largely been ignored.Methods We grew the phalanx plant Carex neurocarpa and the guerrilla plant Bolboschoenus planiculmis alone or in competition in a heterogeneous environment consisting of high-and low-nutrient soil patches.In treatments without competition,one ramet of each species was grown in either a high-or a low-nutrient patch in the heterogeneous environment.In treatments with competition,a ramet of the target species was grown in either a high-or a low-nutrient patch,and a ramet of the competitor species was grown in the same patch as the target species or an adjacent patch with a different nutrient level.Important Findings Without competition C.neurocarpa produced more biomass and ramets when initially grown in a high-nutrient patch than when initially grown in a low-nutrient patch.With competition,these differences disappeared.Consequently,competitive intensity on C.neurocarpa was higher when it initially grew in a high-nutrient patch than when it initially grew in a low-nutrient patch.These impacts were independent of the initial position of its competitor.By contrast,the initial positions of B.planiculmis did not influence its growth or competitive response.Therefore,in heterogeneous environments,initial growing positions of clonal plants may influence their performance in competition-free environments and may also affect their relative competitive ability,and these effects may depend on spatial architecture of the plants.

Effects of soil substrate heterogeneity and moisture on interspecific competition between Alternanthera philoxeroides and four native species

Aims Clonal plant species have the potential for high relative performance in heterogeneous environments,and this might increase the com-petitive ability and invasiveness of introduced clonal plant species.It was hypothesized that clonal species whose performance responds more to heterogeneity of a resource have higher competitive ability in habitats where this resource is more heterogeneous and that this relationship is stronger when other resources are less limiting.Methods To test these hypotheses,the perennial clonal herb Alternanthera philoxeroides,which is invasive in China,was grown alone or with each of four clonal perennial,co-occurring herbs native to China,i.e.Alternanthera sessilis,Cynodon dactylon,Hemarthria altissima and Wedelia chinensis.Plants were given homogeneous or het-erogeneous soil substrate crossed with low and high levels of soil moisture.Important Findings Effects of heterogeneity on the accumulation of mass and ramets and on competitive effect and response of A.philoxeroides differed between native species and interacted with effects of soil moisture.A.philoxeroides reduced the final total mass or ramet number of the native species except A.sessilis,and the negative competitive effects on H.altissima and C.dactylon were more pronounced in heterogeneous than in homogeneous soil.Competitive response of A.philoxeroides was more negative to A.sessilis than to the other native species.Across native species,the competitive response of A.philoxeroides was more negative in heterogeneous than in homo-geneous soils at low moisture level,but the reverse was true at high moisture level.Results do not consistently support either hypoth-esis,but do suggest that competitive ability can be partly explained by individual species traits such as size,and that some competi-tive effects and responses are emergent properties of interspecific interactions.

Current plant diversity but not its soil legacy influences exotic plant invasion

Current plant diversity can influence exotic plant invasion,but it is unclear whether there is a legacy effect of plant diversity on exotic plant invasion.As plant diversity can affect soil microbial communities and physio-chemical properties,which may cascade to impact subsequent exotic plant growth,we hypothesize that the soil legacy effect of plant diversity can influence exotic plant invasion.We conducted a plant–soil feedback experiment.In the conditioning phase,we trained soils by monocultures of 12 plant species from three functional groups(4 grasses,3 legumes and 5 forbs)and mixtures of 8 randomly selected species with all three functional groups from this 12-species pool.In the test phase,we grew the invasive plant Bidens pilosa with a co-occurring native grass(Arthraxon hispidus),with a co-occurring native forb(Pterocypsela indica)or with both in each type of the conditioned soils.The performance of B.pilosa relative to its native competitors varied depending on the functional type of both conditioning plant species in the conditioning phase and competing plant species in the test phase.Diversity of the conditioning plants did not influence the growth difference between B.pilosa and its native competitors.However,increasing diversity of the competing plant species reduced the performance of B.pilosa relative to its native competitors.Our results suggest that current plant diversity can reduce exotic plant invasion through increasing growth inequality between invasive and native plants,but the soil legacy effect of plant diversity may have little impact on exotic plant invasion.

Effects of clonal integration, nutrients and cadmium on growth of the aquatic macrophyte Pistia stratiotes

Aims Many wetlands are polluted with both nutrients and toxic metals and vegetated largely by clonal plants.We hypothesized that eutrophication and clonal integration can increase phytoremediation of toxic metal pollution by increasing plant growth,even under the stress imposed by toxicity.Methods To test this hypothesis,single ramets of the common,widespread,floating,stoloniferous plant Pistia stratiotes L.,were grown for 42 days at two levels of nutrient availability with and without 0.6 mg L^(-1) cadmium.Ramets were either severed from their vegetative offspring to prevent clonal integration or left connected,and severed offspring were either removed to eliminate intraclonal competition or left in place.Important Findings Plants subjected to cadmium addition accumulated almost twice as much dry mass if given the higher nutrient level,due mainly to a doubling of the number of clonal offspring.Severance had little effect on the final mass of the parent plus offspring ramets.Removing offspring following severance had no effect on the final mass of the parental ramet in the presence of added cadmium,but it did increase the final mass of the parent in the absence of cadmium.These results support the hypothesis that eutrophication can increase remediation of toxic metal pollution by aquatic macrophytes but provided no evidence that clonal integration can affect remediation.Species such as P.stratiotes may help remediate co-pollution of wetlands with toxic metals and nutrients,and fragmentation of clones may not affect their remediation capacity.

Effects of salinity and clonal integration on the amphibious plant Paspalum paspaloides:growth,photosynthesis and tissue ion regulation

Aims Clonal integration can increase performance of clonal plants suffer-ing from environmental stress,and clonal plants in many wetlands commonly face stress of flooding accompanied by salinity.However,few studies have tested roles of clonal integration in amphibious plants expanding from terrestrial to aquatic saline habitats.Methods Basal(older)ramets of clonal fragments of Paspalum paspaloides were grown in soil to simulate terrestrial habitats,whereas their apical(younger)ramets were placed at the surface of saline water containing 0,50,150 and 250 mmol l^(−1)NaCl to mimic different salinity levels in aquatic habitats.Stolons connecting the apical and basal ramets were either intact(connected)to allow clonal integra-tion or severed(disconnected)to prevent integration.Important Findings Increasing salinity level significantly decreased the growth of the apical ramets of P.paspaloides,and such effects on the leaf growth were much higher without than with stolon connection after 60-day treatment.Meanwhile,leaf and total mass ratios of the connected to the disconnected apical ramets were higher at high than at low saline treatments.Correspondingly,Fv/Fm and F/Fm′of the apical ramets were higher with than without stolon connection in highly saline treatments.The results suggest that clonal integration can benefit the spread of apical ramets from terrestrial soil into saline water,and that the positive effects increase with increasing salinity.However,clonal integration did not significantly affect the growth of the whole frag-ments.Due to clonal integration,Na^(+)could be translocated from the apical to the basal ramets to alleviate ion toxicity in apical ramets.Our results suggest that clonal integration benefits the expansion of P.paspaloides from terrestrial to aquatic saline habitats via maintained photosynthetic capacities and changed biomass allocation pattern.

Carbon and nutrient physiology in shrubs at the upper limits:a multispecies study

Aims Carbon and nutrient physiology of trees at their upper limits have been extensively studied,but those of shrubs at their upper limits have received much less attention.The aim of this study is to examine the general patterns of nonstructural carbohydrates(NSCs),nitrogen(N)and phosphorous(P)in shrubs at the upper limits,and to assess whether such patterns are similar to those in trees at the upper limits.Methods Across Eurasia,we measured the concentrations of soluble sugars,starch,total NSCs,N and P in leaves,branches and fine roots(<0.5 cm in diameter)of five shrub species growing at both the upper limits and lower elevations in both summer(peak growing season)and winter(dormancy season).Important Findings Neither elevation nor season had significant effects on tissue N and P concentrations,except for lower P concentrations in fine roots in winter than in summer.Total NSCs and soluble sugars in branches were significantly higher in winter than in summer.There were significant interactive effects between elevation and season for total NSCs,starch,soluble sugars and the ratio of soluble sugar to starch in fine roots,showing lower soluble sugars and starch in fine roots at the upper limits than at the lower elevations in winter but not in summer.These results suggest that the carbon physiology of roots in winter may play an important role in determining the upward distribution of shrubs,like that in the alpine tree-line trees.

Interactions of the indigenous evergreen shrub Sabina vulgariswith coexisting species in the Mu Us sandland

Aims Facilitation is widespread in plant communities and particularly common in highly stressful environments.In the semi-arid Mu Us sandland where soil water and nutrients are short and grazing is heavy,many species grow within the large patches formed by the dense individuals of the unpalatable clonal shrub Sabina vulgaris,the only natural evergreen shrub species in the Mu Us sandland.However,the interactions between S.vulgaris and these coexisting species remain unclear,and we hypothesize that S.vulgaris can facilitate at least some species because within the patches vegetation is not grazed and soil water and nutrients may also be higher.Methods We measured the maximum height,coverage and number of individuals of each vascular species,little cover and thickness of biological crust at the soil surface in 1 m×1 m plots in three types of microsites associated with 40 patches of S.vulgaris:(i)at the center,(ii)at the inner edge and(iii)outside the patches.We also took soil samples and measured soil water content and content of total N,P,K and organic matter.Important Findings Soil water,nitrogen,organic matter and litter cover were the highest at the patch center,lowest outside the patches and intermediate at the inner edge of the patches,whereas thickness of biological crust was greater outside than at the center or at the inner edge.Among the 32 species recorded,six species preferred to occur within the patches,suggesting that S.vulgaris can facilitate these species most likely by grazing exclusion,increasing water and/or nitrogen resources in soil.However,most(19)species did not show preference and seven preferred outside.Also,species richness,pooled cover and number of individuals of all species were greater outside than within the patches,and such effects did not vary with the size of the S.vulgaris patches.These results suggest that the dominant interactions between S.vulgaris and the coexisting species are competition.The findings add to our knowledge that facilitation can be shown even when the competitive effects from the potential nurse plants are very strong.

Adaptive plasticity in response to light and nutrient availability in the clonal plant Duchesnea indica

Phenotypic plasticity enables plants to buffer against environmental stresses and match their phenotypes to local conditions.However,consistent conclusive evidence for adaptive plasticity has only been obtained for a few traits.More studies on a wider variety of plant functional traits and environmental factors are still needed to further understand the adaptive significance of plasticity.We grew 21 genotypes of the stoloniferous clonal plant Duchesnea indica under different light and nutrient conditions,and used selection gradient analyses to test the adaptive value(benefits)of morphological and physiological plasticity responding to variation in light and nutrient availability.Plants grown in shade exhibited lower values for fitness measures(fruit number,ramet number and biomass),shortened thinner internode length and decreased adult leaf chlorophyll content,but higher petiole length,specific leaf area and old leaf chlorophyll content,than plants grown without shade.Plants grown in the low nutrient condition had shorter petiole length,thicker and smaller leaf area,lower chlorophyll content,but higher fruit number and root:shoot ratio than plants grown under the high nutrient condition.Selection gradient analyses revealed that plasticity of petiole length and old leaf chlorophyll content in response to light variation was adaptive,and plasticity of old and adult leaf chlorophyll content in response to nutrient variation was adaptive.Therefore,the adaptive value of plasticity in different traits depends on the specific ecological context.Our findings contribute to understanding the adaptive significance of phenotypic plasticity of clonal plants in response to environmental variation.

Spatial heterogeneity in soil particle size:does it affect the yield of plant communities with different species richness?

Aims Soil heterogeneity is ubiquitous in many ecosystems.We hypothesized that plant communities with higher species richness might be better adapted to soil heterogeneity and produce more biomass than those with lower richness.This is because there is niche differentiation among species and different species can complement each other and occupy a broader range of niches when plant species richness is high.However,no study has tested how soil particle heterogeneity affects the yield of plant communities,and whether such effects depend on the spatial scale of the heterogeneity and the species richness within the communities.Methods In a greenhouse experiment,we sowed seeds of four-species or eight-species mixtures in three heterogeneous treatments consisting of 32,8 or 2 patches of both small(1.5 mm)and large quartz(3.0 mm)particles arranged in a chessboard manner and one homogeneous treatment with an even mixture of small and large quartz particles.Important Findings Biomass production was significantly greater in the communities with high species richness than those with low species richness.However,soil particle heterogeneity or its interactions with patch scale or species richness did not significantly affect biomass production of the experimental communities.This work indicates that plant species richness may have a bigger impact on plant productivity than soil particle heterogeneity.Further studies should consider multiple sets of plant species during longer time periods to unravel the potential mechanisms of soil heterogeneity and its interactions with the impacts of species richness on community yield and species coexistence.

Genotypic differences in response to different patterns of clonal fragmentation in the aquatic macrophyte Pistia stratiotes

Connected individuals(ramets)of clonal plants are frequently fragmented due to disturbance,and such clonal fragmentation may influence their growth.However,it is unclear whether different patterns of clonal fragmentation produce differential effects on plant growth and whether such differences vary with genotypes.We collected one group of connected ramets of the stoloniferous floating invasive macrophyte Pistia stratiotes from each of six provinces(Guangdong,Guangxi,Hubei,Jiangsu,Sichuan and Yunnan Provinces)of China,and assumed that these ramets belonged to different genotypes.After several generations of vegetative propagation to remove potential parental effects,new ramets(hereafter referred to as parent ramets)from each of these assumed genotypes were subjected to four patterns of clonal fragmentation,i.e.,all offspring ramets produced during the experiment remained connected to their parent ramet(control),or the primary(1°),secondary(2°)or tertiary(3°)offspring ramets were disconnected from their parent ramet.We found significant growth differences among the assumed genotypes,confirming that the ramets sampled from these six provinces were from different genotypes.Compared with the control,disconnecting the 1°,2°or 3°ramets did not significantly affect biomass of the whole clone(i.e.,the parent ramet plus all offspring ramets)of P.stratiotes.Disconnecting the 1°ramets significantly increased biomass of the parental ramet of all six genotypes compared with the control.However,disconnecting the 2°or 3°ramets had little effect on biomass of the parent ramet for all genotypes except the Guangxi genotype,for which disconnecting the 2°ramets decreased biomass of the parent ramet.Disconnecting the 1°,2°or 3°ramets had no impact on biomass or number of the 1°or the 3°ramets for any of the genotypes.However,disconnecting the 1°ramets decreased biomass of the 2°ramets for the Guangdong and Yunnan genotypes,but had no effect for the other four genotypes.We conclude that different patterns of clonal fragmentation can have different impacts on parent and offspring ramets of P.stratiotes and such an impact may vary with genotypes.