Belowground Bud Bank Is Insensitive to Short-Term Nutrient Addition in the Meadow Steppe of Inner Mongolia

Human activities and industrialization have significantly increased soil nutrients,such as nitrogen(N)and phos-phorus(P),profoundly impacting the composition and structure of plant community,as well as the ecosystem functions,especially in nutrient-limited ecosystems.However,as the key propagule pool of perennial grasslands,how belowground bud bank and its relationship with aboveground vegetation respond to short-term changes in soil nutrients was still unclear.In this study,we conducted a short-term(2021–2022)soil fertilization experiment with N addition(10 g N m^(-2) yr^(-1))and P addition(5 g N m^(-2) yr^(-1))in the meadow steppe of Inner Mongolia,China,to explore the responses of belowground bud bank,aboveground shoot population and their relationships(represented by the ratio of bud to shoot density-meristem limitation index(MLI))for the whole community and three plant functional groups(perennial rhizomatous grasses-PR,perennial bunchgrasses-PB,and perennial forbs-PF)to nutrient addition.The short-term nutrient addition had no significant influences on belowground bud density,aboveground shoot density,and MLI of the whole plant community.Plant functional groups showed different responses to soil fertilization.Specifically,N addition significantly increased the bud density and shoot density of PR,especially in combination with P addition.N addition reduced the shoot density of PF but had no influence on its bud density and MLI.Nutrient addition had significant effects on the three indicators of PB.Our study indicates that the belowground bud bank and its relationship with aboveground vegetation in temperate meadow steppe are insensitive to short-term soil fertilization,but plant functional groups exhibit specific responses in terms of population regeneration,which implies that plant community composition and ecosystem functions will be changed under the ongoing global change.

Soil Moisture Rather than Soil Nutrient Regulates the Belowground Bud Bank of Rhizomatous Species Psammochloa villosa in Arid Sand Dunes

In arid and semi-arid sand dune ecosystems,belowground bud bank plays an important role in population regeneration and vegetation restoration.However,the responses of belowground bud bank size and composition to sand burial and its induced changes in soil environmental factors have been rarely studied.In arid sand dunes of Northwestern China,we investigated belowground bud bank size and composition of the typical rhizomatous psammophyte Psammochloa villosa as well as three key soil environmental factors(soil moisture,total carbon and total nitrogen)under different depths of sand burial.Total buds and rhizome buds increased significantly with increasing burial depth,whereas tiller buds first increased and then decreased,with a peak value at the depth of 20-30 cm.Soil moisture increased significantly with sand burial depth,and was positively correlated with the number of all buds and rhizome buds.Soil total carbon concentration first increased and then decreased with sand burial depth,and total nitrogen concentration was significantly lower under deep sand burial than those at shallow depths,and only the number of tiller buds was positively correlated with soil total nitrogen concentration.These results indicate that soil moisture rather than soil nutrient might regulate the belowground bud bank of P.villosa,and that clonal psammophytes could regulate their belowground bud bank in response to sand burial and the most important environmental stress(i.e.,soil moisture).These responses,as the key adaptive strategy,may ensure clonal plant population regeneration and vegetation restoration in arid sand dunes.

根茎克隆植物芦苇应对风沙活动过程的生长和生殖的权衡关系

生长和繁殖之间的权衡是克隆植物适应性策略的重要组成部分。根茎型沙生植物通过权衡策略应对风沙过程(埋沙和风蚀)对它们在流动沙丘上的定居尤为重要。尽管根茎型物种对风沙过程的响应已经有了部分研究,但这些克隆物种如何通过生长和繁殖中的潜在权衡关系来应对风沙过程仍不清楚。在本研究中,我们采用了野外调查和生物量建模的手段,评估了芦苇(Phragmites communis)在沙埋和风蚀条件下,营养生长和生殖生长以及分株数量和大小之间的权衡关系。研究结果表明,沙埋促进了种子生物量和生殖努力(RE)的增加;风蚀减少了RE,但对种子生物量没有显著影响。沙埋增加了分株的生物量,而风蚀增加了分株种群密度并加速了分株的成熟。这些研究表明,根茎型沙地植物通过调整其生长策略来应对风沙过程,即在沙埋条件下,增加生殖生长和分株大小,而在风蚀条件下,增加营养生长和分株数量。

Which factors have stronger explanatory power for primary wind dispersal distance of winged diaspores:the case of Zygophyllum xanthoxylon(Zygophyllaceae)?

Aims How seed dispersal distance is related to various factors is a major challenge for seed ecologists.However,there are different answers as to which factor is most important in determining wind dispersal distance.This study is to quantitatively describe the relationship between various factors and primary wind dispersal distance of winged diaspores.Methods The dispersal distances of five morphologies of winged diaspores in Zygophyllum xanthoxylum(Zygophyllaceae)were measured under controlled conditions in a wind tunnel.The explanatory power of environmental factor(i.e.wind speed),plant trait(i.e.release height)and diaspore attributes(i.e.wing loading(the ratio of diaspore mass to projected area),settlement-velocity,shape index(the variance of diaspore length,width and thickness))to the variation in dispersal distance was assessed by releasing diaspores at varying wind speeds and release heights.Important Findings Wind speed and seed release height were the strongest explanatory factors to dispersal distance,contributing 41.1%and 24.8%(P<0.01)to total variation in dispersal distance,respectively.Wind speed accounted more for relatively light disc-shaped seeds than for relatively heavy spherical seeds.Wing loading,shape index and settlement-velocity explained 9.0%(P<0.01),1.4%(P<0.01)and 0.9%(not significant)of the variation in dispersal distance,respectively.From disc-shaped to four-winged diaspores,relative contributions of wing loading and shape index decreased but contribution of settlementvelocity increased.The relative contributions of various factors to wind seed dispersal distance may change with the change in seed morphology.

Effects of seed morphology and orientation on secondary seed dispersal by wind

Understanding how diaspore(hereafter‘seed’)morphology and orientation affect secondary seed dispersal by wind is important to link seed dispersal and post-dispersal processes,such as seed lodging,predation and germination.This study aims to describe the effects of seed morphology and orientation on secondary seed dispersal by wind via mechanistic modelling.We extend the mechanistic model of Schurr et al.(2005)in order to describe how secondary seed dispersal by wind is affected by wind conditions,ground surface,seed morphology and orientation.The model simulates the initial landing orientations,dispersal distances and stopping orientations of individual seeds.To parameterize the model,we measured orientation-specific vertical seed projection and seed lift-off velocity(the wind speed at which a seed starts moving on the ground)of the asymmetric seeds of heterocarpous Zygophyllum xanthoxylon,and determined orientation-specific model parameters that depend on properties of seeds and/or the environment.To validate the model,we conducted wind channel experiments in which we released seeds of Z.xanthoxylon onto a sand-coated tar paper,and recorded the initial landing orientations,dispersal distances and stopping orientations of the seeds.The extended model could precisely predict secondary dispersal distance,and explain up to 99%of variation in the observed proportions of seeds which stopped in various orientations.The model predicts that secondary dispersal distance increases with wind speed and decreases with aerodynamic roughness length,and that there might be a positive correlation between dispersal distance and germination success.