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.

Unexpected Diversity in Ecosystem Nutrient Responses to Experimental Drought in Temperate Grasslands

The responses of ecosystem nitrogen (N) and phosphorus (P) to drought are an important component of globalchange studies. However, previous studies were more often based on site-specific experiments, introducing a significantuncertainty to synthesis and site comparisons. We investigated the responses of vegetation and soil nutrientsto drought using a network experiment of temperate grasslands in Northern China. Drought treatment (66%reduction in growing season precipitation) was imposed by erecting rainout shelters, respectively, at the driest,intermediate, and wettest sites. We found that vegetation nutrient concentrations increased but soil nutrient concentrationsdecreased along the aridity gradient. Differential responses were observed under experimentaldrought among the three grassland sites. Specifically, the experimental drought did not change vegetation andsoil nutrient status at the driest site, while strongly reduced vegetation but increased soil nutrient concentrationsat the site with intermediate precipitation. On the contrary, experimental drought increased vegetation N concentrationsbut did not change vegetation P and soil nutrient concentrations at the wettest site. In general, the differentialeffects of drought on ecosystem nutrients were observed between manipulative and observationalexperiments as well as between sites. Our research findings suggest that conducting large-scale, consistent, andcontrolled network experiments is essential to accurately evaluate the effects of global climate change on terrestrialecosystem bio-geochemistry.

A video camera recording method for measuring terminal velocity of seed dispersal by wind

An accurate and convenient method is essential for measuring the terminal velocity of seeds dispersed by wind.Systematic and random errors produced by existing methods lower the accuracy and convenience in determining seed terminal velocity.In this study,a video camera was used to record the falling process of forty-one species of wind-borne seed with eight appendage structures and seven aerodynamic behaviors in a settling tower at a speed of 50 frames per second(fps).The videos were analyzed by Quick Time Player to determine seed acceleration height,acceleration time,and terminal velocity.The results showed that acceleration height and time,terminal velocity,and the diff erence between terminal velocity and descent velocity(DTD)increased with wing loading.Compared with dropping methods,the camera recording method eliminated the eff ect of acceleration and corrected seed terminal velocity.Based on wing loading,release heights were determined for accurate measurement of terminal velocity of diff erent seeds.This method,due to its inexpensive equipment,high accuracy,easy observation and operation,can be applied to measure the terminal velocity of wind dispersed seeds,and provides a promising method in exploring the dispersal process of seeds.

Tree Height-Related Hydraulic Strategy to Cope with Freeze-Thaw Stress in Six Common Urban Tree Species in North China

Urban trees are sensitive to extreme weather events under climate change.Freeze-thaw induced hydraulic failure could induce urban tree dieback and nullify the services they provide.Plant height is a simple but significant trait for plant ecological strategies.Understanding how urban trees with different heights adapt to freeze-thaw stress is increasingly important under climate change.We investigated the relationship between tree height and stem hydraulic functional traits of six common urban tree species in North China to explore tree height-related hydraulic strategies to cope with freeze-thaw stress.Results showed that tall trees had wider vessels,higher hydraulic conductivity,more winter embolism,but lower vessel and wood densities.Positive relationships were found between tree height and vessel diameter,hydraulic conductivity,and freeze-thaw induced embolism,and negative relationships were found between tree height and vessel and wood densities,which implied that short trees employ more conservative ecological strategies than tall trees.Tall and short tree species were well separated by multiple stem hydraulic functional traits;this is consistent with the fact that tall and short trees occupy different niches and indicates that different hydraulic strategies for freeze-thaw stress exist between them.Tall trees might face more pressure to survive under extreme cold weather caused by climate change in the future.Therefore,more attention should be paid to tall urban tree management in North China to cope with extreme cold weather.

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。

The feasibility of using soil seed bank for natural regeneration of degraded sandy grasslands

Desertification in degraded grasslands is manifested through the development of bare sandy patches,which eventually lead to habitat fragmentation.The ability of these bare sandy patches to regenerate naturally through in-situ soil seed banks is not well understood.To fill this knowledge gap,we randomly selected 24 bare sandy patches with areas ranging from 19 to 898 m^(2) in a desertified grassland of the Horqin sandy land,Northern China to determine whether soil seed bank can be used for natural regeneration of bare sandy patches.Species composition and density of soil seed bank as well as aboveground vegetation composition,abundance and coverage were investigated.We then determined their relationships with in-situ habitat characteristics.Our observations showed that the studied area had low soil seed bank density and species richness,as well as depauperate soil seed bank communities.Consequently,local soil seed bank was not able to provide sufficient seed source for natural regeneration.This was indicated by the relationships between aboveground vegetation,soil seed bank and the in-situ habitat characteristics.For bare patches with an area between 300 m^(2) and 900 m^(2),increase the soil seed bank density and species richness should be the main restoration measures.For bare patches with a small area of less than 50 m^(2),restoration of vegetation density should be the main measure.Our data highlighted that different extents of desertification,indicated by different bare patches,are requiring distinct restoration measures.

Level of habitat fragmentation determines its non-linear relationships with plant species richness, frequency and density at desertified grasslands in Inner Mongolia, China

Aims This study aimed to examine the changes in plant species richness,frequency and density along a habitat fragmentation gradient(with varied degrees of habitat fragmentation[DHFs])in a desertified grass-land of Horqin Sandy Land,northeastern Inner Mongolia,China.Methods In this study,six landscape plots(500×500 m each)along a habi-tat fragmentation gradient were established.A new fragmentation index was formulated to study the effects of habitat fragmentation on biodiversity indices(species richness,frequency and density).Regression analyses(linear-or non-linear regression)were con-ducted to assess the changes in species richness,frequency and density along the habitat fragmentation gradient at plant commu-nity,functional group and species scales,respectively.Important Findings There was a non-linear relationship(following a quadratic function)between total species richness and the DHF.Total species richness reached its peak when the DHF was 0.2,beyond which species richness decreased along the fragmentation gradient.Plant func-tional groups showed their specific responses to habitat fragmenta-tion,and some non-linear relationships and thresholds existed.The relative richness of rare species also showed a non-linear response to habitat fragmentation,with the threshold being DHF=0.6.Species became rarer(both some common species and rare spe-cies)with the intensifying habitat fragmentation.Our study dem-onstrates the importance of the non-linear relationships and plant functional groups in exploring the effects of habitat fragmentation on biodiversity and implementing effective biological conservation in sand dunes.

Temporal-spatial changes in the belowground bud bank in interdune lowlands of an active sand dune ecosystem in northeastern China

Aims The belowground bud bank plays an important role in vegetation restoration of sand dune ecosystems in semi-arid regions.However,few studies have focused on the temporal-spatial changes of belowground bud banks in interdune lowlands.Methods The size and composition of belowground bud bank in five interdune lowlands with different sizes were investigated for one growing season to determine the temporal and spatial changes in belowground bud bank.Important Findings Total bud bank density was the highest in the medium-sized interdune lowland as was tiller bud density.The density of stem-base buds exhibited an opposite trend while rhizome bud density did not change with interdune lowland size.There was a significant seasonal change in the bud bank size.The total bud density peaked in August and was the lowest in October.A similar trend was found for rhizome bud density,whereas the density of stem-base buds showed an opposite trend,and tiller bud density did not change signifiesntly during the growing season.We conclude that the belowground bud bank density is changed with interdune lowland size and season.These results contribute to the understanding of adaptive strategies of plants growing in active dune ecosystems and provide pointers for adopting effective measures to restore and conserve dune vegetation in semi-arid regions.