Adaptation Strategies Of Bolboschoenus Planiculmis To Different Salinity Modes And Nutrient Heterogeneity Under Different Water Levels

Due to the superimposed effects of global climate change and human activities,the hydrological process of inland wetlands has changed and the degree of salinization has intensified.Wetland plants are suffering the effects of environmental changes.The interactions between wetland plants and abiotic factors such as hydrology,salinity,and nutrition and biotic factors（e.g.competition）have become an important issue of current concerns.Two greenhouse experiments were conducted using the dominant species Bolboschoenus planiculmis in the Momoge wetlands of the Songnen Plain in northeastern China in order to understand the corresponding strategies of wetland plants in response to different water level,salinity,nutrient heterogeneity,and competitive conditions.Experiment one was set up with five salinity treatments（control,constant NaCl,constant mixed salt（Na HCO₃and NaCl）,pulsed increase of mixed salt and fixed increase of mixed salt）and two competitive treatments（monoculture and interspecific competition with Phragmites australis or Suaeda glauca）,with six replicates per treatment,to explore the effects of different salinity conditions on the growth and competitive ability of B.planiculmis.Experiment two was set up with two water level gradients（0 cm and 5 cm）,two nutrient treatments（homogeneous and heterogeneous）and two harvest duratioms（30 and 60 days）,to study the effects of water level and nutrient heterogeneity on the growth and nutrient uptake of the B.planiculmis.The nutrient heterogeneity included two patch treatments（high and low nutrient patches）.Each treatment had eight replicates.These two experiments were carried out to study the adaptive strategies of B.planiculmis in growth,reproduction,competition and nutrient uptake under different salinity,water levels and nutrient heterogeneity conditions.The main results are as follows:First,compared with the control treatment,salt treatment significantly increased the total biomass of B.planiculmis by 25.1%in the presence of the competing species of Phragmites australis.The competitive response of B.planiculmis was significantly reduced in the presence of the competing species of Suaeda glauca.Second,compared with the constant NaCl treatment,the mixed salt treatment significantly increased the total biomass of B.planiculmis by 38.2%,and the competitive response of B.planiculmis was significantly increased but still lower than that of the competing species of S.glauca.Third,compared with the constant mixed salt treatment,the fluctuating mixed salt significantly increased the total biomass of B.planiculmis by 67.1%in monoculture,and significantly increased 262.7%in the presence of competing species S.glauca.The fluctuating mixed salt treatment enhanced competitive ability of B.planiculmis compared to the constant mixed salt treatment.Forth,compared with the homogeneous nutrient treatment,the number of leaves and stem diameter of B.planiculmis increased by 99.9%and 20.5%,respectively,in heterogeneous nutrient treatment at the first harvest stage.Simultaneously,the number of bulbs and ramets increased by 39.5%and 28.2%,respectively.All traits were inhibited except 98.2%increase in stem diameter at the second harvest stage.High water levels only significantly promoted the accumulation of bulb biomass of B.planiculmis originally grown under low nutrient patches by 29.0%.The 5 cm water level during late growth resulted in total N content being 17.4%lower in high than in low nutrients.Lastly,the number of leaves,bulbs and bulb biomass significantly increased by123.1%,54.1%and 748.3%respectively,in high nutrient patches compared with the low nutrient patches at the first harvest stage for B.planiculmis initially planted in high nutrient patches.While the number of leaves and bulb biomass significantly reduced by 45.5%and 88.7%respectively,in the high nutrient patches compared with the low nutrient patches for B.planiculmis initially planted in low nutrient patches.This effect gradually weakened with the extension of growth period.Additionally,the above-ground biomass of B.planiculmis reduced by 53.0%at 0cm but increased by17.6%in high nutrient patches compared to low nutrient patches at 5 cm water level and at the first harvest stage.In summary,fluctuating saline conditions favored growth,mainly manifested in the accumulation of bulb and rhizome,the increase of stem diameter and improved competitive ability of B.planiculmis,although the traits of B.planiculmis were lower than those of its competitors.These results supported the of competitive pressure hypothesis under different salt modes.In addition,certain water levels promoted the growth,reproduction and nitrogen accumulation of B.planiculmis in nutrient-limited environments and facilitated the ramet placement of B.planiculmis from low to high nutrient patches.This study provides important information for understanding the adaptation mechanisms of wetland clonal species to changing environmental factors and the shifts in community composition and degradation recovery of wetland vegetation.