Fine Root Traits And Their Response To Soil Properties And Tree Species Diversity In Coastal Reclaimed Soil

Plant fine roots???2 mm?are involved in underground ecological processes of plants and play important roles in material turnover and energy flow of the forest ecosystem.Functional traits of fine roots can not only reflect the response strategies of roots to the stressed environment,but also act as a carrier to connect plant individuals,community and ecosystems,and indirectly affect ecosystem functions.The study of the relationship between fine root functional traits and environmental factors can reveal the ecological mechanism of fine roots‘adaptation to the environments and the relationship between fine root functional traits and ecosystem functions.Previous studies on fine roots focused on the relationship between the functional traits of fine roots and the environmental factors of individual plants,while there were few studies on the relationship between the functional traits of fine roots and the environmental gradients and the species diversity.Therefore,it is not clear how the fine root functional traits adapt to the environment and how the fine root functional traits reflect the ecosystem function along the environmental gradients.In this study,five major tree species?Ligustrum lucidum,Salix matsudana,Sapium sebifera,Robinia pseudoacacia,Quercus virginiana?and seven groups of communities on different species richness levels in the coastal reclaimed soil?characterized for high salinity and alkalinity and poor nutrition?were studied.Experimental ecological analysis methods were used.The morphology,biomass,production,decomposition and turnover of fine roots and soil moisture,temperature,water content,electric conductivity,p H,total nitrogen,total phosphorus and organic matter were determined.At the species level,the differences in fine root morphology,biomass,production,decomposition and turnover of major tree species were analyzed to reveal their ecological adaptation strategies.The response strategies of their fine roots to the salt and nutrient gradient were revealed by controled field experiments.At the community level,the differences in morphology,biomass,production and turnover of fine roots in communities with different species richness were examined to explre the mechanism affecting the functional traits of fine roots.The results were as following:?1?The morphological characteristics of fine roots?specific root length and specific surface area?of five species were significantly different?p<0.05?.As a resource acquisition species,R.pseudoacacia had the highest specific root length and specific surface area.While Q.virginiana showed the lowest specific root length and specific surface area,might because of its role of a resource storage species.The fine root biomass and productivity of the five species were significantly different?p<0.05?,with the fine root biomass ranging from 77.05 to 273.42 g·m^-2 and the productivity ranging from 17.80 to 166.00 g·m^-2·a^-1.L.lucidum had the highest biomass and productivity,and R.pseudoacacia had the lowest.The five species had different fine root biomass allocation strategies,as R.pseudoacacia and Q.virginiana were deep root tree species whereas L.lucidum,S.sebifera and S.matsudana were shallow root tree species,by which the fine roots could make full use of deep and shallow soil resources and adapt to the environment.Meanwhile,different tree species adapted to the environment by expanding the horizontal foraging range of their roots,as the horizontal spatial expansion range of R.pseudoacacia root was the largest,and the horizontal distribution range of the roots of L.lucidum and Q.virginiana was smaller.Due to the influence of environmental factors and their own biological characteristics,the decomposition rate and turnover rate of their fine roots were significantly different?p<0.05?.The decomposition rate of S.sebifera was the fastest(0.007 kg·kg^-1·d^-1),the S.matsudana had the slowest(0.002 kg·kg^-1·d^-1).The turnover rate of S.matsudana was the fastest?1.05 times/year?,and the Q.virginiana had the slowest?0.24 times/year?.?2?Soil salinity and nutrient gradient had significant effects on fine root traits.With the increase of soil salinity from the low,middle to high saline area,the fine root biomass,productivity and turnover rate of five species decreased,while the osmotic pressure of fine root tissue increased.Meanwhile,the growth depth of fine roots became shallower,indicating the niche differentiation of fine roots and the change of biomass distribution strategies.Fine roots could adapt to salt stress by increasing diameter,volume,surface area and decreasing total length.In different fertilization treatments,the average biomass,length,surface area,volume,root length density,specific root length and root surface area density of fine roots increased first and then decreased with the increase of nitrogen and phosphorus consentration in the soil compared with the control.Fertilization changed the strategy of fine roots to obtain soil resources and improved the ability of obtaining nutrients by changing the structure of fine roots.?3?With the increase of species diversity,there were no significant differences in the ratio of fine roots to root length and specific surface area?p>0.05?,suggesting that fine roots did not respond to interspecific competition through morphological plasticity.The fine root biomass increased with the aboveground tree species diversity,as fine roots could make better use of soil resources,deepen the growth depth of fine roots and lead to the niche differentiation of fine roots.Due to the development strategy of fine root resources and the complementary effect of ecological niche,the fine root biomass in the community and productivity increased and turnover rate accelerated.The results proved the evidence of positive diversity effects on biomass,productivity and turnover of fine roots in forest communities.Correlation analysis and redundancy analysis of the fine root traits with environmental factors revealed that the total fine root biomass and productivity were significantly positively correlated with species richness,fine root diameter and root length density and root surface area density?p<0.01?,significantly negatively correlated with the soil electrical conductivity?p<0.05?,and significantly positively correlated with soil temperature?p<0.01?.Fine root turnover was positively correlated with species richness,root length density and root surface area density?p<0.05?,negatively correlated with soil conductivity?p<0.05?,and positively correlated with soil temperature,total nitrogen,total phosphorus and organic matter?p<0.05?.In summary,species richness,root functional trait diversity and environmental filtration significantly affected fine root biomass,productivity and turnover.In this thesis,the dynamic patterns of fine root morphology,biomass,production,decomposition and turnover of different tree species and communities in coastal reclaimed soil were systematically analyzed,and the adaptive strategies of fine root traits to reclaimed soil and the response strategies to environmental gradients were intensively studied,and the mechanisms affecting the biomass,production,decomposition and turnover of fine roots were revealed.Our results can provide scientific evidence for the selection of tree species and technical support for greening strategies in saline-alkali land.