Ecosystem Structure And Functions Of The Different Coastal Shelterbelts In Zhejiang Province,China

Coastal shelterbelt ecosystem plays extremely important roles in safeguarding the economic and social development of coastal areas and improving the residential environment.Coastal shelterbelt also enriches the regional forestry resources and biodiversity.The coastal shelterbelt construction project of China has been conducted for more than 30 years and significant achievements have been made.However,we are still facing great challenges on the operation and management of the shelterbelt,such as the stand decline and soil degradation caused by pure shelterbelt serialization and the relatively low overall proportion of mixed shelterbelts,while the species configuration and shelterbelt category allocation still lack scientific basis,which greatly weakens the functions that shelterbelt ecosystems may provide.Unfortunately,few studies have quantized the multiple ecosystem functions of different shelterbelt types.Therefore,four different mixed shelterbelts in the eastern Zhejiang Province,each dominated by a single tree species,i.e.Koelreuteria bipinnata,Taxodium districhum,Populus nigra and Ligustrum compactum separately and associated with two other tree species,were selected as our research objects in this study.Meanwhile,homogeneous non-forested land between stands were set up as control treatment.For each mixed shelterbelt,six arbor plots?20m x 30 m?and 30 herb plots?1 m x 1 m?were set up to conduct stand and plant surveys,collecting soil and plant samples.Thus,field investigation and laboratory measurement methods were combined to explore the growth characteristics,functions including soil fertility promotion,natural regeneration of vegetation etc.as well as the ecosystem multifunctionalities of the different shelterbelts.The results showed that the ecosystem multifunctionality was highest in the P.nigra mixture while lowest in the K.bipinnata mixture,which might be related to the invasion by Solidago canadensis.Therefore,plots on two scales were set up at different experimental sites to study the effects of S.canadensis invasion on the relevant ecosystem functions of K.bipinnata mixture.Besides,During the experimental period,Zhejiang Province suffered from an extreme low temperature climate,which also destroyed some shelterbelts within the experimental sites.As an important shelterbelt species with the strongest photosynthetic capacity,Chinese tallow?Triadica sebifera?shelterbelt was recruited to explore its recovery ability from the low temperature.Through the above experiments,the main results are as follows:?1?There were significant differences in individual growth and shelterbelt structure among four shelterbelts,with P.nigra mixture and L.compactum mixture grow better,while T.districhum mixture and L.compactum mixture have denser shelterbelt structure.The survival rate,health rate,crown width,tree height,DBH and basal area of P.nigra mixture and L.compactum mixture were significantly higher than those of the other two shelterbelts.while the shelterbelt permeability coefficient and porosity of the L.compactum mixture were significantly lower than other shelterbelts.?2?Concerning soil fertility improvement function,the mixed shelterbelts significantly improved soil chemical properties and moisture physical characteristics,with T.districhum mixture had the best soil fertility promotion ability.P.nigra mixture had the highest soil capillary porosity and maximum water holding capacity but the lowest natural water content.The soil permeability coefficient of K.bipinnata mixture(0.29 mm.min^-1)was significantly higher than that of other mixed shelterbelts.Concerning soil chemical properties,T.districhum mixture had the highest contents of soil organic matter,total nitrogen,total potassium,hydrolytic nitrogen and cation exchange capacity in both 0-20 cm and 20-40 cm layers,while K.bipinnata mixture had the highest soil total phosphorus and available phosphorus contents.?3?L.compactum mixture had advantages in herbaceous biodiversity while K.bipinnata mixture did better at tree regeneration.L.compactum mixture had the highest herbaceous species richness and biomass while T.districhum mixture had the highest species evenness.Species richness of the tree seedlings were highest in the K.bipinnata mixture and L.compactum mixture.T.districhum mixture and L.compactum mixture had significant higher coverage,height and biomass but lower density of tree seedling than those of the other two mixtures.At species level,Robinia pseudoacacia seedlings had significant higher coverage,height and biomass than those of other tree seedlings.Soil organic matter,total nitrogen and total potassium plays direct roles in promoting tree seedling regeneration,while soil hydrolytic nitrogen,available potassium and cation exchange capacity had weaker effects on tree seedling regeneration.Shelterbelt canopy coverage,porosity,permeability coefficient and height mostly directly inhibit tree seedling coverage,height and biomass,but have weak effects on tree seedling density.?4?There were significant differences on single ecosystem functions among the four mixed shelterbelts in addition to nutrient cycling and transformation function.Specifically,P.nigra mixture had the best windbreak function and carbon fixation and oxygen release ability,while T.districhum mixture had the strongest water and soil conservation ability.Based on the quantitative evaluation of ecosystem multifunctionality?EMF?,P.nigra mixture had the highest EMF,followed by L.compactum mixture,T.districhum mixture and K.bipinnata mixture,while non-forested land had the lowest EMF.Besides,EMF increased with higher shelterbelt permeability and height,EMF also had a significant linear positive correlation with species richness.?5?The lower ecosystem multifunctionality of K.bipinnata mixture was related to the invasion by S.canadensis,which reduced plant diversity and soil nutrient transformation and cycling ability.The species richness and Margalef index of invasive plots,no matter moderate or severe invaded,were always lower than those of non-invasive plots,but species diversity decreased most when the plots were moderately invaded.The increase of soil C:N ratio and aeration porosity as well as the decrease of soil total phosphorus were all related to the increasing invasive severity of S.canadensis.Soil salinity and humidity were positively correlated with invasion severity,while canopy coverage was negatively correlated with invasion severity.?6?The extreme low temperature significantly inhibited the individual growth and photosynthetic capacity of T.sebifera shelterbelt,which were still recovering a year later.Compared with damaged T.sebifera in the low temperature area,young and middle-aged T.sebifera in the control area grew faster in height and DBH.Seedlings and young-aged T.sebifera had larger leaf area and weight,but the low temperature had no significant effects on the leaf shape characteristics of middle-aged T.sebifera.Meanwhile,the extreme low temperature significantly reduced the leaf net photosynthetic rate?NPR?and stomatal conductance in young and middle-aged T.sebifera.The extreme low temperature also significantly reduced the leaf transpiration rate of young-aged T.sebifera and the water use efficiency?WUE?of young and middle-aged T.sebifera.With the increase of T.sebifera age,leaf NPR,stomatal conductance,transpiration rate and WUE increased,while the intercellular CO₂ concentration and pressure decreased.After being damaged by the extreme low temperature,the effects of environmental factors on leaf photosynthesis of T.sebifera were weakened,in which the leaf photosynthesis was less impacted by the photosynthetic active radiation and air CO₂ concentration?the explanatory variable of the environmental factors decreased from 73.4%to 18.6%?,but mainly impacted by the relative air humidity.In this study,the differences on providing individual ecosystem functions and ecosystem multifunctionality among different mixed coastal shelterbelts were clarified in Zhejiang Province by comparing their ecosystem structure and functions,and the relationship between ecosystem multifunctionality and stand structure and plant diversity in coastal shelterbelt scenario,which is quite different from other continual ecosystems,were also explored.Besides,the ecosystem functional response of the shelterbelts under plant invasion and extreme low temperature disturbance were furthrr evaluated.These results are expected to provide references for the adjustment of stand structure and the multi-functional management and operation of coastal shelterbelts in East China.