Responses And Adaptive Strategies Of Plant Functional Traits To Environment Gradients In Yanhe River Watershed, Shaanxi Province, China

Plants use a variety of adaptive and functional strategies to adapt to environmentalchanges. Plants under specificenvironmental conditions usually share certain common traits,which allow plants to adapt to environment stress. The study of a plant's functional traits iscurrently becoming a high priority area of plant ecology because these traits are both easy toquantify and are closely related to plant functioning. Consequently, variation in thesefunctional traits along environmental gradients reflects variation in plant adaptivemechanisms and each species' interactions with climatic, edaphic or topographic drivers. Inhilly areas of the Loess Plateau, which is the focus area of national ecology restoration theefforts of revegetation has produced great achievements. However, serious soil erosion wasnot be kept within limits, the revegetation is still facingmany problems. Understanding planttraits in different habitats can provide scientific guidance for revegetation. The objective ofthis thesis was to assess the relationships and co-variation of plant functional traits alongenvironmental gradients, and to analyze the adaptive strategies of plants in semi-arid and aridenvironments. We measured plant height(PH), specific leaf area(SLA), leaf tissuedensity(LTD), leaf nitrogen concentrations(LNC), root nitrogen concentrations(RNC),specific root length(SRL) and fine root density(RTD) of149species at24sites in the YanheRiver watershed. By focusing on traits, our study uniquely demonstrates adaptivedifferentiation among species. These results will help the selection of species for restorationprograms in the hilly areas in Loess Plateau. The main results are as follows:1) The general pattern of plant traitsSix plant attributes across all the149species of Yanhe River watershed showed largevariations, with the following range:5.26—9240.53mm²·mg^-1for specific leaf area;0.000789—1.39mg·mm^-1for leaf tissue density;0.218—8.39%for leaf nitrogen concentrations;0.142—2.81%for root nitrogen concentrations;0.158—66.77m·g^-1for specific root length; and0.0256—134.3mg·mm^-1for root tissue density. The atithmetic means of these parameterswere170.1mm²·mg^-1,0.0989mg·mm^-1,2.3%,0.941%,6.67m·g^-1and26.82mg·mm-3.2) Summary of relationships among plant traits We analyzed the patterns of correlations among six organ-level traits and how these traitsallow different species to deal with environmental conditions. The results showed that thesix plant functional traits of the149species were closely related. Leaf nitrogen concentrationswere positively related to specific leaf area and root nitrogen concentrations, and a negativelyrelated to leaf tissue density. Specific root length was negatively related to fine root tissuedensity, whereas no correlation existed between leaf and root traits except for root nitrogenconcentrations.3) Relationships between plant traits and environmental variablesIn general, the correlation between individual traits and environmental variables is nothigh. Specific leaf area increased with slope, and leaf nitrogen concentrations increased withincrease of mean annual temperature. As mean annual precipitation increased, leaf tissuedensity increased and root nitrogen concentrations decreased. Meanwhile, the mean specificleaf area was higher at steep gradient; leaf nitrogen concentrations was higher at hotter,hidden region; and mean leaf and root nitrogen concentrations were higher at drier, sunnyslope sites.4) Variation of trait relationships along environmental gradientThe combinations of RTD-SLA,RTD-LTD and RTD-SRL recur in distantly related taxaacross Yanhe River watershed, which provide evidence for convergent evolution. However, athotter sites, average LNC was higher at a given SLA, RNC was higher at a given LTD. Atdrier sites, LNC was lower at a given LTD. RNC was higher at a given SLA or LTD at sunnyslope sites. And LTD was higher at a given SLA at hidden regions.5) A multi-trait test of CSR(Competitive-stress tolerant-ruderal scheme) plant strategyschemeBased on the dissimilarity of the six traits, the species were classified into three mainplant functional types (PFTs). The species of PFT I are best adapted to an arid environment,with the greatest resistance and resistance to herbivore and physical damage. The species ofPFT III may avoid nutrient stress by having the greatest nutrient conservation efficiency,which is believed to be important in minimizing nutrient losses in a nutrient-poorenvironment. The PFT II group is somewhat intermediate with a greater growth rate, highercompetitive ability and wider distribution in the study area. Based on CSR Triangle theoriesof Grime et al.(1979), both PFT I and PFT III plants adopt a stress-tolerance strategy to theenvironment (S strategy) while PFT II plants use a combination of competitiveness (C) andruderality (R) strategies.6) A multi-trait test of LHS(Leaf-height-seed strategy) plant strategy schemeHere we investigated30species and plus2seed traits(seed mass, seed area) to test Westoby's LHS strategy scheme(1998) in Yanhe River watershed, and the species wereclassified into four main plant functional types. The species of PFT I are the combination ofrapid growth of grazing pressure individuals with low stress. The species of PFT II may avoidstress by having the greatest nutrient conservation efficiency, which is believed to beimportant in minimizing nutrient losses in a nutrient-poor environment. The species of PFTIII may avoid stress and grazing pressure, with high-effective colonizing abilities. The PFT IVgroup is higher competitive, effective colonizing ability and wider distribution in the studyarea.