Variation Of Minor Vein Traits Along The Environmental Gradient In The Loess Plateau Grasslands

Minor leaf venation shows remarkable variation across species,and is a key determinant of plant adaptation in ecosystems past and present.In this study,we studied the variation of leaf minor vein traits along the environmental gradient at the levels of species,different leaf vein types and community.In the Loess Plateau,ten sites were selected along the water and nutrient gradients from east to west,including three grassland types:forest grassland,typical grassland and desert grassland.Leaves of all species(525 in total)within a radius of 2 km were collected from each site,and the vein length per leaf area(VLA),vein diameter(VD)and vein volume(VV)of minor leaf vein were measured.We also set up 8plots of 1 m×1 m,and collected the above-ground biomass of all species within each quadrat and calculated the relative dominance of each species.Based on these data,community-weighted means of each minor vein trait were estimated as the community-level values.In this study,we explored the variation of leaf minor vein traits along the environmental gradient and their influencing factors at the levels of species,different leaf vein types and community,respectively.We aimed to understand how plant communities adapt to environmental changes from the perspective of leaf minor veins.The results showed that:(1)Difference in VLA and VD among trees,shrubs and herbs were not significant(P>0.05),but VV of herbs was significantly larger than that of shrubs(P<0.05).The negative correlation between VLA and VD,VLA and VV,and the positive correlation between VD and VV reached extremely significant levels in the 3 grassland types(P<0.01).VD and VV of grassland plants in the Loess Plateau showed an increasing trend from east to west along the longitude(P<0.01),but VLA did not show obvious longitude pattern(P>0.05).The main environmental factor affecting VLA was soil total organic carbon content(TOC),and VLA decreased with increasing TOC(P<0.01).VD and VV were mainly affected by soil water content(SWC),and decreased with the increase of SWC(P<0.05).Climate,soil and leaf vein types(including reticular vein,parallel vein and single vein)explained30.1-67.90%of the variation in leaf vein traits,and the independent effect of leaf vein type had the largest explanation for leaf vein traits(28.74-62.25%).(2)The VLA of reticulate vein plants was greater than that of parallel vein and single vein(P<0.05),but VD and VV showed the opposite trend.The negative correlation between VLA and VD existed in the reticulate veins and parallel veins(P<0.01).The positive correlation between VLA and VV only existed in reticulate veins(P<0.01).The positive correlation between VD and VV existed in all 3 vein types(P<0.01).Vein traits of plants with different vein types showed different longitudinal trends.VLA,VD and VV of reticulate vein plants showed an increasing trend from east to west(P<0.01).VD and VV of parallel vein plants decreased from east to west(P<0.01),and there was no significant change in the 3 traits of single vein plants(P>0.05).For reticulate vein,the total effect of climate and soil explained 4.67-14.77%of the variation.Among them,the independent effect of soil factors had the greatest influence on the variation(0.62-7.08%).The main factor of vein density was soil total phosphorus content(SP),which decreased with increasing SP(P<0.01).The main environmental factor affecting VD and VV was SWC,and they decreased with the increase of SWC(P<0.01).In parallel vein plants,the total effect of climate and soil factors explained 15.66-15.74%of the variation.There was no significant correlation between VLA and environmental factors(P>0.05).The main environmental factor affecting the diameter of parallel veins is aridity index(AI),and VD increased with the increased AI(P<0.01).The main environmental factor affecting the volume of parallel veins was the soil organic carbon content(TOC).There was no significant correlation between the vein traits of single vein plants and environmental factors(P>0.05).(3)At the community level,there was a significant negative correlation between vein length per leaf area(VLA_C)and leaf vein diameter(VD_C,P<0.01),and a significant positive correlation between VD_Cand leaf vein volume(VV_C,P<0.01),but there was no significant relationship between VLA_Cand VV_C(P>0.05).The VLA_Cshowed no obvious change along the longitude(P>0.05),and VD_Cand VV_Cgradually decreased from east to west(P<0.01).Climate and soil factors explained 56.60-73.40%of the variation of traits,and the independent effect of soil accounted for 19.15-41.18%.The main factor of VLA_Cand VD_Cwas soil p H.VLA_Cincreased with increasing p H(P<0.01),and VD_Cdecreased with increasing p H(P<0.01).The main environmental factor affecting VV_Cwas soil organic carbon content(TOC),VV_Cincreased with the increase of TOC(P<0.01).In summary,leaf vein type was the dominant factor of trait variation at the species level,while at the community level,soil factors explained the most variation.