Effects Of Nitrogen And Phosphorus On Leaf And Root Functional Traits In Seedlings Of 14 Species

Leaves and absorptive roots(i.e.,first order roots)are key capture organs in above-and below-ground resources for plants,respectively.Both organs have close relationships in morphology,anatomy,and physiology,such linkages play very important roles in regulating plant growth,metabolisms and as well as survivals.Plant leaves and roots are sensitively to soil environments,such as fertility.However,previous studies about the effect of fertilization on leaf and root functional traits mainly focused on nitrogen(N)effects,few studies investigated phosphorous(P)effects.The effects of nitrogen and phosphorous on anatomy of first order roots,and their relationships between leaf and root functional traits are unclear,which limits our understanding of the whole-plant functional strategies between above-and below-ground in plants to cope with environmental stress.Here,we chose 14 species(8 woody and 6 herbaceous)in Northeast China and investigated the functional traits of the leaf and first order roots(anatomy,morphology,C,N chemical traits,and mycorrhizal colonization),and explored their internal relations under N and P addition treatments in the greenhouse.The main objectives of this study were to explore the underlying mechanisms of leaf and absorptive root functional traits under N and P addition,including their internal relationships among traits,responsive and adaptive strategies in woody and herbaceous species.This may provide new insights into understanding of the overall functions and ecological strategies for plants in responses to environmental changes.The main results are showed as follows:(1)The average density and proportion of mycorrhizal colonization,passage cells and penetration points of 14 species were significantly reduced under N and P additions.Such negative effects on these traits were greater by N addition than by P addition.More importantly,the mycorrhizal colonization density and proportion showed significant positive correlations with the density and proportion of passage cells and penetration points in woody and herbaceous plants under control or nutrient treatments,suggesting passage cell and penetration point play key role in mycorrhizal colonization.(2)The anatomical structures of leaf and first order roots were changed under N and P additions.Adding N and P significantly increased leaf anatomical traits in some plants(e.g.,upper and lower epidermis thickness,palisade and spongy tissue thickness,central vein thickness,leaf thickness/main vein thickness).By contrast,the obviously change was the leaf sponge thickness(ca+7.70%and+11.73%,respectively,for N and P addition),leading to the reduction of palisade tissue thickness to spongy tissue thickness(P/S)ratio.The increases of these leaf anatomical traits were conducive to photosynthesis and gas exchange within leaf.After N and P additions,the proportion of suberin cells in the first order roots increased,accompanied by the cortex thickness increased 5.27%and 4.85%,respectively,for N and P addition,and the stele diameter increased 19.55%and 6.80%,which will increase their capabilities of resource absorption and transportation.(3)The morphological traits of leaf and first order roots were affected by N and P additions.In term of leaves,adding N and P significantly reduced the average specific leaf area,increased leaf thickness,stomata density and leaf vein density.The increase in leaf thickness is closely related to the increase in mesophyll tissue,reflecting the leaf construction strategy in plant adaptation to the environmental changes.For the first order roots,due to the effect of N and P addition to anatomical traits,the average specific root length decreased under N and P fertilized,but the diameter and tissue density increased,with the increased 5.61%and 3.51%in diameter under N and P fertilized,respectively.These results suggested that plants may adapt to the N and P additions via constructing thicker roots with higher tissue density and shorter root lengths,which indicated that enhanced morphological construction strategy for plants in response to the nutrient availability.(4)Adding N and P strongly affected on C,N concentrations in leaves and the first order roots.By contrast with the control,the leaf total N concentration,on average,significantly increased 167.96%,the leaf C/N ratio significantly decreased 59.07%under N addition treatment,but the trends of leaf total C concentration were differed.Compared with N addition,adding P yielded weakly effect on the leaf C,N chemical traits.The effect of N and P addition on C,N chemical traits in the first order roots was similar as those of leaves.(5)There were differences between leaf and root functional traits in woody species and herbaceous plants with N and P additions.First,the effects of the N and P additions on passage cells and mycorrhizal colonization were stronger in woody species than herbaceous plants.Second,adding N significantly influenced anatomical and morphological traits in woody species,while such effects by adding P showed weakly in herbaceous plants.However,the response of C and N chemical traits to N and P addition in woody and herbaceous plants were also inconsistent.These results reflected that there were some differences between woody and herbaceous plants in the strategies to response to the nutrient availability.(6)There were close relationships between the leaf functional traits,between the first order roots functional traits in woody and herbaceous plants,and the effects of N and P addition are inconsistent,these results reflected the difference between leaves and first order roots morphological construction strategy in different plant life forms.In addition,There were close relationships between the leaves and first order roots in corresponding functional traits for woody and herbaceous plants in this study,such correlations were weakly reduced by adding N and P,consistent with the hypothesis of the similar structure traits with leaves and roots of plants.Finally,the relationships between the leaves and first order roots C,N chemical traits for woody and herbaceous plants are inconsistent,these results reflected the difference between the C,N chemical substances accumulation and consumption in different plant life forms.All the findings in this study showed that N and P addition significantly affected the mycorrhizal colonization,anatomical and morphological,and C,N chemical traits in leaves and first order roots in woody and herbaceous.Overall,the responses of the functional traits examined here to N and P addition were different in woody and herbaceous plants.There were correlations within leaf functional traits,within absorptive root functional traits,and the corresponding functional traits between leaf and first order root.However,such relationships were differences between woody and herbaceous plants,and were less affected by N and P addition,reflecting a functional coordinated strategy between leaves and roots at the wholeplant level when they were affected by soil nutrient changes.The results of this study not only have important theoretical significance for deeper understanding the response mechanism of plant resource acquisition and physiological function strategies to external environmental changes,but also provide a theoretical basis for further research on the growth and nutrition managements for woody and herbaceous plants under environmental changes.