| Cupressus funebris is a subtropical evergreen coniferous tree species and the main vegetation restoration tree species in the upper reaches of the Yangtze River in China.Due to high initial planting density,single tree species,poor site conditions,and slow growth of trees,their growth status is not ideal.Aluns cremastogue is a nitrogen fixing tree species in the Birch family,which has important ecological functions in improving soil.A.cremastogue and C.funebris mixed plantation is the main afforestation model for shelter forest construction in hilly areas of central Sichuan.Due to its simple community structure and poor site conditions,there are significant problems in stability,productivity,and other aspects.Since the interrelationships between the root systems of tree species,the success or failure of mixed forests is determined.Studying the relationship between root functional traits and forest mixing is of great significance for forest transformation and construction.Therefore,this article takes A.cremastogue pure forest,C.funebris pure forest,and A.cremastogue and C.funebris mixed plantation as the research objects,and three 30 m × 30 m plots were set up in each stand.In each pure forest sample plot,3 standard trees with good growth and similar average plant height and crown width were selected.In the mixed forest,3 pairs of standard trees with good growth,mixed roots of A.cremastogue and C.funebris,and moderate distance were selected.root samples of different forest stands in both horizontal and vertical structures using the soil drilling method was obtained.Complete fine roots and rhizosphere soil using tracking method was obtained.A five-point sampling method was used to obtain the non-root soil.Subsurface spatial structure,fine root morphology,root nutrient content and soil physicochemical properties were measured in different stands.The main findings were as follows:(1)On the vertical structure at distances of 50 cm,80 cm,and 120 cm from the tree trunk,both pure and mixed forest A.cremastogue showed a decrease in fine root biomass as the soil depth increased,with the highest biomass observed in the 0-10 cm soil A.cremastogue.The fine root biomass of pure and mixed C.funebris forests is mainly distributed in a soil layer of 30-50 cm.At each level of structure,the fine root biomass of each tree species type shows that the farther it is from the trunk,the smaller it becomes.The fine root traits of mixed A.cremastogue and C.funebris showed significant variability,and the mixture promoted the growth of C.funebris while inhibiting the growth of A.cremastogue.(2)In both pure and mixed stands,the root diameter and root tissue density increased with increasing root order,while the root length and surface area decreased.For C.funebris,the difference in fine root diameter is not significant in classes 1-3 and significantly decreases in mixed stands at classes 4-5 compared to pure stands.1-2 fine root length increases significantly in mixed stands,while the difference in fine root length is not significant in classes 3-5.The difference in root tissue density was not significant for level1,but significantly increased for levels 2-5 in mixed forests.Root diameter and root tissue density increased with increasing root order in both pure and mixed stands of A.cremastogue,while specific root length and specific surface area decreased.The root diameter of fine roots of A.cremastogue was not significantly different at root level 1-2,but the diameter of fine roots at root level 3-4 was significantly larger in mixed forests compared to pure forests.The root length and root tissue density decreased in mixed forests.The root morphological traits of C.funebris and A.cremastogue showed significant variability between species.(3)Total phosphorus and effective phosphorus were the highest in pure A.cremastogue,C.funebris and mixed A.cremastogue forests,the second highest in pure C.funebris and the lowest in mixed A.cremastogue forests.Organic carbon,total nitrogen,alkaline nitrogen,organic matter and fast-acting potassium were all found to be the most abundant in mixed A.cremastogue and C.funebris forests,while the second most abundant in pure A.cremastogue forests,and the least abundant in pure C.funebris forests.Moisture,bulk density and porosity were the highest in mixed A.cremastogue and C.funebris stands,and the second highest in pure C.funebris stands and the smallest in mixed A.cremastogue and C.funebris stands.Effective phosphorus,organic carbon,total nitrogen,alkaline decomposition nitrogen and organic matter in the inter-root soil were greater in pure A.cremastogue than in mixed A.cremastogue stands,while total phosphorus,total potassium,fast-acting potassium and p H were greater in mixed A.cremastogue than in pure stands.Pure stands of C.funebris had greater inter-root soil fast-acting potassium,alkali-dissolved nitrogen and p H than mixed stands,while total phosphorus,organic carbon,total nitrogen,total potassium,organic matter and fast-acting potassium were all smaller than in mixed stands.Overall,mixing caused the non-inter-root soil nutrients to show trait variability.(4)Fine root total potassium,total nitrogen and total phosphorus content differed significantly between C.funebris trees of pure stands and C.funebris trees of mixed stands at levels 1-3.The total nitrogen of the fine roots at levels 1-3 was greater in C.funebris mixed stands than in pure stands,and the total nitrogen of the fine roots at levels 4-5 was greater in pure stands than in mixed stands.The total phosphorus content of fine roots in C.funebris mixed forests was less in mixed forests than in pure forests at levels 1-3.At levels4-5,it was equal to that in pure forests.The total potassium of the fine roots of C.funebris mixed forests at levels 1-3 and 4-5 were smaller in mixed forests than in pure forests,and the total nitrogen,phosphorus and potassium of the fine roots at levels 1-3 were significantly different between pure and mixed A.cremastogue forests.The total nitrogen of the fine roots at levels 1-3 was less in mixed stands than in pure stands,and the total nitrogen of the fine roots at levels 4-5 was greater in mixed stands than in pure stands.The total phosphorus of fine roots in mixed A.cremastogue stands at levels 1-3 was greater in mixed stands than in pure stands.levels 4-5 were smaller in mixed stands than in pure stands.A.cremastogue mixed forests showed less fine root total potassium in mixed forests than in pure forests at levels 1-3,and more fine root total potassium in mixed forests than in pure forests at levels4-5.Overall in the different stands,total nitrogen and phosphorus showed a greater content in roots of classes 1-3 than in roots of classes 4-5,and total potassium showed a greater content in roots of classes 4-5 than in roots of classes 1-3.Overall,the hybrids showed significant variability in root nutrient traits.(5)Inter-root soils were significantly different(P<0.05)between stands.Inter-root soil nutrients were significantly correlated with each other(P<0.05).The most significant interroot soil factor influencing fine root morphology was organic matter(65 % contribution,P<0.01)(Table 8).The results of the analysis in this study also revealed that the fine root forms were significantly different from each other(P<0.01).The inter-root soil factor with the greatest influence on fine root nutrients was total potassium(50.6 % contribution,P<0.05).In conclusion,the mixed forests significantly affected the spatial distribution of fine roots,fine root morphology,root system and soil nutrient traits of A.cremastogue and C.funebris,and to a certain extent promoted changes in the functional traits of C.funebris roots.This provides some theoretical support for a comprehensive understanding of the effects of hybridization on the functional traits of fine roots,and provides a theoretical basis for the sustainable management of protection forest construction in the hilly areas of central Sichuan. |
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