| Jinshantan,Shanxi Province,is one of the typical places for the construction of "Three North" ecological protection forest.In the 1980 s,Populus simonii plantation was physiologically over mature and degraded.After a long-term transformation of degraded forest,it was carried out.However,the status of soil moisture and nutrients under different plantations in this area is still unclear,and the adaptation process and mechanism of different plantations to soil drought are also unclear.In this paper,a typical plantation in Jinshan was selected to study the characteristics of soil dry layer distribution and the differences of drought adaptation strategies of functional branches of representative tree species:(1)There were significant differences in soil water status among the four plantations in Jinshan.The difference of CM average water content in 0-500 fields was as follows: Populus simonii > P.× popularis ‘35-44’> Pinus sylvestris var.mongolica > Pinus tabuliformis,the four plantations all appeared dry soil layer phenomenon,Populus simonii was mainly medium dry soil layer,P.×popularis ‘35-44’,Pinus tabulaeformis and Pinus sylvestris var.mongolica were mainly heavy dry soil layer.Excessive stand density is one of the important reasons for the formation and distribution of soil dry layer.The soil water content of four plantations in spring was generally lower than that in autumn;Before and after the spring rainfall,only the surface soil moisture of the four plantations changed significantly.(2)The soil pH of the four plantations was weakly alkaline.With the increase of soil depth,the total nitrogen content decreased;The content of alkali hydrolyzable nitrogen decreased first and then increased;The total phosphorus content was on the rise;The content of available phosphorus fluctuated greatly and was affected by human factors.There was a significant positive correlation between p H and total phosphorus content in the four plantations.(3)The tissue density and wood ray ratio of Populus simonii and P.× popularis ‘35-44’were significantly higher than that of Pinus sylvestris var.mongolica and Pinus tabulaeformis,while the diameter of branches,NSC content and wood ray width of bark and xylem were smaller than that of Pinus tabulaeformis and Pinus sylvestris var.mongolica;The diameter of twigs,tissue density of branches and NSC content of bark and xylem of 4 plantation species were higher in spring than in autumn;The NSC content of bark and xylem was lower than that before rainfall.The ring width of Pinus sylvestris var.mongolica and Populus simonii showed a trend of decreasing first and then increasing with the increase of year.(4)In summer,Populus simonii and P.× popularis ‘35-44’ could form a large number of sprouting branches in the lower part of the trunk.The results showed that the soluble sugar content,Huber value in autumn,vessel density and wood ray of the top branch were higher than those of the top branch;The specific leaf area,stomatal length and width,spring Huber value and vessel area were smaller than those of the sprouting branches.The top branches showed significantly stronger drought adaptation,while the lower sprouting branches showed the strategy of high water consumption and high yield.The specific leaf area and the length and width of stomata on the top branch in spring were larger than those in autumn,but the stomata number and Huber value were opposite. |
