Study On The Root Foraging Strategies Of Three Tree Species With Different Root Diameter

In this study,the poplars,metasequoia,and ginkgo plantations were used as the research object.The root bag method was used to set up with four treatments:no fertilizer addition,N fertilizer addition,P fertilizer addition,and compound fertilizer addition.Traits related to nutrient foraging（root morphology,architecture and proliferation,AM colonization and nutrient content）across 3 tree species were messured following root pruning and nutrient addition treatments.This paper compared the root nutrient foraging strategies of the 3 tree species,and then discussed the rules of foraging strategy of 3 species based on the diameter of species.The results of this study provide support for understanding the underground ecological process and the mechanism of improving forest productivity.The main conclusions of the research are as follows:（1）The fine roots diameter of poplars was the smallest（0.43mm）among them,and the average length（14.05cm）,root tips（386.20）,RTD(0.27g·cm^-3)、SRL(98.61m·g^-1)、SRA(69.00m²·kg^-1)were the largest,and the middle was metasequoia(7.23cm、66.48、0.95mm、0.22g·cm^-3、15.37m·g^-1、29.24m²·kg^-1);ginkgo is opposite to poplar(2.64cm、46.52、1.17mm、0.20g·cm^-3、9.56m·g^-1、26.42m²·kg^-1).Different fertilization treatments mainly affected the morphology of the first-and second-order fine root and had little effect on the roots from third-to fifth-order.The response of the morphological indexes to fertilization treatment was highest in poplar root,and then metasequoia,ginkgo,except for RTD（ginkgo>metasequoia>poplar）.Fertilization addition treatment reduced the branching ratio of fine roots and increased the branching intensity.Compared with the control,the change of fine roots BR d was the largest under the condition of N fertilizer addition（poplar,-21.53%;metasequoia,-11.86%and ginkgo,-11.84%）.The fine root BI of poplar was significantly higher than that of metasequoia and ginkgo(poplar,1.08cm^-1,metasequo,0.72cm^-1 and ginkgo,0.68cm^-1).The result showed that root foraging with smaller root diameter（such as poplars）,compared to thicker root species（such as ginkgo）,and is more effective through absorption root proliferation,higher fine root morphology plasticity.（2）There was a significant difference in root length growth rate and mass growth rate between poplar and metasequoia or ginkgo,but there was no significant difference between metasequoia and ginkgo.The root length growth rates of the three tree species were 0.81cm·d^-1,0.06cm·d^-1,and 0.04cm·d^-1,and the mass growth rates were 0.030mg·d^-1 and 0.027mg·d^-1,0.025mg·d^-1.The effect of different fertilization addition treatments on fine root proliferation was significant,N application significantly reduced fine root proliferation,and P application had no significant effect on fine root length growth rate;but significantly reduced the mass growth rate of fine root;application of compound fertilizer significantly increased the proliferation rate of fine root.Thinner roots（such as poplars）are more proliferative than thicker roots（such as ginkgo）.（3）The difference of mycorrhizal infection rate among different tree species was extremely significant.Mycorrhizal infestation rate of ginkgo was highest at 65.01%,metasequoia was47.81%,and poplar was at least 25.87%.The fine roots infection rate of poplars had obvious response to the addition of N fertilizer and P fertilizer.The root infection rate of metasequoia had a significant response to P fertilizer and compound fertilizer,while that of ginkgo did not respond to the three fertilizer addition treatments.Coarse roots（such as ginkgo）species are more dependent on arbuscular mycorrhiza for foraging nutrients than fine root species.（4）The content of N and P in fine roots decreased with the increase of root order,and the content of C and C/N increased.Fertilization had no significant effect on N,C content and C/N of fine root.Application of P fertilizer and compound fertilizer significantly increased the P content in fine roots from the first to the third order.The N content and C/N of the fine roots of the three tree species were significantly different.The minimum N content was poplar 8.97mg·g^-1.Fine roots N content of metasequoia and ginkgo was 1.18 times and 1.62 times higher than that of poplars.The smallest C/N value among the three tree species was ginkgo（36.90）,metasequoia was the middle（53.82）,and the largest was poplar（61.27）.