| Under the background that China has become the third largest nitrogen deposition area in the world and is becoming more and more serious,understanding the intrinsic response mechanism of forest ecosystem to persistent nitrogen deposition has become the frontier and hot spot of current ecological research.The root ecological process is the key link of material circulation and energy flow in forest ecosystems.The biomass and functional properties of fine roots(morphological,anatomical,branched,symbiotic fungal,and physicochemical properties)are subject to acute variation in different environments.This paper discusses the distribution mechanism of fine root distribution and functional properties of Chinese fir on long-term nitrogen addition,in order to provide data and theoretical support for the response of forest ecosystem to nitrogen deposition,and provide scientific basis for the management and management of plantation in subtropical regions of China.In this study,12 20×20m2 Chinese fir plantations(24-year-old)with nitrogen added after site and stand conditions were taken as research objects.The nitrogen addition of the plots was N0(0 g N· m-2· a-1),N1(6 g N·m-2·a-1),N2(12 g N·m-2·a-1),N3(24 g N·m-2·a-1)4 different The concentration was repeated 3 times for each treatment to investigate the effects of long-term nitrogen addition on the distribution and functional properties of fine roots of Chinese fir.The results show:(1)Different soil nutrient contents differ between different soil layers.The soil C and N content decreased significantly with the increase of soil depth.Medium N treatment(N2)and high N treatment(N3)resulted in a significant increase in soil C content(P < 0.05).Due to the effects of plant uptake and rainfall scouring,soil N content was not significantly different between treatments.Nitrogen addition had no significant effect on soil P content.The available nitrogen in the soil is mainly ammonium nitrogen,and the content in the soil increases with the increase of nitrogen addition.In the 0-30 cm soil layer,the effective nitrogen content increased with the increase of soil depth and the highest content in the 20-30 cm soil layer,and then decreased with the increase of soil layer.(2)Soil microbial biomass carbon(MBC)decreased significantly with increasing soil depth.Low nitrogen treatment(N1)promoted MBC in all soil layers,while medium N treatment(N2)and high N treatment(N3)pairs MBC showed inhibition(P < 0.05).The activities of soil invertase,acid phosphatase and urease decreased with the increase of soil layer,and the difference between treatments decreased with the increase of soil layer.The responses of the three enzymes to nitrogen addition were also different: soil sucrase activity increased significantly under N1 treatment in 0-10 cm shallow soil layer,and N2 treatment promoted best in the other three soil layers;N1 and N2 treatment promoted The soil urease activity was observed,while the N3 treatment showed inhibition.The soil acid phosphatase activity increased first and then decreased with the nitrogen addition,and reached the highest value under N2 treatment(P < 0.05).(3)The fine roots of Chinese fir are mainly distributed in the soil surface.The fine root biomass of 0-20 cm soil layer accounts for 70% to 90% of the fine root biomass of 0-50 cm soil layer.Low nitrogen and medium nitrogen(N1,N2)promoted the first-order root biomass of each soil layer,while high nitrogen(N3)inhibited the shallow(0-10cm)level 1 root biomass.The soil(10-20,20-30,30-50 cm)grade 1 roots showed a promoting effect.The biomass of each treatment level 1 root in 0-50 cm soil layer showed N2>N1>N3>N0.Nitrogen addition promoted the 2-5 roots of Chinese fir.The total biomass of Chinese fir 2-5 roots in 0-50 cm soil layer is N2>N1>N3>N0.(4)N2 treatment has a significant effect on the length of soil hyphae.The medium-low nitrogen treatment(N2,N1)significantly increased the root length,root surface area and tissue density of the first-order roots,and also promoted the diameter.High nitrogen treatment(N3)significantly inhibited root diameter,length,surface area and tissue density(P<0.05).The ratio of roots and roots of roots 1 and 2 showed a trend of decreasing with the increase of nitrogen treatment.Nitrogen treatment changed the fine root anatomy.The diameter of the column in the first-order root was consistent with the trend of the diameter of the first-order root.The anatomical aspect revealed the nature of the increase in the diameter of the fine root.The level 1 root cortex showed N1>N2>N3>N0 with nitrogen treatment,and the epidermis showed N0>N3>N1>N2 with nitrogen treatment.There is an intrinsic correlation between root length,root diameter,root surface area,mycorrhizal infection rate,branching ratio,column diameter and cortical thickness.They jointly affect the ability of plant roots to absorb nutrients,while changing the characteristics of fine root morphology.To achieve the best nutrient absorption strategy. |
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