Cluster ID	Size	Cluster name	Mean year	Silhouette	Main research contents
0	74	nutrient transfer	2010	0.980	The effects of fungal hyphae in soil on nutrient absorption and transport to host plants, the regulation of fungal-plant interface, the nitrogen cycle in ecosystem and the mechanism of mycelium network (CMN) controlling nutrient transport to a single host plant were studied [32] [33] [34] .
1	71	n-15 tracer	1998	0.974	The nitrogen cycle in forest soil was deeply studied. Isotope data of nitrogen transfer to plants, soil and mycorrhizal fungi were labeled with N-15 tracer to understand the effects of nitrogen on nutrient cycle, plants and soil [35] [36] [37] [38] .
2	68	nutritional ecology	2005	0.974	The effects of crop soil roots on rhizosphere, physical, chemical and biological environment of plant growth, the relationship and interaction among roots, rhizosphere, mycorrhiza and soil, and their effects on the dynamics of carbon flow and nutrient cycle at ecosystem scale were studied [39] [40] [41] .
3	64	complex catchment	2003	0.940	The sources and impacts of phosphorus migration in complex river basins were monitored, and the mitigation strategies of nitrogen and phosphorus migration and diffusion were discussed. Model monitoring and erosion mapping were used to estimate the long-term dynamics and trends of particulate bound phosphorus and nitrate in agricultural rivers [42] [43] .
4	49	antibiotic resistome	2016	0.990	The diffusion mechanism of antibiotic resistance genes in fecal soil and its effects on soil microorganisms, as well as the effects of fecal microbial community and soil microbial community on nitrogen and phosphorus dynamics were studied [44] [45] .
5	45	critical source area	2011	0.956	For the key source areas in agricultural activities, the diffusion and transfer of nutrients in the soil to water sources leads to the enrichment and eutrophication of phosphorus in water bodies, which have caused great pressure on river systems. The mitigation measures to control phosphorus concentration and watershed management should be studied to protect water areas from nitrogen and phosphorus pollution [46] [47] .
6	43	arbuscular mycorrhizal fungi	2015	0.976	AM obtained low-mobility nutrients from soil, and found the physiological, molecular and regulatory mechanisms of nitrogen absorption and plant phosphorus transportation, as well as the main role of AM in plant growth, zinc nutrition and phytoremediation [48] [49] .
9	36	hidden miner	2016	0.962	The influence of soil microbial community activities on soil carbon and nitrogen dynamics, changing the distribution of unstable carbon and nitrogen in soil, affecting the spatial pattern of soil nutrient dynamics, and the interaction between crops and soil microorganisms in the phosphorus cycle of agro-ecosystem [50] [51] .
10	34	tallgrass prairie plant	2002	0.990	Grain-bean intercropping increased the formation of mycorrhiza, and then improved the regulation of leguminous plants, the acquisition of nitrogen and phosphorus and the transfer of nitrogen [52] .
11	33	phosphorus loss	1998	0.997	Excessive phosphorus input in animal husbandry increased the loss of phosphorus from land to water. In order to reduce the loss of phosphorus in water, the overall goal should include optimizing the proportion of animal feed and applying phosphorus as mineral fertilizer and manure on land to balance the input and output of phosphorus at farm and watershed levels [53] [54] .
12	30	redox-mediated reaction	2013	0.994	Biochar-mediated microbial transformation of soil pollutants, the mechanism of biochar promoting electron transfer between microbial cells, pollutants and soil organic matter, and the influence of biochar-microbial community interaction for soil remediation and improvement were studied [55] .
13	26	water eutrophication	2015	0.984	Aiming at the eutrophication caused by agricultural activities, the migration dynamics of total phosphorus, dissolved phosphorus, granular phosphorus and suspended sediment concentrations were evaluated, reasonable and accurate phosphorus loss simulation was provided by using monitoring technology and models, and a comprehensive evaluation of nutrient migration was established to reduce phosphorus migration to water sources [56] [57] [58] .