Ecological Effects Of AMF In The Process Of Abandoned Vegetation Succession And Its Influence On Interspecific Relationships

The shortage of soil nitrogen and phosphorus is an important factor restricting the restoration of grassland vegetation in the semi-arid loess hilly region.Arbuscular mycorrhizal fungi?AMF?can form a symbiotic relationship with more than 70%of terrestrial plants.AMF can improve host plant competitiveness by increasing soil nutrient acquisition and subsequent assimilation into plant tissues?especially phosphorus?.Plant interspecific relationships are important for maintaining grassland vegetation productivity and community stability during vegetation succession.Common mycorrhizal networks?CMNs?can change the absorption and utilization of elements between plants by mediating the transport of nutrients between plants,which in turn has an important impact on plant interspecific relationships.Ecological effects of AMF in the process of abandoned vegetation succession and its influence on interspecific relationships remain to be further studied.This paper firstly investigated the effects of AMF on soil aggregate stability,nutrient accumulation and interspecific relationships during the vegetation succession after farmland abandoned in the loess hilly region via field survey methods,and clarified the synergistic evolution mechanism between different niche plants and AMF,and aimed to explore how shortage of soil nitrogen and phosphorus limited vegetation restoration and AMF ecological effects.Based on the background of the relative lack of soil nitrogen and phosphorus in this region,this paper applied indoor pot stimulation experiment,and took the dominant species of natural grassland in the loess hilly region of northern Shaanxi,Bothriochloa ischaemum and Lespedeza davurica,as the research object.The regulation of AMF on the interspecific relationship of co-exist plants was studied by means of carbon and nitrogen stable isotope labeling,including the effects on the absorption,distribution and accumulation of elements between co-exist plants.The main conclusions were as follows:?1?The distribution and accumulation of glomalin in soil aggregates during the vegetation succession was important for the recovery of soil carbon and nitrogen content and the stability of soil aggregates and soil organic carbon.The restoration of total vegetation biomass during the vegetation succession was mainly limited by soil nitrogen content,and the increase of plant diversity was beneficial to increase the total vegetation biomass.The symbiotic relationship between plants and AMF is limited by the soil total phosphorus content.This relationship is conducive to improving the competitiveness of host plants and promoting the differentiation of niche,thereby promoting the positive succession of vegetation.The total above-ground biomass and symbiotic relationship between plants and AMF promoted the accumulation of glomerin in plant rhizosphere,and further increased soil carbon and nitrogen content.Compared with the associated species,the dominant species accumulate more glomalin in their rhizosphere through AMF,which promotes the accumulation of carbon and nitrogen in their rhizosphere soil.?2?When the soil nitrogen and phosphorus were relatively scarce,the mycorrhizal network in the Bothriochloa ischaemum and Lespedeza davurica communities preferentially supplied nitrogen to B.ischaemum,which significantly increased the total nitrogen contents of above-and below-ground parts of B.ischaemum and the belowground biomass of B.ischaemum?32.22%?.It also significantly reduced the total nitrogen content in the belowground part of L.davurica,but significantly increased its aboveground?34.52%?and belowground biomass?19.44%?.At low nitrogen addition(25 mg kg^-1),the mycorrhizal network increased the nitrogen supply to the belowground part of B.ischaemum and reduced the nitrogen supply to the L.davurica,significantly increasing the belowground biomass?31.75%?of B.ischaemum and the net photosynthetic rate?13.95%?of L.davurica.At high nitrogen addition(50 mg kg^-1),the mycorrhizal network reduced the nitrogen supply to the L.davurica,and significantly decreased the belowground biomass of B.ischaemum,but significantly increased the belowground biomass of L.davurica.The mycorrhizal network reduced the total phosphorus contents in the belowground part of B.ischaemum and the above-and belowgrouns parts of L.davurica,and this negative effect gradually decreased with the addition of nitrogen.When the availability of soil nitrogen increased,the interspecific competition of soil phosphorus between B.ischaemum and L.davurica increased,leading to no promotion effect of mycorrhizal network on the growth of aboveground parts of the two plants.?3?When the soil nitrogen and phosphorus were relatively scarce,the mycorrhizal fungal network significantly increased the soil CBH activity and dissolved carbon and phosphorus content,and significantly increased the soil NAG activity and dissolved organic nitrogen content of L.davurica,but significantly decreased the soil NAG activity and dissolved organic nitrogen content of B.ischaemum.At low nitrogen addition(25 mg kg^-1),the mycorrhizal network significantly increased soil BG,AP,and BX activities,thereby increasing the availability of soil nitrogen and phosphorus,but resulted in a significant decrease in soil dissolved organic carbon content.At high nitrogen addition(50 mg kg^-1),the mycorrhizal network reduced soil AP activity of B.ischaemum and soil NAG activity of L.davurica,resulting in a significant decrease in soil available phosphorus content of B.ischaemum and dissolved inorganic nitrogen content of L.davurica.Although the ability of L.davurica to compete for nitrogen through the mycorrhizal network is weaker than that of B.ischaemum under nitrogen addition,the nitrogen use efficiency of L.davurica was enhanced by reducing nitrogen input from plants to the soil.?4?Phosphorus addition increases the amount of nitrogen absorbed by plants through AMF.At low phosphorus addition(30 mg kg^-1),the mycorrhizal network in the Bothriochloa ischaemum and Lespedeza davurica communities significantly increased the nitrogen supply to the aboveground part of B.ischaemum,and reduced the nitrogen supply to the aboveground part of L.davurica,which significantly increased the net photosynthetic rate of B.ischaemum?42.01%?and L.davurica?109.94%?and the total nitrogen content in the belowground part of B.ischaemum,resulting in a significant increase in the aboveground biomass of B.ischaemum?70.67%?and L.davurica?36.92%?.At high phosphorus addition(100 mg kg^-1),the mycorrhizal network preferentially supplied nitrogen to the aboveground part of L.davurica,and inhibited the photosynthesis of B.ischaemum and L.davurica,and significantly increased the aboveground biomass of L.davurica?46.24%?,but it did not promote the growth of B.ischaemum.Compared with soil nitrogen deficiency,soil phosphorus deficiency had a greater restriction on the reciprocal relationship between co-exist plants.The increase in the availability of soil phosphorus is beneficial to improve the ability of L.davurica to compete with B.ischaemum for soil nitrogen via mycorrhizal network.?5?At low phosphorus addition(30 mg kg^-1),the mycorrhizal network significantly increased soil BG,NAG and AP activities,and promoted the degradation of soil dissolved organic matter,resulting in a significant decrease in soil dissolved carbon,nitrogen and phosphorus contents.At high phosphorus addition(100 mg kg^-1),the mycorrhizal network significantly increased soil NAG,CBH,and LAP activities,and promoted soil nitrogen cycling,and significantly increased soil available phosphorus content,but significantly reduced soil AP activity,leading to a significant decrease in soil dissolved total phosphorus content.With the increase of soil phosphorus availability,the mycorrhizal network significantly reduced the nitrogen content of the plant input into soil,and improved the nitrogen use efficiency between B.ischaemum and L.davurica.