Transient And Legacy Effects Of Heat And Ash On Soil Fungal Communities

Objective: To explore the transient and legacy effect of the main effect factor of fire-heat and ash on soil fungi through designed fire disturbance experiment in field.The result would reveal the succession law and driving mechanism of soil fungi community after fire interference,provide reference for understanding the mechanisms of fire systematically and the change rhythms of soil fungi following fire disturbance.All of this could improve the existing theoretical system of microbial ecology and provide theoretical support for post-fire ecosystem restoration practices.Method:1)Sample plot setting: 0-20 cm of soil under the Yunnan pine vegetation was excavated,mixed evenly and laid in a pre-prepared sample pit(length × width ×height: 2 m × 1.5 m × 0.5 m)at the base for field practice of Dali University.The sample pit were evenly divided into 7 treatment groups by insulation bricks,and each group was divided into 9 small units equally(10 cm×10 cm).2)Method of fire disturbance treatment: dry ash group(GH),cool ash from 260 g complete burning pine needles was laid on the soil surface of each unit;wet ash group(SH),ash from 260 g complete burning pine needles was wetted firstly and laid on the soil surface of each unit;burning group(RS),260 g pine needles were put on each unit and burned,then the ash were left;low-intensity single heat group(DQ),the soil surface of each unit was heated with flame-throwing gun for 20 min;high-intensity single heat group(GQ),the soil surface of each unit was heated with flame-throwing gun for 1 h;charcoal baking group(TH),tin foil was put on each unit and 200 g charcoal was light and laid on the tin foil to bake the soil;blank control group(CK),without any treatment.The temperature of the different soil layers was measured with a two-channel thermocouple instrument pre-buried at 2,5,10,15 and20 cm depth.3)Soil sample collection: Soil samples were collected at upper soil layer(0-10cm)and subsoil layer(10-20 cm)separately after soil cooled down(0 d)and then every 10 days and lasted for 90 days after treatment.Five units of each treatment group were chosen and soil samples at upper and subsoil layers were collected every time,and then the five soil samples from upper or subsoil layer were mixed for test.The upper soil samples were labeled as UGH for dry ash group,USH for wet ash group,URS for burning group,UDQ for low-intensity group,UGQ for high-intensity,UTH for charcoal baking group,UCK for blank control group;the subsoil samples were labeled as DGH for dry ash group,DSH for wet ash group,DRS for burning group,DDQ for low-intensity group,DGQ for high-intensity,DTH for charcoal banking group,DCK for blank control group,respectively.4)Determination of soil physicochemical properties and fungal biomass: total phosphorus(TP),total nitrogen(TN),p H,organic matter(OM),and moisture content(MOT)of soil were measured with reference of forestry standards;The fungal biomass was determined with spread plate method.5)Analysis of fungal community: High-throughput sequencing was performed with ITS as the sequencing target on Illumina platform,and then,the spatiotemporal dynamic change of the soil fungal community was analyzed.Result:1)Soil peak temperature: The peak temperature at 2 cm of burning group(RS),low-intensity group(DQ),high-intensity group(GQ)and charcoal banking group(TH)is 194?,385? 639?,285?;at 5 cm it is 82.8?,46.7?,149.3?,112.3?;the temperature below 10 cm does not change compared with control.2)Soil physicochemical properties: There were significant differences(p < 0.05)in total phosphorus(TP),total nitrogen(TN),organic matter(OM)and p H among the upper soil of each group.When compared to the blank control group(UCK),there was significant increase in total phosphorus(TP)in the upper soil of wet ash group(USH)(p < 0.01),significant decrease in total nitrogen(TN)in the upper soil of high-intensity(UGQ)(p < 0.05),significant increase in p H in the upper soil of dry ash group(UGH),wet ash group(USH),burning group(URS)and low-intensity group(UDQ)(p < 0.01),significant increase in organic matter(OM)in the upper soil of burning group(URS)(p < 0.05)and significant decrease in the upper soil of low-intensity group(UDQ),high-intensity(UGQ)and charcoal baking group(UTH)(p < 0.05).Significant differences(p < 0.05)were also found in organic matter(OM)in the subsoil of burning group(DRS)and charcoal baking group(DTH)compared to subsoil of blank control group(DCK).3)Culturable fungal biomass: Compared with upper soil of blank control group(UCK),the culturable fungal biomass in upper soil of low-intensity group(UDQ),high-intensity(UGQ)and charcoal baking group(UTH)decreased immediately after fire,and the higher the temperature,the greater the impact;That in the upper soil layer of dry ash group(UGH),wet ash group(USH)and burning group(URS)were similar to that of blank control group(UCK);The culturable fungal biomass in subsoil layer after treatment in all treated groups was higher than that of the blank control group(DCK)at 0 d.The biomass in the upper and sub soil layer of all treated groups exceeded the blank control group(CK)at 20 th d and the fungal biomass in the subsoil layer fluctuated substantially throughout the whole monitoring period.Linear model analysis showed that there was significant linear relationship between fungal biomass and total nitrogen(TN),total phosphorus(TP)and moisture content(MOT).4)Soil fungal community structure: The diversity of fungal community in the upper soil layer of high-intensity(UGQ)and charcoal baking group(UTH)were significantly different from those in the upper soil layer of blank control group(UCK),dry ash group(UGH),wet ash group(USH)and burning group(URS)(p < 0.001);There was also significantly difference in the diversity of fungal community in the upper soil layer between low-intensity group(UDQ)and high-intensity(UGQ)(p <0.05).In terms of community structure,all the fungal communities divided to three group,these in UGH and USH groups in the upper soil layer were similar with blank control group(UCK)and those of low-intensity group(UDQ),high-intensity(UGQ)and charcoal baking group(UTH)were similar to each other,while it was between the first two groups in burning group(URS)in the upper soil layer.The difference among all fungal communities in the structure of subsoil fungal community was small.In terms of specie composition,four fungal phyla were identified in the upper and subsoil layers: Ascomycota,Basidiomycota,Rozellomycota,and Mortierellomycota and the first two phyla were the dominant fungi;32 and 36 genera were identified in upper and subsoil layers,respectively.There were species in burning group(RS),low-intensity group(DQ),high-intensity group(GQ)and charcoal banking group(TH)whose abundant was significant difference from the blank control group(CK).The fungal community in upper soil of burning group(RS),low-intensity group(DQ),high-intensity group(GQ)and charcoal banking group(TH)was significantly correlated with moisture content(MOT).Conclusion: Heat effect the culturable biomass,diversity and community structure of soil fungi,with the immediate effect being significant and mainly in upper soil layer and the legacy effect being indirect,mainly through changes in soil physicochemical properties.The immediate effect of ash was weaker,as ash infiltrates into soil and changed soil physicochemical factors so as to exert a slow and weak effect on the soil fungi.Soil culturable fungal biomass recovered above control levels at 20 th d after treatment.Fungal biomass and community structure were relatively stable after 20 d under single heat input.The fungi inhabited in subsoil layer were important for the recovery of the soil fungal community.