Changes Of Soil Nutrient In Pinus Massoniana Stands After Disturbance By Pine Wilt Disease

Bursaphelenchus xylophilus is one of the harmful plant inspection and quarantinepests, which is vectored mainly by a beetle （Monochamus alternatus）. Once a pine tree isinfected by Bursaphelenchus xylophilus, it will die in two to three months. The pine wiltdisease does a destructive harm to ecosystem. Hefei Shushan Forest Park has firstly foundthe pine wilt disease in1999. The damage area has been constantly enlarged. Dozens of muof masson pine stands have been caused seriously damaged with the pine wilt disease since2005. A large number of masson pine trees have withered.In massion pine forest, the changes in the forest structure will cause a series ofchanges in soil properties especially notable after Bursaphelenchus xylophilus invasioned,and this change will cause great change of forest composition and micro-organisms. In thisstudy, some soil chemical properties, the characteristics of carbon and nitrogentransformation and available phosphorus of the Masson pine stands with the differentdamage by pine wilt disease in Shushan Forest Park were studied in order to providetherier basis and useful measures for the restoration ofthe damaged pine stands.The properties of the soils were greatly changed after the disturbance of the pine wiltdisease. In0-10cm soil in the slightly damaged stands, the mean pH （H2O） was4.73, andpH （KCl） was3.77. The mean EC was143.15μS·cm^-1, mean total nitrogen1.71g·kg^-1,mean total potassium13.57g·kg^-1, mean total calcium0.65g·kg^-1, mean total magnesium5.10g·kg^-1and mean total phosphorus117.39mg·kg^-1. In0-10cm soil in seriouslydamaged stands, the mean pH （H2O） was5.03, and pH （KCl）3.96. The mean EC was133.65μS·cm^-1, mean total nitrogen1.95g·kg^-1, mean total potassium11.67g·kg^-1, meantotal calcium was0.46g·kg^-1, mean total magnesium4.43g·kg^-1and mean totalphosphorus103.57mg·kg^-1. However, no significant differences in soil nutriernt occurredbetween the sampling stands.In0-10cm soil, the concentrations of extractable NH4+in the slightly damaged standswere the highest in May (7.25mg·kg^-1) and the lowest in January (2.57mg·kg^-1). Theconcentrations of extractable NH4+in the seriously damaged stands were the highest in July(6.73mg·kg^-1) and the lowest in January (2.74mg·kg^-1).In10-20cm soil, the concentrations of extractable NH4+in November were the highest in the slightly (6.24mg·kg^-1) and seriously damaged stands (5.67mg·kg^-1). The soilin January had the lowest concentrations of extractable NH4+in slightly damaged (1.55mg·kg^-1) and seriously damaged stands (1.40mg·kg^-1).In0-10cm soil, the concentrations of extractable NO3-in the slightly damaged standswere the highest in May (16.97mg·kg^-1) and the lowest in September (5.76mg·kg^-1). Theconcentrations of extractable NO3-in the seriously damaged stands were the highest inMarch (17.59mg·kg^-1) and the lowest in July (6.37mg·kg^-1). In10-20cm soil, theconcentrations of extractable NO3-in the slightly damaged stands were the highest inMarch (8.41mg·kg^-1) and the lowest in July (3.99mg·kg^-1). The concentrations ofextractable NO3-in the seriously damaged stands were the highest in May (10.00mg·kg^-1)and the lowest in July (3.65mg·kg^-1).In0-10cm soil, the concentrations of extractable DOC in the slightly damaged standswere the highest in May (179.74mg·kg^-1) and the lowest in January (100.48mg·kg^-1). Theconcentrations of extractable DOC in the seriously damaged stands were the highest inSeptember (138.51mg·kg^-1) and the lowest in March (88.63mg·kg^-1). In10-20cm soil, theconcentrations of extractable DOC in the slightly damaged stands were the highest in May(130.81mg·kg^-1) and the lowest in January (86.84mg·kg^-1). The concentrations ofextractable DOC in the seriously damaged stands were the highest in May (107.65mg·kg^-1)and the lowest in January (74.18mg·kg^-1).Based on the in situ incubation experiment, the highest annual net rates ofammonification, nitrification and N mineralization were, respectively,37.40μg kg^-1 d^-1（from January to February2012）,627.59μg kg^-1 d^-1（July to August2011） and541.20μg kg^-1 d^-1（July to August2011） for0-10cm in the slightly damaged stands. The lowestwere, respectively,-104.17μg kg^-1 d^-1（November to December2011）,71.85μg kg^-1 d^-1（November to December2011）,-32.32μg kg^-1 d^-1（November to December2011）. Andfor10-20cm soil, the highest annual net rates of ammonification, nitrification and Nmineralization were, respectively,43.66μg kg^-1 d^-1（January to February2012）,271.20μg kg^-1 d^-1（July to August2011）,205.64μg kg^-1 d^-1（July to August2011）. The lowestwere, respectively,-94.87μg kg^-1 d^-1（November to December2011）,33.09μg kg^-1 d^-1（November to December2011）,-61.78μg kg^-1 d^-1（November to December2011）.The highest annual net rates of ammonification, nitrification and N mineralizationwere, respectively,-9.33μg kg^-1 d^-1（September to October2011）、714.15μg kg^-1 d^-1（Julyto August2011）、650.10μg kg^-1 d^-1（July to August2011） for0-10cm in the seriouslydamaged stands. The lowest were, respectively,-97.16μg kg^-1 d^-1（November to December 2011）、76.57μg kg^-1 d^-1（November to December2011）、-20.59μg kg^-1 d^-1（November toDecember2011）. And for10-20cm soil, the highest annual net rates of ammonification,nitrification and N mineralization were, respectively,4.69μg kg^-1 d^-1（January to February2012）、262.81μg kg^-1 d^-1（July to August2011）、196.37μg kg^-1 d^-1（July to August2011）.The lowest were, respectively,-82.96μg kg^-1 d^-1（November to December2011）、-30.35μg kg^-1 d^-1（May to June2011）、-58.17μg kg^-1 d^-1（November to December2011）.The annual net rate of DOC was highest (357.71μg kg^-1 d^-1) from March to April for0-10cm in the slightly damaged stands and the lowest from November to December(-889.73μg kg^-1 d^-1). And in10-20cm soils, the highest rate of DOC was336.76μg kg^-1 d^-1（March to April2011） and the lowest was-685.08μg kg^-1 d^-1（January toFebruary2012）. In the seriously damaged stands, the highest annual net rate of DOC was267.50μg kg^-1 d^-1（March to April2011） for0-10cm and the lowest-914.47μg kg^-1 d^-1（November to December2011）; and for10-20cm, the highest rate of DOC was185.57μg kg^-1 d^-1（July to August2011） in the slightly damaged stands and the lowest-591.58μg kg^-1 d^-1（January to February2012）.Results from the in situ incubation experiment showed that N transformation variedsignificantly for the different damaged stands. This demonstrated that the disturbance bypine wilt disease resulted in a significant changes in soil N mineralization with greatlyincrease in nitrification rate（p<0.01）, which suggests a high potential for N leaching in thedamaged stands.The annual mean concentration of soil microbial biomass carbon （SMBC） in the0-10cm soil was the highest in May in the slightly damaged stands (428.65mg·kg^-1) and thelowest in March (166.58mg·kg^-1). The concentrations of SMBC in the seriously damagedstands were highest in May (433.09mg·kg^-1), lowest in March (170.38mg·kg^-1). Theannual mean concentration of SMBC in the10-20cm soil was highest in May in theslightly damaged stands (368.01mg·kg^-1) and lowest in March (170.33mg·kg^-1). In theseriously damaged stands, the highest SMBC occurred in September (323.57mg·kg^-1), andthe lowest in January (126.34mg·kg^-1).The annual mean concentration of soil microbial biomass nitrogen （SMBN） in the0-10cm soil was highest in May for the slightly damaged stands soil (65.35mg·kg^-1) andlowest in September (39.09mg·kg^-1), while in the seriously damaged stands the highest inMay (88.72mg·kg^-1) and the lowest in September (34.91mg·kg^-1). The annual meanconcentration of SMBN in the10-20cm was highest in May of the slightly damagedstands (76.95mg·kg^-1) and lowest in September (27.04mg·kg^-1), while in the seriously damaged stands the highest in May (65.98mg·kg^-1) and lowest in September (8.73mg·kg^-1). There existed a significant difference in SMBC and SMBN amongst thesampling stands （p<0.01）.The annual mean concentration of available phosphorus in the0-10cm soil washighest in May for the slightly damaged stands (1.13mg·kg^-1) and the lowest in September(0.22mg·kg^-1), while for the seriously damaged stands the highest in January (1.20mg·kg^-1)and the lowest in September (0.21mg·kg^-1). The annual mean concentration of availablephosphorus in the10-20cm soil was the highest in January for the slightly damaged stands(0.55mg·kg^-1) and the lowest in September (0.15mg·kg^-1), while in the seriously damagedstands were highest in January (0.64mg·kg^-1) and lowest in September (0.13mg·kg^-1).However, no significant differences in available phosphorus occurred between thesampling stands.