Impact of pH on Microbial Biomass Carbon and Microbial Biomass Phosphorus in Red Soils

The impact of pH changes on microbial biomass carbon (Cmic) and microbial biomass phosphorus (Pmic)were examined for 3 red soils under citrus production with different lengths of cultivation. Soil pH significantly affected Cmic and Pmic. The Cmic and Pmic changes, as a function of soil pH, appeared to follow a normal distribution with the original soil pH value at the apex and as pH increased or decreased compared to the original soil pH, Cmic and Pmic declined. Moreover, there were critical pH values at both extremes (3.0 on the acidic side and 8.0 to 8.5 on the alkaline side), beyond which most of microorganisms could never survive.The effect of pH on Cmic and Pmic was also related to the original soil pH. The higher the original soil pH was, the less Cmic or Pmic were affected by pH change. It is suggested that soil microorganisms that grow in a soil environment with a more neutral soil pH range (I.e. pH 5.5-7.5) may have a greater tolerance to pH changes than those growing in more acidic or more alkaline soil pH conditions.

Variation of Ecostoichiometric Ratios of Soil Microbes in Zhoushan Forest Park

Taking surrounding woodland soils of Cedrus deodara(Roxb.)G.Don,Prunus ceraifera cv.Pissardii,Ginkgo biloba L.and Ligustrum lucidum in Zhoushan Forest Park of Henan Province as the research objects,the physicochemical properties of sample plots were investigated,and the contents of soil microbial biomass carbon,nitrogen,phosphorus and total soil nutrients were determined.The results showed that the carbon-nitrogen ratios and carbon–phosphorus ratios were 8.0-11.4 and 17.1-25.3,respectively;the percentages of carbon,nitrogen and phosphorus in soil organic carbon(SOC),total nitrogen(TN)and total phosphorus(TP)were 2.84%-5.1%,2.69%-4.44%and 2.19%-5.62%,respectively.The carbon–nitrogen ratio and carbon-phosphorus ratio of P.ceraifera,G.biloba and L.lucidum forests were signifi cantly lower than that of C.deodara forest(P<0.05).The MBC/SOC,MBN/TN and MBP/TP ratios of G.biloba forest were the highest,which had signifi cant difference with those of other tree species(P<0.05).The contents of carbon,nitrogen and phosphorus were extremely or signifi cantly correlated with SOC,TN,TP,tree species and human disturbance,but had no correlation with soil pH,slope,slope direction,etc.Tree species and human disturbance also significantly affected the physical and chemical properties closely related to soil microbial biomass.

Changes in soil biochemical properties following replacement of Banj oak forest with Chir pine in Central Himalaya,India

Introduction:In Central Himalaya,anthropogenic activities have led to the widespread replacement of Banj oak(Quercus leucotrichophora)forest by Chir pine(Pinus roxburghii)for decades.This study was conducted to determine how natural Banj oak,Chir pine,and mixed oak-pine forest would differ in soil microbial biomass and soil nutrients.Soil microbial biomass nitrogen(SMBN)and phosphorus(SMBP),soil organic carbon(SOC)total nitrogen(TN),and total phosphorus(TP)in the 0 to 15 cm soil layer were investigated in the Central Himalayan region in the stands of Banj oak,mixed oak-pine,and Chir pine forest.Results:The SMBN and SMBP were significantly higher in Banj oak and mixed oak-pine forest as compared to Chir pine forest.The ratios of SMBN to TN(SMBN/TN)and SMBP to TP(SMBP/TP)were significantly higher in the Chir pine forest,indicating that in this forest,the proportion of microbial biomass N and P to total soil N and P was higher as compared to Banj oak forest.A similar pattern of variation was found in relation to season across the forests,all with an apparent peak in the rainy season.Conclusion:These results indicate that low microbial biomass N and P may be one of the reasons to create a nutrient poor site in Chir pine forest.The collection of pine litter by local people also impairs the return of nutrients to the soil and makes it difficult for Banj oak to re-invade areas occupied by Chir pine.This calls for cautions in large-scale conversions of the Banj oak forests to coniferous plantations as a forest management practice on concerns of sustaining soil productivity.