2010 CREST Annual Report - Alabama A&M University

instance, the ratio of diester: monoester P is used as a measure of amount of labile organic P present insoil.In conclusion we can suggest that burning and logging have some effect on changing the percent Pforms in soil. The main observation is that the dominant OP form in these soils is monoester-P whichcomprises mainly of inositol phosphates and minor amounts of sugar phosphates, phospho-proteins,and mononucleotides. Relatively high concentration of monoester P forms present in control soilsrelative to treated soils suggests the possibility of fire-induced transformation of some of the monoesterforms to orthophosphates.Most prominent form of diester P observed in the soils studied was from DNA-P. Diester P forms thatmainly consist of nucleic acids (DNA, RNA), phospholipids, and teichioic acids are considered to beincorporated into soils from plants and microbes. Previous studies indicate that changes in diester P isan indicator of changes in microbial P forms where decrease in DNA-P may attribute to decrease ofmicrobial biomass by burning or decrease of plant residue present in soil. In our study a decrease inDNA-P was observed in soils subjected to burning or burning and logging treatments relative to controlsoils indicating the possibility of changes in microbial biomass in treated soils or due to decrease of plantresidues in soils during burning process. The NMR results also indicate decrease in pyrophosphates intreated soils which is an indicative of changes in fungal compounds as affected by logging and burningtreatments.5. MineralogyOur mineralogy data shows that kaolinite, halloysite, vermiculite-hydroxy-interlayered vermiculites, andquartz are common components of soils of the Bankhead National Forest, Alabama. Kaolinite wasidentified in the Mg- and K-saturated clays by XRD peaks of 7.2 and 3.58 Å. When k-saturated sampleswere heated to 500 ºC, the 001 reflection of kaolinite disappeared but the 10 Å Halloysite peakcollapsed to 7.2 Å. Vermiculites first order peak at 14.2 Å in K-saturated samples collapsed and shifted to10.2 Å when heated at 500 ºC. Quartz was identified with the 3.34 Å peak (Figure 63).Vermiculite, kaolinte, and quartz were identified in both the unburned and the burned soils.Vermiculites in the unburned soil appeared to maintain its structural integrity with a sharp peak at 14.2Å. Absence of a peak at between 10-14 Å in K-saturated samples suggest that there was no collapse orshift in vermiculite d-spacing in the unburned soil.In the burned soils, K-saturated soil samples (at 25 ºC) showed the presence of vermiculites (14.2 Å),that may have partially collapsed, and shifted to 10.1 Å d-spacing. Very strong peaks at 7.2 Å in K-saturated samples at 500 ºC suggests that halloysite was present in dehydrated form and remainedcollapsed in the burned soils. Thus the clay fraction of the burned soil showed a 10.1 Å XRD peakprobably because the interlayered-hydroxy vermiculite collapsed during burning. Burning may also haveinduced dehydration of halloysite in the surface horizon of the soils.On further analyses of samples from other sites, other less well identified peaks at 22.5, 7.92 Å, weresuspected to be reflections of a mica-vermiculite-layered mineral (hydrobiotite), a weathering productof mica (Figure 64).Pre-burn soil samples showed 9º 2Ө (10.17Å) peaks that were absent in the x-ray patterns of the postburnsamples. It is not clear which mineral that the peak reflects or how burning resulted in the peaks(Figure 64).We hypothesize that relative K depletion could be accelerating the interlayer K replacement of biotite byother exchangeable cations such as Ca to form vermiculites, mica-vermiculites, and possibly smectites,resulting in the complex mineralogy of the soils.83