Soil Organic Phosphorus Transformations During Pedogenesis

Abstract

Long-term changes in soil phosphorus influence ecosystem development and lead to a decline in the productivity of forests in undisturbed landscapes. Much of the soil phosphorus occurs in a series of organic compounds that differ in their availability to organisms, but changes in the relative abundance of these compounds during pedogenesis remain unknown. We used alkaline extraction and solution phosphorus-31 nuclear magnetic resonance spectroscopy to assess the chemical nature of soil organic phosphorus along a 120,000-year postglacial chronosequence at Franz Josef, New Zealand. Inositol phosphates, DNA, phospholipids, and phosphonates accumulated rapidly during the first 500 years of soil development characterized by nitrogen limitation of biological productivity, but then declined slowly to low concentrations in older soils characterized by intense phosphorus limitation. However, the relative contribution of the various compounds to the total organic phosphorus varied along the sequence in dramatic and surprising ways. The proportion of inositol hexakisphosphate, conventionally considered to be relatively recalcitrant in the environment, declined markedly in older soils, apparently due to a corresponding decline in amorphous metal oxides, which weather to crystalline forms during pedogenesis. In contrast, the proportion of DNA, considered relatively bioavailable in soil, increased continually throughout the sequence, due apparently to incorporation within organic structures that provide protection from biological attack. The changes in soil organic phosphorus coincided with marked shifts in plant and microbial communities, suggesting that differences in the forms and bioavailability of soil organic phosphorus have ecological significance. Overall, the results strengthen our understanding of phosphorus transformations during pedogenesis and provide important insight into factors regulating the composition of soil organic phosphorus.

Identification of inositol hexakisphosphate binding sites in soils by selective extraction and solution 31P NMR spectroscopy

“…In acidic soils, associations with amorphous Al and Fe hydroxides are believed to be the most important mechanism of IP 6 stabilization (Celi and Barberis, 2007). This is supported by correlations between amorphous metals and IP 6 across a wide variety of soils (Anderson et al, 1974;McKercher and Anderson, 1968;Turner et al, 2007Turner et al, , 2003Vincent et al, 2012). However, the relative contribution of these stabilization processes remains poorly understood, in part because most recent studies have extracted IP 6 from soils by a single-step NaOH-EDTA procedure, which is assumed to extract mineral associated IP 6 as well as IP 6 associated with the organic soil matrix (Turner et al, 2005a).…”

How does pedogenesis drive plant diversity?

“…However, because productivity is typically Plimited during the retrogressive phase of ecosystem development [10,25], partitioning of organic N is likely to be less important in promoting plant species coexistence on old soils. By contrast, although total soil P declines over time, organic P accumulates during pedogenesis to become a major fraction of the remaining total P [8], and different forms of organic P vary in their relative abundance as soils age [26]. Therefore, partitioning of P could become important for coexistence in retrogressive ecosystems where P is limiting [20].…”

“…The N and P partitioning hypotheses imply that diversity in N forms could promote plant diversity in younger, N-limited ecosystems, whereas diversity in P forms would be important in older, P-limited ecosystems. The simplest test of these hypotheses would be to: (i) measure fluxes of different N and P fractions along a soil chronosequence, using established methods [18,26]; (ii) quantify the diversity of N or P fractions, using standard metrics [e.g., Simpson diversity index (1/D)]; and (iii) relate the diversity of N or P forms to observed plant species diversity and determine whether these relations depend on soil age.…”

Speciation and distribution of P associated with Fe and Al oxides in aggregate-sized fraction of an arable soil

“…Our study aims to provide a novel method to understand the distribution of Pi and Po on Fe/Al oxides in the alkaline extract of soil. Furthermore, the residual P after alkaline extraction still accounts for significant proportion of P for some soils, most apparent in highpH soil or for unamended soils with low P concentration Cheesman et al, 2012;McDowell et al, 2007;Turner et al, 2007;Turner et al, 2003). The residual P is by definition unidentified and is simply presumed to be recalcitrant in the environment (Cheesman et al, 2010).…”