Bioavailability of slowly cycling soil phosphorus: major restructuring of soil P fractions over four decades in an aggrading forest

Abstract

Although low solubility and slow cycling control P circulation in a wide range of ecosystems, most studies that evaluate bioavailability of soil P use only indices of short-term supply. The objective here is to quantify changes in P fractions in an Ultisol during the growth of an old-field pine forest from 1957 to 2005, specifically changes with organic P (Po) and with inorganic P (Pi) associated with Fe and Al oxides as well as Ca compounds. Changes in soil P were estimated from archived mineral soil samples collected in 1962 shortly after pine seedlings were planted, and on six subsequent occasions (1968, 1977, 1982, 1990, 1997, and 2005) from eight permanent plots and four mineral soil layers (0-7.5, 7.5-15, 15-35, and 35-60 cm). Despite the net transfer of 82.5 kg ha(-1) of P from mineral soil into tree biomass and O horizons, labile soil P was not diminished, as indexed by anion exchange resins, and NaHCO(3) and Mehlich III extractants. An absence of depletion in most labile P fractions masks major restructuring of soil P chemistry driven by ecosystem development. During 28 years of forest growth, decreases were significant and substantial in slowly cycling Po and Pi associated with Fe and Al oxides and Ca compounds, and these accounted for most of the P supplied to biomass and O horizons, and for buffering labile soil fractions as well. Changes in soil P are attributed to the P sink strength of the aggrading forest (at 2.9 kg ha(-1) year(-1) over 28 years); legacies of fertilization, which enriched slowly cycling fractions of Po and Pi; and the changing biogeochemistry of the soil itself.

Patterns of new versus recycled primary production in the terrestrial biosphere

“…For example, standard conceptual models suggest that much of the soil P in occluded forms is not available to terrestrial plants, yet plants have a number of mechanisms to liberate soil-bound P, including mycorrhizae, root exudation and chelation, and rhizosphere redox changes. These interactions (40), as well as those between N and P (41), have the potential to greatly enhance P availability. However, further research on P cycling and availability will be important to better understand and predict longterm patterns of terrestrial NPP.…”

Phosphorus cycling in primary and secondary seasonally dry tropical forests in Mexico

“…Interestingly, these results did not differ from the findings by Johnson et al (2003), who found evidence that Hedley-labile P pools in soils appeared to be several times larger than annual requirement of P in humid tropical forests, even though many tropical forests appeared to be P limited (Vitousek, 1984). On the other hand, the sufficient P availability in the soil could be maintained during succession (despite the expected nutrient accumulation in forest biomass during secondary succession, see Brown and Lugo, 1990) by a substantial cycling of Po and Pi from Ca compounds, as suggested by Richter et al (2006). Clearly, a further understanding of P biogeochemical processes in forest soils is required, especially focused on the relationship between operationally defined plant-available P and plant P nutrition.…”

Phosphorus fractions in soil after successive crops of Pinus taeda L. without fertilization

“…This fact showed that the labile P forms are mostly organic and that Pinus crops can access these fractions. However, even if these values are lower than those reported in other Pinus cultivation systems (BEKELE et al, 2003;RICHTER et al, 2006), there is no evidence of a response of Pinus to isolated P applications. In soils as that studied, the response to P applications is except just at the beginning of the stand (MORO et al, 2014).…”

“…In perennial and forestry crops, the diagnosis of phosphorus (P) availability is more complex, since the longer cycle, the greater is the possibility of buffering of the most labile by the less labile forms. Over the course of time, this Gatiboni et al increases nutrient availability in soils under Pinus stands, as emphasized by RICHTER et al (2006); or in successive crops on unfertilized soil, as pointed out by GATIBONI et al (2007).…”

“…In the forests, the P considered available by routine soil analyses (Mehlich 1 or anionexchange resin) ignores the less labile P forms that may become available, especially the labile organic forms (RICHTER et al, 2006). The common determination procedures do not detect the labile organic forms available to plants.…”