Phosphorus Availability in Acid Organic Soils of the Lower North Carolina Coastal Plain

Abstract

A natural landscape gradient of P—deficient pocosin (evergreen shrub bog) and bay forest ecosystems was used to test three hypotheses concerning P availability and P reabsorption efficiency: (1) that variations in vegetation height and aboveground biomass among even—aged pocosin stands are related to variations in soil P availability; (2) that microbial processes control P availability in these soils; and (3) that the proportion of P reabsorbed from senescing foliage in native plants is inversely related to soil P availability. The natural gradient from short pocosin to bay forest was found to represent a gradient of increasing P availability, as indicated by increases in: (1) total P in surface (0°15 cm) soils, from 19.6 to 118.3 kg/ha; (2) seasonal and annual PO43— supply to in situ anion—exchange resins; and (3) P concentrations in native plant foliage. Increases in P availability were accompanied by a significant decline in the N:P ratios of both plant leaves and surface soils. Microbial processes strongly influenced the supply of available P. Soil microorganisms immobilized up to 90% of added 32PO43— during laboratory incubations, but when microbial uptake was inhibited, as much as 90% of added 32PO43— remained in the available pool. A decline in the ratio of microbial: total P in surface soils, from 56.3 to 37.4%, and an increase in the ratio of net: gross P mineralization (estimated by isotope dilution), suggested that as P availability increased, microbial control decreased. Native plants reabsorbed both P and N efficiently from senescing foliage, reaching maxima of 86.6 and 80.5%, respectively; natural variations in soil P availability did not affect the proportion of either nutrient reabsorbed. In general, however, plants tended to reabsorb greater proportions of foliar P than N. Natural variations in P availability, the factors controlling P availability in these soils, and the potential for differential nutrient reabsorption by native plants have important implications for the cycling and accumulation of P and N in pocosin and bay forest soils. Landscape—Level processes may have contributed to the observed variations in vegetation and P availability along this natural gradient.

Characterization of suspended particles in Everglades wetlands

“…This extract was then filtered and analyzed for TP using persulfate digestion in order to estimate the microbial + labile P fraction. Microbial + labile P concentrations were corrected to account for the incomplete extraction (43.3%; Qualls and Richardson 1995) of microbial P using this method (Walbridge 1991). The second extractant was 0.1 mol L 21 NaOH.…”

Global patterns of plant leaf N and P in relation to temperature and latitude

“…Existing publications (7,10,(13)(14)(15) provide limited insight into broad biogeographic leaf N and P patterns. For example, alpine and arctic herbaceous plant species had higher leaf N and P when examined in colder, rather than warmer, habitats (9,16,17), but leaf N and P were either similar (17,18) or lower (19) for given tree species in colder than warmer sites, and forest communities can have regionally lower (15) or higher (20) leaf N with increasing temperatures.…”

An Old-Growth Definition for Evergreen Bay Forests and Related Seral Communities

“…Richardson and Gibbons (1993) summarized Walbridge's (1986) soil chemistry work on pocosins and bay forests in North Carolina and found results similar to those of Bridgham and Richardson (1993) described above.…”