ABSTRACT
In this contribution we revise the type specimens of Geodia tylastra, Rhabdastrella fibrosa and Geodia corticostylifera, adding new photographs of preserved specimens, skeleton sections, and scanning electron micrographs of the spicules. We demonstrate that the three species are synonyms, with priority to the older name G. tylastra Boury-Esnault, 1973. We also show that Rhabdastrella fibrosa sensu Van Soest (2017) differs from the holotype in spicule composition and is here given a new name, Rhabdastrella vansoesti sp. nov. In addition, we describe a new species of Geodia, G. polytriaena sp. nov., and new records of G. glariosa and G. tylastra from Sergipe State, in the Northeast Brazilian coast. With the description of Geodia polytriaena sp. nov. and the synonymyzation of G. corticostylifera, 20 species of Geodia are now known in the Tropical Western Atlantic Ocean.
Subject(s)
Geodia , Porifera , Animals , Brazil , MicroscopyABSTRACT
The use of grasses as cover crops in the off-season of cash crops under no-till has been largely adopted. However, soil phosphorus (P) uptake was previously shown to be reduced when ruzigrass is introduced in the rotation, affecting the viability and sustainability of this cropping system. The objective of this study was to assess the effect of ruzigrass on soil P availability and desorption kinetics under different P fertilizer application rates. A long-term field experiment where soybean (Glycine max) has been grown in rotation with ruzigrass (Urochloa ruziziensis) or fallow for 10â¯years, with the application of 0, 13, and 26â¯kgâ¯ha-1 of P, was evaluated for two consecutive years. Soil P desorption kinetics was assessed using diffusive equilibrium (DET) and gradient in thin films (DGT) techniques, as well as the DGT-induced fluxes in soils model (DIFS). Microbial biomass P (MBP) was assessed to verify if soil solution P (PDET) was reduced due to immobilization by microorganisms. Ruzigrass reduced MBP and PDET especially when P fertilizer was applied. The concentration of labile P (PDGT) was also lower after ruzigrass than in fallow. The soil ability to resupply P to soil solution was lower after ruzigrass regardless of P rates due to a slower desorption in response to the perturbation imposed by DGT. Growing ruzigrass as cover crop in the soybean off-season decreases soil P availability regardless of P fertilizer application rates by fundamentally reducing P mobility and P resupply from soil solid phase into soil solution.
ABSTRACT
BACKGROUND: Phosphorus (P) fertilizer is usually applied in excess of plant requirement and accumulates in soils due to its strong adsorption, rapid precipitation and immobilisation into unavailable forms including organic moieties. As soils are complex and diverse chemical, biochemical and biological systems, strategies to access recalcitrant soil P are often inefficient, case specific and inconsistently applicable in different soils. Finding a near-universal or at least widely applicable solution to the inefficiency in agricultural P use by plants is an important unsolved problem that has been under investigation for more than half a century. SCOPE: In this paper we critically review the strategies proposed for the remobilization of recalcitrant soil phosphorus for crops and pastures worldwide. We have additionally performed a meta-analysis of available soil 31P-NMR data to establish the potential agronomic value of different stored P forms in agricultural soils. CONCLUSIONS: Soil inorganic P stocks accounted on average for 1006 ± 115 kg ha-1 (57 ± 7%), while the monoester P pool accounted for 587 ± 32 kg ha-1 (33 ± 2%), indicating the huge potential for the future agronomic use of the soil legacy P. New impact driven research is needed in order to create solutions for the sustainable management of soil P stocks.
