Nutrient retention by tropical ecosystems: soil adsorption and plant absorption as synergistic processes

Abstract

Laboratory and growth-chamber experiments were used to evaluate whether there was evidence for nutrient retention by tropical terrestrial ecosystems being a two-stage process involving first soil adsorption and then plant absorption. Quartz sand with and without Fe and Al oxide coatings were treated with nutrient solution, then subjected to a leaching regime that simulated early wet-season conditions at a tropical location. Nutrient cations applied were rapidly lost in the initial leaches from quartz sand without oxide coatings, but showed a more gradual loss from oxide-coated sand, indicating temporary adsorption by the latter. In a second experiment, oxide-coated sand with and without seedlings of Grevillea robusta (a non-mycorrhizal tree species) were subjected to a similar treatment and leaching losses were compared. The presence of seedlings significantly reduced the losses of all nutrient cations, with the effect being minimal for Na and greatest for K, confirming that plants can gain access to temporarily adsorbed nutrients. More typical tropical soil-vegetation systems are likely to possess properties that magnify both the adsorptive and absorptive processes that have been documented in these experiments, justifying extrapolation of the experimental results to these natural systems. The existence of a two-stage process of nutrient retention provides a plausible explanation for the resistance of most tropical ecosystems to rapid loss of nutrients following events such as fires, which provide acute nutrient loading to the system.

Macronutrients along the sediment profile in a subtropical monsoonal wetland in India

“…Two factors might be responsible for lowering P level in wetland sediments; one is plant uptake and the other the sorption of the element on to the mineral matrix. However, plant uptake seems to be a major factor (Kellman 2002;Schrumpf et al 2006). This is also supported by the results of the LSD test among the sediment layers.…”

“…This in turn is subject to the quality of the detritus (Lovett et al 2004), period of water stagnation (Zech et al 1997), presence and/or the activity of macro invertebrates (Bunn 1988b), insects , microbes (Rejmánková et al 2004), and other abiotic properties of the study site/processes (Manlay et al 2004). Kellman (2002) also reports association of SOM with other major nutrients that could be taken up by plants as a function of decomposition and mineralization. The observed value of TN was higher than the range reported by Mandal et al (2003) from North Bihar wetlands in India (0.001-0.47%).…”

Forage Nutritive Quality in the Serengeti Ecosystem: The Roles of Fire and Herbivory

“…Along with other heavy elements, Na is not volatilized during fire, and it may become concentrated in ash deposits (Kellman et al 1985;DeBano et al 1998;Mills and Fey 2004). Evidence exists for slight but significant increases in plant Na absorption following fire (Kellman 2002), which may occur passively through increased uptake rates in plants that have no metabolic demand for Na or actively for C 4 or halophytic species (Brownell 1979;Marschner 1995;McNaughton et al 1997). Similarly, increased inorganic P availability in ash deposits, coupled with the replacement of older leaf tissues, likely explains increased leaf P with fire frequency in our study (Jensen et al 2001).…”

Regeneration of Juvenile Woody Plants after Fire in a Seasonally Dry Tropical Forest of Southern India

“…Nutrients released after a fire are retained for short periods in top layers of soil (Kellman et al 1985, Jensen et al 2001. Although juveniles could benefit from a sudden nutrient influx (Kellman 2002), so too would the grasses. While the possibility of increased juvenile growth due to an elevated level of nutrients cannot be ruled out, the fact that juveniles grow faster during the pre-monsoon season one full year after the fire event implies a possible utilization of stored resources for rapid growth.…”