Artefacts of the pot environment on soil nutrient availability: implications for the interpretation of ecological studies

Abstract

Pot experiments are frequently used to examine plant, soil, and microbial interactions that cannot be studied in situ. Although impacts of the pot environment on seedling growth have long been recognized, they are rarely addressed directly in current ecological studies. Here we examine how commonly used soil conditioners, often necessary to maintain adequate drainage in pots, can influence nutrient availability and seedling growth. Balsawood (Ochroma pyramidalis) seedlings were grown in central Panama in soil combined in a 50:50 mix with one of the following soil conditioners: marine sand, pure sand, perlite, vermiculite, or rice husks. Soil nutrient availability, foliar N and P, and seedling growth were compared after 1 month. Rice husks dramatically reduced soil nitrate, seedling growth, and foliar N. Other conditioners had smaller effects on growth, although vermiculite may be a significant source of base cations in infertile soils. Marine sand had a strong neutralizing effect on acidic soil due to the presence of calcareous shell fragments.Effects of soil conditioners need to be added to other known artifacts of the pot environment influencing nutrient availability, including alterations to N mineralization rates relative to bulk soil, and pot-size effects on N:P availability. These artifacts can strongly influence plant performance and therefore the interpretation of ecological studies.

Two tropical conifers show strong growth and water-use efficiency responses to altered CO2concentration

“…, but was reduced by the addition of the rice husks (Dalling et al, 2013), counteracting the observation of excess N mineralization observed in un-amended soils (e.g. Johnson et al, 1995;Ross and Hales, 2003).…”

“…Soil was air-dried ($27 C) and passed through a 10-mm sieve. Details of the soil used in the experiment and its analysis are described in Dalling et al (2013). Briefly, the soil has a high concentration of exchangeable phosphate (17Á8 mg P kg À1 ), based on extraction from anion exchange membranes, and a high effective cation exchange capacity (53Á2 cmol c kg…”

“…Here we added rice husks as a soil conditioner to stimulate microbial uptake of N. In a previous pot experiment, rice husk addition reduced soil-extractable nitrate availability 10-fold over 7 weeks (Dalling et al, 2013), providing soil conditions more in keeping with the low (<5 mg N g…”

Soil fertility and disturbance interact to drive contrasting responses of co‐occurring native and nonnative species

“…,b, Dalling et al. ). All shoot and root material was removed separately for each plant, dried (60°C, 72 h) and weighed.…”

Testing for allelopathy in invasive plants: it all depends on the substrate!

“…Oftentimes, pot experiments are used to estimate the strength of plantplant interactions and to establish the dominance hierarchy of different species. Pot experiments provide better control than experiments in the field, but they can be plagued by artefacts caused by the limited pot volumes (de Kroon 2007) or unrealistic physicochemical properties of the substrate (Passioura 2006;Dalling et al 2013). Taken together, previous research suggests that substrate should be taken into account when testing for plant competition with pot experiments.…”