The nutrient status of tropical forests is commonly assessed by measuring inorganic nutrients extracted from soil, yet samples from remote research sites may be stored for prolonged periods of time before analysis. We assessed the influence of soil storage conditions on extractable nutrients in three lowland tropical forests soils from the Republic of Panama. The soils spanned a strong rainfall gradient and contained contrasting chemical and physical properties. Storage treatments were: (i) room temperature (22°C in the dark), (ii) refrigerated (4°C in the dark), (iii) air dried (10 d at 22°C and 55% humidity), and (iv) frozen (−35°C). Ammonium and NO3 were extremely unstable and concentrations changed considerably within hours of sampling. Phosphate extracted by anion‐exchange membranes also changed rapidly following sampling, although cations (Ca, K, and Mg) extracted in Mehlich‐3 solution were less influenced by storage. Soil pH declined slowly in all samples during field‐moist storage (4 and 22°C). Freezing and air drying generally caused significant changes in extractable nutrients, although the effects varied among soils and nutrients. We therefore conclude that inorganic nutrients should be extracted from tropical forest soils within 24 h of sampling, and preferably on the day of sampling for N fractions, to ensure that values represent field conditions. Where this is not possible, rapid air drying or storage of field‐moist samples may be acceptable for some measurements (e.g., PO4, cations, pH), but are unlikely to provide realistic measurements of inorganic N.

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We conducted monthly measurements of extractable soil nutrients, including N, P, base cations, and micronutrients, as well as the potential toxin Al, in a long‐term fertilization experiment in lowland tropical rain forest in the Republic of Panama. Our prediction was that the response of individual nutrients to seasonal climate and fertilizer addition would vary depending on the nature of their biogeochemical cycles. We detected significant seasonal variation in soil pH and all nutrients measured, although only extractable K concentrations were greater in the early wet season, while extractable phosphate varied little in plots that did not receive P addition. A decade of N addition increased soil nitrate, had no effect on extractable ammonium, and decreased soil pH (∼0.8 units in plots receiving only N). The decline in pH caused a corresponding decline in extractable base cations (Ca and K) and increased extractable Al, highlighting an important but poorly understood consequence of long‐term atmospheric N deposition onto tropical forests. A decade of P addition increased extractable phosphate by 50‐fold, indicating that chronic fertilizer addition has overcome the high phosphate sorption capacity of the soil. Potassium addition without N increased extractable soil K by 91%, but only by 25% when K was added in combination with N, suggesting that the previously reported N × K interactive effect on trunk growth rates could be a true response to N addition. Extractable Cu and Zn were increased twofold by micronutrient fertilizer addition, were reduced in the dry season, but were not affected by N addition (i.e., soil acidification). We conclude that the response of extractable nutrients to seasonal climate and fertilizer addition varies among nutrients, and suggest that greater attention be paid to the biological implications of acidification in response to long‐term atmospheric N deposition onto strongly‐weathered tropical forest soils.

We investigate the effect of the temperature-size rule upon zooids of the tropical American bryozoan Cupuladria exfragminis. Results show that mean zooid length, zooid width and zooid area vary significantly between clonal replicates of C. exfragminis kept under different controlled temperature conditions. Significantly larger zooids are produced during times of lowered water temperature that are comparable with the temperatures that occur during seasonal upwelling along the Pacific coast of Panama where the animal lives in abundance. Interpolation of data suggests that a drop of 1 °C causes a 5% increase in zooid size, and that almost all variation in zooid size in natural populations can be explained by temperature. Results are discussed in context of the potential use of zooid size variation in cupuladriid bryozoans to measure the strength of seasonal upwelling in ancient seas by analysing zooid size changes in fossil colonies. The technique of cloning cupuladriid colonies by fragmentation is also discussed with reference to its benefits in experimental studies where genotypes need to be controlled or replicated.

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