Stable Isotope Biogeochemistry of Seabird Guano Fertilization: Results from Growth Chamber Studies with Maize (Zea Mays)

Abstract

Background Stable isotope analysis is being utilized with increasing regularity to examine a wide range of issues (diet, habitat use, migration) in ecology, geology, archaeology, and related disciplines. A crucial component to these studies is a thorough understanding of the range and causes of baseline isotopic variation, which is relatively poorly understood for nitrogen (δ 15 N). Animal excrement is known to impact plant δ 15 N values, but the effects of seabird guano have not been systematically studied from an agricultural or horticultural standpoint. Methodology/Principal Findings This paper presents isotopic (δ 13 C and δ 15 N) and vital data for maize ( Zea mays ) fertilized with Peruvian seabird guano under controlled conditions. The level of 15 N enrichment in fertilized plants is very large, with δ 15 N values ranging between 25.5 and 44.7‰ depending on the tissue and amount of fertilizer applied; comparatively, control plant δ 15 N values ranged between −0.3 and 5.7‰. Intraplant and temporal variability in δ 15 N values were large, particularly for the guano-fertilized plants, which can be attributed to changes in the availability of guano-derived N over time, and the reliance of stored vs. absorbed N. Plant δ 13 C values were not significantly impacted by guano fertilization. High concentrations of seabird guano inhibited maize germination and maize growth. Moreover, high levels of seabird guano greatly impacted the N metabolism of the plants, resulting in significantly higher tissue N content, particularly in the stalk. Conclusions/Significance The results presented in this study demonstrate the very large impact of seabird guano on maize δ 15 N values. The use of seabird guano as a fertilizer can thus be traced using stable isotope analysis in food chemistry applications (certification of organic inputs). Furthermore, the fertilization of maize with seabird guano creates an isotopic signature very similar to a high-trophic level marine resource, which must be considered when interpreting isotopic data from archaeological material.

Complexities of nitrogen isotope biogeochemistry in plant-soil systems: implications for the study of ancient agricultural and animal management practices

“…MZ, maize; RC, rice; S, squash; B, bean; P, pepper. Data obtained from: a Szpak et al (2012a), b Szpak et al (2012b), c Choi et al (2002), d Yun et al (2011), e Szpak et al (2014), f Del Amor et al (2008). …”

Carbon and Nitrogen Isotopic Survey of Northern Peruvian Plants: Baselines for Paleodietary and Paleoecological Studies

“…Animal fertilizers are characterized by extremely variable δ 15 N values depending on the relative proportions of N-bearing species in the fertilizer (e.g. urea, uric acid, ammonium, organic matter) [143]. Manures consisting primarily of solid waste derived from terrestrial herbivores tend to have δ 15 N values between 2 and 8 ‰ [144], while those that contain a mix of solid and liquid waste (slurry fertilizers) tend to have higher δ 15 N values, often between 6 and 15 ‰ [145], [146].…”

“…Manures consisting primarily of solid waste derived from terrestrial herbivores tend to have δ 15 N values between 2 and 8 ‰ [144], while those that contain a mix of solid and liquid waste (slurry fertilizers) tend to have higher δ 15 N values, often between 6 and 15 ‰ [145], [146]. The highest δ 15 N values for animal fertilizers (>25 ‰) have been recorded for seabird guano [143], [147], which consists primarily of uric acid and is subject to significant NH 4 + volatilization. The addition of animal fertilizer N to the soil therefore adds an N source with an isotopic composition that is usually enriched in 15 N relative to endogenous soil N. This results in higher δ 15 N values for plants growing in soils fertilized with animal waste than those plants growing in unfertilized soil or soils fertilized with chemical fertilizers [143], [145]–[147].…”

Diet of the prehistoric population of Rapa Nui (Easter Island, Chile) shows environmental adaptation and resilience

“…Manuring can markedly increase the 15 N content of agricultural soils, and this 15 N enrichment is passed on through the food chain to humans (Fraser et al, 2011). The use of seabird guano for manure has been proposed as a mechanism for the elevated δ 15 N values observed in Rapa Nui human collagen (Commendador et al, 2013; Fogel et al, 1997), and it has been demonstrated that guano as a fertilizer can have a substantial effect on δ 15 N values in plants (Szpak, 2014; Szpak, Longstaffe, Millaire, & White, 2012). The manavai were likely used as deposits for household waste (Hunt & Lipo, 2011), and chicken husbandry may also have contributed to the elevated δ 15 N values observed.…”