A climate-driven switch in plant nitrogen acquisition within tropical forest communities

Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 06/2007; 104(21):8902-6. DOI: 10.1073/pnas.0609935104
Source: PubMed


The response of tropical forests to climate change will depend on individual plant species' nutritional strategies, which have not been defined in the case of the nitrogen nutrition that is critical to sustaining plant growth and photosynthesis. We used isotope natural abundances to show that a group of tropical plant species with diverse growth strategies (trees and ferns, canopy, and subcanopy) relied on a common pool of inorganic nitrogen, rather than specializing on different nitrogen pools. Moreover, the tropical species we examined changed their dominant nitrogen source abruptly, and in unison, in response to precipitation change. This threshold response indicates a coherent strategy among species to exploit the most available form of nitrogen in soils. The apparent community-wide flexibility in nitrogen uptake suggests that diverse species within tropical forests can physiologically track changes in nitrogen cycling caused by climate change.

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    • "Therefore, the lack of pronounced nitrogen isotopic differences among forested primate ecosystems in Africa may relate to broadly similar climatic conditions. Further investigation is needed on more subtle variation in nitrogen isotope ratios in African tropical forest plants, particularly relating to variation in N source and deposition [Hietz et al., 2011; Houlton et al., 2007]. "
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    ABSTRACT: Stable isotope analysis is a promising tool for investigating primate ecology although nuanced ecological applications remain challenging, in part due to the complex nature of isotopic variability in plant-animal systems. The aim of this study is to investigate sources of carbon and nitrogen isotopic variation at the base of primate food webs that reflect aspects of primate ecology. The majority of primates inhabit tropical forest ecosystems, which are dominated by C3 vegetation. We used stable isotope ratios in plants from Kibale National Park, Uganda, a well-studied closed-canopy tropical forest, to investigate sources of isotopic variation among C3 plants related to canopy stratification, leaf age, and plant part. Unpredictably, our results demonstrate that vertical stratification within the canopy does not explain carbon or nitrogen isotopic variation in leaves. Leaf age can be a significant source of isotopic variation, although the direction and magnitude of this difference is not consistent across tree species. Some plant parts are clearly differentiated in carbon and nitrogen isotopic composition, particularly leaves compared to non-photosynthetic parts such as reproductive parts and woody stem parts. Overall, variation in the isotopic composition of floral communities, plant species, and plant parts demonstrates that stable isotope studies must include analysis of local plant species and parts consumed by the primates under study from within the study area. Am. J. Primatol. © 2015 Wiley Periodicals, Inc.
    Full-text · Article · Oct 2015 · American Journal of Primatology
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    • "This finding is in accordance with observations in Hawaiian forests, where plants rely on a common N source: NH 4 ? or NO 3 -(Houlton et al. 2007). "
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    ABSTRACT: The foliar stable N isotope ratio (δ(15)N) can provide integrated information on ecosystem N cycling. Here we present the δ(15)N of plant and soil in four remote typical tropical rainforests (one primary and three secondary) of southern China. We aimed to examine if (1) foliar δ(15)N in the study forests is negative, as observed in other tropical and subtropical sites in eastern Asia; (2) variation in δ(15)N among different species is smaller compared to that in many N-limited temperate and boreal ecosystems; and (3) the primary forest is more N rich than the younger secondary forests and therefore is more (15)N enriched. Our results show that foliar δ(15)N ranged from -5.1 to 1.3 ‰ for 39 collected plant species with different growth strategies and mycorrhizal types, and that for 35 species it was negative. Soil NO3 (-) had low δ(15)N (-11.4 to -3.2 ‰) and plant NO3 (-) uptake could not explain the negative foliar δ(15)N values (NH4 (+) was dominant in the soil inorganic-N fraction). We suggest that negative values might be caused by isotope fractionation during soil NH4 (+) uptake and mycorrhizal N transfer, and by direct uptake of atmospheric NH3/NH4 (+). The variation in foliar δ(15)N among species (by about 6 ‰) was smaller than in many N-limited ecosystems, which is typically about or over 10 ‰. The primary forest had a larger N capital in plants than the secondary forests. Foliar δ(15)N and the enrichment factor (foliar δ(15)N minus soil δ(15)N) were higher in the primary forest than in the secondary forests, albeit differences were small, while there was no consistent pattern in soil δ(15)N between primary and secondary forests.
    Full-text · Article · Oct 2013 · Oecologia
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    • "For broadleaved species alone, the difference was usually <3& among species within the same forests (Kitayama and Iwamoto 2001; Cheng et al. 2010; Koba et al. 2010; Fang et al. 2011b). These results indicate that the trees in a given forest may utilize the same N sources as nutrition and/or that fractionation during uptake and assimilation may be similar among species (Schulze et al. 1994; Houlton et al. 2007). A study along the slope of Gongga Mountain showed no significant difference in foliar d 15 N between C 3 and C 4 plants when comparing them growing at the same altitudinal range, suggesting that even photosynthetic pathways had no influence on plant d 15 N values. "
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    ABSTRACT: Foliar δ15N has been used increasingly in research on ecosystem nitrogen (N) cycling, because it can serve as an integrator of ecosystem N cycling and thus has a potential to reveal temporal and spatial patterns of N cycling as well as how the N cycle is altered by disturbances. However, the current understanding on controls of foliar δ15N is based principally on studies from America, Europe, Australia and Africa. Here we compiled data from 65 forests at 33 sites across East Asia to explore regional patterns and what controls foliar δ15N by linking it to climate, species composition, soil depth, slope position, N deposition, and soil N availability. In East Asia, foliar δ15N ranged from −7.1 to +2.7‰. Mean foliar δ15N values for tropical, subtropical and temperate forests were all −3.1‰, which was unexpected. The patterns of foliar δ15N with precipitation, temperature and altitude were not clear. The variation in foliar δ15N among species and between different slope positions appeared to be small within a given forest. The δ15N for both bulk soil N and extractable inorganic N generally increased with soil depth as expected, strengthening the idea that deep-rooted trees may have access to 15N-enriched N. Different from the positive correlations reported across America and Europe, in East Asia we found that foliar δ15N decreased with increasing N deposition and did not relate to soil N availability. These discrepancies deserve more research to elucidate the mechanisms by which foliar δ15N is affected by ecosystem N availability at a regional scale.
    Full-text · Article · Sep 2013 · Ecological Research
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