Article

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: 9.81). 06/2007; 104(21):8902-6. DOI: 10.1073/pnas.0609935104
Source: PubMed

ABSTRACT 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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    • "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.
    Oecologia 10/2013; 174(2). DOI:10.1007/s00442-013-2778-5 · 3.25 Impact Factor
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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.
    Ecological Research 09/2013; 28(5). DOI:10.1007/s11284-012-0934-8 · 1.51 Impact Factor
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    • "It is noteworthy that amino acids account for only a small proportion of DON, and that the bioavailable fraction of DON is expected to be larger than that of amino acids (Neff et al., 2002). To date, only the d 15 N of 'bulk' DON can be measured routinely (Knapp et al., 2005; Koba et al., 2010a,b; Lachouani et al., 2010), but this allows exploration of whether plants indeed prefer NH þ 4 when isotopes of major dissolved N in natural environments are characterized (Houlton et al., 2007; Kahmen et al., 2008; Takebayashi et al., 2010). Thereby, the importance of DON in moss N assimilation can be estimated. "
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    ABSTRACT: Mosses, among all types of terrestrial vegetation, are excellent scavengers of anthropogenic nitrogen (N), but their utilization of dissolved organic N (DON) and their reliance on atmospheric N remain uncharacterized in natural environments, which obscures their roles in N cycles. Natural (15) N abundance of N sources (nitrate (NO3 -), ammonium (NH4 +) and DON in deposition and soil) for epilithic and terricolous mosses was analyzed at sites with different N depositions at Guiyang, China. Moss NO3 - assimilation was inhibited substantially by the high supply of NH4 + and DON. Therefore, contributions of NH4 + and DON to moss N were partitioned using isotopic mass-balance methods. The N contributions averaged 56% and 46% from atmospheric NH4 +, and 44% and 17% from atmospheric DON in epilithic and terricolous mosses, respectively. In terricolous mosses, soil NH4 + and soil DON accounted for 16% and 21% of bulk N, which are higher than current estimations obtained using (15) N-labeling methods. Moreover, anthropogenic NH4 + deposition suppressed utilization of DON and soil N because of the preference of moss for NH4 + under elevated NH4 + deposition. These results underscore the dominance of, and preference for, atmospheric NH4 + in moss N utilization, and highlight the importance of considering DON and soil N sources when estimating moss N sequestration and the impacts of N deposition on mosses.
    New Phytologist 05/2013; 199(2). DOI:10.1111/nph.12284 · 7.67 Impact Factor
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