Spatially robust estimates of biological nitrogen (N) fixation imply substantial human alteration of the tropical N cycle

Sullivan, Benjamin W.; Smith, William K.; Townsend, Alan R.; Nasto, Megan K.; Reed, Sasha C.; Chazdon, Robin L.; Cleveland, Cory C.

doi:10.1073/pnas.1320646111

Cited by 149 publications

(200 citation statements)

References 59 publications

Supporting

Mentioning

185

Contrasting

Unclassified

Order By: Relevance

“…Facultative symbioses in the tropics make evolutionary sense inasmuch as soil nitrogen availability is typically greater there than at the poles and nitrogen fixation carries a carbon cost for the plant. In support, concurrent research suggested that rates of nitrogen fixation may be less in N-rich tropical forests than previously thought (10). N 2 FP differ in their distribution in northern and southern hemispheres, albeit that N 2 FP are common in the tropics in both hemispheres.…”

mentioning

confidence: 67%

“…That insurance and other nitrogen-related advantages have facilitated the spread of N 2 FP throughout the globe and their contributions to global N cycles (37,38). The facultative nature of the symbiosis with respect to soil nitrogen (4,(8)(9)(10)) is augmented by its flexibility in relation to soil water-N 2 FP seldom fix nitrogen under drought conditions (29)(30)(31), although their ability to nodulate may be unimpeded (39) and help restore fixation after drought is relieved. These features facilitate the dominant role played by N 2 FP in both wet and dry tropics as well as large areas of temperate and Mediterranean climates.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Legumes are different: Leaf nitrogen, photosynthesis, and water use efficiency

Adams

Turnbull

Sprent

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

196

185

View full text Add to dashboard Cite

Using robust, pairwise comparisons and a global dataset, we show that nitrogen concentration per unit leaf mass for nitrogen-fixing plants (N 2 FP; mainly legumes plus some actinorhizal species) in nonagricultural ecosystems is universally greater (43-100%) than that for other plants (OP). This difference is maintained across Koppen climate zones and growth forms and strongest in the wet tropics and within deciduous angiosperms. N 2 FP mostly show a similar advantage over OP in nitrogen per leaf area (N area ), even in arid climates, despite diazotrophy being sensitive to drought. We also show that, for most N 2 FP, carbon fixation by photosynthesis (A sat ) and stomatal conductance (g s ) are not related to N area -in distinct challenge to current theories that place the leaf nitrogen-A sat relationship at the center of explanations of plant fitness and competitive ability. Among N 2 FP, only forbs displayed an N area -g s relationship similar to that for OP, whereas intrinsic water use efficiency (WUE i ; A sat /g s ) was positively related to N area for woody N 2 FP. Enhanced foliar nitrogen (relative to OP) contributes strongly to other evolutionarily advantageous attributes of legumes, such as seed nitrogen and herbivore defense. These alternate explanations of clear differences in leaf N between N 2 FP and OP have significant implications (e.g., for global models of carbon fluxes based on relationships between leaf N and A sat ). Combined, greater WUE and leaf nitrogen-in a variety of forms-enhance fitness and survival of genomes of N 2 FP, particularly in arid and semiarid climates.legume | actinorhizal species | nitrogen | photosynthesis | water use efficiency T hrough symbioses with diazotrophic bacteria, legumes and other N 2 -fixing plants (N 2 FP) acquire atmospheric dinitrogen (N 2 ) and are widely expected to maintain greater leaf nitrogen than nonfixing or other plants (OP) (1). N 2 FP can profoundly influence both ecosystem development and responses to changing climate by alleviating nitrogen shortages that limit capacity of ecosystems to fix and sequester CO 2 (2-4). A central tenet of traitbased ecology (5, 6) is that carbon fixation and transpiration are directly related to leaf nitrogen; in turn, leaf nitrogen is used to drive global models of carbon (and water) exchanges between plants and the atmosphere (7).The distribution, abundance, and activity of N 2 FP in terrestrial ecosystems have remained unexplained, even "paradoxical" (8, 9), especially in relation to local and global nitrogen cycles. For the northern hemisphere, one recent explanation of the distribution of N 2 FP (2) and their dominance in wet tropical forests relied on their greater ability to acquire phosphorus from old tropical soils and temperature maxima for N 2 fixation of around 25°C (i.e., similar to prevailing temperatures in the tropics). Menge et al. (8) subsequently noted that the diazotrophic symbioses are typically rhizobial and facultative toward the tropics but actinorhizal and obligate north of about 35°N. Fac...

show abstract

mentioning

confidence: 67%

Section: Discussionmentioning

confidence: 99%

Legumes are different: Leaf nitrogen, photosynthesis, and water use efficiency

Adams

Turnbull

Sprent

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

196

185

View full text Add to dashboard Cite

show abstract

“…Ecosystem Processes: Nitrogen Cycling N 2 fixation, N mineralization, and (de)nitrification are all regulated by the availability of N. Evidence from wet forests suggests that legumes down-regulate symbiotic N 2 fixation as soil N becomes more available through secondary succession (Batterman et al, 2013;Sullivan et al, 2014a). Similarly, rates of free-living N 2 fixation in soils and the forest floor may decrease with increasing N availability, as seen in wet forests of Puerto Rico (Cusack et al, 2009).…”

Section: Ecosystem Processes: Soil Carbon Dynamicsmentioning

confidence: 99%

“…Because of rapidly increasing rates of N deposition across the tropics (Hietz et al, 2011;Sullivan et al, 2014a), most of the studies included in our review focus on effects of N addition. We develop a conceptual model of how added N affects TDFs; because TDFs may be N-or P-limited, our model considers how responses to N addition may vary between forests with low or high P availability.…”

Section: Introductionmentioning

confidence: 99%

Nutrient addition effects on tropical dry forests: a mini-review from microbial to ecosystem scales

et al. 2015

View full text Add to dashboard Cite

Humans have more than doubled inputs of reactive nitrogen globally and greatly accelerated the biogeochemical cycles of phosphorus and metals. However, the impacts of increased element mobility on tropical ecosystems remain poorly quantified, particularly for the vast tropical dry forest biome. Tropical dry forests are characterized by marked seasonality, relatively little precipitation, and high heterogeneity in plant functional diversity and soil chemistry. For these reasons, increased nutrient deposition may affect tropical dry forests differently than wet tropical or temperate forests. Here, we review studies that investigated how nutrient availability affects ecosystem and community processes from the microsite to ecosystem scales in tropical dry forests. The effects of N and P addition on ecosystem carbon cycling and plant and microbial dynamics depend on forest successional stage, soil parent material, and rainfall regime. Responses may depend on whether overall productivity is N-vs. P-limited, although data to test this hypothesis are limited. These results highlight the many important gaps in our understanding of tropical dry forest responses to global change. Large-scale experiments are required to resolve these uncertainties.

show abstract

“…Note that the biologic fixation term was not used for P calculation. Since the tea plantation does not use leguminous crop as fertilizers and the biological fixation in tropical forest is known to be less than 10 kg N ha −1 yr −1 (Sullivan et al, 2014), the IN fix is assumed to be between 0 and 10 kg N ha −1 yr −1 . We did not include the loss through denitrification and volatilization within tea field in the calculation of N retention ratio because we did not have good estimates.…”

Section: Element Fluxesmentioning

confidence: 99%

Effects of mountain tea plantations on nutrient cycling at upstream watersheds

Lin

Shaner

Wang

et al. 2015

Hydrol. Earth Syst. Sci.

View full text Add to dashboard Cite

Abstract. The expansion of agriculture to rugged mountains can exacerbate negative impacts of agricultural activities on ecosystem function. In this study, we monitored streamwater and rainfall chemistry of mountain watersheds at the Feitsui Reservoir Watershed in northern Taiwan to examine the effects of agriculture on watershed nutrient cycling. We found that the greater the proportion of tea plantation cover, the higher the concentrations of fertilizer-associated ions (NO − 3 , K + ) in streamwater of the four mountain watersheds examined; on the other hand, the concentrations of the ions that are rich in soils (SO 2− 4 , Ca 2+ , Mg 2+ ) did not increase with the proportion of tea plantation cover, suggesting that agriculture enriched fertilizer-associated nutrients in streamwater. Of the two watersheds for which rainfall chemistry was available, the one with higher proportion of tea plantation cover had higher concentrations of ions in rainfall and retained less nitrogen in proportion to input compared to the more pristine watershed, suggesting that agriculture can influence atmospheric deposition of nutrients and a system's ability to retain nutrients. As expected, we found that a forested watershed downstream of agricultural activities can dilute the concentrations of NO − 3 in streamwater by more than 70 %, indicating that such a landscape configuration helps mitigate nutrient enrichment in aquatic systems even for watersheds with steep topography. We estimated that tea plantation at our study site contributed approximately 450 kg ha −1 yr −1 of NO 3 -N via streamwater, an order of magnitude greater than previously reported for agricultural lands around the globe, which can only be matched by areas under intense fertilizer use. Furthermore, we constructed watershed N fluxes to show that excessive leaching of N, and additional loss to the atmosphere via volatilization and denitrification can occur under intense fertilizer use. In summary, this study demonstrated the pervasive impacts of agricultural activities, especially excessive fertilization, on ecosystem nutrient cycling at mountain watersheds.

show abstract

Spatially robust estimates of biological nitrogen (N) fixation imply substantial human alteration of the tropical N cycle

Cited by 149 publications

References 59 publications

Legumes are different: Leaf nitrogen, photosynthesis, and water use efficiency

Legumes are different: Leaf nitrogen, photosynthesis, and water use efficiency

Nutrient addition effects on tropical dry forests: a mini-review from microbial to ecosystem scales

Effects of mountain tea plantations on nutrient cycling at upstream watersheds

Contact Info

Product

Resources

About