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A gradient of nutrient enrichment reveals nonlinear impacts of fertilization on Arctic plant diversity and ecosystem function

View Article: PubMed Central - PubMed

ABSTRACT

Rapid environmental change at high latitudes is predicted to greatly alter the diversity, structure, and function of plant communities, resulting in changes in the pools and fluxes of nutrients. In Arctic tundra, increased nitrogen (N) and phosphorus (P) availability accompanying warming is known to impact plant diversity and ecosystem function; however, to date, most studies examining Arctic nutrient enrichment focus on the impact of relatively large (>25x estimated naturally occurring N enrichment) doses of nutrients on plant community composition and net primary productivity. To understand the impacts of Arctic nutrient enrichment, we examined plant community composition and the capacity for ecosystem function (net ecosystem exchange, ecosystem respiration, and gross primary production) across a gradient of experimental N and P addition expected to more closely approximate warming‐induced fertilization. In addition, we compared our measured ecosystem CO2 flux data to a widely used Arctic ecosystem exchange model to investigate the ability to predict the capacity for CO2 exchange with nutrient addition. We observed declines in abundance‐weighted plant diversity at low levels of nutrient enrichment, but species richness and the capacity for ecosystem carbon uptake did not change until the highest level of fertilization. When we compared our measured data to the model, we found that the model explained roughly 30%–50% of the variance in the observed data, depending on the flux variable, and the relationship weakened at high levels of enrichment. Our results suggest that while a relatively small amount of nutrient enrichment impacts plant diversity, only relatively large levels of fertilization—over an order of magnitude or more than warming‐induced rates—significantly alter the capacity for tundra CO2 exchange. Overall, our findings highlight the value of measuring and modeling the impacts of a nutrient enrichment gradient, as warming‐related nutrient availability may impact ecosystems differently than single‐level fertilization experiments.

No MeSH data available.


Boxplots showing a comparison of the subset of measured CO2 flux data (the subset for which we have leaf area index values) and modeled data across nutrient treatments (N = 3 for both modeled and measured data at each treatment level). Statistically significant differences between measured and modeled data within a treatment are indicated by nonoverlapping symbols (i.e., * and +). Measured ER values were significantly higher than modeled values in the F10 treatment. There were no statistically significant differences between measured and modeled NEE or GPP by nonoverlapping symbols (i.e., * and +)
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ece32863-fig-0005: Boxplots showing a comparison of the subset of measured CO2 flux data (the subset for which we have leaf area index values) and modeled data across nutrient treatments (N = 3 for both modeled and measured data at each treatment level). Statistically significant differences between measured and modeled data within a treatment are indicated by nonoverlapping symbols (i.e., * and +). Measured ER values were significantly higher than modeled values in the F10 treatment. There were no statistically significant differences between measured and modeled NEE or GPP by nonoverlapping symbols (i.e., * and +)

Mentions: We calculated modeled NEE, GPP, and ER using a model that required the input of three measured variables: LAI, PAR, and T. LAI ranged from 0.58 to 1.63 (M = 1.11, SE = 0.04) m2 leaf/m2 ground, PAR ranged from 909 to 1,779 (M = 1406, SE = 37.07) μmol photons m−2 ground s−1, and T from 16.58 to 25.17 (M = 21.94, SE = 0.34) °C (Figure 4a–c). For modeled values, NEEM ranged from −11.20 to −3.41 (M = −7.09, SE = 0.30), ERM from 2.47 to 6.28 (M = 4.38, SE = 0.14), and GPPM from 5.88 to 16.28 (M = 11.47, SE = 0.42), all μmol CO2 m−2 ground s−1. We found similar trends for modeled NEE and GPP as those observed for measured fluxes. NEE and GPP were significantly greater (more negative in the case of NEE) at F10 than all other treatments except for F5 (Figure 5a,c). We did not find any significant differences in modeled ER across nutrient addition treatments (Figure 5b).


A gradient of nutrient enrichment reveals nonlinear impacts of fertilization on Arctic plant diversity and ecosystem function
Boxplots showing a comparison of the subset of measured CO2 flux data (the subset for which we have leaf area index values) and modeled data across nutrient treatments (N = 3 for both modeled and measured data at each treatment level). Statistically significant differences between measured and modeled data within a treatment are indicated by nonoverlapping symbols (i.e., * and +). Measured ER values were significantly higher than modeled values in the F10 treatment. There were no statistically significant differences between measured and modeled NEE or GPP by nonoverlapping symbols (i.e., * and +)
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Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5383475&req=5

ece32863-fig-0005: Boxplots showing a comparison of the subset of measured CO2 flux data (the subset for which we have leaf area index values) and modeled data across nutrient treatments (N = 3 for both modeled and measured data at each treatment level). Statistically significant differences between measured and modeled data within a treatment are indicated by nonoverlapping symbols (i.e., * and +). Measured ER values were significantly higher than modeled values in the F10 treatment. There were no statistically significant differences between measured and modeled NEE or GPP by nonoverlapping symbols (i.e., * and +)
Mentions: We calculated modeled NEE, GPP, and ER using a model that required the input of three measured variables: LAI, PAR, and T. LAI ranged from 0.58 to 1.63 (M = 1.11, SE = 0.04) m2 leaf/m2 ground, PAR ranged from 909 to 1,779 (M = 1406, SE = 37.07) μmol photons m−2 ground s−1, and T from 16.58 to 25.17 (M = 21.94, SE = 0.34) °C (Figure 4a–c). For modeled values, NEEM ranged from −11.20 to −3.41 (M = −7.09, SE = 0.30), ERM from 2.47 to 6.28 (M = 4.38, SE = 0.14), and GPPM from 5.88 to 16.28 (M = 11.47, SE = 0.42), all μmol CO2 m−2 ground s−1. We found similar trends for modeled NEE and GPP as those observed for measured fluxes. NEE and GPP were significantly greater (more negative in the case of NEE) at F10 than all other treatments except for F5 (Figure 5a,c). We did not find any significant differences in modeled ER across nutrient addition treatments (Figure 5b).

View Article: PubMed Central - PubMed

ABSTRACT

Rapid environmental change at high latitudes is predicted to greatly alter the diversity, structure, and function of plant communities, resulting in changes in the pools and fluxes of nutrients. In Arctic tundra, increased nitrogen (N) and phosphorus (P) availability accompanying warming is known to impact plant diversity and ecosystem function; however, to date, most studies examining Arctic nutrient enrichment focus on the impact of relatively large (>25x estimated naturally occurring N enrichment) doses of nutrients on plant community composition and net primary productivity. To understand the impacts of Arctic nutrient enrichment, we examined plant community composition and the capacity for ecosystem function (net ecosystem exchange, ecosystem respiration, and gross primary production) across a gradient of experimental N and P addition expected to more closely approximate warming‐induced fertilization. In addition, we compared our measured ecosystem CO2 flux data to a widely used Arctic ecosystem exchange model to investigate the ability to predict the capacity for CO2 exchange with nutrient addition. We observed declines in abundance‐weighted plant diversity at low levels of nutrient enrichment, but species richness and the capacity for ecosystem carbon uptake did not change until the highest level of fertilization. When we compared our measured data to the model, we found that the model explained roughly 30%–50% of the variance in the observed data, depending on the flux variable, and the relationship weakened at high levels of enrichment. Our results suggest that while a relatively small amount of nutrient enrichment impacts plant diversity, only relatively large levels of fertilization—over an order of magnitude or more than warming‐induced rates—significantly alter the capacity for tundra CO2 exchange. Overall, our findings highlight the value of measuring and modeling the impacts of a nutrient enrichment gradient, as warming‐related nutrient availability may impact ecosystems differently than single‐level fertilization experiments.

No MeSH data available.