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

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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 depicting treatment differences between three measured flux variables: net ecosystem exchange (NEE), ecosystem respiration (ER), and gross primary productivity (GPP). Asterisks denote significant differences between means (N = 3) at the highest nutrient addition treatment (F10) for all three CO2 exchange metrics
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ece32863-fig-0003: Boxplots depicting treatment differences between three measured flux variables: net ecosystem exchange (NEE), ecosystem respiration (ER), and gross primary productivity (GPP). Asterisks denote significant differences between means (N = 3) at the highest nutrient addition treatment (F10) for all three CO2 exchange metrics

Mentions: Environmental conditions were relatively stable throughout the sampling period (see Figure S1 in Supporting Information), and there were no statistically significant differences in PAR or T across sampling dates or between nutrient addition treatments (see Figure S2 in Supporting Information). Across all fluxes and treatment plots, measured NEE ranged from −9.12 to −3.61 (M = −5.62, SE = 0.20), ER from 3.73 to 8.69 (M = 5.14, SE = 0.21), and GPP from 8.52 to 16.41 (M = 10.94, SE = 0.38), all μmol CO2 m−2 ground s−1. There were statistically significant differences in GPP (p < .001), NEE (p < .01) and ER (p < .05) across nutrient addition treatments. NEE values were significantly larger (NEE was more negative indicating larger fluxes to the ecosystem) in the highest nutrient addition treatment (F10) when compared to all other treatments (Figure 3a). In addition, GPP and ER were higher at F10 than at all other treatments (Figure 3b,c).


A gradient of nutrient enrichment reveals nonlinear impacts of fertilization on Arctic plant diversity and ecosystem function
Boxplots depicting treatment differences between three measured flux variables: net ecosystem exchange (NEE), ecosystem respiration (ER), and gross primary productivity (GPP). Asterisks denote significant differences between means (N = 3) at the highest nutrient addition treatment (F10) for all three CO2 exchange metrics
© Copyright Policy - creativeCommonsBy
Related In: Results  -  Collection

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

ece32863-fig-0003: Boxplots depicting treatment differences between three measured flux variables: net ecosystem exchange (NEE), ecosystem respiration (ER), and gross primary productivity (GPP). Asterisks denote significant differences between means (N = 3) at the highest nutrient addition treatment (F10) for all three CO2 exchange metrics
Mentions: Environmental conditions were relatively stable throughout the sampling period (see Figure S1 in Supporting Information), and there were no statistically significant differences in PAR or T across sampling dates or between nutrient addition treatments (see Figure S2 in Supporting Information). Across all fluxes and treatment plots, measured NEE ranged from −9.12 to −3.61 (M = −5.62, SE = 0.20), ER from 3.73 to 8.69 (M = 5.14, SE = 0.21), and GPP from 8.52 to 16.41 (M = 10.94, SE = 0.38), all μmol CO2 m−2 ground s−1. There were statistically significant differences in GPP (p < .001), NEE (p < .01) and ER (p < .05) across nutrient addition treatments. NEE values were significantly larger (NEE was more negative indicating larger fluxes to the ecosystem) in the highest nutrient addition treatment (F10) when compared to all other treatments (Figure 3a). In addition, GPP and ER were higher at F10 than at all other treatments (Figure 3b,c).

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 (&gt;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&#8208;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&#8208;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%&ndash;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&mdash;over an order of magnitude or more than warming&#8208;induced rates&mdash;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&#8208;related nutrient availability may impact ecosystems differently than single&#8208;level fertilization experiments.

No MeSH data available.