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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.


Plant diversity by nutrient addition treatment. Species richness (S) is the number of vascular plant species in a community, and the Shannon (H) and Simpson (D) values are unitless index values representing relative abundances of species in a community. Statistically significant differences are represented by nonoverlapping symbols (N = 3). Error bars represent the standard error (SE) of the mean. (a) S was significantly lower at the highest nutrient addition treatment (F10) than all other treatments and the control. There were no significant differences between the remaining treatments or between the control and addition treatments. (b, c) H and D, respectively, decreased from the control treatment to the first addition treatment (F0.5) and again between F0.5 and all other addition treatments (F2, F5 and F10)
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ece32863-fig-0002: Plant diversity by nutrient addition treatment. Species richness (S) is the number of vascular plant species in a community, and the Shannon (H) and Simpson (D) values are unitless index values representing relative abundances of species in a community. Statistically significant differences are represented by nonoverlapping symbols (N = 3). Error bars represent the standard error (SE) of the mean. (a) S was significantly lower at the highest nutrient addition treatment (F10) than all other treatments and the control. There were no significant differences between the remaining treatments or between the control and addition treatments. (b, c) H and D, respectively, decreased from the control treatment to the first addition treatment (F0.5) and again between F0.5 and all other addition treatments (F2, F5 and F10)

Mentions: We detected a statistically significant difference in leaf area index (LAI) with nutrient addition. LAI was significantly greater in the highest nutrient addition treatment (F10) than in all other treatment levels, except for F5 (Figure 1). Mean LAI hovered around 1 for the CT, F0.5, F1, and F2 treatments, and mean LAI was 1.19 (SE = 0.04) and 1.44 (SE = 0.09) at F5 and Fl0, respectively (Figure 1). When examining plant community composition and diversity, we found strikingly divergent trends in plant species richness, the number of species in a community (S), and two abundance‐weighted measures of plant diversity, the Shannon (H) and Simpson (D) indices, in response to nutrient addition. Species richness did not decrease significantly with nutrient addition until the highest level of enrichment (Figure 2a), when mean S dropped to 8.5 (SE = 0.31) compared to 10.4 (SE = 0.20) in control plots. However, when abundance‐weighted measures of plant diversity were considered, control plots had 69% and 76% higher H and D index values, respectively, than the lowest nutrient addition treatment (F0.5) which had 39%–59% higher H values and 41%–64% higher D values than all other treatment levels (Figure 2b,c).


A gradient of nutrient enrichment reveals nonlinear impacts of fertilization on Arctic plant diversity and ecosystem function
Plant diversity by nutrient addition treatment. Species richness (S) is the number of vascular plant species in a community, and the Shannon (H) and Simpson (D) values are unitless index values representing relative abundances of species in a community. Statistically significant differences are represented by nonoverlapping symbols (N = 3). Error bars represent the standard error (SE) of the mean. (a) S was significantly lower at the highest nutrient addition treatment (F10) than all other treatments and the control. There were no significant differences between the remaining treatments or between the control and addition treatments. (b, c) H and D, respectively, decreased from the control treatment to the first addition treatment (F0.5) and again between F0.5 and all other addition treatments (F2, F5 and F10)
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ece32863-fig-0002: Plant diversity by nutrient addition treatment. Species richness (S) is the number of vascular plant species in a community, and the Shannon (H) and Simpson (D) values are unitless index values representing relative abundances of species in a community. Statistically significant differences are represented by nonoverlapping symbols (N = 3). Error bars represent the standard error (SE) of the mean. (a) S was significantly lower at the highest nutrient addition treatment (F10) than all other treatments and the control. There were no significant differences between the remaining treatments or between the control and addition treatments. (b, c) H and D, respectively, decreased from the control treatment to the first addition treatment (F0.5) and again between F0.5 and all other addition treatments (F2, F5 and F10)
Mentions: We detected a statistically significant difference in leaf area index (LAI) with nutrient addition. LAI was significantly greater in the highest nutrient addition treatment (F10) than in all other treatment levels, except for F5 (Figure 1). Mean LAI hovered around 1 for the CT, F0.5, F1, and F2 treatments, and mean LAI was 1.19 (SE = 0.04) and 1.44 (SE = 0.09) at F5 and Fl0, respectively (Figure 1). When examining plant community composition and diversity, we found strikingly divergent trends in plant species richness, the number of species in a community (S), and two abundance‐weighted measures of plant diversity, the Shannon (H) and Simpson (D) indices, in response to nutrient addition. Species richness did not decrease significantly with nutrient addition until the highest level of enrichment (Figure 2a), when mean S dropped to 8.5 (SE = 0.31) compared to 10.4 (SE = 0.20) in control plots. However, when abundance‐weighted measures of plant diversity were considered, control plots had 69% and 76% higher H and D index values, respectively, than the lowest nutrient addition treatment (F0.5) which had 39%–59% higher H values and 41%–64% higher D values than all other treatment levels (Figure 2b,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 (>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.