Insensitivity of Soil Microbial Activity to Temporal Variation in Soil N in Subarctic Tundra: Evidence from Responses to Large Migratory Grazers

Stark, Sari; Väisänen, Maria

doi:10.1007/s10021-014-9768-2

Cited by 40 publications

(62 citation statements)

References 42 publications

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“…The exclusion of grazing amplified the changes induced by decadal heavy grazing intensity (Olofsson et al. , Stark and Väisänen ) by increasing vascular vegetation and graminoids, decreasing bryophytes and increasing microbial activity for carbon decomposition. Thus, instead of bringing the system towards a state prior to grazing, our results suggest that grazer exclusion may induce a further shift of an ecosystem.…”

Section: Discussionmentioning

confidence: 99%

“…Along the difference in vegetation, heavy grazing has increased decomposition rates and nutrient availability and decreased the fungal : bacterial ratio in the soil when compared to the lightly grazed, shrub‐dominated tundra (Olofsson et al. , Stark and Väisänen , Männistö et al. ).…”

Section: Methodsmentioning

confidence: 99%

“…). Further, the effects of grazer exclosures are likely different from the comparison among long‐term grazing regimes as the grazing‐induced changes in ecosystem processes may have become independent of the actual grazing event (Stark and Väisänen , Egelkraut et al. ).…”

Section: Introductionmentioning

confidence: 99%

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Removal of grazers alters the response of tundra soil carbon to warming and enhanced nitrogen availability

Ylänne

Kaarlejärvi

Väisänen

et al. 2019

Ecological Monographs

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The circumpolar Arctic is currently facing multiple global changes that have the potential to alter the capacity of tundra soils to store carbon. Yet, predicting changes in soil carbon is hindered by the fact that multiple factors simultaneously control processes sustaining carbon storage and we do not understand how they act in concert. Here, we investigated the effects of warmer temperatures, enhanced soil nitrogen availability, and the combination of these on tundra carbon stocks at three different grazing regimes: on areas with over 50‐yr history of either light or heavy reindeer grazing and in 5‐yr‐old exlosures in the heavily grazed area. In line with earlier reports, warming generally decreased soil carbon stocks. However, our results suggest that the mechanisms by which warming decreases carbon storage depend on grazing intensity: under long‐term light grazing soil carbon losses were linked to higher shrub abundance and higher enzymatic activities, whereas under long‐term heavy grazing, carbon losses were linked to drier soils and higher enzymatic activities. Importantly, under enhanced soil nitrogen availability, warming did not induce soil carbon losses under either of the long‐term grazing regimes, whereas inside exclosures in the heavily grazed area, also the combination of warming and enhanced nutrient availability induced soil carbon loss. Grazing on its own did not influence the soil carbon stocks. These results reveal that accounting for the effect of warming or grazing alone is not sufficient to reliably predict future soil carbon storage in the tundra. Instead, the joint effects of multiple global changes need to be accounted for, with a special focus given to abrupt changes in grazing currently taking place in several parts of the Arctic.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Removal of grazers alters the response of tundra soil carbon to warming and enhanced nitrogen availability

Ylänne

Kaarlejärvi

Väisänen

et al. 2019

Ecological Monographs

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“…Firstly, we observed an increase in extractable soil N:P with heavy grazing in both the heath and meadow vegetation (Sitters et al, ), indicating that there was relatively more N than P available for plants when reindeer were present in high densities. Secondly, phosphatase activity in heath soil was higher under heavy grazing (Stark & Vaisanen, ). This extracellular enzyme is involved in the breakdown of organic P (Duff, Sarath, & Plaxton, ) to enhance local P supplies for plants.…”

Section: Discussionmentioning

confidence: 99%

Long‐term heavy reindeer grazing promotes plant phosphorus limitation in arctic tundra

et al. 2019

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The potential of large mammalian herbivores to shift plant communities between nitrogen (N) and phosphorus (P) limitation has received little attention so far. However, herbivores can influence the cycling of these growth‐limiting nutrients, and thereby affect plant nutrient limitation and productivity. Tundra ecosystems are nutrient‐poor and commonly grazed by large herbivores like reindeer and may thus be responsive to such changes. Here, we examined the effect of long‐term light and heavy reindeer grazing on nutrient limitation of plant growth in a Scandinavian arctic tundra. We are the first to conduct a factorial N and P fertilization experiment across the two grazing regimes in two functionally contrasting vegetation types: heath and meadow. Annual primary productivity (APP) showed contrasting responses to our fertilization treatments under light and heavy grazing. Under light grazing, APP increased in response to N + P additions in both the heath and meadow. Under heavy grazing, APP increased in response to N in the heath, with an additional positive effect of N + P combined, while APP increased in response to P and N + P additions in the meadow. These results clearly show that an increase in the grazing intensity of reindeer facilitated a shift towards more P‐limited conditions in Scandinavian arctic tundra, by increasing N cycling without having a corresponding positive effect on P cycling. In the N‐poor heath, reindeer increased soil N availability at least partly due to a shift towards more N‐rich graminoids, while in the meadow, reindeer decreased soil P availability. The mechanisms behind this decrease remain unclear, but reindeer may simply export more P from the system than N due to their large P demand for the production of their antlers. Synthesis. We conclude that heavy and long‐term reindeer grazing promoted a more P‐limited tundra, thus experimentally confirming the potential of large mammalian herbivores to influence nutrient limitation of plant growth. A plain language summary is available for this article.

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“…In arctic vegetation, N from droppings (Barthelemy and others 2015) and urine (Sjö gersten and others 2010; Barthelemy and others 2018) is efficiently taken up by the vegetation but also contributes to higher N concentrations in soils, as evidenced by the contiguity of increasing nutrients with reindeer migration (Stark and Vä isä nen 2014). A possible additional factor contributing to increased N availability in HMGs is the higher abundance of feather mosses like Pleurozium schreberi and Hylocomium splendens (Appendix 4 in ESM), as they often grow in association with N 2 -fixing cyanobacteria, adding atmospheric N to the system (Lett and Michelsen 2014).…”

Section: Discussionmentioning

confidence: 99%

Multiple Feedbacks Contribute to a Centennial Legacy of Reindeer on Tundra Vegetation

et al. 2018

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Historical contingency is the impact of past events, like the timing and order of species arrival, on community assembly, and can sometimes result in alternative stable states of ecological communities. Large herbivores, wild and domestic, can cause profound changes in the structure and functioning of plant communities and therefore probably influence historical contingency; however, little empirical data on the stability of such shifts or subsequent drivers of stability are available. We studied the centennial legacy of reindeer (Rangifer tarandus) pressure on arctic tundra vegetation by considering historical milking grounds (HMGs): graminoid-and forb-dominated patches amid shrub-dominated tundra, formed by historical Sami reindeer herding practices that ended approximately 100 years ago. Our results show that the core areas of all studied HMGs remained strikingly stable, being hardly invaded by surrounding shrubs. Soil nitrogen concentrations were comparable to heavily grazed areas. However, the HMGs are slowly being reinvaded by vegetative growth of shrubs at the edges, and the rate of ingrowth increased with higher mineral N availability. Furthermore, our data indicate that several biotic feedbacks contribute to the stability of the HMGs: increased nutrient turnover supporting herbaceous vegetation, strong interspecific competition preventing invasion and herbivore damage to invading shrubs. In particular, voles and lemmings appear to be important, selectively damaging shrubs in the HMGs. We concluded that HMGs provide clear evidence for historical contingency of herbivore effects in arctic ecosystems. We showed that several biotic feedbacks can contribute to subsequent vegetation stability, but their relative importance will vary in time and space.

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Insensitivity of Soil Microbial Activity to Temporal Variation in Soil N in Subarctic Tundra: Evidence from Responses to Large Migratory Grazers

Cited by 40 publications

References 42 publications

Removal of grazers alters the response of tundra soil carbon to warming and enhanced nitrogen availability

Removal of grazers alters the response of tundra soil carbon to warming and enhanced nitrogen availability

Long‐term heavy reindeer grazing promotes plant phosphorus limitation in arctic tundra

Multiple Feedbacks Contribute to a Centennial Legacy of Reindeer on Tundra Vegetation

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