Grazing decreases N partitioning among coexisting plant species

• Published in: Functional Ecology
• Main Authors: Barthelemy, Hélène, Stark, Sari, Kytöviita, Minna‐Maarit, Olofsson, Johan
• Other Authors: Power, Sally, Stiftelsen Oscar och Lili Lamms Minne
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2017
• Subjects: Tundra
• Online Access: http://dx.doi.org/10.1111/1365-2435.12917; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2F1365-2435.12917; https://onlinelibrary.wiley.com/doi/pdf/10.1111/1365-2435.12917; https://onlinelibrary.wiley.com/doi/full-xml/10.1111/1365-2435.12917; https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/1365-2435.12917

Abstract Herbivores play a key role in shaping ecosystem structure and functions by influencing plant and microbial community composition and nutrient cycling. This study investigated the long‐term effects of herbivores on plant resource acquisition. We explored differences in the natural δ 15 N signatures in plant, microbial and soil N pools, and examined mycorrhizal colonization in two tundra sites that have been either lightly or heavily grazed by reindeer for more than 50 years. The study examined changes in nutrient acquisition in five common tundra plants with contrasting traits and mycorrhiza status; the mycorrhizal dwarf shrubs, B etula nana , V accinium myrtillus and E mpetrum hermaphroditum a mycorrhizal grass, D eschampsia flexuosa , and a non‐mycorrhizal sedge, C arex bigelowii . There were large variations in δ 15 N among coexisting plant species in the lightly grazed sites. This variation was dramatically reduced in the heavily grazed sites. At an individual species level, δ 15 N was higher in E . hermaphroditum and lower in C . bigelowii in the heavily grazed sites. Mycorrhizal colonization in B . nana and E . hermaphroditum roots were also lower in the heavily grazed sites. The δ 15 N signatures of the total soil N pool and of the microbial N pools were higher in the heavily grazed sites. Since the strong δ 15 N differentiation among plant species has been interpreted as a result of plants with different mycorrhizal types using different sources of soil nitrogen, we suggest that the lower variation in δ 15 N in heavily grazed sites indicates a lower niche differentiation in nitrogen uptake among plants. Reduced mycorrhiza‐mediated nitrogen uptake by some of the species, a shift towards a more mineral nutrition due to higher nutrient turnover, and uptake of labile nitrogen from dung and urine in the heavily grazed sites could all contribute to the changes in plant δ 15 N. We conclude that herbivores have the potential to influence plant nutrient uptake and provide the first data suggesting that ...