Premium
Grazing decreases N partitioning among coexisting plant species
Author(s) -
Barthelemy Hélène,
Stark Sari,
Kytöviita MinnaMaarit,
Olofsson Johan
Publication year - 2017
Publication title -
functional ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.272
H-Index - 154
eISSN - 1365-2435
pISSN - 0269-8463
DOI - 10.1111/1365-2435.12917
Subject(s) - biology , tundra , herbivore , ecosystem , ecology , plant community , nutrient , botany , grazing , mycorrhiza , agronomy , ecological succession , symbiosis , genetics , bacteria
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 herbivores decrease nutrient partitioning on the basis of chemical N forms among plant species. Reduced niche complementarity among species is potentially important for estimates of the effects of herbivory on plant nutrient availability and species coexistence. A plain language summary is available for this article.