Below-ground root nutrient-acquisition strategies are more sensitive to long-term grazing than above-ground leaf traits across a soil nutrient gradient

Understanding how plant nutrient acquisition strategies respond to grazing
at the community level is critical to understanding ecosystem structure
and functioning in grasslands. However, few studies have simultaneously
compared the difference in aboveground (leaf) and belowground (root)
nutrient-acquisition strategies in response to long-term grazing,
especially at the regional scale. Here, we measured a set of leaf and
fine-root traits that correspond to the fast-slow economic spectrum at the
community level in 10 experimental sites from paired grazed and ungrazed
grasslands across a soil nutrient gradient covering three major types of
grasslands in northern China. We found that patterns of variations of leaf
and fine-root traits were consistent with both a leaf and root economic
spectrum at the community level for both grazed and non-grazed plots.
Grazing had a minor effect on community-level leaf nutrient-acquisition
strategies but strongly influenced community-level root
nutrient-acquisition strategies. Specifically, root nutrient-acquisition
strategies were shifted to more exploitative resource use in grazed
communities. Moreover, soil nutrients contributed to the changes in both
leaf and root nutrient-acquisition strategies, which tended towards a more
resource-acquisition strategy with increasing soil nutrient levels.
Grazing significantly interacted with soil nutrients to affect root
nutrient-acquisition strategies, and grazing contributed more to root
nutrient-acquisition strategies than soil nutrients. Our results
demonstrated completely inconsistent responses of community-level above-
and below-ground resource acquisition strategies to long-term grazing, and
below-ground acquisition strategies were more sensitive to long-term
grazing. Our findings also suggest that high-intensity anthropogenic
activities such as grazing may strongly modify below-ground resource
acquisition strategies.