Above-ground leaf and below-ground root differ in their response to long-term grazing: root traits are more sensitive

Jinting Cai, Xiaobin Pan, Yingli Xiao, Yue Wang, Guangyin Li, Yao Wang, Minna Zhang, Ling Wang

This is a plain language summary of a Functional Ecology research article which can be found here.

Livestock grazing is a complex disturbance that affects grassland ecosystem function through foraging, trampling and excreta. A promising way to understand the consequences of grazing on grassland ecosystem functioning is to focus on how changes in trait composition at the plant community level. It was believed for a long time that livestock grazing has a more significant impact on the above-ground leaf. Most of the existing studies only focus on the effects of grazing on leaf traits but ignore the effects on root traits. We can’t help but wonder if grazing affects above- and below-ground traits for resource acquisition in the same way, especially at the regional scale. If above- and below-ground traits for resource acquisition responses to grazing are similar along a soil nutrient gradient, in future studies we can use more easily measured above-ground traits to predict the response of below-ground traits to grazing.

To our surprise, grazing had minor effect on above-ground acquisition strategies but strongly influenced below-ground acquisition strategies at the community level. Specifically, species that grow in grazed communities tend to use their roots to acquire resources more quickly. Moreover, soil nutrient contributed to the changes in both above-ground leaf and below-ground root, which tended towards a more resource acquisition strategy with increasing soil nutrient levels.

Although both soil nutrient and grazing affect below-ground acquisition strategies, the impact of grazing is greater. 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. This reminds us that in the ‘black box’ that we can’t see, human activities greatly disturb the roots of plants.

Photographs show the study sites at the peak of the growing season, (A) Meadow steppe, (B) Typical steppe, and (C) Desert steppe. (left, enclosed site and right, overgrazed sites) (Credit: Li Guangyin).