Restoration of at least 15% of the world’s degraded ecosystems is one of the 2011-2020 targets of the UN Convention on Biological Diversity. However, soil nitrogen (N) is usually the primary limiting nutrient determining terrestrial ecosystem functions, such as plant growth and plant species composition. Insufficient supply of soil N may result in failure or limited success of vegetation restoration. Hence, knowledge of soil N dynamics following vegetation restoration might provide valuable clues for evaluating to which extent vegetation restoration can return degraded lands into healthy and functional ecosystems.

The highly sensitive and vulnerable karst ecosystem in southwest China is one of the largest exposed carbonate rock areas in the world. In the late 20th century, a large portion of the karst region was severely degraded due to the increasing intensity of human disturbances. Under the support of the "Grain for Green" projects, most of the degraded lands in the region have since undergone ecological restoration, either through natural regeneration or plantations. However, the effects of different vegetation restoration types on soil N have not been fully elucidated.

Furthermore, the removal of agricultural disturbance, reinforced by vegetation restoration, facilitates the gradual but extensive growth of biological soil crusts (biocrusts) in the karst region. Biocrusts have a significant role in the N cycle, and likely regulate short-term soil N availability to support plant growth as well as long-term N accumulation. Until now, most of the studies investigating soil N response to biocrusts under different vegetation types have focused on semiarid and arid regions (drylands). Few studies have simultaneously considered the effects of biocrusts and vegetation types on soil N in tropical or subtropical regions. Thus, it remains unclear how and to what extent the biocrusts affect soil N in the mesic subtropical vegetation zones.

To address the above uncertainties, researchers from the Institute of Subtropical Agriculture (ISA) of the Chinese Academy of Sciences measured the physical and chemical characteristics of the biocrusts and underlying soils, as well as litter properties under different vegetation restoration strategies (i.e., restoration with plantation forest, forage grass, and a combination of forest and grass, and spontaneous regeneration to natural grassland) following cropland abandonment in a subtropical karst region, southwest China.

They found that vegetation restoration promotes the formation and development of biocrusts in the karst region. “Compared with the other vegetation restoration strategies, the mixed cultivation of plantation trees and forage grasses resulted in the most favorable development of biocrusts and significantly improved the related soil N status,” said Prof. WANG Kelin, a researcher in ISA. “We found that biocrust properties were mainly responsible for the variation in soil inorganic N following vegetation restoration in the early stage in the karst area.”

These results suggest that the colonization and development of biocrusts should be incorporated in ecological restoration efforts in subtropical regions. More importantly, emerging vegetation restoration strategies, such as the forest and grass combination, offer mutually beneficial solutions that combine sustainable economic returns with an improvement in plant-available soil N and soil quality, should be favored in vegetation restoration efforts.

This work was supported by the National Key Research and Development Program of China, the National Key Basic Research Program of China, the National Natural Science Foundation of China, and the Chinese Academy of Sciences.

The study entitled “Moss-dominated biological soil crusts modulate soil nitrogen following vegetation restoration in a subtropical karst region” has been published in Geoderma, details could be found at https://www.sciencedirect.com/science/article/pii/S0016706119304434 

Contact: WANG Kelin

E-mail: kelin@isa.ac.cn 

Institute of Subtropical Agriculture, Chinese Academy of Sciences