title: Effects of resource addition on recovery of production and plant functional composition in degraded semiarid grasslands.
abstract: Degradation of semiarid ecosystems from overgrazing threatens a variety of ecosystem services. Rainfall and nitrogen commonly co-limit production in semiarid grassland ecosystems; however, few studies have reported how interactive effects of precipitation and nitrogen addition influence the recovery of grasslands degraded by overgrazing. We conducted a 6-year experiment manipulating precipitation (natural precipitation and simulated wet year precipitation) and nitrogen (0, 25 and 50 kg N ha-1) addition at two sites with different histories of livestock grazing (moderately and heavily grazed) in Inner Mongolian steppe. Our results suggest that recovery of plant community composition and recovery of production can be decoupled. Perennial grasses provide long-term stability of high-quality forage production in this system. Supplemental water combined with exclosures led, in the heavily grazed site, to the strongest recovery of perennial grasses, although widespread irrigation of rangeland is not a feasible management strategy in many semiarid and arid regions. N fertilization combined with exclosures, but without water addition, increased dominance of unpalatable annual species, which in turn retarded growth of perennial species and increased inter-annual variation in primary production at both sites. Alleviation of grazing pressure alone allowed recovery of desired perennial species via successional processes in the heavily grazed site. Our experiments suggest that recovery of primary production and desirable community composition are not necessarily correlated. The use of N fertilization for the management of overgrazed grassland needs careful and systematic evaluation, as it has potential to impede, rather than aid, recovery.
authors.affiliation: College of Resource and Environmental Sciences, China Agricultural University, Beijing, 100193, People's Republic of China.|Tianjin Key Laboratory of Water Resources and Environment, Tianjin Normal University, Tianjin, 300387, People's Republic of China.
authors.forename: Qing
authors.initials: Q
authors.lastname: Chen
authors.affiliation: Department of Biology, Western Washington University, Bellingham, WA, 98225-9160, USA.
authors.forename: David U
authors.initials: DU
authors.lastname: Hooper
authors.affiliation: College of Resource and Environmental Sciences, China Agricultural University, Beijing, 100193, People's Republic of China.
authors.forename: Hui
authors.initials: H
authors.lastname: Li
authors.affiliation: College of Resource and Environmental Sciences, China Agricultural University, Beijing, 100193, People's Republic of China.
authors.forename: Xiao Ying
authors.initials: XY
authors.lastname: Gong
authors.affiliation: College of Resource and Environmental Sciences, China Agricultural University, Beijing, 100193, People's Republic of China.
authors.forename: Fei
authors.initials: F
authors.lastname: Peng
authors.affiliation: College of Resource and Environmental Sciences, China Agricultural University, Beijing, 100193, People's Republic of China.
authors.forename: Hong
authors.initials: H
authors.lastname: Wang
authors.affiliation: Institute of Plant Nutrition and Crop Physiology, University of Goettingen, 37075, Goettingen, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Dittert
authors.affiliation: College of Resource and Environmental Sciences, China Agricultural University, Beijing, 100193, People's Republic of China. linshan@cau.edu.cn.
authors.forename: Shan
authors.initials: S
authors.lastname: Lin
mesh_terms: D000818:Animals; D017753:Ecosystem; D009584:Nitrogen / Q000378:metabolism; D010944:Plants / Q000378:metabolism; D006109:Poaceae / Q000378:metabolism*; D014867:Water
chemical_list: D014867:Water; D009584:Nitrogen
keywords: Nitrogen; Overgrazing; Plant functional group; Recovery; Water availability