Mon, Aug 15, 2022: 2:30 PM-2:45 PM
516A
Background/Question/MethodsWoody plant encroachment to rangeland is controlled by interdependent factors that vary in space and time, including climate, the availability of growth-limiting resources. Owing to higher nitrogen-fixing ability, leguminous woody plant encroachment affects the allocation of nitrogen and water among native herbs, especially in arid grassland, regardless of other nitrogen fertilizers (i.e., livestock excrement and organic fertilizer). The long-term encroachment effects of leguminous woody plants on species richness and plant aboveground biomass of rangeland in arid regions are still unclear.In August 2020, we selected 38 long-term observation sites from Yanchi city and Guyuan city located on the Loess Plateau. The mean annual precipitation are 220 mm and 630 mm, representing extremely arid rangeland (EAR) and semi-arid rangeland (SAR), respectively. Caragana korshinskii was distributed in over a 1-ha area in each site. This ongoing long-term experiment consists of 11 encroachment years (3 to 26 years) and 9 encroachment densities (0.0417 individuals/m2 to 1 individuals/m2). The aboveground biomass was collected from four quadrats (1 m × 1 m) in each plot.
Results/ConclusionsIncreasing precipitation significantly increased species richness and aboveground biomass of the community by 137.1% and 59.2% respectively. Encroachment density did not significantly affect species richness and aboveground biomass in EAR, while increasing encroachment density significantly increased those values in SAR, by 40%-81% and 42%-161%, respectively. With the increase of encroachment year, species richness decreased by 27%-28% in EAR, while aboveground biomass showed an upward curve. In SAR, increasing encroachment years led to higher species richness and lower aboveground biomass. The optimal encroachment densities were 0.0417-0.0556 individuals/m2 and 0.25-0.5 individuals/m2 in EAR and SAR, respectively. The legacy effects of encroachment years (18-yr and 20-yr) increased the water use efficiency of C. korshinskii.Leguminous woody plants affect rangeland productivity through three ways including nitrogen fixation and regulation of soil moisture by the "pumping effect", and changes in canopy structure. The legacy effects of C. korshinskii increased species richness but decreased aboveground biomass associated with increasing precipitation. Our findings provide reference and extension for the resource-ratio hypothesis of invasive ecology.
Results/ConclusionsIncreasing precipitation significantly increased species richness and aboveground biomass of the community by 137.1% and 59.2% respectively. Encroachment density did not significantly affect species richness and aboveground biomass in EAR, while increasing encroachment density significantly increased those values in SAR, by 40%-81% and 42%-161%, respectively. With the increase of encroachment year, species richness decreased by 27%-28% in EAR, while aboveground biomass showed an upward curve. In SAR, increasing encroachment years led to higher species richness and lower aboveground biomass. The optimal encroachment densities were 0.0417-0.0556 individuals/m2 and 0.25-0.5 individuals/m2 in EAR and SAR, respectively. The legacy effects of encroachment years (18-yr and 20-yr) increased the water use efficiency of C. korshinskii.Leguminous woody plants affect rangeland productivity through three ways including nitrogen fixation and regulation of soil moisture by the "pumping effect", and changes in canopy structure. The legacy effects of C. korshinskii increased species richness but decreased aboveground biomass associated with increasing precipitation. Our findings provide reference and extension for the resource-ratio hypothesis of invasive ecology.