; Exotic plant invasions alter ecosystem properties and threaten ecosystem; functions globally. Interannual climate variability (ICV) influences; both plant community composition (PCC) and soil properties, and; interactions between ICV and PCC may influence nitrogen (N) and carbon; (C) pools. We asked how ICV and non-native annual grass invasion covary; to influence soil and plant N and C in a semiarid shrubland undergoing; widespread ecosystem transformation due to invasions and altered fire; regimes. We sampled four progressive stages of annual grass invasion at; 20 sites across a large (25,000 km; 2; ) landscape for; plant community composition, plant tissue N and C, and soil total N and; C in 2013 and 2016, which followed two years of dry and two years of wet; conditions, respectively. Multivariate analyses and ANOVAs showed that; in invasion stages where native shrub and perennial grass and forb; communities were replaced by annual grass-dominated communities, the; ecosystem lost more soil N and C in wet years. Path analysis showed that; high water availability led to higher herbaceous cover in all invasion; stages. In stages with native shrubs and perennial grasses, higher; perennial grass cover was associated with increased soil C and N, while; in annual-dominated stages, higher annual grass cover was associated; with losses of soil C and N. Also, soil total C and C:N ratios were more; homogenous in annual-dominated invasion stages as indicated by; within-site standard deviations. Loss of native shrubs and perennial; grasses and forbs coupled with annual grass invasion may lead to; long-term declines in soil N and C and hamper restoration efforts.; Restoration strategies that use innovative techniques and novel species; to address increasing temperatures and ICV and emphasize maintaining; plant community structure – shrubs, grasses, and forbs – will allow; sagebrush ecosystems to maintain C sequestration, soil fertility and; soil heterogeneity.;
