Interannual climate variability mediates changes in carbon and nitrogen pools caused by annual grass invasion in a semiarid shrubland

Abstract

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 2 years of dry and 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 grassdominated 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 homogeneous 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.

Fuel connectivity, burn severity, and seed bank survivorship drive ecosystem transformation in a semiarid shrubland

“…Herbaceous cover in these dryland systems has high interannual variability (Mahood et al 2022). Because the components of ecosystem structure and disturbance severity in positive feedback cycle described here are continuous mechanistic variables, it may be possible to develop theoretical models (sensu (Archibald, Staver, and Levin 2012)) to estimate the threshold of vegetation cover that will lead to high burn severity.…”

“…Parks and Abatzoglou 2020). These forces can ultimately lead to permanent compositional change, biodiversity losses and the loss of ecosystem services (Ratajczak et al 2018;Mahood and Balch 2019;Mahood et al 2022) due to internal, self-reinforcing mechanisms that arise from those structural and functional changes which then maintain an alternative stable state (Marten Scheffer and Carpenter 2003;Ratajczak et al 2018).…”

Effect of drought and nutrient availability on invaded plant communities in a semi‐arid ecosystem

“…The changes in precipitation and the occurrence of drought events have an impact on soil water availability, which may lead to a decrease in ecosystem structure and function (Germino et al, 2015 ). The increase in nutrient availability due to fertilizer spillover from agriculture into natural areas in addition to increasing fluctuations of extreme weather events (e.g., droughts) will consequently affect nutrient cycling by increasing both, the overall N deposition in the landscape as well as the temporal variability in nutrient availability for plants growing in natural environments (Davis & Pelsor, 2001 ; Mahood et al, 2022 ; Verma & Jayakumar, 2012 ). One of the major aims of global change research is to understand the effects of these changes in abiotic conditions on plant species composition as well as the functional composition of the communities (Cardinale et al, 2012 ).…”

An exotic plant successfully invaded as a passenger driven by light availability

“…Exotic plant invasions threaten biodiversity and ecosystem function with long-term ecological consequences ( Buckley and Catford, 2016 ; Livingstone et al., 2020 ; Mahood et al., 2021 ). An increasing body of evidence confirms that IEPs markedly reduce the species richness of invaded plant communities around the world ( Vilà et al., 2011 ; Bernard-Verdier and Hulme, 2015 ; Carboni et al., 2021 ).…”

“…Similarly, IEPs modify the physical and chemical environment of the soil, which impacts on the composition and structure of the vegetation community in ways different from the original native plants ( Schimel et al., 1991 ; Sardans et al., 2017 ). For instance, some studies indicate that substantially higher above-ground net primary productivity (ANPP) and soil nitrogen (SN) concentrations can be achieved after the establishment of IEPs in the native plant communities ( Rout and Callaway, 2009 ; McLeod et al., 2016 ; Mahood et al., 2021 ). When invasive perennial plants dominate, they not only compete directly with the residents for resources, but also often have profound effects on local ecosystem processes ( Vilà et al., 2011 ; Carboni et al., 2021 ).…”