Abstract
ABSTRACT Climate change is shifting species distributions and altering plant community composition worldwide. For instance, with rising temperatures shrubs are encroaching into alpine ecosystems, resulting in important implications for ecosystem functioning. In particular, woody-plant encroachment could slow decomposition in systems traditionally dominated by herbaceous species. To evaluate how litter decomposition responded jointly to warming and shrub presence, we conducted a passive warming chamber experiment in subalpine and alpine plant communities in the White Mountains of California. Passive warming chambers were placed over plots with and without the range-expanding sagebrush Artemisia rothrockii at two elevations. Litter from A. rothrockii and the common perennial herb Trifolium andersonii decomposed for two years under the experimental treatments. Nitrate availability was measured with ion-exchange resins during the same time period. Warming decreased decomposition rates overall, associated with decreased soil moisture, but did not influence soil nitrate availability. Sagebrush presence decreased both decomposition rates and nitrate availability. Hence, future warming in this system will likely reduce decomposition rates, both directly and indirectly, via shrub encroachment. However, impacts on nutrient mineralization are less clear. These findings highlight how shifting species composition, through processes such as range expansions, can influence ecosystem responses to climate change.
Highlights
High-altitude and high-latitude biomes are predicted to experience disproportionate amounts of warming in the twenty-first century (IPCC 2007; Nogués-Bravo et al 2007)
While soil moisture was only examined at the low elevation, there was an interaction between the warmed treatment and shrub presence (F1,14 = 5.48, P = 0.035) such that there was 24.5 percent lower soil moisture in the warmed treatment containing shrubs (Warm Shrub) compared to the unwarmed treatment with shrubs (Control Shrub; Tukey’s HSD, P = 0.021)
We found that T. andersonii, a common alpine plant in this region, experienced more variable decomposition responses to warming than A. rothrockii, which did not show warming-driven differences in decomposition
Summary
High-altitude and high-latitude biomes are predicted to experience disproportionate amounts of warming in the twenty-first century (IPCC 2007; Nogués-Bravo et al 2007). Warming may alter the rate of nutrient cycling and the associated release of carbon dioxide (CO2) to the atmosphere and have important consequences for the balance of carbon (C) sequestered versus released in these cold biomes (Gorham 1991; Mack et al 2004; Schuur et al 2009; Väisänen et al 2014; Webb et al 2016; Welker et al 2004). Low temperatures limit decomposition rates in alpine systems 2001; Withington and Sanford 2007); warmer temperatures are predicted to increase enzymatic activities and nutrient cycling rates (Coûteaux, Bottner, and Berg 1995; Davidson et al 2006). Warming has the potential to either increase or decrease decomposition rates in alpine systems, mediated through an effect on soil moisture
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