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Our understanding of carbon and nutrient dynamics in globally vast and socioeconomically critical dryland ecosystems lags behind mesic systems. Litter decomposition models consistently underestimate measured decomposition in these regions. Both models and measurements largely represent spatially dominant intercanopy areas; however, little litter resides in these interspaces as transport vectors move litter to other microsites such as beneath plant canopies and buried in soil. Abiotic and biotic conditions differ among microsites, but few studies have characterized microsite impacts on decomposition. We collated data on microsites where litter accumulates. In microsites with sufficient available data, we used meta-analysis to test hypotheses on decomposition relative to litter in intercanopy spaces. Decomposition was lower under woody plant canopies than in intercanopy spaces. Buried litter decomposed faster than surface litter. There was no difference in decomposition between surface litter and litter suspended aboveground to simulate standing dead. All microsite contrasts had exceptions, suggesting that site-specific characteristics influence microclimate and subsequent decomposition. Extrapolation of decomposition rates to the landscape-level (using estimates of microsite-specific decomposition rates multiplied by litter pools), suggests that decomposition estimates based on intercanopy data alone underrepresent landscape-level decomposition. Thus, despite advances in the understanding of mechanistic decomposition drivers in drylands advancing, most studies are spatially unrepresentative analyses in intercanopy areas and this will underestimate decomposition at the landscape level. Expanding the ecological relevance of decomposition processes to be useful for predicting larger-scale carbon and nutrient dynamics requires improved characterization of dryland litter distribution, coupled with a mechanistic understanding of decomposition in microsites where litter accumulates. 

Abstract Increasing fine root carbon (FRC) inputs into soils has been proposed as a solution to increasing soil organic carbon (SOC). However, FRC inputs can also enhance SOC loss through priming. Here, we tested the broad-scale relationships between SOC and FRC at 43 sites across the US National Ecological Observatory Network. We found that SOC and FRC stocks were positively related with an across-ecosystem slope of 7 ± 3 kg SOC m⁻²per kg FRC m⁻², but this relationship was driven by grasslands. Grasslands had double the across-ecosystem slope while forest FRC and SOC were unrelated. Furthermore, deep grassland soils primarily showed net SOC accrual relative to FRC input. Conversely, forests had high variability in whether FRC inputs were related to net SOC priming or accrual. We conclude that while FRC increases could lead to increased SOC in grasslands, especially at depth, the FRC-SOC relationship remains difficult to characterize in forests. 

After 4.5 billion years as an evolving and dynamic planet, the Earth continues to evolve but with human‐altered dynamics. Earth scientists have special opportunities and responsibilities to accelerate our understanding of Earth's changes that are transforming our most remarkable home.