Abstract
Global change is affecting primary productivity in forests worldwide, and this, in turn, will alter long‐term carbon (C) sequestration in wooded ecosystems. On one hand, increased primary productivity, for example, in response to elevated atmospheric carbon dioxide (CO 2), can result in greater inputs of organic matter to the soil, which could increase C sequestration belowground. On other hand, many of the interactions between plants and microorganisms that determine soil C dynamics are poorly characterized, and additional inputs of plant material, such as leaf litter, can result in the mineralization of soil organic matter, and the release of soil C as CO 2 during so‐called “priming effects”. Until now, very few studies made direct comparison of changes in soil C dynamics in response to altered plant inputs in different wooded ecosystems. We addressed this with a cross‐continental study with litter removal and addition treatments in a temperate woodland (Wytham Woods) and lowland tropical forest (Gigante forest) to compare the consequences of increased litterfall on soil respiration in two distinct wooded ecosystems. Mean soil respiration was almost twice as high at Gigante (5.0 μmol CO 2 m−2 s−1) than at Wytham (2.7 μmol CO 2 m−2 s−1) but surprisingly, litter manipulation treatments had a greater and more immediate effect on soil respiration at Wytham. We measured a 30% increase in soil respiration in response to litter addition treatments at Wytham, compared to a 10% increase at Gigante. Importantly, despite higher soil respiration rates at Gigante, priming effects were stronger and more consistent at Wytham. Our results suggest that in situ priming effects in wooded ecosystems track seasonality in litterfall and soil respiration but the amount of soil C released by priming is not proportional to rates of soil respiration. Instead, priming effects may be promoted by larger inputs of organic matter combined with slower turnover rates.
Highlights
Forest ecosystems play a crucial role in the global carbon (C) cycle: They represent the largest terrestrial C stock, because they cover 40% of the total land surface area (Jobbagy & Jackson, 2000), contain 82%–86% of the global aboveground biomass C (Dixon et al, 1994), and regulate a major exchange of C with the atmosphere through photosynthetic uptake and respiration (Malhi, Baldocchi, & Jarvis, 1999)
We aimed to address this by performing a cross-continental study to assess the response of soil C dynamics to experimental litter addition and litter removal in a temperate woodland and a tropical forest
This is the first large-scale experiment comparing the effects of altered aboveground litter inputs on soil respiration across distinct climatic zones
Summary
Forest ecosystems play a crucial role in the global carbon (C) cycle: They represent the largest terrestrial C stock, because they cover 40% of the total land surface area (Jobbagy & Jackson, 2000), contain 82%–86% of the global aboveground biomass C (Dixon et al, 1994), and regulate a major exchange of C with the atmosphere through photosynthetic uptake and respiration (Malhi, Baldocchi, & Jarvis, 1999). As much as 63% of the C stored in temperate forests is contained in soil organic matter, and even in the tropics, forest C storage is more or less partitioned between soil and aboveground biomass (Dixon et al, 1994). The quantity and quality of plant inputs to the soil (i.e., plant litter and root products) are the key drivers of organic matter turnover and residence times as they influence the amount and stability of soil organic C by regulating microbial decomposition processes (De Graaff, Classen, Castro, & Schadt, 2010). Interactions between plants and soil organisms influence a large number of ecosystem processes and play a key role in C cycling (Van der Heijden, Bardgett, & Van Straalen, 2008). Given the importance of forests as major sinks or sources of atmospheric carbon dioxide (CO2), changes in plant-soil interactions in forests could significantly affect the global C balance
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