Worlds apart: Location above‐ or below‐ground determines plant litter decomposition in a semi‐arid Patagonian steppe

Abstract

1. While considerable attention has been devoted to how precipitation modulates net primary productivity in arid and semi-arid ecosystems, the emergence of multi-faceted controls on carbon (C) turnover suggests that there is much to be understood with respect to the mechanistic controls on plant litter decomposition.2. In the Patagonian steppe, we conducted a long-term factorial experiment, evaluating the importance of position, litter quality, tissue origin and soil resources on rates of C turnover under natural field conditions. Leaf and root litter of dominant grass species were placed in litterbags in different positions, on the soil surface and buried at 5-cm depth, with soil treatments of labile C, nitrogen (N) and their combination (C + N) over a 3-year period.3. As predicted, leaf litter decomposed significantly (nearly sixfold) faster aboveground than did root litter below-ground (p < 0.001). Surprisingly, root litter decomposed significantly faster than leaf litter above-ground (p < 0.001), and above-ground decomposition was not strongly affected by soil resource additions.Below-ground decomposition was largely determined by the interaction of litter quality and soil resource availability. Determining a C balance by integrating biomass allocation and primary productivity from this field site, combined with the data from this study, suggests large differences between the contribution of the above-and below-ground biomass to soil organic matter (SOM) pools and a long residence time of undecomposed root litter. 4. Synthesis. Litter position clearly emerged as the predominant variable determining C turnover in this semi-arid steppe ecosystem, with litter quality and soil resources having significant, but more modest, effects. The near complete independence of above-ground litter decomposition from soil resources and rapid decomposition of surface litter, coupled with the counterintuitive relationships with litter quality, suggests that, in the long term, C loss from photodegradation may result in a minimal contribution of above-ground litter to SOM formation. These results have mechanistic implications for the distinct functionality of litter decomposition above-and below-ground in semi-arid ecosystems, and how these differential controls may alter the C balance due to future changes in climate and land use. How to cite this article: Berenstecher P, Araujo PI, Austin AT. Worlds apart: Location above-or below-ground determines plant litter decomposition in a semi-arid Patagonian steppe.

Environmental effects of stratospheric ozone depletion, UV radiation, and interactions with climate change: UNEP Environmental Effects Assessment Panel, Update 2021

“…The role of photodegradation in litter decomposition is well established [ 84 , 112 ]. There is now more evidence that photodegradation plays a key role in moist and temperate systems, such as in temperate forests [ 117 ], as well as in dryland systems [ 118 , 119 ]. How much plant litter gets exposed to solar radiation, including the UV component, varies among ecosystems.…”

“…How much plant litter gets exposed to solar radiation, including the UV component, varies among ecosystems. In dryland ecosystems, litter is left on the ground in the dry season but burial can reduce exposure [ 119 ], while in temperate forests litter becomes exposed when gaps form in the canopy [ 117 ]. Fire also reduces vegetation cover and temporarily increases exposure to solar radiation [ 120 ].…”

Soil carbon stocks in temperate grasslands differ strongly across sites but are insensitive to decade‐long fertilization

“…For example, root mass was positively related to SOC accrual following 27 years of N addition at Cedar Creek in Minnesota, USA (CDR) (Fornara & Tilman, 2012), while lignin-rich root litter promoted soil C stabilization under N fertilization (Dijkstra et al, 2004). Meanwhile, in a dryland site, belowground inputs were the primary contributor to SOM, yet the high lignin content of roots appeared to constrain SOM formation (Berenstecher et al, 2021). In a companion study to this one (at the same NutNet sites), N and P stimulated aboveground biomass but productivity belowground was insensitive to N addition and increased less with P addition (Keller et al, 2017(Keller et al, -2018.…”

Dose–responses for solar radiation exposure reveal high sensitivity of microbial decomposition to changes in plant litter quality that occur during photodegradation

“…Gallo et al ., 2009; Brandt et al ., 2010; Rutledge et al ., 2010; Baker & Allison, 2015; Gaxiola & Armesto, 2015; Austin et al ., 2016; Huang et al ., 2017; Huang & Li, 2017; Day et al ., 2018; Wu et al ., 2018; Marinho et al ., 2020; Keiser et al ., 2021), have shown that exposure to solar radiation can accelerate litter decomposition directly (through photochemical mineralization; Austin & Vivanco,2006; Brandt et al ., 2009; Lee et al ., 2012) and indirectly (through stimulation of biotic decomposition, that is, photofacilitation; Foereid et al ., 2010; Austin et al ., 2016). The magnitude of C loss deriving directly from volatile products of photodegradation is most evident in seasonally dry or arid ecosystems (Austin & Vivanco, 2006; Austin & Ballaré, 2010; Rutledge et al ., 2010; Ma et al ., 2017; Berenstecher et al ., 2020, 2021), but photofacilitation appears to be important in a broad range of ecosystems, with almost universal stimulation of biotic decomposition of plant litter that has been exposed to sunlight (e.g. Brandt et al ., 2010; Foereid et al ., 2010; King et al ., 2012; Araujo & Austin, 2015; Baker & Allison, 2015; Gaxiola & Armesto, 2015; Austin et al ., 2016; Gliksman et al ., 2018; Méndez et al ., 2019; Pieristè et al ., 2019; Day et al ., 2022).…”

“…The most recent conceptual framework for how leaf litter decomposes and returns C to the atmosphere as CO 2 suggests that there is not a strong hierarchy of global, regional and local controls on C turnover, with all controls demonstrating importance at different scales (Cornwell et al ., 2008; Pietsch et al ., 2014; Keiluweit et al ., 2015; Bradford et al ., 2016; Bradford et al ., 2017). As such, an updated vision of the controls on leaf and root litter decomposition is emerging (Hättenschwiler & Jørgensen, 2010; Cotrufo et al ., 2013; Bradford et al ., 2017; See et al ., 2019; Berenstecher et al ., 2020, 2021), coupled with the identification of underappreciated controls on plant litter decomposition such as sunlight exposure (Austin & Vivanco, 2006; Brandt et al ., 2009; Lee et al ., 2012), litter position (Liu et al ., 2015; Gliksman et al ., 2018; Berenstecher et al ., 2021) and precipitation seasonality (Almagro et al ., 2015; Berenstecher et al ., 2020).…”