Paula Berenstecher – Harper Prize Shortlist

Throughout April, we are featuring the articles shortlisted for the 2021 Harper Prize. The Harper Prize is an annual award for the best early career research paper published in Journal of Ecology.

Paula Berenstecher et al.’s article ‘Worlds apart: Location above- or below-ground determines plant litter decomposition in a semi-arid Patagonian steppe‘ was one of those shortlisted for this year’s award.

⭐️About me

I was born and grew up in Buenos Aires, Argentina, one of the largest cities in South America. Although I have enjoyed nature since I was a child, when I finished high school, I decided to study Environmental Sciences at the University of Buenos Aires, motivated to solve some of the city’s environmental problems. During my undergrad, I became increasingly interested in natural ecosystems and agroecosystems. At this time, I joined Amy Austin’s lab, motivated by her studies on litter decomposition in Patagonian ecosystems. At that time, the massive eruption of the Puyehue volcano affected a considerable part of the Patagonian region. For my undergraduate thesis, I studied the effects of this natural disturbance on plant-soil interactions (Berenstecher et al. 2017 Functional Ecology). In 2014, I started my PhD supervised by Amy, studying the role of photodegradation (which is the effect of solar radiation breaking down organic matter) on carbon turnover in a seasonally dry woodland in Patagonia.

During my PhD, I had the opportunity to discover a range of contrasting natural and human modified ecosystems in Patagonia, learning from other inspiring scientists, many of whom were women. I also did a research stay at the University of California, Berkeley. There, I learned about stable isotopes in ecology, an extremely valuable tool for broadening our mechanistic understanding of biotic processes at all scales, but very little widespread in South America. The paper shortlisted for the Harper Prize was my first comprehensive approach to relatively long-term field decomposition studies during my years as a grad student.

Figure 1. The Patagonian steppe is a vast semiarid ecoregion located in the south of South America. It is characterized by discontinuous vegetation cover and clear skies with high incident solar radiation, that together with scarce rainfall, constrain soil biotic activity and soil organic matter formation. Photograph courtesy of A. Austin.

🔎About the shortlisted article

Our study illustrates in a striking fashion the two worlds in which above- and belowground litter decompose, since litter position emerged as the predominant control on C turnover in this semiarid steppe. We observed much faster decomposition when litter was on the surface (for both leaf and root litter), largely driven by photodegradation. Surprisingly, and because of high solar irradiance in the Patagonian steppe, aboveground litter decay is on par with most mesic ecosystems of much higher rainfall. At the same time, belowground, where biotic decomposition dominates, the highly variable soil moisture and scarce soil organic matter and microbial biomass made for extremely slow decomposition of roots. Our modeling of these pools suggests a large biologically recalcitrant detritus pool essentially ‘frozen’, that is largely separated from the bulk soil organic matter in this Patagonian steppe ecosystem.

Figure 2. Carbon pools (boxes, g m-2) and fluxes (arrows, g m−2 year−1) above- and belowground for grasses in the Patagonian steppe. We observed much faster decomposition rates (k) when litter was on the surface, largely driven by photodegradation. Belowground, we found extremely slow decomposition of roots, resulting in a large biologically recalcitrant detritus pool that can be separate from soil organic matter (SOM).

The dichotomy of controls on litter decomposition depending on its position suggests an important clue to explain why soil organic matter content at this semiarid steppe is notably low, particularly in the bare soil areas. The combination of low aboveground C input and slow belowground processing of roots generates an atypical situation of C storage that results in small soil organic pools, and large pools of unprocessed root detritus. The scenario of multi-faceted controls on C turnover presents an important challenge for our understanding of C sequestration in this and other arid and semiarid ecosystems.

This study also provides insight into how the Patagonian steppe and other aridland ecosystems may respond to human-caused global change. Experimental manipulation of rainfall has demonstrated a reduction in net primary productivity with increasing aridity, and intense grazing tends to impoverish carbon (C) and nutrient pools. This study suggests that human impacts that reduce vegetative cover will likely exacerbate C losses due to exposure of plant litter to solar radiation, potentially preventing recovery of vegetation due to overgrazing or drought. Additionally, our results suggest that below-ground contributions are fundamental to the C inputs in this ecosystem. Projected climate change may alter incident radiation, which could accelerate above-ground C losses and combined with grazing removal will reduce below-ground inputs, all negatively affecting the ecosystem C balance. Clearly identifying the mechanisms contributing to SOM formation in semi-arid ecosystems could reduce our uncertainty with respect to how soil C will be affected by global change in the future.

🌱What’s next?

This work joins the two topics I am most passionate about, litter decomposition in semiarid ecosystems and mechanisms involved in soil organic matter formation. Currently, I am a teaching assistant at the University of Buenos Aires and a post-doctoral researcher. The overarching aim of my post-doc is to understand soil organic matter formation and nitrogen dynamic in agricultural rotations with cover crops in the Pampas plain, Argentina, using different tools of stable isotopes, particularly 13C. My experience in natural ecosystems gives me new insight into how managed ecosystems function, and I hope to come back to study natural ecosystems soon, as we have a lot to learn from them.

Find Paula on Twitter.

Read the full list of articles shortlisted for the 2021 Harper Prize here.

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