Agricultural Plant Physiology and Ecology Research Institute

Abstract Plant litter decomposition is the process through which plant-derived organic matter is recycled in terrestrial ecosystems. One of the drivers of decomposition is photodegradation, light-induced reactions that result in litter mass loss and transformations that accelerate the decomposition process. Photodegradation has been mostly studied in arid ecosystems, but mesic grasslands with monsoonal climate have been almost absent in the literature. In these ecosystems, standing dead biomass might remain exposed to solar radiation during dry winters while the effects of photodegradation accumulate. With the start of the warm and humid seasons, biotic decomposition might increase as a consequence of the changes in litter quality caused by sunlight. We aimed to study the impact of different wavelengths of solar radiation on litter mass loss and litter quality changes in a montane grassland with a monsoonal climate. We incubated litter from two dominant grasses under filters that generated treatments of full solar radiation, reduced UV radiation and reduced UV to short-wave visible radiation. We tracked changes in physical litter traits throughout the experiment under the three light treatment levels. We found an increase in litter mass loss due to sunlight exposure for both species, but each species reacted to a different range of wavelengths. We found evidence of enhancement of biotic decomposition by solar radiation (photofacilitation) in one of the two species, through an increase in β -glucosidase enzymatic activity. Seasonality affected litter decomposition of one species only by increasing mass loss depending on whether it was placed in the field during the dry winter or the humid spring. Finally, we found evidence of changes in physical litter traits caused by solar radiation, mainly in leaf mass per area (LMA) and water adsorption capacity. Our results represent the first proof of photodegradation in a productive grassland in this region, and highlight the fact that photodegradation is not constrained only to arid environments. Additionally, this study emphasizes the importance of litter physical traits in regulating carbon cycling through plant litter decomposition in terrestrial ecosystems. Open Research Statement Data are not yet provided as the study is currently under peer review. Upon acceptance, data will be archived in Zenodo. However, full datasets can be made available to the editorial board if required for the evaluation of the manuscript.

The Río de la Plata Grasslands (RPG) experienced a substantial agricultural expansion and intensification over the last three decades, with considerable impacts on C stocks among other ecosystem services. Converting agricultural land back to grassland is thus proposed as a strategy for removing atmospheric CO2 and sequestering carbon in the form of soil organic matter. However, the temporal dynamics of C recovery during spontaneous grassland restoration is still uncertain for this region. This study aims to describe the dynamics of soil organic carbon (SOC) recovery in fields with agricultural use in the past, in one of the most transformed regions of the RPG. For this purpose, we used a spatial chronosequence approach to sample rice old-fields (the main crop in this area) with similar soil types but different times since abandonment (2–25 years), allowing us to assess temporal patterns of SOC recovery in the absence of long-term monitoring data. These empirical data were then compared with simulations from the Century model, which incorporated different agricultural histories and grazing intensities following abandonment. The time required for the stabilization of carbon stocks depends on the magnitude of SOC losses generated by previous agricultural use and the subsequent grazing management, with recovery being slower in old-fields that experienced greater carbon depletion. Both approaches revealed SOC recovery over time; however, early accumulation rates were much higher in empirical data (10.5 vs. 0.6 t C ha⁻1 yr⁻1), likely because they integrate diverse agricultural histories and grazing intensities that the Century model separates into distinct scenarios. The different Century simulations integrate the variability that is not possible to discriminate with a field based approach, allowing us to correct possible artifacts and to generate more accurate predictions of how the system responds to different agricultural and post-agricultural management. After 30 years of agricultural abandonment, accumulation rates derived from both approaches stabilize at values consistent with those expected for grassland ecosystems. This suggests that carbon accumulation could compensate for up to approximately two-thirds of the methane emissions generated by livestock grazing, highlighting the potential contribution of restored grasslands to climate change mitigation.

Abstract The functional consequences of life form coexistence in mixed woody‐herbaceous communities remain a key question within the biodiversity–ecosystem functioning (BEF) framework. Our aim was to test three models proposed for the relationship between vegetation physiognomy and ecosystem functioning in drylands. Furthermore, these natural systems provide an opportunity to disentangle the ecological mechanisms driving biomass production, which have often been oversimplified by using species richness as a proxy for diversity in randomly assembled artificial communities. We conducted a field‐based removal experiment in a Patagonian shrub‐grass steppe, creating experimental communities dominated by a single life form (i.e. grasses or shrubs) and comparing them to mixed communities. We estimated green biomass at the peak of the growing season as a proxy for above‐ground net primary production (ANPP; g·m −2 ·year −1 ) in three censuses conducted during the first 5 years after removals. Furthermore, we applied an ecological adaptation of the Price equation to decompose ANPP differences into components that reveal the mechanisms driving the response. We found that (i) ANPP of shrubs decreased when coexisting with grasses; (ii) ANPP of grasses increased when coexisting with shrubs; (iii) total ANPP was maximized at intermediate densities of life forms. Our analysis revealed that life form coexistence maximizes ANPP through a positive effect exerted by shrubs on grasses, rather than through a more exhaustive use of the limiting resource (i.e. water). Synthesis . The relationship between life form dominance and ANPP remains an unresolved question in woody‐herbaceous communities. More than 20 years ago, three alternative models were proposed, yet they remain unchallenged. Here, we provide evidence supporting the optimum model, which predicts higher ANPP when herbaceous and woody species co‐dominate the community. Although BEF studies have identified niche complementarity as the main mechanism explaining this pattern, our results suggest that facilitation plays a more important role in the functioning of the Patagonian shrub‐grass steppe. By incorporating community assembly processes into ecosystem functioning research, we provide empirical evidence that positive interactions are crucial for ecosystem functioning in mixed woody‐herbaceous communities.

IntroductionIn the temperate grasslands of the UK, forage quality is a key factor influencing both animal performance and environmental impact. Because forage quality strongly affects rumen fermentation, improving it can reduce enteric methane emissions and mitigate animal nutritional stress. However, large-scale monitoring of forage quality remains limited due to the reliance on destructive, labor-intensive, and costly sampling methods. Remote sensing offers a promising alternative for scalable monitoring.MethodsWe explored an indicative approach combining optical remote sensing (Sentinel-2) with random forest regression (RFR) models to predict four critical forage quality attributes: crude protein (CP), water-soluble carbohydrates (WSC), neutral detergent fiber (NDF), and acid detergent fiber (ADF). Calibration and validation were performed using >9,500 georeferenced observations collected between 2020 and 2022 at the North Wyke Farm Platform in southwest UK. Forage quality was measured using near-infrared (NIR) sensors mounted on agricultural machinery across paddocks containing permanent and improved pastures. Sentinel-2 spectral predictors included visible, NIR, and red-edge bands, and model performance was evaluated using R² and RMSE metrics.ResultsModel performance was strong across all four forage quality attributes, with R² values ranging from 0.77 to 0.86 and consistently low RMSE values, indicating high predictive accuracy. Red-edge and NIR wavelengths were the most influential predictors. Improved pastures generally exhibited higher forage quality—characterized by lower ADF and higher WSC concentrations—than permanent pastures. Model-predicted seasonal changes were modest, whereas spatial contrasts between paddocks were much more pronounced.DiscussionThe calibrated models are suitable for forage systems with species composition and quality ranges similar to those represented in our dataset but should not be directly applied to other forage types without recalibration. Overall, this work demonstrates the potential of Sentinel-2 remote sensing combined with machine-learning approaches for tolerably accurate, large-scale forage quality monitoring. Such advancements could help improve grazing management, support nutritional planning, and contribute to efforts aimed at reducing methane emissions from livestock systems.

Abstract Agricultural practices that promote or introduce plant symbionts, such as arbuscular mycorrhizal fungi (AMF) and foliar fungal endophytes of grasses, may offer a sustainable alternative to traditional agricultural models, reducing environmental costs while preserving agroecosystem functions and productivity. However, their interactive effects within long‐term agricultural systems remain underexplored. Here, we investigate how promoted AMF and introduced foliar fungal endophytes influence grass and legume wellness. We tested whether the mycorrhizal community promoted through crop–pasture rotation favours plant growth by improving the associational protection against insects and pathogens provided by a foliar endophyte introduced through the seeding of its host. We conducted an outdoor mesocosm experiment using soil from the Pampa region of Argentina, with an intensive agricultural history. Half of the mesocosms were inoculated with spores extracted from an adjacent system where agricultural activities ceased 5 years ago, and a grass–legume pasture was established to start a crop–pasture rotation. Additionally, we set up a factorial design by sowing half of the mesocosms with Lolium multiflorum plants with high and low association with the endophyte Epichloë occultans . A mixture of grasses and legumes was sown in all mesocosms. The presence of E. occultans‐ associated L. multiflorum conferred associational protection to non‐host neighbouring plants against pests and diseases. In powdery mildew and aphid incidence, this endophyte protection was further enhanced when the AMF community was enriched with spores from the 5‐year grass–legume pasture, while in barley yellow dwarf virus (BYDV) and chewing insects in T. pratense , the addition of these AMF spores increased susceptibility. Nevertheless, AMF promoted by crop–pasture rotations favoured legume biomass over grasses and can either improve plant wellness by enhancing the associational protection provided by E. occultans or directly increase plant susceptibility. Synthesis and applications . Our results demonstrate that the interaction between promoted AMF and introduced endophytes can enhance plant resilience by mitigating biotic threats, thereby enhancing plant health and productivity. This underscores the importance of symbiotic microorganisms in agroecosystem sustainability and highlights the need to foster more diverse microbial communities by adopting agronomic practices, such as crop–pasture rotations with perennial forage species.

Reactions leading to dormancy release (DR) in 'dry', orthodox seeds are still poorly understood, as well as their dependence on moisture content (MC) and temperature. In this study, sunflower achenes were used to explore the effects of MC combined with a wide range of storage temperatures (ST°) on DR dynamics, tested at 10 °C and 25 °C. Embryo sensitivity to abscisic acid and oxygen uptake were determined and ageing indicators were assessed and complemented with dynamics for predicted viability loss. Water status was examined using sorption isotherms and the glass transition temperature (Tg). The results showed that small variations in MC and ST° had profound effects on achene dormancy and embryo responsiveness to ABA. Using a 'temperature-by-humidity' coordinate system we mapped three regions allowing DR during the glassy, rubbery, and fluid states of the achenes. Full DR (allowing germination at 10 °C and 25 °C) occurred only in the rubbery state (above Tg), and the optimal ST° for full DR dropped from 30 °C to -18 °C with MC increasing from 0.045 gH2O g-1 DW to 0.10 gH2O g-1 DW. In contrast, under both glassy and fluid states, DR was incomplete (allowing germination at 25 °C but not at 10 °C) and required warm ST° that promoted ageing.