Mariano Oyarzabal

Grassland intensification practices including, overseeding with exotic species and P fertilisation (hereafter ‘overseeding’), the replacement of natural grasslands by sowing perennial pastures (‘perennial pasture’) and the replacement of natural grassland by winter–spring forage crop (‘forage crop’), are widely used to enhance production in livestock systems. Most studies have evaluated the effects of these practices on forage production in ungrazed experimental plots using non‐comparable protocols. To our knowledge, few studies have jointly assessed the effect of different intensification practices on forage production and its variability under a standardised protocol across grazed commercial paddocks. We evaluated the effect of these three intensification practices on forage production across 45 commercial farms located in the temperate grasslands of Uruguay. We quantified the mean annual Enhanced Vegetation Index (EVI), a proxy for forage production and its inter‐ and intra‐annual variability. We compared grazed paired paddocks, consisting of a natural grassland and one of the three intensification practices, and expressed the effect of each practice relative to natural grassland. Mean annual EVI increased by 2% with overseeding, 3% with perennial pasture and 9% with forage crop. Inter‐annual variability increased by 6% with overseeding, 19% with perennial pasture and 24% with forage crop. Intra‐annual variability increased by 8% with overseeding and 22% with perennial pasture. In summary, forage production increased slightly under all intensification practices and variability increased more markedly. These findings highlight that while forage production can be enhanced by intensification, increased temporal variability may represent a challenge under future scenarios of more frequent extreme climatic events.

Plants are consumed by a variety of organisms, including herbivores and pathogens, which significantly impact plant biomass, diversity, community composition, and ecosystem functioning. While the impacts of vertebrate herbivores are well established, the effects of consumer groups such as insect herbivores, mollusks, and fungal pathogens on plant communities are less clear and remain understudied in many systems. Existing evidence of how they affect plant biomass, diversity, and community composition is mixed, and most studies have focused on individual consumer groups in isolation. However, different consumer groups interact with each other, directly or indirectly, in ways that alter their impacts on plants, and the consequences of these interactions for plant community structure and ecosystem function remain understudied. Further, consumer impacts vary across environmental gradients and likely depend on abiotic conditions such as climate, soil type, or elevation, and biotic conditions such as plant productivity, diversity, or community composition. Existing studies testing the impacts of invertebrate herbivores and fungal pathogens on plant communities differ substantially in methodology, making generalities across large scales difficult. This calls for experimental approaches that implement standardized protocols across many sites. Here, we introduce and report on the methodology of a novel global research network, The Bug‐Network (BugNet), that implements standardized consumer‐reduction experiments across 5 continents and 18 countries in diverse, herbaceous‐ or shrub‐dominated ecosystems to investigate: (1) the influence of fungal pathogens, insect herbivores, and mollusks on plant diversity and ecosystem functioning, (2) interactions among these consumer groups, and (3) the abiotic and biotic drivers of context‐dependent consumer impacts. BugNet aims to advance a predictive understanding of plant‐consumer interactions in order to test fundamental ecological hypotheses and improve predictions of global change impacts on biodiversity and ecosystem functioning.

There are several plant below‐ground biomass databases for grasslands, but the contribution from the southern hemisphere is minimal. Particularly, no study has compiled the published values of plant below‐ground biomass for the temperate subhumid grasslands of South America. In these grasslands, called Río de la Plata grasslands, grazing is the most frequent disturbance. We set two objectives: (1) to compile and synthesize data of four variables: below‐ground biomass, fraction of total biomass allocated below‐ground, below‐ground net primary productivity and below‐ground biomass turnover rate; (2) to estimate the effect of grazing exclusion on below‐ground biomass by means of a meta‐analysis. There are 15 studies published on six out of eight regional sub‐divisions of the Río de la Plata grasslands. The most evaluated variable was below‐ground biomass, followed by below‐ground net primary productivity, while the other two variables were scarcely registered. Below‐ground biomass in the shallow portion of the soil (0–10 cm) was on average 877 g m⁻². Below‐ground net primary productivity resulted in an average of 245 g m⁻² year⁻¹ (estimated using the ingrowth core method) or 560 g m⁻² year⁻¹ (core method). The fraction of total biomass allocated below‐ground was on average 0.75. Below‐ground biomass turnover rate presented an average of 2.5 years. On average, the effect of grazing exclusion on below‐ground biomass depended on exclusion time. When exclusion time was shorter than or equal to 3 years, grazing exclusion did not affect below‐ground biomass. In contrast, when exclusion time was longer than 3 years, grazing exclusion reduced below‐ground biomass by 62% (0–10 cm depth) and by 40% (total depth). Excluding South American grasslands from the global databases may introduce some biases in the observed patterns.

There is little evidence on the extent that multiple factors simultaneously limit ecosystem function of grasslands with year-round production. Here we test if multiple factors simultaneously limit (i.e., more than one factor at a time) grassland functioning in different seasons and how they interacted with N availability. In a Flooding Pampa grassland, we ran a separate factorial experiment in spring, summer, and winter with several treatments: control, mowing, shading, P addition, watering (only in summer), and warming (only in winter), each of them crossed with two nitrogen treatments: control and N addition. Grassland functioning was assessed by aboveground net primary productivity (ANPP), green and standing dead biomass, and N content at the species group level. Out of 24 potential cases (three seasons by eight response variables), 13 corresponded to just one limiting factor, 4 to multiple limiting factors, and the other 7 to no evidence of limitation. In conclusion, grassland functioning in each season was most often limited by just one factor, while multiple limiting factors were rarer. Nitrogen was the prevailing limiting factor. Our study expands our knowledge of limitations imposed by factors associated with disturbance and stress, such as mowing, shading, water availability, and warming in grasslands with year-round production.

The flora of high mountain areas is one of the least known and one of the most threatened by climate change. In addition, the phytogeographic delimitation of the mountains is difficult and not accurate enough. In this work we describe the flora of the Altoandina province in the Southern Cone of South America based on the geographical distribution of taxa exclusive to this province, we characterize the subdivisions at a regional level and generate a map of the identified districts. The results show that 883 taxa are exclusive of this province, of which 151 are only present in Chile, 220 in Argentina, and 512 are shared by both countries or are also present in Bolivia or other Andean countries. Asteraceae, Poaceae, Fabaceae, and Violaceae are the richest families in the province, while Senecio, Viola and Nototriche are the richest genera. Through a network-based analysis, we confirm the presence of three Districts in the Altoandina province: Quechua, Cuyano-Pikumche, and Nothoandino. This work aims to contribute to the knowledge on geographical patterns of the High Andean flora and its conservation.

Legume overseeding along with P fertilization is a common practice used in natural temperate and subtropical grasslands to increase forage production. This practice has been evaluated at experimental plots but not at the paddocks level of commercial farms. The latter are realistic evaluation units to generate knowledge for livestock management. In this study, the enhanced vegetation index (EVI), a proxy of forage production, was used to evaluate the effect of this practice on grazed paddocks in Uruguay. Twenty paired paddocks under similar grazing conditions were selected with natural grassland (NG) and natural grassland with legume overseeding and P fertilization (NG-LP). Paired paddocks were compared in terms of EVI mean and its temporal variability. After nine years of the intensification practice, mean annual EVI of NG-LP was 4% higher than that of NG, while the mean winter–spring EVI of NG-LP was 7.5% higher. EVI intra- and inter-annual variability of NG-LP was 8–11% higher than that of NG. Additionally, forage production was estimated using a radiative transfer model. Differences between NG-LP and NG were amplified six to seven times. Legume overseeding along with P fertilization increased forage production in pastoral livestock paddocks, particularly in the period of forage deficit, while it also increased intra and inter-annual variability of forage production.

There is little evidence on the extent that multiple factors simultaneously limit ecosystem function of grasslands with year-round production. Here we test if multiple factors simultaneously limit grassland functioning in different seasons (i.e., more than one factor at a time), and how they interacted with N availability. In a Flooding Pampa grassland, we ran a separate factorial experiment in spring, summer, and winter with several treatments: control, mowing, shading, P addition, watering (only in summer), and warming (only in winter), each of them crossed by two nitrogen treatments: control and N addition. Grassland functioning was assessed by aboveground net primary productivity (ANPP), green and standing dead biomass and N content at species group level. Out of 24 potential cases (three seasons by eight response variables), 13 corresponded to just one limiting factor, 4 to multiple limiting factors, and the other 7 to no evidence of limitation. In conclusion, grassland functioning in each season was most often limited by just one factor, while multiple limiting factors were rarer. Nitrogen was the prevailing limiting factor. In grasslands, the multiple factors hypothesis was tested broadly only with nutrient manipulations. Our study expands our knowledge to limitations imposed by factors associated to disturbance and stress, as mowing, shading, water availability and warming in grasslands with year-round production.

CONTEXT Mechanistic models have been mostly used to estimate sorghum grain yield under optimal growth conditions. There is a lack of model testing for crop growth and development responses for forage genotypes and information for phenological parameterization under sub-optimal water and nitrogen stress conditions in forage systems.OBJETIVEThe aims of this study were to (i) use NDVI to parametrize APSIM model to estimate sorghum phenology, (ii) calibrate APSIM to simulate green cover, intercepted solar radiation and aboveground biomass, and (iii) quantify the variance of inter-annual aboveground biomass and the effect of water availability on biomass under sub-optimal environment × management combinations.METHODSWe use climate, soil, management records and sorghum crop observations collected from farm and field experiments in Argentina and Australia. NDVI values were gathered from Sentinel-2 and a handheld optical sensor and then related to fAPAR measurements. Phenological stages were derived from fAPAR seasonal dynamics and implemented as input in the APSIM calibration. Finally, we assessed the temporal AGB variability through a long-term simulation.RESULTS AND CONCLUSIONSNDVI seasonal dynamics accurately represent the fraction of the absorbed photosynthetically active radiation (R 2 =0.92) and then, the remote-sensing parametrized APSIM model satisfactorily simulated crop phenology (CCC=0.75-0.92, NRMSE=9-22%). The model was also able to satisfactorily simulate crop growth (CCC=0.89 and NRMSE=24.8% for green cover; CCC=0.81 and NRMSE=34.6% for intercepted solar radiation; CCC=0.91 and NRMSE=37% for aboveground biomass). APSIM simulations during 22 years across 5 contrasting locations showed high inter-annual variability of aboveground biomass (CV=47%), mainly driven by inter-annual variation of soil water availability (CV=20%). This study demonstrated the validity of APSIM, using remote sensing data, to simulate crop growth and development of forage sorghum under sub-optimal growth conditions across several genotype × environment × management combinations. Also, demonstrate that water availability is the main driver of aboveground biomass inter-annual variability.SIGNIFICANCEGiven the pressure of the global human population to satisfy an increasing demand for food, our results provide a new path for the combined use of remote sensing and mechanistic modelling to improve forage sorghum biomass estimations in marginal environments.