Species losses, gains, and changes in persistent species are associated with distinct effects on ecosystem functioning in global grasslands

Global change drivers such as anthropogenic nutrient inputs simultaneously alter biodiversity, species composition, and ecosystem functions such as above ground biomass. These changes are interconnected by complex feedbacks among extinction, invasion, and shifting relative abundance. Here, we use a novel temporal application of the Price equation to separate species richness and biomass change through time and quantify the functional contributions of species that are lost, gained, and persist under ambient and experimental nutrient addition in 59 global grasslands. Under ambient conditions, compositional and biomass turnover was high, but species losses (i.e., local extinctions) were balanced by gains (i.e. colonization). Under fertilization, there was biomass loss associated with species loss. Few species were gained in fertilized conditions over time but those that were, and species that persisted, contributed to net biomass gains, outweighing biomass loss. These components of community change are associated with distinct effects on measures of ecosystem functioning.

Metabolic strategies of sharing pioneer bacteria mediating fresh macroalgae breakdown

Macroalgae represent huge amounts of biomass worldwide, largely recycled by marine heterotrophic bacteria. We investigated the strategies of pioneer bacteria within the flavobacterial genus Zobellia to initiate the degradation of fresh brown macroalgae, which has received little attention compared to the degradation of isolated polysaccharides. Zobellia galactanivorans DsijT could use macroalgae as a sole carbon source and extensively degrade algal tissues without requiring physical contact, via the secretion of extracellular enzymes. This indicated a sharing behaviour, whereby pioneers release public goods that can fuel other bacteria. Comparisons of eight Zobellia strains, and strong transcriptomic shifts in Z. galactanivorans cells using fresh macroalgae vs. isolated polysaccharides, revealed potential overlooked traits of pioneer bacteria. Besides brown algal polysaccharide degradation, they notably include stress resistance proteins, type IX secretion system proteins and novel uncharacterized Polysaccharide Utilization Loci. Overall, this work highlights the relevance of studying fresh macroalga degradation to fully understand the niche, metabolism and evolution of pioneer degraders, as well as their cooperative interactions within microbial communities, as key players in macroalgal biomass turnover.

Global evaluation of the nutrient-enabled version of the land surface model ORCHIDEE-CNP v1.2 (r5986)

The availability of phosphorus (P) and nitrogen (N) constrains the ability of ecosystems to use resources such as light, water and carbon. In turn, nutrients impact the distribution of productivity, ecosystem carbon turnovers and their net exchange of CO2 with the atmosphere in response to variation of environmental conditions in both space and time. In this study, we evaluated the performance of the global version of the land surface model ORCHIDEE-CNP (v1.2), which explicitly simulates N and P biogeochemistry in terrestrial ecosystems coupled with carbon, water and energy transfers. We used data from remote sensing, ground-based measurement networks and ecological databases. Components of the N and P cycle at different levels of aggregation (from local to global) are in good agreement with data-driven estimates. When integrated for the period 1850 to 2017 forced with variable climate, rising CO2 and land use change, we show that ORCHIDEE-CNP underestimates the land carbon sink in the Northern Hemisphere (NH) during recent decades despite an a priori realistic gross primary productivity (GPP) response to rising CO2. This result suggests either that processes other than CO2 fertilization, which are omitted in ORCHIDEE-CNP such as changes in biomass turnover, are predominant drivers of the northern land sink and/or that the model parameterizations produce emerging nutrient limitations on biomass growth that are too strict in northern areas. In line with the latter, we identified biases in the simulated large-scale patterns of leaf and soil stoichiometry as well as plant P use efficiency, pointing towards P limitations that are too severe towards the poles. Based on our analysis of ecosystem resource use efficiencies and nutrient cycling, we propose ways to address the model biases by giving priority to better representing processes of soil organic P mineralization and soil inorganic P transformation, followed by refining the biomass production efficiency under increasing atmospheric CO2, phenology dynamics and canopy light absorption.

Dung-beetle (Coleoptera: Scarabaeidae: Scarabaeinae) assemblage in two livestock production systems in a southern Mexican High Plateau semiarid ecosystem

In this work, we used measures of diversity and biogeographic patterns to evaluate the response of dung-beetle assemblages (Coleoptera: Scarabaeidae: Scarabaeinae) at two cattle ranches with different management systems on the southern Mexican High Plateau. The number of individuals and biomass were used as the primary diversity attributes of the assemblage. The 1D and 2D true diversity indexes of these attributes were examined, and the attributes were classified according to Halffter’s biogeographical patterns. In total, 1375 Scarabaeinae adults were collected, representing 11 species and seven genera. Site management regime did not significantly affect species richness or assemblage structure when the number of individuals was considered. However, species diversity and biomass turnover were higher in the system with holistic management than in that with semitechnified management. The proportions of Halffter’s biogeographical patterns also differed between the two production systems. In conclusion, the location under holistic management, despite having cattle production, contained a significant proportion of the Scarabaeinae species that are typical of the Mexican High Plateau. In contrast, the semitechnified system negatively impacted beetle abundance, leading to half the individuals, the dominance of species with high biomass, and the absence of groups typical of the region.