Biology subjects

Tognetti, P. M.

Publications and source records attributed to Tognetti, P. M..

3 recordsLinked to original sources

bioRxiv2025

Plant litter decomposition in global drylands is better predicted by precipitation seasonality and temperature than by aridity

Understanding the global carbon (C) balance in terrestrial ecosystems is crucial for predicting their current and future roles as C sources or sinks in the context of global change. Drylands, covering nearly 45% of Earths land surface, contribute significantly to net primary production (NPP) and influence the interannual variability of the terrestrial C sink. However, the controls on plant litter decomposition, a major pathway of C release, remain unclear in these ecosystems. Here, we present a global analysis of plant litter decomposition in drylands, using a dataset from 116 sites across five continents spanning diverse climates and ecosystems. We found that litter decomposition does not correlate with mean annual precipitation (MAP) at the global scale, challenging the paradigm that water availability is the primary constraint on ecological processes in drylands. Instead, our analysis identifies mean annual temperature (MAT), precipitation-temperature synchrony, precipitation variability, and cloud cover frequency as key drivers. Specifically, our model predicted faster decomposition rates for warmer and more monsoonal ecosystems, but vary independently of MAP. Additionally, decomposition correlated positively with both lignin and nitrogen content, in contrast to the negative lignin-decomposition relationship commonly observed in mesic ecosystems. These findings suggest a fundamental mismatch between aridity and its expected effects on decomposition rates in terrestrial ecosystems. Given the ongoing expansion of drylands, rising temperatures and changes in precipitation variability under climate change; our results underscore the need to refine decomposition models beyond traditional aridity frameworks. Such refinement is essential for accurately predicting dryland contributions to the global C balance.

ecology↗

bioRxiv2024

Nutrient addition in grasslands worldwide reveals proportional plant diversity decline across spatial scales but little change in beta diversity

Nutrient enrichment typically causes local plant diversity declines. A common but untested expectation is that nutrient enrichment also reduces variation in nutrient conditions among localities and selects for a smaller pool of species, causing greater diversity declines at larger than local scales and thus biotic homogenization. Here we apply a framework that links changes in species richness across scales to changes in the numbers of spatially restricted and widespread species for a standardized nutrient addition experiment across 72 grasslands on six continents. Overall, we find proportionally similar species loss at local and larger scales, suggesting similar declines of spatially restricted and widespread species, and no biotic homogenization after 4 years and up to 14 years of treatment. These patterns of diversity changes are generally consistent across species groups. Thus, nutrient enrichment poses threats to plant diversity, including for widespread species that are often critical for ecosystem functions.

ecology↗

bioRxiv2022

Temperature seasonality and nutrient enrichment drive intra-annual community turnover in global grasslands

In many grasslands, species with specific traits occupy unique temporal positions within communities. Such intra-annual segregation is predicted to be greatest in systems with high intra-annual climate variability because fluctuating environmental conditions provide opportunities for temporal niche partitioning among species. However, because most studies on intra-annual community dynamics have been conducted at individual sites, relationships between intra-annual climate variability and seasonal community dynamics at global scales have not yet been identified. Furthermore, the same characteristics that promote species-specific responses to fluctuations in environmental conditions may also drive species-specific responses to global change drivers such as eutrophication. Research provides evidence that eutrophication alters inter-annual plant community dynamics yet understanding of how it alters intra-annual dynamics remains limited. We used early-season and late-season compositional data collected from 10 grassland sites around the world to ask how intra-annual variability in precipitation and temperature as well as nutrient enrichment shape intra-annual species segregation, or seasonal {beta}-diversity, in plant communities. We also assessed whether changes in the abundances of specific functional groups including annual forbs, perennial forbs, C3 and C4 graminoids, and legumes underpin compositional differences between early- and late-season communities and treatments. We found that intra-annual temperature variability and seasonal {beta}-diversity were positively related but observed no relationship between intra-annual precipitation variability and seasonal {beta}-diversity. This suggests that positive relationships between -diversity and intra-annual temperature variability identified in earlier studies may be underpinned by the positive influence of intra-annual temperature variability on temporal segregation of species within growing seasons. We found that nutrient enrichment increased seasonal {beta}-diversity via increased turnover of species between early- and late-season communities. This finding mirrors patterns observed at inter-annual scales and suggests fertilization can alter compositional dynamics via similar mechanisms at varied temporal scales. Finally, fertilization reduced the abundance of C4 graminoids and legumes and eliminated intra-annual differences in these groups. In contrast, fertilization resulted in intra-annual differences in C3 graminoids which were not observed in control conditions, and increased abundance of C3 graminoids and annual forbs overall. Our study provides new insight into how intra-annual climate variability and nutrient enrichment influence biodiversity and seasonal dynamics in global grasslands.

ecology↗