Abstract Plant populations are limited by resource availability and exhibit physiological trade‐offs in resource acquisition strategies. These trade‐offs may constrain the ability of populations to exhibit fast growth rates under water limitation and high cover of neighbours. However, traits that confer drought tolerance may also confer resistance to competition. It remains unclear how fitness responses to these abiotic conditions and biotic interactions combine to structure grassland communities and how this relationship may change along a gradient of water availability. To address these knowledge gaps, we estimated the low‐density growth rates of populations in drought conditions with low neighbour cover and in ambient conditions with average neighbour cover for 82 species in six grassland communities across the Central Plains and Southwestern United States. We assessed the relationship between population tolerance to drought and resistance to competition and determined if this relationship was consistent across a precipitation gradient. We also tested whether population growth rates could be predicted using plant functional traits. Across six sites, we observed a positive correlation between low‐density population growth rates in drought and in the presence of interspecific neighbours. This positive relationship was particularly strong in the grasslands of the northern Great Plains but weak in the most xeric grasslands. High leaf dry matter content and a low (more negative) leaf turgor loss point were associated with high population growth rates in drought and with neighbours in most grassland communities. Synthesis : A better understanding of how both biotic and abiotic factors impact population fitness provides valuable insights into how grasslands will respond to extreme drought. Our results advance plant strategy theory by suggesting that drought tolerance increases population resistance to interspecific competition in grassland communities. However, this relationship is not evident in the driest grasslands, where above‐ground competition is likely less important. Leaf dry matter content and turgor loss point may help predict which populations will establish and persist based on local water availability and neighbour cover, and these predictions can be used to guide the conservation and restoration of biodiversity in grasslands.
Abstract Fine root traits span two independent axes of variation, the conservation and collaboration axes, which define the root economic space (RES). However, whether early‐stage fine root decomposition rates (quantified as proportion mass loss, i.e. pml ) are more strongly related to collaboration or conservation traits remains unclear. We studied 63 tree species in New Zealand's temperate rain forest. We determined the phylogenetic signal in pml and fine root traits, conducted phylogenetic principal component analysis and used phylogenetic generalized least squares to determine which traits are most strongly related to pml . Root decomposition exhibited a high phylogenetic signal and was more strongly related to the conservation than the collaboration axis. Root tissue density (RTD) was negatively correlated and root nitrogen (RN) was positively correlated with pml . Root diameter was positively yet weakly correlated with pml , but specific root length was uncorrelated with pml . The lignin‐to‐N ratio and root cellulose were the strongest predictors of pml . Synthesis : Early‐stage fine root decomposition is most strongly driven by tissue quality traits, such as root nitrogen, tissue density and lignin‐to‐N ratio, which all align with the conservation axis of the root economics space. However, root diameter plays a weak yet undeniable role in early‐stage fine root decomposition. Some thick‐rooted species decomposed faster, possibly due to the higher quality cortical tissue. Thin‐rooted species decomposed slower, possibly because of their higher cellulose concentration that maintains the structural integrity of small diameter roots. Relationships between decomposition and other traits that align with the collaboration gradient deserve further study across the phylogeny of vascular plants.
ditorial Eddy van der Maarel passed away on 4 April 2021.With his death, the International Association for Vegetation Science lost one of its longest standing members and a person who has shaped modern vegetation science and has served and fostered our society in so many ways.Many of the IAVS officers, editors of our journals and members have lost a close colleague and friend, some of us considering him as an academic father.Eddy was born in 1934 in Amsterdam and spent the first part of his academic career at different universities in the Netherlands.In 1981, he moved to the famous Växtbiologiska institutionen (Institute of Plant Biology) in Uppsala, Sweden, and assumed the oldest and most prestigious chair in our field.After his retirement he moved back to his home country.Eddy's favourite study objects as a plant ecologist were dune ecosystems and alvar grasslands.Already early in his scientific career he showed a strong interest in theoretical vegetation science and computational data processing, scientific fields for which he (co-)founded innovative and ground-breaking IAVS working groups.In his engagement for the association he served as member of the Advisory Council and Vice-President for many years.Eddy became globally renowned as a long-time Editor-in-Chief of Vegetatio and as one of the founders of the Journal of Vegetation Science and later Applied Vegetation Science.His outstanding work and services were recognized by memberships of the Royal Netherlands Academy of Arts and Sciences and the Royal Swedish Academy of Sciences, as well as by honorary membership of the IAVS.Eddy's professional life, however, went well beyond these formal achievements.We, as his colleagues and pupils, also remember his tireless efforts to bring together people from different countries and cultures, to enable students from low-income countries to come to his institute in Sweden and to the annual symposia of IAVS, and to make the society journals accessible to as many libraries and personal subscribers as possible.He was the initiator of the Global Fund of IAVS, which lives on in the activities of our Global Sponsorship Committee.His vision of a global community of, and friendship between, vegetation ecologists was also reflected in the many field campaigns, for example in the Great Alvar on Öland that united researchers and students from many different countries, and in the many social evenings in his home in Uppsala where he played the piano and his wife Marijke and his children offered an unforgettable hospitality.
