Faster returns on ‘leaf economics’ and different biogeochemical niche in invasive compared with native plant species

Plant‐invasive success is one of the most important current global changes in the biosphere. To understand which factors explain such success, we compared the foliar traits of 41 native and 47 alien‐invasive plant species in Oahu Island (Hawaii), a location with a highly endemic flora that has evolved in isolation and is currently vulnerable to invasions by exotic plant species. Foliar traits, which in most cases presented significant phylogenetic signal, i.e. closely related species tended to resemble each other due to shared ancestry, separated invasive from native species. Invasive species had lower leaf mass per area and enhanced capacities in terms of productivity (photosynthetic capacity) and nutrient capture both of macro‐ (N, P, K) and microelements (Fe, Ni, Cu and Zn). All these differences remain highly significant after removing the effects of phylogenetic history. Alien‐invasive species did not show higher efficiency at using limiting nutrient resources, but they got faster leaf economics returns and occupied a different biogeochemical niche, which helps to explain the success of invasive plants and suggests that potential increases in soil nutrient availability might favor further invasive plant success.     

Changes in N and S Leaf Content, Stomatal Density and Specific Leaf Area of 14 Plant Species during the Last Three Centuries of CO2 Increase

Parallel to the increase in atmospheric CO² from 278 µmolmol^–1 in AD 1750 to the current ambient level of 348 µmolmol^–1, there have been overall decreases in leaf nitrogencontent and stomatal density from 144% and 121%, respectively,in AD 1750 to 100% today of herbarium specimens of 14 trees,shrubs, and herbs collected over the last 240 years in Catalonia,a Mediterranean climate area. These decreases were steeper duringthe initial slower increases in CO₂ atmospheric levels as comparedwith the relatively faster CO₂ increases in recent years. Thedeclines in leaf N content and stomatal density have also beenreported in experimental studies on leaves of plants grown underenriched CO₂ environments. Meanwhile, the stomatal index andoverall carbon and sulphur leaf contents have not changed significantly.Leaf S content was higher in the 1940s samples coinciding withthe burning of increased quantities of sulphur-rich coal. Consequently,the epidermal cell density has decreased parallel to the stomataldensity and the C/N ratio of leaves has increased, implyingpossible important consequences on herbivores, decomposers,and ecosystems. An overall decrease in the specific leaf area(SLA) from 184% in the 18th century to 100% today has also beenfound, as would be expected under CO₂ enrichment, but whichmight also be an artifact of prolonged storage. Key words: Carbon dioxide increase, leaf nitrogen content, leaf sulphur content, stomatal density, last centuries     

Variations in the Mineral Composition of Herbarium Plant Species Collected During the Last Three Centuries

Mineral content (dry weight basis) was determined for herbariumspecimens of 12 C₃ plants (trees, shrubs and herbs) collectedduring the last 250 years in N.E. Spain. Present values of Al,Ca, Cu, Sr, Fe, P, Mg, Mn, K, Na, S, and Zn were always lowerthan in any other period of the last three centuries. Only oneC₄ plant was analysed. It presented a similar pattern to theC₃ plants. These results are in accordance with experimentalresults that have shown that the mineral content of plants grownin elevated CO₂ is generally lowered. Increased atmosphericCO₂ and other anthropogenic environmental changes are suggestedas possible causes of the changes in mineral content. Key words: Leaf mineral content, Al, Ca, Cu, Sr, Fe, P, Mg, Mn, K, Na, S, Zn, herbaria, last three centuries