Global trends in senesced-leaf nitrogen and phosphorus

Aim Senesced-leaf litter plays an important role in the functioning of terrestrial ecosystems. While green-leaf nutrients have been reported to be affected by climatic factors at the global scale, the global patterns of senesced-leaf nutrients are not well understood. Location Global. Methods Here, bringing together a global dataset of senesced-leaf N and P spanning 1253 observations and 638 plant species at 365 sites and of associated mean climatic indices, we describe the world-wide trends in senesced-leaf N and P and their stoichiometric ratios. Results Concentration of senesced-leaf N was highest in tropical forests, intermediate in boreal, temperate, and mediterranean forests and grasslands, and lowest in tundra, whereas P concentration was highest in grasslands, lowest in tropical forests and intermediate in other ecosystems. Tropical forests had the highest N : P and C : P ratios in senesced leaves. When all data were pooled, N concentration significantly increased, but senesced-leaf P concentration decreased with increasing mean annual temperature (MAT) and mean annual precipitation (MAP). The N : P and C : P ratios also increased with MAT and MAP, but C : N ratios decreased. Plant functional type (PFT), i.e. life-form (grass, herb, shrub or tree), phylogeny (angiosperm versus gymnosperm) and leaf habit (deciduous versus evergreen), affected senesced-leaf N, P, N : P, C : N and C : P with a ranking of senesced-leaf N from high to low: forbs approximate to shrubs approximate to trees > grasses, while the ranking of P was forbs approximate to shrubs approximate to trees < grasses. The climatic trends of senesced-leaf N and P and their stoichiometric ratios were similar between PFTs. Main conclusions Globally, senesced-leaf N and P concentrations differed among ecosystem types, from tropical forest to tundra. Differences were significantly related to global climate variables such as MAT and MAP and also related to plant functional types. These results at the global scale suggest that nutrient feedback to soil through leaf senescence depends on both the climatic conditions and the plant composition of an ecosystem.