Global organization of terrestrial plant-nutrient interactions.

Abstract

The global extent of earth system change is challenging plant ecologists and physiologists to understand the organization of plant–nutrient relations across scales of observation, from leaf physiology to biosphere feedbacks. Central to this concern are the roles of nitrogen (N) and phosphorus (P) as the major growth-limiting nutrients for plant communities worldwide (1, 2) and as determinants of key physiological processes such as photosynthetic CO2 fixation (N-rich enzymes; refs. 3 and 4) and cellular biosynthesis (P-rich RNA and ATP; ref. 5). Thus far, terrestrial ecologists and physiologists have largely focused on local and site-specific insights, with few attempts to understand geographically broad variations in plant–nutrient interactions (however, see refs. 4, 6, and 7), or the factors that may give rise to such trends. On page 11001 of this issue of PNAS, Reich and Oleksyn (8) analyze data from plant species worldwide to document dramatically broad variations in leaf N and P vs. carbon (C) contents as functions of latitude and mean annual temperature (MAT; both factors are highly correlated worldwide). This paper constitutes one of three current and complementary efforts (refs. 8, 9, and A. J. Kerkhoff, B. J. Enquist, J. J. Elser, and W. F. Fagan, unpublished work) to document such global-scale variations in plant nutrient investment, and to search for the factors that govern their origin and maintenance. Reich and Oleksyn (8) identify two fundamental and geographically broad trends in leaf N and P investment: ( i ) decreasing leaf P content, and to a lesser degree N content, with decreasing latitude (increasing MAT), and ( ii ) increasing leaf N:P ratio with decreasing latitude (increasing MAT). The strength of this analysis comes from their use of an extraordinarily rich and diverse data set (cf., ref. 10): 1,280 plant species in 704 genera, across 452 locations …