Testing the Growth Rate vs. Geochemical Hypothesis for latitudinal variation in plant nutrients

Abstract

Two hypotheses have been proposed to explain increases in plant nitrogen (N) and phosphorus (P) concentrations with latitude: (i) geochemical limitation to P availability in the tropics and (ii) temperature driven variation in growth rate, where greater growth rates (requiring greater nutrient levels) are needed to complete growth and reproduction within shorter growing seasons in temperate than tropical climates. These two hypotheses were assessed in one forest type, intertidal mangroves, using fertilized plots at sites between latitudes 36 masculine S and 27 masculine N. The N and P concentrations in mangrove leaf tissue increased with latitude, but there were no trends in N : P ratios. Growth rates of trees, adjusted for average minimum temperature showed a significant increase with latitude supporting the Growth Rate Hypothesis. However, support for the Geochemical Hypothesis was also strong; both photosynthetic P use efficiency and nutrient resorption efficiency decreased with increasing latitude, indicating that P was less limiting to metabolism at the higher latitudes. Our study supports the hypothesis that historically low P availability in the tropics has been an important selective pressure shaping the evolution of plant traits.

Lower P contents and more widespread terpene presence in old Bornean than in young Hawaiian tropical plant species guilds

“…In fact, not all the studies have detected general patterns of leaf N:P content ratios between and within the climate areas (Lovelock et al 2007, Townsend et al 2007, Vitousek et al 2010 and there are soil chronosequence studies that have observed that soil available-P was greater in the intermediate ages than in the young and old ages within the time sequence (Crews et al 1995. The average of leaf N:P content ratios observed in Hawaii plants (21.6 6 1.0) and in Borneo plants, (21.8 6 0.7) are high compared to other studies for woody plants throughout the world that report an average leaf N:P content ratio between 14 and 16 (Koerselman andMeuleman 1996, Gü sewell andBollens 2003).…”

“…v www.esajournals.org ships are observed between leaf N:P content ratios and either latitude or annual mean precipitation within the tropical area (Townsend et al 2007, Lovelock et al 2007. He et al (2008) investigated the changes of N:P ratios of 213 plant species across 199 research sites located in a climatic gradient.…”

“…Most studies have focused mainly on P and N, whereas other important nutrients and elements have not received much attention. On average, leaf N:P ratios of tropical forest are elevated (Davidson and Howarth 2007) and do not seem to vary much with either latitude or annual mean precipitation within the tropical area (Townsend et al 2007, Lovelock et al 2007, He et al 2008.…”

Growth and nutrient uptake among three wetland plant species occurring in Lake Victoria basin in Kenya

“…Mean N concentration in plant tissues was greater in plants grown at higher nutrient availability levels than in control treatments. Nitrogen is an essential component of all enzymes and phosphorus is vital for protein synthesis forming an essential component of RNA (Lovelock et al, 2007). The concentration of N and P in tissues also influences the rates of ecological processes, for example, grazing, parasitism and decomposition have been observed to be influenced by the stoichiometery of N and P within tissues (Lovelock et al, 2007).…”

Heterogeneity of elemental composition and natural abundance of stables isotopes of C and N in soils and leaves of mangroves at their southernmost West Atlantic range

“…At their latitudinal limits of occurrence frost is added to the environmental constraints for mangrove establishment, survival, and structural development (Lugo and Zucca, 1977;McMillan and Sherrod, 1986;Lovelock et al, 2007;Soares et al, 2012).…”