N availability and mechanisms of N conservation in deciduous and semideciduous tropical forest legume trees

Abstract

RESUMO -(Disponibilidade de N e mecanismos de conservação de N em leguminosas arbóreas decíduas e semidecíduas de floresta tropical). Antes da abscisão, os nutrientes são removidos das folhas e redistribuídos para outras partes da planta. Quando se relaciona o reaproveitamento de nutrientes à fertilidade do solo, ou à longevidade foliar, os dados da literatura são controversos. Foram comparados mecanismos de conservação de nitrogênio (N) em quatro leguminosas arbóreas (Hymenaea courbaril L. var. stilbocarpa (Hayne) Lee et Lang., Lonchocarpus guilleminianus (Tul.) Malme, Enterolobium contortisiliquum (Vell.) Morong e Peltophorum dubium (Spreng.) Taub.), com longevidades foliares diferentes, de uma Floresta Semidecídua, remanescente da mata Atlântica. O objetivo do trabalho foi verificar se esses mecanismos são diferentes nas quatro espécies e se são afetados pela longevidade foliar e disponibilidade de N, tanto mineral, como proveniente de fixação simbiótica, no caso de L. guilleminianus e E. contortisiliquum, que apresentam associação com rizóbios. As plantas foram cultivadas em vasos contendo solo da mata, enriquecido (50 ou 100 mg de NH 4 NO 3 planta -1 semana -1 ) ou não com N mineral. H. courbaril, uma semidecídua que não fixa N e possui a maior longevidade foliar dentre as espécies analisadas, apresentou a maior eficiência de reaproveitamento de N (ERN), proficiência de reaproveitamento de N (PRN) e eficiência de utilização de N (EUN). O acréscimo de N no solo e a presença de fixação simbiótica de N levaram a decréscimos em ERN, PRN e EUN.Palavras-chave: longevidade foliar, fixação de nitrogênio, eficiência de reaproveitamento de nitrogênio, proficiência de reaproveitamento de nitrogênio, eficiência do uso de nitrogênio ABSTRACT -(N availability and mechanisms of N conservation in deciduous and semideciduous tropical forest legume trees). Prior to abscission, nutrients are redeployed from leaves and redistributed to other parts of the plant. Data comparing nutrient resorption to soil fertility and leaf life span remains controversial in the literature. We compared nitrogen (N) conservation mechanisms among four legume trees with different leaf life spans (Hymenaea courbaril L. var. stilbocarpa (Hayne) Lee et Lang., Lonchocarpus guilleminianus (Tul.) Malme, Enterolobium contortisiliquum (Vell.) Morong and Peltophorum dubium (Spreng.) Taub.), from a semideciduous tropical forest, remnant of the Atlantic Forest. We hypothesized that these mechanisms differ among the four species and are affected by their leaf life span and by the availability of N, both as a mineral in the soil and, in the case of L. guilleminianus and E. contortisiliquum, from symbiotic nitrogen fixation (SNF), as these species form associations with rhizobia. The plants were grown in a greenhouse using pots filled with forest soil, enriched (50 or 100 mg of NH 4 NO 3 plant -1 week -1 ) or not with nitrogen. H. courbaril, a semideciduous tree, without SNF, and with the highest leaf life span, presented the greatest N-resorption efficiency (NR...

Dinitrogen‐fixing Acacia species from phosphorus‐impoverished soils resorb leaf phosphorus efficiently

“…As A. robeorum derived a significant proportion (75%) of its leaf N from the air, and soil total [N] at its location was the highest among the study sites, the species probably obtained enough N through N 2 ‐fixation and N uptake from the soil without resorbing N from senescing leaves. There are reports that increase in soil N and the presence of symbiotic N 2 ‐fixation result in a decrease in NRE (Killingbeck 1996; Lima et al . 2006), even though N 2 ‐fixation is an energy‐costly process (Houlton et al .…”

Nitrogen availability, leaf life span and nitrogen conservation mechanisms in leaves of tropical trees

“…There is little data in the literature relating leaf longevity to resorption proficiency. Oleksyn et al (2003) and Lima et al (2006b) verified that the species with the highest leaf life span presented the greatest nitrogen resorption proficiency. Our results are consistent with these observations since nitrogen resorption proficiency for A. occidentale was higher than for B. orellana (Table 2), indicating that A. occidentale losses this element to the environment are smaller.…”

“…Pugnaire & Chapin, 1993). However, when an attempt is made to relate this parameter to soil fertility, the results are controversial (Cordell et al, 2001;Carrera et al, 2003;Feller et al, 2003;Distel et al, 2003;Richardson et al, 2004;Lima et al, 2006b). Nitrogen resorption efficiency data did not have a clear relationship with the availability of this element in the substrate (Table 3).…”

“…Nevertheless, there is no consensus when comparing these two groups of plants (Lal et al, 2001;Diehl et al, 2003). The relationship between nutrient resorption efficiency and soil fertility is also controversial (Carrera et al, 2003;Lima et al, 2006b). Resorption proficiency, the absolute value by which nutrients are reduced in senescent leaves is a more objective measure of the degree by which the plants minimize nutrient loss (Killingbeck, 1996).…”

The soil-plant relationship of nitrogen use in three tropical tree species

“…One of them is the high efficiency of nitrogen resorption observed by Lima et al (2006) combined with the longer life of its leaves, which represents a form of nutrient conservation and mineral loss reduction during senescence and leaf fall (Aerts, 1996;Carrera et al, 2003;Eckstein et al, 1999, Lima et al, 2006. This is an important adaptation mechanism (May and Killingbeck, 1992;Pugnaire and Chapin, 1993) that favors its use in the recolonization of low fertility soils (Aerts, 1996;Eamus and Prichard, 1998).…”