The resorption of phosphorus is greater than that of nitrogen in senescing leaves of vascular epiphytes from lowland Panama

Abstract

The epiphytic habitat is assumed to be nutrient deficient, although this generally held notion is based almost completely on circumstantial evidence (Zotz & Hietz 2001). Most studies on the nutrient relations of vascular epiphytes focus on nitrogen (Bergstrom & Tweedie 1998, Hietz & Wanek 2003, Stewart et al. 1995). Although nitrogen plays a key role in limiting plant growth worldwide, there is an on-going discussion whether nitrogen or rather phosphorus are more limiting in many tropical forests (Grubb 1989, Harrington et al. 2001, Vitousek & Howarth 1991). To identify which nutritional factor is most limiting for plant growth, nutrient ratios have been proposed as a very useful tool (Koerselman & Meuleman 1996). These authors stated that N:P ratios exceeding 16 are indicative of P limitation, while an N:P ratio <14 suggests N limitation. Some reports of such ratios in the epiphyte literature indicate that phosphorus may indeed be limiting for epiphytes in tropical forests. For example, the N:P ratio of two field-grown bromeliads (Tillandsia circinnata and T. usneoides) decreased dramatically from 23.6 and 40.4, respectively, to 3.6 and 3.4, respectively, when fertilized with both N and P in the laboratory (Benzing & Renfrow 1974a). On the other hand, however, the average N:P ratios of mature leaves of 41 epiphyte species compiled from a number of papers did not appear particularly high (12.1±10.5, cf. Zotz & Hietz 2001).

Contrasting nitrogen and phosphorus resorption efficiencies in trees and lianas from a tropical montane rain forest in Xishuangbanna, south-west China

“…Liana species showed similar NRE to tree species (P > 0.05), but had significantly lower PRE (F = 5.1, P = 0.033) than the tree species. In accordance with findings of other studies of nutrient relations during leaf senescence (Aerts 1996, Wright & Westoby 2003, Zotz 2004, nutrient resorption was not correlated with the nutrient status of green leaves prior to senescence (r = 0.19-0.37, P > 0.05) in either lianas or trees. These findings indicate that the efficiency of the resorption process is not determined by plant nitrogen status, as previously concluded in an analysis of data from temperate species (Aerts 1996) and demonstrated for various tropical forest tree species (Del Arco et al 1991, Lal et al 2001, Wright & Westoby 2003.…”

Are vascular epiphytes nitrogen or phosphorus limited? A study of plant 15N fractionation and foliar N : P stoichiometry with the tank bromeliad Vriesea sanguinolenta

“…In wetlands, critical N : P ratios were found to range between 14 and 16, with N-limited plants having lower and P-limited plants having higher N : P ratios than this critical value (Koerselman & Meuleman, 1996;Güsewell, 2004). In vascular epiphytes, foliar N : P ratios were found to be 12.1 ± 10.5 (n = 41) (Zotz & Hietz, 2001), 16.1 ± 5.8 (n = 20) (Zotz, 2004) and 19.0 ± 5.3 (n = 195) (Cardelus & Mack, 2010), which implies a continuum between N-limited and P-limited vascular epiphytes. However, critical N : P ratios vary between plant species, and between developmental stages, and therefore the range of 14-16 cannot be applied universally (Güsewell, 2004).…”

Fertilizantes agrícolas aplicados via solução nutritiva em Cattleya labiata Lindl

“…Outro ponto relevante é que em sistemas naturais o P é absorvido rapidamente de soluções altamente diluídas e transitórias do dossel e, para plantas epífitas é o nutriente mais limitante. Deste modo as mesmas possuem alta eficiência na sua absorção bem como alta capacidade de realocação do nutriente (ZOTZ, 2004 …”

“…É reconhecido que o habitat epifítico possui baixa disponibilidade de nutrientes, no qual as plantas epífitas apresentam eficiente capacidade de absorção e remobilização de nutrientes (ZOTZ, 2004). Entretanto em cultivos comerciais as fontes naturais de nutrientes ficam comprometidas, Naik et al (2009), destacam em orquídeas epífitas, que os nutriente N, P e K são os mais estudados na fertilização inorgânica.…”