Edaphic Specialization in Tropical Trees: Physiological Correlates and Responses to Reciprocal Transplantation

Abstract

Abstract. Recent research has documented the importance of edaphic factors in determining the habitat associations of tree species in many tropical rain forests, but the underlying mechanisms for edaphic associations are unclear. At Sepilok Forest Reserve, Sabah, Malaysian Borneo, two main soil types derived from sandstone (ridges) and alluvium (valleys) differ in nutrient and water availability and are characterized by forests differing markedly in species composition, structure, and understory light availability. We use both survey and reciprocal transplants to examine physiological adaptations to differences in light, nutrient, and water availability between these soil types, and test for the importance of resource-use efficiency in determining edaphic specialization. Photosynthetic surveys for congeneric and confamilial pairs (one species per soil type) of edaphic specialists and for generalists common to both soil types show that species specializing on sandstonederived soil had lower stomatal conductance at a given assimilation rate than those occurring on alluvial soil and also had greater instantaneous and integrated water-use efficiencies. Foliar dark respiration rates per unit photosynthesis were higher for sandstone ridge than alluvial lowland specialists. We suggest that these higher respiration rates are likely due to increases in photosynthetic enzyme concentrations to compensate for lower internal CO 2 concentrations resulting from increased stomatal closure. This is supported by lower photosynthetic nitrogen-use efficiencies in the sandstone ridge specialists. Generalist species had lower water-use efficiencies than sandstone ridge specialists when growing on the drier, sandy ridgetops, but their nitrogen-use efficiencies did not differ from the species specialized to the more resource-rich alluvial valleys. We varied light environment and soil nutrient availability in a reciprocal transplant experiment involving two specialist species from each soil type. Edaphic specialist species, when grown on the soil type for which they were not specialized, were not capable of acclimatory shifts to achieve similar resource-use efficiencies as species specialized to that soil type. We conclude that divergent water-use strategies are an important mechanism underlying differences in edaphic associations and thus contributing to maintenance of high local tree species diversity in Bornean rain forests.

Trait-based community assembly of understory palms along a soil nutrient gradient in a lower montane tropical forest

“…The 5 N ratio of plant leaves generally represents the (5 15 N ratio of the soil source the plant takes up, with nitrate having a lower (5 15 N ratio than ammonium in most cases (Hogberg 1997;but see Houlton 2007). Carbon isotope ratios have been used to represent integrated water-use efficiency over the leaf lifespan (Farquhar et al 1989;Baltzer et al 2005;Cernusak et al 2007). Leaf 5 C ratios arise from differences in the diffusivity of C and C in air and through the stomatal pathway, as well as from the enzymatic discrimination of the isotopes.…”

“…Leaf 5 C ratios arise from differences in the diffusivity of C and C in air and through the stomatal pathway, as well as from the enzymatic discrimination of the isotopes. Plants that use water more efficiently exhibit less negative (5 13 C ratios (Farquhar et al 1989;Baltzer et al 2005;Cernusak et al 2007). Instantaneous water use efficiency (WUE) was calculated from A max ( area ) and transpiration according to Lambers et al (1998) where A max (area ) -area-based photosynthetic rate (umol CO2 m~ s~ ) and N area -area-based leaf N content (g N cm -2 ).…”

“…Leaf size and quality have also been found to increase with soil nutrient availability in other studies (Reich et al 2003;Cavender-Bares et al 2004;Ordonez et al 2009). Reciprocal transplant experiments comparing species performance in high and low nutrient soils have shown that differences in resourceuse efficiency (Baltzer et al 2005) and trade-offs between growth and herbivore defense (Cunningham et al 1999;Fine et al 2004) are important in maintaining soil-based habitat associations in other tropical forests. Thus, resource-use strategies may influence community structure of understory palms in the lower montane forests of western Panama by promoting species turnover along soil nutrient gradients.…”

“…Rachis length, foliar 5 N, WUE and g s differed among sites in G. cuneata and were related to soil nutrient and water availability variables. Several studies have linked species distribution patterns with drought tolerance along rainfall or edaphic gradients (Baltzer et al 2005;Engelbrecht et al 2007) and leaf economics strategies with soil nutrient gradients (Craine et al 2002;Paoli 2006;Baltzer and Thomas 2010). Thus, plasticity along multiple trait axes may be important in allowing G. cuneata to persist at high densities at multiple sites despite strong environmental filters.…”

“…Soil-based habitat associations can arise directly from a combination of morphological or physiological functional traits, or indirectly via the effects of herbivores on survivorship or growth (Fine et al 2004;Palmiotto et al 2004;Baltzer et al 2005). Species specializing in low nutrient habitats share a suite of traits such as greater leaf lifespan and leaf toughness, and decreased foliar nutrient concentration, leaf area per unit mass (specific leaf area, SLA), photosynthetic potential and respiration rates (Chapin 1980;Chapin et al 1993;Aerts and Chapin 2000).…”