Functional traits determine tree growth and ecosystem productivity of a tropical montane forest: Insights from a long‐term nutrient manipulation experiment

Abstract

Trait-response effects are critical to forecast community structure and biomass production in highly diverse tropical forests. Ecological theory and few observation studies indicate that trees with acquisitive functional traits would respond more strongly to higher resource availability than those with conservative traits. We assessed how long-term tree growth in experimental nutrient addition plots (N, P, and N + P) varied as a function of morphological traits, tree size, and species identity. We also evaluated how trait-based responses affected stand scale biomass production considering the community structure. We found that tree growth depended on interactions between functional traits and the type or combination of nutrients added. Common species with acquisitive functional traits responded more strongly to nutrient addition, mainly to N + P. Phosphorous enhanced the growth rates of species with acquisitive and conservative traits, had mostly positive effects on common species and neutral or negative effects in rare species. Moreover, trees receiving N + P grew faster irrespective of their initial size relative to trees in control or to trees in other treatment plots.Finally, species responses were highly idiosyncratic suggesting that community processes including competition and niche dimensionality may be altered under increased resource availability. We found no statistically significant effects of nutrient additions on aboveground biomass productivity because acquisitive species had a limited potential to increase their biomass, possibly due to their generally lower wood density. In contrast, P addition increased the growth rates of species characterized by more conservative resource strategies (with higher wood density) that were poorly represented in the plant community. We provide the first long-term experimental evidence that trait-based responses, community structure, and community processes modulate the effects of increased nutrient availability on biomass productivity in a tropical forest.

Plant community responses to stand‐level nutrient fertilization in a secondary tropical dry forest

“…A similar experiment in a Costa Rican wet forest found no stand-level responses to N or P, although smaller stems exhibited faster wood growth with P addition (Alvarez-Clare et al 2013). A long-term fertilization experiment in a tropical montane forest found no net effect of nutrients on aboveground productivity, reflecting both positive and negative growth responses of individual species (Baez and Homeier 2017). Finally, two recent metaanalyses have failed to detect significant responses of tropical tree growth to added nutrients (Schulte-Uebbing and de Vries 2017, Wright et al 2018).…”

“…). A long‐term fertilization experiment in a tropical montane forest found no net effect of nutrients on aboveground productivity, reflecting both positive and negative growth responses of individual species (Baez and Homeier ). Finally, two recent meta‐analyses have failed to detect significant responses of tropical tree growth to added nutrients (Schulte‐Uebbing and de Vries , Wright et al.…”

Moderate phosphorus additions consistently affect community composition of arbuscular mycorrhizal fungi in tropical montane forests in southern Ecuador

“…Previous studies have shown that at small to intermediate spatial scales, neutral and environmental drivers interact to determine the structure of AMF communities (Caruso et al, 2012;Veresoglou et al, 2019). In tropical forests, there is wide array of available hosts which are likely employing a variety of strategies to cope with nutrient limitations (Nasto et al, 2014;Sayer & Banin, 2016;Baez & Homeier, 2018). Yet the degree to which individual tree species may influence the distribution and assemblage of AMF communities has yet to be firmly established in the tropics.…”

“…Changes in AMF community structure elicited by fertilization could also set feedback loops in motion (Bever et al, 2012;Neuenkamp et al, 2018). This could favor plants adapted to high nutrient availability and promote their dominance (Baez & Homeier, 2018). In the long-term, an increasing dominance of fewer plant hosts, the so called 'homogenization' of the mycorrhizal environment (Caruso et al, 2012), could support less diverse AMF communities (Alguacil et al, 2012;Liu et al, 2012;Johnson et al, 2015).…”

Expanding the toolbox of nutrient limitation studies: A novel method of soil microbial in‐growth bags to evaluate nutrient demands in tropical forests

“…This part of the Andes was characterized as a “biodiversity hotspot” (Brehm, Pitkin, Hilt, & Fiedler, ; Homeier, Werner, Gradstein, Breckle, & Richter, ; Myers, Mittermeier, Mittermeier, da Fonseca, & Kent, ). The tested altitudinal gradient has been characterized previously in detail (Beck et al., ), and a large‐scale nutrient manipulation experiment ( NUMEX ) revealed a shift from N/P co‐limitation towards N limitation of primary productivity with elevation (Báez & Homeier, ; Homeier et al., ). Our experiment was established close to NUMEX control plots: sites used here are located at three altitudinal levels (1,000–1,140 m a.s.l., 4°11′S, 78°96′W; 2,050–2,150 m a.s.l., 3°98′S, 79°08′W; 2,880–2,960 m a.s.l., 4°12′S, 79°17′W) and are characterized by high precipitation of 3,000–4,500 mm/year with low seasonal variability (Rollenbeck & Bendix, ).…”