Resource allocation in Copaifera langsdorffii (Fabaceae): how a supra-annual fruiting affects plant traits and herbivory?

Abstract

Abstract:Plants have limited resources to invest in reproduction, vegetative growth and defense against herbivorous. Trade-off in resources allocation promotes changes in plant traits that may affect higher trophic levels. In this study, we evaluated the trade-off effect between years of high and low fruiting on the investment of resources for growth and defense, and their indirect effects on herbivory in Copaifera langsdorffii. Our questions were: (i) does the resource investment on reproduction causes a depletion in vegetative growth as predicted by the Carbon/Nutrient Balance hypothesis (CNBH), resulting in more availability of resources to be allocated for defense?, (ii) does the variation in resource allocation for growth and defense between years of high and low fruiting leads to indirect changes in herbivory? Thirty-five trees located in a Cerrado area were monitored during 2008 (year of high fruiting) and 2009 (year of no fruiting) to evaluate the differential investment in vegetative traits (biomass, growth and number of ramifications), plant defense (tannin concentration and plant hypersensitivity) and herbivory (galling attack and folivory). According to our first question, we observed that in the fruiting year, woody biomass negatively affected tannin concentration, indicating that fruit production restricted the resources that could be invested both in growth as in defense. In the same way, we observed an inter-annual variation in herbivorous attack, and found that plants with higher leaf biomass and tannin concentration, experienced higher galling attack and hypersensitive reaction, regardless years. These findings suggested that plants' resistance to herbivory is a good proxy of plant defense and an effective defense strategy for C. langsdorffii, besides the evidence of indirect responses of the third trophic level, as postulated by the second question. In summary, the supra-annual fruiting pattern promoted several changes on plant development, demonstrating the importance of evaluating different plant traits when characterizing the vegetative investment. As expected by theory, the trade-off in resource allocation favored changes in defense compounds production and patterns of herbivory. The understanding of this important element of insect-plant interactions will be fundamental to decipher coevolutionary life histories and interactions between plant species reproduction and herbivory. Besides that, only through long-term studies we will be able to build models and develop more accurate forecasts about the factors that trigger the bottom-up effect on herbivory performance, as well the top-down effect of herbivores on plant trait evolution. Rev. Biol. Trop. 64 (2): 507-520. Epub 2016 June 01.

Does inter-plant variation in sprouting time affect the growth/reproduction trade-off and herbivory in a tropical tree species?

“…However, this hypothesis was refuted in our study because the variation in sprouting time did not differ among reproductive and non-reproductive plants. Moreover, as observed by Costa et al (2016), flowering plants showed greater vegetative growth in comparison to no flowering plants. Because the study plants are located in a very homogenous environment, and the sprouting time did not differ between flowering and non-flowering plants, it is probable that resource acquisition and accumulation in previous years may be important in determining the probability that plants display reproductive events (Costa et al 2016;Obeso 2002;Sandvik & Eide 2009).…”

“…This region is located between the Cerrado and Caatinga domains and has a semi-arid climate characterized by well-defined dry and rainy seasons (Fagundes et al 2013). The average annual temperature is approximately 23°C, and the average precipitation is about 1,000 mm/year, with the rainy season being concentrated between November and February (Costa et al 2016). The soil of the study area is dystrophic with a well-developed herbaceous subshrub layer (Fagundes et al 2011;Souza & Fagundes 2016).…”

“…During a phenological cycle, plants must acquire resources to invest in growth, reproduction and the production of compounds for defence against herbivores (Herms & Mattson 1992;Stamp 2003;Costa et al 2016). Usually the resource demand for these three processes cannot be met simultaneously, thereby generating a tradeoff in resource allocation among the different nutrient drains of the plant (Obeso 2002;Weiner et al 2009).…”

“…Indirectly, variation in sprouting time produce resource patches that change in quantity and quality for herbivores. For example, early-sprouting plants can accumulate more resources during an extended vegetative stage, resulting in greater vegetative growth and a greater amount of secondary compounds (Forister 2005;Costa et al 2016). Thus, phenological asynchronies within a plant population can generate patches of resources that vary in quality (e.g., concentrations of primary and secondary metabolites and morphological traits) and quantity over time (Forister 2005;Parachnowitsch et al 2012;Fagundes 2014).…”

“…Flowering occurs from November to December and fruits ripen from August to September of the following year (Fagundes et al 2013). C. langsdorffii experiences a high diversity of free-feeding herbivorous insects, but the mechanism that regulates this diversity is still poorly known (see Silva et al 2009;Costa et al 2016). We formulated the hypothesis that early-sprouting plants of C. langsdorffii accumulate more resources due their extended vegetative stage.…”