Soil fertility and rainfall during specific phenological phases affect seed trait variation in a widely distributed Neotropical tree, Copaifera langsdorffii.

PREMISE: Knowledge of intra-specific variation in seed traits and its environmental determinants is important for predicting plant responses to environmental changes. Here, we tested the hypothesis that differences in soil fertility and rainfall during specific phenological phases drive variation in seed traits in a widely distributed tree, Copaifera langsdorffii. We also tested the hypothesis that climatic heterogeneity increases within-plant variation in seed traits. METHODS: Inter- and intra-population and within-plant variation in seed mass, number, and seed size/seed number were evaluated for 50 individuals from five populations distributed along a rainfall gradient and occurring on varying soil types. Using multivariate approaches, we tested the effects of soil fertility characteristics and rainfall in five reproductive phenological phases on seed traits. RESULTS: The seed traits varied greatly both among populations and within plants. Inter-population variation in seed mass was driven by total rainfall during fruit development, and variation in seed number was influenced by total rainfall during the dry season before the reproductive phase. Phosphorus levels and potential acidity of the soil also explained the variations in seed mass and seed mass/seed number, respectively. A positive association between intra-annual variation in rainfall and within-plant variation in seed mass and seed number was found. CONCLUSION: Both rainfall during specific reproductive phases and soil conditions shape the variation in the seed mass and number of C. langsdorffii. Environment-driven seed trait variation may contribute to this species' broad niche breadth, which in turn may determine the species' persistence under future climatic conditions.

Reproductive strategy of Copaifera langsdorffii (Fabaceae): more seeds or better seeds?

The trade-off seed size/number is a recognized phenomenon capable of shaping ecological processes of colonization and establishment of plant species. Studies that describe trade-offs size/number of seeds in supra-annual fruiting species are still rare. In this study, two predictions for trade-off size/number hypothesis were tested: (i) on a population scale, seeds produced during years of greater reproductive investment showed reduced size, and (ii) on individual scale there is an inverse relationship between size and number of seeds produced by individual plant. To test these predictions, 102 Copaifera langsdorffii adult plants were monitored monthly from January to September during four consecutive years (2008 to 2011) in order to study the reproductive investment of plants. C. langsdorffii plants exhibited reproductive activity only during years 2008 and 2011. The mean number of seeds per branch was 26.4 % greater in 2008 comparatively to 2011. It was also observed that seed size was greater in the year of 2008, when plants produced greater number of fruits. Thus, the data did not support the first prediction of seed size/number hypothesis. In both reproductive years, there was a negative relationship between seed size and number of seeds, supporting the second prediction of the seed size/number hypothesis. The interaction term with the reproductive year suggests that the trade-off size/number of seeds was indeed stronger in 2011, when the plants produced lower seed number. Finally, this study calls the attention to supra-annual fruiting pattern in C. langsdoffii, and suggests that the phenological patterns contribute to explain the wide variation in their seed size and geographical distribution.

El compromiso o balance adaptativo de las semillas en tamaño/ número (trade-off seed size/number) es un reconocido fenómeno capaz de dar forma a los procesos ecológicos de la colonización y el establecimiento de especies de plantas. Los estudios que describen el compromiso adaptativo de las semillas en tamaño/número en especies con fructificación supra-anual siguen siendo raros. En este estudio, se probaron dos hipótesis predictivas para compromiso adap-tativo de las semillas en tamaño/número: (i) una a escala poblacional, semillas producidas durante el año de mayor inversión reproductiva mostraran un tamaño reducido, y (ii) otra a escala individual que se dará una relación inversa entre el tamaño y número de semillas producidas por la planta individual. Para probar estas predicciones, 102 plantas adultas de Copaifera langsdorffii fueron monitoreadas mensualmente entre enero y septiembre, durante cuatro años consecutivos (2008-2011) con el fin de estudiar la inversión reproductiva de las plantas. Plantas langsdorffii C. exhibieron actividad reproductiva sólo durante el 2008 y 2011. El número promedio de semillas por rama fue 26.4 % mayor en 2008 en comparación con 2011. También se observó que el tamaño de la semilla fue mayor en 2008, cuando las plantas producen mayor número de frutos. Por lo tanto, los datos no apoyan la primera hipótesis de predicción de tamaño/número. En ambos años reproductivos, existía una relación negativa entre el tamaño de la semilla y el número de semillas, comprobando la segunda hipótesis de predicción del tamaño/número de semillas. El periodo de interacción con el año reproductivo sugiere que el compromiso adaptativo de las semillas en tamaño/número fue de hecho más fuerte en 2011, cuando las plantas produjeron baja cantidad de semillas. Por último, este estudio llama la atención por el patrón de fructificación supra-anual en C. langsdoffii, y sugiere que los patrones fenológicos contribuyen a explicar la amplia variación en el tamaño de la semilla y la distribución geográfica.