How may plants respond to the Global Climate Changes in the Neotropics?

Marcos S. Buckeridge

Department of Botany, Laboratory of Plant Physiological Ecology (LAFIECO), Institute of Biosciences, University of São Paulo, msbuck@usp.br

Abstract

The responses of plants to the effects of the Global Climate Changes (GCC) have been studied for many years. Such studies have been focused primarily on temperate species and on crops of high economical importance, soybean (Glycine max) being one of the most studied species to date. Although a significant amount of the biomass is held in the tropical regions of the world, native and crop species to these regions have been poorly studied. In 1999, my laboratory initiated a research program to study some of these species. We started by growing native tree species to the Atlantic Forest, all from the family Leguminosae: Hymenaea courbaril (jatobá), Dalbergia nigra (jacarandá-da-bahia), Schyzolobium parahyba (guapuruvú), Piptadenia gonoacantha (pau-jacaré) and Sesbania virgata (feijão-do-mato). This monophyletic approach was adopted on the basis of the fact that these species belong to different stages of ecological succession. The idea was that, being from the same family, their adaptation strategies could be compared without having much interference of the differences among families. At the same time, we initiated a program of studies of some important crops for Brazil: sugarcane, common bean and soybean. Later on, our studies were extended to comparisons among Hymenaea species from savannah and forest and also to understand the physiological and biochemical responses of two Amazonian species: Senna reticulata (mata-pasto) and Euterpe oleracea (assai palm). Our experiments have been performed with plants growing in elevated CO2 (twice the ambient concentration) and more recently combinations of elevated CO2 and temperature and also CO2 and flooding.

Our results led to the following general findings:

1. 
   all species present responses to elevated CO2 in the form of increased photosynthesis rate, growth and source-sink relationship;
   
2. 
   the effect is stronger in fast-growing species, what implies that ecological succession in the Atlantic Forest may be differentially affected by GCC;
   
3. 
   the proportion o carbon in relation to nitrogen increases in all species analysed for this parameter;
   
4. 
   elevated temperature in combination with elevated CO2 (750ppm) had a positive effect in Hymenaea courbaril (+3^oC) and soybean (+5^oC). In the former species, the combination of elevation of the two factors led to a modified temperature optima for photosynthesis, increasing its range in about 5^oC;
   
5. 
   Sugarcane presented a strong response to elevated CO2, with modified gene expression and proteomic patterns. Common bean and soybean produced more fruits and seeds in elevated CO2 and the combination of it with elevated temperature respectively;
   
6. 
   Elevation of CO2 and temperature affected carbohydrate metabolism, especially the non-structural sugars. In all species, a significant increase in starch has been observed and in some of them cell walls were also altered.
   
7. 
   In all cases studied, stomatal indexes decreased with the elevation of CO2, corroborating the observations made for leaves obtained from herbarium exsiccates collected in the beginning of the 20th Century
   

The partial conclusion is that tropical species will continue to respond to the GCC, through responses to the elevation of CO2 and temperature, with increased growth and biomass accumulation. The next step will be to test the effects of another important factor related to GCC: water availability. This is expected to complement the three most important factors related to the GCC for plants. Our hypothesis is that water stress may revert the positive effects observed for the two other factors. Preliminary results with flooding of plants of the Amazonian species Senna reticulata, corroborates this hypothesis.

Buckeridge, M.S., Aidar M.P.M., Martinez, C.A., Silva, E.A. (2008) Respostas de plantas às mudanças climáticas. In: Biologia & Mudanças Climáticas no Brasil (Ed. M.S.Buckeridge) Cap 4. pg.77-91.

DaMatta, F.M., Grandis, A., Arenque, B.C., Buckeridge, M.S. (2009) Impacts of climate changes on crop physiology and food quality. Food Research International 43:1814–1823

Grandis, A., Godoi, S. & Buckeridge, M.S. (2010) Respostas fisiológicas de plantas amazônicas de regiões alagadas às mudanças climáticas globais. Revista brasileira de Botânica 33: 1-12