Coffee trees under rainfall exclusion: evidences for canopy acclimation to water shortage

Abstract

The intensification and amplification of dry periods, as predicted by climatic scenarios for the years 2015-2050, indicate that there is a probability that the south of Minas Gerais could become inapt for coffee production, the same way the coffee crop is conducted nowadays. In the field, drought usually occurs as a multidimensional stress, resulting in a decrease in the amount of rainfall, concomitantly accompanied by high temperatures, which normally increases the evapotranspiration leading to soil water scarcity. The role of water in growth, development and yielding of coffee trees has a remarkable importance in different phenological phases of the crop. For instance, water must be freely available during the period of fast fruit expansion to make sure that a large yield of high-quality coffee beans happens. However, due to the unpredictability of the occurrence and magnitude of the dry periods, as well as the lack of knowledge of the plant limits, the coffee crops might be placed in a condition of vulnerability to maintain its vital activities without declining its yielding and productivity. The aim of this study was to verify if a reduction of ¼ of the rainfall would affect the dynamic of leaf area and source-sink relationship in a six-year-old coffee crop subjected to a rain exclusion system. The experiment was composed of one treatment of rain exclusion, one with the system but with no exclusion, and one without the system and no exclusion. Our measurements verified that the reduction of ¼ rainfall through the exclusion system affected the stem, branches and leaf area growth rates, which, in the case of the branch leaf area was highly correlated with the normalized difference vegetation index and the next-year-production data, as well as the microclimatic values such as temperature, vapor pressure deficit, evapotranspiration of the crop, and the reduction of the rainfall load. The drought monitoring models did not find any trend of longer drought duration for the following decades. Furthermore, our study rendered a new tool to validate the use of nondestructive leaf area index (LAI), since leaves are in the interface between plants and the atmosphere, precisely obtaining LAI is important to give an idea of coffee tree canopy acclimation to water shortage.