Produção de biomassa e necromassa de espécies invasoras e controle mecânico e químico de Hedychium coronarium König. (Zingiberaceae) em zonas ripárias neotropicais

Abstract

Biological invasions are common. Riparian zones are among those that undergo major biological invasions. The accumulation of biomass and necromass interferes in the dynamics of the plant community in a significant way. Considering the potential harmfulness of invasive species, it is interesting that we think of forms of control. Our objectives are to determine if: 1) biomass and necromass production of Hedychium coronarium, Urochloa decumbens, Melinis minutiflora and Pennisetum purpureum are related to climatic variables, 2) the net primary aerial production of H. coronarium, U. decumbens, M. minutiflora and P. purpureum throughout the year, 3) to test the effect of once and twice-yearly cutting of H. coronarium ramets on their growth 4) to test the effect of H. coronarium rhizome cutting off once a year, 5) to test the effect on growth of H. coronarium with injection in its rhizomes of alcoholic extract of Typha dominguens in two concentrations (5% e 10%) and from leaves and rhizome, 6) to test the effect on growth of H. coronarium with injections of glyphosate into its rhizomes and 7) with spray of glyphosate on its leaves. Our hypotheses are 1) the production of biomass and necromass will be related to climatic variables, 2) the net primary aerial production of all species will be high in the year of study and 3) there will be effect in the growth of H. coronarium with the application of the treatments. For one year we collected monthly aerial biomass and necromass of the four species. To calculate net primary aerial production, we used Smalley’s method. We tested the data for normality using Shapiro-Wilks test. Relations among climatic variables were tested with Spearman’s test. Variables not related to each other were tested with a mixed linear model (GLM) in its relationship with climate. To select most adequate model of explanation, we used AKAIKE test (AIC), within R environment. For mechanical control we established three plots in five sites subdivided into four sub plots: i) control, ii) cutting off ramets once a year, iii) cutting off ramets twice a year and iv) pulling out ramets and rhizomes. For the experiment of chemical control of H. coronarium planted five pieces of 10 cm of rhizomes in aquariums of 30 cm x 30 cm x 20 cm with 5 cm of fertilized soil. Aquariums were kept in a room with 12 hours of light and 12 hours of dark and temperature 24+/-2°C. To test glyphosate injection and spray, we left four aquariums for control, four for injection and four for spray. Injections were made with 10 mL of the product undiluted. Five months after the first injection, we repeated the procedure. To test glyphosate spray, we repeated the application two months after the first spray, and again after four months. To test Typha domingensis alcoholic extract, three aquariums were left for control, three had its ramets injected with leaf alcoholic extract at 5 % and 10 % concentration, three had its ramets injected with rhizome alcoholic extract at 5 % and 10 Once a month, we numbered the ramets and measured their diameter on soil level and the total height for all experiments. To test the differences for height and diameter among treatments, we used linear mixed models. All analysis was conducted within the R statistical environment. We also used mortality rates expressed in percentage of dead ramets. The species studied have a direct relationship with the environmental variables in question and cause great impacts on riparian zone due to its high production of biomass and necromass throughout the year, especially H. coronarium and P. purpureum. Therefore, control measures are of extreme interest. The control experiments of H. coronarium were efficient, treatment with glyphosate injection in the rhizomes of the plant was the one that obtained the best result, with mortality rate of 97,3 %. The locality of H. coronarium should be considered so that there is no mortality of other species when applying the herbicide.