Impact of water supply on stomatal conductance, light use efficiency and growth of tropical Eucalyptus plantation in Brazil

Eucalyptus plantations of Brazil are expanding to areas subjected to water stress, and the water stress is considered a main environmental factor that limit growth and productivity of plantations, this occurrence implies the necessity for advance knowledge about physiological processes of Eucalyptus under different conditions of water availability. In this study, leaf gas exchange and light use efficiency of Eucalyptus under tropical field conditions in Brazil was evaluated to assess the effect of water supply on wood production. The experiment was performed in Eunápolis, Bahia, Brazil (16°22'40''S, 39°34'48''W) and we evaluated two treatments (irrigated and rainfed) of Eucalyptus forest clonal plantation on second rotation, established in August 2009. Leaf gas-exchange parameters were analyzed in 15-month plants using a Portable Photosynthesis System LI-6400xt and to calculate the light use efficiency, the vegetation area index (VAI) were measured through hemispherical photos using a camera - model Cyber shot ® Digital Camera Sony DSC - F828 coupled with a Fisheye Lens Opteka 0.22X AF ®. Irrigated trees showed higher biomass increment as a result of higher light use efficiency and lower absorbed photosynthetically active radiation, less carbon allocation to the below-ground; and lower stomatal conductance in relation to vapor pressure deficit (VPD) variation. These results showed that Eucalyptus species are responsive to water supply, and the reduction of stomatal conductance in relation to the VPD variation explains the higher stem biomass increase and greater LUE in the irrigated treatment

Respostas fisiológicas de espécies florestais ao estresse hídrico

Abiotic and biotic stresses affect tree growth and play a major role in determining the geographic distribution of species. The objective of this study is to elucidate the following questions: (1) are GABA aminoacid and stomatal control good indicators of tolerance to water stress in Eucalyptus clones? In addition, what are the anatomical differences between drought-tolerant and drought-sensitive clones of Eucalyptus? (2) Are there differences of xylem vulnerability to cavitation in Pinus flexilis families susceptible and resistant to white pine blister rust (WPBR) and with different origins (high and low altitudes)? Two studies were carried out to elucidate the issues above. On chapters 1, eight Eucalyptus clones from different geographical and climatological conditions, three drought-sensitive (CNB, FIB and JAR), three drought-tolerant (GG, SUZ and VM), and two plastics (VER and COP), were studied in normal water supply (control treatment) and in water stress conditions (stress treatment). The first chapter concluded that GABA is an aminoacid very sensitive to water stress, but there was no relation between GABA concentration and tolerance to water stress of the clones. In addition, all clones decreased stomatal conductance with increasing vapor pressure deficit, and plastics and drought-tolerant clones (except GG) presented lower stomatal sensitivity to vapor pressure deficit under stress conditions than drought-sensitive clones. Besides, all clones showed differences on the anatomical parameters between, and only COP (plastic) and SUZ (drought-tolerant) showed homogeneous mesophyll and amphi-hipostomatic leaves. All clones increased the number of stomata and reduced leaf thickness of the leaves formed after water stress period. On the chapter 2, we studied 12 families of Pinus flexilis originating from high and lower altitudes, in which six families previously shown to contain the dominant C4 allele (resistant to WPBR) and six families without C4 allele (susceptible to WPBR). This study showed that the mean cavitation pressure (MCP) of Pinus flexilis varying between 3.63 a -4.84 Mpa, although there was a significant difference in vulnerability to cavitation comparing all families, this variable was not related to WPBR and origin region. These studies highlight that the physiological responses of plants under water stress conditions are important tools that can be used to complement the strategies of genotype selection in forest breeding programs.Estresses abióticos e bióticos podem afetar o crescimento das árvores e desempenham um papel importante na determinação da distribuição geográfica das espécies. O objetivo deste estudo, foi elucidar as seguintes questões: (1) o aminoácido GABA e o controle estomático são bons indicadores da tolerância ao estresse hídrico em clones de Eucalyptus? E quais são as diferenças anatômicas entre clones de Eucalyptus tolerantes e sensíveis ao estresse hídrico? (2) existem diferenças de vulnerabilidade a cavitação do xilema entre famílias de Pinus flexilis suscetíveis e resistentes à ferrugem do pinho branco (WPBR) e com diferentes procedências (elevada e baixa altitudes)? Dois estudos foram desenvolvidos para elucidar as questões acima descritas. No capítulo 1, oito clones de Eucalyptus de diferentes procedências e condições climáticas, sendo três clones sensíveis ao estresse hídrico (CNB, FIB e JAR), três clones tolerantes ao estresse hídrico (GG, SUZ e VM) e dois clones plásticos (VER e COP), foram estudados sob duas condições distintas: sob adequado suprimento de água (tratamento controle) e sob condições de estresse hídrico (tratamento estresse). Do primeiro capítulo concluiu-se que o GABA é um aminoácido que possui alta sensibilidade ao estresse hídrico, no entanto, não houve relação entre a concentração de GABA e os níveis de tolerância ao estresse hídrico dos clones. Além disso, todos os clones reduziram a condutância estomática em relação ao aumento do déficit de pressão de vapor (DPV), sendo que, sob condições de estresse hídrico, os clones plásticos e tolerantes à seca (exceto o clone GG) apresentaram menor sensibilidade estomática ao DPV do que os clones sensíveis ao estresse hídrico. Além disso, todos os clones apresentaram diferenças anatômicas, sendo que, diferentemente dos demais, os clones COP (plástico) e SUZ (tolerante) apresentaram mesofilo homogêneo e folhas anfi-hipoestomáticas. Todos os clones aumentaram a quantidade de estômatos e reduziram a espessura foliar das folhas formadas após períodos de estresse hídrico. No segundo capítulo foram avaliadas 12 famílias de Pinus flexilis procedentes de regiões de baixa e alta altitudes, sendo seis famílias contendo um alelo dominante C4 (resistente à WPBR) e seis famílias sem o alelo C4 (suscetíveis à WPBR). Este estudo apresentou uma variação da pressão média da cavitação (MCP) para Pinus flexilis de -3,63 a -4,84 Mpa, e embora tenha havido uma diferença significativa da susceptibilidade a cavitação entre todas as famílias estudadas, esta variável não relacionou-se com a susceptibilidade a doença WPBR e com a região de procedência das famílias. Estes estudos comprovam que a avaliação das respostas fisiológicas das plantas sob condições de estresse hídrico são importantes ferramentas que podem ser utilizadas para complementar as estratégias da seleção de genótipos em programas de melhoramento florestal

Fotossíntese, condutância estomática e produtividade de clones de Eucalyptus sob diferentes condições edafoclimáticas

O objetivo deste trabalho foi avaliar a fotossíntese, condutância estomática e produtividade de clones de Eucalyptus em duas áreas distintas: uma no Município de Eunápolis, Sul da Bahia, com precipitação bem distribuída ao longo do ano (área úmida); e outra em Salto da Divisa, Leste de Minas Gerais, com precipitação concentrada nos meses quentes do ano (área seca). Foram estudados quatro clones, avaliando-se o crescimento, através do inventário das árvores; e as variáveis fotossintéticas, medidas com o aparelho Infrared Gas Analyser (IRGA). Dentro de cada área só houve diferença significativa entre clones na área úmida quanto à variável volume de madeira. A produtividade dos clones na área úmida foi 3,3 vezes superior à produtividade da área seca. Na área úmida, todos os clones diminuíram a condutância estomática com o aumento do déficit de pressão de vapor, com queda de 0,16 mol m² s-1 para cada 1 kPa de aumento no DPV e taxa fotossintética máxima variando de 12,5 a 16,4 µmol m² s-1. A comparação entre os clones da área úmida resultou em diferença significativa do clone A, que apresentou fotossíntese máxima superior à dos demais. Na área seca não houve relação entre condutância estomática e DPV e não se observou diferença na fotossíntese entre os clones, que variou de 1,2 a 3,4 µmol m² s-1. Verificou-se relação linear entre a fotossíntese máxima e a produtividade dos clones, evidenciando que a taxa fotossintética foi um dos fatores responsáveis pela maior produtividade do Eucalyptus na área úmida

Fertilization Response, Light Use, and Growth Efficiency in Eucalyptus Plantations across Soil and Climate Gradients in Brazil

Fertilization increases productivity in Eucalyptus plantations, but losses in productivity associated with soil fertility continue at operational scales. In this study, we evaluated the fertilization response (FR), light use efficiency (LUE) and growth efficiency (GE), i.e., the amount of wood biomass accumulated per unit of light absorbed (LUE) and per unit of leaf area index of Eucalyptus plantations. We used a “twin plot” approach, with 161 blocks representing 52,700 ha of planted forests that spanned a broad range of edaphoclimatic conditions in southeastern Brazil. The normal plots (NP) were part of a permanent inventory network, whereas the twin plots (TP) received extra high levels of fertilization and extra weed control after fertilization. The intensive management (twin plots) led to a large increase of 5.3 Mg·ha−1·year−1 of wood increment. The region without dry periods and with soils with high clay content was most responsive to fertilization, with a 15% increment in the LUE and 10% increase in the GE of the TPs compared with those of the NPs. Our results suggested that water availability was the primary element affecting productivity and potential response to fertilization. With this information, decisions can be made on which regions should receive priority fertilization investments. However, more research is required to determine the most limiting nutrient in each type of environment

Changes in γ-aminobutyric acid concentration, gas exchange, and leaf anatomy in Eucalyptus clones under drought stress and rewatering

Drought stress promotes biochemical and physiological alterations in plant metabolism that limit growth and yield. This study investigated the accumulation of γ-aminobutyric acid (GABA) in plant tissue, the stomatal conductance (gs) and changes in leaf anatomy in Eucalyptus following drought stress situation. In this study, eight Eucalyptus clones were evaluated under normal water supply (control) and drought stress conditions (stress). For the control treatment, plants were irrigated every day with an automated system until the soil was saturated, and for the stress treatment, drought stress was imposed by non-irrigation of plants, and pots were covered using plastic sheeting to avoid rainfall and humidity. This study has shown that: (1) all clones decreased gs with increasing vapor pressure deficit (D) in both treatments. All plastics and drought-tolerant clones (except GG) presented lower stomatal sensitivity to D under stress conditions than drought-sensitive clones; (2) GABA concentrations increased fast after drought stress, but we could not find correlation with these changes and resistance to water stress; and (3) all clones increased the number of stomata and reduced leaf thickness after water stress. The finding is that GABA is a fast stress-signaling molecule in Eucalyptus, but the response of gs to D is a best physiological variable to differentiate drought-tolerant and drought-sensitive Eucalyptus clones