Leaf growth of Eucalyptus globulus seedlings under water deficit

Treasured exceptions: Association of morphoanatomical leaf traits with cup quality of Coffea arabica L. cv. "Catuaí"

The morphoanatomical characteristics of leaves were associated with altitude, hillside, and the cup quality of coffee produced in the Matas de Minas region. Although the small magnitude, there are correlations between cup quality with altitude and morpho-anatomical traits. Despite facing the differences of management inherent to 363 sampling sites, Northwestern hillside had significant lower cup quality, whereas only stomata density (SD) and thickness of the leaf epidermis in the adaxial face (AdET) showed significant differences between hillsides. Altitude, leaf mass per area (LMA) and SD, and to a lesser extent the thickness of the leaf epidermis in the abaxial face (AbET), were correlated (Spearman's correlation) with cup quality. Interestingly, AbET correlations were negative. Mantel's test significant correlations were found between coffee cup quality vs. altitude, LMA and petiole phloem area (PPhA). The spatial autocorrelation was significant only with LMA. Also, SD, to a lesser extent, was associated with cup quality. Despite the complexity of the association among the environment, plant growth and development, this is the first report to associate morpho-anatomical features of the leaf with the coffee cup traits. Even with the expectation of genotype/species vs environment interactions, and the influence of other parameters associated with post-harvest, roasting and brewing, the evaluation of LMA, SD, AdET, AbET and the thickness of the palisade parenchyma (PPT) allow a novel approach to access coffee cup quality.

Phenotypic Plasticity of Drought Tolerance Traits in a Widespread Eucalypt (Eucalyptus obliqua)

Long-term studies of tree responses to drought stress help us to understand the capacity of species to adapt to their environment. In this study, we investigated how Eucalyptus obliqua adjusts physiological and morphological traits in response to seasonal and multi-year droughts. We monitored physiological and morphological traits over multiple years in undisturbed control and throughfall reduction plots in a eucalypt forest in south-eastern Australia. The throughfall reduction treatment did not induce significantly lower soil moisture in the throughfall reduction plots compared with the control plots. However, natural variability in precipitation and evaporative demand induced drought stress of varying intensity each summer in all plots. We observed a significant relationship between seasonal precipitation and leaf pre-dawn water potential (ΨPD), with less precipitation over summer, resulting in a decline in ΨPD and drought stress when ΨPD fell below −0.75 MPa. Eucalyptus obliqua responded to short-term summer drought through rapid leaf osmotic adjustment which lowered the leaf water potential at the turgor loss point beyond the minimum leaf water potential. Morphological adjustments, such as the reduction of leaf area to sapwood area (higher Huber Value) were moderate during the measurement period and only occurred under severe drought stress (pre-dawn water potential < −1.2 MPa). Overall, E. obliqua responded to short-term mild drought stress through physiological trait plasticity, while morphological adjustment only occurred under a more severe water deficit.

Phenotypic plasticity and genetic adaptation of functional traits influences intra-specific variation in hydraulic efficiency and safety

Understanding which hydraulic traits are under genetic control and/or are phenotypically plastic is essential in understanding how tree species will respond to rapid shifts in climate. We quantified hydraulic traits in Eucalyptus obliqua L'Her. across a precipitation gradient in the field to describe (i) trait variation in relation to long-term climate and (ii) the short-term (seasonal) ability of traits to adjust (i.e., phenotypic plasticity). Seedlings from each field population were raised under controlled conditions to assess (iii) which traits are under strong genetic control. In the field, drier populations had smaller leaves with anatomically thicker xylem vessel walls, a lower leaf hydraulic vulnerability and a lower water potential at turgor loss point, which likely confers higher hydraulic safety. Traits such as the water potential at turgor loss point and ratio of sapwood to leaf area (Huber value) showed significant adjustment from wet to dry conditions in the field, indicating phenotypic plasticity and importantly, the ability to increase hydraulic safety in the short term. In the nursery, seedlings from drier populations had smaller leaves and a lower leaf hydraulic vulnerability, suggesting that key traits associated with hydraulic safety are under strong genetic control. Overall, our study suggests a strong genetic control over traits associated with hydraulic safety, which may compromise the survival of wet-origin populations in drier future climates. However, phenotypic plasticity in physiological and morphological traits may confer sufficient hydraulic safety to facilitate genetic adaptation.

Water stress and recovery in the performance of two Eucalyptus globulus clones: physiological and biochemical profiles

Eucalyptus plantations are among the most productive forest stands in Portugal and Spain, being mostly used for pulp production and, more recently, as an energy crop. However, the region's Mediterranean climate, with characteristic severe summer drought, negatively affects eucalypt growth and increases mortality. Although the physiological response to water shortage is well characterized for this species, evidence about the plants' recovery ability remains scarce. In order to assess the physiological and biochemical response of Eucalyptus globulus during the recovery phase, two genotypes (AL-18 and AL-10) were submitted to a 3-week water stress period at two different intensities (18 and 25% of field capacity), followed by 1 week of rewatering. Recovery was assessed 1 day and 1 week after rehydration. Drought reduced height, biomass, water potential, NPQ and gas exchange in both genotypes. Contrarily, the levels of pigments, chlorophyll fluorescence parameters (F(v) /F(m) and (φPSII)), MDA and ABA increased. During recovery, the physiological and biochemical profile of stressed plants showed a similar trend: they experienced reversion of altered traits (MDA, ABA, E, g(s), pigments), while other parameters did not recover ((φPSII), NPQ). Furthermore, an overcompensation of CO(2) assimilation was achieved 1 week after rehydration, which was accompanied by greater growth and re-establishment of oxidative balance. Both genotypes were tolerant to the tested conditions, although clonal differences were found. AL-10 was more productive and showed a more rapid and dynamic response to rehydration (namely in carotenoid content, (φPSII) and NPQ) compared to clone AL-18.

Observed and modelled leaf area index in Eucalyptus globulus plantations: tests of optimality and equilibrium hypotheses

This paper reports on variation in leaf area index (L) in five Eucalyptus globulus Labill. plantations in response to application of nitrogen, thinning at age 2 years and variation in climate wetness index (the ratio of rainfall to potential evaporation). Observed L is compared with: (i) L predicted to optimize net primary productivity for a given average annual temperature, annual water use and potential evaporation (L(opt)) and (ii) L calculated as a linear function of climate wetness index (L(eq)). L peaked in fertilized plots at between 4 and 5 years of age or immediately after canopy closure. The value of L from canopy closure to age 8 years was not strongly related to annual rainfall or climate wetness index. At two sites with total soil nitrogen <1.2 mg g(-)(1), L in fertilized plots was about two units greater than in unfertilized plots. This difference persisted until measurements ended in 2004 when the trees were 8 years old. The L of plots thinned to 300 and 600 stems ha(-)(1) at age 2 years recovered quickly and was not significantly different from L in unthinned plots when the trees were 8 years old. L(opt) was a good predictor of the leaf area index of 8-year-old plots of E. globulus when nitrogen and phosphorus were non-limiting (model efficiency (EF) was 0.5). For the same plots, L(eq) underestimated observed L by an average of two units, and the model efficiency was low (-3.25). Data from two nitrogen-limited sites demonstrated that for fertilized plots L(opt) (EF = 0.6) was a much better predictor of L than L(eq) (EF = -3.36). At the same sites, L(eq) (EF = 0.42) was a better model for predicting L of unfertilized plots than L(opt) (-3.59). These results provide evidence that comparing observed L with L(opt) can identify stands limited by factors other than growing climate.