Produtividade do fósforo em Eucalyptus globulus

Congresso Florestal Nacional: a floresta e as gentes - Actas das ComunicaçõesO objectivo deste trabalho foi estudar a produtividade do fósforo (aumento de biomassa por unidade de fósforo na planta e por unidade de tempo, PP) em Eucalyptus globulus. A metodologia utilizada foi desenvolvida por Ingestad & Lund (1979), na qual as relações nutrição/crescimento são estudadas em condições de nutrição e crescimento em equilíbrio dinâmico, ou seja, com concentrações internas de nutrientes constantes e taxa de crescimento relativo constante. As aplicações deste método são inúmeras, desde uma melhor utilização de fertilizantes em viveiro até à compreensão do comportamento das plantas e do crescimento em condições naturais, em termos fisiológicos. O estudo incluiu três clones e um lote seminal, que foi utilizado como controlo, aos quais foram aplicados 3 níveis de nutrição, um óptimo (OP, com livre acesso de nutrientes) e dois sub-óptimos de nutrição de fósforo (PA e PB, com taxas de adição relativa de fósforo de 4 e 2%, respectivamente). Determinaram-se os valores da taxa máxima de crescimento relativo (RGmax), da concentração óptima de fósforo (conteúdo mínimo de fósforo na planta necessário para alcançar a taxa máxima de crescimento relativo, Popt) e da produtividade do fósforo (PP). Observaram-se diferenças significativas na PP entre o clone MP11 e o lote seminal. O clone MP11 foi o que apresentou a maior PP, mas com a mais baixa RGmax, embora não significativamente diferente dos outros clones ou lote seminal (4.58 - 7.08 % dia-1). Os valores obtidos para a PP (14.1 - 29.18 g (PS) g-1 (P) dia-1) estão em consonância com outros estudos

After more than a decade of soil moisture deficit, tropical rainforest trees maintain photosynthetic capacity, despite increased leaf respiration

Determining climate change feedbacks from tropical rainforests requires an understanding of how carbon gain through photosynthesis and loss through respiration will be altered. One of the key changes that tropical rainforests may experience under future climate change scenarios is reduced soil moisture availability. In this study we examine if and how both leaf photosynthesis and leaf dark respiration acclimate following more than 12 years of experimental soil moisture deficit, via a through-fall exclusion experiment (TFE) in an eastern Amazonian rainforest. We find that experimentally drought-stressed trees and taxa maintain the same maximum leaf photosynthetic capacity as trees in corresponding control forest, independent of their susceptibility to drought-induced mortality. We hypothesize that photosynthetic capacity is maintained across all treatments and taxa to take advantage of short-lived periods of high moisture availability, when stomatal conductance (gs) and photosynthesis can increase rapidly, potentially compensating for reduced assimilate supply at other times. Average leaf dark respiration (Rd) was elevated in the TFE-treated forest trees relative to the control by 28.2 ± 2.8% (mean ± one standard error). This mean Rd value was dominated by a 48.5 ± 3.6% increase in the Rd of drought-sensitive taxa, and likely reflects the need for additional metabolic support required for stress-related repair, and hydraulic or osmotic maintenance processes. Following soil moisture deficit that is maintained for several years, our data suggest that changes in respiration drive greater shifts in the canopy carbon balance, than changes in photosynthetic capacity.</p

Carbon-nitrogen interactions in European forests and semi-natural vegetation - Part 1: Fluxes and budgets of carbon, nitrogen and greenhouse gases from ecosystem monitoring and modelling

The impact of atmospheric reactive nitrogen (N$_{r}$) deposition on carbon (C) sequestration in soils and biomass of unfertilized, natural, semi-natural and forest ecosystems has been much debated. Many previous results of this dC/dN response were based on changes in carbon stocks from periodical soil and ecosystem inventories, associated with estimates of N$_{r}$ deposition obtained from large-scale chemical transport models. This study and a companion paper (Flechard et al., 2020) strive to reduce uncertainties of N effects on C sequestration by linking multi-annual gross and net ecosystem productivity estimates from 40 eddy covariance flux towers across Europe to local measurement-based estimates of dry and wet N$_{r}$ deposition from a dedicated collocated monitoring network. To identify possible ecological drivers and processes affecting the interplay between C and N$_{r}$ inputs and losses, these data were also combined with in situ flux measurements of NO, N$_{2}$O and CH$_{4}$ fluxes; soil NO$_{3}$̅ leaching sampling; and results of soil incubation experiments for N and greenhouse gas (GHG) emissions, as well as surveys of available data from online databases and from the literature, together with forest ecosystem (BASFOR) modelling. Multi-year averages of net ecosystem productivity (NEP) in forests ranged from -70 to 826 gCm$^{-2}$ yr$^{-1}$ at total wet+dry inorganic N$_{r}$ deposition rates (N$_{dep}$) of 0.3 to 4.3 gNm$^{-2}$ yr$^{-1}$ and from -4 to 361 g Cm$^{-2}$ yr$^{-1}$ at N$_{dep}$ rates of 0.1 to 3.1 gNm$^{-2}$ yr$^{-1}$ in short semi-natural vegetation (moorlands, wetlands and unfertilized extensively managed grasslands). The GHG budgets of the forests were strongly dominated by CO$_{2}$ exchange, while CH$_{4}$ and N$_{2}$O exchange comprised a larger proportion of the GHG balance in short semi-natural vegetation. Uncertainties in elemental budgets were much larger for nitrogen than carbon, especially at sites with elevated N$_{dep}$ where N$_{r}$ leaching losses were also very large, and compounded by the lack of reliable data on organic nitrogen and N$_{2}$ losses by denitrification. Nitrogen losses in the form of NO, N$_{2}$O and especially NO$_{3}$̅ were on average 27%(range 6 %–54 %) of N$_{dep}$ at sites with N$_{dep}$ 3 gNm$^{-2}$ yr$^{-1}$. Such large levels of N$_{r}$ loss likely indicate that different stages of N saturation occurred at a number of sites. The joint analysis of the C and N budgets provided further hints that N saturation could be detected in altered patterns of forest growth. Net ecosystem productivity increased with N$_{r}$ deposition up to 2–2.5 gNm$^{-2}$ yr$^{-1}$, with large scatter associated with a wide range in carbon sequestration efficiency (CSE, defined as the NEP = GPP ratio). At elevated N$_{dep}$ levels (> 2.5 gNm$^{-2}$ yr$^{-1}$), where inorganic N$_{r}$ losses were also increasingly large, NEP levelled off and then decreased. The apparent increase in NEP at low to intermediate N$_{dep}$ levels was partly the result of geographical cross-correlations between N$_{dep}$ and climate, indicating that the actual mean dC/dN response at individual sites was significantly lower than would be suggested by a simple, straightforward regression of NEP vs. N$_{dep}$

Soil-atmosphere greenhouse gases (CO2, CH4 and N2O) exchange in evergreen oak woodland in southern Portugal

A 10-20% decrease in annual precipitation is predicted in the Mediterranean basin, and in particular to the Iberian Peninsula, with foreseen effects on the exchange of soil-atmosphere greenhouse gases (GHGs; CO 2, CH 4, and N 2O. To simulate this scenario, we setup an experimental design in the particularly dry period of 2008-2009 using rainfall exclusion and irrigation, to obtain plots receiving 110% (538 mm), 100% (493 mm) and 74% (365 mm) of the natural precipitation. Soil CO 2 fluxes showed a strong increase from summer to autumn as a consequence of increasing soil heterotrophic respiration that resulted from rewetting. Fluxes of N 2O were negligible. According to our data, soil was a permanent CH 4 sink independent of the soil water content (in the range between 6-26% WFPS - water-filled pore space) and of soil temperature (in the range of 7-28°C), supporting the concept that seasonally dry ecosystems (Mediterranean) may represent a significant sink of atmospheric CH 4. The study provides evidence that the 26% decrease or 10% increase in the ambient rainfall from annual precipitation of ca 500 mm did not significantly affect soil functionality and had a limited impact on soil-atmosphere net GHGs exchange in evergreen oak woodlands in southern Portugal

The response of methane and nitrous oxide fluxes to forest change in Europe

Forests in Europe are changing due to interactions between climate change, nitrogen (N) deposition and new forest management practices. The concurrent impact on the forest greenhouse gas (GHG) balance is at present difficult to predict due to a lack of knowledge on controlling factors of GHG fluxes and response to changes in these factors. To improve the mechanistic understanding of the ongoing changes, we studied the response of soil–atmosphere exchange of nitrous oxide (N&lt;sub&gt;2&lt;/sub&gt;O) and methane (CH&lt;sub&gt;4&lt;/sub&gt;) at twelve experimental or natural gradient forest sites, representing anticipated future forest change. The experimental manipulations, one or more per site, included N addition (4 sites), changes of climate (temperature, 1 site; precipitation, 2 sites), soil hydrology (3 sites), harvest intensity (1 site), wood ash fertilisation (1 site), pH gradient in organic soil (1 site) and afforestation of cropland (1 site). &lt;br&gt;&lt;br&gt; On average, N&lt;sub&gt;2&lt;/sub&gt;O emissions increased by 0.06 &amp;plusmn; 0.03 (range 0–0.3) g N&lt;sub&gt;2&lt;/sub&gt;O-N m&lt;sup&gt;−2&lt;/sup&gt; yr&lt;sup&gt;−1&lt;/sup&gt; across all treatments on mineral soils, but the increase was up to 10 times higher in an acidic organic soil. Soil moisture together with mineral soil C / N ratio and pH were found to significantly influence N&lt;sub&gt;2&lt;/sub&gt;O emissions across all treatments. Emissions were increased by elevated N deposition, especially in interaction with increased soil moisture. High pH reduced the formation of N&lt;sub&gt;2&lt;/sub&gt;O, even under otherwise favourable soil conditions. &lt;br&gt;&lt;br&gt; Oxidation (uptake) of CH&lt;sub&gt;4&lt;/sub&gt; was on average reduced from 0.16 &amp;plusmn; 0.02 to 0.04 &amp;plusmn; 0.05 g CH&lt;sub&gt;4&lt;/sub&gt;-C m&lt;sup&gt;−2&lt;/sup&gt; yr&lt;sup&gt;−1&lt;/sup&gt; by the investigated treatments. The CH&lt;sub&gt;4&lt;/sub&gt; exchange was significantly influenced by soil moisture and soil C / N ratio across all treatments, and CH&lt;sub&gt;4&lt;/sub&gt; emissions occurred only in wet or water-saturated conditions. &lt;br&gt;&lt;br&gt; For most of the investigated forest manipulations or natural gradients, the response of both N&lt;sub&gt;2&lt;/sub&gt;O and CH&lt;sub&gt;4&lt;/sub&gt; fluxes was towards reducing the overall GHG forest sink. The most resilient forests were dry Mediterranean forests, as well as forests with high soil C / N ratio or high soil pH. Mitigation strategies may focus on (i) sustainable management of wet forest areas and forested peatlands, (ii) continuous forest cover management, (iii) reducing atmospheric N input and, thus, N availability, and (iv) improving neutralisation capacity of acid soils (e.g. wood ash application)

Quantifying in situ phenotypic variability in the hydraulic properties of four tree species across their distribution range in Europe

Many studies have reported that hydraulic properties vary considerably between tree species, but little is known about their intraspecific variation and, therefore, their capacity to adapt to a warmer and drier climate. Here, we quantify phenotypic divergence and clinal variation for embolism resistance, hydraulic conductivity and branch growth, in four tree species, two angiosperms (Betula pendula, Populus tremula) and two conifers (Picea abies, Pinus sylvestris), across their latitudinal distribution in Europe. Growth and hydraulic efficiency varied widely within species and between populations. The variability of embolism resistance was in general weaker than that of growth and hydraulic efficiency, and very low for all species but Populus tremula. In addition, no and weak support for a safety vs. efficiency trade-off was observed for the angiosperm and conifer species, respectively. The limited variability of embolism resistance observed here for all species except Populus tremula, suggests that forest populations will unlikely be able to adapt hydraulically to drier conditions through the evolution of embolism resistance

The response of methane and nitrous oxide fluxes to forest change in Europe

Forests in Europe are changing due to interactions between climate change, nitrogen (N) deposition and new forest management practices. The concurrent impact on the forest greenhouse gas (GHG) balance is at present difficult to predict due to a lack of knowledge on controlling factors of GHG fluxes and response to changes in these factors. To improve the mechanistic understanding of the ongoing changes, we studied the response of soil-atmosphere exchange of nitrous oxide (N 2O) and methane (CH 4) at twelve experimental or natural gradient forest sites, representing anticipated future forest change. The experimental manipulations, one or more per site, included N addition (4 sites), changes of climate (temperature, 1 site; precipitation, 2 sites), soil hydrology (3 sites), harvest intensity (1 site), wood ash fertilisation (1 site), pH gradient in organic soil (1 site) and afforestation of cropland (1 site). On average, N 2O emissions increased by 0.06 \ub1 0.03 (range 0-0.3) g N 2O-N m -2 yr -1 across all treatments on mineral soils, but the increase was up to 10 times higher in an acidic organic soil. Soil moisture together with mineral soil C / N ratio and pH were found to significantly influence N 2O emissions across all treatments. Emissions were increased by elevated N deposition, especially in interaction with increased soil moisture. High pH reduced the formation of N 2O, even under otherwise favourable soil conditions. Oxidation (uptake) of CH 4 was on average reduced from 0.16 plusmn; 0.02 to 0.04 plusmn; 0.05 g CH 4-C m -2 yr -1 by the investigated treatments. The CH 4 exchange was significantly influenced by soil moisture and soil C / N ratio across all treatments, and CH 4 emissions occurred only in wet or water-saturated conditions. For most of the investigated forest manipulations or natural gradients, the response of both N 2O and CH 4 fluxes was towards reducing the overall GHG forest sink. The most resilient forests were dry Mediterranean forests, as well as forests with high soil C / N ratio or high soil pH. Mitigation strategies may focus on (i) sustainable management of wet forest areas and forested peatlands, (ii) continuous forest cover management, (iii) reducing atmospheric N input and, thus, N availability, and (iv) improving neutralisation capacity of acid soils (e.g. wood ash application). \ua9 Author(s) 2012

Osmolality and non-structural carbohydrate composition in the secondary phloem of trees across a latitudinal gradient in Europe

COST Action FP1106 STReESS ; EU Life Programme (LIFE12 ENV/FI/000409 ; Ajut Marie Curie IF fellowship (No 659191)Phloem osmolality and its components are involved in basic cell metabolism, cell growth, and in various physiological processes including the ability of living cells to withstand drought and frost. Osmolality and sugar composition responses to environmental stresses have been extensively studied for leaves, but less for the secondary phloem of plant stems and branches. Leaf osmotic concentration and the share of pinitol and raffinose among soluble sugars increase with increasing drought or cold stress, and osmotic concentration is adjusted with osmoregulation. We hypothesize that similar responses occur in the secondary phloem of branches. We collected living bark samples from branches of adult Pinus sylvestris, Picea abies, Betula pendula and Populus tremula trees across Europe, from boreal Northern Finland to Mediterranean Portugal. In all studied species, the observed variation in phloem osmolality was mainly driven by variation in phloem water content, while tissue solute content was rather constant across regions. Osmoregulation, in which osmolality is controlled by variable tissue solute content, was stronger for Betula and Populus in comparison to the evergreen conifers. Osmolality was lowest in mid-latitude region, and from there increased by 37% toward northern Europe and 38% toward southern Europe due to low phloem water content in these regions. The ratio of raffinose to all soluble sugars was negligible at mid-latitudes and increased toward north and south, reflecting its role in cold and drought tolerance. For pinitol, another sugar known for contributing to stress tolerance, no such latitudinal pattern was observed. The proportion of sucrose was remarkably low and that of hexoses (i.e., glucose and fructose) high at mid-latitudes. The ratio of starch to all non-structural carbohydrates increased toward the northern latitudes in agreement with the build-up of osmotically inactive C reservoir that can be converted into soluble sugars during winter acclimation in these cold regions. Present results for the secondary phloem of trees suggest that adjustment with tissue water content plays an important role in osmolality dynamics. Furthermore, trees acclimated to dry and cold climate showed high phloem osmolality and raffinose proportion

Effects of population and site on <i>P</i>_<i>50</i> (MPa), xylem-specific hydraulic conductivity (<i>K</i>_<i>s</i>, kg m^-1 MPa^-1 s^-1) and branch growth (BG, estimated as branch radius/xylem age (mm/year)) of study species, according to nested ANOVAs.

<p>The F, p-values and degrees of freedom are shown. Pop: population.</p