Introducing Acacia mangium trees in Eucalyptus grandis plantations: consequences for soil organic matter stocks and nitrogen mineralization

Background and aims

Eucalyptus plantations cover 20 million hectares on highly weathered soils. Large amounts of nitrogen (N) exported during harvesting lead to concerns about their sustainability. Our goal was to assess the potential of introducing A. mangium trees in highly productive Eucalyptus plantations to enhance soil organic matter stocks and N availability.

Methods

A randomized block design was set up in a Brazilian Ferralsol soil to assess the effects of mono-specific Eucalyptus grandis (100E) and Acacia mangium (100A) stands and mixed plantations (50A:50E) on soil organic matter stocks and net N mineralization.

Results

A 6-year rotation of mono-specific A. mangium plantations led to carbon (C) and N stocks in the forest floor that were 44% lower and 86% higher than in pure E. grandis stands, respectively. Carbon and N stocks were not significantly different between the three treatments in the 0–15?cm soil layer. Field incubations conducted every 4?weeks for the two last years of the rotation estimated net soil N mineralization in 100A and 100E at 124 and 64?kg?ha^?1?yr^?1, respectively. Nitrogen inputs to soil with litterfall were of the same order as net N mineralization.

Conclusions

Acacia mangium trees largely increased the turnover rate of N in the topsoil. Introducing A. mangium trees might improve mineral N availability in soils where commercial Eucalyptus plantations have been managed for a long time.     

Rainfall reduction impacts rhizosphere biogeochemistry in eucalypts grown in a deep Ferralsol in Brazil

Plant and Soil - Comparing root functioning under contrasting rainfall regimes can help assessing the capacity of plant species to cope with more intense and frequent drought predicted under...     

Enzymes in pancreatic islets that use NADP(H) as a cofactor including evidence for a plasma membrane aldehyde reductase

Molecular and Cellular Biochemistry -     

Measured and modeled interactive effects of potassium deficiency and water deficit on gross primary productivity and light‐use efficiency in Eucalyptus grandis plantations

Global climate change is expected to increase the length of drought periods in many tropical regions. Although large amounts of potassium (K) are applied in tropical crops and planted forests, little is known about the interaction between K nutrition and water deficit on the physiological mechanisms governing plant growth. A process‐based model (MAESPA) parameterized in a split‐plot experiment in Brazil was used to gain insight into the combined effects of K deficiency and water deficit on absorbed radiation (aPAR), gross primary productivity (GPP), and light‐use efficiency for carbon assimilation and stem biomass production (LUE_C and LUE_s) in Eucalyptus grandis plantations. The main‐plot factor was the water supply (undisturbed rainfall vs. 37% of throughfall excluded) and the subplot factor was the K supply (with or without 0.45 mol K m^?2 K addition). Mean GPP was 28% lower without K addition over the first 3 years after planting whether throughfall was partly excluded or not. K deficiency reduced aPAR by 20% and LUE_C by 10% over the whole period of growth. With K addition, throughfall exclusion decreased GPP by 25%, resulting from a 21% decrease in LUE_C at the end of the study period. The effect of the combination of K deficiency and water deficit was less severe than the sum of the effects of K deficiency and water deficit individually, leading to a reduction in stem biomass production, gross primary productivity and LUE similar to K deficiency on its own. The modeling approach showed that K nutrition and water deficit influenced absorbed radiation essentially through changes in leaf area index and tree height. The changes in gross primary productivity and light‐use efficiency were, however, driven by a more complex set of tree parameters, especially those controlling water uptake by roots and leaf photosynthetic capacities.     

Alterations of the bioenergetics systems of the cell in acute and chronic myocardial ischemia

The aim of the works presented here is to analyze the alterations induced by acute ischemia-reperfusion and chronic ischemia on mitochondrial function, in relation to alterations on heart function. Parameters of mitochondrial function were assessed on skinned fibers coming from isolated perfused rat hearts. The effects of chronic ischemia were studied on a rat model of left descending coronary artery stenosis. Two key events observed after acute ischemia-reperfusion and chronic ischemia are the decrease (or the loss) of the stimulatory effect of creatine and the alteration of outer mitochondrial permeability to cytochrome c and ADP. Taken together, these effects indicate the alteration of the intermembrane space architecture leading to the loss of intracellular adenine nucleotides compartmentation and possibly of functional coupling of mitochondrial creatine kinase and adenine nucleotide translocase. These alterations result in the impairment of intracellular energy transfer (channeling) from mitochondria to ATP-utilizing sites located in the cytosol. This may play a significant role in ischemic injury and alterations in heart function. We show that these effects were prevented by effective cardioprotective strategies like ischemic preconditioning or pharmacological preconditioning by perfusion of mitochondrial ATP-sensitive potassium channel openers. We hypothesize that an open mitochondrial ATP-sensitive potassium channel during ischemia maintains the tight structure of the intermembrane space that is required to preserve the normal low outer membrane permeability to ADP and ATP.     

Mixing Eucalyptus and Acacia trees leads to fine root over-yielding and vertical segregation between species

The consequences of diversity on belowground processes are still poorly known in tropical forests. The distributions of very fine roots (diameter <1 mm) and fine roots (diameter <3 mm) were studied in a randomized block design close to the harvest age of fast-growing plantations. A replacement series was set up in Brazil with mono-specific Eucalyptus grandis (100E) and Acacia mangium (100A) stands and a mixture with the same stocking density and 50 % of each species (50A:50E). The total fine root (FR) biomass down to a depth of 2 m was about 27 % higher in 50A:50E than in 100A and 100E. Fine root over-yielding in 50A:50E resulted from a 72 % rise in E. grandis fine root biomass per tree relative to 100E, whereas A. mangium FR biomass per tree was 17 % lower than in 100A. Mixing A. mangium with E. grandis trees led to a drop in A. mangium FR biomass in the upper 50 cm of soil relative to 100A, partially balanced by a rise in deep soil layers. Our results highlight similarities in the effects of directional resources on leaf and FR distributions in the mixture, with A. mangium leaves below the E. grandis canopy and a low density of A. mangium fine roots in the resource-rich soil layers relative to monospecific stands. The vertical segregation of resource-absorbing organs did not lead to niche complementarity expected to increase the total biomass production.     

Unexpected phenology and lifespan of shallow and deep fine roots of walnut trees grown in a silvoarable Mediterranean agroforestry system

Plant and Soil - Fine roots play a major role in the global carbon cycle through respiration, exudation and decomposition processes, but their dynamics are poorly understood. Current estimates of...     

Nutrient supply modulates species interactions belowground: dynamics and traits of fine roots in mixed plantations of Eucalyptus and Acacia mangium

Plant and Soil - Belowground interactions are still poorly understood in mixed-species forests. We investigated the effects of soil fertility on belowground processes in mixed planted forests. The...     

Influence of potassium and sodium nutrition on leaf area components in Eucalyptus grandis trees

Background and Aims

Recent studies showed a positive tree response to Na addition in K-depleted tropical soils. Our study aimed to gain insight into the effects of K and Na fertilizations on leaf area components for a widely planted tree species.

Methods

Leaf expansion rates, as well as nutrient, polyol and soluble sugar concentrations, were measured from emergence to abscission of tagged leaves in 1-year-old Eucalyptus grandis plantations. Leaf cell size and water status parameters were compared 1 and 2 months after leaf emergence in plots with KCl application (+K), NaCl application (+Na) and control plots (C).

Results

K and Na applications enhanced tree leaf area by increasing both leaf longevity and the mean area of individual leaves. Higher cell turgor in treatments +K and +Na than in the C treatment resulting from higher concentrations of osmotica contributed to increasing both palisade cell diameters and the size of fully expanded leaves.

Conclusions

Intermediate total tree leaf area in treatment +Na compared to treatments C and +K might result from the capacity of Na to substitute K in osmoregulatory functions, whereas it seemed unable to accomplish other important K functions that contribute to delaying leaf senescence.     

Enzymes in pancreatic islets that use NADP(H) as a cofactor including evidence for plasma membrane aldehyde reductase

Recent evidence of a pyruvate malate shuttle capable of transporting a large amount of NADPH equivalents out of mitochondria in pancreatic islets suggests that cytosolic NADP(H) plays a role in beta cell metabolism. To obtain clues about these processes the activities of several NADPHutilizing enzymes were estimated in pancreatic islets. Low levels of pyrroquinolone quinone (PQQ) and low levels of enzyme activity that reduce PQQ were found in islets. Low activities of palmitoylCoA and stearoylCoA desaturases were also detected. Significant activities of glutathione reductase, aldose reductase (EC.1.1.1.21) and aldehyde reductase (EC.1.1.1.2) were present in islets. Potent inhibitors of aldehyde and aldose reductases inhibited neither glucoseinduced insulin release nor glucose metabolism in islets indicating that these reductases are not directly involved in glucoseinduced insulin reaction. Over 90% of aldose reductase plus aldehyde reductase enzyme activity was present in the cytosol. Kinetic and chromatographic studies indicated that 60–70% of this activity in cytosol was due to aldehyde reductase and the remainder due to aldose reductase. Aldehyde reductaselike enzyme activity, as well as aldose reductase immunoreactivity, was detected in rat islet plasma membrane fractions purified by a polyethylene glycolDextran gradient or by a sucrose gradient. This is interesting in view of the fact that voltagegated potassium channel beta subunits that contain aldehyde and aldose reductaselike NADPH-binding motifs have been detected in plasma membrane fractions of islets [Receptors and Channels 7: 237–243, 2000] and suggests that NADPH might have a yet unknown function in regulating activity of these potassium channels. Reductases may be present in cytosol to protect the insulin cell from molecules that cause oxidative injury.