Tree Uptake Research Articles

The early spring N uptake of young peach trees (Prunus persica) is affected by past and current fertilizations and levels of C and N stores

In deciduous trees, shoot development in early spring is assumed to be achieved mainly at the expense of nitrogen (N) stores. Indeed, the possible compensation for poor autumn N storage by early spring N uptake has been little studied. We therefore determined the dynamics of spring N uptake in relation to spring N supply, carbon and N storage and shoot development. Young peach trees (Prunus persica L. Batsch, cv. 'GF305') were raised outdoors in a hydroponic set-up during the spring and summer, with an excessive N supply. During the autumn, half of the trees were then N limited. The following spring, the N supply remained either high or low, or changed from high to low or low to high. Between 6 March and 13 May, N uptake was measured automatically on an hourly basis, while shoot growth was monitored once a week. These in situ measurements were completed by three destructive harvests to assess organ composition in N and total non-structural carbohydrates (TNC). Until the end of April, N uptake was dependent on the autumn N treatment, being higher in trees that had been N limited in the autumn. Total non-structural carbohydrate mobilization was also higher in those trees that had lost at least 17 g TNC by 24 April, while TNC levels in non-limited trees remained stable or even rose. Shoot development, estimated by the number of elongated axes and leaves per axis, was also slightly delayed by an N limitation in autumn. After 24 April, N uptake rates increased notably under all treatments and was determined by the spring N supply. In trees receiving a high N supply in the spring, the uptake rates also displayed marked short-term variations. That reduced the differences between treatments and by 13 May no differences could be evidenced between the trees in terms of organ biomass and TNC and N contents, whatever the treatment. We concluded that in the early spring, N uptake may compensate for a deficit of N storage insofar as large quantities of TNC can be mobilized for that purpose.

Soil nitrification and foliar δ15N declined with stand age in trembling aspen and jack pine forests in northern Alberta, Canada

Understanding changes in soil N cycling with stand development is critical for forest management as tree growth is affected by soil N availability. The aim of this study was to evaluate the changes in soil N availability and loss with stand development in trembling aspen (Populus tremuloides Michx.) and jack pine (Pinus banksiana Lamb.) in northeastern Alberta, Canada. Soil inorganic N availability (measured as N supply rate) and foliar N chemistry (N concentration and δ15N) in trembling aspen stands ranged from 52 to 70 years old (n = 7) and jack pine stands 43 to 78 years old (n = 8) were investigated in 2008 and 2009. The relationships among the ratios of NO3 --N to total inorganic N (NO3 --N/TIN), foliar N concentration, and foliar δ15N with stand age were also explored by regression analyses. Total inorganic N supply rates did not systematically change with stand age across stand types, soil layers and measurement periods; whereas NO3 --N/TIN showed a decreasing tendency with stand age, suggesting that nitrification and associated N loss potential became smaller in older stands with greater limitation in soil N availability. Foliar δ15N decreased with stand age from −1.7 to −4.7‰ for aspen and from −4.1 to −7.1‰ for jack pine, and there were positive correlations between foliar δ15N and soil NO3 --N/TIN, suggesting that decreased soil N loss led to less 15N-depletion in the inorganic N available for tree uptake in older stands. However, foliar N concentration did not significantly change with stand age, suggesting that there were other N sources such as organic N in the forest floor, in addition to the inorganic N, available for plant uptake. Our results suggest that soil inorganic N availability became more limited as stand age increased. In addition, the ratio of NO3 --N/TIN and its relationship with foliar δ15N indicated decreased soil N loss potential and shifted N sources with stand age in boreal forests that are typically N-limited. Our study demonstrated that declining nitrification with increasing stand age might be one of the mechanisms mediating N-limitation in the studied boreal forests.

CO2 uptake of Opuntia ficus-indica (L.) Mill. whole trees and single cladodes, in relation to plant water status and cladode age

Most of net photosynthesis determinations in Opuntia ficus-indica come from measurements on individual cladodes. However, they have limitations when used to scale up to whole canopy gas exchange, because a large variability of carbon assimilation may occur within the canopy, due to, among others, differences in cladode age and intercepted radiation or individual cladode response to abiotic stresses. The aim of this work was to evaluate the application of open gas exchange chambers, simultaneously applied around the whole canopy, to measure net CO 2 uptake, continuously over a 24 h period, in single Opuntia ficus-indica (L.) Mill. potted trees and in relation with their water status. Net CO2 uptake was also measured for single cladodes differentiated by age. O. ficus-indica trees continued their photosynthetic activity 60 days after the irrigation was stopped, when soil water content was lower than 5%. At this stage, current-year and 1-year-old cladodes had become flaccid but still the daily net CO 2 uptake of non-irrigated trees kept the same rate than at the beginning of the experiment, while watered trees had doubled their net CO 2 uptake. The highest instantaneous rates and total daily net CO 2 uptake for both well-watered and non-irrigated trees occurred 60 days after the onset of the dry period, when maximal instantaneous rates were 11.1 in well-watered trees and 8.4 mol m –2 s –1 in non-irrigated trees. During the drought period, the chlorenchyma fresh weight decreased by 45% and 30%, in 1- and 2-yearold drought cladodes respectively, and marginally increased in currentyear ones (+20%). Net CO 2 uptake for 1-year-old and 2-year-old cladodes changed only at highest photosynthetic photon flux density and temperatures, and average seasonal net CO 2 uptake of 2-year-old cladodes was 15% lower than for 1-year-old ones. Whole-tree gas exchange measurements applied for the first time to O. ficus-indica indicated that whole cactus pear trees maintain similar net CO 2 uptake, contrary to previous evidence gathered on single leaves, even after 60 days of drought. A substantial water loss in the most photosynthetically active cladodes was not sufficient to alter this response. Differences in growth accrued by wet and non-irrigated trees were due to the fact that, as the season progressed, the former were able to increase their total daily CO 2 uptake and the latter were not.

Tracing the Water Sources of Trees and Streams: Isotopic Analysis in a Small Pre-Alpine Catchment

We used a dual stable isotope approach (2H and 18O) and electrical conductivity data in combination with hydrometric measurements to trace water fluxes in the soil, stream and trees in a small forested watershed in the Italian Pre-Alps. The aim was to understand the main water sources for plant transpiration and runoff generation. The data were collected between events and during rainfall events in order to assess the sources of tree uptake under different conditions. Sampling and analysis are still continuing but preliminary results show that the isotopic composition of tree water was similar to soil water and rain water but statistically different from streamflow and groundwater. This suggests that trees used predominantly soil water, rather than groundwater, during the study period. No marked difference was found between the isotopic composition of the sap of trees in the riparian zone and the sap of trees on the hillslope. However, during dry conditions sap in riparian trees slowly became more similar to deep soil water and groundwater, indicating a possible switch in water uptake from shallow to deeper soil water. In contrast to the quick response of the stream, the composition of tree water did not change immediately after a rainfall event, even though the composition of shallow soil water had changed, which may be caused by storage of water in the tree and the low vapor pressure deficit that suppressed transpiration after the rainfall event. Future work will be carried out to monitor the seasonal variability in water uptake and its response to rainfall events in more detail.

Four years of simulated N and S depositions did not cause N saturation in a mixedwood boreal forest ecosystem in the oil sands region in northern Alberta, Canada

We conducted a simulated nitrogen (N) and sulfur (S) deposition experiment in the Athabasca oil sands region (AOSR) where NOx and SO2 have been emitted from oil sands mining/extracting and upgrading activities and then deposited to the surrounding ecosystems for decades. To evaluate changes in tree growth rates, N pool sizes, and nutrient losses by S and N deposition, the following four treatments were applied: control (CK), N addition (+N, 30kgNha−1yr−1), S addition (+S, 30kgSha−1yr−1), and +NS additions (+NS, 30kgN and 30kgSha−1), from 2006 through 2009. Nitrogen addition increased (p<0.05) tree growth in the +N and +NS treatments, indicating N-limitation in the studied forest, while none of the treatments affected understory growth or soil microbial biomass. The treatments affected inorganic N concentrations in the soil only immediately following N addition. Minimal amounts of NO3- were leached below 45cm (considered to be below the main rooting zone) of the soil profile in any of the treatments. Decreases in exchangeable Ca2+ and Mg2+ by N and S additions were likely due to increased tree uptake following increased tree growth in the former and increased leaching with sulfate in the latter. Although the lack of significant N leaching indicates that the risk of N saturation was low after 4yr of elevated N deposition, reduction of exchangeable base cations implies that nutrient imbalance remains a concern in AOSR in the long term.

Intra-annual Secondary Growth Rate-Climate Relations of Fagus orientalis Lipsky in the Center of Hyrcanian Forests

Weekly rate of Beech tree ring increment were related to the changes of climatic factors in weekly intervals. In order to do so, small samples were extracted from 5 Oriental beech trees located in Nowshahr educational forest in the central part of the Hyrcanian forests of Iran during 2008 growing season. Microscopic sections were prepared and average increases in tree ring width were measured, standardized and modeled using Gompertz equation. The results showed that the minimum air temperature and water evaporation had the strongest and positive effect on the secondary growth rate while the role of precipitation was minor and negative. Air temperature and evaporation variations during growing season were assumed to remain in their optimum level; increasing xylem formation by accelerating carbohydrate production and carbon uptake of trees, respectively. Since the studied site had warm and humid climate receiving sufficient amount of rainfall before and during growing season, water availability was not a limiting factor of radial growth and its minor negative relation was interpreted according to its small hampering effect on the air temperature and sunlight absorption of trees. It was concluded that meteorological factors affecting secondary growth rate of trees should be interpreted as a package rather than analyzed disconnectedly.

Contribution of phosphorus (32P) absorption and remobilization for citrus growth

Background and aims Phosphorus (P) is a mobile nutrient in the plant so growth depends on its internal remobilization and a plant’s ability to respond to its availability in the growing media. This study was conducted to evaluate the influence of P status and rootstocks on the patterns of P uptake and remobilization in orange trees. Methods Sweet orange trees on Cleopatra mandarin (CM) or Rangpur lime (RL) rootstocks were grown for nine months in nutrient solution (NS) that was either P-deficient (DNS) or was P-sufficient (SNS). After this period, half of the trees were reciprocally transferred between DNS and SNS (from D to S and S to D), while the others remained in their initial P availability. Results Trees on RL had more shoot and root growth, accumulated more P and had greater efficiency of P absorption and transport to the shoot (PAE) than those on CM. The major source of P for growth was previously stored P even with an adequate current P supply to the roots. This suggested the dominance of P remobilization over P uptake and the requirement that trees had sufficient stored P to meet P demand of new growth. Trees on CM had greater concentrations of remobilized P in new shoots than trees on RL. Conclusion Trees grafted on rootstocks less able to take up P (CM) were more dependent on the internal reserves of P for new growth than rootstocks with higher PAE (RL).

Response of ‘Hass’ avocado trees to irrigation management and root constraint

Abstract The performance of ‘Hass’ avocado trees grown in lysimeters under different irrigation regimes obtained by manipulating drip irrigation frequency and root volume was examined. The experimental design comprised six treatments (3 × 2) with three irrigation frequencies and two container volumes (100- and 200-L). The three irrigation frequencies were: pulsed irrigation (10–20 min every 30 min) throughout the day (Irg1), one daily irrigation event beginning at night and terminated in the morning every day (Irg2) and one irrigation event every two days (Irg3). Irrigation management induced significant differences in water availability in the root zone and subsequently, the diurnal and periodic water uptake. Water uptake of trees in the Irg1 treatment closely followed changes in the meteorological conditions (air temperature, pan evaporation and vapour pressure deficit) while that of trees in the Irg2 and Irg3 treatments was depressed by intermediate and severe water stress, respectively. The experimental treatments had little effect on the vegetative growth, flowering or fruit-set processes. However there were significant treatment differences on fruitlet abscission and accordingly, on fruit yield. Black spots initiated from the seed became apparent on some of the fruits at the beginning of June, and about two weeks later an intensive abscission of fruitlet begun that ended at the beginning of July. The abscission was more intense in the 100-L than the 200-L containers, in the following order: Irg3 > Irg2 ≫ Irg1 regardless of the container volume. Net CO2 assimilation during periods of fruit growth decreased in trees exposed to moderate or severe water stress (Irg2 and Irg3, respectively) and therefore, it is plausible that fruitlet abscission resulted from carbohydrate stress. Improvement of water and nutrient availability, especially in periods where the activity of the root system was weak as a result of low carbohydrate supply presumably played a dominant role in seeds or fruit function.

Water sources of urban trees in the Los Angeles metropolitan area

In semi-arid cities, urban trees are often irrigated, but may also utilize natural water sources such as groundwater. Consequently, the sources of water for urban tree transpiration may be uncertain, complicating efforts to efficiently manage water resources. We used a novel approach based on stable isotopes to determine tree water sources in the Los Angeles basin, where we hypothesized that trees would rely on irrigation water in the soil rather than develop deep roots to tap into groundwater. We evaluated the oxygen (δ18O) and hydrogen (δD) isotope ratios of xylem water, irrigation water, soil water, and groundwater in a study of temporal patterns in water sources at two urban sites, and a study of spatial patterns at nine urban sites and one “natural” riparian forest. Contrary to our hypothesis, we found that despite frequent irrigation, some trees tap into groundwater, although in most species this was a small water source. Some trees appeared to be using very shallow soil water at <30 cm depth, suggesting that these mature urban trees were quite shallowly rooted. In the natural site, trees appeared to be using urban runoff in addition to shallow soil water. We were able to identify tree uptake of precipitation at only 3 sites. The results show that some irrigated trees utilize groundwater and do not rely solely on irrigation water, which may make them able to withstand drought and/or water conservation measures. However, some irrigated trees may develop very shallow root systems, which may make them more susceptible.

Sources of increased N uptake in forest trees growing under elevated CO2: results of a large-scale 15N study

Nitrogen availability in terrestrial ecosystems strongly influences plant productivity and nutrient cycling in response to increasing atmospheric carbon dioxide (CO2). Elevated CO2 has consistently stimulated forest productivity at the Duke Forest free-air CO2 enrichment experiment throughout the decade-long experiment. It remains unclear how the N cycle has changed with elevated CO2 to support this increased productivity. Using natural-abundance measures of N isotopes together with an ecosystem-scale 15N tracer experiment, we quantified the cycling of 15N in plant and soil pools under ambient and elevated CO2 over three growing seasons to determine how elevated CO2 changed N cycling between plants, soil, and microorganisms. After measuring natural-abundance 15N differences in ambient and CO2-fumigated plots, we applied inorganic 15N tracers and quantified the redistribution of 15N for three subsequent growing seasons. The natural abundance of leaf litter was enriched under elevated compared to ambient CO2, consistent with deeper rooting and enhanced N mineralization. After tracer application, 15N was initially retained in the organic and mineral soil horizons. Recovery of 15N in plant biomass was 3.5 ± 0.5% in the canopy, 1.7 ± 0.2% in roots and 1.7 ± 0.2% in branches. After two growing seasons, 15N recoveries in biomass and soil pools were not significantly different between CO2 treatments, despite greater total N uptake under elevated CO2. After the third growing season, 15N recovery in trees was significantly higher in elevated compared to ambient CO2. Natural-abundance 15N and tracer results, taken together, suggest that trees growing under elevated CO2 acquired additional soil N resources to support increased plant growth. Our study provides an integrated understanding of elevated CO2 effects on N cycling in the Duke Forest and provides a basis for inferring how C and N cycling in this forest may respond to elevated CO2 beyond the decadal time scale.

Hydraulic adjustments underlying drought resistance of Pinus halepensis

Drought-induced tree mortality has increased over the last decades in forests around the globe. Our objective was to investigate under controlled conditions the hydraulic adjustments underlying the observed ability of Pinus halepensis to survive seasonal drought under semi-arid conditions. One hundred 18-month saplings were exposed in the greenhouse to 10 different drought treatments, simulating combinations of intensities (fraction of water supply relative to control) and durations (period with no water supply) for 30 weeks. Stomata closed at a leaf water potential (Ψ(l)) of -2.8 MPa, suggesting isohydric stomatal regulation. In trees under extreme drought treatments, stomatal closure reduced CO(2) uptake to -1 µmol m(-2) s(-1), indicating the development of carbon starvation. A narrow hydraulic safety margin of 0.3 MPa (from stomatal closure to 50% loss of hydraulic conductivity) was observed, indicating a strategy of maximization of CO2 uptake in trees otherwise adapted to water stress. A differential effect of drought intensity and duration was observed, and was explained by a strong dependence of the water stress effect on the ratio of transpiration to evapotranspiration T/ET and the larger partitioning to transpiration associated with larger irrigation doses. Under intense or prolonged drought, the root system became the main target for biomass accumulation, taking up to 100% of the added biomass, while the stem tissue biomass decreased, associated with up to 60% reduction in xylem volume.

A comparison between stomatal ozone uptake and AOT40 of deciduous trees in Japan

Abstract: A comparison of the maps of stomatal ozone uptake (AFst0) and concentrations exceeding 40 ppb (AOT40) for dominant temperate deciduous tree species (Quercus serrata, Fagus crenata, Betula ermanii) was conducted in Japan. Estimations of stomatal ozone uptake were accomplished using estimated ozone concentration, climate data, and vegetation data. Key parameters such as stomatal conductance parameters for each species were collected from scientific literature in Japan. Stomatal closure induced by vapour pressure deficit affected the AFst0 values in warmer part of Japan. For this reason, the areas with high AOT40 did not always correspond to the areas with high AFst0. The result showed that ozone risk assessment using AOT40 is VPD-constrained in central Japan, which implies an overestimation of risk compared to AFst0. While in Europe AOT40 is higher where water stress is recurrent, AOT40 peaked in the cool and humid climate region of central-eastern Japan where also stomatal ozone uptake reached maximum values.

Estimation of stomatal ozone uptake of deciduous trees in East Asia

To assess ozone risks to temperate deciduous forest trees in East Asia, the stomatal ozone uptake was estimated based on a flux-based modeling approach. In this model, key parameters were obtained from scientific literatures on deciduous tree species in East Asia. In addition, regional characteristics of the leaf duration were estimated using a phenological model. The result showed a difference in spatial pattern between AFst0 (accumulative stomatal ozone uptake) and AOT40 (accumulative exposure above a threshold concentration of 40 ppb during daylight hours). Although most of the areas of high ozone concentration corresponded to humid climate areas, not only the ozone concentration, but also the length of the leaf duration and the species-specific stomatal response to environmental factors, limited AFst0 in East Asia. These results suggested that an approach based on stomatal ozone uptake would be a useful tool for ozone risk assessment in East Asia.

Increases in the flux of carbon belowground stimulate nitrogen uptake and sustain the long-term enhancement of forest productivity under elevated CO2

The earth's future climate state is highly dependent upon changes in terrestrial C storage in response to rising concentrations of atmospheric CO₂. Here we show that consistently enhanced rates of net primary production (NPP) are sustained by a C-cascade through the root-microbe-soil system; increases in the flux of C belowground under elevated CO₂ stimulated microbial activity, accelerated the rate of soil organic matter decomposition and stimulated tree uptake of N bound to this SOM. This process set into motion a positive feedback maintaining greater C gain under elevated CO₂ as a result of increases in canopy N content and higher photosynthetic N-use efficiency. The ecosystem-level consequence of the enhanced requirement for N and the exchange of plant C for N belowground is the dominance of C storage in tree biomass but the preclusion of a large C sink in the soil.

Root functioning in tropical high-elevation forests: Environmental vs. biological control of root water absorption

Lowered temperatures may reduce the root water uptake of tropical trees at high elevations through several mechanisms; however, field studies to test their relevance are lacking. We measured sap flux density ( J) in small-diameter tree roots across a 2000-m elevation transect in a tropical mountain forest for quantifying the effects of temperature ( T a ), VPD and soil moisture ( θ) on root water flow and uptake at different elevations. Recently developed miniature heat balance-sap flow gauges were applied to roots of about 10 mm in diameter in mountain forest stands at 1050, 1890 and 3060 m a.s.l. in the Ecuadorian Andes and the measured flow was related to anatomical properties of the root xylem. Between 1050 and 3060 m, mean J decreased to about a third. VPD was the most influential environmental factor controlling J at 1050 and 1890 m, while T a was the key determinant at 3060 m. Large vessels were absent in the root xylem of high-elevation trees which resulted in a 10-fold decrease of theoretical hydraulic conductivity ( k h theor) between 1050 and 3060 m. We conclude that both physical limitations (reduced VPD, increased viscosity of water) and biological constraints (large decrease of k h theor) result in a significantly reduced J and root water uptake of the trees in high-elevation tropical forests.

Assessment of radionuclide and metal contamination in a thorium rich area in Norway

The Fen Central Complex in southern Norway, a geologically well investigated area of magmatic carbonatite rocks, is assumed to be among the world largest natural reservoirs of thorium ((232)Th). These rocks, also rich in iron (Fe), niobium (Nb), uranium ((238)U) and rare earth elements (REE), were mined in several past centuries. Waste locations, giving rise to enhanced levels of both radionuclides and metals, are now situated in the area. Estimation of radionuclide and metal contamination of the environment and radiological risk assessment were done in this study. The average outdoor gamma dose rate measured in Fen, 2.71 μGy h(-1), was significantly higher than the world average dose rate of 0.059 μGy h(-1). The annual exposure dose from terrestrial gamma radiation, related to outdoor occupancy, was in the range 0.18-9.82 mSv. The total activity concentrations of (232)Th and (238)U in soil ranged from 69 to 6581 and from 49 to 130 Bq kg(-1), respectively. Enhanced concentrations were also identified for metals, arsenic (As), lead (Pb), chromium (Cr) and zinc (Zn), in the vicinity of former mining sites. Both radionuclide and heavy metal concentrations suggested leaching, mobilization and distribution from rocks into the soil. Correlation analysis indicated different origins for (232)Th and (238)U, but same or similar for (232)Th and metals As, Cr, Zn, nickel (Ni) and cadmium (Cd). The results from in situ size fractionation of water demonstrated radionuclides predominately present as colloids and low molecular mass (LMM) species, being potentially mobile and available for uptake in aquatic organisms of Norsjø Lake. Transfer factors, calculated for different plant species, showed the highest radionuclide accumulation in mosses and lichens. Uptake in trees was, as expected, lower. Relationship analysis of (232)Th and (238)U concentrations in moss and soil samples showed a significant positive linear correlation.

Long-term effect of fertilization on137Cs concentration in Scots pine needles

Long-term observations on the effects of a fertilization treatment on 137 Cs concentrations in forest vegetation are scarce. Needles of Scots pine were used as biological indicators of radionuclide uptake of trees. The fertilization experiments are located in western Finland in an area where radioactive contamination from the Chernobyl accident in 1986 was relatively high (22–75 kBq m−2 ) compared to other parts of Finland. Fertilization treatments included different combinations of major nutrients, i.e. nitrogen, phosphorus, potassium and calcium. Needle 137 Cs concentrations of Scots pine were analyzed during 1991–2006. The effect of fertilization on 137 Cs concentration was tested 5 to 20 years after radioactive contamination from the Chernobyl accident in 1986. Fertilization clearly decreased 137 Cs concentration in Scots pine needles 1–21 growing seasons after application. Single K fertilization decreased significantly 137 Cs concentration 21 growing seasons after radioactive deposition on a drained mire. Mineral nutrients (application of commercial fertilizer or wood ash) can well be recommended for remediation of forests contaminated by accidental radionuclide deposition. The site conditions need to be taken into account in planning of remediation.

Inter-specific and seasonal variations in photosynthetic capacity and water use efficiency of five temperate tree species in Northeastern China

Photosynthetic capacity (P max) and water use efficiency (WUE) are useful indices for describing CO2 uptake and H2O loss of trees. Inter-specific and seasonal variations in P max and WUE of five tree species were quantified in a Chinese temperate forest. The study included pioneer (white birch), mid-successional (Amur cork-tree, Manchurian walnut, Mongolian oak), and late-successional (Amur linden) species. The P max and WUE differed significantly among species, but the inter-specific variations were smaller than previously reported. Leaf-area-based P max varied from 5.1 for linden to 11.0 µmol m−2s−1 for birch, whereas leaf-mass-based P max ranged from 154 for linden to 252 µmol kg−1s−1 for walnut. Linden had the highest WUE, whereas walnut had the lowest. The seasonal patterns of P max and WUE were significantly different between species. The P max of birch increased as the season proceeded, whereas the P max of the other four species was lowest in May, and peaked in June. The seasonality of P max was influenced by stomatal conductance, apparent carboxylation efficiency, and specific leaf area, but the determining factor varied with species and leaf development. This study suggests that a deeper understanding of inter-specific and seasonal variations of gas exchange parameters would improve our ability to predict the carbon metabolism in the temperate forests.

NUTRIENT PARTITIONING IN POTTED PEACH (PRUNUS PERSICA L.) TREES SUPPLIED WITH MINERAL AND ORGANIC FERTILIZERS

The aim of the experiment was to evaluate the effect of organic fertilization on nutrient uptake and partitioning in potted peach trees. The study was carried out on 72 peach (Prunus persica L.) plants. The following treatments were compared: 1) unfertilized control, 2) mineral fertilization [713 mg nitrogen (N), 119 mg phosphorus pentoxide (P2O5), 476 mg potassium oxide (K2O) pot−1], 3) cow manure (119 g dw pot−1) and 4) compost (119 g dw pot−1). Compared to the untreated control, plant biomass was improved by supplying cow manure and compost. Potassium concentration in fine roots and leaves was higher in compost treated trees. Leaf concentrations of calcium (Ca) and magnesium (Mg) were decreased by applications of compost and cow manure. Nutrient concentrations in fine roots were always positively correlated with nutrients in coarse roots, only N showed a negative correlation. With the exception of Ca and Mg, macronutrients removed by trees were higher after compost fertilization than in unfertilized controls.

The output and bio-cycling of Si in a tropical rain forest developed on young basalt flows (La Reunion Island)

The importance of plant bio-cycling in the biogeochemical cycle of Si has been pointed out by recent studies. We analysed the litter and wood chemical composition of a lowland rainforest (Marelongue Reserve, Réunion Island, Indian ocean) not impacted by human activities, developed on a recent basalt flow dated ci 500 years. The amount of elements stored in the above ground biomass falls within the range of tropical forests developed on moderately fertile older soils with Ca, K, Mg and Si values respectively at 1458 kg ha −1, 1506 kg ha −1, 246 kg ha −1and 17 kg ha −1. The estimated mineral uptake of the old trees gives a flux equivalent to 5 ± 2% of the elements returned to the soil with litterfall. The four species that contribute the most to the litterfall with 70% of the leaf fall represent only 45% of the annual Si bio cycling. The result demonstrates that species that are not highly productive in a rain forest could be significant for the bio-cycling of parent-rock elements such as Si. A mass balance calculation shows that the dissolved silicon (DSi) issued from the dissolution of basalt is 1.8 times the DSi from litterfall. Here, the biogeochemical cycle of Si is characterized by a limited contribution of the bio-cycling compartment compared to other cases reported for rainforests.