Elena Baldi

Iron deficiency-induced changes in carbon fixation and leaf elemental composition of sugar beet (Beta vulgaris) plants

In this experiment we (i) tested the hypothesis that, besides decreasing leaf C fixation, lime induced iron (Fe) deficiency increases root C fixation via PEP carboxylase and (ii) assessed the Fe-induced modifications in the elemental composition of plant tissues. Sugar beet plants were grown in nutrient solutions with Fe (45 μM Fe-EDTA; +Fe control) or in a similar nutrient solution without Fe (−Fe) and in presence of CaCO3 (1.0 gL−1), either labelled with 13C (20xa0at. %) or unlabelled. After 7 and 17 days from treatment imposition, plants were harvested and single organs analysed for total O, C, H, macro and micronutrients. 13C abundance was also assessed in control, unlabelled and labelled −Fe plants. Iron deficiency caused significant growth reductions; chlorophyll and net photosynthesis decreased markedly in Fe-deficient plants when compared to the controls, whereas leaf transpiration rates and stomatal conductance were not affected by Fe deficiency. Iron deficient plants had leaf biomass with lower C (2 to 4%) and higher O (3 to 5%) concentrations than +Fe plants. The δ13C was higher (less negative) in +Fe than in −Fe unlabelled plants. Iron deficient plants grown in the nutrient solution enriched with labelled CaCO3 absorbed a relatively small amount of labelled C, which was mainly recovered in the fine roots and accounted for less than 2% of total C gain in the 10 d treatment period. Evidences suggest that iron deficient sugar beets grown in the presence of CaCO3 do not markedly shift their C fixation from leaf RuBP to root PEPC.

Organic fertilization leads to increased peach root production and lifespan

We evaluated the effects of mineral and organic fertilizers on peach root dynamics in the growing season from 2003 to 2006 in a nectarine (Prunus persica L.) orchard, planted in 2001 and located in the Po valley, northeastern Italy. Very few studies have conducted long-term investigations of root dynamics of fruit crops. Our main objective was to determine whether organic fertilizers affect root dynamics differently than mineral fertilizers. The experiment was a completely randomized block design with four replicates of three treatments: unfertilized, mineral fertilized and composted with municipal waste. Mineral fertilizers included P (100xa0kgxa0ha(-1)xa0year(-1)) and K (200xa0kgxa0ha(-1)xa0year(-1)) applied only at planting and N (70-130xa0kgxa0ha(-1)xa0year(-1)) split into two applications, one at 40 days after full bloom (60%) and the other in September (40%) each year. The compost fertilization represented a yearly rate of 10 metric tons (t) dry weightxa0ha(-1), which approximates (in kgxa0ha(-1)xa0year(-1)) 240 N, 100 P and 200 K, split similarly to that described for the mineral fertilization of N. Both root growth and survival were evaluated at 20-day intervals during the growing season by the minirhizotron technique. Compost increased the production of new roots compared with the other treatments (Pxa0<xa00.01). Roots were mainly produced at a depth of 41-80xa0cm and from March to May and in late summer. An analysis of covariance indicated no significant effect of soil nitrate on root production (Pxa0=xa00.47). The root lifespan was longer in compost-treated trees than in mineral-fertilized or unfertilized trees (Pxa0<xa00.01) and it was strongly affected by time of birth; roots born later in the summer lived longer than those born in the spring. Across years and treatments, the average root lifespan was positively correlated with soil nitrate (rxa0=xa00.60; Pxa0<xa00.001). Variation in root lifespan with method of fertilization could be accounted for by variation in soil nitrate concentration as indicated by no effect of fertilizer treatment on root lifespan when soil nitrate was included as a covariate. These results reveal how shifting from mineral to organic fertilizers may shift both soil properties and nutrient availability, leading to changes in both root production and lifespan.

Response of Potted Pear Trees to Increasing Copper Concentration in Sandy and Clay-Loam Soils

ABSTRACT The response of potted pear trees grafted on quince (Cydonia oblonga Mill.) Sydo stock to increasing concentrations (0, 50, 100, 200, 400, 600, 800, and 1000 mg kg−1) of copper (Cu) in sandy and clay-loam soils were evaluated and crop toxicity thresholds and symptoms were determined. Reductions of shoot growth and leaf area were observed only for pear grown in sandy soil with more than 400 mg Cu/kg. During the growing season, carbon assimilation and soil microbial biomass were reduced as concentration of soil Cu increased. However, the effect was always stronger in sandy than clay-loam soil. Copper accumulated in roots, with response to soil Cu additions described by a linear and a quadratic function for sandy and clay-loam soil, respectively. A possible antagonism was observed between Cu and zinc (Zn) in the roots. Root Zn concentration decreased as soil Cu concentration increased.

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.

USE OF SOIL-AND FOLIAR-APPLIED CALCIUM CHLORIDE TO REDUCE PEAR SUSCEPTIBILITY TO BROWN SPOT (STEMPHYLIUM VESICARIUM)

We evaluated the effectiveness of soil and foliar applications of calcium chloride (CaCl2) on reducing pear susceptibility of brown spot (Stemphylium vesicarium). Two experiments were done using pear trees of the variety Abbé Fetel grafted on quince (Cydonia oblonga) rootstock. Potted trees were treated with soil and foliar application of CaCl2, while commercial trees were subjected only to soil application of 5.6 g CaCl2 L−1, and 11.2 g CaCl2 L−1. In a controlled environment, leaf and fruit brown spot incidence decreased with the increase of residual calcium (Ca) concentration in the tissue, according to a second degree function. In fruits from field experiment, disease symptoms were decreased by soil application of CaCl2 that increased Ca fruit concentration above 1000 mg kg−1 dw; however, no clear correlation between fruit Ca and brown spot incidence was found. Leaf water and osmotic potential were not related to brown spot incidence.