ЭКСПЕРИМЕНТАЛЬНЫЕ СТАТЬИ
УДК 581.1
EVALUATING THE EFFECT OF ROOTSTOCKS AND POTASSIUM LEVEL ON PHOTOSYNTHETIC PRODUCTIVITY AND YIELD OF PEAR TREES1
© 2014 K. Bosa*, E. Jadczuk-Tobjasz*, H. M. Kalaji**, M. Majewska*, S. I. Allakhverdiev***
* Department of Pomology, Warsaw University of Life Sciences SGGW, Warsaw, Poland ** Department of Plant Physiology, Warsaw University of Life Sciences SGGW, Warsaw, Poland *** K.A. Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, Moscow
Received April 15, 2013
In this experiment, leaf gas exchange, photosynthetic efficiency, area index, and chlorophyll content were measured in pear (Pyrus communis L.) trees grown on different rootstocks and potassium fertilization doses. Our results showed that trees budded on the Pyrodwarf rootstock had the biggest leaf area and the highest photosynthetic efficiency, photosynthesis rate, and chlorophyll content. There was no correlation between the applied potassium fertilization dosage and the photosynthetic efficiency of the trees. This paper is addressed to discuss various mechanisms and selected factors responsible for pear tree photosynthetic productivity.
Keywords: Pyrus communis — chlorophyll content — chlorophyll fluorescence — LAI — photosynthesis — photosystem II
DOI: 10.7868/S001533031402002X
INTRODUCTION
Pear (Pyrus communis L.) is one of the favorite fruits in Poland and other northern countries. However, the cultivation area of pear is just over 10 thousand ha in Poland, which accounts for only 3% of the total fruit crops [1]. The reason for this limited cultivation seems to be that pear has high climatic requirements. The trees are less resistant to frost than apple, and the flowers are often damaged by frost due to early flowering
[1]. Furthermore, pear cultivation needs high request to the soil conditions and nutrients, because pear is sensitive to mineral deficiencies, especially potassium
[2], which is responsible for the quality of flower buds, fruit size, color, and flavor [3]. Potassium plays an important biophysical role in maintaining osmotic pressure. It is also involved in some biochemical and enzymatic functions. It apparently influences photosynthesis [4, 5], nutrient and assimilates transport, and
1 This text was submitted by the authors in English.
Abbreviations: Chl — chlorophyll; Fv/Fm — maximum quantum yield of PSII; Gs — stomatal conductance; LAI — leaf area index; PI — performance index; Pn — net photosynthetic rate; PSII — photosystem II; TCSA — trunk cross-sectional area; ®PSII — yield efficiency of PSII of light-adapted leaves. Corresponding authors: Suleyman I. Allakhverdiev and Hazem M. Kalaji. S.I.A., K.A. Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, Botanicheskaya ul. 35, Moscow, 127276 Russia; fax: +7 (499) 977-8018; e-mail: suleyman.allakhverdiev@ gmail.com; H.M.K, Department of Plant Physiology, Warsaw University of Life Sciences SGGW, Nowoursynowska 159, 02-776 Warsaw, Poland; e-mail: hazem@kalaji.pl
enzyme activation for protein synthesis. Another important factor influencing pear yield and quality is rootstocks [6].
Photosynthetic activity has been widely used as an important physiological parameter to evaluate the plant growth vigor, and ultimately biomass or economic yield [7—9]. One of these parameters is plant gas exchange, which is a major factor influencing the final yield of fruit trees. Additionally, tree architecture and the use efficiency of photosynthetically active radiation (PAR) can also be decisive for tree growth yielding [10]. It is well known that plant productivity depends on the interaction between light intercepting of the leaf area and the efficiency of the CO2 assimilation process taking place in the leaves. The ability to measure leaf area is fundamental to accurate modeling these physiological and functional processes [11]. The first principle is that total dry matter production and, in many cases, crop yield are related to total light interception. In some models, an increase in leaf area index (LAI) enhanced light interception and hence dry matter production. Although the maximum fruit yield is ultimately limited by light interception, economic fruit yield is a function of the efficiency of light use and light distribution within the canopy. Moreover, LAI can increase significantly following fertilization; thus it is proposed that the measurement of LAI changes may provide a good estimate of potential responsiveness to fertilization.
All plants absorb light mainly through chlorophyll (Chl). Thus, Chl fluorescence is a suitable probe for
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PSII activity, and has been routinely used for many years to non-invasively monitor the photosynthetic performance of plants [9, 12, 13]. Factors causing damage of the photosynthetic systems can therefore be recognized through changes in different fluorescence parameters. Chl fluorescence can also be used to determine potential photosynthetic productivity of plants together with gas exchange [14].
Due to the increased interest in pear cultivation in Poland during the last decade, we conducted experiments to monitor the influence ofbudding on different rootstocks and various potassium levels on photosyn-thetic productivity, growth, and yield of the pear cv. Conference. Our results provide a better understanding of the physiological factors behind pear growth and yield.
MATERIALS AND METHODS
The research was conducted at the experimental field of the Department of Pomology (52°9'26" N and 21°6'24" E), WULS-SGGW (Warsaw, Poland). This site is located in the postglacial valley of the Vistula River on the alluvial land with a fertile silt loam, where potassium fertilization has been applied continuously since 1980. The mean temperature in 2011 was 9.3°C, and annual rainfall was 620.2 mm. The pear (Pyrus communis L.) trees were planted in 2004 at (4 + 1) x 1.5 m (2666 trees/ha). The distance between trees in a row was 1.5 m and the distance of rows in strip was 1 m. The distance between strips was 4 m. In trees rows were maintained under herbicide fallow, while sward in inter-rows had been growing since the first year after planting trees. The average height and diameter were about 3 m and 7 cm, respectively. Tree training, protection against diseases and pests were carried out according to the recommendations for commercial orchards in Poland. Pear trees of cv. Conference grown with five different treatments of potassium fertilization were studied: without potassium fertilization (control), 200 kg K2O/ha applied on the whole surface of the field every year (200/y), 800 kg K2O/ha, and 400 kg K2O/ha applied on the whole surface of the field every four years (800/4y and 400/4y), 200 kg K2O/ha applied within herbicide strips every year (200H/y).
Plant gas exchange, Chl content, Chl fluorescence, and leaf area index measurements (see details below) were performed once a month during the period of May to August 2011 on trees budded on three root-stocks: quince S, quince A, and Pyrodwarf.
Plant gas exchange parameters (net photosynthesis rate, transpiration intensity, stomatal conductance, and intracellular CO2 concentration) were measured on sunny days, between 8:00 and 11:00 a.m. in vivo on fully expanded, directed to sun leaves, at middle part of the crown (12 measurements for each experimental combination, 4 measurements per tree) by means of the Ciras-2 Photosynthesis Measurement System
("PP Systems", United States). Mean values of ambient light intensity, air temperature, and CO2 concentration were 1350 ^mol photons/(m2 s), 21 °C, and 380 ppm, respectively. Leaf area index (LAI) was measured for 12 trees of each experimental combination using an AccuPAR-LP 80 Ceptometer ("Decagon Devices", United States). Quantum efficiency of leaf photosynthetic light energy conversion (36 measurements for each experimental combination, 9 measurements per tree) was measured in vivo after leaf dark adaptation (for 30 min, using leaf clips) using a continuous excitation system — the HandyPEA fluorimeter ("Hansatech Instruments", United Kingdom) and under ambient light using the pulse-modulated system of the FMS2 fluorimeter ("Hansatech Instruments"). In the case of continuous excitation measurements, a saturation light pulse of 1 s duration and 3500 ^mol photons/(m2 s) intensity was applied after dark adaptation of the sample, and the maximum quantum yield of PSII (Fv/Fm) and performance index (PI) were measured. For pulse-modulated measurements (under ambient light), a saturation light of 0.7 s duration and 15300 ^mol photons/(m2 s) intensity were applied and the yield efficiency of PSII of light-adapted leaves (OPSII) was measured. A CL-01 (Chlorophyll Content Meter, "Hansatech Instruments") was used to measure relative Chl content in vivo (36 measurements for each experimental combination, 9 measurements per tree).
Tree vigor was assessed on the basis of the trunk cross-sectional area (TCSA) parameter. The TCSA parameter was derived from a diameter measurement at 30 cm above the ground (12 replications). The yield was assessed on the basis of yield per tree.
Measurements of plant gas exchange, Chl fluorescence, and its content were done on the same leaves. The results presented are average values from the entire season. The results were elaborated by a two-way analysis of variance with the use of FR—ANALWAR software. Tukey's test at a = 0.05 was used to evaluate the significance of differences between treatment means. However, only significantly different data are shown in this work.
RESULTS AND DISCUSSION
In this work, we studied the effect of rootstock and potassium fertilization on the productivity and yield of pear. These factors have been considered to be important in Polish pear cultivation [1]. To date, pear productivity has been evaluated based on the growth model and yield parameters. Recently, some studies began to consider certain physiological parameters, suc
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