The effect of partial root drying on growth and photosynthesis on tomato (Lycopersicon esculentum L.)

Efekat delimičnog sušenja korenova (DSK) na biljke paradajza (Lycopersicon esculentum L.) je bio predmet istraživanja u ovoj magistarskoj tezi. Biljke paradajza su gajene u komercijalnom supstratu sa korenovim sistemom podeljenim u dve plastične posude. Na kraju vegetativnog i u toku generativnog perioda razvića biljaka polovina korenovog sistema je izlagana suši, dok je ostatak zalivan. Posle c. 10 dana (kada je vlažnost zemljišta redukovana na 30%) izvršena je inverzija što je omogućilo da se optimalno zalivana polovina izlaže suši, dok se suva polovina zaliva. Za merenje ispitivanih parametara odabrano je deset biljaka po tretmanu. Visina biljaka, broj i površina listova su mereni svakih 5 dana kao i broj cvetnih grana. U toku istog vremenskog intervala mereni su i broj i dijametar plodova. U distalnom delu najmlađeg razvijenog lista merenja razmene gasova (fotosinteze i transpiracije - pomoću infra-crvenog gasnog analizatora), potencijala vode u listovima (pomoću komore pritiska) i apoplastičnog pH (metodom centrifugiranja). Efikasnost korišćenja vode (WUE) je obračunat na nivou listova (kao odnos intenziteta fotosinteze i transpiracije) i na nivou biljaka (kao suva masa plodova po jedinici evapotranspirisane vode). Merenja suve mase izdanka i korena su obavljena na kraju eksperimenata i na osnovu tih rezultata izračunat je odnos koren/izdanak. Rezultati merenja visine i suve mase su pokazali da je kao posledica DSK tretmana došlo do redukcije rastenja celih biljaka. Redukcija rastenja listova je bila posledica opadanja i broja i površine listova. Odnos koren/izdanak je bio sličan u oba tretmana i stoga nije potvrdio da je DSK tretman ubrzao rastenje korenovog sistema. Vrednosti potencijala vode DSK biljaka nisu se značajno razlikovale od onih koje su izmerene kod optimalno zalivanih biljaka. To je potvrdilo hipotezu da za redukciju rastenja kod DSK biljaka bili odgovorni signali poreklom iz korena a ne iz lista. U našim istraživanjima nije utvrđen efekat DSK tretmana na provodljivost stoma (transpiraciju) i fotosintezu, verovatno zbog toga što nije utvrđen efekat na pH apoplasta, koji bi sa svoje strane mogao da utiče na provodljivost stoma. Alternativno objašnjenje bi moglo da bude u neosetljivosti stominih ćelija ovog genotipa na hemijske signale korena. U poređenju sa efektom na vegetativne organe, DSK efekat na generativne organe je bio manji. Dobijeni rezultati su pokazali da je DSK tretman izazvao značajnu redukciju broja cvetnih grana, ali ne i broja plodova, njihove biomase i dijametra. Efikasnost korišćenja vode listova (WUE) nije se značajno razlikovala između tretmana, dok je WUE na nivou biljaka bila značajno veća kod DSK u odnosu na kontrolne biljke. DSK biljke su obrazovale c. 30% više biomase plodova po dm-3 vode u odnosu na kontrolne biljke. Ti rezultati ukazuju da je primenom DSK tehnike moguća redukcija količine vode za navodnjavanje, a da se pri tome ne redukuje prinos paradajza.The objective of presented master degree thesis was the effect of partial root drying (PRD) on tomato plants (Lycopersicon esculentum L.). Tomato plants were grown in commercial compost with the root system divided equally between two plastic pots. At the end of vegetative and during generative stage of development, half of the root system of PRD plants was exposed to drought, while the remainder of the root system was irrigated. After c.10 days (when soil water content was reduced to 30%) the treatment was reversed, allowing the previously well-watered side of the root system to dry down while fully irrigating the previously dry side. For measurements of the investigated parameters ten plants per treatment were selected. Plant height, leaf number and leaf area were determined every 5 days, as well as number of flower trusses per plants. Number and diameter of fruit were also monitored during the same time course. In the distal part of the youngest fully expanded leaf, measurements of leaf gas exchange (photosynthesis and transpiration-by infrared gas analyzer), leaf water potential (by pressure probe) and leaf apoplastic pH (by the centrifugation method) were done several times during the experimental period. Water-use efficiency (WUE) was calculated on a leaf level (as the ratio between photosynthetic rate and transpiration rate) and on a crop level (as a fruit dry weight per unit evapotranspired water). At the end of the experiments, measurements of shoot and root dry weight were done and root/shoot ratio was calculated. Obtained results of plants height and dry weight showed that as a consequence of PRD treatment the growth of whole plants was reduced. Leaf growth reduction was the result of both decrease of the number of leaves and leaf area. Root/shoot ratios were similar in both treatments and they didn’t confirm that PRD treatment enhanced root growth. Water potentials values of PRD plants did not differ significantly from those of well-watered plants. During the whole experimental period bulk values were c. -0.4 MPa. These results support the hypothesis that a root-sourced signal and not a leaf-sourced signal may be responsible for triggering growth reduction in these PRD plants. In our investigations we founded no effect of PRD on stomatal conductance (or transpiration) and photosynthesis probably because our results didn’t confirm any significant differences in apoplastic pH values that in turn might cause changes in stomatal conductance. An alternative explanation is that stomata of the tomato genotype we used were insensitive to the root-sourced chemical signal. Comparing to the PRD effect on vegetative parts, the effects on generative plants organ was smaller. Obtained results showed that PRD caused a significant reduction in fruit trusses but not in fruits numbers, their biomass and diameters. Leaf WUE was not different between treatments, although crop water-use efficiency was significantly higher in PRD than in control plants. PRD plants produced c.30% more fruit biomass per dm-3 water compared to control plants. It is clear that highly significant increases in crop WUE have been achieved. These results pointed out that with PRD technique is possible to reduce irrigation water without significant reduction effect on tomato yield.Slađana Popović (devojačko prezime