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Ontogeny, root-zone temperature and growth irradiance effect on temperate and subtropical vegetable crops grown in the tropics
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Type
Thesis
Author
Qin, Lin
Supervisor
He, Jie
Lee, Sing Kong
Abstract
Lactuca sativa L. (CV. Baby butterhead) and Brassica chinensis L. (CV. Nai Bai) are respectively temperate and subtropical plants used in the present study. To optimize growth conditions in the tropics, aerial parts of the plants were maintained at hot fluctuating ambient (A) temperature (ranging from 22°C to 4I0C) while their roots were exposed to three different root zone temperatures (RZTs). All plants were exposed to three different growth irradiances. Productivities of shoot and root and maximum photosynthetic rate for plant grown at cool-RZT (C-RZT) under 100% of prevailing solar radiation were higher than those grown under 60% and 30% of prevailing solar radiation. The optimum growth conditions are 20°C-RZT and 25°C-RZT respectively for Baby butterhead lettuce and Nai Bai under 100% of prevailing solar. Response of plants to RZT depends on both species and growth stage. Total number of leaves, leaf area; fresh and dry weights of shoot were linear correlated with the duration plants spent at C-RZT Both species grown at A-RZT at early state and then were transferred to C-RZT in the later growth stage (A-C-RZT) achieved similar high shoot productivity with that of plants maintained at C-RZT for whole life cycle. However, both species grown at C-ET during the early stage but transferred to A-RZT at late growth stage (C-A-RZT) had much lower productivity compared to those plants grown at C-RZT for whole life cycle. These results confirm that RZ cooling is critical for optimal growth during the late growth stage for both species. Decreases of total root length, surface area and number of root tips, occurred in C+A-RZT plants of both species. Increase of average root diameter was observed in C-A-RZT Baby butterhead while this phenomenon was absent in Nai Bai. However, development of root system was significantly promoted in A-C-RZT plants.
Supraoptimum A- RZT caused both stomata1 (decrease of Ψshoot, leaf water content, a. maximum photosynthetic O2 evolution rate) and non-stomata1 limitations of photosynthesis (decreases of chlorophyll content; Fv/Fm ratio, maximum Rubisco activity, leaf total soluble and Rubisco protein contents) in both species. Lon, 0 term A-RZT reduced leaf soluble protein: NO3- and total reduced N concentrations of both roots and leaves in both species. In Nai Bai, A-RZT reduced the maximum nitrate reductase activities (NRA) in mature leaves and roots. However, for Raby butterhead lettuce, A-RZT caused a decrease in leaf NRA. but an increase in root NRA. Total carbohydrate concentrations in leaves and roots of both species increased at A-RZT. In Nai Bai, an increase of leaf total sugar concentration caused by A-RZT was contributed by the increases of glucose. fructose and starch; while in roots, glucose and fructose were the major components of increased total sugar concentration. In A-RZT Baby butterhead lettuce, an increase of leaf total sugar concentration resulted from the increases of hexose and sucrose. However, higher root total sugar concentration of A-FUT Baby butterhead lettuce was due to higher hexose concentration. It was clear that A-RZT resulted in decreases maximum sucrose phosphate synthase (SPS) activities and SPS activation states in leaves of Baby butterhead lettuce while these two parameters in leaves of A-RZT Nai Bai did not change significantly as compared with those of C-RZT plants. Transferring plants from C-RZT to A-RZT mimicked the negative effects caused by A-RZT stated above. The earlier the plants were transferred from C-RZT to A-RZT, the more depressed effects were observed even though the plants spent the same number of day at A-RZT. However, transfer of plants from P,-RZT to C-RZT may alleviate the above negative effects caused by A-FZT and the extent of recovery depends on the starting time of the RZT transfer. The earlier plants were transferred from A-RZT to C-RZ1; the faster the recoveries. High temperature (38°C) retarded root elongation of both species, while stimulated root radial expansion of Raby bulterhead lettuce. Results of the present study with ethylene biosynthesis promoter 1 -aminocyclopropane-I-carboxylic acid (ACC) or inhibitor aminooxl-actic acid (AO.L\)!an~inoisobutyric acid (AIB) suggest that ethylene may be involved in the induction of root thickening under hot A-RZT conditions in greenhouse, especially for Baby butterhead lettuce. A-RZT induced ethylene synthesis might also be involved in the regulation of stomata1 and non-stomata1 limitations of photosynthesis caused by A-lCT in both species.
Supraoptimum A- RZT caused both stomata1 (decrease of Ψshoot, leaf water content, a. maximum photosynthetic O2 evolution rate) and non-stomata1 limitations of photosynthesis (decreases of chlorophyll content; Fv/Fm ratio, maximum Rubisco activity, leaf total soluble and Rubisco protein contents) in both species. Lon, 0 term A-RZT reduced leaf soluble protein: NO3- and total reduced N concentrations of both roots and leaves in both species. In Nai Bai, A-RZT reduced the maximum nitrate reductase activities (NRA) in mature leaves and roots. However, for Raby butterhead lettuce, A-RZT caused a decrease in leaf NRA. but an increase in root NRA. Total carbohydrate concentrations in leaves and roots of both species increased at A-RZT. In Nai Bai, an increase of leaf total sugar concentration caused by A-RZT was contributed by the increases of glucose. fructose and starch; while in roots, glucose and fructose were the major components of increased total sugar concentration. In A-RZT Baby butterhead lettuce, an increase of leaf total sugar concentration resulted from the increases of hexose and sucrose. However, higher root total sugar concentration of A-FUT Baby butterhead lettuce was due to higher hexose concentration. It was clear that A-RZT resulted in decreases maximum sucrose phosphate synthase (SPS) activities and SPS activation states in leaves of Baby butterhead lettuce while these two parameters in leaves of A-RZT Nai Bai did not change significantly as compared with those of C-RZT plants. Transferring plants from C-RZT to A-RZT mimicked the negative effects caused by A-RZT stated above. The earlier the plants were transferred from C-RZT to A-RZT, the more depressed effects were observed even though the plants spent the same number of day at A-RZT. However, transfer of plants from P,-RZT to C-RZT may alleviate the above negative effects caused by A-FZT and the extent of recovery depends on the starting time of the RZT transfer. The earlier plants were transferred from A-RZT to C-RZ1; the faster the recoveries. High temperature (38°C) retarded root elongation of both species, while stimulated root radial expansion of Raby bulterhead lettuce. Results of the present study with ethylene biosynthesis promoter 1 -aminocyclopropane-I-carboxylic acid (ACC) or inhibitor aminooxl-actic acid (AO.L\)!an~inoisobutyric acid (AIB) suggest that ethylene may be involved in the induction of root thickening under hot A-RZT conditions in greenhouse, especially for Baby butterhead lettuce. A-RZT induced ethylene synthesis might also be involved in the regulation of stomata1 and non-stomata1 limitations of photosynthesis caused by A-lCT in both species.
Date Issued
2004
Call Number
QK755 Qin
Date Submitted
2004