Abstract: This research investigated the problem of warm season Zoysia tenuifolia turf degradation caused by invading Imperata koenigii in the subtropical region of China. Pots 30 cm in diameter were prepared containing the two species in a replacement series; 9∶1, 8∶2, 7∶3, 6∶4, 5∶5 Z. tenuifolia∶I. koenigii. The Z. tenuifolia was planted first and after it had formed 2-3 true leaves, the rhizomes of I. koenigii were inserted into Z. tenuifolia turf. After 40 days of normal culture, 3 replicate pots of each of the replacement series mixtures were placed into each of three controlled temperature chambers at 40, 42 and 44 ℃, for 2 hours each day over a period of 30 days, to provide a ‘high temperature shock’. Various parameters, including underground and aboveground relative yield, total relative yield, attack power and competition balance index, plant height, tiller number, leaf area, chlorophyll and physiological active substance, among others, were were determined on the 71st day. Subsequently, ‘resilience’ data such as photo-assimilate levels, regeneration capacity and resistance physiology were also collected. The aim was to study the effect of the high temperature shock on actual and potential competitiveness of Z. tenuifolia when challenged by I. koenigii invasion. It was found that: 1) High temperature shock was detrimental to Z. tenuifolia, and resulted in decline in the aboveground: below-ground relative yield, and a decline in competitiveness of Z. tenuifolia against I. koenigii. The high temperature shock increased the antagonism between the aerial parts of the two species. Invasion by I. koenigii had a greater effect on relative yield of Z. tenuifolia than high temperature shock. The synergistic effect of greater than 30% I. koenigii invasion and high temperature shock, sharply decreased the aboveground relative yield of Z. tenuifolia compared with underground yield. 2) Aboveground and underground attack force index and competition balance index for Z. tenuifolia were all at their maximum with a 42 ℃ heat shock. High temperature shock over 42 ℃ significantly reduced the attack power and competition balance index of Z. tenuifolia, and increased same indexes for I. koenigii. Only at 40 and 42 ℃, and with 20% I. koenigii invasion or less, was the competitiveness of Z. tenuifolia superior. At 44 ℃ or with 30% or greater presence of I. koenigii, the aboveground and underground attack power of I. koenigii were superior to Z. tenuifolia, as reflected by invasion and expansion of I. koenigii in the artificial turves. 3) High temperature shock increased height and tiller number of I. koenigii, and high temperature over 42 ℃ limited tiller number of Z. tenuifolia. The invasion of 30% I. koenigii or more, inhibited tillering but promoted height of Z. tenuifolia (P<0.05). High temperature shock also reduced the number of leaves and leaf area of Z. tenuifolia and increased these two traits in I. koenigii. Invasion by 10% or more I. koenigii reduced leaf area of Z. tenuifolia, and invasion by 30% or more I. koenigii reduced leaf thickness and leaf number of Z. tenuifolia. 4) High temperature shock and invasion of I. koenigii significantly affected the content of chlorophyll, superoxide dismutase, peroxidase, catalase, malondialdehyde and proline of Z. tenuifolia, indicating that the physiological response of Z. tenuifolia was more susceptible to high temperature shock than that of I. koenigii. 5) The influence of high temperature shock on morphology, physiology, relative yield and attack power of Z. tenuifolia was greater than the influence on the same indexes of I. koenigii. Invasion by I. koenigii caused significant damage to Z. tenuifolia turf. The synergistic effect of high temperature and I. koenigii invasion reduced the actual competitiveness of Z. tenuifolia and limited its potential competitiveness. Therefore, the basic requirement for conservating Z. tenuifolia turf is to control the proportion of invading I. koenigii to less than 20% in summer.

Key words: Zoysia tenuifolia, Imperata koenigii, attack power, competitiveness, high temperature shock