Study On Photosynthetic Characteristics Of Psidium Guajava

Psidium guajava belongs to Myricaceae , Psidium, also is called Bozi, Jishiguo. In this dissertation, the new varieties of 'Xinshiji' and 'Hongbaoshi', which are introduced from Taiwan, are selected as experimental material. In order to explore the photosynthesis pattern and reveal the mechanism of photosynthesis responding system, the effects of photosynthetic characteristics and environment on their photosynthesis are studied from the angles of ecophysiology and anatomical physiology; and the effect of photosynthetic characteristics on factors such as light, temperature and the concentration of CO₂ under natural circumstances are also studied. The results obtained are helpful to determine cultivation techniques such as deciding reasonable tree shape, the density of cultivation and reasonable loading on each tree, selecting optimal cultivation area. Main research results are mentioned as follows:(1)The optimal temperature for the photosynthesis of Psidium guajava rose with the temperature of environment (10³3℃), but at this range of temperature the difference between the biggest value of Pn and the smallest value of Pn could be more than 40%. The optimal temperature for the photosynthesis of Xinshiji and Hongbaoshi were 25±0.5³5±0.5℃ and 20±0.5³4±0.5℃, and for both of varieties the strength of photosynthesis were more than 40% of their Pn max value. High temperature (Hongbaoshi >34℃, Xinshiji >38℃) could inhibit the photosynthesis of leaves notably. High temperature plus drought could not only decrease Pn value to a greater extent but also changed the daily changing process of Pn..(2)The light compensation point for Xinshiji and Hongbaoshi were rather low: 23.57 μmol.m^-2.s^-1 and 22.15²4.41μmol.m^-2.s^-1 respectively. The light saturationpoint for Xinshiji and Hongbaoshi were 1000±21μmol.m^-2.s^-1 and 1500±21μmol.m^-2.s^-1 respectively. Increasing light intensity could inhibit the photosynthesis of leaves.(3)Within the CO₂ concentration of 50 400μmolmol^-1, two test varieties photosynthetic speed both showed linear raise followed the ascending concentration of CO₂. Compared with other fruits the guava CO₂ compensation point lower, about 11μmolmol^-1, but different variety had different concentration saturation point of CO₂, the variety Xinshiji was 600⁷00μmolmol^-1 and Hongbaoshi was 800 900μmolmol^-1. Under the concentration saturation point of CO₂, the Xinshiji and Hongbaoshi reached the biggest net photosynthetic speed were 23.1μmol co₂.m^-2.s^-1 and 28.8μmol co₂.m^-2.s^-1 respectively. This indicated that within the offering test concentration of CO2, the net photosynthetic speed of Hongbaoshi was higher than Xinshiji and the photosynthetic conduction and CO₂ assimilation of former were comparatively better.(4)When guava laminae developed maturation, also 35 45 day's leaf age phase(after leaf unfold 25-—35 day), the content of chlorophyll chl(a+b) in laminae were comparatively higher, the number of chloroplast in laminae's cell was comparatively great. In the laminae the development of granum was fine, stack piled up in order, all this were benefit the progression of photosynthesis, simultaneity the concentration of Pn raised rapidly and reached the most. In 75 day after leaf unfolded, the content of chlorophyll chl(a+b) in laminae descend, and Pn enter fast descend phase, and the CO2 stoma transmit degree decline greatly,stomatal limitation value increase: but the concentration of CO2 in cell interspace maintained comparative higher level. All this showed that photosynthesis at this time was restricted by non-stoma factor as well as the ability of CO2 assimilation in laminae cell.(5)The daytime change process of photosynthesis in cloudy sky was single apex curve, in sunshine day was double apex curve: in high temperature and drought weather, the photosynthesis and accumulation of photosynthetic production were main appeared before 15 o'clock, the difference of season changes process of photosynthesis in different weather were: guava growth fastigium was in the 4 month, the equal Pn reached the most: when the forenoon temperature comparative lower in the seven month, the Pn comparative higher, but follow the temperature ascending, the Pn descend rapidly afternoon: the Pn comparative lower in the first and ten month, especially the low temperature in the first month , the value of Pn was the lowest in all year, the main environment factor restricted photosynthesis were illumination intensity, temperature and humidity.