Influence Mechanism Of Environment Factors On The Growth And Development Of Submerged Macrophytes

In the ecosystem of shallow lake, submerged macrophytes play pivotal roles in the construction of healthy and stable fresh water system, whose restorative and decaying process was closely related to the environmental factors. The impact of environmental factors like illumination and water temperature on the growth and development of submerged macrophytes would be discussed, providing the evidence for the ecological restoration of water environment.This article would study the effect of the natural temperature on the birth, growth and propagation of Potamogeton cripus with its bud and seedling as objective by utilizing seasonal temperature change. Results revealed that the photosynthesis of the seedling would be inhibited at water temperature below 7℃, while increased greatly at water temperature above 9-10°C with gradual rising of F_v/F_m andΔF_v'/F_m' and the gain of exhausted energy of photochemical quenching and non photochemical quenching. The most appropriate breeding temperature was around 20℃tor Potamogeton cripus.When submerged macrophytes had grown up to or above water surface in spring and summer, more intense illumination and higher water temperature would be inhibitive even harmful to the development of P. cripus and Vallisneria asiatica L., but produce little effect on Myriophyllum spicatum and Cerruophyllurn demersum. At time when P. cripus reached the water surface at the end of spring, it was easy for the floated leave of P. cripus to produce photoinhibition (F_t,F_m' andΔF_v'/F_m' decreased markedly). Despite higher photosynthesis, photosynthetic structure PSII was easily harmed because of the limited dissipative capability to excessive energy, resulting in the rapid declination of the photosynthetic ability and the decaying of the leaves, which suggested that high temperature and strong illumination were the leading reasons for the fading and death of P. cripus in summer. The case was similar for V. asiatica L., while different for M. spicatum and C. demersum.Under weak illumination, the increase of plant height and leave width was not restrained in the condition of 4.9% of full illumination for V. asiatica L., instead of P. cripus. The content of each component of the chlorophyll in the leaves was decreased notably below 0.56% of full illumination, indicating the sharply decreased photosynthetic capability and the inhibition of growth.Water with different turbidities was respectively prepared and then planted with seedlings of P. cripus, V. asiatica and Hydrilla verticillata to investigate the influence of underwater illumination on the growth and development of paint. From results, it was showed that the development was completely suppressed in muddy and turbid water at water turbidities above 120NTU for P. cripus, above 60NTU for V. asiatica and above 90NTU for H. verticillata. By applying the mature macrophytes of V. spiralis, H. verticillata, P. cripus, M. spicatum and C. demersum in the muddy and turbid water with turbidities of 30, 60 and 90NTU respectively (water depth below 1.5m), it was proved that with the gradual development and heightening of submerged macrophytes, the power of the underwater illumination on the plant was minished; with the increase of water turbidity, the photosynthetic ability of the leaves of mature V. spirali inclined to rise, relative to the diminishing of photoinhibition with the reduction of receipted inllumination, consequently relieving the aging and damage of the leaves. Howere, it was converse for the leaves of M. spicatum and C. demersum.Sand attachment was the cause of the increasing content of chla and chlb by enhancing the resorption and transmission of light energy to satisfy the fundamental needs for photosynthetic function, which was opposite for P. cripus and H. verticillata with the decrease of chla and chlb content of leaves and the photosynthetic capability. As for the three submerged macrophytes, the order of resistant capability to sand attachment followed: H. verticillata < P. cripus < V. spiralis.Besides, the impact of H. reticulatum attchment on the photosynthetic fluorescent characteristic was also investigated, revealing that F_v/F_m,ΔF_v'/F_m',qP,ETR and chlorophyl content were heavily reduced when attached by multiple H. reticulatum, contrary to qN, which suggested the observable declination of the photosynthetic ability.Based on the result of this research, to cultivate and restore submerged macrophytes in muddy and turbid water, it was preferable to choose seeding P. cripus bud and seedling in winter and spring for the shallower water line and relatively higher underwater illumination, while selecting submerged macrophytes like H. verticillata seedling, mature plants of V. spiralis, M. spicatum and C. demersum in summer and autumn for the deeper water level. Indeed, for there existed remarkable temporal and spatial difference for the adaptation of submerged macrophytes to surroundings at different developmental stages, in complicated natural environment, this article only supplied certain laboratory support for the design of complex and multi-systemic ecological system in the deteriorated environmental conditions.