Study On Cyclobalanopisis Glauca Root Vertical Growth And Its Physiecology Under Simulated Karst Environment

Karst region is considered as one of the most fragile and ecological hazardous environment in China. Karst is naturally double-layer structures, covering thin soil on the surface. The ground is rugged and porous, rain water commonly leakages into blind valleys and underground rivers, causing surface soil unusually short of water, leading to frequent karst seasonal geological drought. Seasonal drought is the the main features in karst ecosystem. However, in the south china karst, particular the bare rocks karst area, plants formed characteristics of rock and xeric in the long-term evolution of karst formation, its dominant plants are commonly rich roots. Plants can grow good in the upper part of the rocky Mountains even it is less soil on it, forming karst forest. We simulate double-layer karst structure basing on karst environment, and transplanted C. glauca on it. We controled the soil water using different treatments, and observe soil water dynamic and the root growth. We monitoring the physiological indicators (diurnal course of photosynthesis, photosynthesis light response curve, water potential in different seasons, related parameters of PV curves) and test the biochemical substances, hence to understand the water adaptation mechanisms, the photosynthetic productivity, the water sources and water use pattern for the plant under karst water condition, and to find theory and methodology for karst ecologyical studies, provid a theory for vegetation restoration and ecological rehabilitation in karst region.The main results as follows:1 Water in below-Rock layer plays an important role in driving C. glauca root penetration into rocky fissureIn studying the C. glauca root growth under simulate karst double layer structure we found that wheater the root reach to rock-below depends on wheather there is water in the rock-below. In the treatment groupⅡ, which there is no water in the rock-below, there is not C. glauca roots penetrating through the rock fissure and reach the water in four soil water treatments, indicating no mater how much soil water content is dry water in rock–below would not drive the root penetrate through the rock fissue; However, in the groupⅠ, which there is water in the rock-below, the roots penetrated through the rock fissure and reached to the ground water in all four soil water treatments. The result suggest that the ground water the rock-below(epkarst water) plays an important role in driving the C. glauca root penetration.2 Physiological and biochemical adaptation of C. glauca under different conditionsSimulation results shows that temporary soil drought but with water rich in the rock-below can drive the root grow though porous rocks and rich the water, thus, the root can use the ground water to alleviate water stress. Therefore, it is a key factor that karst plant root can grow through rock fissure to epkarst water in alleviating temporary drought in karst region. Our experiment shows that: after a large number of root reach the epkarst, the soil water contents doesn't effect on leaf Pro and dissoluble glycogen of C. glauca, which maintained at a very low level. However, with the exception of soil water saturated treatment, leaf Pro and dissoluble glycogen of C. glauca in group II treatments which root grow simply in soil is significantly higher than that in group I, indicating the epkarst water's effect on allivation the soil water shortage. The MDA is higher in conditions with epkarst water, by comparing the evidence that MDA increases along with soil water increase, we speculate that the plant probably suffered by hypoxia stress when the root sink in the epkarst water. But a suitable soil water content of soil could moderate this hypoxia stress. This is probably a mechanism for plant to adapt to karst environment of drought - flood regime in karst terrain.3 The influence epikarst water on C. glauca leaf water contentThe features of C. glauca leaf RWC andψin different treatment shows that leaf retain higher relative water content in condition with the roots reach to epkarst groundwater than without ones, and the diurnal course of RWC andψindicate the plant has ability to resist soil drought by the roots uptaking water from epkarst to maintain high leaf water content, shows that it is very important for the root reach the epkarst water table, as it can add the water for leaves transpiration effective when soil is short of water. This suggests that the roots active in water uptake, the roots of C. glauca could adapt to the epkarst water hypoxia stress. As a result, the plant can grow very well in both the soil water deficiency and epkarst water hypoxia stress .4 The C. glauca water potential and characteristic parameter of PV curves in different simulate habitats.The diurnal course of C. glauca water potential shows high-low-high pattern from day to night. The water potential of leaf decreased in daytime due to transpiration, then begin to rise in the evening. The water potential can be fully restored at night in the treatment of soil water content above 70%, even though there is no water in the rock-below. However, in the treatment of soil water content below 70% without water in the rock-below, the leaf water potential may be insufficiently restored at night. However, the water potential can be fully restored at night no mater how dry of soil but with water in the rock-below. Drought exercise could increase ratio of bound water in the leaf of C. glauca. The results of PV curve show that with the decrease of soil water content, the leaf capacity of water holding enhanced, the saturated osmotic potential(?ssat) and extracellular osmotic potential(ψtlp) decreased, which the difference between absolute value of ?ssat andψtlp increased, suggesting that with the aggravation of water stress, the drought tolerance of C. glauca increased.This is the evidence for plant adaptation to the environment. While in the treatment with water in epkarst, with the decrease of soil water content, the extracellular osmotic potential decrease, suggesting that soil drought exercise could increase the drought tolerance, even the root could absorb the water from the epkarst water.5 The diffferent karst surface structure effects on C.glauca photosynthetic productivityThe leaf net photosynthetic rate of change in groupⅠ(epkarst water treatment) in summer show that regardless variation of soil moisture, the leaf net photosynthetic rate of diurnal course photosynthetic rates are two-peaks and higher than group II(exception of saturated soil water treatment), implicating that a mass roots reaching to epkarst water can alleviate the water stress, thus improve the net photosynthetic rate of C. glauca effectively,; the plants didn't reduce the accumulation of organic matter when soil is drought. The correlation between Gs and Tr in four different treaments is significant, showing Gs can regulate the Tr effectively. However, it is different during the winter, the photosynthesis - light response curves of C. glauca showed the photosynthetic parameters are very similar between groupⅠand the GroupⅡ, the Pnmax, AQY, LSP, LCP is closely related to soil water content in both group. the result suggest that because low temperature in winter, root of C. glauca in the epkarst water is dormancy and did not actively to obtain water from epkarst water, but the root in soil recover from low temperature, as in the sunny monitoring day, high air temperature in the greenhouse resulted in much higher soil temperature than rock water temperature, thus the photosynthesis is affected by soil water deficiency. Therefore plant might be photosynthesis suffered by soil water deficiency during winter.eventhough there is rich epkarst water.6 The pattern of C.glauca water use in karst conditions. The water in epkarst can drive a lot of root distribution as long as reaching to epkarst water table. By the soil moisture monitoring in the fixed point, we found that, in the summer, the soil water decreasing rate is much quicker in group II than group I. After a large number of roots reach to the epkarst water, soil water tended to be stable at 19%. But without roots reach to the epkarst water, the soil moisture content continue to drop down and be stable 14.5%( the plants begin to wither). This give the evidence that C.glauca can use the groundwater effectively. karst deep-rooted plants with the features of using epkarst water, enable them to adapt to the soil temporary drought in karst environment, which play an important role in alleviate its water competition with seedlings and shallow-root plants during in dry period; it might be a "key species" in maintaining the diversity in karst forest ecosystem.In winter, when the soil water is deficient or semi-deficient eventhouth root reach to epkarst water table, plant leaf water potential, Pn still decline significantly, simply resembling to that without root reaching to epkarst water table. This suggests that low temperature affect root activity in absorbing epkarst water, thus can not alleviate drought stress; the water source of C.glauca mainly comprise the soil water.This is probably the main reason that photosynthesis was still limited even there are enough root reach to epkarst water during winter.7 Hydraulic lift might be evidence by karst plant rootBy fixed point soil moisture monitoring, we finded that, in the treatment with a mass root reaching to water of rock-below, the soil water content change in a regular fluctuation pattern from day to night at the stable low water line. The soil moisture content began to slightly increase after 15:00 and continue till 20:00. The soil water decline again soon after sunrise(8:00) in the next day. The soil moisture content does't changed before 15:00. This trends is negative relation to temperature change. This evidence did not occurs in the treatment without root reach to epkarst water, which soil water continue drop down. The result suggests that there might be hydraulic phenomenon by karst plant root which worth extension studies.