Growth And Physiological Responses Of Salix To Cadmium Stress

As the most common non-degradable pollutants, heavy metal is harmful to organisms,which have caused an increasing concern around the world. Cadmium is a common, highlytoxic heavy metal. There is a cause that cadimium is easily absorbed and accumulated by plants,and thus it is easy to suppress the physiological processes in plants. It leads to inhibit theplants' normal growth and development, even to death. Willow(Salix spp.) is a kind ofcadmium high-accumulation-type fast-growing tree, which has great potential forenvironmental cadmium pollution repair. There is academic significance to study physiologicalchanges in Salix under cadimium stress. Main results obtained are as following:1. Studied on the effect of Cd²⁺solution on morphology in root of Salix matsudana, Salixintegra, Salix leucopithecia under sand culture condition. The results showed that, under Cd²⁺stress for6days,9days, Salix matsudana root length was significantly lower than CK; treated9days, Salix integra root length was significantly lower than CK; treated9days, Salixleucopithecia root length was lower than CK without significantly difference. This showed thatSalix leucopithecia had stronger cadmium tolerance than Salix matsudana and Salix integraunder Cd²⁺stress.Under Cd²⁺stress for6days,9days, Salix matsudana root surface area, volume had nosignificant difference on CK; but roots (diameter≤0.5mm) which take leading role inabsorption, their length, surface area, volum were significantly lower than CK. It was probablycaused by their strong absorption, which passive absorpted and enriched more cadmium. UnderCd²⁺stress for3days,6days, in Salix integra, there was no significant difference betweentreatment and CK in root length, surface area, average diameter, root tip number androots(diameter≤0.5mm) length, surface area, volum; treated9days, there were significantdiffernces. This confirmed that the Cd²⁺stress strongly inhibited the growth of apical cell,resulted that root tip number was significantly lower than CK. 2. Studied on the cadmium accumulation characteristics and effect on the distribution ofmineral elements in Salix matsudana, Salix integra, Salix leucopithecia under highconcentration of Cd²⁺solution treatment with sand culture. The results showed that, with theprolonged Cd²⁺stress, concentration of cadmium in the three kind of willow roots, stems,leaves gradually increased. Treated9days under Cd²⁺stress, the cadmium concentrations inshoots of the three kind of willow were more than100mg/kg respectively; the shoots and rootsbiomass of the three kind of willow were not significantly affected; the three kind of willowhad strong resistance to cadmium, with the potential for cadmium phytoremediation plant.Under Cd²⁺stress, the concentration of cadmium in roots of the three kind of willow weremuch higher than stems and leaves. cadmium in plants was limitedly transported to the stems,leaves to reduce the poisoning of cadmium in shoots. Under Cd²⁺stress, the potassiumconcentration was significantly decreased in roots of the three kind of willow, and treated9days under Cd²⁺stress, potassium concentration in stems and leaves were lower than3days.Capacities of absorb potassium and transport potassium to aboveground in root of the threekind of willow were suppressed by Cd²⁺stress.Treated9days under Cd²⁺stress, the concentration of cadmium in root, stem, leaf of Salixmatsudana, increased3.04,2.36,21.56times respectively than treated3days; ability ofcadmium accumulation in shoot of Salix matsudana continued to increase with prolongedtreatment. Treated3,6days under Cd²⁺stress, the cadmium content in shoot of Salixmatsudana was more than root; treated9days, capacity of transport cadmium was suppressed,it resulted that cadium content in root was more than shoot. Under Cd²⁺stress, Salix matsudanaroot accelerated the absorption of calcium, and transported to shoot. Treated9days, theconcentration of calcium in stem of Salix matsudana significantly increased21.73%,23.66%than3days,6days respectively. The capacity of transport magnesium of Salix matsudana stem,leaf was suppressed by Cd²⁺stress. Treated9days, the concentration of potassium in Salixmatsudana root significantly decreased than3,6days by51.98%,66.79%respectively. UnderCd²⁺stress, the distribution ratio of magnesium in Salix matsudana root significantly increased, compared with treated3,6days, treated9days significantly increased80.22%,77.57%respectively.Under Cd²⁺stress, in the three kind of willow, the proportions of distribution of themineral elements were not significantly affect by Cd²⁺stress except that the proportions ofdistribution of magnesium and cadmium in root of Salix matsudana were significantlypositively correlated, and the proportions of distribution of potassium and cadmium in stem ofSalix integra were significantly positively correlated. Salix matsudana, Salix integra, Salixleucopithecia had strong abilities to regulate the distribution of mineral elements.3. The efects of Cd²⁺stress on rapid light-response curves of photochemical andnon-photochemical chlorophyll fluorescence quenching parameters including darkfluorescence yield (Fo), maximal fluorescence yield (Fm), maximal PSâ…¡ quantum yield(Fv/Fm), and latent PSâ…¡ quantum yield (Fv/Fo) of Salix leucopithecia were investigatedunder different concentrations of Cd²⁺solutions (0,50,100,200,400mg/L) byMini-Imaging-PAM Chlorophyll Fluorometer.The results showed that Fo and Fm present trend of first increased and then decreased, andthe two parameters reached the maximum when Salix leucopithecia were subjected to200mg/L Cd²⁺solution after four weeks. The Fv/Fm declined significantly under cadmium-bearingsolution, but it was higher in the same Cd²⁺solution after four weeks than after two weeks. TheFv/Fm rebounded slightly in200mg/L Cd²⁺condition after two weeks and then dropped tothe minimum in the same condition after four weeks. Fv/Fo was also inhibited significantly byCd²⁺stress, and showed the similar trend with the changes of Fv/Fm.The rapid light-response curves of chlorophyll fluorescence parameters were alsomeasured at various light intensities (0,20,60,100,300,500,600,800,1000, and1200μmol·m-2·s-1). The effective PSâ…¡ quantum yield(Y(â…¡)) and coefficient of photochemicalquenching(qP) decreased with the increase of light intensity. The Y(â…¡) and qP declinedsignificantly subjected to high concentration of Cd²⁺solution compared with low concentrationunder the same light intensity. The parameters of quantum yield of regulated energy dissipation(Y(NPQ)), coefficient of nonphotochemical quenching (qN), and electron transportrate (ETR) increased with elevation of light intensity. The Y(NPQ), qN, and ETR increasedsharply subjected to high concentration of Cd²⁺solution compared with low concentrationunder the same light condition. Quantum yield of non-regulated energy dissipation(Y(NO))kept a lower level, although Y(NO) increased slightly with the aggrandizement of light intensity.The results indicate that Salix leucopithecia has strong tolerance to Cd²⁺stress by irreversibleinactivation of PSâ…¡reaction centers. However, under high concentration of Cd²⁺solution forprolonged stress, PSâ…¡reaction centers were closed or irreversible inactivated with showing thephenomenon of photoinhibition.Therefore, Salix matsudana, Salix integra, Salix leucopithecia have strong tolerance tohigh concentration Cd²⁺stress. They can be used for phytoremediation of severe cadmiumpolluted area, and they are good material for breeding of willow varieties for heavy metalphytoremediation.4. Using classification statistical function and Fisher discriminate function, analyzed7indexes (leaf length, leaf width, distance from the widest to the tip, petiole length, axillary budLength, leaf density, phyllotaxis ratio) of9species of Salix (Salix gracilistyla, Salix babylonica,Salix matsudana, Salix viminalis, Salix integra, Salix psammophila, Salix JiangsuensisCL.'172', Salix Jiangsuensis CL.'799', Salix babylonica×Salix fragilis). It resulted thediscriminate function equation of the9species of Salix and constructed identification model,then put morphological indexes data of the9species of Salix into the correspondingidentification model to test its discriminate results. The results indicated that precision of the9species of Salix recognition was higher than95%.