Ecophysiology Compensatory Mechanisms Of Caragana Korshinskii After Clipping

Sprouting plants often have characteristics that allow them to tolerate some levels of damage, such as grazing, cutting, frost and tramping, and they also have the ability to regrow for compensating the lost biomass, which is an important way to recover from different kinds of biotic and abiotic damage. Under the conditions, plants often appears negative, neutral or positive effect of compensation, among which the overcompensation plays an practical role in satisfying our needs. Plants can also respond to herbivory by increasing their defence levels. Caragana korshinskii is a long-lived shrub and commonly found in desert, semi-desert and Loess Plateau in northwestern China, where it plays an important role in soil and water conservation and desertification control, and its shoots are cut by local farmers to use as fuel energy or browsed by many sheep before grasses turn green. In this experiment, with the aboveground tissue of C. korshinskii being cut, we examined the plant's physiological and biological machanisms from the following three aspects, including: (1)hydraulic architecture and gas exchange parameters between the control and the resprouts during the different growing years from 1 to 7;(2)the relationship of plant hormone andα-amylase activity in current year after clipping(;3)the free amino acids'contents in different parts of C. korshinskii in the growing season, which could provide a theoretical basis for taking advantage of C. korshinskii reasonably and better. The main results were as follows:1. With the sprout tillers damaged and their aboveground tissues cut, the root/shoot ratio changed and the roots system would absorb water to supply the limited aboveground tissues, which made the water level in the resprouts improved. Hydraulic architecture and gas exchange parameters were tested to illustrate the changes. The control had higher internal resistance than the sprouts in translating water. In the 7 growing years, Ks and Kl of the sprout tillers appeared rising trend, while the wood density was not different obviously among groups. In terms to the gas exchange parameters, LWP,A and gs in the sprouts decreased year after year, and the superiority lasted 4 years. Afterwards, the result wouldn't keep the level balanced with the control but decreased continually. When the plants encountered the drought stress, the stoma conductance and intercellular CO₂ was probably regulated by Kl in order to prevent the water loss and contain the assimilation to CO₂. Besides, gs played a certain role in weakening the degree of decrease and recovery of the hydraulic conductivity.In addition, the biomass allocations of the sprouts changed among the different growing-year sprouts, with the hydraulic architecture and gas exchange improved after clipping. The sprouts absorbed more water and nutrient, and after 4 or 5 years later, the stem biomass reached 70% of the control. In the 6⁷ year-old sprouts, the biomass was similar to the control. During the 7 years, the water stress increasing, the biomass allocation in spine and leaf decreased and that in stem increased. At the same time, the leaf area lowered and LMA rised. In 1⁵ year-old sprout tillers, the N content was higher than the control, while the 7 year-old plant lower, the reason for this was related to the diminished leaf area.2. The initial change in current sprout tillers after the aboveground shoot removed was the plant hormone. When the aboveground tissues was lost, the apical dominance disappeared; in addition, the content of CKs increased dramatically, which made the IAA/CKs ratio decreased, therefore not only the cell division and lateral bud sprouting were benefited, but also GAs for promoting cell elongation was increased. The increased plant hormones induced the higherα-amylase activity, as made the starch stored in the root broken down largely and supplied raw materials for the rapid recovery of the aboveground shoots.3. In the growing season, the contents of free amino acids in roots, stems and leaves in current resprouts were compared with those in the controls at pod set and seed maturity, to investigate mechanisms underlying plant regrowth. The result showed that: between the resprouts and controls, the differences of the free amino acid content in leaves and roots were larger than that in stems. At the period of pod set, the contents of aspartate(ASP),threonine(THR),serine(SER),alanine(ALA),valine(VAL),leucine(LEU),tyrosine(TYR), histidine(HIS),arginine(ARG) in leaf, and that of ASP,SER,VAL,cystin(CYS) in root were 1.5 times more in resprouts than that in controls. At the seed maturity, the contents of ASP,THR,SER,glutamic(GLU),TYR,phenylalanine(PHE),ARG,cystine(CYS) in resprouts were dramatically higher than in controls, and among the above amino acids, the contents of ASP and ARG decreased markedly compared with that of pod set stage. Besides, ASP,SER,VAL,HIS and ARG in reprouts'root were were 1.5 times higher than that in controls, as exhibited the same tendency to the pod set period. Therefore, we could see that it was advantageous for the resprouts'compensatory growth and biomass that the contents of most free amino acids in leaves and roots of sprouts were higher than controls by degrees at each sampling time. Among the 17 free amino acids, not only did that the more relative content of ASP existed in all tissues of the sprouts provid effective condition for the formation of other essential amino acids such as lysine(LYS), but also ARG, as the pattern of storing N, played an important role in the N circulation and boosting cell division. In addition, proline(PRO), an essential ingredient for osmotic regulation, whose content were high in the plant of the experimental site, was effected obviously by the rainfall. Except PRO, the total content of the other 16 free amino acids in sprouts' leaves and roots were 2.7 and 1.96 times higher than the controls, respectively. In conclusion, after clipping, the contents of most free amino acids in sprouts were rich enough for regrowth, which may be one of the important mechanisms underlying regrowth following all shoot removal.