| Root system is an important part of the trees,which has important physiological and ecological functions.Fine root morphology and biomass are important basic information about knowing root branch law and predicting growth, death, and the turnover process of root of forest ecosystem underground.In addition, Fine root senescence and speediskey to studying on ontogenesis, longevity and turnover offine root, which has implications for the growth and development of plants,the productivity of forest stand andforest ecological system of material and energy flow.Robinia pseudoacacia plantation in maliantan forest farm of Yongshou country of Shaanxi province was selected in this paper,the dynamic change of the fine root morphology(diameter, root length, specific root length, volume and biomass), physiological and biochemical indexes(root vitality, the content of soluble sugar and soluble protein, membrane permeability) and nutrient elements(C、N、P、C/N、N/P) were determined in different phenological phase(leaf shoots period,early leaf extension stage,the middle of leaf expansion stage,leaf extension stage,the vigorous growth period, the early stage of the fallen leaves), which studies and analyzed the difference about fine root morphology and physiological and biochemical in different root sequence(level 1-5) and phenological phase.1.Robinia pseudoacacia root morphological indexes: with the increase of root orders, fine root diameter, root length, biomass(except for volume)were significantly increased(P< 0.05), but specific root length was significantly reduced(P> 0.05).Along with the passage of the phenological phase,fine root diameter was increased in a fluctuating tendency,and 1~3 roots lengthwasdecreased gradually.In leaf bud stage, specific root length was maximum, but it was minimum in leaf expansion medium.The volume of root was increased gradually, which significantly changed in the fifth order roots. Biomass of fine root appeared two peak values in the whole growing season.2.With the increase of fine root orders, root vigor was decreased(except the sprout leaves premature), and the content of soluble protein showed two trends.Generally speaking, the content of soluble protein was increased, soluble sugar content and cell membrane penetration had no obvious variety regulation.With phenological period goes on,the root vigor presented a rule of fluctuation decreases(except for the 1 level of root vigor), the soluble sugarcontent of fine roots decreased with the change of the growing season, which had the maximum value in leaf bud or initial stage of leaf expansion and theminimum valueappeared in the exuberant growth periodorthe early stage of the fallen leaves.The soluble sugar content changed in the opposite trend simultaneously in leaf and root, which had the maximum value in the early stage of the fallen leaves. The change of soluble protein content of fine roots was inverted "W" type during the whole growth season, whichwere two peaks(leaf stage and whole leaf stage).The soluble protein content of leaves was decreased gradually with seasonal changes,and fine root membrane permeability was first increased and then decreased, which had the maximum value in the vigorous growth period.3. With the increase of root orders, the total carbon content of Robinia pseudoacacia root showed an increasing trend, but the total nitrogen content of fine roots had no obviousvariety regulation, the total phosphoruscontent was gradually(expect for the vigorous growth period).Along with the passage of the phenological phase, the total carbon content of fine roots was inconsistent, including wherein the1 and 2levelsof fine roots was maximum value in full-leaf stage, and the total carbon content presented "first decreases, then increases and finally decreases again" in 3 to 5 leves fine roots. The total carbon content of leaves had the maximum value in the leaf bud stage, and the minimum value in the early stage of the fallen leaves. The total nitrogen content of fine root was decreasedfirst then increasedthroughout the whole phenology, which had the minimum value in the middle of leaf extension stage and had maximum value in the early stage of the fallen leaves.The maximum totalnitrogen content of leaves appeared in the Leaf full expansion period. The same phenophase of total nitrogen content in leaves was higher than that of root. The total phosphorus content of fine roots showed the trend of first increased and then decreased with the phenological period,which reached the maximum in theexuberant growth period, but the total phosphorus content of leaves decreased in a fluctuant way.4.With the increase of root order, C / N appeared two phenomena:(1) it was gradually increased trend(leaf bud, leaf expansion period, leaf expansion mid),(2) it was the basic stability of the in a range that was 11.286~20.242.In front of the four stages, N / P wasincreased ina fluctuating tendency. Along with the passage of the phenological phase, C/N of fine roots showed increased first and then decreased, which had the maximum value in the Leaf expansion medium and had the minimum in the early stage of the fallen leaves(except root level 2), but the variation in leafof C/N content showed N shape. The ratio of nitrogen and phosphorus showed “W” typeof fine root,which has been increased in the blade.In aword, Robinia pseudoacacia root morphology(fine root diameter, root length, specific root length, volume, biomass)was not only closely related to the sequence of fine roots level,and changed along with the growing season. The seasonal change trend of physiological indexes(the content of soluble protein and sugar) and nutrient elements(such as the content of total carbon, nitrogen and phosphorus) were not completely consistent in roots and leaves of Robinia pseudoacacia. Therefore,the accurate evaluation ofRobinia pseudoacacia plantation of nutrient cycling and energyflow is necessary to considerthe role of fine root orders and the seasonal variation offine root nutrientsand physiological metabolism. |
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