Seasonal stem radial growth and wood formation of trees have become research hotspots because of their significance for dendroclimatological and dendroecological studies. However, until recently, these studies concent...Seasonal stem radial growth and wood formation of trees have become research hotspots because of their significance for dendroclimatological and dendroecological studies. However, until recently, these studies concentrated on coniferous tree species in high-altitude and high-latitude regions,while detailed information on arid-zone riparian forests is scarce. The main focus of this study is to monitor the intra-annual dynamics of radial growth and tree ring formation in a deciduous species, Populus euphratica. In 2013, we combined the dendrometer and microcoring methods to study this species in the riparian forest of the Ejina Oasis, in arid northwestern China. Vessel enlargement began in early May, and the maximum rate of cell production occurred in early June. The cell division then ceased from early to mid-July. The dendrometer method failed to reliably detect the date of growth initiation and cessation, but succeeded to detect the time of maximum growth rate just like the microcoring method did. We found that weekly stem radial increment data described xylem growth more accurately than daily datasets. Based on correlation analysis among climatic and hydrologic variables, and weekly stem radial increment, weekly ring width increase dataset, the depth to groundwater was the main factor that limited tree ring growth. From a practical perspective, such studies of intra-annual wood formation can provide empirical guidance for seasonal water allocations within a river basin.展开更多
Soybean genotypes show diverse physiological responses to drought, but specific physiological traits that can be used to evaluate drought tolerance have not been identified. In the present study we investigated physio...Soybean genotypes show diverse physiological responses to drought, but specific physiological traits that can be used to evaluate drought tolerance have not been identified. In the present study we investigated physiological traits of soybean genotypes under progressive soil drying and rewetting, using a treatment mimicking field conditions.After a preliminary study with eight soybean genotypes, two drought-tolerant genotypes and one susceptible genotype were grown in the greenhouse and subjected to water restriction. Leaf expansion rate, gas exchange, water relation parameters, total chlorophyll(Chl), proline contents of leaves, and root xylem p H were monitored in a time course, and plant growth and root traits were measured at the end of the stress cycle. Drought-tolerant genotypes maintained higher leaf expansion rate, net photosynthetic rate(Pn), Chl content,instantaneous water use efficiency(WUEi), % relative water content(RWC), water potential(ψw), and turgor potential(ψp) during progressive soil drying and subsequent rewetting than the susceptible genotypes. By contrast, stomatal conductance(gs) and transpiration rate(Tr)of tolerant genotypes declined faster owing to dehydration and recovered more sharply after rehydration than the same parameters in susceptible ones. Water stress caused a significant increase in leaf proline level and root xylem sap p H of both genotypes but tolerant genotypes recovered to pre-stress levels more quickly after rehydration. Tolerant genotypes also produced longer roots with higher dry mass than susceptible genotypes. We conclude that rapid perception and adjustment in response to soil drying and rewetting as well as the maintenance of relatively high Pn, %RWC, and root growth constitute the mechanisms by which drought-tolerant soybean genotypes cope with water stress.展开更多
Genetic manipulation of cellulose biosynthesis in trees may provide novel insights into the growth and development of trees. To explore this possibility, the overexpression of an aspen secondary wall-associated cellul...Genetic manipulation of cellulose biosynthesis in trees may provide novel insights into the growth and development of trees. To explore this possibility, the overexpression of an aspen secondary wall-associated cellulose synthase （PtdCesAS） gene was attempted in transgenic aspen （Populus tremuloides L.） and unexpectedly resulted in silencing of the transgene as well as its endogenous counterparts. The main axis of the transgenic aspen plants quickly stopped growing, and weak branches adopted a weeping growth habit. Furthermore, transgenic plants initially developed smaller leaves and a less extensive root system. Secondary xylem （wood） of transgenic aspen plants contained as little as 10% cellulose normalized to dry weight compared to 41% cellulose typically found in normal aspen wood. This massive reduction in cellulose was accompanied by proportional increases in lignin （35%） and non-cellulosic polysaccharides （55%） compared to the 22% lignin and 36% non-cellulosic polysaccharides in control plants. The transgenic stems pro- duced typical collapsed or ＇irregular＇ xylem vessels that had altered secondary wall morphology and contained greatly reduced amounts of crystalline cellulose. These results demonstrate the fundamental role of secondary wall cellulose within the secondary xylem in maintaining the strength and structural integrity required to establish the vertical growth habit in trees.展开更多
基金supported by the National Key Research and Development Program of China(2016YFC0501001)National Natural Science Foundation of China(No.91125026,No.41471082)the STS project of the Chinese Academy of Sciences(KFJ-EW-STS-00502)
文摘Seasonal stem radial growth and wood formation of trees have become research hotspots because of their significance for dendroclimatological and dendroecological studies. However, until recently, these studies concentrated on coniferous tree species in high-altitude and high-latitude regions,while detailed information on arid-zone riparian forests is scarce. The main focus of this study is to monitor the intra-annual dynamics of radial growth and tree ring formation in a deciduous species, Populus euphratica. In 2013, we combined the dendrometer and microcoring methods to study this species in the riparian forest of the Ejina Oasis, in arid northwestern China. Vessel enlargement began in early May, and the maximum rate of cell production occurred in early June. The cell division then ceased from early to mid-July. The dendrometer method failed to reliably detect the date of growth initiation and cessation, but succeeded to detect the time of maximum growth rate just like the microcoring method did. We found that weekly stem radial increment data described xylem growth more accurately than daily datasets. Based on correlation analysis among climatic and hydrologic variables, and weekly stem radial increment, weekly ring width increase dataset, the depth to groundwater was the main factor that limited tree ring growth. From a practical perspective, such studies of intra-annual wood formation can provide empirical guidance for seasonal water allocations within a river basin.
基金supported by the Hong Kong RGC Collaborative Research Fund (CUHK3/CRF/ 11G) to Prof. H.-M. Lam. and J.H. Zhang
文摘Soybean genotypes show diverse physiological responses to drought, but specific physiological traits that can be used to evaluate drought tolerance have not been identified. In the present study we investigated physiological traits of soybean genotypes under progressive soil drying and rewetting, using a treatment mimicking field conditions.After a preliminary study with eight soybean genotypes, two drought-tolerant genotypes and one susceptible genotype were grown in the greenhouse and subjected to water restriction. Leaf expansion rate, gas exchange, water relation parameters, total chlorophyll(Chl), proline contents of leaves, and root xylem p H were monitored in a time course, and plant growth and root traits were measured at the end of the stress cycle. Drought-tolerant genotypes maintained higher leaf expansion rate, net photosynthetic rate(Pn), Chl content,instantaneous water use efficiency(WUEi), % relative water content(RWC), water potential(ψw), and turgor potential(ψp) during progressive soil drying and subsequent rewetting than the susceptible genotypes. By contrast, stomatal conductance(gs) and transpiration rate(Tr)of tolerant genotypes declined faster owing to dehydration and recovered more sharply after rehydration than the same parameters in susceptible ones. Water stress caused a significant increase in leaf proline level and root xylem sap p H of both genotypes but tolerant genotypes recovered to pre-stress levels more quickly after rehydration. Tolerant genotypes also produced longer roots with higher dry mass than susceptible genotypes. We conclude that rapid perception and adjustment in response to soil drying and rewetting as well as the maintenance of relatively high Pn, %RWC, and root growth constitute the mechanisms by which drought-tolerant soybean genotypes cope with water stress.
文摘Genetic manipulation of cellulose biosynthesis in trees may provide novel insights into the growth and development of trees. To explore this possibility, the overexpression of an aspen secondary wall-associated cellulose synthase （PtdCesAS） gene was attempted in transgenic aspen （Populus tremuloides L.） and unexpectedly resulted in silencing of the transgene as well as its endogenous counterparts. The main axis of the transgenic aspen plants quickly stopped growing, and weak branches adopted a weeping growth habit. Furthermore, transgenic plants initially developed smaller leaves and a less extensive root system. Secondary xylem （wood） of transgenic aspen plants contained as little as 10% cellulose normalized to dry weight compared to 41% cellulose typically found in normal aspen wood. This massive reduction in cellulose was accompanied by proportional increases in lignin （35%） and non-cellulosic polysaccharides （55%） compared to the 22% lignin and 36% non-cellulosic polysaccharides in control plants. The transgenic stems pro- duced typical collapsed or ＇irregular＇ xylem vessels that had altered secondary wall morphology and contained greatly reduced amounts of crystalline cellulose. These results demonstrate the fundamental role of secondary wall cellulose within the secondary xylem in maintaining the strength and structural integrity required to establish the vertical growth habit in trees.
