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1.
Global patterns of root turnover for terrestrial ecosystems   总被引:42,自引:1,他引:42  
Root turnover is a critical component of ecosystem nutrient dynamics and carbon sequestration and is also an important sink for plant primary productivity. We tested global controls on root turnover across climatic gradients and for plant functional groups by using a database of 190 published studies. Root turnover rates increased exponentially with mean annual temperature for fine roots of grasslands ( r 2 = 0.48) and forests ( r 2 = 0.17) and for total root biomass in shrublands ( r 2 = 0.55). On the basis of the best-fit exponential model, the Q 10 for root turnover was 1.4 for forest small diameter roots (5 mm or less), 1.6 for grassland fine roots, and 1.9 for shrublands. Surprisingly, after accounting for temperature, there was no such global relationship between precipitation and root turnover. The slowest average turnover rates were observed for entire tree root systems (10% annually), followed by 34% for shrubland total roots, 53% for grassland fine roots, 55% for wetland fine roots, and 56% for forest fine roots. Root turnover decreased from tropical to high-latitude systems for all plant functional groups. To test whether global relationships can be used to predict interannual variability in root turnover, we evaluated 14 yr of published root turnover data from a shortgrass steppe site in northeastern Colorado, USA. At this site there was no correlation between interannual variability in mean annual temperature and root turnover. Rather, turnover was positively correlated with the ratio of growing season precipitation and maximum monthly temperature ( r 2 = 0.61). We conclude that there are global patterns in rates of root turnover between plant groups and across climatic gradients but that these patterns cannot always be used for the successful prediction of the relationship of root turnover to climate change at a particular site.  相似文献   

2.
Six cultivars of spring barley ( Hordeum vulgare L. cvs Salve, Nümberg II, Bomi, Risø 1508, Mona and Sv 73 608) were grown in water culture for three weeks with various combinations of mineral supply and differential roots/shoot temperatures during the growth period. Most important for growth and accumulation of N, K+, Ca2+ and Mg2+ was the mineral supply, followed by the root temperature and the choice of cultivar. Treatments with low mineral supply or low root temperature induced a uniform reduction in growth and accumulation of the ions studied. The effects of low mineral supply and low root temperature on growth and N accumulation was additive, which indicates that these factors exert their influence independently of each other.
Roots grown at 10°C were smaller and Rb+(86Rb) influx was higher than in roots grown at 20°C. It is suggested that the control of Rb+(86Rb) influx is affected by the root temperature and the age of the plants. The higher 86Rb+ (86Rb) influx into the low temperature roots could not compensate for the smaller root size. However, the lower total mineral accumulation made up for the needs of the smaller plants and cannot explain the reduction in growth.  相似文献   

3.
Annual measurements of the diameter growth and litter fall of trees began in 1998 using a 1.0 ha permanent plot beneath a flux tower at the Takayama flux site, central Japan. This opened up an opportunity for studies that compare the interannual variability in tree growth with eddy covariance-based net ecosystem production (NEP). A possible link between multiyear biometric-based net primary production (NPP) and eddy covariance-based NEP was investigated to determine the contribution of autotrophic production and heterotrophic respiration (HR) to the interannual variability of NEP in deciduous forest ecosystems. We also defined the NEP* as the measurable organic matter stored in an ecosystem during the interval in which soil respiration (SR) measurements were taken. The difference of biometric-based NEP* from eddy covariance-based NEP within a given year varied between 55% and 105%. Woody tissue NPP (stems and coarse roots) varied markedly from 0.88 to 1.96 Mg C ha−1 yr−1 during the 8-year study period (1999–2006). Annual woody tissue NPP was positively correlated with eddy covariance-based NEP ( r 2=0.52, P <0.05). However, neither foliage NPP ( r 2=0.03) nor HR ( r 2=0.06) were correlated with eddy covariance-based NEP. Therefore, it was hypothesized that interannual variability in the ecosystem carbon exchange was directly responsible for much of the interannual variation in autotrophic production, especially carbon accumulation in the woody components of the ecosystem. Moreover, similar interannual variations of biometric-based NEP* and eddy covariance-based NEP with small variations in SR and foliage NPP suggest a constant net accumulation of carbon in nonliving pools at the Takayama site.  相似文献   

4.
The present study investigated the relative importance of leaf and root carbon input for soil invertebrates. Experimental plots were established at the Swiss Canopy Crane (SCC) site where the forest canopy was enriched with 13C depleted CO2 at a target CO2 concentration of c . 540 p.p.m. We exchanged litter between labelled and unlabelled areas resulting in four treatments: (i) leaf litter and roots labelled, (ii) only leaf litter labelled, (iii) only roots labelled and (iv) unlabelled controls. In plots with only 13C-labelled roots most of the soil invertebrates studied were significantly depleted in 13C, e.g. earthworms, chilopods, gastropods, diplurans, collembolans, mites and isopods, indicating that these taxa predominantly obtain their carbon from belowground input. In plots with only 13C-labelled leaf litter only three taxa, including, e.g. juvenile Glomeris spp. (Diplopoda), were significantly depleted in 13C suggesting that the majority of soil invertebrates obtain its carbon from roots. This is in stark contrast to the view that decomposer food webs are based on litter input from aboveground.  相似文献   

5.
Araucaria angustifolia (Bertol.) Kuntze is an indigenous conifer tree restricted to the southern region of South America that plays a key role in the dynamics of regional ecosystems where forest expansion over grasslands has been observed. Here, we evaluate the changes in intrinsic water use efficiency (iWUE) and basal area increment (BAI) of this species in response to atmospheric CO2, temperature and precipitation over the last century. Our investigation is based on tree-rings taken from trees located in forest and grassland sites in southern Brazil. Differences in carbon isotopic composition ( δ 13C), 13CO2 discrimination (Δ13C) and intracellular carbon concentration ( C i ) are also reported. Our results indicate an age effect on Δ13C in forest trees during the first decades of growth. This age effect is not linked to an initial BAI suppression, suggesting the previous existence of nonforested vegetation in the forest sites. After maturity all trees show similar temporal trends in carbon isotope-derived variables and increasing iWUE, however, absolute values are significantly different between forest and grassland sites. The iWUE is higher in forest trees, indicating greater water competition or nutritional availability, relative to grassland, or both. BAI is also higher in forest trees, but it is not linked with iWUE or atmospheric CO2. Nevertheless, in both forest and grassland sites A. angustifolia has had growth limitations corresponding to low precipitation and high temperatures observed in the 1940s.  相似文献   

6.
Alterations in forest productivity and changes in the relative proportion of above‐ and belowground biomass may have nonlinear effects on soil organic matter (SOM) storage. To study the influence of plant litter inputs on SOM accumulation, the Detritus Input Removal and Transfer (DIRT) Experiment continuously alters above‐ and belowground plant inputs to soil by a combination of trenching, screening, and litter addition. Here, we used biogeochemical indicators [i.e., cupric oxide extractable lignin‐derived phenols and suberin/cutin‐derived substituted fatty acids (SFA)] to identify the dominant sources of plant biopolymers in SOM and various measures [i.e., soil density fractionation, laboratory incubation, and radiocarbon‐based mean residence time (MRT)] to assess the stability of SOM in two contrasting forests within the DIRT Experiment: an aggrading deciduous forest and an old‐growth coniferous forest. In the deciduous forest, removal of both above‐ and belowground inputs increased the total amount of SFA over threefold compared with the control, and shifted the SFA signature towards a root‐dominated source. Concurrently, light fraction MRT increased by 101 years and C mineralization during incubation decreased compared with the control. Together, these data suggest that root‐derived aliphatic compounds are a source of SOM with greater relative stability than leaf inputs at this site. In the coniferous forest, roots were an important source of soil lignin‐derived phenols but needle‐derived, rather than root‐derived, aliphatic compounds were preferentially preserved in soil. Fresh wood additions elevated the amount of soil C recovered as light fraction material but also elevated mineralization during incubation compared with other DIRT treatments, suggesting that not all of the added soil C is directly stabilized. Aboveground needle litter additions, which are more N‐rich than wood debris, resulted in accelerated mineralization of previously stored soil carbon. In summary, our work demonstrates that the dominant plant sources of SOM differed substantially between forest types. Furthermore, inputs to and losses from soil C pools likely will not be altered uniformly by changes in litter input rates.  相似文献   

7.
Vitamin D3 at low concentration (10−9 M) inhibited the growth of Phaseolus vulgaris L. (cv. Contrancha) roots in vitro as measured by elongation (14 h) and [3H]-leucine incorporation into protein (2 h), and increased their labelling with 45Ca2+ (2 h). Cycloheximide and puromycin (50 u.M) blocked vitamin D3 stimulation of root 45Ca2+ labelling, indicating that it is mediated by de novo protein synthesis. The calcium ionophore X-537A (10−5JW) induced similar changes both in root elongation and 45Ca2+ uptake (14 h). This may indicate that the inhibitory effects of the sterol on root growth are mediated by changes in Ca2+ fluxes. However, this interpretation should be further strengthened by additional studies as the ionophore may have acted on root growth, affecting physiological processes other than Ca2+ transport.  相似文献   

8.
Using a new approach involving one-time measurements of radiocarbon (14C) in fine (<2 mm diameter) root tissues we have directly measured the mean age of fine-root carbon. We find that the carbon making up the standing stock of fine roots in deciduous and coniferous forests of the eastern United States has a mean age of 3-18 years for live fine roots, 10-18 years for dead fine roots, and 3-18 years for mixed live+dead fine roots. These 14C-derived mean ages represent the time C was stored in the plant before being allocated for root growth, plus the average lifespan (for live roots), plus the average time for the root to decompose (for dead roots and mixtures). Comparison of the 14C content of roots known to have grown within 1 year with the 14C of atmospheric CO2 for the same period shows that root tissues are derived from recently fixed carbon, and the storage time prior to allocation is <2 years and likely <1 year. Fine-root mean ages tend to increase with depth in the soil. Live roots in the organic horizons are made of C fixed 3-8 years ago compared with 11-18 years in the mineral B horizons. The mean age of C in roots increases with root diameter and also is related to branching order. Our results differ dramatically from previous estimates of fine-root mean ages made using mass balance approaches and root-viewing cameras, which generally report life spans (mean ages for live roots) of a few months to 1-2 years. Each method for estimating fine-root dynamics, including this new radiocarbon method, has biases. Root-viewing approaches tend to emphasize more rapidly cycling roots, while radiocarbon ages tend to reflect those components that persist longest in the soil. Our 14C-derived estimates of long mean ages can be reconciled with faster estimates only if fine-root populations have varying rates of root mortality and decomposition. Our results indicate that a standard definition of fine roots, as those with diameters of <2 mm, is inadequate to determine the most dynamic portion of the root population. Recognition of the variability in fine-root dynamics is necessary to obtain better estimates of belowground C inputs.  相似文献   

9.
Plantago lanceolata L. seedlings were grown in sand microcosm units over a 43‐day experimental period under two CO2 regimes (800 or 400 µmol mol−1) to investigate the effect of elevated atmospheric CO2 concentration on carbon partitioning and exudate release. Total organic carbon (TOC) content of the collected exudate material was measured throughout the experimental period. After 42 days growth the seedlings were labelled with [14C]‐CO2 and the fate of the label within the plant and its release by the roots monitored. Elevated CO2 significantly (P ≤ 0.001) enhanced shoot, root and total dry matter production although the R:S ratio was unaltered, suggesting no alteration in gross carbon partitioning. The cumulative release of TOC (in mg C) over 0‐42 days was unaltered by CO2 treatment however, when expressed as a percentage of net assimilated C, ambient‐grown plants released a significantly (P≤ 0.001) higher percentage from their roots compared to elevated CO2‐grown plants (i.e. 8 vs 3%). The distribution of 14C‐label was markedly altered by CO2 treatment with significantly (P≤ 0.001) greater per cent label partitioned to the roots under elevated CO2. This indicates increased partitioning of recent assimilate below‐ground under elevated CO2 treatment although there was no significant difference in the percentage of 14C‐label released by the roots. Comparison of plant C budgets based on 14C‐pulse‐chase methodology and TOC measurements is discussed.  相似文献   

10.
1. Changes of δ13C and its relation to leaf development, biochemical content and water stress were monitored over a 2 year period in two co-occurring Mediterranean oak species: the deciduous Quercus pubescens and the evergreen Quercus ilex .
2. The time course of leaf δ13C showed different patterns in the two species. Young Q. pubescens leaves had a high δ13C and a marked decrease occurred during leaf growth. In contrast, leaves at budburst and maturity did not differ significantly in the case of Q. ilex . We suggest that the difference between δ13C of young leaves was linked to differential use of reserves of carbon compounds in the two species.
3. δ13C values of mature leaves were negatively correlated with minimum seasonal values of predawn water potential, suggesting that a functional adjustment to water resources occurred.
4. There was a significant correlation between individual δ13C values for two successive years. This interannual dependence showed that δ13C rankings between trees were constant through time.  相似文献   

11.
In the sugar beet plant ( Beta vulgaris L. ssp. altissima ) the vascular bundles of old leaves lead to the center and those of young leaves to the periphery of the storage root. Whether the flux of assimilates follows these anatomical routes was tested by applying 14CO2 for 4 h to either an old (10th) or a young (20th) leaf in intact sugar beet plants. Four-month-old plants, which had about 30 leaves, were used in the experiment. The 14C distribution in the storage root was measured by autoradiography and counting in about 20 cross and longitudinal sections per root.
About 37% of assimilated 14C from an old leaf and 23% from a young leaf were exported within 24 h. Although some 14C moved into younger leaves, most was exported into the storage root. During its rapid movement towards the root tip, which took place perferentially in the orthostichon belonging to the [14C]-treated leaf, the label spread laterally.
The autoradiograms indicate that the distribution of assimilates within the storage root is roughly determined by the course of the vascular bundles extending from the source leaf. The fine distribution, however, seems to be controlled by sucrose gradients between storage cells.  相似文献   

12.
Burgos cheese was manufactured from pasteurized ewes milk inoculated with Staphylococcus aureus strains FRI 137 and FRI 361, at levels of ca 103 and 105 cfu/ml and stored at 4°, 10° and 15°C and at room temperature (10°-15°C). Populations of Staph. aureus and mesophilic aerobes, pH, and production of thermonuclease and enterotoxins C1 and C2 were investigated. Aerobic counts increased during cheese-making and storage. With both test strains, important growth was observed only during the storage period, the larger levels corresponding to the higher temperatures. Although Staph. aureus strains attained populations of over 108 cfu/g, no enterotoxin was detected. Strain FRI 361 reached 107 cfu/g without production of a detectable amount of thermonuclease. With strain FRI 137, the minimal population associated with enzyme activity was influenced by the inoculum size. Staphylococcus aureus counts are better indicators of staphylococcal growth in Burgos cheese than the thermonuclease test.  相似文献   

13.
Carbon dioxide fixation in orchid aerial roots   总被引:1,自引:0,他引:1  
Acidity fluctuation, CO2 gas exchange, δ13C value, PEP carboxylase and RuBP carboxylase activities in aerial roots of selected thick-leaved orchid hybrids ( Arachnis and Aranthera ) were studied. Both aerial roots and leaves showed acidity fluctuation over a 24 h period. Dark acidification in aerial roots was enhanced at low temperature (15°C). Aerial roots had δ13C values close to those of leaves which have been previously demonstrated to possess crassulacean acid metabolism. Variation in δ13C values along the length of the roots was observed; the root tip having a less negative δ13C value (—13.34%‰) than the older portions of the roots (—14.55%‰). There was no net CO2 fixation by aerial root, although 1432CO2 fixation was observed in light and in darkness. The pattern of fluctuation in activities of PEP carboxylase and RuBP carboxylase in aerial roots was similar to that obtained for the leaves. In both aerial roots and leaves, PEP carboxylase activity was several times higher than that of RuBP carboxylase.  相似文献   

14.
Hasenstein, K. H. and Evans, M. L. 1988. The influence of calcium and pH on growth in primary roots of Zea mays. - Physiol. Plant. 72: 466–470.
We investigated the interaction of Ca2+ and pH on root elongation in Zea mays L. cv. B73 × Missouri 17 and cv. Merit. Seedlings were raised to contain high levels of Ca2+ (HC, imbibed and raised in 10 m M CaCl2) or low levels of Ca2+ (LC, imbibed and raised in distilled water). In HC roots, lowering the pH (5 m M MES/Tris) from 6.5 to 4.5 resulted in strong, long-lasting growth promotion. Surprisingly, increasing the pH from 6.5 to 8.5 also resulted in strong growth promotion. In LC roots acidification of the medium (pH 6.5 to 4.5) resulted in transient growth stimulation followed by a gradual decline in the growth rate toward zero. Exposure of LC roots to high pH (pH shift from 6.5 to 8.5) also promoted growth. Addition of EGTA resulted in strong growth promotion in both LC and HC roots. The ability of EGTA to stimulate growth appeared not to be related to H+ release from EGTA upon Ca2+ chelation since, 1) LC roots showed a strong and prolonged response to EGTA, but only a transient response to acid pH, and 2) promotion of growth by EGTA was observed in strongly buffered solutions. We also examined the pH dependence of the release of 45Ca2+ from roots of 3-day-old seedlings grown from grains imbibed in 45Ca2+. Release of 45Ca2+ from the root into agar blocks placed on the root surface was greater the more acidic the pH of the blocks. The results indicate that Ca2+ may be necessary for the acid growth response in roots.  相似文献   

15.
Carbon density and distribution of six Chinese temperate forests   总被引:2,自引:0,他引:2  
Quantifying forest carbon (C) storage and distribution is important for forest C cycling studies and terrestrial ecosystem mod-eling. Forest inventory and allometric approaches were used to measure C density and allocation in six representative temper-ate forests of similar stand age (42–59 years old) and growing under the same climate in northeastern China. The forests were an aspen-birch forest, a hardwood forest, a Korean pine plantation, a Dahurian larch plantation, a mixed deciduous forest, and a Mongolian oak forest. There were no significant differences in the C densities of ecosystem components (except for detritus) although the six forests had varying vegetation compositions and site conditions. However, the differences were significant when the C pools were normalized against stand basal area. The total ecosystem C density varied from 186.9 tC hm-2 to 349.2 tC hm-2 across the forests. The C densities of vegetation, detritus, and soil ranged from 86.3–122.7 tC hm-2, 6.5–10.5 tC hm-2, and 93.7–220.1 tC hm-2, respectively, which accounted for 39.7%±7.1% (mean±SD), 3.3%±1.1%, and 57.0%±7.9% of the total C densities, respectively. The overstory C pool accounted for > 99% of the total vegetation C pool. The foliage bio-mass, small root (diameter < 5mm) biomass, root-shoot ratio, and small root to foliage biomass ratio varied from 2.08–4.72 tC hm-2, 0.95–3.24 tC hm-2, 22.0%–28.3%, and 34.5%–122.2%, respectively. The Korean pine plantation had the lowest foliage production efficiency (total biomass/foliage biomass: 22.6 g g-1) among the six forests, while the Dahurian larch plantation had the highest small root production efficiency (total biomass/small root biomass: 124.7 g g-1). The small root C density de-creased with soil depth for all forests except for the Mongolian oak forest, in which the small roots tended to be vertically dis-tributed downwards. The C density of coarse woody debris was significantly less in the two plantations than in the four natu-rally regenerated forests. The variability of C allocation patterns in a specific forest is jointly influenced by vegetation type, management history, and local water and nutrient availability. The study provides important data for developing and validating C cycling models for temperate forests.  相似文献   

16.
Radiocarbon (14C) provides a measure of the mean age of carbon (C) in roots, or the time elapsed since the C making up root tissues was fixed from the atmosphere. Radiocarbon signatures of live and dead fine (<2 mm diameter) roots in two mature Amazon tropical forests are consistent with average ages of 4–11 years (ranging from <1 to >40 years). Measurements of 14C in the structural tissues of roots known to have grown during 2002 demonstrate that new roots are constructed from recent (<2‐year‐old) photosynthetic products. High Δ14C values in live roots most likely indicate the mean lifetime of the root rather than the isotopic signature of inherited C or C taken up from the soil. Estimates of the mean residence time of C in forest fine roots (inventory divided by loss rate) are substantially shorter (1–3 years) than the age of standing fine root C stocks obtained from radiocarbon (4–11 years). By assuming positively skewed distributions for root ages, we can effectively decouple the mean age of C in live fine roots (measured using 14C) from the rate of C flow through the live root pool, and resolve these apparently disparate estimates of root C dynamics. Explaining the 14C values in soil pore space CO2, in addition, requires that a portion of the decomposing roots be cycled through soil organic matter pools with decadal turnover time.  相似文献   

17.
We examined the environmental variables that influence the δ 13C value of needle and phloem sugars in trees in a subalpine forest. We collected sugars from Pinus contorta , Picea engelmannii and Abies lasiocarpa from 2006 to 2008. Phloem and needle sugars were enriched in 13C during the autumn, winter and early spring, but depleted during the growing season. We hypothesized that the late-winter and early-spring 13C enrichment was due to the mobilization of carbon assimilated the previous autumn; however, needle starch concentrations were completely exhausted by autumn, and we observed evidence of new starch production during episodic warm weather events during the winter and early-spring. Instead, we found that 13C enrichment was best explained by the occurrence of cold night-time temperatures. We also observed seasonal decoupling in the 13C/12C ratios of needle and phloem sugars. We hypothesized that this was due to seasonally-changing source-sink patterns, which drove carbon translocation from the needles towards the roots early in the season, before bud break, but from the roots towards the needles later in the season, after bud break. Overall, our results demonstrate that the 13C/12C ratio of recently-assimilated sugars can provide a sensitive record of the short-term coupling between climate and tree physiology.  相似文献   

18.
19.
Elevated CO2 and conifer roots: effects on growth, life span and turnover   总被引:5,自引:4,他引:1  
Elevated CO2 increases root growth and fine (diam. 2 mm) root growth across a range of species and experimental conditions. However, there is no clear evidence that elevated CO2 changes the proportion of C allocated to root biomass, measured as either the root:shoot ratio or the fine root:needle ratio. Elevated CO2 tends to increase mycorrhizal infection, colonization and the amount of extramatrical hyphae, supporting their key role in aiding the plant to more intensively exploit soil resources, providing a route for increased C sequestration. Only two studies have determined the effects of elevated CO2 on conifer fine-root life span, and there is no clear trend. Elevated CO2 increases the absolute fine-root turnover rates; however, the standing crop root biomass is also greater, and the effect of elevated CO2 on relative turnover rates (turnover:biomass) ranges from an increase to a decrease. At the ecosystem level these changes could lead to increased C storage in roots. Increased fine-root production coupled with increased absolute turnover rates could also lead to increases in soil organic C as greater amounts of fine roots die and decompose. Although CO2 can stimulate fine-root growth, it is not known if this stimulation persists over time. Modeling studies suggest that a doubling of the atmospheric CO2 concentration initially increases biomass, but this stimulation declines with the response to elevated CO2 because increases in assimilation are not matched by increases in nutrient supply.  相似文献   

20.
W.G. VAN DOORN AND K. D'HONT. 1994. Flowering stems of four rose cultivars (Sonia, Madelon, Jacaranda and Frisco) were placed in aqueous suspensions of bacteria at 104 and 108 colony-forming units (cfu) ml-1 for 24 h at 5C, then stored dry or held in water for 24 h at 8C and subsequently placed in vase-water at 20C. The effects of these treatments on vase-water uptake were similar to the effects on flower opening. In Sonia and Madelon roses flower opening was negatively affected both by 108 cfu ml-1 of bacteria and by dry storage. No effect was found at 104 cfu ml-1, but this concentration had a detrimental effect on flower opening when combined with dry storage. Although flower development in Jacaranda roses was not affected by the bacteria treatments it was inhibited by dry storage. This inhibition was progressively greater when the stems had previously been pulse-treated with a larger number of bacteria. Flower opening in Frisco roses was not affected by even the highest concentration of bacteria, nor by the period of dry storage. It is concluded that placing flowers in water containing bacteria (up to 108 cfu ml-1) may not always have a negative effect on flower development in cut rose flowers but, together with the effects of dry storage, the presence of even a low number of exogenous bacteria (104 cfu ml-1) inhibits the development in several cultivars. Such bacterial counts are nearly always found in samples of water used for standing roses during distribution to the consumers.  相似文献   

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