Carbohydrates in individual poplar fine roots: effects of root age and defoliation

Late-summer starch accumulation in fine roots of poplars (Populus x canadensis Moench.) defoliated by gypsy moth (Lymantria dispar L.) lagged behind that in fine roots of undefoliated trees. If starch concentration declines with age, defoliation-induced changes in root system age structure could be partly responsible for this difference. To test this hypothesis, we measured fine-root starch and soluble sugar concentrations in roots of known age from trees in defoliated and undefoliated plots. There was a significant interaction between the effects of defoliation and root type (white, brown, or dead) on fine root soluble sugar concentration because of the high concentration of soluble sugars in white roots from trees in undefoliated plots. Both root starch and soluble sugar concentrations were variable among individuals of each age class. The population frequency distributions for starch and soluble sugar concentrations were both right-skewed, and fit by exponential functions. These data are most consistent with direct defoliation effects on a labile and dynamic pool of carbohydrates in poplar fine roots, rather than indirect defoliation effects on root system age structure.     

Biomass and nitrogen dynamics in an irrigated hybrid poplar plantation

A 3-year study measured the effects of ground cover treatments and N fertilization on biomass and nitrogen dynamics in an irridiated hybrid poplar (Populus deltoides Bartr. X P. trichocarpa Torr. and Gray, clone NC-9922) plantation in northern Wisconsin, U.S.A. Annually fertilized (112 kg N ha⁻¹ year⁻¹) and unfertilized plots were maintained weed free (bare soil), allowed to revegetate with native weeds, or seeded to birdsfoot trefoil (Lotus corniculatus L.). Biomass and N in trees and ground-cover vegetation were sampled before and after each growing season.Trees in bare-soil plots responded to fertilization primarily in the third growing season, but total biomass of 3-year-old trees was not increased by annual fertilization. In plots with a ground cover,fertilization increased tree growth but cover crop treatment had no effect. Ground cover biomass peaked during the second growing season, but declined thereafter, primarily due to reductions in below-ground biomass. Estimated recovery of fertilizer N was low in bare soil plots after 3 years, with 2% in the ‘perennial’ portion of the trees and 13% in the leaf litter. In contrast, recovery in the cover crop plots was 44%–51% in years 2–4. During that period, both biomass and N pool dominance shifted from primarily cover crop to primarily trees. The ground cover appeared to reduce tree growth in years 1–3, but total tree biomass after 4 years was greater in fertilized plots with ground cover (22.7 Mg/ha) than in fertilized bare soil plots (16.7 Mg/ha). Biomass production in fertilized trefoil plots in the fourth year (15.1 Mg ha⁻¹ year⁻¹, excluding leaves) exceeds that of local forests by 50%, and may be comparable to corn productivity in the area.     

Impact factors on fine root seasonal dynamics in Fraxinus mandshurica plantations

Fine root turnover plays important roles in carbon allocation and nutrient cycling in forest ecosystems. Seasonal dynamics of fine roots is critical for understanding the processes of fine root turnover. From May to October 2002, soil core method was used for estimating the seasonal pattern of fine root (diameter < 1 mm) parameters (biomass, specific root length (SRL) and root length density (RLD)) in a Manchurian ash (Fraxinus mandshurica) plantation located at the Maoershan Experiment Station, Heilongjiang Province, northeast of China. The relationships of fine root biomass, SRL and RLD with available nitrogen in soil, average soil temperature per month in 10 cm depth and soil moisture content were analyzed. Seasonal variation of fine root biomass was significant (P < 0.05). The peak values of fine root biomass were observed both in spring and in autumn, but SRL and RLD were the highest in spring and lowest in autumn. Specific root length and root length density were higher in spring and summer, which means that fine root diameter was thinner. In autumn, both parameters decreased significantly due to secondary incrassation of fine root diameter or the increase of tissue density. Seasonal dynamics of fine roots was associated with available nitrogen in soil, soil temperature in 10 cm depth and moisture content. Fine root biomass has a significant relationship with available NH₄ ⁺-N in soil. Available NO₃ ⁻-N in soil, soil temperature in 10-cm depth and moisture content have a positive correlation with fine root biomass, SRL and RLD, although these correlations are not significant (P > 0.05). But the compound effects of soil available N, soil temperature and soil moisture content are significant to every root parameter. The variations of these three root parameters in different seasons show different physiological and ecological functions in different growing periods. Translated from Scientia Silvae Sinicae, 2006, 42(9): 7–12 [译自: 林业科学]     

Interactive effects of nitrogen and water availabilities on gas exchange and whole-plant carbon allocation in poplar

Cuttings of balsam spire hybrid poplar (Populus trichocarpa var. Hastata Henry x Populus balsamifera var. Michauxii (Dode) Farwell) were grown in sand culture and irrigated every 2 (W) or 10 (w) days with a solution containing either 3.0 (N) or 0.5 (n) mol nitrogen m(-3) for 90 days. Trees in the WN (control) and wn treatments had stable leaf nitrogen concentrations averaging 19.4 and 8.4 mg g(-1), respectively, over the course of the experiment. Trees in the Wn and wN treatments had a similar leaf nitrogen concentration, which increased from 12.0 to 15.8 mg g(-1) during the experiment. By the final harvest, mean stomatal conductances of trees in the wN and wn treatments were less than those of trees in the Wn and WN treatments (1.8 versus 4.6 mm s(-1)). Compared to the WN treatment, biomass at the final harvest was reduced by 61, 72 and 75% in the Wn, wN and wn treatments, respectively. At the final harvest, WN trees had a mean total leaf area of 4750 +/- 380 cm(2) tree(-1) and carried 164 +/- 8 leaves tree(-1) with a specific leaf area of 181 +/- 16 cm(2) g(-1), whereas Wn trees had a smaller mean total leaf area (1310 +/- 30 cm(2) tree(-1)), because of the production of fewer leaves (41 +/- 6) with a smaller specific leaf area (154 +/- 2 cm(2) g(-1)). A greater proportion of biomass was allocated to roots in Wn trees than in WN trees, but component nitrogen concentrations adjusted such that there was no Wn treatment effect on nitrogen allocation. Compared with WN trees, rates of photosynthesis and respiration per unit weight of tissue of Wn trees decreased by 28 and 31%, respectively, but the rate of photosynthesis per unit leaf nitrogen remained unaltered. The wN and Wn trees had similar leaf nitrogen concentrations; however, compared with the Wn treatment, the wN treatment decreased mean total leaf area (750 +/- 50 cm(2) tree(-1)), number of leaves per tree (29 +/- 2) and specific leaf area (140 +/- 6 cm(2) g(-1)), but increased the allocation of biomass and nitrogen to roots. Net photosynthetic rate per unit leaf nitrogen was 45% lower in the wN treatment than in the other treatments. Rates of net photosynthesis and respiration per unit weight of tissue were 48 and 33% less, respectively, in wN trees than in Wn trees.     

沼液施肥对杨树林地土壤微生物量碳氮的影响

沼液是沼气发酵过后的液体残留物,是一种优质的有机肥料。研究了不同沼液施肥对杨树林地土壤微生物量碳氮的影响。结果表明:施用沼液可以提高土壤微生物量碳、氮的含量,微生物量碳、氮含量增加范围分别为4.29%~61.62%和6.08%~76.10%,土壤微生物量碳氮含量随沼液施用量增加逐渐提高。土壤微生物量碳氮呈正相关。土壤微生物量碳氮比随沼液施用量增加逐渐下降,其变化范围为9.92~10.81,土壤微生物量碳氮比与微生物量碳、氮含量负相关。     

Thinning effects on carbon allocation to fine roots in a Quercus ilex forest

The dynamics of the fine root system are relevant to calculations of the carbon balance of the ecosystem, and there is also a need to quantify changes in this component caused by disturbances. Mediterranean forest systems have historically been coppiced to obtain charcoal. As a result of the resprouting capacity of holm oaks (Quercus ilex L.), these forests present more than 50% of their biomass below ground (stump + roots > 1 cm in diameter), but the effects of thinning on the fine root system are unknown. Fine root biomass, production, mortality and longevity were studied in a control and a thinned Mediterranean holm oak forest by minirhizotron methodology. Observations of fine roots started 2 years after thinning and continued for almost 3 years. Extraction of 80% of the former basal area of the forest greatly affected carbon allocation patterns. Biomass increased by more than 100%, production increased by 76%, mortality increased by 32% and longevity decreased by around 2 weeks. The greatest differences between treatments were associated with differences in growth during autumn months in the top 40 cm of soil, particularly between 10 and 20 cm depth.     

Dynamics of nitrogen and phosphorus concentrations of fine roots in a mixed forest ofCunninghamia lanceolata andTsoongiodendron odorum

From September 1999 to July 2000, N and P concentrations of fine roots were measured with the method of sequential soil core at bimonthly intervals in a mixed forest of Tsoong's tree (Tsoongiodendron odorum Chun) and Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) in Sanming, Fujian. The results showed that N, P concentration of Chinese fir and Tsoong's tree in fine roots were negatively related to root diameter size. The concentrations of N and P in living roots and dead roots were compared. The order of N concentration in fine roots in different samples was Tsoong's tree>undergrowth>Chinese fir, while that of P was undergrowth>Tsoong's tree>Chinese fir. For Chinese fir, the seasonal change of N, P concentrations in fine roots with various diameter classes showed a single-apex curve with a maximum in September. For Tsoong's tree, maximized concentration of N in fine roots appeared in July or September and maximized P concentration in May. Foundation item: The project was supported by The Foundation of Post-doctoral Research of China (1999, No 10), the Foundation for University Key Teacher by the Ministry of Education, and the Research Programs on Basic Theory of Fujian Province (2000F004). Biography: YANG Yu-sheng (1964-), male, professor in Fujian Agricultural and Forestry University, Nanping 353001, P.R. China. Responsible editor: Zhu Hong     

绿竹林碳,氮动态研究

主要讨论了闽南绿竹（Dendrocalamopsisoldhami）林C、N元素的含量、库存量、年动态及C／N。结果表明：（1）绿竹林各组分C、N元素含量有一定差异,含量范围分别为：C38．74％～44．77％、No．557％～1．012％;C／N在38．281～77．792之间。（2）绿竹林C、N元素的现存库存量分别为6760．0369／m2和112．3979／m2,其中地上部分别为5891．5739／m2和94．101g／m2;地下部分别为868．463g／m2和18．296g／m2。（3）1996年7月至1997年6月一年中绿竹叶的C、N元素含量基本上是在生长期的春末夏初含量高,在冬季含量低：C／N在24．707～38．281之间,在生长期的春季比例低,在冬季比例高。（4）绿竹细根的分解过程中C、N元素含量处于释放或累积的相间波动之中,而C／N在细根分解的前几个月下降,而后处于上升和下降的波动之中。     

Response of nitrogen mineralization dynamics and biochemical properties to litter amendments to soils of a poplar plantation

Understanding the impact of plant litters on soil nitrogen(N) dynamics could facilitate development of management strategies that promote plantation ecosystem function.Our objective was to evaluate the effects of different litter types on N mineralization and availability,microbial biomass, and activities of L-asparaginase and odiphenol oxidase(o-DPO) in soils of a poplar(Populus deltoides) plantation through 24 weeks of incubation experiments.The tested litters included foliage(F), branch(B), or root(R) of poplar trees, and understory vegetation(U) or a mixture of F, B, and U(M).Litter amendments led to rapid N immobilization during the first 4 weeks of incubation, while net N mineralization was detected in all tested soils from 6 to 24 weeks of incubation, with zeroorder reaction rate constants(k) ranging from 7.7 to9.6 mg N released kg~(-1) soil wk~(-1).Moreover, litter addition led to increased microbial biomass carbon(C) 49–128% and increased MBC:MBN ratio by 5–92%,strengthened activities of L-asparaginase and o-DPO by14–74%; Up to about 37 kg N ha~(-1) net increase in mineralized N in litter added soils during 24 weeks of incubation suggests that adequate poplar and understory litter management could lead to reduced inputs while facilitate sustainable and economic viable plantation production.     

Biomass and production of fine roots in Japanese forests

To better understand the control of fine-root dynamics in Japanese forests, we reviewed studies conducted in Japan on fine-root biomass and production. Most of the data on fine-root biomass were obtained for conifer plantations in limited regions; the average fine-root biomass of dominant trees ranged from ∼50 g m₋₂ for Pinus species (n = 3) to ∼600 g m₋₂ for Cryptomeria japonica (n = 4) and Chamaecyparis obtusa (n = 3). These values are comparable with or less than those reported for other temperate forests mainly in North America or Europe. Information on fine-root production in Japanese forests remains limited. Fine-root production accounted for ∼30% of the net primary productivity in two deciduous forests, but similar data was not reported for coniferous forests in Japan. In Japanese forests, slope position is a key parameter controlling fine-root biomass that is greater on upper slopes than on lower slopes, probably because soil resource availability decreases upslope. Studies in manipulated soil environments (e.g., removing throughfall to simulate drought) also suggested that fine-root biomass and production were greatly affected by altered soil environments. Physiological control of fine-root dynamics was recently discussed via anatomical analyses of Chamaecyparis obtusa. Findings from Japanese studies generally support data on fine-root biomass and production obtained from other temperate regions. Further attempts to elucidate the influence of slope position (soil resource availability) on fine-root production would be useful to gain a more detailed understanding of the fine-root dynamics in Japanese forests.     

Responses of condensed tannins in poplar roots to fertilization and gypsy moth defoliation

We examined the effects of fertilization and gypsy moth defoliation on condensed tannin concentration (%CT) of hybrid poplar (Populus x canadensis cv 'Eugeneii') fine roots in the summers of 1997 and 1998. This factorial experiment included two defoliation treatments (defoliated and a foliated control) and fertilization treatments (100 kg nitrogen (N) ha(-1) and an unfertilized control). Gypsy moth (Lymantria dispar L.) populations were experimentally increased to obtain defoliation in the summers of 1996, 1997 and 1998; fertilization subplots were supplemented with NH4NO3 (100 kg N ha(-1)) in the spring of each year. Despite the severity of defoliation, the effects were small, and significant on only two sampling dates: in May 1997, when fine root %CT was 23% lower in the defoliated trees, and in November 1997, when trees in the defoliated unfertilized plots had 35% higher root %CT than trees in all other plots. Defoliation effects on root %CT did not follow the same seasonal pattern as defoliation effects on root starch content, N uptake capacity or leaf %CT. Regulation of root condensed tannin concentration appeared to be partially uncoupled from these traits. The small transient effects on root defense reflect the resilience of this early successional tree to severe early season defoliation.     

Partitioning of nitrate assimilation among leaves,stems and roots of poplar

Plants differ in tissue localization of nitrate reduction and assimilation. Some species reduce nitrate primarily in the leaves, whereas other species localize nitrate reduction and assimilation in the roots. We determined how nitrate assimilation is partitioned among leaves, stems and roots of poplar (Populus tremula L. x P. alba L.) by comparing tissue differences in in vivo nitrate reductase activity (NRA), nitrate reductase abundance and tissue nitrate concentration. Compared with stems or roots, NRA was greater in leaves, and the highest leaf NRA was found in young leaves. Leaf and root NRA increased with increasing nitrate supply, whereas stem NRA remained constant. Leaf NRA was at least 10-fold greater than root NRA at all external nitrate concentrations. Nitrate reductase abundance increased in all tissues with increasing nitrate availability, and nitrate reductase abundance was at least 10-fold greater in leaves than in stems or roots at all nitrate availabilities. Tissue nitrate concentration increased with increasing nitrate supply and was greater in roots than in stems and leaves. Photoperiod influenced NRA, with leaf NRA declining in nitrate-fertilized plants with short daily photoperiods (8-h). We conclude that different tissues of poplar vary in nitrate assimilation with little nitrate assimilation occurring in roots and the most nitrate assimilation taking place in leaves.     

Translocation of nitrogen in the xylem of field-grown cherry and poplar trees during remobilization

Studies of small trees growing in pots have established that individual amino acids or amides are translocated in the xylem sap of a range of tree species following bud burst, as a consequence of nitrogen (N) remobilization from storage. This paper reports the first study of N translocation in the xylem of large, deciduous, field-grown trees during N remobilization in the spring. We applied 15N fertilizer to the soil around 10-year-old Prunus avium L. and Populus trichocharpa Torr. & Gray ex Hook var. Hastata (Dode) A. Henry x Populus balsamifera L. var. Michauxii (Dode) Farwell trees before bud burst to label N taken up by the roots. Recovery of unlabeled N in xylem sap and leaves was used to demonstrate that P. avium remobilizes N in both glutamine (Gln) and asparagine (Asn). Sap concentrations of both amides rose sharply after bud burst, peaking 14 days after bud burst for Gln, and remaining high some 45 days for Asn. There was no 15N enrichment of either amide until 21 days after bud burst. In the Populus trees, nearly all the N was translocated in the sap as Gln, the concentration of which peaked and then declined before the amide was enriched with 15N, 40 days after bud burst. Xylem sap of clonal P. avium trees was sampled at different positions in the crown to assess if the amino acid and amide composition of the sap varied within the crown. Sap was sampled during remobilization (when the concentration of Gln was maximal), at the end of remobilization and at the end of the experiment (68 days after bud burst). Although the date of sampling had a highly significant effect on sap composition, the effect of position of sampling was marginal. The results are discussed in relation to N translocation in adult trees and the possibility of measuring N remobilization by calculating the flux of N translocation in the xylem.     

Carbon balance and soil carbon input in a poplar short rotation coppice plantation as affected by nitrogen and wood ash application

New Forests - The increasing importance of short rotation coppice (SRC) plantations for bioenergy production makes it crucial to evaluate their carbon (C) sink potential and to understand which...     

Inter- and intra-annual variations in canopy fine litterfall and carbon and nitrogen inputs to the forest floor in two European coniferous forests

? Context

The amount and chemistry of litterfall have been known to strongly vary among the years with important implications for ecosystem nutrient cycles, but there are few quantitative data describing such variations.

? Aims

We studied the climatic implications on the variation in litterfall and its C and N input to soil in two distinct European coniferous forests.

? Methods

Year-to-year variations in canopy litterfall were measured in a Scots pine stand (Hyytiälä, Finland) over 13 years, and a Douglas fir stand (Speulderbos, The Netherlands) over 3 years.

? Results

Important inter-annual variations in litterfall were observed in Scots pine. Litterfall was mainly driven by leaf senescence; however, premature needle fall was observed in high wind speed and early frost events. The seasonal variation in litterfall was characterized by a maximum in September in Scots pine, and by a biphasic variation pattern in Douglas fir, in May and November. Lower seasonal variations and lower annual average in litterfall N content were observed in Scots pine.

? Conclusion

Significant inter- and intra-annual variations in litterfall and chemistry and between the sites were demonstrated; and it depended on year-to-year differences in climate and extreme weather events.     

中国杨树生物量和碳储量研究进展

本文总结了中国近20年来有关杨树生物量产量、生物量增长模型、生物量测定、生物量与林分密度,以及杨树碳储量方面的研究进展。对研究方面存在的问题进行了讨论,并提出提高杨树生物量的一些建议和措施。     

水曲柳落叶松混交林中细根空间分布

采用根钻取样方法对年生水曲柳落叶松混交林中细根空间分布状况进行了研究。结果表明,水曲柳落叶松地下生物量的空间分配差异显著。在林分水平上,水曲柳的根生物量密度高于落叶松(分别为4442.3和2234.9g/m3)。两树种在相邻区域中分配的细根生物量较高,表明种间根系竞争较弱。落叶松行间的水曲柳细根生物量密度和根长密度均高于水曲柳行间的落叶松细根,表明水曲柳地下部分具有较强能力。根系的空间分布有利于混交林中水曲柳的生长。图1表4参19。     

Vitality of tree fine roots: reevaluation of the tetrazolium test

Reduction of triphenyltetrazolium chloride (TTC) by tissue to the red-colored insoluble triphenylformazan (TF) is directly linked to the activity of the mitochondrial respiratory chain. Thus, only living tissues should reduce TTC to TF. However, TF production can be detected when the TTC test is applied to control tissues boiled in water. This artifact is mainly the result of the hot ethanol extraction step, which is used to disintegrate the cells and solubilize the TF. We observed that cell wall materials such as cellulose and pectin interact with TTC at temperatures above 60 degrees C, reducing the TTC to TF. By replacing the hot ethanol extraction step with an extraction procedure that involved grinding the boiled tissues and extracting the TF with ethanol at room temperature, the formation of TF was almost entirely eliminated. Application of the modified TTC assay to fine roots of Norway spruce from forest topsoil indicated that the extent of TTC reduction was related to root morphological class as: white fine roots > brown fine roots > black fine roots > boiled fine roots, corresponding to formation of 10.8, 6.1, 0.2 and 0.1 mM TFg(-1)DW, respectively. No significant differences in TTC reduction were recorded between fresh and frozen tissues (frozen in liquid N2) for any fine root class. Application of the modified TTC assay to seedling roots stressed either by drying or by exposure to the toxic metals Cd or Al resulted in significant decreases in TF formation that were related to both the duration of stress and the concentrations of toxic substances, indicating that the modified TTC assay can be used to assess the physiological condition of roots.     

Comparing growth and fine root distribution in monocultures and mixed plantations of hybrid poplar and spruce

Disease prevention, biodiversity, productivity improvement and ecological considerations are all factors that contribute to increasing interest in mixed plantations. The objective of this study was to evaluate early growth and productivity of two hybrid poplar clones, P. balsamifera x trichocarpa (PBT) and P. maximowiczii x balsamifera (PMB), one improved family of Norway spruce (Picea glauca (PA)) and one improved family of white spruce (Picea abies (PG)) growing under different spacings in monocultures and mixed plots. The plantations were established in 2003 in Abitibi-Témiscamingue, Quebec, Canada, in a split plot design with spacing as the whole plot factor (1 × 1 m, 3 × 3 m and 5 × 5 m) and mixture treatments as subplot factor (pure: PBT, PMB, PA and PG, and 1:1 mixture PBT:PA, PBT:PG, PMB:PA and PMB:PG). Results showed a beneficial effect of the hybrid poplar-spruce mixture on diameter growth for hybrid poplar clones, but not for the 5 × 5 m spacing because of the relatively young age of the plantations. Diameter growth of the spruces decreased in mixed plantings in the 1 × 1 m, while their height growth increased, resulting in similar aboveground biomass per tree across treatments. Because of the large size differences between spruces and poplars, aboveground biomass in the mixed plantings was generally less than that in pure poplar plots. Leaf nitrogen concentration for the two spruce families and hybrid poplar clone PMB was greater in mixed plots than in monocultures, while leaf nitrogen concentration of clone PBT was similar among mixture treatments. Because of its faster growth rate and greater soil resources demands, clone PMB was the only one showing an increase in leaf N with increased spacing between trees. Fine roots density was greater for both hybrid poplars than spruces. The vertical distribution of fine roots was insensitive to mixture treatment.