Component and whole-system respiration fluxes in northern deciduous forests

We measured component and whole-system respiration fluxes in northern hardwood (Acer saccharum Marsh., Tilia americana L., Fraxinus pennsylvanica Marsh.) and aspen (Populus tremuloides Michx.) forest stands in Price County, northern Wisconsin from 1999 through 2002. Measurements of soil, leaf and stem respiration, stem biomass, leaf area and biomass, and vertical profiles of leaf area were combined with biometric measurements to create site-specific respiration models and to estimate component and whole-system respiration fluxes. Hourly estimates of component respiration were based on site measurements of air, soil and stem temperature, leaf mass, sapwood volume and species composition. We also measured whole-system respiration from an above-canopy eddy flux tower. Measured soil respiration rates varied significantly among sites, but not consistently among dominant species (P < 0.05 and P > 0.1). Annual soil respiration ranged from 8.09 to 11.94 Mg C ha(-1) year(-1). Soil respiration varied linearly with temperature (P < 0.05), but not with soil water content (P > 0.1). Stem respiration rates per unit volume and per unit area differed significantly among species (P < 0.05). Stem respiration per unit volume of sapwood was highest in F. pennsylvanica (up to 300 micro mol m(3) s(-1)) and lowest in T. americana (22 micro mol m(3) s(-1)) when measured at peak summer temperatures (27 to 29 degrees C). In northern hardwood stands, south-side stem temperatures were higher and more variable than north-side temperatures during leaf-off periods, but were not different statistically during leaf-on periods. Cumulative annual stem respiration varied by year and species (P < 0.05) and averaged 1.59 Mg C ha(-1) year(-1). Leaf respiration rates varied significantly among species (P < 0.05). Respiration rates per unit leaf mass measured at 30 degrees C were highest for P. tremuloides (38.8 nmol g(-1) s(-1)), lowest for Ulmus rubra Muhlenb. (13.1 nmol g(-1) s(-1)) and intermediate and similar (30.2 nmol g(-1) s(-1)) for T. americana, F. pennsylvanica and Q. rubra. During the growing season, component respiration estimates were dominated by soil respiration, followed by leaf and then stem respiration. Summed component respiration averaged 11.86 Mg C ha(-1) year(-1). We found strong covariance between whole-ecosystem and summed component respiration measurements, but absolute rates and annual sums differed greatly.     

Leaf exchange in a Mediterranean shrub: water, nutrient, non-structural carbohydrate and osmolyte dynamics

Leaf exchange is an abrupt phenological event that drastically modifies the morphology and physiology of the aerial portion of the plant. We examined if water and osmolyte differences between old leaves and new organs trigger leaf exchange, and whether the differences are closely linked to the resource resorption process in senescing leaves. We monitored concentrations of osmolyte, water, non-structural carbohydrate, nitrogen and potassium in senescing leaves and in emerging new leaves and inflorescences of a Mediterranean leaf exchanger (Cistus laurifolius L.) growing in NE Spain. Old leaves rehydrated markedly during most of the senescence process, which co-occurred with the extension of new shoots, suggesting the lack of a clear-cut switch in water supply from old to new organs. The accumulation of osmolytes in the early stage of leaf senescence might account for this rehydration. Osmolyte dynamics in old leaves depended largely on the progression of resource resorption from senescing organs but were mostly unrelated to water content during late senescence. We conclude that dehydration of old leaves is not a prerequisite for the triggering of leaf exchange. The finding that most nutrients and carbohydrates accumulated in new organs before senescing leaves massively exported resources, and the absence of relevant differences between the dynamics of old leaves at the base of inflorescences and those at the base of vegetative shoots, indicate that the nutrient and carbohydrate demands of new organs do not trigger leaf exchange.     

Comparative water relations of three successional hardwood species in central Wisconsin

Water relations of co-occurring understory saplings of Quercus ellipsoidalis E.J. Hill, an early successional, xeric species, Populus tremuloides Michx., an early successional, mesic species, and Acer rubrum L., a late successional species that occurs on both wet and dry sites, were evaluated on four dates during the 1986 growing season. The understory was characterized by high soil water content, low irradiance and low vapor pressure deficit throughout the growing season. Stomatal conductance and calculated transpiration flux were lowest for A. rubrum and highest for P. tremuloides and Q. ellipsoidalis. Except early in the growing season, leaf water potentials were lower in P. tremuloides than in the other species. Populus tremuloides had the highest bulk modulus of elasticity, Q. ellipsoidalis the lowest. Over the growing season, Populus tremuloides and Q. ellipsoidalis, but not A. rubrum, exhibited a decrease in osmotic potential at both full and zero turgor. Of the three species, Populus tremuloides exhibited the sharpest decrease in leaf water potential and turgor pressure with decreasing relative water content.     

Transfer of salt and nutrients in Bruguiera gymnorrhiza leaves during development and senescence

The life span of leaves in Bruguiera gymnorrhiza, non-secretor of salt, can be divided into a leaf developing stage, a leaf functioning stage and a leaf senescing stage. The concentrations (mg/g) and the contents (mg/leaf) of Na and Cl increased at the leaf developing stage and remained almost constant at the leaf functioning stage. At the leaf senescing stage, the concentrations of Na and Cl increased markedly by 45 and 31% respectively, while their contents only increased by 16 and 4% respectively. The K/Na ratio remained constant at the leaf functioning stage, and decreased at the leaf senescing stage. During leaf senescence, there was a marked decline in leaf mass (20%) and in leaf area (15%). During senescence, 60% of its N, 48% of its P and 46% of its K was transferred out of the senescing leaf.     

Rapid temperature acclimation of leaf respiration rates in Quercus alba and Quercus rubra

We conducted controlled (chamber) and natural (field) environment experiments on the acclimation of respiration in Quercus alba L. and Quercus rubra L. Three-year-old Louisiana, Indiana and Wisconsin populations of Q. alba were placed in growth chambers and exposed to alternating 5-week periods of cool (20 degrees C mean) and warm (26 degrees C mean) temperatures. We measured respiration rates on fully expanded leaves immediately before and approximately every 2 days after a switch in mean temperature. In a second chamber experiment, 3-year-old potted Q. alba seedlings were exposed to alternating warm (26 degrees C mean) and cool (16 degrees C mean) temperatures at 4-day intervals. Leaf dark respiration rates were measured on days 2, 3 and 4 after each change in temperature. In a third, field-based study, we measured leaf respiration rates in the same three sources of Q. alba and in Arkansas, Indiana and Minnesota sources of Q. rubra before and after a natural 16 degrees C change in mean daily ambient temperature. We observed rapid, significant and similar acclimation of leaf respiration rates in all populations of Q. alba and Q. rubra. Cold-origin populations were no more plastic in their acclimation responses than populations from warmer sites. All geographic sources showed lower respiration rates when measured at 24 degrees C after exposure to higher mean temperatures. Respiration rates decreased 13% with a 6 degrees C increase in mean temperature in the first chamber study, and almost 40% with a 10 degrees C increase in temperature in the second chamber study. Acclimation was rapid in all three studies, occurring after 2 days of exposure to changed temperature regimes. Acclimation was reversible when changes in ambient temperature occurred at 4-day intervals. Respiration response functions, ln(R) = ln(beta0) + beta1T, were statistically different among treatments (cool versus warm, first chamber study) and among sources in a pooled comparison. Pair-wise comparisons indicated statistically significant (P<0.05) differences in cool- versus warm-measured temperature/respiration response functions for Indiana and Wisconsin sources of Q. alba. Log-transformed base respiration rates were significantly lower during periods of higher mean temperatures. Indiana Q. alba showed a significantly higher beta1 when plants were grown at 16 degrees C than when grown at 26 degrees C. Acclimation in Q. alba was unaccompanied by changes in leaf nitrogen concentration, but was associated with a change in leaf total nonstructural carbohydrate concentration. Total nonstructural carbohydrate concentration was slightly, but statistically, lower (13.6 versus 12%, P<0.05) after a 10 degrees C increase in temperature.     

Coarse and fine root respiration in aspen (Populus tremuloides)

Coarse and fine root respiration rates of aspen (Populus tremuloides Michx.) were measured at 5, 15 and 25 degrees C. Coarse roots ranged from 0.65 to 4.45 cm in diameter, whereas fine roots were less than 5 mm in diameter. To discriminate between maintenance and growth respiration, root respiration rates were measured during aboveground growing periods and dormant periods. An additional measurement of coarse root respiration was made during spring leaf flush, to evaluate the effect of mobilization of resources for leaf expansion on root respiration. Fine roots respired at much higher rates than coarse roots, with a mean rate at 15 degrees C of 1290 micromol CO2 m-3 s-1 during the growing period, and 660 micromol CO2 m-3 s-1 during the dormant period. The temperature response of fine root respiration rate was nonlinear: mean Q10 was 3.90 for measurements made at 5-15 degrees C and 2.19 for measurements made at 15-25 degrees C. Coarse root respiration rates measured at 15 degrees C in late fall (dormant season) were higher (370 micromol CO2 m-3 s-1) than rates from roots collected at leaf flush and early summer (200 micromol CO2 m-3 s-1). The higher respiration rates in late fall, which were accompanied by decreased total nonstructural carbohydrate (TNC) concentrations, suggest that respiration rates in late fall included growth expenditures, reflecting recent radial growth. Neither bud flush nor shoot growth of the trees caused an increase in coarse root respiration or a decrease in TNC concentrations, suggesting a limited role of coarse roots as reserve storage organs for spring shoot growth, and a lack of synchronization between above- and belowground growth. Pooling the data from the coarse and fine roots showed a positive correlation between nitrogen concentration and respiration rate.     

Gas exchange and leaf aging in an evergreen oak: causes and consequences for leaf carbon balance and canopy respiration

Leaves of Mediterranean evergreens experience large variations in gas exchange rates over their life span due to aging and seasonally changing environmental conditions. Accounting for the changing respiratory physiology of leaves over time will help improve estimations of leaf and whole-plant carbon balances. Here we examined seasonal variations in light-saturated net CO(2) assimilation (A(max)), dark respiration (R(d)) and the proportional change in R(d) per 10 °C change in temperature (Q(10) of R(d)) in previous-year (PY) and current-year (CY) leaves of the broadleaved evergreen tree Quercus ilex L. A(max) and R(d) were lower in PY than in CY leaves. Differences in nitrogen between cohorts only partly explained such differences, and rates of A(max) and R(d) expressed per unit of leaf nitrogen were still significantly different between cohorts. The decline in A(max) in PY leaves did not result in the depletion of total non-structural carbohydrates, whose concentration was in fact higher in PY than CY leaves. Leaf-level carbon balance modeled from gas exchange data was positive at all ages. Q(10) of R(d) did not differ significantly between leaf cohorts; however, failure to account for distinct R(d) between cohorts misestimated canopy leaf respiration by 13% across dates when scaling up leaf measurements to the canopy. In conclusion, the decline in A(max) in old leaves that are close to or exceed their mean life span does not limit the availability of carbohydrates, which are probably needed to sustain new growth, as well as R(d) and nutrient resorption during senescence. Accounting for leaf age as a source of variation of R(d) improves the estimation of foliar respiratory carbon release at the stand scale.     

Responses of leaf respiration to temperature and leaf characteristics in three deciduous tree species vary with site water availability

We measured responses of leaf respiration to temperature and leaf characteristics in three deciduous tree species (Quercus rubra L., Quercus prinus L. and Acer rubrum L.) at two sites differing in water availability within a single catchment in the Black Rock Forest, New York. The response of respiration to temperature differed significantly among the species. Acer rubrum displayed the smallest increase in respiration with increasing temperature. Corresponding Q(10) values ranged from 1.5 in A. rubrum to 2.1 in Q. prinus. Dark respiration at ambient air temperatures, expressed on a leaf area basis (Rarea), did not differ significantly between species, but it was significantly lower (P < 0.01) in trees at the wetter (lower) site than at the drier (upper) site (Q. rubra: 0.8 versus 1.1 micromol m(-2) s(-1); Q. prinus: 0.95 versus 1.2 micromol m(-2) s(-1)). In contrast, when expressed on a leaf mass basis (R(mass)), respiration rates were significantly higher (P < 0.01) in A. rubrum (12.5-14.6 micromol CO(2) kg(-1) s(-1)) than in Q. rubra (8.6-9.9 micromol CO(2) kg(-1) s(-1)) and Q. prinus (9.2-10.6 micromol CO(2) kg(-1) s(-1)) at both the lower and upper sites. Respiration on a nitrogen basis (R(N)) displayed a similar response to R(mass). The consistency in R(mass) and R(N) between sites indicates a strong coupling between factors influencing respiration and those affecting leaf characteristics. Finally, the relationships between dark respiration and A(max) differed between sites. Trees at the upper site had higher rates of leaf respiration and lower A(max) than trees at the lower site. This shift in the balance of carbon gain and loss clearly limits carbon acquisition by trees at sites of low water availability, particularly in the case of A. rubrum.     

毛竹叶片衰老过程碳氮元素及灰分含量的季节动态

于2006年4月—2007年3月,对福建永春毛竹(Phyllostachys pubescens)成熟叶和老叶的C、N元素及灰分含量的季节动态及元素的内吸收率进行研究。结果表明:①毛竹成熟叶和老叶的C、N元素含量存在一定的季节变化,从成熟叶到老叶,C含量保持相对稳定,而N含量呈现下降趋势。②毛竹成熟叶、老叶灰分含量月变化趋势相似,毛竹成熟叶、老叶的灰分含量在秋季(10月)至翌年春季(3月)灰分含量较高,而春夏季相对较低;毛竹成熟叶的灰分含量在7.56%～15.91%之间,老叶的灰分含量在7.46%～16.67%,老叶灰分含量高于成熟叶(P=0.0199)。③毛竹叶片衰老过程N的内吸收率为36.68%。     

Photosynthetic acclimation of overstory Populus tremuloides and understory Acer saccharum to elevated atmospheric CO2 concentration: interactions with shade and soil nitrogen

We exposed Populus tremuloides Michx. and Acer saccharum Marsh. to a factorial combination of ambient and elevated atmospheric CO2 concentrations ([CO2]) and high-nitrogen (N) and low-N soil treatments in open-top chambers for 3 years. Our objective was to compare photosynthetic acclimation to elevated [CO2] between species of contrasting shade tolerance, and to determine if soil N or shading modify the acclimation response. Sun and shade leaf responses to elevated [CO2] and soil N were compared between upper and lower canopy leaves of P. tremuloides and between A. saccharum seedlings grown with and without shading by P. tremuloides. Both species had higher leaf N concentrations and photosynthetic rates in high-N soil than in low-N soil, and these characteristics were higher for P. tremuloides than for A. saccharum. Electron transport capacity (Jmax) and carboxylation capacity (Vcmax) generally decreased with atmospheric CO2 enrichment in all 3 years of the experiment, but there was no evidence that elevated [CO2] altered the relationship between them. On a leaf area basis, both Jmax and Vcmax acclimated to elevated [CO2] more strongly in shade leaves than in sun leaves of P. tremuloides. However, the apparent [CO2] x shade interaction was largely driven by differences in specific leaf area (m2 g-1) between sun and shade leaves. In A. saccharum, photosynthesis acclimated more strongly to elevated [CO2] in sun leaves than in shade leaves on both leaf area and mass bases. We conclude that trees rooted freely in the ground can exhibit photosynthetic acclimation to elevated [CO2], and the response may be modified by light environment. The hypothesis that photosynthesis acclimates more completely to elevated [CO2] in shade-tolerant species than in shade-intolerant species was not supported.     

Physiological significance of anthocyanins during autumnal leaf senescence

The light screen hypothesis states that foliar anthocyanins shade the photosynthetic apparatus from excess light. In this paper we extend the light screen hypothesis, postulating that plant species at risk of photoinhibitory conditions during autumnal leaf senescence often utilize anthocyanins to protect the photosynthetic apparatus during the period of nutrient resorption. When senescence-related photosynthetic instabilities are compounded by other environmental stresses, particularly low temperature, severe photoinhibition may result in reduced resorption of critical foliar nutrients, which can significantly affect plant fitness. There is evidence that environments where low and often freezing temperatures are common in autumn selectively favor the production of anthocyanins in senescing foliage. The stimuli for, and the timing and location of, autumnal anthocyanin production are all consistent with a photoprotective role for these pigments in senescing leaves. Furthermore, differences in nitrogen allocation strategies between early and late successional species appear to affect photosynthetic stability during leaf senescence, resulting in a reduced need for foliar autumnal anthocyanins in many early successional plants. The ecological and physiological evidence presented in this paper suggest that, for many deciduous species, the production of anthocyanins provides effective photoprotection during the critical period of foliar nutrient resorption.     

Foliar temperature-respiration response functions for broad-leaved tree species in the southern Appalachians

We measured leaf respiration in 18 eastern deciduous forest tree species to determine if there were differences in temperature-respiration response functions among species or among canopy positions. Leaf respiration rates were measured in situ and on detached branches for Acer pensylvanicum L., A. rubrum L., Betula spp. (B. alleghaniensis Britt. and B. lenta L.), Carya glabra (Mill.) Sweet, Cornus florida L., Fraxinus spp. (primarily F. americana L.), Liriodendron tulipifera L., Magnolia fraseri Walt., Nyssa sylvatica Marsh., Oxydendrum arboreum L., Platanus occidentalis L., Quercus alba L., Q. coccinea Muenchh., Q. prinus L., Q. rubra L., Rhododendron maximum L., Robinia psuedoacacia L., and Tilia americana L. in the southern Appalachian Mountains, USA. Dark respiration was measured on fully expanded leaves at 10, 15, 20, 25, and 30 degrees C with an infrared gas analyzer equipped with a temperature-controlled cuvette. Temperature-respiration response functions were fit for each leaf. There were significant differences in response functions among species and by canopy position within species. These differences were observed when respiration was expressed on a mass, nitrogen, or area basis. Cumulative nighttime leaf respiration was calculated and averaged over ten randomly selected nights for each leaf. Differences in mean cumulative nighttime respiration were statistically significant among canopy positions and species. We conclude that effects of canopy position and species on temperature-respiration response functions may need to be considered when making estimates of whole-tree or canopy respiration.     

檫木叶片秋季衰老时叶色、色素和营养元素的关系

【目的】从叶片衰老角度研究檫木叶片叶色、色素和营养元素的变化规律,为秋色叶观赏树种檫木的选育以及栽培提供理论依据。【方法】以栽植于同一环境条件下的3年生檫木为试验材料,从檫木叶片停止生长到脱落,分5个时期对叶片的叶色值、色素含量和营养元素含量进行观测和分析。【结果】观测前期与观测后期,檫木叶片叶色值、色素含量和营养元素含量存在极显著差异;叶片进入衰老阶段后,叶绿素含量和类胡萝卜素含量呈下降趋势,而花色素苷含量逐渐上升;N、P、K含量在叶片衰老阶段逐渐下降。由典型相关分析可知,叶色a*值与叶绿素含量具有显著负相关,与花色素苷含量呈显著正相关;花色素苷含量与N含量成反比,类胡萝卜素含量与P含量成正比;N元素再利用效率的载荷值符号与N含量载荷值的符号相反,而P元素再利用效率的载荷值符号与P含量载荷值的符号相同;檫木叶片衰老分为3个阶段,第1阶段从9月中下旬到10月上旬,为叶片衰老准备期;第2阶段从10月中下旬到11月上旬,为叶片缓慢衰老期;第3阶段从11月中下旬到叶片脱落,为叶片衰老末期。【结论】檫木叶色最佳观赏期是从10月中下旬到11月上旬的叶片缓慢衰老期;从叶片衰老准备期到叶片衰老末期,叶绿素和类胡萝卜素被分解,花色素苷合成;N、P、K 3种营养元素逐渐被转移,其中N含量越高,N元素再利用效率就越低;与之相反,P含量越高,P元素再利用效率就越高。     

Photosynthesis and carbon allocation of six boreal tree species grown in understory and open conditions

One-year-old seedlings of Abies balsamea (L.) Mill, Picea glauca (Moench) Voss, Pinus contorta Loudon, Betula papyrifera Marsh., Populus tremuloides Michx. and Populus balsamifera L. were transplanted in the spring, in pots, to the understory of a mixed P. tremuloides-P. balsamifera stand or to an adjacent open site. Growth and leaf characteristics were measured and photosynthetic light response curves determined in mid-August. Overall, the coniferous seedlings showed less photosynthetic plasticity in response to growth conditions than the deciduous species. Abies balsamea, P. glauca and B. papyrifera responded to the understory environment with higher leaf area ratios, and lower photosynthetic light saturation points and area-based leaf respiration relative to values for open-grown seedlings, while they matched or exceeded the height growth of open-grown seedlings. In contrast, seedlings of Pinus contorta, P. tremuloides and P. balsamifera displayed characteristics that were not conducive to survival in the understory. These characteristics included a high light saturation point and leaf dark respiration rate in P. contorta, and lower leaf area variables combined with higher carbon allocation to roots in P. tremuloides and P. balsamifera. By the second growing season, all seedlings of P. tremuloides and P. balsamifera growing in the understory had died.     

Vertical gradients in photosynthetic gas exchange characteristics and refixation of respired CO(2) within boreal forest canopies

We compared vertical gradients in leaf gas exchange, CO(2) concentrations, and refixation of respired CO(2) in stands of Populus tremuloides Michx., Pinus banksiana Lamb. and Picea mariana (Mill.) B.S.P. at the northern and southern boundaries of the central Canadian boreal forest. Midsummer gas exchange rates in Populus tremuloides were over twice those of the two conifer species, and Pinus banksiana rates were greater than Picea mariana rates. Gas exchange differences among the species were attributed to variation in leaf nitrogen concentration. Despite these differences, ratios of intercellular CO(2) to ambient CO(2) (c(i)/c(a)) were similar among species, indicating a common balance between photosynthesis and stomatal conductance in boreal trees. At night, CO(2) concentrations were high and vertically stratified within the canopy, with maximum concentrations near the soil surface. Daytime CO(2) gradients were reduced and concentrations throughout the canopy were similar to the CO(2) concentration in the well-mixed atmosphere above the canopy space. Photosynthesis had a diurnal pattern opposite to the CO(2) profile, with the highest rates of photosynthesis occurring when CO(2) concentrations and gradients were lowest. After accounting for this diurnal interaction, we determined that photosynthesizing leaves in the understory experienced greater daily CO(2) concentrations than leaves at the top of the canopy. These elevated CO(2) concentrations were the result of plant and soil respiration. We estimated that understory leaves in the Picea mariana and Pinus banksiana stands gained approximately 5 to 6% of their carbon from respired CO(2).     

Acclimation of shade-developed leaves on saplings exposed to late-season canopy gaps

We hypothesized that photoinhibition of shade-developed leaves of deciduous hardwood saplings would limit their ability to acclimate photosynthetically to increased irradiance, and we predicted that shade-tolerant sugar maple (Acer saccharum Marsh.) would be more susceptible to photoinhibition than intermediately shade-tolerant red oak (Quercus rubra L.). After four weeks in a canopy gap, photosynthetic rates of shade-developed leaves of both species had increased in response to the increase in irradiance, although final acclimation was more complete in red oak. However, photoinhibition occurred in both species, as indicated by short-term reductions in maximum rates of net photosynthesis and the quantum yield of oxygen evolution, and longer-term reductions in the efficiency of excitation energy capture by open photosystem II (PSII) reaction centers (dark-adapted F(v)/F(m)) and the quantum yield of PSII in the light (phi(PSII)). The magnitude and duration of this decrease were greater in sugar maple than in red oak, suggesting greater susceptibility to photoinhibition in sugar maple. Photoinhibition may have resulted from photodamage, but it may also have involved sustained rates of photoprotective energy dissipation (especially in red oak). Photosynthetic acclimation also appeared to be linked to an ability to increase leaf nitrogen content. Limited photosynthetic acclimation in shade-developed sugar maple leaves may reflect a trade-off between shade-tolerance and rapid acclimation to a canopy gap.     

Differences between coarse woody debris and leaf litter in the response of heterotrophic respiration to rainfall events

Heterotrophic respiration strongly influences carbon cycles at the ecosystem and global scales. We used an automated chamber system to measure the heterotrophic respiration of coarse woody debris (CWD) and leaf litter in a secondary broadleaved forest in southern Kyoto Prefecture. This system, which targeted only organic matter, could detect heterotrophic respiration responses to changes in environmental factors, especially rainfall events. The temporal trends and responses of respiration to environmental factors differed dramatically between CWD and leaf litter. CWD respiration showed a clear diurnal change corresponding to changes in CWD temperature and a clear decrease during rainfall events. Leaf litter respiration did not change clearly but increased at the beginning of rain events and returned to pre-rain rates when soil water content declined. The temporal patterns of the residuals between the observed respiration and baseline respiration, developed from the temperature?Cresponse curves under pre-rain conditions, differed between CWD and leaf litter respiration. The typical trend in CWD respiration response to rainfall events was a clear decrease and then gradual increase in the residuals after the event. The response of leaf litter respiration to wetting was an increase in the residuals during rainfall events and then a gradual decrease during drying. The difference in the responses of these respirations to wetting and drying processes are likely caused by differences in the physical characteristics of the CWD and the leaf litter layer. Measurements targeting only organic matter using an automated chamber system could detect the responses of heterotrophic respiration to environmental factors.     

Field measurements of root respiration indicate little to no seasonal temperature acclimation for sugar maple and red pine

Increasing global temperatures could potentially cause large increases in root respiration and associated soil CO2 efflux. However, if root respiration acclimates to higher temperatures, increases in soil CO2 efflux from this source would be much less. Throughout the snow-free season, we measured fine root respiration in the field at ambient soil temperature in a sugar maple (Acer saccharum Marsh.) forest and a red pine (Pinus resinosa Ait.) plantation in Michigan. The objectives were to determine effects of soil temperature, soil water availability and experimental N additions on root respiration rates, and to test for temperature acclimation in response to seasonal changes in soil temperature. Soil temperature and soil water availability were important predictors of root respiration and together explained 76% of the variation in root respiration rates in the red pine plantation and 71% of the variation in the sugar maple forest. Root N concentration explained an additional 6% of the variation in the sugar maple trees. Experimental N additions did not affect root respiration rates at either site. From April to November, root respiration rates measured in the field increased exponentially with increasing soil temperature. For sugar maple, long-term Q10 values calculated from the field data were slightly, but not significantly, less than short-term Q10 values determined for instantaneous temperature series conducted in the laboratory (2.4 versus 2.62.7). For red pine, long-term and short-term Q10 values were similar (3.0 versus 3.0). Sugar maple root respiration rates at constant reference temperatures of 6, 18 and 24 degrees C were measured in the laboratory at various times during the year when field soil temperatures varied from 0.4 to 16.8 degrees C. No relationship existed between ambient soil temperature just before sampling and root respiration rates at 6 and 18 degrees C (P = 0.37 and 0.86, respectively), and only a very weak relationship was found between ambient soil temperature and root respiration at 24 degrees C (P = 0.08, slope = 0.09). We conclude that root respiration in these species undergoes little, if any, acclimation to seasonal changes in soil temperature.     

Determination of lignin,holocellulose, and organic solvent extractives in fresh leaf,litterfall, and organic material on forest floor using near-infrared reflectance spectroscopy

We report the results of a study regarding the near-infrared reflectance spectra of various leaf stages from fresh to senescing, and to decomposing leaf. A broad absorbance feature increased in the region of 1100–1400nm with the advance of the leaf senescence and leaf decomposition. A decrease was seen in the region over 1440nm during the senescence and decomposition process. These differences of spectra showed the changes in constituents of leaf in terms of the degree of the senescence and decomposition. A comparison of multiple linear regression between the near-infrared reflectance spectra and proximate chemical analyses showed that near-infrared reflectance spectroscopy achieved a certain level of useful accuracy. We consider that near-infrared reflectance spectroscopy has the potential to predict the contents of carbon fractions in plant materials, and that this method can replace previous methods due to faster determination of carbon fractions, and its ability to significantly increase the number of samples that can be collected and measured.     

Seasonal dynamics,especially autumnal retranslocation,of nitrogen and phosphorus in foliage of dominant and suppressed trees of beech,Fagus sylvatica

Seasonal changes in the N and P content of foliage in a young forest of Fagus sylvatica were measured. Leaves from branches of the upper and lower crown of dominant trees and from suppressed trees were compared. Nutrient retranslocation rates during senescence differed considerably between trees. This variation appeared not to be related to any differences in environmental factors or tree vigour, and was probably genetically induced. In dominant trees the most efficient retranslocation of N was recorded in the upper crown and probably resulted from higher leaf temperatures and a longer senescent period in the sun leaves than in the shade leaves. Phosphorus retranslocation efficiency was higher in suppressed trees than in dominant ones, but no such tendency was observed with N. The most obvious difference between leaves at different crown levels concerned the time at which P translocation began; an outflow of P from leaves in the lower crown began in June, while in the upper crown this outflow did not begin until September/October.