Production efficiency of loblolly pine and sweetgum in response to four years of intensive management

We tested the hypothesis that productivity of intensively managed loblolly pine (Pinus taeda L.) and sweetgum (Liquidambar styraciflua L.) stands is dependent not only on leaf area, but also on foliar photosynthetic rate. Effects of irrigation (irrigation treatment), irrigation with a fertilizer solution (fertigation treatment), and fertigation + pest control (loblolly pine only; fertigation + pest control treatment) on leaf physiology and growth were compared with control plots during the third and fourth growing seasons. Complete weed control was maintained on all plots. Aboveground net primary productivity of loblolly pine and sweetgum increased from 16.3 to 40.5 Mg ha(-1) and from 4.2 to 23.9 Mg ha(-1), respectively, in response to the most intensive treatment. Relative to the control treatment, neither fertigation of sweetgum nor fertigation + pest control of loblolly pine had a significant or consistent influence on foliar N concentration, quantum yield, carboxylation efficiency, net photosynthesis, stomatal conductance, or production efficiency (increment in woody biomass per unit leaf area). Irrigation increased predawn leaf water potential and photosynthesis of loblolly pine, but it had no effect on production efficiency. Leaf area was the predominant determinant of maximum productivity in these rapidly growing plantations.     

Gavitropism of Pine Radicles in the Dark

Although gravitropism of maize (Zea mays L.) roots is dependent on light, it is not known if light affects the gravitropism of pine radicles. Therefore, seeds of slash pine (Pinus elliottii Englm.) and loblolly pine (Pinus taeda L.) were germinated under constant light or constant darkness. A gravitropic set-point angle (GSA) of 90° indicates the radicle is pointed horizontally while a GSA of 0° indicates the radicle is growing toward the center of the earth. After 20 days from sowing, the GSA was less than 10° in both light and darkness. Therefore, gravitropism of both pine species occurred in the dark. The presence of light initially stimulated gravitropism but this effect was ephemeral. After 25 days from sowing, there was no significant difference in radicle growth among light treatments, suggesting that darkness did not affect pine radicle gravitropism. However, light did increase germination of both species. Radicle length was slightly increased when seeds germinated in the dark.     

Evaluating changes in switchgrass physiology,biomass, and light-use efficiency under artificial shade to estimate yields if intercropped with Pinus taeda L.

There is growing interest in using switchgrass (Panicum virgatum L.) as a biofuel intercrop in forestry systems. However, there are limited data on the longevity of intercropped bioenergy crops, particularly with respect to light availability as the overstory tree canopy matures. Therefore, we conducted a greenhouse study to determine the effects of shading on switchgrass growth. Four treatments, each with different photosynthetically active radiation (PAR) levels, were investigated inside the greenhouse: control (no shade cloth, 49 % of full sunlight), low (under 36 % shade cloth), medium (under 52 % shade cloth), and heavy shade (under 78 % shade cloth). We determined the effect of shading from March to October 2011 on individually potted, multi-tillered switchgrass transplants cut to a stubble height of 10 cm. In the greenhouse, there was a reduction in tiller number, tiller height, gas exchange rates (photosynthesis and stomatal conductance), leaf area, above- and belowground biomass and light-use efficiency with increasing shade. Total (above- and belowground) biomass in the control measured 374 ± 22 compared to 9 ± 2 g pot^?1 under heavy shade (11 % of full sunlight). Corresponding light-use efficiencies were 3.7 ± 0.2 and 1.4 ± 0.2 g MJ^?1, respectively. We also compared PAR levels and associated aboveground switchgrass biomass from inside the greenhouse to PAR levels in the inter-row regions of a range of loblolly pine (Pinus taeda L.) stands from across the southeastern United States (U.S.) to estimate when light may limit the growth of intercropped species under field conditions. Results from the light environment of loblolly pine plantations in the field suggest that switchgrass biomass will be significantly reduced at a loblolly pine leaf area index between 1.95 and 2.25, which occurs on average between ages 6 and 8 years across the U.S. Southeast in intensively managed pine plantations. These leaf area indices correspond to a 60–65 % reduction in PAR from open sky.     

Effects of needle age, long-term temperature and CO(2) treatments on the photosynthesis of Scots pine

Naturally regenerated 20-25-year-old Scots pine (Pinus sylvestris L.) trees were grown in open-top chambers in the presence of an elevated temperature or CO(2) concentration, or both. The elevated temperature treatment was administered year-round for 3 years. The CO(2) treatment was applied between April 15 and September 15 for 2 years. The photosynthetic responses of 1- and 2-year-old needles to varying photon flux densities (0-1500 micro mol m(-2) s(-1)) and CO(2) concentrations (350, 700 and 1400 micro mol mol(-1)) during measurement were determined. The CO(2) treatment alone increased maximum photosynthetic rate and light-use efficiency, but decreased dark respiration rate, light compensation and light saturation regardless of needle age. In contrast, the temperature treatment decreased maximum photosynthetic rate and photosynthetic efficiency, but increased dark respiration rate, light compensation and light saturation. The aging of needles affected the photosynthetic performance of the shoots; values of all parameters except photosynthetic efficiency were less in 2- than in 1-year-old needles. The CO(2) treatment decreased and the temperature treatment enhanced the reduction in maximum photosynthesis due to needle aging.     

4种油松混交灌木树种的耐阴性研究

为探讨油松混交灌木树种的耐阴性,通过设置不同程度的遮阴处理,对柠条、紫穗槐、荆条、沙棘等4个辽西地区常见的油松混交灌木树种的叶绿素含量及光响应曲线参数进行了测定。研究结果表明,不同树种间叶绿素a/b值差异不显著,不同遮阴处理间差异极显著。4个灌木树种随着遮阴强度的增大,其叶片叶绿素a/b值均表现出波浪式的变化趋势,变化曲线的最低值出现在45%透光率处理时,全光状态下和5%透光率遮阴处理时,各树种的叶绿素a/b值基本相近。从4个灌木树种的光响应曲线参数数值上看,沙棘的各项指标数值均最高,其次是紫穗槐。荆条的光补偿点、表观量子效率、暗呼吸速率都是最低的,虽然其光能利用率较低,但是因为其呼吸速率低,所以进入积累干物质状态的速度较快,且其最大净光合速率较低,利用弱光的能力较强,是4个灌木树种中耐阴性最强的,其次是柠条,耐阴性最差的是沙棘。     

The effect of weed control and fertilization on survival and growth of four pine species in the Virginia Piedmont

The growth response of loblolly pine (Pinus taeda L.), shortleaf pine (Pinus echinata Mill.), Virginia pine (Pinus virginiana Mill.), and white pine (Pinus strobus L.) to weed control and fertilization in the Piedmont of Virginia was assessed. Four different silvicultural treatments were evaluated: (1) check (no treatment); (2) weed control; (3) fertilization; (4) weed control plus fertilization. The weed control treatment included a series of herbicide and mechanical treatments to eliminate competing hardwoods. The fertilizer treatments added N, P, K, and S. Survival and growth was measured annually through age 5. There were significant differences in survival and growth among species. Survival was greatest for loblolly pine, lower in shortleaf and Virginia pine, and lowest in white pine. Fertilization without controlling the competing hardwoods decreased survival in all planted pines due to the increased hardwood competition. Loblolly pine was tallest through the 5-year period, shortleaf and Virginia pine were shorter and white pine was shortest. Silvicultural treatments had no impact on tree height but significantly affected DBH. Weed control increased DBH while fertilization did not. When applied in combination with weed control, there was no additional increase in growth of the pines due to fertilization beyond that from weed control only. Fertilization stimulated the growth of the competing hardwoods which were significantly taller in the fertilized plots.     

Effects of nitrogen on leaf physiology and growth of different families of loblolly and slash pine

Leaf physiology and fractional dry weight allocation were examined in four open-pollinated families of loblolly pine (Pinus taeda L.) and slash pine (Pinus elliottii Englm. var. elliottii) in response to growth under low and high N supply for six months. Nitrogen greatly influenced dry weight allocation, total mass, leaf net photosynthesis and leaf conductance in seedlings of both species. Family variation in fine root allocation was observed under low but not high N treatment, but for the majority of physiological and growth traits, family variation was stable under varying N treatment. Family rankings based on juvenile height, diameter and biomass accretion were similar to rankings based on field performance at 22 years in slash pine but not loblolly pine. Lower leaf maintenance respiration rates were associated with families exhibiting the most rapid juvenile growth.     

Fertilization,weed control,and pine litter influence loblolly pine stem productivity and root development

Following site preparation, three cultural treatments and three open-pollinated loblolly pine (Pinus taeda L.) families were studied on a gently sloping Beauregard silt loam in central Louisiana. The treatments were: (1) fertilization (either broadcast application of 177 kg N and 151 kg P/ha or none); (2) herbicide application (either broadcast application of herbicides during the first through third growing seasons, and felling of a few, scattered volunteer hardwood trees greater than 2.5 cm dbh during the third growing season or none); and (3) litter application (either broadcast application of 37 Mg/ha (oven-dried weight) of pine straw over the plots to form a 10 to 15 cm layer or none). The subplot treatment was planting stock, where in November 1988, 28-week-old container-grown loblolly pine seedlings from three open-pollinated families were randomly assigned to planting locations. Through five growing seasons, fertilization and weed control with herbicides resulted in the greatest loblolly pine productivity, but the use of herbicides severely reduced other vegetation. Applying litter, which was less effective than herbicides as a weed control treatment, increased the presence of blackberry (Rubus spp.) when herbicides were not applied. Applying litter resulted in a decrease and fertilization resulted in an increase in the number and length of live lateral roots. Soil temperature was reduced by litter application. Treatment responses were not influenced by loblolly pine family.     

Changes in rates of photosynthesis and respiration during needle development of loblolly pine

Net photosynthetic rates of developing foliage and one-year-old foliage of loblolly pine (Pinus taeda L.) were measured under field conditions. In the subsequent year, net photosynthesis and dark respiration rates of current-year and one-year-old foliage were measured under controlled environmental conditions. Loblolly pine foliage grows slowly, reaching its final size 3.5 to 4 months after bud burst. Positive rates of net photosynthesis were recorded when the foliage was 13 and 18% of final length, in the controlled-environment and field study, respectively. However, because of high rates of dark respiration during the initial growth period, a positive diurnal carbon balance did not occur until foliage was about a third of final length (40 days after bud burst). Two months after bud burst, when foliage was about 55% of final length, its photosynthetic capacity exceeded that of one-year-old foliage. The highest rates of net photosynthesis were achieved when foliage was more than 90% fully expanded.     

Fine root biomass,distribution, and production in young pine-hardwood stands

Patterns of fine root biomass, production, and distribution were estimated for pure stands and mixtures of three-year-old loblolly pine (Pinus taeda L.) with red maple (Acer rubrum L.) or black locust (Robinia pseudoacacia L.) on the Virginia Piedmont to determine the role of fine roots in interference between pine and hardwood tree species. Estimates were based on amounts of live and dead fine roots separated from monthly core samples during the third growing season after planting. Live and dead fine root biomass and production varied by species, but mixtures of loblolly pine and black locust generally had greater fine root biomass and fine root production than pure stands or loblolly pine-red maple mixtures. Hardwood species had greater live fine root biomass per tree in mixtures with pine compared to pure stands. Greater live fine root biomass in pine-locust stands may be attributed to differential utilization of the soil volume by fine roots of these species. For all stands, approximately 50% of live five root biomass was located in the upper 10 cm of soil.     

Light quality treatments enhance somatic seedling production in three southern pine species

Embryogenic cultures of loblolly pine (Pinus taeda L.), slash pine (Pinus elliottii Engelm.), longleaf pine (Pinus palustris Mill.) and slash pine x longleaf pine hybrids were initiated from immature seeds on an initiation medium containing 13.57 microM 2,4-dichlorophenoxyacetic acid and 2.22 microM benzylaminopurine. Embryogenic cultures proliferated and somatic embryos developed, matured and germinated following a modified protocol and media originally developed for radiata pine (Pinus radiata D. Don.) somatic seedling production. A discrete, light-sensitive pre-germination stage and a later germination (radicle emergence) stage were identified by the differential response of somatic embryos to light of different wavelengths. Different light quality treatments were applied during the pre-germination and germination steps, using cool white fluorescent bulbs or light-emitting diodes (LEDs), or both. In general, red wavelengths provided by LEDs during these steps resulted in higher frequencies of somatic embryo germination (up to 64%) and conversion (up to 50%), longer tap roots and more first-order lateral roots than the standard cool white fluorescent treatments or treatment with blue wavelengths from LEDs. In addition, exposure to red light allowed germination of somatic embryos of some clones that failed to produce germinants under fluorescent light. Germination and conversion were further enhanced by sequential application of cool white fluorescent light and red light, resulting in up to 100% germination and conversion in one experiment. Longleaf pine somatic embryos were especially responsive to the light quality treatments, resulting in the first report of somatic seedling production for this species.     

日本落叶松×长白落叶松杂种光合性状的父、母本效应研究

以辽宁大孤家杂种实生采穗园中的采穗母株为研究材料,对3个不同母本与同一多父本混合花粉杂交组合家系及3个同一母本与不同单一父本杂交组合家系进行了光响应曲线及CO₂响应曲线的测定,以分析父母本对日本落叶松×长白落叶松杂种光合性状的影响。结果表明:不同母本与同一多父本混合花粉杂交组合间的表观量子效率、暗呼吸速率、羧化效率存在显著差异,光补偿点、CO₂补偿点存在极显著差异,其他指标差异不显著,表现出较强的母本效应;同一母本与不同父本杂交组合间只有暗呼吸速率差异极显著,其他指标差异不显著,表现出较弱的父本效应。在高光效亲本选择时,应特别重视母本对杂种的影响。     

Pine growth response to management of the subterranean clover understory

Management of subterranean clover (Trifolium subterraneum L.) understory grown with loblolly pine (Pinus taeda L.) and slash pine (Pinus elliottii Engelm.) resulted in differences in both clover yield and pine diameter. Loblolly and slash pines were planted into a subterranean clover pasture in 1984. Suppression of warm season herbaceous vegetation by applying herbicides or disking the site in late summer resulted in significantly greater subterranean clover production than on the control site where no additional understory management was applied. Pine species had no effects on clover yield. The N content of the pine foliage on the blocks managed with herbicide application or disking generally was significantly greater than the control from the 5th through 7th growing seasons (1988–1990). The dbh of the pine trees in the disked and herbicide treatments was greater than the control after the 7th growing season (1990).     

Temporal and spatial patterns of net photosynthesis in 12-year-old loblolly pine five growing seasons after thinning

Physiological parameters were measured under natural light conditions and needle orientation from towers and walkways erected in the canopy of a loblolly pine (Pinus taeda L.) plantation. Four silvicultural treatments were randomly assigned to the twelve plots in the fall of 1988. Plots were thinned to a density of 731 trees per hectare or left unthinned, at a density of 2990 trees per hectare. The plots were left unfertilized or fertilized with 744 kg/ha of diammonium triple superphosphate was applied. During the fifth growing season (1993) following thinning and fertilization, needle level physiology was not different with respect to the thinning treatment for fertilized or unfertilized plots. In contrast, upper crown levels within the fertilized and unfertilized plots had significantly higher light levels and photosynthetic rates than lower crown foliage. Light levels were greater in the thinned, fertilized plots than in the unthinned, fertilized plots. In contrast, no effect of thinning on canopy light levels was found in the unfertilized plots. Within crown variation in photosynthesis was strongly dependent on canopy light levels. A strong interaction of canopy level with thinning was apparent for net photosynthesis. Loblolly pine, being a shade intolerant species, showed only small physiological differences between needles from different parts of the crown. Because of the variability found in this study, more extensive sampling is needed to correctly describe the physiology of a forest canopy with adequate precision.     

红皮云杉幼树不同光环境下生理生态特征研究

为了探讨红皮云杉光舍特征与树木枝叶分布格局，生物量及其分配的关系，采用人工控制光照环境，在4个光照条件下进行红皮云杉生长试验，结果表明，红皮云杉幼树瞬时最大净光合速率以透光70％处理最大，10％处理最小，对数据进行方差分析，结果差异显著；并且净光合速率最大的处理其暗呼吸速率也最大，光补偿点和光饱和点也随透光率而变化，透光率小(10％)的处理光补偿点也小，说明云杉幼树对庇荫环境的适应；不同光照条件下幼树的形态特征也表现出明显差异，长期生活在相对较暗的光环境中，形成细而高的树干，侧枝数量增加、长度加长，侧枝角度增大；云杉小苗(9年生以前)以相对照度70％处理生物量最大，9年生以后以全光区生物量最大，说明云杉在9年生以前耐庇荫，9年生以后喜光。     

Effects of CO2 enrichment on the photosynthetic light response of sun and shade leaves of canopy sweetgum (Liquidambar styraciflua) in a forest ecosystem

To investigate whether sun and shade leaves respond differently to CO2 enrichment, we examined photosynthetic light response of sun and shade leaves in canopy sweetgum (Liquidambar styraciflua L.) trees growing at ambient and elevated (ambient + 200 microliters per liter) atmospheric CO2 in the Brookhaven National Laboratory/Duke University Free Air CO2 Enrichment (FACE) experiment. The sweetgum trees were naturally established in a 15-year-old forest dominated by loblolly pine (Pinus taeda L.). Measurements were made in early June and late August 1997 during the first full year of CO2 fumigation in the Duke Forest FACE experiment. Sun leaves had a 68% greater leaf mass per unit area, 63% more leaf N per unit leaf area, 27% more chlorophyll per unit leaf area and 77% greater light-saturated photosynthetic rates than shade leaves. Elevated CO2 strongly stimulated light-saturated photosynthetic rates of sun and shade leaves in June and August; however, the relative photosynthetic enhancement by elevated CO2 for sun leaves was more than double the relative enhancement of shade leaves. Elevated CO2 stimulated apparent quantum yield by 30%, but there was no interaction between CO2 and leaf position. Daytime leaf-level carbon gain extrapolated from photosynthetic light response curves indicated that sun leaves were enhanced 98% by elevated CO2, whereas shade leaves were enhanced 41%. Elevated CO2 did not significantly affect leaf N per unit area in sun or shade leaves during either measurement period. Thus, the greater CO2 enhancement of light-saturated photosynthesis in sun leaves than in shade leaves was probably a result of a greater amount of nitrogen per unit leaf area in sun leaves. A full understanding of the effects of increasing atmospheric CO2 concentrations on forest ecosystems must take account of the complex nature of the light environment through the canopy and how light interacts with CO2 to affect photosynthesis.     

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.     

Leaf traits in relation to crown development, light interception and growth of elite families of loblolly and slash pine

Crown architecture and size influence leaf area distribution within tree crowns and have large effects on the light environment in forest canopies. The use of selected genotypes in combination with silvicultural treatments that optimize site conditions in forest plantations provide both a challenge and an opportunity to study the biological and environmental determinants of forest growth. We investigated tree growth, crown development and leaf traits of two elite families of loblolly pine (Pinus taeda L.) and one family of slash pine (P. elliottii Mill.) at canopy closure. Two contrasting silvicultural treatments -- repeated fertilization and control of competing vegetation (MI treatment), and a single fertilization and control of competing vegetation treatment (C treatment) -- were applied at two experimental sites in the West Gulf Coastal Plain in Texas and Louisiana. At a common tree size (diameter at breast height), loblolly pine trees had longer and wider crowns, and at the plot-level, intercepted a greater fraction of photosynthetic photon flux than slash pine trees. Leaf-level, light-saturated assimilation rates (A(max)) and both mass- and area-based leaf nitrogen (N) decreased, and specific leaf area (SLA) increased with increasing canopy depth. Leaf-trait gradients were steeper in crowns of loblolly pine trees than of slash pine trees for SLA and leaf N, but not for A(max). There were no species differences in A(max), except in mass-based photosynthesis in upper crowns, but the effect of silvicultural treatment on A(max) differed between sites. Across all crown positions, A(max) was correlated with leaf N, but the relationship differed between sites and treatments. Observed patterns of variation in leaf properties within crowns reflected acclimation to developing light gradients in stands with closing canopies. Tree growth was not directly related to A(max), but there was a strong correlation between tree growth and plot-level light interception in both species. Growth efficiency was unaffected by silvicultural treatment. Thus, when coupled with leaf area and light interception at the crown and canopy levels, A(max) provides insight into family and silvicultural effects on tree growth.     

Vegetation response to intensity of herbaceous weed control in a newly planted loblolly pine plantation

Growth of loblolly pine (Pinus taeda L.) seedlings through three growing seasons after planting increased with intensity of herbaceous weed control using herbicides. Weed control had no effect on pine survival. Two years of complete herbaceous weed control (CHC, control throughout the first two growing seasons after planting) and operational herbaceous weed control (OHC, sulfometuron at 0.42 kg ai/ha at the beginning of the first growing season), resulted in lower biomass of weeds plus trees than with no herbaceous weed control (NHC) during the first growing season. Differences in total biomass during the first year were due to differences in biomass of herbaceous weeds. Total biomass on CHC and OHC plots was at least as great as NHC the second year, and greater by the third year, as pines assumed dominance as a result of increased growth from reduction of herbaceous weeds. The operational herbicide treatment had no significant impact on overall herbaceous weed biomass and cover, and little effect on species composition compared to no herbaceous weed control two and three growing seasons after treatment. The CHC treatment significantly reduced herbaceous weed biomass, cover and composition through three growing seasons.     

Acclimation of loblolly pine (Pinus taeda) seedlings to high temperatures

To determine the extent to which loblolly pine seedlings (Pinus taeda L.) acclimate to high temperatures, seedlings from three provenances-southeastern Texas (mean annual temperature 20.3 degrees C), southwestern Arkansas (mean annual temperature 16.2 degrees C) and Chesapeake, Maryland (mean annual temperature 12.8 degrees C)-were grown at constant temperatures of 25, 30, 35 or 40 degrees C in growth chambers. After two months, only 14% of the seedlings in the 40 degrees C treatment survived, so the treatment was dropped from the experiment. Provenance and family differences were not significant for most measured variables. Total biomass was similar in the 25 and 30 degrees C treatments, and less in the 35 degrees C treatment. Foliage biomass was higher, and root biomass lower, in the 30 degrees C treatment compared with the 25 degrees C treatment. Net photosynthesis and dark respiration of all seedlings were measured at 25, 30 and 35 degrees C. Both net photosynthesis and dark respiration exhibited acclimation to the temperature at which the seedlings were grown. For each temperature treatment, the highest rate of net photosynthesis was measured at the growth temperature. Dark respiration rates increased with increasing measurement temperature, but the basal rate of respiration, measured at 25 degrees C, decreased from 0.617 &mgr;mol m(-2) s(-1) in the 25 degrees C treatment to 0.348 &mgr;mol m(-2) s(-1) in the 35 degrees C treatment, resulting in less carbon loss in the higher temperature treatments than if the seedlings had not acclimated to the growth conditions. Temperature acclimation, particularly of dark respiration, may explain why total biomass of seedlings grown at 30 degrees C was similar to that of seedlings grown at 25 degrees C.