Understanding the dynamic evolution of hemicellulose during Pinus taeda L. growth.

Pinus taeda L. is a fast-growing softwood with significant commercial value. Understanding structural changes in hemicellulose during growth is essential to understanding the biosynthesis processes occurring in the cell walls of this tree. In this study, alkaline extraction is applied to isolate hemicellulose from Pinus taeda L. stem segments of different ages (1, 2, 3, and 4 years old). The results show that the extracted hemicellulose is mainly comprised of O-acetylgalactoglucomannan (GGM) and 4-O-methylglucuronoarabinoxylan (GAX), with the molecular weights and ratios (i.e., GGM:GAX) of GGM and GAX increasing alongside Pinus taeda L. age. Mature Pinus taeda L. hemicellulose is mainly composed of GGM, and the ratio of (mannose:glucose) in the GGM main chain gradually increases from 2.45 to 3.60 with growth, while the galactose substitution of GGM decreases gradually from 21.36% to 14.65%. The acetylation of GGM gradually increases from 0.33 to 0.45 with the acetyl groups mainly substituting into the O-3 position in the mannan. Furthermore, the contents of arabinose and glucuronic acid in GAX gradually decrease with growth. This study can provide useful information to the research in genetic breeding and high-value utilization of Pinus taeda L.

Genome-wide identification and characterization of the AP2/ERF gene family in loblolly pine (Pinus taeda L.).

The loblolly pine (Pinus taeda L.) is one of the most profitable forest species worldwide owing to its quick growth, high wood yields, and strong adaptability. The AP2/ERF gene family plays a widespread role in the physiological processes of plant defense responses and the biosynthesis of metabolites. Nevertheless, there are no reports on this gene family in loblolly pine (P. taeda). In this study, a total of 303 members of the AP2/ERF gene family were identified. Through multiple sequence alignment and phylogenetic analysis, they were classified into four subfamilies, including AP2 (34), RAV (17), ERF (251), and Soloist (1). An analysis of the conservation domains, conserved motifs, and gene structure revealed that every PtAP2/ERF transcription factor (TF) had at least one AP2 domain. While evolutionary conservation was displayed within the same subfamilies, the distribution of conserved domains, conserved motifs, and gene architectures varied between subfamilies. Cis-element analysis revealed abundant light-responsive elements, phytohormone-responsive elements, and stress-responsive elements in the promoter of the PtAP2/ERF genes. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses of potential target genes showed that the AP2/ERF gene family might play a critical role in plant growth and development, the response to environmental stresses, and metabolite biosynthesis. Utilizing quantitative real-time PCR (qRT-PCR), we examined the expression patterns of 10 randomly selected genes from Group IX after 6 h of treatments with mechanical injury, ethephon (Eth), and methyl jasmonate (MeJA). The AP2/ERF gene family in the loblolly pine was systematically analyzed for the first time in this study, offering a theoretical basis for exploring the functions and applications of AP2/ERF genes.

Possible mechanisms for the generation of phenyl glycoside-type lignin-carbohydrate linkages in lignification with monolignol glucosides.

The existence and formation of covalent lignin-carbohydrate (LC) linkages in plant cell walls has long been a matter of debate in terms of their roles in cell wall development and biomass use. Of the various putative LC linkages proposed to date, evidence of the native existence and formation mechanism of phenyl glycoside (PG)-type LC linkages in planta is particularly scarce. The present study aimed to explore previously overlooked mechanisms for the formation of PG-type LC linkages through the incorporation of monolignol glucosides, which are possible lignin precursors, into lignin polymers during lignification. Peroxidase-catalyzed lignin polymerization of coniferyl alcohol in the presence of coniferin and syringin in vitro resulted in the generation of PG-type LC linkages in synthetic lignin polymers, possibly via nucleophilic addition onto quinone methide (QM) intermediates formed during polymerization. Biomimetic lignin polymerization of coniferin via the ß-glucosidase/peroxidase system also resulted in the generation of PG-type as well as alkyl glycoside-type LC linkages. This occurred via non-enzymatic QM-involving reactions and also via enzymatic transglycosylations involving ß-glucosidase, which was demonstrated by in-depth structural analysis of the synthetic lignins by two-dimensional NMR. We collected heteronuclear single-quantum coherence (HSQC) NMR for native cell wall fractions prepared from pine (Pinus taeda), eucalyptus (Eucalyptus camaldulensis), acacia (Acacia mangium), poplar (Populus × eurarnericana) and bamboo (Phyllostachys edulis) wood samples, which exhibited correlations, albeit at low levels, that were well matched with those of the PG-type LC linkages in synthetic lignins incorporating monolignol glucosides. Overall, our results provide a molecular basis for feasible mechanisms for the generation of PG-type LC linkages from monolignol glucosides and further substantiates their existence in planta.

Assessment of flux through oleoresin biosynthesis in epithelial cells of loblolly pine resin ducts.

The shoot system of pines contains abundant resin ducts, which harbor oleoresins that play important roles in constitutive and inducible defenses. In a pilot study, we assessed the chemical diversity of oleoresins obtained from mature tissues of loblolly pine trees (Pinus taeda L.). Building on these data sets, we designed experiments to assess oleoresin biosynthesis in needles of 2-year-old saplings. Comparative transcriptome analyses of single cell types indicated that genes involved in the biosynthesis of oleoresins are significantly enriched in isolated epithelial cells of resin ducts, compared with those expressed in mesophyll cells. Simulations using newly developed genome-scale models of epithelial and mesophyll cells, which incorporate our data on oleoresin yield and composition as well as gene expression patterns, predicted that heterotrophic metabolism in epithelial cells involves enhanced levels of oxidative phosphorylation and fermentation (providing redox and energy equivalents). Furthermore, flux was predicted to be more evenly distributed across the metabolic network of mesophyll cells, which, in contrast to epithelial cells, do not synthesize high levels of specialized metabolites. Our findings provide novel insights into the remarkable specialization of metabolism in epithelial cells.

Exploring the genetic basis of gene transcript abundance and metabolite levels in loblolly pine (Pinus taeda L.) using association mapping and network construction.

BACKGROUND: Identifying genetic variations that shape important complex traits is fundamental to the genetic improvement of important forest tree species, such as loblolly pine (Pinus taeda L.), which is one of the most commonly planted forest tree species in the southern U.S. Gene transcripts and metabolites are important regulatory intermediates that link genetic variations to higher-order complex traits such as wood development and drought response. A few prior studies have associated intermediate phenotypes including mRNA expression and metabolite levels with a limited number of molecular markers, but the identification of genetic variations that regulate intermediate phenotypes needs further investigation. RESULTS: We identified 1841 single nucleotide polymorphisms (SNPs) associated with 191 gene expression mRNA phenotypes and 524 SNPs associated with 53 metabolite level phenotypes using 2.8 million exome-derived SNPs. The identified SNPs reside in genes with a wide variety of functions. We further integrated the identified SNPs and the associated expressed genes and metabolites into networks. We described the SNP-SNP interactions that significantly impacted the gene transcript abundance and metabolite level in the networks. Key loci and genes in the wood development and drought response networks were identified and analyzed. CONCLUSIONS: This work provides new candidate genes for research on the genetic basis of gene expression and metabolism linked to wood development and drought response in loblolly pine and highlights the efficiency of using association-mapping-based networks to discover candidate genes with important roles in complex biological processes.

Evapotranspiration and water yield of a pine-broadleaf forest are not altered by long-term atmospheric [CO2 ] enrichment under native or enhanced soil fertility.

Changes in evapotranspiration (ET) from terrestrial ecosystems affect their water yield (WY), with considerable ecological and economic consequences. Increases in surface runoff observed over the past century have been attributed to increasing atmospheric CO2 concentrations resulting in reduced ET by terrestrial ecosystems. Here, we evaluate the water balance of a Pinus taeda (L.) forest with a broadleaf component that was exposed to atmospheric [CO2 ] enrichment (ECO2 ; +200 ppm) for over 17 years and fertilization for 6 years, monitored with hundreds of environmental and sap flux sensors on a half-hourly basis. These measurements were synthesized using a one-dimensional Richard's equation model to evaluate treatment differences in transpiration (T), evaporation (E), ET, and WY. We found that ECO2 did not create significant differences in stand T, ET, or WY under either native or enhanced soil fertility, despite a 20% and 13% increase in leaf area index, respectively. While T, ET, and WY responded to fertilization, this response was weak (<3% of mean annual precipitation). Likewise, while E responded to ECO2 in the first 7 years of the study, this effect was of negligible magnitude (<1% mean annual precipitation). Given the global range of conifers similar to P. taeda, our results imply that recent observations of increased global streamflow cannot be attributed to decreases in ET across all ecosystems, demonstrating a great need for model-data synthesis activities to incorporate our current understanding of terrestrial vegetation in global water cycle models.

Saltational evolution of the heterotrimeric G protein signaling mechanisms in the plant kingdom.

Signaling proteins evolved diverse interactions to provide specificity for distinct stimuli. Signaling complexity in the G protein (heterotrimeric guanosine triphosphate-binding protein) network was achieved in animals through subunit duplication and incremental evolution. By combining comprehensive and quantitative phenotypic profiles of Arabidopsis thaliana with protein evolution informatics, we found that plant heterotrimeric G protein machinery evolved by a saltational (jumping) process. Sequence similarity scores mapped onto tertiary structures, and biochemical validation showed that the extra-large Gα (XLG) subunit evolved extensively in the charophycean algae (an aquatic green plant) by gene duplication and gene fusion. In terrestrial plants, further evolution uncoupled XLG from its negative regulator, regulator of G protein signaling, but preserved an α-helix region that enables interaction with its partner Gßγ. The ancestral gene evolved slowly due to the molecular constraints imposed by the need for the protein to maintain interactions with various partners, whereas the genes encoding XLG proteins evolved rapidly to produce three highly divergent members. Analysis of A. thaliana mutants indicated that these Gα and XLG proteins all function with Gßγ and evolved to operate both independently and cooperatively. The XLG-Gßγ machinery specialized in environmental stress responses, whereas the canonical Gα-Gßγ retained developmental roles. Some developmental processes, such as shoot development, involve both Gα and XLG acting cooperatively or antagonistically. These extensive and rapid evolutionary changes in XLG structure compared to those of the canonical Gα subunit contrast with the accepted notion of how pathway diversification occurs through gene duplication with subsequent incremental coevolution of residues among interacting proteins.

Eucalyptus urograndis and Pinus taeda enhance removal of chlorobenzene and benzene in sand culture: A greenhouse study.

Contamination of soils and groundwater by chlorobenzene and benzene is a common problem at industrial sites worldwide. Since chemical remediation techniques are rarely completely effective, remnants of these contaminants often persist at levels that can still influence ecosystem health. We evaluated the potential of Pinus taeda and Eucalyptus urograndis to accelerate the removal of these compounds from sand/water systems using a completely randomized block greenhouse experiment with a no-plant control. At 2-day intervals, we added a solution containing both chlorobenzene and benzene with the same concentration of 50 mg L(-1) (25 mg pot(-1)), and we monitored leachate concentrations daily. The planted treatments showed greater decrease of contaminants over time. In the absence of plants, the contaminant mass decreased 50-60% during each 2-day cycle; whereas, in the planted treatments the contaminant mass decreased 91-98%. At the end of the experiment the plant roots, leaves, and the sand-substrate each contained less than 1 mg kg(-1) of contaminants, which is ∼1% of the total contaminant mass added. In addition, we observed no tree mortality even at concentrations exceeding the aqueous solubility limit of both compounds. Our results suggest both trees are good candidates for remediating chlorobenzene and benzene in soils and groundwater.

Canopy level emissions of 2-methyl-3-buten-2-ol, monoterpenes, and sesquiterpenes from an experimental Pinus taeda plantation.

Emissions of Biogenic Volatile Organic Compounds (BVOCs) observed during 2007 from an experimental Pinus taeda plantation in Central North Carolina are compared with model estimates from the Model of Emissions of Gases and Aerosols from Nature (MEGAN) version 2.1. Relaxed eddy accumulation (REA) estimates of 2-methyl-3-buten-2-ol (MBO) fluxes are a factor of 3-4 higher than MEGAN estimates. MEGAN monoterpene emission estimates were a factor of approximately two higher than REA flux measurements. MEGAN ß-caryophyllene emission estimates were within 60% of growing season REA flux estimates but were several times higher than REA fluxes during cooler, dormant season periods. The sum of other sesquiterpene emissions estimated by MEGAN was several times higher than REA estimates throughout the year. Model components are examined to understand these discrepancies. Measured summertime leaf area index (LAI) (and therefore foliar biomass) is a factor of two higher than assumed in MEGAN for the P. taeda default. Increasing the canopy mean MBO emission factor from 0.35 to 1.0mgm(-2)h(-1) also reduces MEGAN vs. REA flux differences. This increase is within current MBO emission factor uncertainties. The algorithm within MEGAN which adjusts isoprene emission estimates as a function of the temperature and light of the previous 24h seems also to improve the seasonal MEGAN MBO correlation with REA fluxes. Including the effects of the previous 240h, however, seems to degrade temporal model correlation with fluxes. Monoterpene and sesquiterpene composition data from the REA are compared with MEGAN2.1 estimates and also branch enclosure and needle extract data collected at this site. To our knowledge, the flux data presented here are the first reported for MBO and sesquiterpenes from a P. taeda ecosystem.

Effects of tropospheric ozone on loblolly pine seedlings inoculated with root infecting ophiostomatoid fungi.

Seedlings from four loblolly pine (Pinus taeda L.) families were exposed in open-top chambers to charcoal-filtered air (CF), non-filtered air (NF) or air amended with ozone to 2 times ambient (2×). Two of the families used were selected for their tolerance to fungi associated with Southern Pine Decline while two were selected for their susceptibility. Seedlings were treated with five inoculation treatments: no wound (NW), wound only (W), wound + media (WM), Grosmannia huntii (GH) and Leptographium terebrantis (LT). After 118 days of exposure (AOT40 = 31 ppm-hr(-1) for 2× ozone) seedling volume, dry matter, chlorophyll content, water potential and lesions were measured and analyzed using ANOVA procedures. Our results indicate that seedlings selected for their susceptibility to root infecting ophiostomatoid fungi were also more sensitive to ozone. Overall lesion length was greater on seedlings exposed to elevated ozone concentrations but was not specific to either root infecting ophiostomatoid fungi.

Discovering candidate genes that regulate resin canal number in Pinus taeda stems by integrating genetic analysis across environments, ages, and populations.

Genetically improving constitutive resin canal development in Pinus stems may enhance the capacity to synthesize terpenes for bark beetle resistance, chemical feedstocks, and biofuels. To discover genes that potentially regulate axial resin canal number (RCN), single nucleotide polymorphisms (SNPs) in 4027 genes were tested for association with RCN in two growth rings and three environments in a complex pedigree of 520 Pinus taeda individuals (CCLONES). The map locations of associated genes were compared with RCN quantitative trait loci (QTLs) in a (P. taeda × Pinus elliottii) × P. elliottii pseudo-backcross of 345 full-sibs (BC1). Resin canal number was heritable (h(2) ˜ 0.12-0.21) and positively genetically correlated with xylem growth (rg ˜ 0.32-0.72) and oleoresin flow (rg ˜ 0.15-0.51). Sixteen well-supported candidate regulators of RCN were discovered in CCLONES, including genes associated across sites and ages, unidirectionally associated with oleoresin flow and xylem growth, and mapped to RCN QTLs in BC1. Breeding is predicted to increase RCN 11% in one generation and could be accelerated with genomic selection at accuracies of 0.45-0.52 across environments. There is significant genetic variation for RCN in loblolly pine, which can be exploited in breeding for elevated terpene content.

Effect of liquefaction temperature on hydroxyl groups of bio-oil from loblolly pine (Pinus taeda).

Loblolly pine was liquefied with ethylene glycol at 100, 150, 200 and 250 °C in order to analyze the effect of liquefaction temperature on hydroxyl groups of bio-oil, and to determine the source and variation of hydroxyl groups. The optimum temperature was found to be 150-200 °C. Hydroxyl number (OHN) of the bio-oil was ranged from 632 to 1430 mg KOH/g. GC-MS analysis showed that 70-90% of OHN was generated from unreacted EG. (31)P NMR analysis showed that the majority of hydroxyl groups were aliphatic, and none of the bio-oil exhibited any detectable hydroxyl groups from phenolic sources. Finally, it was found that all bio-oils were stable in terms of OHN for 2 months when stored at -10 °C.

Interacting effects of insects and flooding on wood decomposition.

Saproxylic arthropods are thought to play an important role in wood decomposition but very few efforts have been made to quantify their contributions to the process and the factors controlling their activities are not well understood. In the current study, mesh exclusion bags were used to quantify how arthropods affect loblolly pine (Pinus taeda L.) decomposition rates in both seasonally flooded and unflooded forests over a 31-month period in the southeastern United States. Wood specific gravity (based on initial wood volume) was significantly lower in bolts placed in unflooded forests and for those unprotected from insects. Approximately 20.5% and 13.7% of specific gravity loss after 31 months was attributable to insect activity in flooded and unflooded forests, respectively. Importantly, minimal between-treatment differences in water content and the results from a novel test carried out separately suggest the mesh bags had no significant impact on wood mass loss beyond the exclusion of insects. Subterranean termites (Isoptera: Rhinotermitidae: Reticulitermes spp.) were 5-6 times more active below-ground in unflooded forests compared to flooded forests based on wooden monitoring stakes. They were also slightly more active above-ground in unflooded forests but these differences were not statistically significant. Similarly, seasonal flooding had no detectable effect on above-ground beetle (Coleoptera) richness or abundance. Although seasonal flooding strongly reduced Reticulitermes activity below-ground, it can be concluded from an insignificant interaction between forest type and exclusion treatment that reduced above-ground decomposition rates in seasonally flooded forests were due largely to suppressed microbial activity at those locations. The findings from this study indicate that southeastern U.S. arthropod communities accelerate above-ground wood decomposition significantly and to a similar extent in both flooded and unflooded forests. Seasonal flooding has the potential to substantially reduce the contributions of these organisms to wood decomposition below-ground, however.

Expression patterns of conserved microRNAs in the male gametophyte of loblolly pine (Pinus taeda).

MicroRNAs (miRNAs) are small RNAs that regulate genes involved in various aspects of plant development, but their presence and expression patterns in the male gametophytes of gymnosperms have not yet been established. Therefore, this study identified and compared the expression patterns of conserved miRNAs from two stages of the male gametophyte of loblolly pine (Pinus taeda), which are the mature (ungerminated) and germinated pollen. Microarray was used to identify conserved miRNAs that varied in expression between these two stages of the loblolly pine male gametophyte. Forty-seven conserved miRNAs showed significantly different expression levels between mature and germinated loblolly pine pollen. In particular, miRNAs representing 14 and 8 families were up- and down-regulated in germinated loblolly pine pollen, respectively. qRT-PCR was used to validate their expression patterns using representative miRNAs. Target genes and proteins were identified using psRNATarget program. Predicted targets of the 22 miRNA families belong mostly to classes of genes involved in defense/stress response, metabolism, regulation, and signaling. qRT-PCR was also used to validate the expression patterns of representative target genes. This study shows that conserved miRNAs are expressed in mature and germinated loblolly pine pollen. Many of these miRNAs are differentially expressed, which indicates that the two stages of the male gametophyte examined are regulated at the miRNA level. This study also expands our knowledge of the male gametophytes of seed plants by providing insights on some similarities and differences in the types and expression patterns of conserved miRNAs between loblolly pine with those of rice and Arabidopsis.

On-site enzymes produced from Trichoderma reesei RUT-C30 and Aspergillus saccharolyticus for hydrolysis of wet exploded corn stover and loblolly pine.

Cellulase production by two filamentous fungi Trichoderma reesei RUT-C30 and novel fungal strain, Aspergillus saccharolyticus on pretreated corn stover was investigated. Cellulase production was followed by the hydrolysis of two feedstocks, wet-exploded corn stover (WECS) and wet-exploded loblolly pine (WELP) by on-site produced enzyme cocktails containing cellulase from T. reesei RUT-C30 and ß-glucosidase from A. saccharolyticus. The sugar yields using the on-site enzyme cocktails were compared with commercial enzymes preparations, Celluclast 1.5L and Novozym 188 at two substrate concentrations, 5% and 10% (w/w) and enzyme loading at 5 and 15 FPU/g glucan for WECS and WELP. The highest sugar yields were obtained at 5% (w/w) substrate concentration and 15 FPU/g glucan for both feedstocks. Glucose yields of 81% and 88% were obtained from on-site and commercial enzymes, respectively using WECS as feed stock. The sugar yields were 55% and 58% for WELP samples hydrolyzed with on-site and commercial enzymes, respectively.

SO2 -catalyzed steam explosion: the effects of different severity on digestibility, accessibility, and crystallinity of lignocellulosic biomass.

Lignocellulosic biomass is the most promising feedstock for biofuels production. To enhance the efficiency of enzymatic hydrolysis, lignocellulosics needs to be pretreated to lower their recalcitrance. SO(2) -catalyzed steam explosion is an efficient and relatively cost-efficient pretreatment method for softwood. This work investigates the effects of steam explosion severity on the digestibility, accessibility, and crystallinity of Loblolly pine. Higher severity was found to increase the accessibility of the feedstock while also promoting nonselective degradation of carbohydrates. The adsorption behavior of Celluclast® enzymes on steam-exploded Loblolly pine (SELP) can be described by a Langmuir isotherm. Cellulose crystallinity was found to first increase and then decrease with increasing pretreatment severity. A linear relationship between initial hydrolysis rates and crystallinity index (CrI) of pretreated Loblolly pine was found; moreover, a strong correlation between X-ray diffraction intensities and initial rates was confirmed. The findings demonstrate the significance of CrI in enzymatic hydrolysis of pretreated lignocellulosic biomass.

On the complementary relationship between marginal nitrogen and water-use efficiencies among Pinus taeda leaves grown under ambient and CO2-enriched environments.

BACKGROUND AND AIMS: Water and nitrogen (N) are two limiting resources for biomass production of terrestrial vegetation. Water losses in transpiration (E) can be decreased by reducing leaf stomatal conductance (g(s)) at the expense of lowering CO(2) uptake (A), resulting in increased water-use efficiency. However, with more N available, higher allocation of N to photosynthetic proteins improves A so that N-use efficiency is reduced when g(s) declines. Hence, a trade-off is expected between these two resource-use efficiencies. In this study it is hypothesized that when foliar concentration (N) varies on time scales much longer than g(s), an explicit complementary relationship between the marginal water- and N-use efficiency emerges. Furthermore, a shift in this relationship is anticipated with increasing atmospheric CO(2) concentration (c(a)). METHODS: Optimization theory is employed to quantify interactions between resource-use efficiencies under elevated c(a) and soil N amendments. The analyses are based on marginal water- and N-use efficiencies, λ = (∂A/∂g(s))/(∂E/∂g(s)) and η = ∂A/∂N, respectively. The relationship between the two efficiencies and related variation in intercellular CO(2) concentration (c(i)) were examined using A/c(i) curves and foliar N measured on Pinus taeda needles collected at various canopy locations at the Duke Forest Free Air CO(2) Enrichment experiment (North Carolina, USA). KEY RESULTS: Optimality theory allowed the definition of a novel, explicit relationship between two intrinsic leaf-scale properties where η is complementary to the square-root of λ. The data support the model predictions that elevated c(a) increased η and λ, and at given c(a) and needle age-class, the two quantities varied among needles in an approximately complementary manner. CONCLUSIONS: The derived analytical expressions can be employed in scaling-up carbon, water and N fluxes from leaf to ecosystem, but also to derive transpiration estimates from those of η, and assist in predicting how increasing c(a) influences ecosystem water use.

Fungal communities influence root exudation rates in pine seedlings.

Root exudates are hypothesized to play a central role in belowground food webs, nutrient turnover, and soil C dynamics in forests, but little is known about the extent to which root-associated microbial communities influence exudation rates in trees. We used a novel experimental technique to inoculate loblolly pine (Pinus taeda L.) seedlings with indigenous forest fungi to examine how diverse fungal communities influence exudation. Surface-sterilized seeds were sown in intact, unsieved soil cores for 14 weeks to promote root colonization by fungi. After 14 weeks, we transferred seedlings and root-associated fungi into cuvettes and measured exudate accumulation in trap solutions. Both the abundance and identity of root-associated fungi influenced exudation. Exudation rates were greatest in root systems least colonized by ectomycorrhizal (ECM) fungi and most colonized by putative pathogenic and saprotrophic fungi. However, the ECM community composition was not a strong determinant of exudation rates. These results suggest that environmental conditions that influence the degree to which tree roots are colonized by pathogenic and saprotrophic vs. mutualistic fungi are likely to mediate fluxes of labile C in forest soils, with consequences for soil biogeochemistry and ecosystem processes.

Intra-annual nutrient flux in Pinus taeda.

Intra-annual nutrient (nitrogen, phosphorus, potassium, calcium and magnesium) flux was quantified for Pinus taeda L. at a nutrient-poor, well-drained sandy site in Scotland County, NC, USA where a 2 × 2 factorial of irrigation and nutrition was applied in four replications in a 10-year-old stand with 1200 stems ha(-1). Treatments were applied with the goal of providing optimum nutrition (no nutritional deficiencies) and water availability. Component (foliage, branch, stem and root) nutrient content was estimated monthly for 2 years using nutrient concentration and phenology assessments combined with destructive harvests. Positive flux values indicated nutrient accumulation in the trees while negative values indicated nutrient loss from the trees. Fertilization significantly increased nitrogen, phosphorus, potassium, calcium and magnesium flux 140%, on average, over non-fertilized. Irrigation significantly increased calcium flux 28% while there was no significant irrigation effect on nitrogen, phosphorus, potassium or magnesium. Maximum nutrient fluxes (kg ha(-1) day(-1)) for non-fertilized and fertilized stands were 0.36 and 1.05 for nitrogen, 0.042 and 0.095 for phosphorus, 0.13 and 0.51 for potassium, 0.27 and 0.42 for calcium, and 0.04 and 0.12 for magnesium, respectively. Maximum flux was coincident with ephemeral tissue (foliage and fine root) development and likely would be higher in stands with more foliage than those observed in this study (projected leaf area indices were 1.5 and 3.0 for the non-fertilized and fertilized stands). Minimum nutrient fluxes (kg ha(-1) day(-1)) for non-fertilized and fertilized stands were -0.18 and -0.42 for nitrogen, -0.029 and -0.070 for phosphorus, -0.05 and -0.18 for potassium, -0.04 and -0.05 for calcium, and -0.02 and -0.03 for magnesium, respectively. Minimum fluxes were typically observed in the dormant season and were linked to foliage senescence and branch death. Foliage and branch component nutrient contents were out of phase for nitrogen, phosphorus, potassium and magnesium, indicating nutrient retranslocation and storage in branches prior to foliage development and after foliage senescence. In contrast to current operational fertilizer programs which often target winter application these data suggest the best application times would be during foliage development.

Timing and magnitude of C partitioning through a young loblolly pine (Pinus taeda L.) stand using 13C labeling and shade treatments.

The dynamics of rapid changes in carbon (C) partitioning within forest ecosystems are not well understood, which limits improvement of mechanistic models of C cycling. Our objective was to inform model processes by describing relationships between C partitioning and accessible environmental or physiological measurements, with a special emphasis on short-term C flux through a forest ecosystem. We exposed eight 7-year-old loblolly pine (Pinus taeda L.) trees to air enriched with (13)CO(2) and then implemented adjacent light shade (LS) and heavy shade (HS) treatments in order to manipulate C uptake and flux. The impacts of shading on photosynthesis, plant water potential, sap flow, basal area growth, root growth and soil CO(2) efflux rate (CER) were assessed for each tree over a 3-week period. The progression of the (13)C label was concurrently tracked from the atmosphere through foliage, phloem, roots and surface soil CO(2) efflux. The HS treatment significantly reduced C uptake, sap flow, stem growth and fine root standing crop, and resulted in greater residual soil water content to 1 m depth. Soil CER was strongly correlated with sap flow on the previous day, but not the current day, with no apparent treatment effect on the relationship. Although there were apparent reductions in new C flux belowground, the HS treatment did not noticeably reduce the magnitude of belowground autotrophic and heterotrophic respiration based on surface soil CER, which was overwhelmingly driven by soil temperature and moisture. The (13)C label was immediately detected in foliage on label day (half-life = 0.5 day), progressed through phloem by Day 2 (half-life = 4.7 days), roots by Days 2-4, and subsequently was evident as respiratory release from soil which peaked between Days 3 and 6. The δ(13)C of soil CO(2) efflux was strongly correlated with phloem δ(13)C on the previous day, or 2 days earlier. While the (13)C label was readily tracked through the ecosystem, the fate of root C through respiratory, mycorrhizal or exudative release pathways was not assessed. These data detail the timing and relative magnitude of C flux through various components of a young pine stand in relation to environmental conditions.