Effects of Down- and Up-regulated Lignin Biosynthesis in Populus of Soil Carbon Transformation and Storage
Our objective is to understand how rates of soil C formation and plant biomass are influenced by changes in plant growth and performance resulting from lowered lignin and altered lignin S/G ratios. A greenhouse study of the effects of altered lignin in SOC formation and plant biomass has been completed as of November 2009. Wild-type (control) and three transgenic aspen lines expressing reduced stem lignin concentrations and/or increased syringyl (S) to guaiacyl (G) ratio lignin were grown in greenhouse mesocosms. Soil was collected from the Colorado Central Plains Experimental Range (CPER) northeast of Fort Collins, Colorado. The Colorado soil is an Olney fine sandy loam (fine-loamy, mixed, superactive, mesic Ultic Haplargrid). Plants at the surface mineral soil up to 5 cm depth were removed and the underlying soil was sampled to a depth of 30 cm. Soils were immediately shipped to Reno, NV. This C4 soil was then used to trace belowground C inputs by the C3 plants into the soil using the 13C natural abundance methods as described in the DOE proposal. Transgenic quaking aspen were generated by the Forest Biotechnology Group at North Carolina State University (NCSU) using Agrobacterium-mediated transformation, the seedlings were then shipped to Reno, NV. Rooted seedlings were transferred from sterile agar into small pots with 250 g of C4 grass-dominated soil and kept in mist chambers in a greenhouse for four to six weeks. Plants were arranged randomly in adjacent greenhouse benches, soil blanks were placed randomly among the plants and treated in the same manner as pots with plants. Growth measurements were conducted for all plants in both groups and consisted of height, width at base of stem, number of leaves and length and width of every leaf in every tree. Plants were grown for a period of 120-140 days. At harvest, the aboveground portions of the trees were separated into leaves, litter, and stems. Soils were immediately frozen after harvest and roots were subsequently removed from thawed soil. Roots were further separated into coarse (> 1mm) and fine (< 1mm) roots. All tissue samples were dried for 48 h at 65 ºC, weighed, and then milled for analysis. Fine roots were analyzed for C and N concentrations and 13C (± 0.25‰). All other plant tissues were analyzed for C and N concentrations. Soils were analyzed for available soil nutrients, after harvest and root extraction, soils (including soil blanks pots) were analyzed for C and N concentrations and 13C using the same procedure as the fine roots. Growth measurements from both experiments showed that plant lines differed in heights, number of leaves, total biomass, and total leaf area; but did not differ in average leaf size or stem width. The low lignin line (23) and the control line (271) were similar to each other for all measured characteristics and were significantly larger than the low lignin + high S/G ratio lines (72 and 75). C/N ratios were highest for low lignin plants (line 23) in the woody tissue (roots and stems). The soil C concentrations and total C contents in the soil did not vary significantly among lines. There were no significant difference among lines in the amount (g) of new soil C, however, the soil from the control line (271) and low lignin line (23) had the highest new C concentration and total new C input into the soil. All soils with plants lost some of the existing “old” C, but the loss of old C was not significantly different among lines. Our findings support our first hypothesis, that high S/G ratio lines (72, 75, and 93) have less biomass, and soil C formation is affected as a result of the lower biomass. Our second hypothesis, that low lignin lines (23) would have more biomass and greater soil C formation, was partially supported. Although line 23 did not significantly out-perform the control line (271), the values for all measured growth and soil C characteristics were either comparable or greater than those for 271. The second part of this hypothesis, that line 23 would mobilize more old soil C and alter C/N ratios, was only partially supported by our data. Line 23 did not mobilize more old soil C, but the woody tissue C/N ratios were significantly higher than other lines, suggesting that tissue from line 23 plants is possibly more recalcitrant to decomposition. The comparable performance to the control lines coupled with the reduced lignin in the wood structure gives line 23 an advantage over line 271 in terms of pulping efficiency. The higher C/N ratios in the woody tissue could also suggest it has an advantage for C sequestration in tissue.
- Research Organization:
- North Carolina State University, Raleigh, NC
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- FG02-04ER63754
- OSTI ID:
- 992851
- Report Number(s):
- DOE/ER63754 - Final Report; 522769; TRN: US201107%%28
- Country of Publication:
- United States
- Language:
- English
Similar Records
GENETIC MODIFICATION OF GIBBERELLIC ACID SIGNALING TO PROMOTE CARBON SEQUESTRATION IN TREE ROOTS AND STEMS
Fine root morphology is phylogenetically structured, but nitrogen is related to the plant economics spectrum in temperate trees