ROOT SYSTEM ARCHITECTURE OF KOSTELETZKYA PENTACARPOS (MALVACEAE) AND BELOWGROUND ENVIRONMENTAL INFLUENCES ON ROOT AND AERIAL GROWTH DYNAMICS1
Introduction Changes in the global climate including rising temperatures and sea levels along with increases in the world population have put strains on the earths’ natural resources. Demand for fossil fuels have pushed agricultural focus to bio fuel production causing a strain on land resources for food production and contributing to rising food costs. At the same time, rising sea levels are taking away some of the arable land traditionally used for food production.
A crop that could be grown in areas where normal food and bio fuel crops will not grow would provide multiple resources for solving several global economic issues. Kosteletzkya pentacarpos is a plant whose seeds can be used as feedstock for bio fuels; its stems for animal feed rich in protein; and other parts for other products including fiber. K. pentacarpos is a salt tolerant crop so it be grown in coastal areas where rising sea levels and dredging have made it impossible to grow other bio fuel or food crops.
“Studies have been conducted on many aspects of K. pentacarpos growth, including salt tolerance, water-use efficiency, competition with wetland grasses, and seed germination”.2 The hypothesis of this study was that K. pentacarpos is a viable option as a bio fuel alternative as well as for other products. In this study, the objective was to gain further insight into the domestication of this plant for these purposes by:
determining quantity of newly produced root biomass during the growing season;
quantifying the total non-structural carbohydrates stored by two-year old plants;
documenting the mass, surface area, and length of two-year old field-grown plants.
Materials and Methods
Forty-five samples of K. pentacarpos in PVC pipes were taken from a commercial farm near Lewes, Delaware. These samples were divided into five groups of nine plants. The plants were placed into bi-level growing chambers with five different mediums in the bottom chambers. Four treatment groups were grown in the light in a greenhouse while one was grown in dark.
The treatment groups were set up as follows:
1) Control: grown in native Sassafras sandy loam soil with no amendments;
2) Dredge spoil material from a recent dredging of the Lewes-Rehoboth Canal;
3) Sassafras sandy loam with a small addition of nutrients;
4) Sassafras sandy loam soil with a high addition of nutrients.
5) Sassafras sandy loam with no amendments-grown in the dark.
All other growing conditions such as light and temperature were maintained consistent across the groups except for the one group grown in the dark.
Plants were grown from a period of March through October. Plants grown in the light went through two growth periods. During this time, growth of the plants was measured by counting stems and harvesting the biomass of the aerial portion of the plants. Aerial biomass was measured and sorted as to type: stems, leaves, flowers, and seed capsules. At the end of the second growing period, the entire plant was harvested. Root mass was harvested, cleaned, and measured. Counts of fine root mass versus coarse root mass were also taken.
Root morphology was measured by taking three samples of field grown plants. These samples were laid out, cleaned and allowed to dry. Each sample was divided into fifteen sections which were photographed, analysed, and root samples counted and measured by sections which represented soil depths.
Total coarse root biomass was significantly affected by the soil treatment with the high nutrient group having more than any other group. Ratio of fine root mass to coarse root mass was highest in the control group.
Aerial growth of the plants also was greatest during both growth cycles in the high nutrient group, with the dredge group being the lowest among the groups grown in the light. The group grown in the dark had only one growth period and the lowest biomass.
Allocation of resources varied between the two growth periods. Although the total biomass increased with the addition of nutrients, the percentage of biomass allocated to reproductive growth was constant as a percentage across all groups.
In answering the question of what the effects of growing K. pentacarpos in dredged material would have, there were mixed results. The number of stems produced and the root biomass was not significantly different between the control and the dredge group. The root-to-shoot ratios were also not statistically different.
Addition of nutrients increased the production of overall biomass including seed capsules which is important for the production of bio fuel.
The majority of both coarse and fine roots were located within the top twenty centimeters (cm) of soil. The distribution of roots affects the ability of a plant to access water and nutrients and also to provide for stability of the plant. “Soil stability will be increased in fields with the perennial
growth of K. pentacarpos because large quantities of fine roots will stabilize the soils. This stabilization is extremely beneficial in coastal areas where low-lying farmlands are subject to persistent winds and tidal flooding from storms.”3
The growth response of K. pentacarpos to differing soil types and nutrient conditions as well as its root architecture make it a promising plant for further development as a bio fuel crop in otherwise unusable saline coastal land. The results show that this plant can produce adequately in soil dredged from salt water, and can contribute to stabilizing this soil from coastal erosion forces.
Some of the limitations of the study included:
Not being able to harvest the total root biomass from the samples taken in the field. This resulted in lower measured masses compared to other species.
Growing the plants in a greenhouse caused them to go through two growth cycles compared to just one in the field. This could have been due to the signalling of warmer temperatures earlier than normal, to different day length signals, or the accumulation of heat units. Although this could affect the results compared to field grown units, the conditions were consistent across the groups for the affects being studied (i.e. soil conditions and nutrient availability). There was also not a measured difference in growth between the study groups and field grown groups during the second growth period.
Blits , K. C. , and J. L. Gallagher . 1990a . Salinity tolerance of Kosteletzkya virginica . I. Shoot growth, ion and water relations. Plant, Cell & Environment 13 : 409 – 418 .
Gallagher , J. L. 1985 . Halophytic crops for cultivation at seawater salinity.
Plant and Soil 89 : 323 – 336;.
Gallagher , J. L. , J. L. Halchak and D. M. Seliskar 2010. Root system architecture of Kosteletzkya pentacarpos (Malvacea) and belowground environmental influences on root and aerial growth dynamics. College of Earth, Ocean, and Environment — University of Delaware, 700 Pilottown Road, Lewes, Delaware 19958 USA. American Journal of Botany 98(2): 163–174. 2011.
Poljakoff-Mayber , A. , G. F. Somers , E. Werker , and J. L. Gallagher . 1992 . Seeds of Kosteletzkya virginica (Malvaceae): Their structure, germination, and salt tolerance. I. Seed structure and germination. American Journal of Botany 79 : 249 – 256 .
Somers , G. F. 1978 . Natural halophytes as a potential resource for new salt-tolerant crops: Some progress and prospects. In A. Hollaender, J. C. Aller, E. Epstein, A. San Pietro, and O. R. Zaborsky [eds.], The biosaline concept, 101 – 115. Plenum Press, New York, New York, USA.
1 Gallagher , J. L. , J. L. Halchak and D. M. Seliskar 2010. Root system architecture of Kosteletzkya pentacarpos (Malvacea) and belowground environmental influences on root and aerial growth dynamics. College of Earth, Ocean, and Environment — University of Delaware, 700 Pilottown Road, Lewes, Delaware 19958 USA. American Journal of Botany 98(2): 163–174. 2011. p163