The legibility of the names was not as important as the way the surface became progressively dense over the weeks of writing them. Parker realized that the process was “like a record of the soil growing. It’s like when you make your own compost and put it into the soil: it just continues to grow. So this painting may never be finished.”Mechanical eradication of Arundo can be attempted in many different manners. The most frequently used method is the cutting of the above ground material, the plant’s tall stems. Another method of mechanical eradication is digging out the underground biomass, the rhizomes.The large amount of standing above ground biomass, up to 45 kg/m2 impedes the removal of the cut material, because the costs will be too high. The costs associated with the removal of the large biomass of the stems, has led to the use of “chippers” that will cut the stems into pieces of approximately 5 – 10 cm in situ. After these efforts, the chipped fragments are left in place. A small fraction of the fragments left behind after chipping will contain a meristem. The stem pieces of these fragments may have been left intact, or split lengthwise. In the second case the node at which the meristem at located will have been split as well. On many pieces with a meristem, the meristem itself may still be intact. These stem fragments might sprout and regenerate into new Arundo plants . If stems are not cut into small pieces, or removed after cutting, the tall, cut stems can be washed into the watershed during a flood event. This material can accumulate behind bridges and water control structures with possible consequences as described in the introduction.

Meristems on the stems can also sprout, and lead to the establishment of new stands of Arundo at the eradication project site, bato bucket or down river . A. donax stands have a high stem density. The outer stalks of dense stands will start to lean to the outside because the leaves produced during the growing season push the stems in the stand apart. After the initial leaning due to crowding, gravity will pull the tall outside stems almost horizontal . Throughout this report these outside hanging stems will be referred to as “hanging stems”. The horizontal orientation causes hormonal asymmetry in these stems. The main hormones involved are IAA , GA and ethylene . The unusual IAA and GA distributions cause the side shoots developing on these hanging stems, to grow vertically. IAA also plays an important role in plant root development , and may therefore have a stimulative effect on root emergence from the adventious shoot meristem on fragments that originated from hanging stems, that would be absent in stem fragments from upright stems. In a preliminary experiment comparing root emergence between stem fragments from hanging and upright stems, 38% of the hanging stem stem fragments developed roots, while none of the upright stem-stem fragments showed root emergence . These results indicated the need for further study into the possibility that new A. donax plants can regenerate from the stem fragments with shoot meristems that might be dispersed during mechanical Arundo removal efforts. In order to apply herbicides at that time that the rate of downward translocation of photosynthates and herbicide would be greatest, this time period has to be established. Carbohydrate distribution and translocation within indeterminate plants, such as Arundo, results from the balance between the supply of carbon compounds to and the nitrogen concentration in the different plant tissues. Carbon and nitrogen are the most important elements in plant tissues. Due to different diffusion rates of NO3 – and NH4 + in soil water versus that of CO2 in air, and differences in plant N and C uptake rates, plant growth will earlier become nitrogen limited than carbon limited. During plant development tissue nitrogen concentrations are diluted by plant growth , which is mainly based on the addition of carbohydrates to the tissues.

When plant growth becomes nitrogen limited, the tissue will maintain the minimum nitrogen content needed for the nucleic acids and proteins that maintain metabolic function. At this low tissue nitrogen content, there is not enough nitrogen in an individual cell to provide the nucleic acids and proteins to support the metabolism of two cells, therefore the cells cannot divide. This means that the tissue cannot grow anymore , until it receives a new supply of nitrogen. When plant tissues cannot grow due to nitrogen limitation, they cannot incorporate or store additional carbohydrates. This lower physiological limit of tissue nitrogen content, at which no more cell division or incorporation of carbon is possible, is called the critical nitrogen content of the tissue . The CNC is expressed on a carbon basis .The CNC can be determined for whole plants , and for the different functional tissues of the plant. Different plant parts perform different functions, and therefore have different minimum nitrogen requirements for metabolism maintenance. In previous research with the dicotyledonous storage root perennial Ipomoea batatas , it was determined that the most photosynthetically active tissues, the leaves, and the fibrous roots, which are involved in nutrient uptake, have the highest CNC of all vegetative plant tissues . The storage roots of I. batatas had a significantly lower CNC than any of the other Ipomoea tissues. The difference between the actual tissue nitrogen content and the CNC determines the capacity of these different plant tissues to incorporate or store carbohydrates. Tissues with nitrogen contents that are above the CNC can still incorporate or store carbohydrates. These tissues have a positive carbon sink strength . Photosynthetically active tissues that have reached their CNC will not incorporate the produced carbohydrates, because that would dilute the nitrogen content of these tissues below the CNC, and metabolism would be impaired. Instead, the photosynthetically active tissues deposit the produced carbohydrates in the phloem, which transports them to those tissues that still have the ability to incorporate or store carbohydrates .

This is how leaves, that because of their high CNC loose the ability to incorporate the photosynthates in their own tissues relatively early during the development of the plant, can still produce photosynthates and translocate them down to the reserve storage organs, such as I. batatas storage roots, which maintain their positive carbon sink strength, and tissue growth , the longest of all plant tissues, due to their low CNC.Regeneration from stem fragments starts with the growth of a new stem from the meristem. Root growth from the meristem always follows shoot growth, and not all meristems with shoots will grow roots. Therefore, rooting of the stem fragment was selected as the criteria of successful regeneration from a meristem on a stem fragment. The stem fragments were checked for rooting three times per week. Rooting success was calculated in percent of all meristems in the container. The speed with which rooting occurred was expressed is t50. That is the number of days needed for 50% of the total number of meristems that eventually would root in a container, to root. When a stem fragment had rooted, the diameter of the stem at the point of the meristem was determined,dutch bucket hydroponic to assess the effect of the relative age of the meristem on the speed with which they rooted. The effect of the temperature at the time of rooting was tested for hanging A. donax stem fragments at two times in the growing season. In April 1998, 32 stem fragments were randomly distributed over 4 containers with aerated nutrient solution each at 10 and 20 °C. The stem fragments were monitored every day for rooting. Rooting success was calculated in percent of all meristems in each individual container, and mean rooting percentages were calculated for the four replicate containers for each fragment type. The speed with which rooting occurred was expressed using t50. This experiment was repeated in April 1999 at 15, 17.5, and 22.5. A repeat 20 °C treatment was included in the 1999 experiment, to allow for comparison with the 1998 experiment. Rooting of Arundo donax stem fragments under controlled temperatures at different exogenous indole acetic acid concentrations. Hanging stems and upright stems of A. donax were collected along the Santa Ana River, in Riverside County, CA, every month from February, 1999 through May, 2000. Eighty meristem containing fragments of each stem type were cut and surface sterilized. Twenty replicate fragments each , were randomly assigned to a control and three different exogenous IAA treatment levels . The fragments were placed in individual culture tubes , that had been auto claved containing 15 ml of plant growth medium with 4.4 g/L MS salts, 2 g/L Gel Gro, and the assigned concentration of IAA .

Each stem fragment was placed with its lower end in the rooting medium and its meristem submerged but near the interface of the rooting medium and the air. The upper end of the stem fragment extended above the rooting medium. The tubes were placed in a climate-controlled chamber with a temperature/light regime of 14 h of 27 °C in the light, and 10 h of 15 °C in the dark. The rooting of the fragments in the tubes was monitored daily for 30 days. Rooting success was calculated as percent of all meristems at the different IAA concentrations. The speed with which rooting occurred was expressed for each month using the t50 for each IAA concentration and stem type combination. The remaining meristem containing fragments from the hanging and upright A. donax stems that were collected monthly to test the effect of exogenous IAA were stored in tap water in separate containers. The containers were placed in the growth chamber under the temperature and light regime described previously, and the water was aerated. After approximately 10 days, the meristems on the fragments had developed into shoots and roots. Three replicate samples of approximately 10 g of the new shoot material were harvested from the stem fragments of both the hanging and the upright stems, and placed on ice. For the extraction of endogenous IAA, the samples were dipped in grinding media , placed in glass tubes, and flash frozen in liquid nitrogen. The tissues were homogenized for 2 minutes in 20 ml grinding medium with an Omnimixer . The homogenates were incubated on a wrist action shaker for 20 minutes and filtered through micro-cloth. The filtered solution was centrifuged at 10,000 rpm in a JA-17 rotor, and the supernatant was saved. The tissue material on the filter and the centrifugation pellet were combined and incubated again in 10 ml grinding media, and the sample was filtered and centrifuged as before. The supernatants were combined and their volume was reduced to 1 ml using a speed vacuum evaporator at 37 C. The concentrated samples were centrifuged at 13,000 rpm for 10 minutes at 4 °C. The supernatants were filtered through a 2 µm syringe filter . The resulting tissue extracts were stored in 1.5 ml centrifuge tubes, and stored at -80 °C. For the HPLC, the extracts were eluted from a C18 reverse phase column with an analytical SB-18 guard column , with a gradient solution of 20-35% acetonitrile with 20 mM sodium acetate at a flow rate of 1.5 ml/min. The samples were monitored using a spectrofluorimeter detection system at an excitation wavelength of 280 ± 10 nm, and an emission wavelength of 350 ± 10 nm. The IAA peaks of the sample extracts were identified and quantified using 0.1 and 0.5 µM standard solutions.The critical nitrogen content of Arundo leaf tissue was determined in a hydroponics experiment. One hundred Arundo stem fragments were collected in June 1998 from the Santa Ana River near River Road in Riverside county. In the greenhouse, the stem fragments were placed in water for 2 weeks to allow for root and shoot growth. After two weeks, 48 young plants that sprouted from the meristems on the stem fragments were randomly selected for use in the experiment. Four stems were placed in each of eleven 120-liter plastic containers, that were filled with 100 L aerated, half strength Hoagland nutrient solution .