Competition between of invasive Hydrilla verticillata L . f . and native Ceratophyllum demersum L . in monocultures and mixed cultures experimental

The present study aims to assess inter-specific competition between Hydrilla verticillata and Ceratophyllum demersum. A competition experiment design has five treatment combinations to terminal shoots of C. demersum only, terminal shoots of H. verticillata only and three different treatment combinations of C. demersum and H. verticillata together. Our results showed parameters growth of C. demersum were decreased of which, total chlorophyll, protein, and biomass while Superoxide dismutase (SOD), and Catalase (CAT) enzymes increase were significantly (p<0.05) compare with control treatment. While H. verticillata were increased total chlorophyll, biomass, CAT and little increase in protein and SOD were significantly (p<0.05) compare with control treatment. Therefore, due to the competition, with the introduction of C. demersum, the performances growth of H. verticillata were increased. Based on our result, showed H. verticillata and C. demersum species were coexist, C. demersum will have a competitive advantage over H. verticillata. Therefore, this study suggests, H. verticillata could out-compete for C. demersum in many situations, that despite the similar ecology.


Experimental Design
Both species were cut of terminal shoots into 10 cm length fragments. The existing branches (roots and flower buds) were eliminated. They were brought to the laboratory in nylon bags and well washed with river water. Then, they were washed several times with tap water and distilled water to clean from the dirt and materials attached and remove of the remnants of adherent algae and small river animals. Then, planted for 10 days to adapt the plant to live in the tap water [19]. They were planted in plastic containers all were equal dimensions (40cm length x 25cm width x 25cm height) filled with 15 liters of water per container and water level was in each container maintained at the same level throughout the experiment. Our experiment was designed in 63 containers (plastic tank). divided into five treatments, everyone has four combinations, each combination has 12 containers. In each combination, three different concentrations (three containers for each concentration), A fourth combinations were only planted without nutrients (control), Remain 3 containers were water control (only water) Table-1. Our experimental were arranged in a Randomized Design Completely and plant growth parameters (Chlorophyll content, protein content, catalase, superoxide dismutase, and biomass) were recorded after (15,30, and 45) day of planting after acclimatized of the plant for 14 days in tap water; after acclimation, plant exposed to chosen concentrations of the nutrients; nitrogen (2, 6 and 10) ppm and phosphorus (0.1, 0.5 and 1) ppm, each 15 days with constant light irrationally (400 Lux.); photoperiod 12/12 light/dark (h./h.) and temperature 30C . Data were analyzed using SPSS statistical software (version 16).

. Chlorophyll
Plant growth parameters measured total chlorophyll, chlorophyll a and chlorophyll b according to [20] by spectroscopy type (Spectrophotometer SP-300) at waves (645 and 663) nm.

Proteins
Used the Biuret method to estimate the protein in plant tissues, were measured Absorbance by Spectrophotometer (SP-300) at a 555 nm wavelength. Bovine protein solution was used in the preparation of the standard curve and the protein content was expressed in mg / g plant tissue [21].

CAT enzyme
According to the method [22] was used to estimate the effectiveness of catalase enzyme, then read the absorbance with a wavelength of 240 nm.

SOD enzyme
The used method that according to [23] estimate the effectiveness of the SOD enzyme, and then the optical absorption was read at wavelength 420 nm.

Statically Analysis
The experimental plots were arranged in a Random Design Completely; data were analyzed by using SPSS statistical software (version 16)

Total chlorophyll
Our results showed a clear variation in the ratio of total chlorophyll of plants under study, the total chlorophyll was recorded with a maximum value 17.2 µg/g in (T2) in H. verticillata plant at high concertation and the minimum value was 2.45 µg/g in (T5) in control during 15 th days of experimental ( Figure-1).
During 30 th days of experimental, where record a maximum value in low concertation was 17.87 µg/g in T2 of H. verticillata and the minimum value was 4.71 µg/g recorded in T2 of C. demersum at moderate concertation (Figure-2); and during 45 th days period of experimental the maximum value recorded was 17.45 µg/g in T4 at low concertation and the minimum value was 3.62 µg/g in T1 of H. verticillata at control (Figure-3).
Statically analysis under probability (p˂0.05) showed there are significant differences between all interactions. Showed H. verticillata higher level of chlorophyll content than C. demersum in all combinations at 15 days in low concertation of nitrogen and phosphor. Stress decreases the ability of photosynthetic Iraqi Journal of Science, 2019, Vol. 60, No. 9, pp: 1933-1947 Alzurfi et al.

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systems to utilize incident photons, thus leading to photoinhibition, and reduced quantum yields of photochemistry and chlorophyll fluorescence. Photoinhibition causes inhibition of PSII, while also increasing thermal de-excitation of excited Chlorophyll [24]. The decrease in plant growth may be due to the accumulation of high concentration of nutrients as well as the reduction of pigment content, damage to root cells and deformation of the ultrastructure of chloroplasts and cell membrane [3]. On the other hand, the results of the study showed the highest rate of building chlorophyll pigment in T2 of H. verticillata, and the lowest rate of building chlorophyll pigment in the same model but in the other plant, and this may show us, that there is a clear dominance of the H. verticillata at the expense of C. demersum in this standard.

Chlorophyll a and b
The average of chlorophyll a of plants in the current study was recorded with a maximum value 4.1 µg/g and the minimum value recorded 0.57 µg/g during 15 th days (Figure- Chlorophyll is the major photosynthetic and aquatic plants pigment in a lot of phytoplankton and a trophy index in aquatic ecosystems [25]. Our results of chlorophyll showed a high significant increase in H. verticillata compare C. demersum, as recorded high value in competing model 10N and 30N. This is due to portability growth of H. verticillata in competing with C. demersum so showed in high concentration is significant value increase in H. verticillata but in C. demersum no significant between concentrations. Changes in chlorophyll content can occur as a result of nutrient deficiencies during plant growth. Thereby Chlorophyll contents can be used to manage nutrient optimization programs that both improve crop yield and help to protect the environment [26]. The previous studies confirmation chlorophyll a (Chl-a) could be predicted as a positive log-linear function of total P [27]. Perhaps the most likely interpretation of our study is that the results of this measurement match the results of the previous measurement (total chlorophyll), The highest construction rates for chlorophyll A were recorded in the H. verticillata compared to the lowest construction rates in the C. demersum, Where presence a clear dominance of the H. verticillata at the expense of C. demersum in this standard also.
Either, content of chlorophyll b may increase under pressure, possibly due to increased plant tolerance to stress, and that the plant can adapt to difficult conditions by controlling chlorophyll and a and b [28]. On the other hand, it was observed that the values of chlorophyll b were not changed in the early days of the experiment; however, there was a significant increase in the values of chl.b after reaching the last days under high concentrations, this may lead us to the fact that nutrients play a role in stimulating the buildup of chlorophyll b but slowly, So the effect of phosphorus and nitrogen may need time to show its effectiveness in the plant's body. Generally, the results of chlorophyll b were identical to our previous two measured results (total chlorophyll and chlorophyll A), there has been an evolution in the construction of chlorophyll b at the H. verticillata, and in contrast, a reduction in the rate of chlorophyll b construction at C. demersum. This congruence in the results between our parameters may raise the validity of the interpretation of the superiority of the H. verticillata to a higher degree of emphasis.

3-3 Total protein
Clearly Figure-10, the mean total protein of study plants during 15 th days of experimental showed a maximum value was 14.75 mg/g in (T2) of C. demersum plant at moderate concentration and the minimum value was 6.4 mg/g in (T3) of C. demersum at high concentration; and the higher concentration recorded in (T5) in moderate concentration was 16.17 mg/g and the minimum value was 4.17 µg/g in moderate concentration of H. verticillata in T3 during 30 th days of experimental (Figure-11); but recorded higher value during 45 th days was 12. 4 mg/g in H. verticillata in (T2) at control and minimum value was 3.58 mg/g recorded (T4) at high concentration (Figure-12). The results of the statistical analysis showed significant differences in the probability level (p˂0.05) between all interactions. The decrease in protein content of plant during experimental period is maybe due to plant stress for the formation of ROS (Reactive Oxygen species), which is an oxygen-containing chemical reaction molecule such as hydrogen peroxide, Superoxide anion (O 2 ), and hydroxyl radical (OH -), leading to a oxidative stress that produces these compounds as transverse products during metabolism that effect in plant cells and lead to their death as well as the breakdown of protein, fat, and DNA [29]. The increased nitrogen rates resulted in a significant decrease in protein content as opposed to the increased potassium rates. An opposite relationship was found in earlier studies [30]. On the other hand, in other study on Eruca vesicaria grew during the autumn season accumulated protein in a similar amount, regardless of increasing nitrogen rate [31]. Although decrease the protein content of both plants is generally under various nutrient concentrations. But, the current study showed the highest content of protein when C. demersum grows alone were recorded the highest value in (T5) with 16.17 mg/g while the less content appeared when the H. verticillata grows alone where recorded the lowest value in (T4) with 3.58 mg/g, While in the interference treatments, a significant reduction in protein content was observed in C. demersum offset by a significant increase in the protein content of the H. verticillata. This may lead to the belief that the growth of the H. verticillata alongside the C. demersum inhibits protein synthesis in the latter.  Figure-15. Results of the statistical analysis showed significant differences in the probability level (p˂0.05) between all interactions excepted plant and experimental period no significant. Enzyme activity increase during the 30 days and it decreased in the 15 days of the experiment may be due to the plant's susceptibility to possibly stress conditions for the period or maybe to the role of high concentration in simulating the bioprocessing of antioxidant enzymes [32]. In this study, the efficacy of the CAT enzyme was a good indicator of the competition between the two plants, the early days saw the dominance of the C. demersum and the rise in the values of the CAT against the weak efficiency of the H. verticillata; However, after 30 days, the CAT in the C. demersum appeared to be down to less effective, while the H. verticillata regained its activity and scored a clear dominance in the last days of the experiment. Enzyme activity decreased during the 15 th day and it increases in the 30 th day of the experiment, may be due to the plant's susceptibility to possibly stress

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L M H C Iraqi Journal of Science, 2019, Vol. 60, No. 9, pp: 1933-1947 4319 conditions for the period or maybe to the role of high concentration in simulating the bioprocessing of antioxidant enzymes [33].

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3-5 Super Oxide dismutase (SOD) enzyme
SOD enzyme values recorded high value in C. demersum were 0.24units/mg in (T2) at control and the lowest value recorded in the H. verticillata in (T4) was 0.012 unit/mg at moderate and high concertation during 15 th days of experimental ( Figure-16) while the higher value recorded in low concertation was 0.053 unit/mg in T1 of H. verticillata and minimum value recorded in high concertation was 0.011 unit/mg in (T5) during 30 th days of experimental (Figure-17 ), during 45 th days of experimental recorded higher value was 0.077 unit/mg in (T3) of C. demersum at moderate concertation while minimum value recorded was 0.010 unit/mg in low concertation (Figure-18). The results of the statistical analysis showed significant differences in the probability level (p˂0.05) between all interactions. The high efficiency of the enzyme in the leaves is similar to the leakage of electrons from the chain of transmission of electrons in photosynthesis to the oxygen molecule [34,35]. The results of the current study showed a gradual decreased in the SOD values and attributed the reasons for the effectiveness of the enzyme may be due to the fact that the antioxidants of the enzyme have differed in their effectiveness [35]. The low efficiency of the enzyme may be due to the sensitivity of the plant to high concentrations that reduce its effectiveness and thus lead to the collection of ROS in plant tissues and increase the rate of DNA destruction [36]. In the competitive aspect between the two plants, there was a common dominance between the two plants throughout the experiment, except for the last few days, Appeared the superiority of the C. demersum in (T3). This may explain the possibility of C. demersum to stimulate the increased production of the enzyme SOD when it's under stress.

3-6 Biomass
Values of biomass recorded a high value in C. demersum. were 34.4g at (40N) in low concentration and the lowest value recorded in the H. verticillata at 10N in moderate concentration was 2.1g. Results of the statistical analysis showed significant differences in the probability level (p˂0.05) between all interactions excepted plant and number no significant. (Figure-19). High biomass appeared in C. demersum compare to H. verticillata, due to a probability of C. demersum to grow faster than H. verticillata plant in low and moderate concentration only. In contrast to [37]. increase in biomass or area submerged aquatic plants, came from invasive species (H. verticillata), which may not provide the same ecological benefits as native freshwater species.

Conclusion
Both Hydrilla verticillata and Ceratophyllum demersum could live in a similar ecosystem conditions, However; if coexist both plants, will compete for the similar nutrients (N,P). Based on the present study. In a situation where Hydrilla and Ceratophyllum coexist, H. verticillata will have a competition advantage over C. demersum in our parameters, are necessary increased in Hydrilla,