Competitive Interactions between Rice and Caesulia <em>axillaris</em> or <em>Echinochloa crus-galli</em>: A Replacement Series Study

Special Article - Crop Production

Ann Agric Crop Sci. 2017; 2(1): 1025.

Competitive Interactions between Rice and Caesulia axillaris or Echinochloa crus-galli: A Replacement Series Study

Singh V¹, Kumar M1,2* and Singh H¹*

¹Department of Botany, Ecosystem Analysis Laboratory, Banaras Hindu University, Uttar Pradesh, India

²Department of High Altitude Biology, CSIR-Institute of Himalayan Bioresource Technology, India

*Corresponding author: Kumar M, Department of Botany, Ecosystem Analysis Laboratory, Banaras Hindu University, Uttar Pradesh, India

Singh H, Department of Botany, Ecosystem Analysis Laboratory, Banaras Hindu University, Uttar Pradesh, India

Received: February 01, 2017; Accepted: April 13, 2017; Published: April 20, 2017

Abstract

A replacement series study was conducted to evaluate the competition between rice and Caesulia axillaris Roxburgh or Echinochloa crus-galli (L.) Beauv at two nutrient levels to investigate that how differences in nutrient availability may change the competitive relationship between rice and weeds. Plants were established in mixture proportions of 4:0, 3:1, 2:2, 1:3 and 0:4 (weed: rice) plants pot-1. Both weeds were more competitive than rice under high nutrients. C. axillaris exhibited higher Relative Yield (RY) as well Aggressivity (Agr) than rice, whereas E. crus-galli showed comparable RY but greater competitive ability (Agr) than rice. Further, nutrient stress had different effects on both weeds; although, nutrient stress decreased the competition intensity of C. axilaris against rice, it did not change its position in hierarchy (C. axilaris dominated rice). Whereas E. crus-galli was outcompeted by rice under low nutrient. Thus, our study showed that weeds are better at high nutrient than are the crop. However, the effect of nutrient on weed competitiveness is not straightforward rather it depends on growth traits and nutrient use efficiency of species.

Keywords: Aggressivity; Competitive ability; Replacement series; Rice; Weed

Introduction

Weeds are one of the most important biological constraints in rice production [1,2]. According to study by, rice research directorate, India [3], grain yield losses due to weeds in these rice fields ranged from 15% to 90%. Studies indicate that among grasses Echinochloa crus-galli and broad-leaved weeds Caesulia axillaris are the most serious weeds of rice under rice–wheat system of the Indian subcontinent [4-6]. E. crus-galli, a vigorous C4 annual species, is one of the world’s most serious grassy weed in rice [7,8]. This species is highly competitive, and its morpho-physiological similarities with rice make control measures difficult [9]. Its infestation in the rice field results in the reduced rice tillering, which results in loss of yield [10] because it strongly competes with the rice for soil N by removing up to 80% of it [10,11]. The aggressiveness of E. crus-galli is probably due to its efficient C4 photosynthetic pathway, high nitrogen and water use efficiency [12]. In contrast, Caesulia axillaris (pink node flower) is C3 broad-leaved weed of family Asteraceae. It is an annual weed, with extended emergence period, relatively fast growth and high seed production; in these studies, it reduced the rice yield by 33% [13,14].

Weed management decisions for a particular species can be derived from a detailed knowledge of its biology and competitive ability [15]. Therefore, understanding the relationship between plant traits and competitive ability has emerged as a major research area [16,17]. Such an understanding would provide a better insight into the processes shaping the vigour of weeds. Generally, plant biomass, height and leaf area has been used to provide information on the size and aggressiveness of the plant, which may determine its competitive ability [18]. In recent years, physiological basis for competitive ability offered a powerful means to predict the consequences of competitive interaction. The physiological traits such as Specific Leaf Area (SLA) and photosynthetic rate (Aarea), are thought to be linked with resource capture and use efficiency [19]. Differential photosynthetic responses to changes in environmental factors such as nutrient, light can affect species aggressivity. However, little is known about the photosynthetic activity of E. cruss-gali and C. axillaris growing along with rice.

The competitive performance of weeds and crop often depends on environmental conditions [20]. The resources and the fluctuations in their availability can also play a significant role in the competitive ability of species [21,22]. It has been recognized that among the major resources (light, nutrient and water) competition in rice field between weeds and crop are greatest for nutrients [6,14]. Because in tropics, the majority of rice crop grown in lowland areas by transplanting method (rice field is flooded throughout the crop growth period until the grain matuaration), and as summer crop [5,6]. Therefore, in these areas, water and light were never a limiting factor. It has been found that added nutrients increased the competitive ability of weeds more than their crop [23,24]. Conversely, some studies showed that growth of some weed species is decreased while that of the crop is favored under high soil nutrient levels [25,26]. C. axillaris and E. cruss-galli are documented as fast growing and nitrophilic species [7]. Singh et al. [27] reported that fertilization increased the biomass of C. axillaris and E. crus-galli more than that of rice; however, the biomass of same weeds was decreased as compared to the crop at a low dose of N fertilizer. Therefore, it is important to investigate that how altered nutrient availability may change the competitive relationship between rice and weeds and which plant traits are the most important to determine competitive ability of weeds and crop. In order to do so for rice agroecosystem, we designed a replacement series study to elucidate how C. axillaris and E. crus-galli respond in terms of biomass production and physiological performance, when in competition with rice under different nutrient ability. The objectives of the present study was: (i) to study the responses of E. crus-galli and C. axillaris (including physiological performance, biomass accumulation and partitioning) and rice to one another, and (ii) to elucidate how nutrient stress alters the competitive performance of the weeds (iii) identification of plant trait associated with competitive ability of plant. We hypothesized that weeds would be more competitive than crop at high nutrient but that the crop would outcompete the weeds under low nutrient conditions.

Materials and Methods

The competitive interference of Caesulia axillaris Roxburgh and Echinochloa crus-galli (L.) Beauv against rice (BPT var.) was studied in a replacement series in an ambient light-temperature condition (natural weather condition) in the green house at the Botanical Garden of Banaras Hindu University Varanasi, (25°15'N latitudes and 80°59’E longitudes) from July to October 2011.

Treatments and experimental design

Treatments comprised growing the test crop (rice) and weeds (C. axillaris and E. crus-galli) in pure stand and, in mixed cultures; with two strength of nutrient solution viz. 50% Hoagland’s (HN treatment) and 25% Hoagland’s nutrient solution (LN treatment). Hoagland’s solutions were prepared according to Arnon and Hoagland [28]. The full strength (l/l) solution has a nitrogen concentration of 3mm Ca(NO3)2.4H2O and 2mm KNO3. Five planting ratios of the two species used in the study were 4:0, 3:1, 2:2, 1:3 and 4:0. Treatments were replicated five times in a randomized complete block design. For calculations, we report only three replicates for each treatment because some pots were damaged providing a lower number of replicates per treatment. Thus to maintain uniformity, data measured from three replicates. In some mixture proportion where no damage was recorded, we had taken result from all five replicates, but it was not significantly different from the data measured at three replicates. The final sizes of the plants in HN treatments were consistent with the range of sizes observed in the field, suggesting that the nutrient levels were within the range that these species experienced in the field. To ensure that planting density would be enough to result in interference; pilot studies were conducted before deciding to set total plant density in monocultures at four plants pot-1. Species were grown from seeds, collected from a nearby agricultural field. Seeds were germinated on moist filter paper in petridishes at 25°C before the experiment started germination rates were above 90%. To avoid the replacement series experiment problem of initial size bias [29], all seedlings were used in the experiment of similar size. Plants were grown in plastic pot (20-cm-diam by 18-cm-deep). Each pot was filled to a depth of 15 cm with fine river sand. Sufficient water per day and 100 ml of Hoagland nutrient solution at the interval of three days were provided to assure normal plant growth. Pots were flushed once a month with distilled water to prevent salt accumulation. Supplementary watering without nutrients was applied during the evening. Each pot is covered with perlite (about 2.0 cm) to reduce the compaction caused by watering and evaporation from soil surface. Pots were re-randomized weekly to avoid the creation of microclimates and species in mixtures were mixed uniformly and distributed equidistantly in the sand.

Plants were harvested at 70 days after transplantation when physiological maturity achieved in plants. Three replicates were collected for each species in each treatment. Shoots and roots were separated and placed in separate paper bags and transported to the laboratory in ice bags. Harvested plant parts were then dried in an oven at 80°C for 48 h. From the biomass data, the aggressivity of the species towards each other and relative yield and Relative Yield Total (RYT) of each species combination were computed. Leaf Area (LA) was determined using a leaf area meter (SYSTRONICS, Leaf area meter-211). Specific Leaf Area (SLA) (cm2 g-1) was calculated as area per unit mass. Leaf Area Ratio (LAR) was calculated as the ratio of leaf area to plant weight. LA, SLA and LAR are widely used variable in comparative plant ecology, because they are associated with many important attributes of plant growth and survival. A superior SLA may increase the capacity of the plant to assimilate CO2 because more leaves are produced for a given mass of carbon invested in photosynthetic tissues [30,31]; and therefore, provides a higher rate of return on the resources invested when compared to species with a lower SLA. For herbs and grasses, variation in LAR is the key determinant of interspecific variation in RGR [32]. Thus, the more plant invests in leaf area, the higher the total carbon gain and the faster growth will be achieved.

Photosynthetic rate (Aarea), the plants was measured by LI-6400 gas exchange system (LI-COR, Lincoln, Nebraska, USA) on the upper-most, fully expanded and apparently healthy leaves from each individual on sunny days in natural light condition between 0800 and 1100 hours local time. Flow rate was maintained at 500-μmol s-1. Air temperature was 32 ± 0.15°C and CO2 concentration was 385±5 μmol CO2 mol-1. Photosynthetic Active Radiation (PAR) was 1221±36.20 μmol mol-1 at the time of experiment. Higher rates of photosynthesis can lead to increased growth rates, biomass accumulation and overall production [33]. Additionally, high carbon gain and growth may confer high competitive ability to species so that they easily out compete the slow growing species by facilitating colonization or resource acquisition [30].

Competition indices

Relative Yield (RY) and Relative Yield Total (RYT):

RY = Yab/Yaa

RYba = Yba/Ybb

In this study, RY and RYT were calculated by whole plant dry weight data. Yab is the total biomass production of species ‘a’ in a mixture with species ‘b’ and Yaa is the biomass production of species ‘a’ in monoculture. Yab/Yaa is relative yield of species ‘a’ in mixture with species ‘b’ and vice versa; Yba is the total biomass production for species ‘b’ in mixture with species ‘a’, and Ybb is the biomass production of species ‘b’ in monoculture.

RYT is a measure of resource complementarity. RYT value of 1.0 indicates that the two species have equal demands for the same limiting resources of the environment. A RYT value greater than 1.0 means that, although the species may compete for the same resources, they also make demands on different resources. A RYT value less than 1.0 indicates mutual antagonism [34,35].

In replacement diagrams, actual RY of each species was plotted against the appropriate planting proportion. Expected RY for a species occurs when plants of this species grow equally well in mixture and monoculture. Comparisons of actual RY of each species with their expected RY (diagonal dashed line in replacement diagrams) indicate: (1) competition if the actual RY curve of one species is concave and that of the second convex, (2) niche differentiation if actual RY curves of both species are convex, or (3) mutual antagonism if actual RY curves of both species are concave. If actual RY curves are linear (i.e., do not differ from expected), the ability of one species to interfere with the other is equivalent.

Aggressivity (Agr): It is an index for the measure of the intensity of plant competition. It is used by McGilchrist & Trenbath [36] for the first time. Gain or loss of biomass due to interspecific competition was determined by calculating Aggressivity (Agr) for each species. A dominant species will have a higher aggressivity index than a dominated species [37].

Aab = (Yab/Yaa×Zab) – (Yba/Ybb×Zba)

Where Yab, Yba, Yaa, and Ybb are as defined in previous equation. Zab and Zba are sown proportions of crop “a” and “b” in the mixture. If Aab=0, both species are equally competitive, and if Aab is positive then species ‘a’ is the dominant species, while a negative value for Aab means that ‘a’ is the dominated species and vice versa.

Statistical analysis

An analysis of variance (Procedures in SPSS 17.0) was used to partition the main effects of species, mixture ratios, nutrient level. RY and RYT from each mixed culture were compared to the value of 1.00 using t-tests (P=0.05). The data were log-transformed before analysis to normalize statistical distributions and meet with the assumptions of the ANOVA.

Results

Biomass production

ANOVA indicated that species, nutrient treatment and the mixture proportion had significant effects on plant biomass. A summary of the analysis of variance of the effects of species, nutrient level, mixture ratio is presented in (Table 1).