Physiological parameters usually available when using an Infra Red Gas Analyzer (IRGA). Parameters available vary among manufacturers as well as among models of the same manufacturer. The equipment supplies some parameters while others have to be calculated. * These data should be represented as a graph showing the relation between variables as the concentration of one of them is increased; thus, the original units are maintained.
The application of knowledge with strong physiological basis of crop yield, allied to genetic and environmental factors, is essential in developing proper practices for crop management aiming high yields. Several aspects determine the performance of a particular crop plant in a given environment, such as temperature, water availability, incidence of pests, plant genetics and management applied. Although it is virtually impossible to control all these factors, plant behavior can be assessed when submitted to different levels of these factors to understand how the responses of the plant to that given stress are formed [1; 2].
Sugarcane is the most widely planted crop in Brazil for bioenergy, being grown in about 8.1 million hectares in the year 2011 . The high yields associated to the suitability for fabrication of ethanol, as well as easiness for bulk processing in high-capacity industrial facilities, catches the attention from businessmen and researchers. Furthermore, this crop is currently considered the best option for biofuel generation from the economical, energetic and environmental points of view.
There is still a big gap between physiological, high-specialized studies and application of these results for practical everyday crop management. Crop scientists, usually do not use physiological parameters in association to the directly measured variables as tools for supporting their findings. Basic research materials, which support applied studies [1; 4; 2; 5], propose changes to this scenario.
Among the factors which limit sugarcane yield, the interference caused by weed species can be highlighted. Weeds compete with sugarcane for resources as water, CO2, nutrients, physical space and light, being responsible for considerable losses in crop yield and quality, also reducing the useful life of the sugarcane plantation under high infestation levels. The useful life of a sugarcane plantation is defined by the number of times the crop is able to sprout and form new canes, which grow from the stubble, left behind from previous harvest (called
If from one side weeds are the main biotic factor that causes reduction in sugarcane yield, herbicides used for weeds management are usually considered the main abiotic factor impacting yields. Several herbicides are usually applied at high doses in sugarcane, often causing high toxicity levels to the crop . Herbicidal toxicity to sugarcane should not be evaluated based only in visual symptoms, once there are herbicides known to reduce crop yields with almost no external symptoms. There are some herbicides, however, known to cause severe external toxicity symptoms, which disappear after some days with little to no impact on final crop yield.
It is known that sugarcane varieties behave differently to some herbicides, and as consequence it is common to observe different levels of intoxication by given herbicides . Thus, there is the need to classify varieties in terms of susceptibility to the most widely used herbicides for weed control in sugarcane fields. The application of herbicides will, as mandatory, cause some level of harm to crops – from almost no harm to near total plant death. These impacts are sometimes not easily visible externally at the plant, but the physiological parameters would be imbalanced resulting in lower plant performance. Because of that, more susceptible parameters like the ones associated to the photosynthesis and water use of plants are essential tools for monitoring herbicide safety for crops.
The data presented in this chapter includes the state-of-the-art about sugarcane susceptibility to herbicides, plus the most up-to-date knowledge about this subject generated by a group of researchers which are reference in herbicide physiology, from different Brazilian institutions. Parameters associated to the photosynthetic efficiency, as CO2 concentration in the environment and in the leaf mesophyll, leaf temperature, and parameters associated to the dynamics of use of water - including Water Use Efficiency - impact the photosynthesis rate, thus affecting yield.
2. Chemical weed control
The wide acceptance of chemical weed control with herbicides can be attributed to: (1) less demand of human labor; (2) efficient even under rainy seasons; (3) efficient in controlling weeds at the crop row with no damage to crop root system; (4) essential tool for no-till planting systems; (5) efficient in controlling vegetatively propagated weed species; and (6) allows free decision about planting system (in rows, sowing) and crop row spacing .
It is important to consider, however, that an herbicide is a chemical molecule that should be correctly managed to avoid human intoxication as well as environmental contamination . The knowledge in plant physiology, chemical herbicide groups and technology of pesticide application is essential for the success of the chemical weed control . Surely there are risks involved at this method, but if they are known they can be avoided and controlled.
Chemical weed control should be applied as an auxiliary method. Efforts should be focused on the cultural method of weed management once it allows the best conditions for the development of crops while at the same time creating barriers for the proper development of seedlings of weed species [8; 9].
3. Traits related to the photosynthesis and water use efficiency
The photosynthesis rate surely is one of the main processes responsible for high crop yields, but the liquid photosynthesis is a result of interaction among several processes, and each one of these processes, alone or in sets, may limit plant gain in terms of photoassimilates . The genetic variation among species and even among biotypes of the same species may shift the enzymatic mechanism and make a given species more capable than other in extracting or using efficiently a given environmental resource, aiming to maximize its photosynthetic rate. Until recently, it was widely accepted that light affected indirectly the stomatal opening through the CO2 assimilation dependent on light – i.e., light increased the photosynthesis rate, which would reduce the internal CO2 concentration in the leaf and as a consequence the stomata would open [5; 10]. More accurate studies, however, concluded that stomatal response is less connected to the internal CO2 concentration of the leaf than anticipated; most of the response to light in stomatal opening is direct, not mediated by CO2 .
Distinct light regimes, both in terms of quantity and composition, influence almost all physiological processes like photosynthesis and respiration rates, affecting also variables like plant height, fresh and dry mass and water content of the plant . Water content, on the other hand, shifts both the stem length and leaf area of the plant, in a way to adapt the plant to the amount or quality of light intercepted . Interspecific and intraspecific plant competition affects the amount and the quality of the final product, as well as its efficiency in utilization of environmental resources [13; 14]. This is noted when assessing physiological traits associated to photosynthesis, such as concentration of internal and external gases , light composition and intensity  and mass accumulation by plants under different conditions.
Although gas exchange capability by stomata is considered a main limitation for photosynthetic CO2 assimilation , it is unlikely that gas exchange will limit the photosynthesis rate when interacting with other factors. However, photosynthetic rate is directly related to the photosynthetically active radiation (composition of light), to water availability and gas exchange. Plants have specific needs for light, predominantly in bands of red and blue . When plants do not receive these wavelengths in a satisfactory manner, they need to adapt themselves in order to survive . When under competition for light, the red and far-red ratio affected by shading is also important  and influences the photosynthetic efficiency .
4. Physiological parameters
Table 1 presents the main physiological parameters evaluated by the equipment called Infra Red Gas Analyzer (IRGA). Details on the principles of measurements by this equipment, as well as cares to be taken to avoid reading errors, can be found in ,  and in the technical manual of the equipment. Please note that the parameters available vary among equipments from different manufacturers, as well as among models of the same manufacturer. Some of them (∆C, Tleaf, ∆T and WUE) are usually not automatically supplied, but may be easily calculated based on parameters supplied by most of the equipments. The measuring units of the parameters also vary, and the most common units were adopted at Table 1. Water use efficiency (WUE) has several interpretations and may be presented in several different units, for distinct purposes. For a more comprehensive overview of this parameter, please consult .
|A||µmol m-2 s-1||
|E||mol H2O m-2 s-1||
|Gs||mol m-1 s-1||
|WUE||µmol CO2 mol H2O-1||
The photosynthesis (A) and thus the respiration, depend upon a constant flux of CO2 and O2 in and out of the cell; this free flux is a function of the concentration of CO2 (Ci) and O2 at the intercellular spaces, which depend on the stomatal opening, major controller of the gas flux through stomata [22; 23]. This is mainly controlled by the turgescence both of the guard cells (which control stomatal opening) as well as by the epidermic cells at the stomata . A low water potential will promote reduction in stomatal opening and reduce the leaf conductance, inhibiting photosynthesis and also the respiration , and increasing the gradient of CO2 concentration between the leaf mesophyll and the exterior of the leaf (∆C).
6. Water use efficiency
When plants are studied in terms of the efficiency they present when using water, the parameters stomatal conductance of water vapor (Gs), vapor pressure at the sub-stomatal chamber (Ean), transpiration rate (E) and water use efficiency (WUE) should be considered. The WUE is obtained by the relation between CO2 incorporated in the plant and the amount of water lost by transpiration during the same period . The more efficient water use is directly related to the photosynthetic efficiency as well as the dynamics of stomatal opening, because while the plant absorbs CO2 for the photosynthesis, it also loses water to the atmosphere by transpiration, in rates that depend on the potential gradient between the interior and the exterior of the leaf . Water exchange also allows the plant to keep adequate temperature levels, which can be evaluated by the leaf temperature (Tleaf), as well as by the difference between the leaf temperature and the temperature of the air surrounding the leaf (∆T).
7. Interference of
Brachiaria brizantha in the morphology and physiology of sugarcane
The study was installed at the experimental station of Horta Nova, owned by the Federal University of Viçosa (UFV), Viçosa-MG, Brazil, in an Acrisol. The planting of sugarcane was carried out under conventional system of 1-year sugarcane, after the operations of plowing and harrowing, in rows spaced in 1.4m. Planting density was 18 buds m-1 with fertilization performed at planting according to the results of physicochemical analysis of the soil and following the recommendations for the crop, using 500 kg ha-1 NPK 08-28-16, supplemented by topdressing of 160 kg ha-1 KCl.
The experimental unit measured 8.4m wide by 5.0m long (42 m2 per plot). Treatments consisted of 12 populations of
The populations of
The evaluations of the final populations of
The yield of stalks was estimated by counting stalks present in the four central rows of 0.5m, disregarding borders on each side and front portion. Later, 30 stalks were collected at random then weighed. With the average weight of stalks and number of stalks per unit area, sugarcane yield was estimated in t ha-1.
At the same time of the morphological evaluations, the physiological parameters of the treatments were evaluated by using an Infra Red Gas Analyzer (IRGA), model LCA Pro+. The sub-stomatal CO2 concentration (Ci - µmol mol-1), photosynthesis rate (A - µmol m-2 s-1), a stomatal conductance (GS – mol m-1 s-1), transpiration rate (E – mol H2O m-2 s-1) water use efficiency (EUA – mol CO2 mol H2O-1) were obtained. To avoid excessive interference of the environmental parameters on the readings, each block of the experiment was evaluated in a different day, between 07:00 and 10:00 am.
Data were tested for homoscedasticity and then submitted to analysis of variance. Subsequently, analyses of linear and nonlinear regression were performed to evaluate the effects of populations of
The leaf area (LA) of sugarcane was reduced as the population of
The results show that there was less accumulation of dry mass (DM) in the variety RB72454 as a function of increase in population of
With the increase in the population of
It was also observed a reduction in the number of stalks per meter, with increases in the population of the weed for RB72454, while the other varieties were not affected (Figure 2B). This demonstrates that RB72454 is more susceptible to competition compared to the other varieties. The number of stalks of RB72454 was reduced until the population of 10 plants m-2 of
Differences in competitive ability of crops versus weeds were observed by several researchers: sugarcane with signalgrass , soybean with oil radish , rice with barnyardgrass , rice with red rice , and sorghum with Johnsongrass . Temperature, humidity, soil fertility and light are the major determinants of plant growth, each of these elements may be more or less limiting in specific situations .
With increases in the population of
Some authors hypothesized that ecotypes (or varieties) of the same species might have differential capacity to adapt to distinct light intensities [37; 38]. Researches emphasize that all individuals of the same species are technically able to adjust their physiology to the light intensity to which they are exposed, i.e., an individual which grew originally in the sun can adapt itself to a shaded environment and vice versa [39; 40]. Thus, it is implied that the varieties of sugarcane that develop simultaneously and more rapidly in height and leaf area compete more effectively for light.
The number of leaves per plant of the variety RB72454 was negatively influenced by increasing the plant population of
The stalk yield was reduced with the increase in the population of
The substomatal CO2 concentration (Ci) decreased with increasing plant population of
There was a reduction in stomatal conductance (Gs) of the sugarcane with increasing plant population of
The transpiration rate (E) for RB867515 and RB72454 was reduced as the density of plants of
A reduction in the photosynthesis rate (A) for RB72454 was observed, with the increase in the density of the competitor, being the same not observed for the other varieties (Figure 8). Photosynthesis rate is limited, in this case, by the reduced availability of CO2 in the inner space of the leaf due to the lower influx of CO2, as observed for Ci and Gs. However, some plants are more efficient in the stomatal adjustment, so that even with a small reduction in water availability there is not necessarily a reduction in the photosynthesis rate .
Some environmental factors impact the stomatal regulation, such as water stress, because highly negative water potentials induce stomatal closure with a consequent reduction in stomatal conductance , reducing the influx of CO2 to the leaves and limiting the photosynthesis by deficiency of substrate. The nutritional deficiency may also lead to deficiency, for example, of proteins, enzymes and nutrients, such as potassium, which acts directly on the stomatal adjustment, and such deficiency could limit the photosynthesis rate . From the results it is unlikely that the photosynthetic activity of plants was limited by the interference of radiation, or by the smaller change in the proportion of red and far-red light, because in this case, there would most likely be no changes in Ci and Gs .
The water use efficiency (WUE) is characterized as the amount of water lost by transpiration while a certain amount of CO2 is captured for dry mass accumulation. Thus, plants, which present high photosynthesis rate while losing small amounts of water through transpiration, are considered more efficient in the use of water . As the density of
Based on the results, the infestation of
In relation to the physiological components, the variety RB72454 suffered the greatest effect by the competition for environmental resources, particularly for light and water, as the density of
8. Changes in physiological traits of sugarcane varieties under herbicide application
The experiment was installed in a randomized block design, with three replications in a factorial scheme 3 x 8. Factor A consisted of sugarcane varieties (RB867515, RB855156 and SP80-1816) and factor B by the herbicides tembotrione (Soberan® 200 mL ha1 + Aureo® 1,0 L ha-1); MSMA (Volcane® 3,0 L ha-1); diuron + hexazinone (Velpar-K GRDA® 2,0 kg ha-1); sulfentrazone (Solara® 1,2 L ha-1); trifloxysulfuron-sodium (Envoke® 30,0 g ha-1+ Extravon® 0,2% v/v); tebuthiuron (Combine 500 SC® 2,0 L ha-1); clomazone (Gamit® 3,0 L ha-1), plus a check treatment with no herbicide.
The experimental units consisted of plastic pots containing 12 dm3 of substrate - Red Latosol, previously limed and fertilized according to the analysis: pH water 4.3; OM = 2.5 dag kg1; P = 1.5 mg dm3; K = 40 mg dm3; Al3+ = 0.5 cmol c dm3 ; Ca2+ = 1.3 cmol c dm3; Mg2+ = 0.2 cmol c dm3; CTC(t) = 2.1 cmol c dm3; CTC( T ) = 6.39 cmol c dm3; H+Al = 4.79 cmol c dm3; SB = 1.6 cmol c dm3; V = 25%; and clay = 38%. After filling out pot with the substrate, two buds of sugarcane were planted in each experimental unit. Ten days after emergence (DAE) only one plant was left per pot. Herbicide application was accomplished 50 DAE of sugarcane, at the stage of four to six fully expanded leaves. For the application, it was used a backpack sprayer, propelled by CO2 and connected to a 2m wide bar with four nozzles Teejet TT 110.02, calibrated to spray 150 L ha1. Forty five days after application of the herbicides, physiological evaluations were done in the middle third of the first fully expanded leaf of the main tiller of the sugarcane plants. For that, an Infra Red Gas Analyzer (IRGA LCA Pro+) was used, in an open greenhouse, allowing free movement of the air. The photosynthesis rate (mol m2 s1), stomatal conductance of water vapor (Gs - mol m1 s1), transpiration rate (E - mol H2O m2 s1) and the water use efficiency (WUE - mol CO2 mol H2O1) were obtained. The evaluations were conducted between 7:00 and 10:00 am. All data was analyzed by the F-test, and when significant, means were grouped by the test of Scott-knot at 5% probability.
There was interaction between herbicides and varieties for the photosynthesis rate, stomatal conductance, transpiration rate and the water use efficiency. The variety RB867515, when sprayed with sulfentrazone, tebuthiuron or clomazone, showed lower transpiration rate (E) compared with the check with no herbicide (Table 2). It is noteworthy that these herbicides act directly or not in the photosynthetic apparatus of plants that are applied. Sulfentrazone inhibits the enzyme protoporphyrinogen oxidase (PROTOX), acting indirectly on chlorophyll synthesis in sensitive plants. Tebuthiuron is an inhibitor of photosystem II acting on D1 protein, and clomazone inhibits the synthesis of carotenoids, whose function is the protection of chlorophyll against excess of light .
|Tembotrione||2.66 Aa||2.57 Aa||2.62 Aa|
|MSMA||2.76 Aa||2.56 Aa||2.06 Bb|
|Diuron+hexazinone||2.87 Aa||2.54 Aa||3.05 Aa|
|Sulfentrazone||2.08 Bb||2.17 Bb||2.81 Aa|
|Trifloxysulfurom-sodium||2.70 Aa||2.24 Bb||1.82 Bb|
|Tebuthiuron||2.24 Bb||2.03 Bb||2.83 Aa|
|Clomazone||2.35 Ab||2.07 Ab||2.77 Aa|
|Check||2.85 Aa||2.87 Aa||2.72 Aa|
Means followed by the same letter, uppercase in the rows and lowercase in the columns, are included in the same group by the test of Scott-Knot at 5% probability.
The application of sulfentrazone, trifloxysulfuron-sodium, clomazone and tebuthiuron on the variety RB855156 caused reduction in E. For variety SP80-1816, however, only trifloxysulfuron-sodium and MSMA had negative impact (Table 2). Trifloxysulfuron-sodium is an inhibitor of the enzyme acetolactate synthase (ALS), with indirect effect on phososynthesis because it acts on the production of the branched-chain amino acids valine, leucine and isoleucine, responsible for the production of proteins in plants.
With regard to the water use efficiency (WUE), no differences were observed inside variety or herbicide (Table 3). The water use efficiency is characterized as the amount of water transpired by a plant to produce a certain amount of dry mass . Thus, more efficient crops in the water use can produce bigger amounts of dry mass per gram of water transpired. The most efficient use of water is directly related to stomatal opening, therefore, while the plant absorbs CO2 for photosynthesis, water is lost with variable intensity, following a gradient of water potentials from the leaf surface to its surrounding air .
|Tembotrione||8.06 Aa||9.50 Aa||6.40 Aa|
|MSMA||6.36 Aa||5.65 Aa||6.29 Aa|
|Diuron+hexazinone||7.37 Aa||8.43 Aa||6.95 Aa|
|Sulfentrazone||5.10 Aa||6.88 Aa||8.69 Aa|
|Trifloxysulfurom-sodium||7.53 Aa||7.04 Aa||7.49 Aa|
|Tebuthiuron||7.88 Aa||7.95 Aa||6.66 Aa|
|Clomazone||7.28 Aa||6.14 Aa||6.64 Aa|
|Check||10.12 Aa||8.41 Aa||9.56 Aa|
Means followed by the same letter, uppercase in the rows and lowercase in the columns, are included in the same group by the test of Skott-Knott at 5% probability.
With regard to the photosynthesis rate (A), it was observed that only sulfentrazone affected the variety RB867515, while the remaining treatments did not differ from the check (Table 4). Another research  evaluated varieties of sugarcane and found that RB867515 was the least affected by the application of commercially formulated mixture ametryn + trifloxysulfuron-sodium in greenhouse.
The influx of CO2 in the leaf may be compromised due to the action of herbicides which inhibit the enzyme PROTOX, because there is formation of nitric oxide by the reactive oxygen species (ROS). This oxide stimulates the synthesis and activity of abscisic acid (ABA) - hormone that acts regulating stomatal closure . Stomatal closure can also occur by the direct action of ROS, favoring the accumulation of calcium in the cytosol , or due to peroxidation of membranes of cells adjacent to stomata.
For the variety RB855156, MSMA, sulfentrazone, trifloxysulfuron–sodium, tebuthiuron and clomazone caused a reduction in A (Table 3). For SP80-1816, diuron + hexazinone and sulfentrazone did not affect this variable. It is noteworthy that hexazinone + diuron in mixture, even both being photosystem II inhibiting herbicides, did not cause reductions in A for the three varieties compared to control (Table 3). , working with six sugarcane varieties, found that under application of ametryn, RB855113 presented A similar to the control treatment, and the other varieties showed a decrease in this parameter under application of ametryn.
|Tembotrione||22.10 Aa||24.48 Aa||16.45 Ab|
|MSMA||17.54 Aa||14.51 Ab||13.75 Ab|
|Diuron+hexazinone||21.15 Aa||21.17 Aa||21.22 Aa|
|Sulfentrazone||10.56 Ba||15.59 Bb||24.94 Aa|
|Trifloxysulfurom-sodium||20.53 Aa||15.85 Ab||13.90 Ab|
|Tebuthiuron||17.86 Aa||16.25 Ab||18.64 Ab|
|Clomazone||16.89 Aa||12.96 Ab||18.45 Ab|
|Check||28.44 Aa||24.07 Aa||26.03 Aa|
Means followed by the same letter, uppercase in the rows and lowercase in the columns, are included in the same group by the test of Scott-Knot at 5% probability.
When evaluating varieties under each herbicide, there was no correlation between them for all the products tested, except for sulfentrazone applied over SP80-1816, where there was higher A compared to the other varieties under the same herbicide (Table 4).  observed that the photosynthetic rate in sugarcane plants treated with trifloxysulfuron-sodium was similar to the respective control without herbicide application for all varieties evaluated in this study. Most of the herbicides used in this work, except MSMA and trifloxysulfuron-sodium, affect directly the photosynthesis rate because they have as a site of action either the chloroplast, inhibiting the transport of electrons, or the synthesis of chlorophyll, also interfering in the synthesis of pigments responsible for protecting the photosynthetic apparatus.
In RB867515 and SP80-1816, herbicides did not cause differences for stomatal conductance (Gs), but for RB855156, Gs decreased in the presence of all herbicides (Table 5). When evaluating the Gs of varieties within each herbicide, there was no difference among them. However, in the absence of herbicide, RB855156 showed greater Gs than the other two varieties (Table 5). Reduction of stomatal conductance was reported in soybean and
|Tembotrione||0.67 Aa||0.46 Ab||0.48 Aa|
|MSMA||0.60 Aa||0.46 Ab||0.28 Aa|
|Diuron+hexazinone||0.74 Aa||0.44 Ab||0.70 Aa|
|Sulfentrazone||0.27 Aa||0.34 Ab||0.59 Aa|
|Trifloxysulfurom-sodium||0.52 Aa||0.31 Ab||0.20 Aa|
|Tebuthiuron||0.33 Aa||0.28 Ab||0.56 Aa|
|Clomazone||0.36 Aa||0.27 Ab||0.57 Aa|
|Check||0.61 Ba||1.00 Aa||0.47 Ba|
Means followed by the same letter, uppercase in the rows and lowercase in the columns, are included in the same group by the test of Scott-Knot at 5% probability.
According to the results, the herbicides tested affected differently the physiological traits of the three sugarcane varieties evaluated. Overall, the variety RB867515 showed the lowest variation in the photosynthesis rate in the presence of the herbicides, compared to the check. The varieties SP80-1816 and RB855156 presented lower photosynthesis rates under application of most of the herbicides evaluated. It was also observed a decrease in stomatal conductance of the variety RB855156 after application of all herbicides.
9. Influence of herbicides on the photosynthetic activity of sugarcane genotypes
According to , the application of late post emergence herbicides in sugarcane fields may result in high toxicity to the crop, limiting yields. These authors attribute this to physiological changes in sugarcane plants, which would result in negative effects, also on the quality of the harvest.  studied the following herbicides, applied over several sugarcane varieties: ametryn - 2000 g ha-1; trifloxysulfuron-sodium – 22.5 g ha-1; and a commercial mixture containing ametryn + trifloxysulfuron-sodium at 1463 + 37.0 g ha-1, respectively. Treatments were compared against a check with no herbicide. Results are summarized in Table 6.
||A 5.77 a||A 5.46 a||A 4.93 a||A 5.02 a||A 5.02 a||B 2.46 a|
||B 2.83 b||B 3.69 ab||B 2.89 b||A 5.97 a||B 3.38 ab||B 3.63 a|
||A 5.21 ab||B 2.81 b||B 3.81 ab||B 2.99 b||B 2.03 b||B 2.30 a|
||A 2.90 b||A 1.99 b||A 2.46 ab||A 2.09 b||A 1.66 b||A 1.30 a|
||A 124 ab||AB 149 a||B 120 a||AB 139 a||A 177 a||B 117 a|
||A 109 b||B 75 c||AB 105 b||AB 91 b||AB 102 b||A 110 a|
||AB 119 ab||B 106 b||AB 114 ab||AB 118 ab||A 144 ab||B 108 a|
||A 131 a||A 107 b||AB 112 ab||A 95 b||A 118 b||A 111 a|
||AB 102 a||A 177 a||AB 104 b||AB 123 b||B 68 c||AB 120 b|
||A 165 a||A 136 ab||A 169 a||A 178 a||A 134 a||A 157 a|
||AB 126 ab||AB 127 ab||AB 128 ab||AB 114 b||B 88 b||A 137 ab|
||AB 146 ab||B 87,7 b||AB 125 ab||A 179 a||AB 145 a||A 158 a|
||AB 45.1 a||AB 51.2 a||B 41.3 a||AB 47.9 a||A 60.7 a||AB 48.0 a|
||A 37.5 b||B 25.8 b||A 36.1 a||B 28.9 b||A 37.0 b||A 37.3 b|
||B 41.1 ab||B 36.6 ab||B 38.9 a||B 40.3 ab||A 49.5 ab||B 38.8 b|
||A 42.1 ab||A 36.4 ab||A 38.4 a||B 32.8 b||A 40.5 b||A 40.1 b|
In general terms, the CO2 consumed by photosynthesis (ΔC) was smaller in treatments including the herbicide ametryn. There were also remarkable differences among varieties. The ΔC is directly related to the photosynthesis rate of the plant by the time of the evaluation. In this situation, it is possible to observe that the variety RB72454 and SP80-1816 were less susceptible to ametryn than the other genotypes.
The concentration of CO2 within the leaf (Ci) was affected by the herbicide treatments, being also observed once more differences among genotypes. As expected, this parameter presented, in general terms, opposite behavior in comparison to ΔC. The application of the herbicide ametryn, a photosynthesis II (PSII) inhibitor, resulted in higher concentrations of CO2 within the leaf, once the photosynthesis of the genotypes under application of this herbicide was more severely affected. The CO2 concentration within the leaf was about 50% higher in treatments involving ametryn than to the check with no herbicide. Trifloxysulfuron-sodium also caused changes in Ci, but not at the same magnitude of ametryn.
In general terms, the photosynthesis rate (A) observed at the treatment with trifloxysulfuron alone was similar to the control with no herbicide. On the same way, treatments involving the PSII inhibitor presented photosynthesis rate inferior to rates observed at the control treatment. When considering the treatment containing ametryn + trifloxysulfuron, it was possible to highlight the variety RB947520. The authors report that, even the damages caused by ametryn being more easily identified by parameters associated to the photosynthesis, variations due to the application of trifloxysulfuron-sodium were also detectable by changes in these parameters by using an Infra Red Gas Analyzer (IRGA). In other words, herbicide damage on crops can be effectively quantified by evaluating direct and indirect damage to the photosynthetic route. Furthermore, the accumulation of dry mass did not correlate directly with most of the studied physiological parameters, because plant growth is a result of biomass accumulation since the emergence until the moment of the evaluation. In this way, the authors remark the importance of evaluating both types of variables, physiological and biomass/growth-related, before concluding about the efficacy or impact of a given herbicide treatment. In addition, the authors remark the existence of differences among varieties in terms of susceptibility to herbicides, which were effectively identified by physiological parameters.
Both the abiotic and biotic factors, represented in this study respectively by the environmental conditions and the presence of a competitor, present impact on the sugarcane crop. This impact is differential on distinct varieties, and some should be preferred over others in situations where the types of stress differ. Sugarcane varieties to be planted should be chosen, besides commercial traits, based on their ability to avoid or to overcome the negative impact of the stress to which they are submitted. This will help reaching high yields under field conditions.
Under application of herbicides, the variety RB867515 showed to be less sensitive to most of the herbicides tested, compared to SP80-1816 and RB855156. Herbicide damage to sugarcane can be effectively quantified by using an IRGA. Furthermore, the accumulation of dry mass usually did not correlate directly with most of the studied physiological parameters.
It is highlighted the importance of evaluating both types of variables, physiological and biomass/growth-related, before concluding about the efficacy or impact of a given herbicide treatment. It is also remarkable the existence of differences among sugarcane varieties in terms of susceptibility to herbicides, which were effectively identified by physiological parameters.
Radosevich, S.R., Holt, J.S. & Ghersa, C.M. (2007). Ecology of Weeds and Invasive Plants: Relationship to Agriculture and Natural Resource Management(3rd Ed.), John Wiley & Sons, ISBN 978-047-1767-79-4, Hoboken, USA.
Gurevitch, J., Scheiner, S.M. & Fox, G.A. (2009). Ecologia Vegetal(2nd Ed.), Artmed, ISBN 978-853-6319-18-6, Porto Alegre, Brazil.
CONAB – Companhia Nacional do Abastecimento. Safra 2011. Available at http://www.conab.gov.br. Access in June 134, 2012.
Larcher, W. Ecofisiologia vegetal. São Carlos: RiMa, 2004. 531p.
Aliyev, J.A. (2010). Photosynthesis, photorespiration and productivity of wheat and soybean genotypes. Proceedings of ANAS (Biological Sciences), Vol.65, No.5/6, pp.7-48.
GALON, L. et al. (2009). Influência de herbicidas na qualidade da matéria-prima de genótipos de cana-de-açúcar. Planta Daninha, v. 27, n. 3, p. 555-562, ISSN 0100-8358.2009.
FERREIRA, E.A., SILVA, A.F., SILVA, A.A., SILVA, D.V., GALON, L., FRANÇA, A.C., & SANTOS, J.B. (2009). Toxidade de herbicidas a genótipos de cana-de-açucar. Trópica, v.6, n.1, on-line, ISSN 1982-4831.
Silva, A.A., Ferreira, F.A., Ferreira, L.R. & Santos, J.B. (2007). Biologia de plantas daninhas, In: Tópicos em Manejo de Plantas Daninhas, Silva, A.A. & Silva, J.F., pp.17-61, Universidade Federal de Viçosa, ISBN 978-857-2692-75-5, Viçosa, Brazil.
Floss, E.L. (2008). Fisiologia das Plantas Cultivadas(4th Ed.), Universidade de Passo Fundo, ISBN 978-857-5156-41-4, Passo Fundo, Brazil.
Sharkey, T.D. & Raschke, K. (1981). Effect of light quality on stimatal opening in leaves of Xanthium strumarium. Plant Physiology, Vol.68, No.5, (November 1981), pp.1170-1174, ISSN 0032-0889.
Pystina, N.V. & Danilov, R.A. (2001). Influence of light regimes on respiration, activity of alternative respiratory pathway and carbohydrates content in mature leaves of Ajuga reptansL. Revista Brasileira de Fisiologia Vegetal, Vol.13, No.3, (December 2001), pp. 285-292, ISSN 0103-3131.
Aspiazú, I., Concenço, G., Galon, L., Ferreira, E.A. & Silva, A.F. (2008). Relação colmos/folhas de biótipos de capim-arroz em condição de competição. Revista Trópica, Vol.2, No.1, pp.22-30, ISSN 1982-4831.
Vanderzee, D. & Kennedy, R.A. (1983). Development of photosynthetic activity following anaerobic germination in rice-mimic grass ( Echinochloa crus-gallivar. oryzicola). Plant Physiology, Vol.73, No.2, (October 1983), pp.332-339, ISSN 0032-0889.
Melo, P.T.B.S., Schuch, L.O.B., Assis, F. & Concenço, G. (2006). Comportamento de populações de arroz irrigado em função das proporções de plantas originadas de sementes de alta e baixa qualidade fisiológica. Revista Brasileira de Sementes, Vol.12, No.1, pp.37-43, ISSN 0101-3122.
Kirschbaum, M.U.F. & Pearcy, R.W. (1988). Gas exchange analysis of the relative importance of stomatal and biochemical factors in photosynthetic induction in Alocasia macrorrhiza. Plant Physiology, Vol.86, No.3, (March 1988), pp.782-785, ISSN 0032-0889.
Merotto Jr., A., Fischer, A.J. & Vidal, R.A. (2009). Perspectives for using light quality knowledge as an advanced ecophysiological weed management tool. Planta Daninha, Vol.27, No.2, (April/June 2009), pp.407-419, ISSN 0100-8358.
Hutmacher, R.B. & Krieg, D.R. (1983). Photosynthetic rate control in cotton. Plant Physiology, Vol.73, No.3, (November 1983), pp.658-661, ISSN 0032-0889.
Da Matta, F.M., Loos, R.A., Rodrigues, R. & Barros, R. (2001). Actual and potential photosynthetic rates of tropical crop species. Revista Brasileira de Fisiologia Vegetal, Vol.13, No.1, (Abril 2001), pp.24-32, ISSN 0103-3131.
Dutton, R.G., Jiao, J., Tsujita, J. & Grodzinski, B. (1988). Whole plant CO2 exchange measurements for non destructive estimation of growth. Plant Physiology, Vol.86, No.2, (February 1988), pp.355-358, ISSN 0032-0889.
Long, S.P. & Bernacchi, C.J. (2003). Gas exchange measurements, what can they tell us about the underlying limitations to photosynthesis? Procedures and sources of error. Journal of Experimental Botany, Vol.54, No.392, (November 2003), pp.2393-2401, ISSN 0022-0957.
Tambuci, E.A., Bort, J. & Araus, J.L. (2011). Water use efficiency in C3 cereals under mediterranean conditions: a review of some physiological aspects. Options Méditerranéennes, Series B, No.57, pp.189-203, ISSN 1016-1228.
Taylor Jr., G.E. & Gunderson, C.A. (1986). The response of foliar gas exchange to exogenously applied ethylene. Plant Physiology, Vol.82, No.3, (November 1986), pp.653-657, ISSN 0032-0889.
Messinger, S.M., Buckley, T.N. & Mott, K.A. (2006). Evidence for involvement of photosynthetic processes in the stomatal response to CO2. Plant Physiology, Vol.140, No.2, (February 2006), pp.771-778, ISSN 0032-0889.
Humble, G.D. & Hsiao, T.C. (1970). Light-dependent influx and efflux of potassium of guard cells during stomatal opening and closing. Plant Physiology, Vol.46, No.3, (September 1970), pp.483-487, ISSN 0032-0889.
Attridge, T.H. (1990). The natural environment, In: Light and Plant Responses, Attridge, T.H. (Ed.), pp.1-5, Edward Arnold, ISBN 978-052-1427-48-7, London, England.
Fereira, E.A. et al. (2008). Potencial competitivo de biótipos de azevém ( Lolium multiflorum). Planta Daninha, Vol.26, No.2, (June 2008), pp.261-269, ISSN 0100-8358.
Rizzardi, M.A. et al. (2001). Competição por recursos do solo entre ervas daninhas e culturas. Ciencia Rural, Vol.31, No.4, (December 2001), pp.707-714, ISSN 0103-8478.
Pedrosa, R.M.B. (2005). Avaliação dos parâmetros dos colmos da cana-de-açúcar, segunda folha, submetida a níveis de irrigação e adubação. R. Biol. Ci. Terra, Vol.5, No.1, (March 2005), pp.1-5, ISSN 1519-5228.
Santos, B.R. et al. (2006). Estresse ambiental e produtividade agrícola, In: Fisiologia e produção vegetal,Paiva, R., Oliveira, L.M. (Eds.), PP.71-91, Universidade Federal de Lavras, ISBN 85-87693-30-5, Lavras, Brazil.
Kuva, M.A. et al. (2003). Período de interferência de plantas daninhas na cultura da cana-de-açúcar. III - capim-braquiária ( Brachiaria decumbens) e capim-colonião ( Panicum maximum). Planta Daninha, Vol.21, No.1, (March 2003), ISSN 0100-8358.
Galon, L., & Agostinetto, D. (2009). Comparison of empirical models for predicting yield loss of irrigated rice ( Oryza sativa) mixed with Echinochloaspp. Crop Protection, Vol.28, No.10, (October 2009), pp.825-830, ISSN 0261-2194.
Pantone, D.J. & Baker, J.B. (1991). Reciprocal yield analysis of red rice ( Oryza sativa) competition in cultivated rice. Weed Science, Vol.39, No.1, (January 1991), pp.42-47, ISSN 1939-747X.
Hoffman, M.L. & Buhler, D.D. (2002). Utilizing Sorghumas a functional model of crop weed competition. I. Establishing a competitive hierarchy. Weed Science, Vol.50, No.4, (April 2002), pp.466-472, ISSN 1939-747X.
Bianchi, M.A., Fleck, N.G. & Lamego, F.P. (2006). Proporção entre plantas de soja e plantas competidoras e as relações de interferência mútua. Ciencia Rural, Vol.36, No.5, (May 2006), pp.1380-1387, ISSN 0103-8478.
BALLARÉ Ballaré, C.L., Scopel, A.L. & Sánchez, R.A. (1990). Far-red radiation reflected from adjacent leaves an early signal of competition in plant canopies. Science, Vol. 247, No.4940, (January 1990), pp. 329-332, ISSN 0036-8075.
Almeida, M.L. & Mundstock, C.M. (2001). A qualidade da luz afeta o afilhamento em plantas de trigo, quando cultivadas sob competição. Ciencia Rural, Vol.31, No.3, (September 2001), pp.401-408, ISSN 0103-8478.
Bjorkman, O. & Holmgren, P. (1966). Photosynthetic adaptation to light intensity in plants native to shaded and exposed habitats. Plant Physiology, Vol.19, No.3, (September 1966), pp.854-859, ISSN 0032-0889.
Bjorkman, O. (1968). Further studies on differentiation of photosynthetic properties in sun and shade ecotypes of Solidago virgaurea. Plant Physiology, Vol.21, No.1, pp.84-99, ISSN 0032-0889.
Walker, G.K., Blackshaw, R.E. & Dekker, J. (1988). Leaf area and competition for light between plant species using direct sunlight transmission. Weed Technology, Vol.2, No.2, (March 1988), pp.159-165, ISSN 0890-037X.
Sims, D.A. & Kelley, S. (1998). Somatic and genetic factors in sun and shade population differentiation in Plantago lanceolataand Anthoxanthum odoratum. New Phytologist, Vol.140, No.1, (February 1998), pp.75-84, ISSN 1469-8137.
Wiedenfeld, B. (2003). Enhanced sugarcane establishment using plant growth regulators. Journal of the American Society of Sugarcane Technology, Vol.23, No.1, (February 2003), pp.48-61.
Galon, L., Ferreira, F.A., Silva, A.A., Concenço, G., Ferreira, E.A., Barbosa, M.H.P., Silva, A.F., Aspiazú. I., França, A.C. & Tironi, S.P. (2010). Influência de herbicidas na atividade fotossintética de genótipos de cana-de-açúcar. Planta Daninha, Vol.28, No.3, (June 2010), pp.591-597, ISSN 0100-8358.
Concenço, G. et al. (2009). Uso da água por plantas híbridas ou convencionais de arroz irrigado. Planta Daninha, Vol.27, No.3, (September 2009), pp.447-453, ISSN 0100-8358.
Concenço, G. et al. (2007) Uso da água em biótipos de azevém ( Lolium multiflorum) em condição de competição. Planta Daninha, Vol.25, No.3, (September 2007), pp.449-455, ISSN 0100-8358.
Ferreira, E.A. et al. (2005). Sensibilidade de cultivares de cana-de-açúcar à mistura trifloxysulfuron-sodium + ametryn. Planta Daninha, Vol.23, No.1, (March 2005), pp.93-99, ISSN 0100-8358.
Taiz, L. & Zeiger, E. (2009). Fisiologia Vegetal. 4.ed. Porto Alegre: Artmed, 848p. ISBN 9788536316147.
Wichert, R.A. & Talbert, R.E. (1993). Soybean [ Glycine max(L.) ] response to lactofen. Weed Science, Vol.41, No.1, (February 1993), pp.23-27, ISSN 1939-747X.
Azania, C.A.M. & Azania, A.A.P.M. (2005). Cana: limpa e lucrativa. Caderno Técnico Cultivar Grandes Culturas, No.79, pp.3-10, not indexed.